related publications
Scale-free behavioral cascades and effective leadership in schooling fish
Múgica, Julia;Torrents, Jordi ; Cristín, Javier ;Puy, Andreu; Miguel, M. Carmen,; Pastor-Satorras, Romualdo
Scientific Reports
20452322
(2022)
Behavioral contagion and the presence of behavioral cascades are natural features in groups of animals showing collective motion, such as schooling fish or grazing herbivores. Here we study empirical behavioral cascades observed in fish schools defined as avalanches of consecutive large changes in the heading direction of the trajectory of fish. In terms of a minimum turning angle introduced to define a large change, avalanches are characterized by distributions of size and duration showing scale-free signatures, reminiscent of self-organized critical behavior. We observe that avalanches are generally triggered by a small number of fish, which act as effective leaders that induce large rearrangements of the group’s trajectory. This observation motivates the proposal of a simple model, based in the classical Vicsek model of collective motion, in which a given individual acts as a leader subject to random heading reorientations. The model reproduces qualitatively the empirical avalanche behavior observed in real schools, and hints towards a connection between effective leadership, long range interactions and avalanche behavior in collective movement.
Temporal mapping of derived high-frequency gene variants supports the mosaic nature of the evolution of Homo sapiens
Andirkó, Alejandro, Moriano, Juan ; Vitriolo, Alessandro, ;Kuhlwilm, Martinf, ;Testa, Giuseppe, ; Boeckx, Cedric
Scientific Reports
20452322
(2022)
Large-scale estimations of the time of emergence of variants are essential to examine hypotheses concerning human evolution with precision. Using an open repository of genetic variant age estimations, we offer here a temporal evaluation of various evolutionarily relevant datasets, such as Homo sapiens-specific variants, high-frequency variants found in genetic windows under positive selection, introgressed variants from extinct human species, as well as putative regulatory variants specific to various brain regions. We find a recurrent bimodal distribution of high-frequency variants, but also evidence for specific enrichments of gene categories in distinct time windows, pointing to different periods of phenotypic changes, resulting in a mosaic. With a temporal classification of genetic mutations in hand, we then applied a machine learning tool to predict what genes have changed more in certain time windows, and which tissues these genes may have impacted more. Overall, we provide a fine-grained temporal mapping of derived variants in Homo sapiens that helps to illuminate the intricate evolutionary history of our species.
From radial to unidirectional water pumping in zeta-potential modulated Nafion nanostructures
Esplandiu, María J. ;Reguera, David ;Romero-Guzmán, Daniel ;Gallardo-Moreno, Amparo M. ;Fraxedas, Jordi
NATURE COMMUNICATIONS
20411723
(2022)
Chemically propelled micropumps are promising wireless systems to autonomously drive fluid flows for many applications. However, many of these systems are activated by nocuous chemical fuels, cannot operate at high salt concentrations, or have difficulty for controlling flow directionality. In this work we report on a self-driven polymer micropump fueled by salt which can trigger both radial and unidirectional fluid flows. The micropump is based on the cation-exchanger Nafion, which produces chemical gradients and local electric fields capable to trigger interfacial electroosmotic flows. Unidirectional pumping is predicted by simulations and achieved experimentally by nanostructuring Nafion into microarrays with a fine tune modulation of surrounding surface zeta potentials. Nafion micropumps work in a wide range of salt concentrations, are reusable, and can be fueled by different salt cations. We demonstrate that they work with the common water-contaminant cadmium, using the own capture of this ion as fuel to drive fluid pumping. Thus, this system has potential for efficient and fast water purification strategies for environmental remediation. Unidirectional Nafion pumps also hold promise for effective analyte delivery or preconcentration for (bio)sensing assays
From motility-induced phase-separation to glassiness in dense active matter
Paoluzzi, Matteo ;Levis, Demian ;Pagonabarraga, Ignacio
COMMUNICATIONS PHYSICS
23993650
(2022)
Dense active systems are widespread in nature, examples range from bacterial colonies to biological tissues. Dense clusters of active particles can be obtained by increasing the packing fraction of the system or taking advantage of a peculiar phenomenon named motility-induced phase separation (MIPS). In this work, we explore the phase diagram of a two-dimensional model of active glass and show that disordered active materials develop a rich collective behaviour encompassing both MIPS and glassiness. We find that, although the glassy state is almost indistinguishable from that of equilibrium glasses, the mechanisms leading to its fluidization do not have any equilibrium counterpart. Our results can be rationalized in terms of a crossover between a low-activity regime, where glassy dynamics is controlled by an effective temperature, and a high-activity regime, which drives the system towards MIPS. © 2022, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.
Analysis of co-isogenic prion protein deficient mice reveals behavioral deficits, learning impairment, and enhanced hippocampal excitability
Matamoros-Angles A. ;Hervera A. ; Soriano J. ;Martí E. ;Carulla P. ;Llorens F. ;Nuvolone M.l, ;Aguzzi A.l; Ferrer I. ;Gruart A. ;Delgado-García J.M. ; Del Río J.A.
BMC BIOLOGY
17417007
(2022)
Background: Cellular prion protein (PrPC) is a cell surface GPI-anchored protein, usually known for its role in the pathogenesis of human and animal prionopathies. However, increasing knowledge about the participation of PrPC in prion pathogenesis contrasts with puzzling data regarding its natural physiological role. PrPC is expressed in a number of tissues, including at high levels in the nervous system, especially in neurons and glial cells, and while previous studies have established a neuroprotective role, conflicting evidence for a synaptic function has revealed both reduced and enhanced long-term potentiation, and variable observations on memory, learning, and behavior. Such evidence has been confounded by the absence of an appropriate knock-out mouse model to dissect the biological relevance of PrPC, with some functions recently shown to be misattributed to PrPC due to the presence of genetic artifacts in mouse models. Here we elucidate the role of PrPC in the hippocampal circuitry and its related functions, such as learning and memory, using a recently available strictly co-isogenic Prnp0/0 mouse model (PrnpZH3/ZH3). Results: We performed behavioral and operant conditioning tests to evaluate memory and learning capabilities, with results showing decreased motility, impaired operant conditioning learning, and anxiety-related behavior in PrnpZH3/ZH3 animals. We also carried in vivo electrophysiological recordings on CA3-CA1 synapses in living behaving mice and monitored spontaneous neuronal firing and network formation in primary neuronal cultures of PrnpZH3/ZH3 vs wildtype mice. PrPC absence enhanced susceptibility to high-intensity stimulations and kainate-induced seizures. However, long-term potentiation (LTP) was not enhanced in the PrnpZH3/ZH3 hippocampus. In addition, we observed a delay in neuronal maturation and network formation in PrnpZH3/ZH3 cultures. Conclusion: Our results demonstrate that PrPC promotes neuronal network formation and connectivity. PrPC mediates synaptic function and protects the synapse from excitotoxic insults. Its deletion may underlie an epileptogenic-susceptible brain that fails to perform highly cognitive-demanding tasks such as associative learning and anxiety-like behaviors
Reconstructing Mesolithic social networks on the Iberian Peninsula using ornaments
Cucart-Mora, Carolina;Gómez-Puche, Magdalenaa;Romano, Valéria ;de Pablo, Javier Fernández-López .;Lozano, Sergi
ARCHEOLOGICAL AND ANTROPOLOGICAL SCIENCES
18669557
(2022)
Archaeologists have been reconstructing interactions amongst hunter-gatherer populations for a long time. These exchanges are materialised in the movements of raw materials and symbolic objects which are found far from their original sources. Social network, i.e. the structure constituted by these interactions, is a well-established concept in archaeology that is used to address the connectivity of hunter-gatherer populations. The heuristic potential of formal network analysis, however, has been scarcely exploited in prehistoric hunter-gatherer archaeology. Here, social network analysis is used to analyse the interactions amongst hunter-gatherers on the Iberian Peninsula in the Early and Late Mesolithic (10,200 to 7600 cal BP). We used ornaments to explore social interaction and constructed one network per phase of the Iberian Mesolithic. We applied a three-steps analysis: First, we characterised the overall structure of the networks. Second, we performed centrality analysis to uncover the most relevant nodes. Finally, we conducted an exploratory analysis of the networks’ spatial characteristics. No significant differences were found between the overall network topology of the Early and Late Mesolithic. This suggests that the interaction patterns amongst human groups did not change significantly at a peninsular scale. Moreover, the spatial analysis showed that most interactions between human groups took place over distances under 300 km, but that specific ornament types like Columbella rustica were distributed over more extensive distances. Our findings suggest that Iberian Mesolithic social networks were maintained through a period of environmental, demographic and cultural transformation and that interactions took place at different scales of social integration.
Moving beyond domain-specific versus domain-general options in cognitive neuroscience
Asano, Rie .;Boeckx, Cedric ;Fujita, Kojie
CORTEX
00109452
(2022)
Comparative research on language, music, and action in cognitive neuroscience keeps finding evidence for both shared and non-shared components of cognitive systems. The discussions, then, tend to quickly fall into the sterile dichotomy between domain-specific versus domain-general options. In this position paper, we take issue with this dichotomy and argue for an alternative account based on neural reuse theories to understand findings on the relationship between language, music, and action. We argue that the differences between those cognitive systems can be explained in terms of the specialization of the same brain mechanism(s) for each domain, which emerges in the course of development and/or evolution.
Dynamics of topological defects in the noisy Kuramoto model in two dimensions
Rouzaire, Ylann; Levis, Demian
FRONTIERS IN PHYSICS
2296424X
(2022)
We consider the two-dimensional (2D) noisy Kuramoto model of synchronization with short-range coupling and a Gaussian distribution of intrinsic frequencies, and investigate its ordering dynamics following a quench. We consider both underdamped (inertial) and over-damped dynamics, and show that the long-term properties of this intrinsically out-of-equilibrium system do not depend on the inertia of individual oscillators. The model does not exhibit any phase transition as its correlation length remains finite, scaling as the inverse of the standard deviation of the distribution of intrinsic frequencies. The quench dynamics proceeds via domain growth, with a characteristic length that initially follows the growth law of the 2D XY model, although is not given by the mean separation between defects. Topological defects are generically free, breaking the Berezinskii-Kosterlitz-Thouless scenario of the 2D XY model. Vortices perform a random walk reminiscent of the self-avoiding random walk, advected by the dynamic network of boundaries between synchronised domains; featuring long-time super-diffusion, with the anomalous exponent α = 3/2.
Onsager reciprocal relations and chemo-mechanical coupling for chemically active colloids
De Corato, Marco; Pagonabarraga, Ignacio
JOURNAL OF CHEMICAL PHYSICS
00219606
(2022)
Similar to cells, bacteria, and other micro-organisms, synthetic chemically active colloids can harness the energy from their environment through a surface chemical reaction and use the energy to self-propel in fluidic environments. In this paper, we study the chemo-mechanical coupling that leads to the self-propulsion of chemically active colloids. The coupling between chemical reactions and momentum transport is a consequence of Onsager reciprocal relations. They state that the velocity and the surface reaction rate are related to mechanical and chemical affinities through a symmetric matrix. A consequence of Onsager reciprocal relations is that if a chemical reaction drives the motion of the colloid, then an external force generates a reaction rate. Here, we investigate Onsager reciprocal relations for a spherical active colloid that catalyzes a reversible surface chemical reaction between two species. We solve the relevant transport equations using a perturbation expansion and numerical simulations to demonstrate the validity of reciprocal relations around the equilibrium. Our results are consistent with previous studies and highlight the key role of solute advection in preserving the symmetry of the Onsager matrix. Finally, we show that Onsager reciprocal relations break down around a nonequilibrium steady state, which has implications for the thermal fluctuations of the active colloids used in experiments.
Pulsatile parallel flow of air and a viscoelastic fluid with multiple characteristic times. An application to mucus in the trachea and the frequency of cough
De La Guerra, Pablo Alberto ;Corvera Poiré E.
JOURNAL OF PHYSICS CONDENSED MATTER
09538984
(2022)
We study the dynamics of a binary fluid, where the two fluids are flowing parallel to each other in a cylindrical geometry, and driven by a pulsatile pressure gradient. One of the fluids is a low viscosity Newtonian fluid, the other one is viscoelastic. In order to be able to apply the model to different biofluids, we consider that the viscoelastic fluid has several characteristic times. We characterize the dynamics of the fluids as generalized Darcy's laws, with linear response functions to pulsatile pressure gradients, whose parameters are coupled for both fluids through the fluid-fluid boundary conditions. We apply our results to the dynamics of mucus and air in the trachea and find that the frequency that allows for a larger movement of the mucus, coincides with the experimental frequency of cough. This allows us to propose a plausible explanation for the frequency of cough in healthy individuals, a mechanical process to expel noxious substances from the respiratory system.
BRAVO self-confined expression through WOX5 in the Arabidopsis root stem-cell niche
Mercadal, Josep ;Betegón-Putze, Isabel ;Bosch, Nadj; Caño-Delgado, Ana ;Ibañes, Marta
DEVELOPMENT
14779129
(2022)
In animals and plants, stem-cell niches are local microenvironments that are tightly regulated to preserve their unique identity while communicating with adjacent cells that will give rise to specialized cell types. In the primary root of Arabidopsis thaliana, two transcription factors, BRAVO and WOX5, among others, are expressed in the stem-cell niche. Intriguingly, BRAVO, a repressor of quiescent center divisions, confines its own gene expression to the stem-cell niche, as evidenced in a bravo mutant background. Here, we propose through mathematical modeling that BRAVO confines its own expression domain to the stem-cell niche by attenuating a WOX5-dependent diffusible activator of BRAVO. This negative feedback drives WOX5 activity to be spatially restricted as well. The results show that WOX5 diffusion and sequestration by binding to BRAVO are sufficient to drive the experimentally observed confined BRAVO expression at the stem-cell niche. We propose that the attenuation of a diffusible activator can be a general mechanism acting at other stem-cell niches to spatially confine genetic activity to a small region while maintaining signaling within them and with the surrounding cells.
Janssen effect in columns of fire ants
Anderson, Caleb J. ;Gibson, Pryor A. ;Fernandez-Nieves, Alberto
PHYSICAL REVIEW E
24700045
(2022)
We study fire-ant columns, an active version of passive granular columns, and find that, despite the inherent activity of the ants and their natural tendency to rearrange, the ants develop force-chain structures that help support the weight of the column. Hence, the apparent mass at the bottom of the column saturates with added mass in a Janssen-like fashion, reminiscent of what is seen in passive-grain columns in wide containers. Activity-induced rearrangements within the column, however, lead to changes in the force-chain structure that slightly reduce the supportive nature of the force-chains over time and to fluctuations in the pressure at the bottom of the column that scale like the law of large numbers. We capture the experimental results in simulations that include not only friction with the walls, but also a fluctuating force that introduces activity and that effectively affects the force-chain structure of the ant collective.
Maximizing friction by liquid flow clogging in confinement
Chen, Shan; Guo, Zhenjiang ;Zhang, Hongguang ;Pagonabarraga, Ignacio .;Zhang, Xianren
EUROPEAN PHYSICAL JOURNAL
12928941
(2022)
In the nanoscale regime, flow behaviors for liquids show qualitative deviations from bulk expectations. In this work, we reveal by molecular dynamics simulations that plug flow down to nanoscale induces molecular friction that leads to a new flow structure due to the molecular clogging of the encaged liquid. This plug-like nanoscale liquid flow shows several features differ from the macroscopic plug flow and Poiseuille flow: It leads to enhanced liquid/solid friction, producing a friction of several order of magnitude larger than that of Couette flow; the friction enhancement is sensitively dependent of the liquid column length and the wettability of the solid substrates; it leads to the local compaction of liquid molecules that may induce solidification phenomenon for a long liquid column.
Impact of dipole-dipole interactions on motility-induced phase separation
Sesé-Sansa, Elena; Liao, Guo-Jun ;Levis, Demian ;Pagonabarraga, Ignacio ;Klapp, Sabine H. L.
SOFT MATTER
1744683X
(2022)
We present a hydrodynamic theory for systems of dipolar active Brownian particles which, in the regime of weak dipolar coupling, predicts the onset of motility-induced phase separation (MIPS), consistent with Brownian dynamics (BD) simulations. The hydrodynamic equations are derived by explicitly coarse-graining the microscopic Langevin dynamics, thus allowing for a mapping of the coarse-grained model and particle-resolved simulations. Performing BD simulations at fixed density, we find that dipolar interactions tend to hinder MIPS, as first reported in [Liao et al., Soft Matter, 2020, 16, 2208]. Here we demonstrate that the theoretical approach indeed captures the suppression of MIPS. Moreover, the analysis of the numerically obtained, angle-dependent correlation functions sheds light into the underlying microscopic mechanisms leading to the destabilization of the homogeneous phase.
Characterization and Evolution of Mental Health Problems Attended to in a Telephone Helpline During the Lockdown and De-Escalation by COVID-19
Pérez-González, Alba ;Benítez-Borrego, Sonia ;Garcia-Sicard, Jordi ;Cuartero, Andrés ;Ruiz-Torras, Silvia ;Guàrdia-Olmos, Joan
INTERNATIONAL JOURNAL OF PUBLIC HEALTH
16618564
(2022)
Objectives: To picture the psychological impact on the general population consulting the Emergency Medical System (EMS) of Catalonia for psychological assistance due to the COVID-19. Methods: Calls received to the 061 emergency phone number between the months of March and June 2020 (period of lockdown and de-escalation) were analyzed. The reason, most prevalent psychological symptoms, presence of psychological antecedents, and type of intervention that was carried out were analyzed. Results: A total of 2,516 calls were analyzed. Weeks 6, 7, 8 and 9 of lockdown saw the highest volume of calls (298, 314, 282 and 290 daily calls, respectively). The main profile of the affected person was women, under the age of 50 who are responsible for others. Psychologically, they present symptoms of depression (7.33%) and anxiety (39.44%). The greatest impacts on mental health throughout lockdown seem to be related to an increase of interpersonal conflict (8.8% < 11.2%), work-related problems (1.7% < 4.6%), and problems of psychological distress (6.5% < 17.0%). Conclusion: The information obtained enables us to better understand the possible evolution of the impacts on mental health derived from the lockdown.
Breaking action-reaction with active apolar colloids: emergent transport and velocity inversion
Codina, Joan ;Massana-Cid, Helena ;Tierno, Pietro ;Pagonabarraga, Ignacio
SOFT MATTER
1744683X
(2022)
Artificial active particles are autonomous agents able to convert energy from the environment into net propulsion, breaking detailed balance and the action-reaction law, clear signatures of their out-of-equilibrium nature. Here we investigate the emergence of directed motion in clusters composed of passive and catalytically active apolar colloids. We use a light-induced chemophoretic flow to rapidly assemble hybrid self-propelling clusters composed of hematite particles and passive silica spheres. By increasing the size of the passive cargo, we observe a reversal in the transport direction of the pair. We explain this complex yet rich phenomenon using a theoretical model which accounts for the generated chemical field and its coupling with the surrounding medium. We exploit further our technique to build up more complex, chemically driven, architectures capable of carrying several passive or active species, that quickly assemble and disassemble under light control
A lattice Boltzmann model for self-diffusiophoretic particles near and at liquid-liquid interfaces
Palacios, Lucas S.; Scagliarini, Andrea ;Pagonabarraga, Ignacio
JOURNAL OF CHEMICAL PHYSICS
00219606
(2022)
We introduce a novel mesoscopic computational model based on a multiphase-multicomponent lattice Boltzmann method for the simulation of self-phoretic particles in the presence of liquid-liquid interfaces. Our model features fully resolved solvent hydrodynamics, and, thanks to its versatility, it can handle important aspects of the multiphysics of the problem, including particle wettability and differential solubility of the product in the two liquid phases. The method is extensively validated in simple numerical experiments, whose outcome is theoretically predictable, and then applied to the study of the behavior of active particles next to and trapped at interfaces. We show that their motion can be variously steered by tuning relevant control parameters, such as the phoretic mobilities, the contact angle, and the product solubility.
Hydrodynamic synchronization and clustering in ratcheting colloidal matter
Leyva, Sergi G.a, b;Stoop, Ralph L.a;Pagonabarraga, Ignacioa, b, c;Tierno, Pietro
SCIENCE ADVANCES
23752548
(2022)
Ratchet transport systems are widespread in physics and biology; however, the effect of the dispersing medium in the collective dynamics of these out-of-equilibrium systems has been often overlooked. We show that, in a traveling wave magnetic ratchet, long-range hydrodynamic interactions (HIs) produce a series of remarkable phenomena on the transport and assembly of interacting Brownian particles. We demonstrate that HIs induce the resynchronization with the traveling wave that emerges as a “speed-up” effect, characterized by a net raise of the translational speed, which doubles that of single particles. When competing with dipolar forces and the underlying substrate symmetry, HIs promote the formation of clusters that grow perpendicular to the driving direction. We support our findings both with Langevin dynamics and with a theoretical model that accounts for the fluid-mediated interactions. Our work illustrates the role of the dispersing medium on the dynamics of driven colloidal matter and unveils the growing process and cluster morphologies above a periodic substrate.
The long cross-over dynamics of capillary imbibition
Ruiz-Gutiérrez, Élfego ;Armstrong, Steven ;Lévêque, Simon ;Michel, Célestin ;Pagonabarraga, Ignacio ;Wells, Gary G. ;Hernández-Machado, Aurora ;Ledesma-Aguilar, Rodrigo
JOURNAL OF FLUID MECHANICS
00221120
(2022)
Spontaneous capillary imbibition is a classical problem in interfacial fluid dynamics with a broad range of applications, from microfluidics to agriculture. Here we study the duration of the cross-over between an initial linear growth of the imbibition front to the diffusive-like growth limit of Washburn's law. We show that local-resistance sources, such as the inertial resistance and the friction caused by the advancing meniscus, always limit the motion of an imbibing front. Both effects give rise to a cross-over of the growth exponent between the linear and the diffusive-like regimes. We show how this cross-over is much longer than previously thought - even longer than the time it takes the liquid to fill the porous medium. Such slowly slowing-down dynamics is likely to cause similar long cross-over phenomena in processes governed by wetting.
Involvement of Mechanical Cues in the Migration of Cajal-Retzius Cells in the Marginal Zone During Neocortical Development
López-Mengual, Ana ;Segura-Feliu, Miriam ;Sunyer, Raimon ;Sanz-Fraile, Héctor ;Otero, Jorge ;Mesquida-Veny, Francina ;Gil, Vanessa ;Hervera, Arnau ;Ferrer, Isidre ;Soriano, Jordi ;Trepat, Xavier ;Farré, Ramon
Frontiers in Cell and Developmental Biology
2296634X
(2022)
Emerging evidence points to coordinated action of chemical and mechanical cues during brain development. At early stages of neocortical development, angiogenic factors and chemokines such as CXCL12, ephrins, and semaphorins assume crucial roles in orchestrating neuronal migration and axon elongation of postmitotic neurons. Here we explore the intrinsic mechanical properties of the developing marginal zone of the pallium in the migratory pathways and brain distribution of the pioneer Cajal-Retzius cells. These neurons are generated in several proliferative regions in the developing brain (e.g., the cortical hem and the pallial subpallial boundary) and migrate tangentially in the preplate/marginal zone covering the upper portion of the developing cortex. These cells play crucial roles in correct neocortical layer formation by secreting several molecules such as Reelin. Our results indicate that the motogenic properties of Cajal-Retzius cells and their perinatal distribution in the marginal zone are modulated by both chemical and mechanical factors, by the specific mechanical properties of Cajal-Retzius cells, and by the differential stiffness of the migratory routes. Indeed, cells originating in the cortical hem display higher migratory capacities than those generated in the pallial subpallial boundary which may be involved in the differential distribution of these cells in the dorsal-lateral axis in the developing marginal zone.
Nanoparticle anisotropy induces sphere-to-cylinder phase transition in block copolymer melts
Diaz, Javier ;Pinna, Marco ;Zvelindovsky, Andrei ;Pagonabarraga, Ignacio
SOFT MATTER
1744683X
(2022)
Block copolymer nanocomposites including anisotropic nanoparticles have been previously found to co-assemble into complex structures with nanoparticle alignment. Anisotropic nanoparticles with large aspect ratios are found to modify the morphology of block copolymers at modest concentrations, inducing a sphere-to-cylinder phase transition by breaking the local symmetry in the vicinity of a solid particle. This transition takes place over a wide range of NP lengths comparable with the BCP spacing. Controlling the orientation of uniaxial nanoparticles provides additional control over the global orientation of the block copolymer, as previously reported by experiments.
Adsorption of amphiphilic grafted polymers as polymer corrosion inhibitors: insights from mesoscopic simulations
Díaz, Javier .;Soltau, Marko ;Lísal, Martin; Carbone, Paola ;Pagonabarraga, Ignacio
Physical Chemistry Chemical Physics
14639076
(2022)
The homogeneous covering of amphiphillic polymer molecules onto metallic surfaces is of great importance for corrosion inhibitor applications. Lyophillic side chains grafted onto a lyophobic backbone act as anchors that allow the molecule to absorb at the metallic surface preventing the exposure with the solvent. Coarse-grained simulations are used to study the sorption and conformation behaviour of amphiphillic grafted polymers for corrosion inhibition. The backbone insolubility is found to play a key role in the sorption and conformation behaviour in the dilute limit. For finite concentrations, moderate backbone solubility and moderate molecule concentrations achieve optimal surface coverage, while highly a lyophobic backbone leads to bulk-like structures as a consequence of aggregation.
Contact line dynamics of pulsatile fluid interfaces modulated by patterned substrates
Flores Gerónimo J. ;Hernández-Machado A.;Corvera Poiré E.
PHYSICS OF FLUIDS
10706631
(2022)
We study the dynamics of microfluidic fronts driven by pulsatile pressures in the presence of patches of hydrophilic wetting on the walls of the confining media. To do so, we use a recently developed phase-field model that takes inertia into account. We track the interface position in channels with different spacing between the patches and observe that the smaller the spacing, the faster the advancement of the front. We find that the wetting patterning induces a modulating dynamics of the contact line that causes an effective wetting, which in turn determines the modulation of the interface velocity. We characterize the modulation frequency in terms of wetting pattern, inertia, and surface tension, via the capillary pressure, viscosity, and confinement.
Glass-Based Devices to Generate Drops and Emulsions
Guerrero, Josefa .;Rojo, Javier ;de La Cotte, Alexis ;Vila, Enric ;Fernandez-Nieves, Alberto
Journal of Visualized Experiments
1940087X
(2022)
In this manuscript, three different step-by-step protocols to generate highly monodisperse emulsion drops using glass-based microfluidics are described. The first device is built for the generation of simple drops driven by gravity. The second device is designed to generate emulsion drops in a coflowing scheme. The third device is an extension of the coflowing device with the addition of a third liquid that acts as an electric ground, allowing the formation of electrified drops that subsequently discharge. In this setup, two of the three liquids have an appreciable electrical conductivity. The third liquid mediates between these two and is a dielectric. A voltage difference applied between the two conducting liquids creates an electric field that couples with hydrodynamic stresses of the coflowing liquids, affecting the jet and drop formation process. The addition of the electric field provides a path to generate smaller drops than in simple coflow devices and for generating particles and fibers with a wide range of sizes.
TASE: Task-Aware Speech Enhancement for Wake-Up Word Detection in Voice Assistants
Cámbara, Guillermo; López, Fernando; Bonet, David ;Gómez, Pablo ;Segura, Carlos ;Farrús, Mireia ;Luque, Jordi
Applied Sciences
20763417
(2022)
Wake-up word spotting in noisy environments is a critical task for an excellent user experience with voice assistants. Unwanted activation of the device is often due to the presence of noises coming from background conversations, TVs, or other domestic appliances. In this work, we propose the use of a speech enhancement convolutional autoencoder, coupled with on-device keyword spotting, aimed at improving the trigger word detection in noisy environments. The end-to-end system learns by optimizing a linear combination of losses: a reconstruction-based loss, both at the log-mel spectrogram and at the waveform level, as well as a specific task loss that accounts for the cross-entropy error reported along the keyword spotting detection. We experiment with several neural network classifiers and report that deeply coupling the speech enhancement together with a wake-up word detector, e.g., by jointly training them, significantly improves the performance in the noisiest conditions. Additionally, we introduce a new publicly available speech database recorded for the Telefónica’s voice assistant, Aura. The OK Aura Wake-up Word Dataset incorporates rich metadata, such as speaker demographics or room conditions, and comprises hard negative examples that were studiously selected to present different levels of phonetic similarity with respect to the trigger words “OK Aura”.
Citizen science at public libraries: Data on librarians and users perceptions of participating in a citizen science project in Catalunya, Spain
Cigarini, Anna ;Bonhoure, Isabelle ;Vicens, Julián ;Perelló, Josep
Data in Brief
(2022)
As libraries struggle to keep pace with the changing societal landscape, emerging practices such as citizen science (CS) initiatives are being incorporated to reinforce the idea of public libraries as gathering, meeting, and collaboration spaces within the context of shared community and shared learning resources. However, there is little empirical evidence of whether the most open and participatory ways that CS puts forward can converge with and be nurtured by the essence of public libraries. Also, the roles of librarians and users in the ‘next generation public library’ have been under-developed. As the number of CS initiatives at public libraries grows, so does the need to collect evidence on the impact and the capacity of assimilation of CS practices. The data describes librarians and users' perceptions of participating in a citizen science project. Two hands-on activities for librarians of the Barcelona Network of Public Libraries were implemented. One was a training course for 30 librarians from 24 libraries which allowed them to envisage citizen science implementation in each library. The second activity consisted in the co-creation of a citizen social science project. 40 library users, 7 librarians from 3 different cities, and professional scientists, were involved. The data on librarians and users' perception was collected through participant observation, surveys, and a focus group to identify strengths and challenges of implementing citizen science at public libraries. The data covers librarians and users attitudes towards citizen science, their motivations to participate, their perceived ability to implement a citizen science project (as for librarians) or to contribute to science (as for library users), and the participants intention to keep engaged with citizen science, drawing on the Theory of Planned Behavior. Responses to closed-ended survey questions are analyzed at a descriptive level. The qualitative feedback from the focus group and the open-ended survey question on motivations is subjected to a thematic analysis. The data offers interesting insights to identify opportunities and challenges of implementing citizen science at public libraries, contributing to the debate over the public library's mission as local community hub.
Unified analysis of topological defects in 2D systems of active and passive disks
Digregorio, Pasquale ;Levis, Demian ;Cugliandolo, Leticia F. ;Gonnella, Giuseppe ;Pagonabarraga, Ignacio
SOFT MATTER
1744683X
(2022)
We provide a comprehensive quantitative analysis of localized and extended topological defects in the steady state of 2D passive and active repulsive Brownian disk systems. We show that, both in and out-of-equilibrium, the passage from the solid to the hexatic is driven by the unbinding of dislocations, in quantitative agreement with the KTHNY singularity. Instead, extended clusters of defects largely dominate below the solid-hexatic critical line. The latter percolate in the liquid phase very close to the hexatic-liquid transition, both for continuous and discontinuous transitions, in the homogeneous liquid regime. At critical percolation the clusters of defects are fractal with statistical and geometric properties that are independent of the activity and compatible with the universality class of uncorrelated critical percolation. We also characterize the spatial organization of point-like defects and we show that the disclinations are not free, but rather always very near more complex defect structures. At high activity, the bulk of the dense phase generated by Motility-Induced Phase Separation is characterized by a density of point-like defects, and statistics and morphology of defect clusters, set by the amount of activity and not the packing fraction. Hexatic domains within the dense phase are separated by grain-boundaries along which a finite network of topological defects resides, interrupted by gas bubbles in cavitation. This structure is dynamic in the sense that the defect network allows for an unzipping mechanism that leaves free space for gas bubbles to appear, close, and even be released into the dilute phase.
Visualisation of hierarchical multivariate data: Categorisation and case study on hate speech
Kavaz, Ecem ;Puig, Anna , b;Rodríguez, Inmaculada ;Chacón, Reyes ;De-La-Paz, David ;Torralba, Adrià ;Nofre, Montserrat ;Taule, Mariona
Information Visualization
14738716
(2022)
Multivariate hierarchical data has an important role in many applications. To find the best visualisation that best fits a concrete data is crucial to explore and understand the relationships between the data. This paper proposes a categorisation – Elongated and Compact – of hierarchical data based on the inner shapes of the hierarchies, that is the connectivity degree of the internal nodes, the number of nodes, etc, that can be applied to any hierarchical data. Based on this taxonomy, we explore implicit and explicit layouts – Tree, Circle Packing, Force and Radial – to provide users with a complete view of the data. We hypothesise that Tree and Circle Packing fit with Elongated structures, and Force and Radial fit with Compact ones. In addition, we cluster multivariate features to embed them in the hierarchical layouts. Especially, we propose two different glyphs –one-by-one and all-in-one, and we bet for the one-by-one glyphs as the most suitable for showing the distribution of several features along with the hierarchical structures. To validate our hypotheses, we conducted a user study with 35 participants using a hate speech annotated corpus. This corpus comes from 4359 comments posted in online Spanish newspapers. The results indicated that users preferred the Tree layout over the other three layouts (Circle, Force, Radial) with both types of structures (EC and CC). However, when we focused the analysis only on Radial and Force layouts, both of them scored significantly higher with Compact than with Elongated data. Moreover, participants scored the one-by-one glyph higher than the all-in-one glyph, but the difference was not significant.
Friction Induces Anisotropic Propulsion in Sliding Magnetic Microtriangles
Junot, Gasparda;Leyva, Sergi G. ;Pauer, Christoph ;Calero, Carles ;Pagonabarraga, Ignacio ;Liedl, Tim ;Tavacoli, Joe ;Tierno, Pietro
Nano Letters
15306984
(2022)
In viscous fluids, motile microentities such as bacteria or artificial swimmers often display different transport modes than macroscopic ones. A current challenge in the field aims at using friction asymmetry to steer the motion of microscopic particles. Here we show that lithographically shaped magnetic microtriangles undergo a series of complex transport modes when driven by a precessing magnetic field, including a surfing-like drift close to the bottom plane. In this regime, we exploit the triangle asymmetric shape to obtain a transversal drift which is later used to transport the microtriangle in any direction along the plane. We explain this friction-induced anisotropic sliding with a minimal numerical model capable to reproduce the experimental results. Due to the flexibility offered by soft-lithographic sculpturing, our method to guide anisotropic-shaped magnetic microcomposites can be potentially extended to many other field responsive structures operating in fluid media.
Effective Early Stopping of Point Cloud Neural Networks
Zoumpekas, Thanasis ;Salamó, Maria ;Puig, Anna
Lecture Notes in Computer Science
03029743
(2022)
Early stopping techniques can be utilized to decrease the time cost, however currently the ultimate goal of early stopping techniques is closely related to the accuracy upgrade or the ability of the neural network to generalize better on unseen data without being large or complex in structure and not directly with its efficiency. Time efficiency is a critical factor in neural networks, especially when dealing with the segmentation of 3D point cloud data, not only because a neural network itself is computationally expensive, but also because point clouds are large and noisy data, making learning processes even more costly. In this paper, we propose a new early stopping technique based on fundamental mathematics aiming to upgrade the trade-off between the learning efficiency and accuracy of neural networks dealing with 3D point clouds. Our results show that by employing our early stopping technique in four distinct and highly utilized neural networks in segmenting 3D point clouds, the training time efficiency of the models is greatly improved, with efficiency gain values reaching up to 94%, while the models achieving in just a few epochs approximately similar segmentation accuracy metric values like the ones that are obtained in the training of the neural networks in 200 epochs. Also, our proposal outperforms four conventional early stopping approaches in segmentation accuracy, implying a promising innovative early stopping technique in point cloud segmentation.
Valuing the Future and Discounting in Random Environments: A Review
Masoliver, Jaume ;Montero, Miquel ;Perelló, Josep ;Farmer, J. Doyne ;Geanakoplos, John
ENTROPY
10994300
(2022)
We address the process of discounting in random environments, which allows valuation of the future in economic terms. We review several approaches to the problem regarding different well-established stochastic market dynamics in the continuous-time context and include the Feynman–Kac approach. We also review the relation between bond-pricing theory and discounting and introduce both the market price of risk and the risk neutral measure from an intuitive point of view devoid of excessive formalism. We provide the discount for each economic model and discuss their key results. We finally present a summary of our previous empirical studies for several countries on the long-run discount problem.
Dynamical robustness of collective neuronal activity upon targeted damage in interdependent networks
Faci-Lázaro, Sergio ;Lor, Tatiana ;Ródenas, Guillermo ;Mazo, Juan J. ;Soriano, Jordi ;Gómez-Gardeñes, Jesús
European Physical Journal: Special Topics
19516355
(2022)
In the last decades, the availability of data about the structure of social, technological and biological systems has provided important insights on the mechanisms governing their correct functioning and robustness. These mechanisms are grounded on the complex backbone of interactions among the constituents of the system, which include both topological and dynamical aspects. Here, we analyze interdependent networks composed of two layers of interacting neuronal units and explore their robustness when these synthetic cultures are subjected to damage in the form of either targeted attack or failure. Our results show that the functionality of these networks does not decrease monotonically with damage but, on the contrary, they are able to increase their level of activity when the experienced damage is sufficiently strong.
Age Effects Aggressive Behavior: RNA-Seq Analysis in Cattle with Implications for Studying Neoteny Under Domestication
Eusebi, Paulina G. ;Sevane, Natalia ;O’Rourke, Thomas ;Pizarro, Manuela ;Boeckx, Cedric ;Dunner, Susana
Behavior Genetics
00018244
(2022)
The reactive type of aggression is regulated mostly by the brain’s prefrontal cortex; however, the molecular changes underlying aggressiveness in adults have not been fully characterized. We used an RNA-seq approach to investigate differential gene expression in the prefrontal cortex of bovines from the aggressive Lidia breed at different ages: young three-year old and adult four-year-old bulls. A total of 50 up and 193 down-regulated genes in the adult group were identified. Furthermore, a cross-species comparative analysis retrieved 29 genes in common with previous studies on aggressive behaviors, representing an above-chance overlap with the differentially expressed genes in adult bulls. We detected changes in the regulation of networks such as synaptogenesis, involved in maintenance and refinement of synapses, and the glutamate receptor pathway, which acts as excitatory driver in aggressive responses. The reduced reactive aggression typical of domestication has been proposed to form part of a retention of juvenile traits as adults (neoteny).
Dynamics and interactions of magnetically driven colloidal microrotors
Hernández, Raúl Josué Hernández ;Fischer, Thomas M. ;Tierno, Pietro
Applied Physics Letters
(2022)
We study the pair interactions between magnetically driven colloidal microrotors with an anisotropic shape. An external precessing magnetic field induces a torque to these particles spinning them at a fixed angular frequency. When pair of rotors approach each other, the anisotropic particles interact via dipolar forces and hydrodynamic interactions (HIs) excited by their rotational motion. For applied field spinning close to the magic angle, m = 54.7 °, dipolar interactions vanish and the dynamic assembly of the pair is driven only by HIs. Further, we provide a theoretical description based on the balance between dipolar forces and HIs that allow understanding the role of anisotropy on the collective dynamics. Investigating microscopic colloidal rotors and understanding their collective dynamics are important tasks for both fundamental reasons, but also to engineer similar fluid stirrers that can be readily used for precise microscale operations or as microrheological probes.
The heritability of vocal tract structures estimated from structural MRI in a large cohort of Dutch twins
Dediu, Dan ;Jennings, Emily M.d, e;van’t Ent, Dennis ;Moisik, Scott R. ;Di Pisa, Grazia ;Schulze, Jannah ;de Geus, Eco J. C. ;den Braber, Anouk ;Dolan, Conor V. ;Boomsma, Dorret I.
Human Genetics
03406717
(2022)
While language is expressed in multiple modalities, including sign, writing, or whistles, speech is arguably the most common. The human vocal tract is capable of producing the bewildering diversity of the 7000 or so currently spoken languages, but relatively little is known about its genetic bases, especially in what concerns normal variation. Here, we capitalize on five cohorts totaling 632 Dutch twins with structural magnetic resonance imaging (MRI) data. Two raters placed clearly defined (semi)landmarks on each MRI scan, from which we derived 146 measures capturing the dimensions and shape of various vocal tract structures, but also aspects of the head and face. We used Genetic Covariance Structure Modeling to estimate the additive genetic, common environmental or non-additive genetic, and unique environmental components, while controlling for various confounds and for any systematic differences between the two raters. We found high heritability, h2, for aspects of the skull and face, the mandible, the anteroposterior (horizontal) dimension of the vocal tract, and the position of the hyoid bone. These findings extend the existing literature, and open new perspectives for understanding the complex interplay between genetics, environment, and culture that shape our vocal tracts, and which may help explain cross-linguistic differences in phonetics and phonology.
Analysis of Biases in Calibrated Recommendations
Rojas, Carlos ;Contreras, David ;Salamó, Maria
Communications in Computer and Information Science
978-303109315-9
(2022)
While recommender systems have mainly focused on the effectiveness of their results, beyond-accuracy perspectives have been recently explored. One of the most prominent is algorithmic bias, which analyzes if existing imbalances in the input data are exacerbated in the produced recommendations. On the other hand, calibrated recommendations ensure that the recommendations reflect the distribution of the original preferences of each user (e.g., in terms of item genres). In this paper, we connect these two perspectives, to analyze how the original calibration method deals with the bias in the state-of-the-art recommendation models. Our analysis on real-world data shows that the calibration effectiveness is impacted by how a recommendation model handles bias.
NEW KNOWLEDGE ENVIRONMENTS On the possibility of a citizen social science
Perelló, Josep
Metode
21743487
(2022)
Citizen science is in a process of consolidation, with a wide variety of practices and perspectives. Social sciences and humanities occupy a small space despite the obvious social dimension of citizen science. In this sense, citizen social science can enrich the concept of citizen science both because the research objective can also be of a social nature and because it provides greater reflection on the active participation of individuals, groups, or communities in research projects. Based on different experiences, this paper proposes that citizen social science should have the capacity to empower participants and provide them with skills to promote collective actions or public policies based on a co-created knowledge. © 2022, Universitat de Valencia. All rights reserved.
Active Turbulence
Alert, Ricard ;Casademunt, Jaume ;Joanny, Jean-Francois
Annual Review of Condensed Matter Physics
19475454
(2022)
Active fluids exhibit spontaneous flows with complex spatiotemporal structure, which have been observed in bacterial suspensions, sperm cells, cytoskeletal suspensions, self-propelled colloids, and cell tissues. Despite occurring in the absence of inertia, chaotic active flows are reminiscent of inertial turbulence, and hence they are known as active turbulence. Here, we survey the field, providing a unified perspective over different classes of active turbulence. To this end, we divide our review into sections for systems with either polar or nematic order, and with or without momentum conservation (wet or dry). Comparing to inertial turbulence, we highlight the emergence of power-law scaling with either universal or nonuniversal exponents. We also contrast scenarios for the transition from steady to chaotic flows, and we discuss the absence of energy cascades. We link this feature to both the existence of intrinsic length scales and the self-organized nature of energy injection in active turbulence, which are fundamental differences from inertial turbulence. We close by outlining the emerging picture, remaining challenges, and future directions.
Collective durotaxis of cohesive cell clusters on a stiffness gradient
Pi-Jaumà, Irina ;Alert, Ricard ;Casademunt, Jaume
European Physical Journal E
12928941
(2022)
Abstract: Many types of motile cells perform durotaxis, namely directed migration following gradients of substrate stiffness. Recent experiments have revealed that cell monolayers can migrate toward stiffer regions even when individual cells do not—a phenomenon known as collective durotaxis. Here, we address the spontaneous motion of finite cohesive cell monolayers on a stiffness gradient. We theoretically analyze a continuum active polar fluid model that has been tested in recent wetting assays of epithelial tissues and includes two types of active forces (cell–substrate traction and cell–cell contractility). The competition between the two active forces determines whether a cell monolayer spreads or contracts. Here, we show that this model generically predicts collective durotaxis, and that it features a variety of dynamical regimes as a result of the interplay between the spreading state and the global propagation, including sequential contraction and spreading of the monolayer as it moves toward higher stiffness. We solve the model exactly in some relevant cases, which provides both physical insights into the mechanisms of tissue durotaxis and spreading as well as a variety of predictions that could guide the design of future experiments.
Role of Time Scales in the Coupled Epidemic-Opinion Dynamics on Multiplex Networks
Jankowski, Robert ;Chmiel, Anna
ENTROPY
10994300
(2022)
Modelling the epidemic’s spread on multiplex networks, considering complex human behaviours, has recently gained the attention of many scientists. In this work, we study the interplay between epidemic spreading and opinion dynamics on multiplex networks. An agent in the epidemic layer could remain in one of five distinct states, resulting in the SIRQD model. The agent’s attitude towards respecting the restrictions of the pandemic plays a crucial role in its prevalence. In our model, the agent’s point of view could be altered by either conformism mechanism, social pressure, or independent actions. As the underlying opinion model, we leverage the q-voter model. The entire system constitutes a coupled opinion–dynamic model where two distinct processes occur. The question arises of how to properly align these dynamics, i.e., whether they should possess equal or disparate timescales. This paper highlights the impact of different timescales of opinion dynamics on epidemic spreading, focusing on the time and the infection’s peak.
Reconstructing social networks of Late Glacial and Holocene hunter-gatherers to understand cultural evolution
Romano, Valéria ;Lozano, Sergi ;Fernández-López De Pablo, Javier
Philosophical Transactions of the Royal Society B: Biological Sciences
09628436
(2022)
Culture is increasingly being framed as a driver of human phenotypes and behaviour. Yet very little is known about variations in the patterns of past social interactions between humans in cultural evolution. The archaeological record, combined with modern evolutionary and analytical approaches, provides a unique opportunity to investigate broad-scale patterns of cultural change. Prompted by evidence that a population's social connectivity influences cultural variability, in this article, we revisit traditional approaches used to infer cultural evolutionary processes from the archaeological data. We then propose that frameworks considering multi-scalar interactions (from individuals to populations) over time and space have the potential to advance knowledge in cultural evolutionary theory. We describe how social network analysis can be applied to analyse diachronic structural changes and test cultural transmission hypotheses using the archaeological record (here specifically from the Marine Isotope Stage 3 ca 57-29 ka onwards). We argue that the reconstruction of prehistoric networks offers a timely opportunity to test the interplay between social connectivity and culture and ultimately helps to disentangle evolutionary mechanisms in the archaeological record. This article is part of a discussion meeting issue 'The emergence of collective knowledge and cumulative culture in animals, humans and machines'.
Towards Adaptive Gamification: A Method Using Dynamic Player Profile and a Case Study
Rodríguez, Inmaculada ;Puig, Anna ;Rodríguez, Àlex
Applied Sciences
20763417
(2022)
The design of gamified experiences following the one-fits-all approach uses the same game elements for all users participating in the experience. The alternative is adaptive gamification, which considers that users have different playing motivations. Some adaptive approaches use a (static) player profile gathered at the beginning of the experience; thus, the user experience fits this player profile uncovered through the use of a player type questionnaire. This paper presents a dynamic adaptive method which takes players’ profiles as initial information and also considers how these profiles change over time based on users’ interactions and opinions. Then, the users are provided with a personalized experience through the use of game elements that correspond to their dynamic playing profile. We describe a case study in the educational context, a course integrated on Nanomoocs, a massive open online course (MOOC) platform. We also present a preliminary evaluation of the approach by means of a simulator with bots that yields promising results when compared to baseline methods. The bots simulate different types of users, not so much to evaluate the effects of gamification (i.e., the completion rate), but to validate the convergence and validity of our method. The results show that our method achieves a low error considering both situations: when the user accurately (Err = 0.0070) and inaccurately (Err = 0.0243) answers the player type questionnaire.
Nematic Ordering of Anisotropic Nanoparticles in Block Copolymers
Diaz, Javier ;Pinna, Marco ;Zvelindovsky, Andrei V. ;Pagonabarraga, Ignacio
Advanced Theory and Simulations
25130390
(2022)
Block copolymer melts have been previously used to control the position and alignment of anisotropic nanoparticles. In this work, 2D and 3D mesoscopic simulations are used to explore the phase behavior of block copolymer/nanoparticle systems. The method combines a time-dependent Ginzburg-Landau for the polymer and Brownian dynamics for the anisotropic nanoparticles. Rhomboidal and spheroidal shaped particles are simulated in two and three dimensions, respectively. It is found that the nanoparticle nematic order aligned by the block copolymer domains enhances the lamellar phase of the block copolymer, due to an anisotropy-driven phase transition. Additionally, anisotropic nanoparticles within circular-forming block copolymer leads to a competition between the nematic colloidal ordering and the hexagonally ordered mesophase. At large concentrations, the nematic order dominates, deforming the block copolymer mesophase.
Collective motion of run-And-Tumble repulsive and attractive particles in one-dimensional systems
Gutiérrez, C. Miguel Barriuso ;Vanhille-Campos, Christian ;Alarcón, Francisco ;Pagonabarraga, Ignacio ;Brito, Ricardo ;Valeriani, Chantal
SOFT MATTER
1744683X
(2022)
Active matter deals with systems whose particles consume energy at the individual level in order to move. To unravel features such as the emergence of collective structures, several models have been suggested, such as the on-lattice model of run-And-Tumble particles implemented via the persistent exclusion process (PEP). In our work, we study a one-dimensional system of run-And-Tumble repulsive or attractive particles, both on-lattice and off-lattice. Additionally, we implement cluster motility dynamics in the on-lattice case (since in the off-lattice case, cluster motility arises from the individual particle dynamics). While we observe important differences between discrete and continuous dynamics, few common features are of particular importance. Increasing particle density drives aggregation across all different systems explored. For non-Attractive particles, the effects of particle activity on aggregation are largely independent of the details of the dynamics. In contrast, once attractive interactions are introduced, the steady-state, which is completely determined by the interplay between these and the particles' activity, becomes highly dependent on the details of the dynamics.
Predator-prey model for stock market fluctuations
Montero, M
JOURNAL OF ECONOMIC INTERACTION AND COORDINATION
(2021)
We present a dynamical model for the price evolution of financial assets. The model is based on a two-level approach: In the first stage, one finds an agent-based model that describes the current state of investors' beliefs, perspectives or strategies. The dynamics is inspired by a model for describing predator-prey population evolution: Agents change their mind through self- or mutual interaction, and the decision is adopted on a random basis, with no direct influence of the price itself. One of the most appealing properties of such a system is the presence of large oscillations in the number of agents sharing the same perspective, what may be linked with the existence of bullish and bearish periods in financial markets. In the second stage, one has the pricing mechanism, which will be driven by the relative population in the different groups of investors. The price equation will depend on the specific nature of the species, and thus, it may change from one market to the other: We will present a simple model of excess demand in the first place and then consider a more elaborate liquidity model. The outcomes of both models are analyzed and compared.
Network geometry
Marián Boguñá, Ivan Bonamassa, Manlio De Domenico, Shlomo Havlin, Dmitri Krioukov & M. Ángeles Serrano
Nature Reviews Physics
3
114 135
(2021)
Networks are finite metric spaces, with distances defined by the shortest paths between nodes. However, this is not the only form of network geometry: two others are the geometry of latent spaces underlying many networks and the effective geometry induced by dynamical processes in networks. These three approaches to network geometry are intimately related, and all three of them have been found to be exceptionally efficient in discovering fractality, scale invariance, self-similarity and other forms of fundamental symmetries in networks. Network geometry is also of great use in a variety of practical applications, from understanding how the brain works to routing in the Internet. We review the most important theoretical and practical developments dealing with these approaches to network geometry and offer perspectives on future research directions and challenges in this frontier in the study of complexity.
Optimal cost tuning of frustration: Achieving desired states in the Kuramoto-Sakaguchi model
Rosell-Tarrago, Gemma; Diaz-Guilera, Albert
Physical review. E
103
012216
(2021)
There are numerous examples of studied real-world systems that can be described as dynamical systems characterized by individual phases and coupled in a networklike structure. Within the framework of oscillatory models, much attention has been devoted to the Kuramoto model, which considers a collection of oscillators interacting through a sinus function of the phase differences. In this paper, we draw on an extension of the Kuramoto model, called the Kuramoto-Sakaguchi model, which adds a phase lag parameter to each node. We construct a general formalism that allows us to compute the set of lag parameters that may lead to any phase configuration within a linear approximation. In particular, we devote special attention to the cases of full synchronization and symmetric configurations. We show that the set of natural frequencies, phase lag parameters, and phases at the steady state is coupled by an equation and a continuous spectra of solutions is feasible. In order to quantify the system's strain to achieve that particular configuration, we define a cost function and compute the optimal set of parameters that minimizes it. Despite considering a linear approximation of the model, we show that the obtained tuned parameters for the case of full synchronization enhance frequency synchronization in the nonlinear model as well.
Amplitude death and restoration in networks of oscillators with random-walk diffusion
Clusella, P; Miguel, MC; Pastor-Satorras, R
COMMUNICATIONS PHYSICS
4
13
(2021)
Systems composed of reactive particles diffusing in a network display emergent dynamics. While Fick's diffusion can lead to Turing patterns, other diffusion schemes might display more complex phenomena. Here we study the death and restoration of collective oscillations in networks of oscillators coupled by random-walk diffusion, which modifies both the original unstable fixed point and the stable limit-cycle, making them topology-dependent. By means of numerical simulations we show that, in some cases, the diffusion-induced heterogeneity stabilizes the initially unstable fixed point via a Hopf bifurcation. Further increasing the coupling strength can moreover restore the oscillations. A numerical stability analysis indicates that this phenomenology corresponds to a case of amplitude death, where the inhomogeneous stabilized solution arises from the interplay of random walk diffusion and heterogeneous topology. Our results are relevant in the fields of epidemic spreading or ecological dispersion, where random walk diffusion is more prevalent.
Since Turing's seminal work, combining local reaction with diffusion is key to understand how patterns can appear in interacting systems. Here, the authors investigate the effect of coupling local dynamics with a non-traditional type of diffusion mechanism, random-walk diffusion, showing that this simple modification can give rise to previously unobserved amplitude death and restoration of collective oscillations
In Vitro Development of Human iPSC-Derived Functional Neuronal Networks on Laser-Fabricated 3D Scaffolds.
Koroleva, Anastasia; Deiwick, Andrea; El-Tamer, Ayman; Koch, Lothar; Shi, Yichen; Estevez-Priego, Estefania; Ludl, Adriaan-Alexander; Soriano, Jordi; Guseva, Daria; Ponimaskin, Evgeni; Chichkov, Boris
ACS applied materials & interfaces
13
7
(2021)
Focus of negation: Its identification in Spanish
Taule, M; Nofre, M; Gonzalez, M; Marti, MA
NATURAL LANGUAGE ENGINEERING
27
2
(2021)
This article describes the criteria for identifying the focus of negation in Spanish. This work involved an in-depth linguistic analysis of the focus of negation through which we identified some 10 different types of criteria that account for a wide variety of constructions containing negation. These criteria account for all the cases that appear in the NewsCom corpus and were assessed in the annotation of this corpus. The NewsCom corpus consists of 2955 comments posted in response to 18 different news articles from online newspapers. The NewsCom corpus contains 2965 negative structures with their corresponding negation marker, scope, and focus. This is the first corpus annotated with focus in Spanish and it is freely available. It is a valuable resource that can be used both for the training and evaluation of systems that aim to automatically detect the scope and focus of negation and for the linguistic analysis of negation grounded in real data.
Telegraphic Transport Processes and Their Fractional Generalization: A Review and Some Extensions
Masoliver, J
ENTROPY
23
3
(2021)
We address the problem of telegraphic transport in several dimensions. We review the derivation of two and three dimensional telegrapher's equations-as well as their fractional generalizations-from microscopic random walk models for transport (normal and anomalous). We also present new results on solutions of the higher dimensional fractional equations.
Jump-Diffusion Models for Valuing the Future: Discounting under Extreme Situations
Masoliver, J; Montero, M; Perello, J
MATHEMATICS
9
4
(2021)
We develop the process of discounting when underlying rates follow a jump-diffusion process, that is, when, in addition to diffusive behavior, rates suffer a series of finite discontinuities located at random Poissonian times. Jump amplitudes are also random and governed by an arbitrary density. Such a model may describe the economic evolution, specially when extreme situations occur (pandemics, global wars, etc.). When, between jumps, the dynamical evolution is governed by an Ornstein-Uhlenbeck diffusion process, we obtain exact and explicit expressions for the discount function and the long-run discount rate and show that the presence of discontinuities may drastically reduce the discount rate, a fact that has significant consequences for environmental planning. We also discuss as a specific example the case when rates are described by the continuous time random walk.
Quasi-symmetries in complex networks: a dynamical model approach
Rosell-Tarrago, G; Diaz-Guilera, A
JOURNAL OF COMPLEX NETWORKS
9
3
(2021)
The existence of symmetries in complex networks has a significant effect on network dynamic behaviour. Nevertheless, beyond topological symmetry, one should consider the fact that real-world networks are exposed to fluctuations or errors, as well as mistaken insertions or removals. Therefore, the resulting approximate symmetries remain hidden to standard symmetry analysis-fully accomplished by discrete algebra software. There have been a number of attempts to deal with approximate symmetries. In the present work we provide an alternative notion of these weaker symmetries, which we call 'quasi-symmetries'. Differently from other definitions, quasi-symmetries remain free to impose any invariance of a particular network property and they are obtained from the phase differences at the steady-state configuration of an oscillatory dynamical model: the Kuramoto-Sakaguchi model. The analysis of quasi-symmetries unveils otherwise hidden real-world networks attributes. On the one hand, we provide a benchmark to determine whether a network has a more complex pattern than that of a random network with regard to quasi-symmetries, namely, if it is structured into separate quasi-symmetric groups of nodes. On the other hand, we define the 'dual-network', a weighted network (and its corresponding binnarized counterpart) that effectively encodes all the information of quasi-symmetries in the original network. The latter is a powerful instrument for obtaining worthwhile insights about node centrality (obtaining the nodes that are unique from that act as imitators with respect to the others) and community detection (quasi-symmetric groups of nodes).
Optimal cost tuning of frustration: Achieving desired states in the Kuramoto-Sakaguchi model
Rosell-Tarrago, G; Diaz-Guilera, A
PHYSICAL REVIEW E
103
1
(2021)
There are numerous examples of studied real-world systems that can be described as dynamical systems characterized by individual phases and coupled in a networklike structure. Within the framework of oscillatory models, much attention has been devoted to the Kuramoto model, which considers a collection of oscillators interacting through a sinus function of the phase differences. In this paper, we draw on an extension of the Kuramoto model, called the Kuramoto-Sakaguchi model, which adds a phase lag parameter to each node. We construct a general formalism that allows us to compute the set of lag parameters that may lead to any phase configuration within a linear approximation. In particular, we devote special attention to the cases of full synchronization and symmetric configurations. We show that the set of natural frequencies, phase lag parameters, and phases at the steady state is coupled by an equation and a continuous spectra of solutions is feasible. In order to quantify the system's strain to achieve that particular configuration, we define a cost function and compute the optimal set of parameters that minimizes it. Despite considering a linear approximation of the model, we show that the obtained tuned parameters for the case of full synchronization enhance frequency synchronization in the nonlinear model as well.
Modeling partial lockdowns in multiplex networks using partition strategies
Plazas, A; Malvestio, I; Starnini, M; Diaz-Guilera, A
APPLIED NETWORK SCIENCE
6
27
(2021)
National stay-at-home orders, or lockdowns, were imposed in several countries to drastically reduce the social interactions mainly responsible for the transmission of the SARS-CoV-2 virus. Despite being essential to slow down the COVID-19 pandemic, these containment measures are associated with an economic burden. In this work, we propose a network approach to model the implementation of a partial lockdown, breaking the society into disconnected components, or partitions. Our model is composed by two main ingredients: a multiplex network representing human contacts within different contexts, formed by a Household layer, a Work layer, and a Social layer including generic social interactions, and a Susceptible-Infected-Recovered process that mimics the epidemic spreading. We compare different partition strategies, with a twofold aim: reducing the epidemic outbreak and minimizing the economic cost associated to the partial lockdown. We also show that the inclusion of unconstrained social interactions dramatically increases the epidemic spreading, while different kinds of restrictions on social interactions help in keeping the benefices of the network partition.
Random Walks with Invariant Loop Probabilities: Stereographic Random Walks
Montero, M
ENTROPY
23
6
(2021)
Random walks with invariant loop probabilities comprise a wide family of Markov processes with site-dependent, one-step transition probabilities. The whole family, which includes the simple random walk, emerges from geometric considerations related to the stereographic projection of an underlying geometry into a line. After a general introduction, we focus our attention on the elliptic case: random walks on a circle with built-in reflexing boundaries.
Hierarchical control as a shared neurocognitive mechanism for language and music
Asano, R; Boeckx, C; Seifert, U
COGNITION
216
104847
(2021)
Although comparative research has made substantial progress in clarifying the relationship between language and music as neurocognitive systems from both a theoretical and empirical perspective, there is still no consensus about which mechanisms, if any, are shared and how they bring about different neurocognitive systems. In this paper, we tackle these two questions by focusing on hierarchical control as a neurocognitive mechanism underlying syntax in language and music. We put forward the Coordinated Hierarchical Control (CHC) hypothesis: linguistic and musical syntax rely on hierarchical control, but engage this shared mechanism differently depending on the current control demand. While linguistic syntax preferably engages the abstract rule-based control circuit, musical syntax rather employs the coordination of the abstract rule-based and the more concrete motor-based control circuits. We provide evidence for our hypothesis by reviewing neuroimaging as well as neuropsychological studies on linguistic and musical syntax. The CHC hypothesis makes a set of novel testable predictions to guide future work on the relationship between language and music.
Measuring institutional thickness in tourism: An empirical application based on social network analysis
Restrepo, N; Lozano, S; Clave, SA
TOURISM MANAGEMENT PERSPECTIVES
37
100770
(2021)
This article uses social network analysis to measure institutional thickness in a regional tourism destination in Colombia. Through the analysis of 107 institutions, the empirical findings show that the configuration of formal interaction spaces determine the governance system of the destination turning certain institutions into hubs or authorities. The contribution of this research is two-fold. Firstly, it provides a new approach to the study of institutional thickness by applying a social network analysis methodology making possible to identify the components theoretically defined such as the role of institutional presence, levels of interaction, structures of domination, and common agendas in tourism. Secondly, it highlights the importance of understanding the role of the regional institutional environment and the governance framework of tourism destinations to better plan and their and effects.
Defect Superdiffusion and Unbinding in a 2D XY Model of Self-Driven Rotors
Rouzaire, Y; Levis, D
PHYSICAL REVIEW LETTERS
127
8
(2021)
We consider a nonequilibrium extension of the 2D XY model, equivalent to the noisy Kuramoto model of synchronization with short-range coupling, where rotors sitting on a square lattice are self-driven by random intrinsic frequencies. We study the static and dynamic properties of topological defects (vortices) and establish how self-spinning affects the Berezenskii-Kosterlitz-Thouless phase transition scenario. The nonequilibrium drive breaks the quasi-long-range ordered phase of the 2D XY model into a mosaic of ordered domains of controllable size and results in self-propelled vortices that generically unbind at any temperature, featuring superdiffusion < r(2)(t)> similar to t(3/2) with a Gaussian distribution of displacements. Our work provides a simple framework to investigate topological defects in nonequilibrium matter and sheds new light on the problem of synchronization of locally coupled oscillators.
Topological Boundary Constraints in Artificial Colloidal Ice
Rodriguez-Gallo, C; Ortiz-Ambriz, A; Tierno, P
PHYSICAL REVIEW LETTERS
126
18
(2021)
The effect of boundaries and how these can be used to influence the bulk behavior in geometrically frustrated systems arc both long-standing puzzles, often relegated to a secondary role. Here, we use numerical simulations and "proof of concept" experiments to demonstrate that boundaries can be engineered to control the bulk behavior in a colloidal artificial ice. We show that an antiferromagnetic frontier forces the system to rapidly reach the ground state (GS), as opposed to the commonly implemented open or periodic boundary conditions. We also show that strategically placing defects at the corners generates novel bistable states, or topological strings, which result from competing GS regions in the bulk. Our results could be generalized to other frustrated micro- and nanostructures where boundary conditions may be engineered with lithographic techniques.
Gene expression profiles underlying aggressive behavior in the prefrontal cortex of cattle
Eusebi, PG; Sevane, N; O'Rourke, T; Pizarro, M; Boeckx, C; Dunner, S
BMC GENOMICS
22
1
(2021)
Fluctuation-dissipation relations in the absence of detailed balance: formalism and applications to active matter
Dal Cengio, S; Levis, D; Pagonabarraga, I
JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT
2021
043201
(2021)
We present a comprehensive study about the relationship between the way detailed balance is broken in non-equilibrium systems and the resulting violations of the fluctuation-dissipation theorem. Starting from stochastic dynamics with both odd and even variables under time-reversal, we derive an explicit expression for the time-reversal operator, i.e. the Markovian operator which generates the time-reversed trajectories. We then exploit the relation between entropy production and the breakdown of detailed balance to establish general constraints on the non-equilibrium steady-states (NESS), which relate the non-equilibrium character of the dynamics with symmetry properties of the NESS distribution. This provides a direct route to derive extended fluctuation-dissipation relations, expressing the linear response function in terms of NESS correlations. Such framework provides a unified way to understand the departure from equilibrium of active systems and its linear response. We then consider two paradigmatic models of interacting self-propelled particles, namely active Brownian particles and active Ornstein-Uhlenbeck particles. We analyze the non-equilibrium character of these systems (also within a Markov and a Chapman-Enskog approximation) and derive extended fluctuation-dissipation relations for them, clarifying which features of these active model systems are genuinely non-equilibrium.
Precise transcriptional control of cellular quiescence by BRAVO/WOX5 complex in Arabidopsis roots
Betegon-Putze, I; Mercadal, J; Bosch, N; Planas-Riverola, A; Marques-Bueno, M; Vilarrasa-Blasi, J; Frigola, D ; Burkart, RC; Martinez, C; Conesa, A; Sozzani, R; Stahl, Y; Prat, S; Ibanes, M; Cano-Delgado, AI
MOLECULAR SYSTEMS BIOLOGY
17
e9864
(2021)
Understanding stem cell regulatory circuits is the next challenge in plant biology, as these cells are essential for tissue growth and organ regeneration in response to stress. In the Arabidopsis primary root apex, stem cell-specific transcription factors BRAVO and WOX5 co-localize in the quiescent centre (QC) cells, where they commonly repress cell division so that these cells can act as a reservoir to replenish surrounding stem cells, yet their molecular connection remains unknown. Genetic and biochemical analysis indicates that BRAVO and WOX5 form a transcription factor complex that modulates gene expression in the QC cells to preserve overall root growth and architecture. Furthermore, by using mathematical modelling we establish that BRAVO uses the WOX5/BRAVO complex to promote WOX5 activity in the stem cells. Our results unveil the importance of transcriptional regulatory circuits in plant stem cell development.
Public libraries embrace citizen science: Strengths and challenges
Cigarini, A; Bonhoure, I; Vicens, J; Perello, J
LIBRARY & INFORMATION SCIENCE RESEARCH
43
101090
(2021)
Can public libraries become hubs for citizen science? In line with the principles of citizen science, this question was answered collaboratively with librarians from the Barcelona Network of Public Libraries who performed two hands-on activities. One activity was a training course taken by 30 librarians from 24 different libraries which enabled them to envisage citizen science implementation at each library. The other activity consisted of cocreating a citizen social science project and involved 40 library users, seven librarians from three different cities, and professional scientists. The analysis considers the perspectives of both librarians and users, through participant observation, surveys, and a focus group to identify strengths and challenges. The overall results suggest that public libraries can offer leadership in the promotion of citizen science and contribute to the mission of public libraries to act as local community hubs. The main challenges identified were related to the complexity of collaboration, uncertainty regarding research co-creation, and participant retention strategies.
Estimating Central Pulse Pressure From Blood Flow by Identifying the Main Physical Determinants of Pulse Pressure Amplification
Geronimo, JF; Poire, EC; Chowienczyk, P; Alastruey, J
FRONTIERS IN PHYSIOLOGY
12
608098
(2021)
Several studies suggest that central (aortic) blood pressure (cBP) is a better marker of cardiovascular disease risk than peripheral blood pressure (pBP). The morphology of the pBP wave, usually assessed non-invasively in the arm, differs significantly from the cBP wave, whose direct measurement is highly invasive. In particular, pulse pressure, PP (the amplitude of the pressure wave), increases from central to peripheral arteries, leading to the so-called pulse pressure amplification (Delta PP). The main purpose of this study was to develop a methodology for estimating central PP (cPP) from non-invasive measurements of aortic flow and peripheral PP. Our novel approach is based on a comprehensive understanding of the main cardiovascular properties that determine Delta PP along the aortic-brachial arterial path, namely brachial flow wave morphology in late systole, and vessel radius and distance along this arterial path. This understanding was achieved by using a blood flow model which allows for workable analytical solutions in the frequency domain that can be decoupled and simplified for each arterial segment. Results show the ability of our methodology to (i) capture changes in cPP and Delta PP produced by variations in cardiovascular properties and (ii) estimate cPP with mean differences smaller than 3.3 +/- 2.8 mmHg on in silico data for different age groups (25-75 years old) and 5.1 +/- 6.9 mmHg on in vivo data for normotensive and hypertensive subjects. Our approach could improve cardiovascular function assessment in clinical cohorts for which aortic flow wave data is available.
A continuum model to study fluid dynamics within oscillating elastic nanotubes
Torres-Herrera, U; Poire, EC
JOURNAL OF FLUID MECHANICS
916
A16
(2021)
We derive equations of motion that describe the dynamics of a fluid confined within an elastic nanotube subject to periodic bending deflections. We use the principle of least action applied to a continuous open system at constant temperature. We solve the equations analytically in two limiting situations: when the tube oscillations are so small that they do not affect the fluid motion, but this one affects the tube dynamics; and when the flow magnitude is so small that it has no influence on the tube dynamics, but this one affects fluid motion. In the first case, we find out that the characteristic bending frequency spectrum of the tube depends not only on the magnitude of flow velocity, as previously stated in the literature, but also on the fluid velocity profile. This could constitute the basis of a strategy for indirect determination of the slip length in carbon nanotubes conveying flow via measurement of the buckling speed. In the second case, we find that tube vibrations can modify the dynamics of the fluid. Particularly, for a fluid subject to a constant pressure gradient, the tube motion induces an oscillatory motion in the fluid with twice the frequency of the tube. Moreover, the amplitude of the oscillatory fluid motion persists at high frequencies. This could constitute a strategy to generate high-frequency flows at nanoscales. Our results open up a panorama to control flow across nanotubes via tube vibrations, which could be complementary to chemical functionalization of nanostructures.
Singular behavior of microfluidic pulsatile flow due to dynamic curving of air-fluid interfaces
Vazquez-Vergara, P; Torres-Herrera, U; Olguin, LF; Poire, EC
PHYSICAL REVIEW FLUIDS
6
024003
(2021)
Pulsatile pressure gradients are widely present in microfluidic multiphase systems where the movement of fluids is affected by the presence of fluid-fluid interfaces. We present a simple theoretical model that incorporates dynamic interfacial curvatures produced as a response to pulsatile external forcing. Our equations make evident a singular character of the dynamics at low frequencies, due to surface tension. Analytical solution of the model shows the emergence of a resonant behavior for the dynamic permeability. We have designed and implemented microfluidic experiments to observe both the low-frequency dynamics and the resonance. We have studied a fluid slug whose length was chosen in order to look for resonances as predicted by our theoretical model, in the range of operational frequencies of our piezoelectric actuator. We have obtained the experimental dynamic permeability for water and a 70.0% glycerol solution in water and observed agreement with theoretical findings. Our model, validated by experiments, allows us to understand differences of several orders of magnitude in the amplitude of flow velocity at low frequencies, between systems with and without interfaces.
Transport and Assembly of Magnetic Surface Rotors
Tierno, P; Snezhko, A
CHEMNANOMAT
7
8
(2021)
This minireview focuses on recent advances with surface magnetic rotors, namely field-responsive spherical or anisotropic microparticles that translate close to, or are embedded in a confining surface. The application of external magnetic modulations allows these microscopic wheels to be remotely spun and steered while also tuning their interactions and inducing assembly from a collection of disordered, moving units. With optical microscopy one can observe and characterize the complex collective phenomena that emerge in dissipative colloidal systems driven far from equilibrium by external fields. From a technological point of view, magnetic surface rotors envisage implementation into microfluidic devices, and can be used for drug delivery, mixing as well as a model system for biological active matter.
Capturing the Effects of Domestication on Vocal Learning Complexity
O'Rourke, T; Martins, PT; Asano, R; Tachibana, RO; Okanoya, K; Boeckx, C
TRENDS IN COGNITIVE SCIENCES
25
6
(2021)
Domesticated and vocal learning species can serve as informative model organisms for the reduction of reactive aggression and emergence of speech in our lineage. Amidst mounting evidence that domestication modifies vocal repertoires across different species, we focus on the domesticated Bengalese finch, which has a more complex song than the wild-type white-rumped munia. Our explanation for this effect revolves around the glutamate neurotransmitter system. Glutamate signaling (i) is implicated in birdsong learning, (ii) controls dopamine activity in neural circuits crucial for vocal learning, (iii) is disproportionately targeted in the evolution of domesticates, and (iv) regulates stress responses and aggressive behaviors attenuated under domestication. We propose that attenuated excitation of stress-related neural circuits potentiates vocal learning via altered dopaminergic signaling.
An intelligent framework for end-to-end rockfall detection
Zoumpekas, T; Puig, A; Salamo, M; Garcia-Selles, D; Nunez, LB; Guinau, M
INTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS
(2021)
Rockfall detection is a crucial procedure in the field of geology, which helps to reduce the associated risks. Currently, geologists identify rockfall events almost manually utilizing point cloud and imagery data obtained from different caption devices such as Terrestrial Laser Scanner (TLS) or digital cameras. Multitemporal comparison of the point clouds obtained with these techniques requires a tedious visual inspection to identify rockfall events which implies inaccuracies that depend on several factors such as human expertize and the sensibility of the sensors. This paper addresses this issue and provides an intelligent framework for rockfall event detection for any individual working in the intersection of the geology domain and decision support systems. The development of such an analysis framework presents major research challenges and justifies exhaustive experimental analysis. In particular, we propose an intelligent system that utilizes multiple machine learning algorithms to detect rockfall clusters of point cloud data. Due to the extremely imbalanced nature of the problem, a plethora of state-of-the-art resampling techniques accompanied by multiple models and feature selection procedures are being investigated. Various machine learning pipeline combinations have been examined and benchmarked applying well-known metrics to be incorporated into our system. Specifically, we developed machine learning techniques and applied them to analyze point cloud data extracted from TLS in two distinct case studies, involving different geological contexts: the basaltic cliff of Castellfollit de la Roca and the conglomerate Montserrat Massif, both located in Spain. Our experimental results indicate that some of the above-mentioned machine learning pipelines can be utilized to detect rockfall incidents on mountain walls, with experimentally validated accuracy.
Aggregation of discoidal particles due to depletion interaction
Calero, C; Diaz-Morata, M; Pagonabarraga, I
JOURNAL OF CHEMICAL PHYSICS
155
074904
(2021)
Depletion interactions between colloids of discoidal shape can induce their self-assembly into columnar aggregates. This is an effect of entropic origin with important implications in a range of colloidal systems, particularly in the clustering of erythrocytes that determine the rheological properties of blood. Here, we investigate the equilibrium state reached by discoidal colloids in a solution of smaller depletant particles. We develop a thermodynamic model of depletion-induced aggregation based on self-assembly theory and solve it analytically. We test the validity of the model by using Langevin simulations of a system of discs and depletant particles in which the depletion interaction emerges naturally. In addition, we consider the effect of an attractive interaction between depletant and discoidal particles, which we show induces a re-entrant dependence of aggregation with temperature.
Noise-driven amplification mechanisms governing the emergence of coherent extreme events in excitable systems
Hernandez-Navarro, L; Faci-Lazaro, S; Orlandi, JG; Feudel, U; Gomez-Gardenes, J; Soriano, J
PHYSICAL REVIEW RESEARCH
3
023133
(2021)
The physics governing the formation of extreme coherent events, i.e., the systemwide emergence of an observable taking extraordinary values in a short time window, is a relevant yet elusive problem to a variety of disciplines ranging from climate science to neuroscience. Despite their inherent differences, systems exhibiting episodes of extreme coherence can be abstracted as a set of coupled nonlinear elements in a noisy and networked environment. Here, we propose a model describing the generation of extreme coherence by exploring theoretically and numerically the capacity of noise and network correlations to amplify a critical core of the system and trigger an extreme event. Although we principally center our study in modeling bursting phenomena in neuronal circuits, we extend our analysis to other systems such as algae blooms and infectious diseases. We show that extreme events originate in a relatively small core of the system and that different cores may coexist. We also show that the amplification mechanisms within a system are highly robust, so that the deletion of central nodes leads to other nodes taking leadership.
Guided accumulation of active particles by topological design of a second-order skin effect
Palacios, LS; Tchoumakov, S; Guix, M; Pagonabarraga, I; Sanchez, S; Grushin, AG
NATURE COMMUNICATIONS
12
4691
(2021)
Collective guidance of out-of-equilibrium systems without using external fields is a challenge of paramount importance in active matter, ranging from bacterial colonies to swarms of self-propelled particles. Designing strategies to guide active matter and exploiting enhanced diffusion associated to its motion will provide insights for application from sensing, drug delivery to water remediation. However, achieving directed motion without breaking detailed balance, for example by asymmetric topographical patterning, is challenging. Here we engineer a two-dimensional periodic topographical design with detailed balance in its unit cell where we observe spontaneous particle edge guidance and corner accumulation of self-propelled particles. This emergent behaviour is guaranteed by a second-order non-Hermitian skin effect, a topologically robust non-equilibrium phenomenon, that we use to dynamically break detailed balance. Our stochastic circuit model predicts, without fitting parameters, how guidance and accumulation can be controlled and enhanced by design: a device guides particles more efficiently if the topological invariant characterizing it is non-zero. Our work establishes a fruitful bridge between active and topological matter, and our design principles offer a blueprint to design devices that display spontaneous, robust and predictable guided motion and accumulation, guaranteed by out-of-equilibrium topology.
Static and Dynamic Self-Assembly of Pearl-Like-Chains of Magnetic Colloids Confined at Fluid Interfaces
Martinez-Pedrero, F; Gonzalez-Banciella, A; Camino, A ; Mateos-Maroto, A; Ortega, F; Rubio, RG; Pagonabarraga, I; Calero, C
SMALL
17
2101188
(2021)
Magnetic colloids adsorbed at a fluid interface are unique model systems to understand self-assembly in confined environments, both in equilibrium and out of equilibrium, with important potential applications. In this work the pearl-chain-like self-assembled structures of superparamagnetic colloids confined to a fluid-fluid interface under static and time-dependent actuations are investigated. On the one hand, it is found that the structures generated by static fields transform as the tilt angle of the field with the interface is increased, from 2D crystals to separated pearl-chains in a process that occurs through a controllable and reversible zip-like thermally activated mechanism. On the other hand, the actuation with precessing fields about the axis perpendicular to the interface induces dynamic self-assembled structures with no counterpart in non-confined systems, generated by the interplay of averaged magnetic interactions, interfacial forces, and hydrodynamics. Finally, how these dynamic structures can be used as remotely activated roller conveyors, able to transport passive colloidal cargos at fluid interfaces and generate parallel viscous flows is shown. The latter can be used in the mixture of adsorbed molecules and the acceleration of surface-chemical reactions, overcoming diffusion limitations.
Parkinson's disease patient-specific neuronal networks carrying the LRRK2 G2019S mutation unveil early functional alterations that predate neurodegeneration
Carola, G; Malagarriga, D; Calatayud, C; Pons-Espinal, M; Blasco-Agell, L; Richaud-Patin, Y; Fernandez-Carasa, I; Baruffi, V; Beltramone, S; Molina, E; Dell'Era, P; Toledo-Aral, JJ; Tolosa, E; Muotri, AR; Ojalvo, JG; Soriano, J; Raya, A; Consiglio, A
NPJ PARKINSONS DISEASE
7
55
(2021)
A deeper understanding of early disease mechanisms occurring in Parkinson's disease (PD) is needed to reveal restorative targets. Here we report that human induced pluripotent stem cell (iPSC)-derived dopaminergic neurons (DAn) obtained from healthy individuals or patients harboring LRRK2 PD-causing mutation can create highly complex networks with evident signs of functional maturation over time. Compared to control neuronal networks, LRRK2 PD patients' networks displayed an elevated bursting behavior, in the absence of neurodegeneration. By combining functional calcium imaging, biophysical modeling, and DAn-lineage tracing, we found a decrease in DAn neurite density that triggered overall functional alterations in PD neuronal networks. Our data implicate early dysfunction as a prime focus that may contribute to the initiation of downstream degenerative pathways preceding DAn loss in PD, highlighting a potential window of opportunity for pre-symptomatic assessment of chronic degenerative diseases.
Single-file dynamics of colloids in circular channels: Time scales, scaling laws and their universality
Villada-Balbuena, A; Ortiz-Ambriz, A; Castro-Villarreal, P; Tierno, P; Castaneda-Priego, R; Mendez-Alcaraz, JM
PHYSICAL REVIEW RESEARCH
3
033246
(2021)
In colloidal systems, Brownian motion emerges from the massive separation of time and length scales associated with characteristic dynamics of the solute and solvent constituents. This separation of scales produces several temporal regimes in the colloidal dynamics when combined with the effects of the interaction between the particles, confinement conditions, and state variables, such as density and temperature. Some examples are the short- and long-time regimes in two- and three-dimensional open systems and the diffusive and subdiffusive regimes observed in the single-file (SF) dynamics along a straight line. In this paper, we address the way in which a confining geometry induces new time scales. We report on the dynamics of interacting colloidal particles moving along a circle by combining a heuristic theoretical analysis of the involved scales, Brownian dynamics computer simulations, and video-microscopy experiments with paramagnetic colloids confined to lithographic circular channels subjected to an external magnetic field. The systems display four temporal regimes in the following order: one-dimensional free diffusion, SF subdiffusion, free-cluster rotational diffusion, and the expected saturation due to the confinement. We also report analytical expressions for the mean-square angular displacement and crossover times obtained from scaling arguments, which accurately reproduce both experiments and simulations. Our generic approach can be used to predict the long-time dynamics of many other confined physical systems.
Scaling Regimes of Active Turbulence with External Dissipation
Berta Martínez-Prat, Ricard Alert, Fanlong Meng, Jordi Ignés-Mullol, Jean-François Joanny, Jaume Casademunt, Ramin Golestanian, and Francesc Sagués
Phys. Rev. X
11
031065
(2021)
Active fluids exhibit complex turbulentlike flows at low Reynolds number. Recent work predicted that 2D active nematic turbulence follows scaling laws with universal exponents. However, experimentally testing these predictions is conditioned by the coupling to the 3D environment. Here, we measure the spectrum of the kinetic energy E(q) in an active nematic film in contact with a passive oil layer. At small and intermediate scales, we find the scaling regimes E(q)∼q−4 and E(q)∼q−1, respectively, in agreement with the theoretical prediction for 2D active nematics. At large scales, however, we find a new scaling E(q)∼q, which emerges when the dissipation is dominated by the 3D oil layer. In addition, we derive an explicit expression for the spectrum that spans all length scales, thus explaining and connecting the different scaling regimes. This allows us to fit the data and extract the length scale that controls the crossover to the new large-scale regime, which we tune by varying the oil viscosity. Overall, our work experimentally demonstrates the emergence of scaling laws with universal exponents in active turbulence, and it establishes how the spectrum is affected by external dissipation.
Hierarchical control as a shared neurocognitive mechanism for language and music
Asano, R, Boeckx, C, Seifert, U.
COGNITION
216
104847
(2021)
Although comparative research has made substantial progress in clarifying the relationship between language and music as neurocognitive systems from both a theoretical and empirical perspective, there is still no consensus about which mechanisms, if any, are shared and how they bring about different neurocognitive systems. In this paper, we tackle these two questions by focusing on hierarchical control as a neurocognitive mechanism underlying syntax in language and music. We put forward the Coordinated Hierarchical Control (CHC) hypothesis: linguistic and musical syntax rely on hierarchical control, but engage this shared mechanism differently depending on the current control demand. While linguistic syntax preferably engages the abstract rule-based control circuit, musical syntax rather employs the coordination of the abstract rule-based and the more concrete motor-based control circuits. We provide evidence for our hypothesis by reviewing neuroimaging as well as neuropsychological studies on linguistic and musical syntax. The CHC hypothesis makes a set of novel testable predictions to guide future work on the relationship between language and music.
Active microrheology in corrugated channels: Comparison of thermal and colloidal baths.
Malgaretti, Paolo Puertas, Antonio M Pagonabarraga, Ignacio
Journal of colloid and interface science
(2021)
HYPOTHESIS: The dynamics of colloidal suspension confined within porous materials strongly differs from that in the bulk. In particular, within porous materials, the presence of boundaries with complex shapes entangles the longitudinal and transverse degrees of freedom inducing a coupling between the transport of the suspension and the density inhomogeneities induced by the walls.
METHOD: Colloidal suspension confined within model porous media are characterized by means of active microrheology where a net force is applied on a single colloid (tracer particle) whose transport properties are then studied. The trajectories provided by active microrheology are exploited to determine the local transport coefficients. In order to asses the role of the colloid-colloid interactions we compare the case of a tracer embedded in a colloidal suspension to the case of a tracer suspended in an ideal bath.
FINDING: Our results show that the friction coefficient increases and the passage time distribution widens upon increasing the corrugation of the channel. These features are obtained for a tracer suspended in a (thermalized) colloidal bath as well as for the case of an ideal thermal bath. These results highlight the relevance of the confinement on the transport and show a mild dependence on the colloidal/thermal bath. Finally, we rationalize our numerical results with a semi-analytical model. Interestingly, the predictions of the model are quantitatively reliable for mild external forces, hence providing a reliable tool for predicting the transport across porous materials.
Spontaneous chiralization of polar active particles
De Corato, M; Pagonabarraga, I; Natale, G
PHYSICAL REVIEW E
104
044607
(2021)
Polar active particles constitute a wide class of active matter that is able to propel along a preferential direction, given by their polar axis. Here, we demonstrate a generic active mechanism that leads to their spontaneous chiralization through a symmetry-breaking instability. We find that the transition of an active particle from a polar to a chiral symmetry is characterized by the emergence of active rotation and of circular trajectories. The instability is driven by the advection of a solute that interacts differently with the two portions of the particle surface and it occurs through a supercritical pitchfork bifurcation.
Collective motion of run-and-tumble repulsive and attractive particles in one-dimensional systems
Gutierrez, CMB; Vanhille-Campos, C;Alarcon, F; Pagonabarraga, I; Brito, R; Valeriani, C
SOFT MATTER
(2021)
Active matter deals with systems whose particles consume energy at the individual level in order to move. To unravel features such as the emergence of collective structures, several models have been suggested, such as the on-lattice model of run-and-tumble particles implemented via the persistent exclusion process (PEP). In our work, we study a one-dimensional system of run-and-tumble repulsive or attractive particles, both on-lattice and off-lattice. Additionally, we implement cluster motility dynamics in the on-lattice case (since in the off-lattice case, cluster motility arises from the individual particle dynamics). While we observe important differences between discrete and continuous dynamics, few common features are of particular importance. Increasing particle density drives aggregation across all different systems explored. For non-attractive particles, the effects of particle activity on aggregation are largely independent of the details of the dynamics. In contrast, once attractive interactions are introduced, the steady-state, which is completely determined by the interplay between these and the particles' activity, becomes highly dependent on the details of the dynamics.
Alignment interactions drive structural transitions in biological tissues
Paoluzzi, M; Angelani, L; Gosti, G; Marchetti, MC; Pagonabarraga, I; Ruocco, G
PHYSICAL REVIEW E
104
044606
(2021)
Experimental evidence shows that there is a feedback between cell shape and cell motion. How this feedback impacts the collective behavior of dense cell monolayers remains an open question. We investigate the effect of a feedback that tends to align the cell crawling direction with cell elongation in a biological tissue model. We find that the alignment interaction promotes nematic patterns in the fluid phase that eventually undergo a nonequilibrium phase transition into a quasihexagonal solid. Meanwhile, highly asymmetric cells do not undergo the liquid-to-solid transition for any value of the alignment coupling. In this regime, the dynamics of cell centers and shape fluctuation show features typical of glassy systems.
Emergent colloidal currents across ordered and disordered landscapes
Lips, D; Stoop, RL; Maass, P; Tierno, P
COMMUNICATIONS PHYSICS
4
224
(2021)
Many-particle effects in driven systems far from equilibrium lead to a rich variety of emergent phenomena. Their classification and understanding often require suitable model systems. Here we show that microscopic magnetic particles driven along ordered and defective lattices by a traveling wave potential display a nonlinear current-density relationship, which arises from the interplay of two effects. The first one originates from particle sizes nearly commensurate with the substrate in combination with attractive pair interactions. It governs the colloidal current at small densities and leads to a superlinear increase. We explain such effect by an exactly solvable model of constrained cluster dynamics. The second effect is interpreted to result from a defect-induced breakup of coherent cluster motion, leading to jamming at higher densities. Finally, we demonstrate that a lattice gas model with parallel update is able to capture the experimental findings for this complex many-body system.
Emergent phenomena in complex many-body systems driven far from equilibrium are currently a subject of intense study. Here, the authors report on a nonlinear current-density relationship in experiments of magnetic colloids driven above disordered energy landscapes, and explain the underlying mechanisms through analytical modeling
Why musical hierarchies?
Hilton, CB; Asano, R ; Boeckx, C
BEHAVIORAL AND BRAIN SCIENCES
44
e100
(2021)
Credible signaling may have provided a selection pressure for producing and discriminating increasingly elaborate protomusical signals. But, why evolve them to have hierarchical structure? We argue that the hierarchality of tonality and meter is a byproduct of domain-general mechanisms evolved for reasons other than credible signaling.
Scaling Regimes of Active Turbulence with External Dissipation
Martinez-Prat, B; Alert, R; Meng, FL; Ignes-Mullol, J; Joanny, JF; Casademunt, J; Golestanian, R; Sagues, F
PHYSICAL REVIEW X
11
031065
(2021)
Active fluids exhibit complex turbulentlike flows at low Reynolds number. Recent work predicted that 2D active nematic turbulence follows scaling laws with universal exponents. However, experimentally testing these predictions is conditioned by the coupling to the 3D environment. Here, we measure the spectrum of the kinetic energy E(q) in an active nematic film in contact with a passive oil layer. At small and intermediate scales, we find the scaling regimes E(q) similar to q(-4) and E(q) similar to q(-1), respectively, in agreement with the theoretical prediction for 2D active nematics. At large scales, however, we find a new scaling E(q) similar to q, which emerges when the dissipation is dominated by the 3D oil layer. In addition, we derive an explicit expression for the spectrum that spans all length scales, thus explaining and connecting the different scaling regimes. This allows us to fit the data and extract the length scale that controls the crossover to the new large-scale regime, which we tune by varying the oil viscosity. Overall, our work experimentally demonstrates the emergence of scaling laws with universal exponents in active turbulence, and it establishes how the spectrum is affected by external dissipation.
Novel mechanism for oscillations in catchbonded motor-filament complexes
Guha, S; Mitra, MK; Pagonabarraga, I; Muhuri, S
BIOPHYSICAL JOURNAL
120
18
(2021)
Generation of mechanical oscillations is ubiquitous to a wide variety of intracellular processes, ranging from activity of muscle fibers to oscillations of the mitotic spindle. The activity of motors plays a vital role in maintaining the integrity of the mitotic spindle structure and generating spontaneous oscillations. Although the structural features and properties of the individual motors are well characterized, their implications on the functional behavior of motor-filament complexes are more involved. We show that force-induced allosteric deformations in dynein, which result in catchbonding behavior, provide a generic mechanism to generate spontaneous oscillations in motor-cytoskeletal filament complexes. The resultant phase diagram of such motor-filament systems-characterized by force-induced allosteric deformations-exhibits bistability and sustained limit-cycle oscillations in biologically relevant regimes, such as for catchbonded dynein. The results reported here elucidate the central role of this mechanism in fashioning a distinctive stability behavior and oscillations in motor-filament complexes such as mitotic spindles.
Thermally active nanoparticle clusters enslaved by engineered domain wall traps
Tierno, P; Johansen, TH; Straube, AV
NATURE COMMUNICATIONS
12
5813
(2021)
Assembling nanoparticles on surfaces has great technological potential. Here, Tierno et al demonstrate the confinement of magnetic nanoparticles in traps created by magnetic domain walls. The magnetic gradient and location of the domain walls can be finely tuned, allowing for precise control of the constituent nanoparticles.
The stable assembly of fluctuating nanoparticle clusters on a surface represents a technological challenge of widespread interest for both fundamental and applied research. Here we demonstrate a technique to stably confine in two dimensions clusters of interacting nanoparticles via size-tunable, virtual magnetic traps. We use cylindrical Bloch walls arranged to form a triangular lattice of ferromagnetic domains within an epitaxially grown ferrite garnet film. At each domain, the magnetic stray field generates an effective harmonic potential with a field tunable stiffness. The experiments are combined with theory to show that the magnetic confinement is effectively harmonic and pairwise interactions are of dipolar nature, leading to central, strictly repulsive forces. For clusters of magnetic nanoparticles, the stationary collective states arise from the competition between repulsion, confinement and the tendency to fill the central potential well. Using a numerical simulation model as a quantitative map between the experiments and theory we explore the field-induced crystallization process for larger clusters and unveil the existence of three different dynamical regimes. The present method provides a model platform for investigations of the collective phenomena emerging when strongly confined nanoparticle clusters are forced to move in an idealized, harmonic-like potential.
Single-file dynamics of colloids in circular channels: Time scales, scaling laws and their universality
Villada-Balbuena, A; Ortiz-Ambriz, A; Castro-Villarreal, P; Tierno, P; Castaneda-Priego, R; Mendez-Alcaraz, JM
PHYSICAL REVIEW RESEARCH
3
033246
(2021)
In colloidal systems, Brownian motion emerges from the massive separation of time and length scales associated with characteristic dynamics of the solute and solvent constituents. This separation of scales produces several temporal regimes in the colloidal dynamics when combined with the effects of the interaction between the particles, confinement conditions, and state variables, such as density and temperature. Some examples are the short- and long-time regimes in two- and three-dimensional open systems and the diffusive and subdiffusive regimes observed in the single-file (SF) dynamics along a straight line. In this paper, we address the way in which a confining geometry induces new time scales. We report on the dynamics of interacting colloidal particles moving along a circle by combining a heuristic theoretical analysis of the involved scales, Brownian dynamics computer simulations, and video-microscopy experiments with paramagnetic colloids confined to lithographic circular channels subjected to an external magnetic field. The systems display four temporal regimes in the following order: one-dimensional free diffusion, SF subdiffusion, free-cluster rotational diffusion, and the expected saturation due to the confinement. We also report analytical expressions for the mean-square angular displacement and crossover times obtained from scaling arguments, which accurately reproduce both experiments and simulations. Our generic approach can be used to predict the long-time dynamics of many other confined physical systems.
Degeneracy and hysteresis in a bidisperse colloidal ice
Rodriguez-Gallo, C; Ortiz-Ambriz, A ; Tierno, P
PHYSICAL REVIEW RESEARCH
3
043023
(2021)
We use numerical simulations to investigate the low-energy states of a bidisperse colloidal ice, realized by confining two types of magnetic particles into double wells of different lengths. For this system, theoretical calculations predict a highly degenerate ground state where all the vertices with zero topological charge have equal energy. When raising the applied field, we find a re-entrant transition where the system passes from the initial disordered state to a low-energy one and then back to disorder for large interaction strengths. The transition is due to the particle localization on top of the central hill of the double wells, as revealed from the position distributions. When we decrease the applied field, the system displays hysteresis in the fraction of low-energy vertices, and a small return point memory by cycling the applied field.
Phase separation of self-propelled disks with ferromagnetic and nematic alignment
Elena Sesé-Sansa, Demian Levis, and Ignacio Pagonabarraga
Phys. Rev.
104
(2021)
We present a comprehensive study of a model system of repulsive self-propelled disks in two dimensions with ferromagnetic and nematic velocity alignment interactions. We characterize the phase behavior of the system as a function of the alignment and self-propulsion strength, featuring orientational order for strong alignment and motility-induced phase separation (MIPS) at moderate alignment but high enough self-propulsion. We derive a microscopic theory for these systems yielding a closed set of hydrodynamic equations from which we perform a linear stability analysis of the homogenous disordered state. This analysis predicts MIPS in the presence of aligning torques. The nature of the continuum theory allows for an explicit quantitative comparison with particle-based simulations, which consistently shows that ferromagnetic alignment fosters phase separation, while nematic alignment does not alter either the nature or the location of the instability responsible for it. In the ferromagnetic case, such behavior is due to an increase of the imbalance of the number of particle collisions along different orientations, giving rise to the self-trapping of particles along their self-propulsion direction. On the contrary, the anisotropy of the pair correlation function, which encodes this self-trapping effect, is not significantly affected by nematic torques. Our work shows the predictive power of such microscopic theories to describe complex active matter systems with different interaction symmetries and sheds light on the impact of velocity-alignment interactions in motility-induced phase separation.
Arrested phase separation in chiral fluids of colloidal spinners
Helena Massana-Cid, Demian Levis, Raúl Josué Hernández Hernández, Ignacio Pagonabarraga, and Pietro Tierno
Phys. Rev. Research
3
(2021)
We investigate phase separation in a chiral fluid, made of spinning ferromagnetic colloids that interact both via hydrodynamic and dipolar forces and collectively organize into separated circulating clusters. We show that, at high spinning frequency, hydrodynamics dominate over attractive magnetic interactions and impede coarsening, forcing the particles to assemble into a collection of finite rotating clusters of controllable size. We introduce a minimal particle-based model that unveils the fundamental role of hydrodynamics and the boundary plane in the self-organization process of the colloidal spinners. Our results shed light on the control of coarsening and dynamic self-assembly in chiral active systems and the key role played by fluid mediated long-range interactions.
Active microrheology in corrugated channels: Comparison of thermal and colloidal baths.
Malgaretti, Paolo Puertas, Antonio M Pagonabarraga, Ignacio
Journal of colloid and interface science
(2021)
HYPOTHESIS: The dynamics of colloidal suspension confined within porous materials strongly differs from that in the bulk. In particular, within porous materials, the presence of boundaries with complex shapes entangles the longitudinal and transverse degrees of freedom inducing a coupling between the transport of the suspension and the density inhomogeneities induced by the walls.
METHOD: Colloidal suspension confined within model porous media are characterized by means of active microrheology where a net force is applied on a single colloid (tracer particle) whose transport properties are then studied. The trajectories provided by active microrheology are exploited to determine the local transport coefficients. In order to asses the role of the colloid-colloid interactions we compare the case of a tracer embedded in a colloidal suspension to the case of a tracer suspended in an ideal bath.
FINDING: Our results show that the friction coefficient increases and the passage time distribution widens upon increasing the corrugation of the channel. These features are obtained for a tracer suspended in a (thermalized) colloidal bath as well as for the case of an ideal thermal bath. These results highlight the relevance of the confinement on the transport and show a mild dependence on the colloidal/thermal bath. Finally, we rationalize our numerical results with a semi-analytical model. Interestingly, the predictions of the model are quantitatively reliable for mild external forces, hence providing a reliable tool for predicting the transport across porous materials.
Hierarchical control as a shared neurocognitive mechanism for language and music
Asano, R; Boeckx, C; Seifert, U
COGNITION
216
104847
(2021)
Although comparative research has made substantial progress in clarifying the relationship between language and music as neurocognitive systems from both a theoretical and empirical perspective, there is still no consensus about which mechanisms, if any, are shared and how they bring about different neurocognitive systems. In this paper, we tackle these two questions by focusing on hierarchical control as a neurocognitive mechanism underlying syntax in language and music. We put forward the Coordinated Hierarchical Control (CHC) hypothesis: linguistic and musical syntax rely on hierarchical control, but engage this shared mechanism differently depending on the current control demand. While linguistic syntax preferably engages the abstract rule-based control circuit, musical syntax rather employs the coordination of the abstract rule-based and the more concrete motor-based control circuits. We provide evidence for our hypothesis by reviewing neuroimaging as well as neuropsychological studies on linguistic and musical syntax. The CHC hypothesis makes a set of novel testable predictions to guide future work on the relationship between language and music.
Hydrodynamic interactions can induce jamming in flow-driven systems
Eric Cereceda-López, Dominik Lips, Antonio Ortiz-Ambriz, Artem Ryabov, Philipp Maass, Pietro Tierno
Phys. Rev. Lett.
127
214501
(2021)
Hydrodynamic interactions between fluid-dispersed particles are ubiquitous in soft matter and biological systems and they give rise to intriguing collective phenomena. While it was reported that these interactions can facilitate force-driven particle motion over energetic barriers, here we show the opposite effect in a flow-driven system, i.e. that hydrodynamic interactions hinder transport across barriers. We demonstrate this result by combining experiments and theory. In the experiments, we drive colloidal particles using rotating optical traps, thus creating a vortex flow in the corotating reference frame. We observe a jamming-like decrease of particle currents with density for large barriers between traps. The theoretical model shows that this jamming arises from hydrodynamic interactions between the particles. The impact of hydrodynamic interactions is reversed compared to force-driven motion, suggesting that our findings are a generic feature of flow-driven transport
The Shortest Path to Network Geometry
M. Ángeles Serrano and Marián Boguñá
Cambridge University Press
(2021)
Real networks comprise from hundreds to millions of interacting elements and permeate all contexts, from technology to biology to society. All of them display non-trivial connectivity patterns, including the small-world phenomenon, making nodes to be separated by a small number of intermediate links. As a consequence, networks present an apparent lack of metric structure and are difficult to map. Yet, many networks have a hidden geometry that enables meaningful maps in the two-dimensional hyperbolic plane. The discovery of such hidden geometry and the understanding of its role have become fundamental questions in network science giving rise to the field of network geometry. This Element reviews fundamental models and methods for the geometric description of real networks with a focus on applications of real network maps, including decentralized routing protocols, geometric community detection, and the self-similar multiscale unfolding of networks by geometric renormalization.
The Romans before adversity
J.M. BERMÚDEZ LORENZO, J. PÉREZ GONZÁLEZ
logo Aracne
(2021)
The book "The Romans before adversity, Forms of reaction and strategies to manage change" has been editated by J.M.Bermúdez Lorenzo and J.Pérez Gonzalez, UBICS members.
The book was born with the aim of offering a space for reflection and debate on the forms of intellectual analysis and reaction developed by Roman society in relation to catastrophic phenomena, both those of natural origination and those derived from concrete human decision-making. The main interest was focused on understanding those moments in which the daily life of Romans changed for the worse and on describing the different responses on the part of policy-makers and individuals before these critical situations, in which not everyone is able to overcome these episodes and some even take advantage of the situation opportunistically.
Scaling up real networks by geometric branching growth
Muhua Zheng, Guillermo García-Pérez, Marián Boguñá, M. Ángeles Serrano
Proceedings of the National Academy of Sciences USA
118
21
(2021)
Branching processes underpin the complex evolution of many real systems. However, network models typically describe network growth in terms of a sequential addition of nodes. Here, we measured the evolution of real networks—journal citations and international trade—over a 100-y period and found that they grow in a self-similar way that preserves their structural features over time. This observation can be explained by a geometric branching growth model that generates a multiscale unfolding of the network by using a combination of branching growth and a hidden metric space approach. Our model enables multiple practical applications, including the detection of optimal network size for maximal response to an external influence and a finite-size scaling analysis of critical behavior.
An intelligent framework for end-to-end rockfall detection
Zoumpekas T., Puig A., Salamó M., Garcı́a-Sellés D., Blanco Nuñez L., Guinau M.
International Journal of Intelligent Systems
6
6471 6502
(2021)
Rockfall detection is a crucial procedure in the field of geology, which helps to reduce the associated risks. Currently, geologists identify rockfall events almost manually utilizing point cloud and imagery data obtained from different caption devices such as Terrestrial Laser Scanner (TLS) or digital cameras. Multitemporal comparison of the point clouds obtained with these techniques requires a tedious visual inspection to identify rockfall events which implies inaccuracies that depend on several factors such as human expertize and the sensibility of the sensors. This paper addresses this issue and provides an intelligent framework for rockfall event detection for any individual working in the intersection of the geology domain and decision support systems. The development of such an analysis framework presents major research challenges and justifies exhaustive experimental analysis. In particular, we propose an intelligent system that utilizes multiple machine learning algorithms to detect rockfall clusters of point cloud data. Due to the extremely imbalanced nature of the problem, a plethora of state-of-the-art resampling techniques accompanied by multiple models and feature selection procedures are being investigated. Various machine learning pipeline combinations have been examined and benchmarked applying well-known metrics to be incorporated into our system. Specifically, we developed machine learning techniques and applied them to analyze point cloud data extracted from TLS in two distinct case studies, involving different geological contexts: the basaltic cliff of Castellfollit de la Roca and the conglomerate Montserrat Massif, both located in Spain. Our experimental results indicate that some of the above-mentioned machine learning pipelines can be utilized to detect rockfall incidents on mountain walls, with experimentally validated accuracy.
We Are Not the Same Either Playing: A Proposal for Adaptive Gamification
Rodríguez I., Puig A., Rodríguez A.
Frontiers in Artificial Intelligence and Applications
339
185 194
(2021)
Gamification consists in applying game mechanics in non-game contexts aiming at motivating and shaping behaviours. This paper proposes an adaptive approach for gamification, which takes as initial information players profiles – gathered from Hexad player type questionnaire – and considers also how these profiles change over time based on users interactions. Then, we provide the users with a personalised experience through the use of game elements that correspond to their dynamic playing profile. We present a preliminary evaluation of the approach by means of a simulator that yields promising results when comparing it with baseline configurations, i.e randomized and fixed player profile.
Maximum Likelihood Estimation of Power-Law Exponents for Testing Universality in Complex Systems
Navas-Portella V., González Á., Serra I., Vives E., Corral Á.
SEMA SIMAI Springer Series
11
65 89
(2021)
Power-law-type distributions are extensively found when studying the behavior of many complex systems. However, due to limitations in data acquisition, empirical datasets often only cover a narrow range of observations, making it difficult to establish power-law behavior unambiguously. In this work, we present a statistical procedure to merge different datasets, with two different aims. First, we obtain a broader fitting range for the statistics of different experiments or observations of the same system. Second, we establish whether two or more different systems may belong to the same universality class. By means of maximum likelihood estimation, this methodology provides rigorous statistical information to discern whether power-law exponents characterizing different datasets can be considered equal to each other or not. This procedure is applied to the Gutenberg–Richter law for earthquakes and for synthetic earthquakes (acoustic emission events) generated in the laboratory: labquakes (Navas-Portella et al. Phys Rev E 100:062106, 2019).
Amplitude death and restoration in networks of oscillators with random-walk diffusion
Clusella P., Miguel M.C., Pastor-Satorras R.
Communications Physics
4
(2021)
Systems composed of reactive particles diffusing in a network display emergent dynamics. While Fick’s diffusion can lead to Turing patterns, other diffusion schemes might display more complex phenomena. Here we study the death and restoration of collective oscillations in networks of oscillators coupled by random-walk diffusion, which modifies both the original unstable fixed point and the stable limit-cycle, making them topology-dependent. By means of numerical simulations we show that, in some cases, the diffusion-induced heterogeneity stabilizes the initially unstable fixed point via a Hopf bifurcation. Further increasing the coupling strength can moreover restore the oscillations. A numerical stability analysis indicates that this phenomenology corresponds to a case of amplitude death, where the inhomogeneous stabilized solution arises from the interplay of random walk diffusion and heterogeneous topology. Our results are relevant in the fields of epidemic spreading or ecological dispersion, where random walk diffusion is more prevalent.
Active nematic flows confined in a two-dimensional channel with hybrid alignment at the walls: A unified picture
Rorai C., Toschi F., Pagonabarraga I.
Physical Review Fluids
6
(2021)
Active nematic fluids confined in narrow channels are known to generate spontaneous flows when the activity is sufficiently intense. Recently, it was demonstrated [R. Green, J. Toner, and V. Vitelli, Phys. Rev. Fluids 2, 104201 (2017)] that if the molecular anchoring at the channel walls is conflicting, i.e., perpendicular on one plate and parallel on the other, flows are initiated even in the zero activity limit. An analytical laminar velocity profile for this specific configuration was derived within a simplified nematohydrodynamic model in which the nematic order parameter is a fixed-magnitude unit vector n. The solution holds in a regime where the flow does not perturb the nematic order imposed by the walls. In this study, we explore systematically active flows in this confined geometry with a more general theoretical model that uses a second-rank tensor order parameter Q to express both the magnitude and orientation of the nematic phase. The Q-model allows for the presence of defects and biaxial, in addition to uniaxial, molecular arrangements. Our aim is to provide a unified picture, beyond the limiting regime explored previously, to serve as a guide for potential microfluidic applications that exploit the coupling between the orientational order of the molecules and the velocity field to finely control the flow and overcome the intrinsic difficulties of directing and pumping fluids at the microscale. We reveal how the nematic-flow coupling is not only dependent on geometrical constraints, but is also highly sensitive to material and flow parameters. We specifically stress the key role played by the activity and the flow aligning parameter, and we show that solutions mostly depend on two dimensionless parameters. We find that for large values of the activity parameter, the flow is suppressed for contractile particles while it is either sustained or suppressed for extensile particles depending on whether they tend to align or tumble when subject to shear. We explain these distinct behaviors by an argument based on the results of the stability analysis applied to two simpler configurations: active flows confined between parallel plates with either orthogonal or perpendicular alignment at both walls. We show that the analytical laminar solution derived for the n model in the low activity limit is found also in the Q model, both analytically and numerically. This result is valid for both contractile and extensile particles and for a flow-tumbling as well as aligning nematics. We remark that this velocity profile can be derived for generic boundary conditions. To stress the more general nature of the Q model, we conclude by providing a numerical example of a biaxial three-dimensional thresholdless active flow for which we show that biaxiality is especially relevant for a weakly first-order isotropic-nematic phase transition.
Collective hydrodynamic transport of magnetic microrollers
Junot G., Cebers A., Tierno P.
Soft Matter
17
8605 8611
(2021)
We investigate the collective transport properties of microscopic magnetic rollers that propel close to a surface due to a circularly polarized, rotating magnetic field. The applied field exerts a torque to the particles, which induces a net rolling motion close to a surface. The collective dynamics of the particles result from the balance between magnetic dipolar interactions and hydrodynamic ones. We show that, when hydrodynamics dominate, i.e. for high particle spinning, the collective mean velocity linearly increases with the particle density. In this regime we analyse the clustering kinetics, and find that hydrodynamic interactions between the anisotropic, elongated particles, induce preferential cluster growth along a direction perpendicular to the driving one, leading to dynamic clusters that easily break and reform during propulsion.
Multiphase CFD modeling of front propagation in a Hele-Shaw cell featuring a localized constriction
Mac Intyre J.R., Puisto A., Korhonen M., Alava M., Ortín J.
Physical Review Fluids
6
(2021)
We study a liquid-gas front propagation in a modulated Hele-Shaw cell by means of multiphase computational fluid mechanics based on the three-dimensional Navier-Stokes equations. In the simulations an obstacle that partially fills the gap is placed at the center of the cell, and the liquid-gas interface is driven at a constant velocity. We study the morphological differences between imbibition and drainage for a wide range of capillary numbers, and explore how the wetting properties of the constriction affect the amount of liquid that remains trapped in the draining process. We observe increasing remaining volumes with increasing capillary number and decreasing contact angle. The present CFD implementation for a single mesa defect provides insight into a wide number of practical applications.
Transport and Assembly of Magnetic Surface Rotors
Tierno P., Snezhko A.
ChemNanoMat
7
881 893
(2021)
Magnetic rotors energized by external fields represent a promising platform for investigation of complex dynamics and self-organization in fluid media. The intricate balance between magnetic and hydrodynamic interactions drives rotor's dynamics, and promotes novel self-assembled states. Non-invasive nature of actuation of particles by external fields suggests their applications as microscale mixers and cargo carriers.
Parallel Hybrid Simulations of Block Copolymer Nanocomposites using Coarray Fortran
Diaz J., Pinna M., Zvelindovsky A.V., Pagonabarraga I.
Macromolecular Theory and Simulations
30
(2021)
Computer simulations of experimentally comparable system sizes in soft matter often require considerable elapsed times. The use of many cores can reduce the needed time, ideally proportionally to the number of processors. In this paper a parallel computational method using coarray Fortran is implemented and tested for large systems of purely block copolymer melts, as well as block copolymer nanocomposites. A satisfactory strong scaling is shown up to 512 cores while a weak scaling with a drop in performance is achieved up to 4096 cores. The scaling of the parallel cell dynamic simulations scheme displays no drawbacks over MPI and provides an example of the simplicity of the coarray approach. The code has been tested on several architectures and compilers. The hybrid block copolymer/nanoparticle algorithm can achieve previously unavailable system sizes.
Stochastic quorum percolation and noise focusing in neuronal networks
Orlandi J.G., Casademunt J.
EPL
133
(2021)
Recent experiments have shown that the spontaneous activity of developing dissociated neuronal cultures can be described as a process of highly inhomogeneous nucleation and front propagation due to the localization of noise activity, i.e., noise focusing. However, the basic understanding of the mechanisms of noise build-up leading to the nucleation remains an open fundamental problem. Here we present a minimal dynamical model called stochastic quorum percolation that can account for the observed phenomena, while providing a robust theoretical framework. The model reproduces the first- and second-order phase transitions of bursting dynamics and neuronal avalanches, respectively, and captures the profound effect metric correlations in the network topology can have on the dynamics. The application of our results to other systems such as in the propagation of infectious diseases and of rumors is discussed.
Task-Related Brain Connectivity Activation Functional Magnetic Resonance Imaging in Intellectual Disability Population: A Meta-Analytic Study
Cañete-Massé C., Carbó-Carreté M., Peró-Cebollero M., Guàrdia-Olmos J.
Brain Connectivity
11
788 798
(2021)
Neuroimaging studies of intellectual disability (ID) have been published over the last three decades, but the findings are often inconsistent, and therefore, the neural correlates of ID remain elusive. This article aims to study the different publications in task-functional magnetic resonance imaging (fMRI) and different ID populations to make a qualitative and quantitative analysis on this field.
Benefits of Cultural Activities on People With Cognitive Impairment: A Systematic Review
Delfa-Lobato L., Guàrdia-Olmos J., Feliu-Torruella M.
Frontiers in Psychology
12
(2021)
Museums and cultural institutions are increasingly striving to respond to the interests and needs of the society that hosts them. This means, apart from other actions, that these institutions must be involved in the health and wellbeing of society, and the creation of cultural activities aimed at people with cognitive impairment, a group of individuals that is growing worldwide due to the aging of society and the increasing prevalence of dementia. The involved sectors are aware of the potential and benefits of activities for this population, even though there is much research to be conducted. To date, no systematic review has focused on the benefits of cultural activities for cognitively impaired people. This study aimed to explore the benefits of different modalities of cultural activities with evidence from 145 studies from various databases, which met the inclusion criteria. Significant improvements in general cognition, quality of life (QoL), emotional wellbeing, socialization, and communication were generally reported after interventions, with a reduction in depression symptoms. There was not enough evidence to prove memory, language, or daily functioning improvements attributable to cultural interventions. There were no significant reductions reported in apathy, sadness, agitation, or anxiety.
Alzheimer’s disease caregiver characteristics and their relationship with anticipatory grief
Pérez-González A., Vilajoana-Celaya J., Guàrdia-Olmos J.
International Journal of Environmental Research and Public Health
18
(2021)
In Alzheimer’s disease, two fundamental aspects become important for caregivers: ambiguity and ambivalence. Thus, anticipatory grief is considered an active psychological process that is very different from the mere anticipation of death. The present study aims to determine which characteristics of family caregivers of people with dementia, such as age, gender, educational level, relationship with the person with dementia, years with dementia or years as a caregiver, are related to the presence of anticipatory grief. A cross-sectional design was employed. The sample consisted of a total of 129 subjects who cared for a family member with dementia. A sociodemographic data sheet and a battery of tests measure the presence of anticipatory grief, caregiver burden and/or psychopathology. The results obtained allowed us to confirm some of the hypotheses regarding the anticipatory grief construct, the importance of the care time factor, in years and per day, as well as the relevance of the previous demographic and psychopathological profile (being female, spouse function and possible depressive symptomatology). Likewise, from the prediction analyzes performed, it seems that these variables can predict anticipatory grief. These results propose interesting opportunities to formulate care proposals to professionals and family caregivers in relation to care tasks and caregiver skills
Structural equation models to estimate dynamic effective connectivity networks in resting fMRI. A comparison between individuals with Down syndrome and controls
Figueroa-Jiménez M.D., Cañete-Massé C., Carbó-Carreté M., Zarabozo-Hurtado D., Guàrdia-Olmos J.
Behavioural Brain Research
405
(2021)
Emerging evidence suggests that an effective or functional connectivity network does not use a static process over time but incorporates dynamic connectivity that shows changes in neuronal activity patterns. Using structural equation models (SEMs), we estimated a dynamic component of the effective network through the effects (recursive and nonrecursive) between regions of interest (ROIs), taking into account the lag 1 effect. The aim of the paper was to find the best structural equation model (SEM) to represent dynamic effective connectivity in people with Down syndrome (DS) in comparison with healthy controls. Twenty-two people with DS were registered in a functional magnetic resonance imaging (fMRI) resting-state paradigm for a period of six minutes. In addition, 22 controls, matched by age and sex, were analyzed with the same statistical approach. In both groups, we found the best global model, which included 6 ROIs within the default mode network (DMN). Connectivity patterns appeared to be different in both groups, and networks in people with DS showed more complexity and had more significant effects than networks in control participants. However, both groups had synchronous and dynamic effects associated with ROIs 3 and 4 related to the upper parietal areas in both brain hemispheres as axes of association and functional integration. It is evident that the correct classification of these groups, especially in cognitive competence, is a good initial step to propose a biomarker in network complexity studies.
Universal nomenclature for oxytocin–vasotocin ligand and receptor families
Theofanopoulou C., Gedman G., Cahill J.A., Boeckx C., Jarvis E.D.
Nature
592
747 755
(2021)
Oxytocin (OXT; hereafter OT) and arginine vasopressin or vasotocin (AVP or VT; hereafter VT) are neurotransmitter ligands that function through specific receptors to control diverse functions1,2. Here we performed genomic analyses on 35 species that span all major vertebrate lineages, including newly generated high-contiguity assemblies from the Vertebrate Genomes Project3,4. Our findings support the claim5 that OT (also known as OXT) and VT (also known as AVP) are adjacent paralogous genes that have resulted from a local duplication, which we infer was through DNA transposable elements near the origin of vertebrates and in which VT retained more of the parental sequence. We identified six major oxytocin–vasotocin receptors among vertebrates. We propose that all six of these receptors arose from a single receptor that was shared with the common ancestor of invertebrates, through a combination of whole-genome and large segmental duplications. We propose a universal nomenclature based on evolutionary relationships for the genes that encode these receptors, in which the genes are given the same orthologous names across vertebrates and paralogous names relative to each other. This nomenclature avoids confusion due to differential naming in the pre-genomic era and incomplete genome assemblies, furthers our understanding of the evolution of these genes, aids in the translation of findings across species and serves as a model for other gene families.
Complexity analysis of the default mode network using resting-state fmri in down syndrome: Relationships highlighted by a neuropsychological assessment
Figueroa-Jimenez M.D., Carbó-Carreté M., Cañete-Massé C., Zarabozo-Hurtado D., Peró-Cebollero M., Salazar-Estrada J.G., Guàrdia-Olmos J.
Brain Sciences
11
1 19
(2021)
Background: Studies on complexity indicators in the field of functional connectivity derived from resting-state fMRI (rs-fMRI) in Down syndrome (DS) samples and their possible relationship with cognitive functioning variables are rare. We analyze how some complexity indicators estimated in the subareas that constitute the default mode network (DMN) might be predictors of the neuropsychological outcomes evaluating Intelligence Quotient (IQ) and cognitive performance in persons with DS. Methods: Twenty-two DS people were assessed with the Kaufman Brief Test of Intelligence (KBIT) and Frontal Assessment Battery (FAB) tests, and fMRI signals were recorded in a resting state over a six-minute period. In addition, 22 controls, matched by age and sex, were evaluated with the same rs-fMRI procedure. Results: There was a significant difference in complexity indicators between groups: the control group showed less complexity than the DS group. Moreover, the DS group showed more variance in the complexity indicator distributions than the control group. In the DS group, significant and negative relationships were found between some of the complexity indicators in some of the DMN networks and the cognitive performance scores. Conclusions: The DS group is characterized by more complex DMN networks and exhibits an inverse relationship between complexity and cognitive performance based on the negative parameter estimates.
Resting-state default mode network connectivity in young individuals with Down syndrome
Figueroa-Jimenez M.D., Cañete-Massé C., Carbó-Carreté M., Zarabozo-Hurtado D., Peró-Cebollero M., Salazar-Estrada J.G., Guàrdia-Olmos J.
Brain and Behavior
11
(2021)
Down syndrome (DS) is a chromosomal disorder that causes intellectual disability. Few studies have been conducted on functional connectivity using resting-state fMRI (functional magnetic resonance imaging) signals or more specifically, on the relevant structure and density of the default mode network (DMN). Although data on this issue have been reported in adult DS individuals (age: >45 years), the DMN properties in young DS individuals have not been studied. The aim of this study was to describe the density and structure of the DMN network from fMRI signals in young DS (age: <36 years).
Confirmatory factor analysis with missing data in a small sample: cognitive reserve in people with Down Syndrome
Cañete-Massé C., Carbó-Carreté M., Figueroa-Jiménez M.D., Oviedo G.R., Guerra-Balic M., Javierre C., Peró-Cebollero M., Guàrdia-Olmos J.
Quality and Quantity
(2021)
The presence of missing data and small sample sizes are very common in social and health sciences. Concurrently to present a methodology to solve the small sample size and missing data, we aim to present a definition of Cognitive Reserve for people with Down Syndrome. This population has become an appealing focus to study this concept because of the high incidence of dementia. The accidental sample comprised 35 persons with DS (16–35 years). A total of 12 variables were acquired, four of them had missing data. Two types of multiple imputation were made. Confirmatory factor analysis with Bayesian estimations was performed on the final database with non-informative priors. However, to solve the sample size problem, two additional corrections were made: first, we followed the Jiang and Yuan (2017) schema, and second, we made a Jackknife correlation correction. The estimations of the confirmatory factor analysis, as well as the global fit, are adequate. As an applied perspective, the acceptable fit of our model suggests the possibility of operationalizing the latent factor Cognitive Reserve in a simple way to measure it in the Down Syndrome population.
Cardiorespiratory Coordination During Exercise in Adults With Down Syndrome
Oviedo G.R., Garcia-Retortillo S., Carbó-Carreté M., Guerra-Balic M., Balagué N., Javierre C., Guàrdia-Olmos J.
Frontiers in Physiology
12
(2021)
Down syndrome (DS) is a chromosomal disorder affecting simultaneously cardiovascular and respiratory systems. There is no research studying the coupling between these systems during cardiorespiratory exercise testing in a population with DS. Cardiorespiratory coordination (CRC), evaluated through principal component analysis (PCA), measures the covariation of cardiorespiratory variables during exercise.
Abusive Supervision: A Systematic Review and New Research Approaches
Gallegos I., Guàrdia-Olmos J., Berger R.
Frontiers in Communication
6
(2021)
Abusive leaders affect employees’ emotions and health and produce counterproductive behaviors that cause economic damage to organizations. The literature has focused predominantly on the antecedents of abusive supervision and its negative impact, providing knowledge on mechanisms that link abusive supervision to consequences for subordinates. There has been limited research on the supervisor perspective, on the group level, and on recovery. This review makes three contributions: first, we examine the theoretical approaches used by previous research studies to understand abusive supervision. Second, we analyze the types of mechanisms that explain how and when an abusive supervision process occurs. Third, we identify and discuss applied methodologies and limitations. Based on the preferred reporting items for systematic reviews and meta-analysis guidelines, and transactional well-being process perspective, we analyzed 171 empirical manuscripts and 239 samples between 2010 and July 2020. We identified a growth in abusive supervision research between 2018 and 2020 and found 101 different theories. Most of these theories view abusive supervision from a social, relational, or affective perspective, but seldom from an emotional perspective. We classified four types of mechanisms: simple relations between abusive supervision and antecedent-consequences (12), moderators (47), mediators (26), and a combination of mediators and moderators (86). We found that research has mostly been performed at the employee level or on dyads; studies that analyze the team level are rarely found. We identified two methodological problems: cross-sectional designs, which do not allow the analysis of its causality, and the increased risk of common method variance that may influence the results obtained via single-source data. In conclusion, the theories used have focused on employee perceptions, which have not enabled the broadening of the abusive supervision concept to include the supervisor’s perspective and a recovery-related perspective. Research on how and when abusive supervision occurs analyzed with complex mechanisms using emotional variables and appropriate daily methodologies has been scarce. We propose a theoretical expansion including emotional theories to uncover emotional consequences of abusive supervision and the recovery concept to provide a deeper insight into abusive supervision process. We contend that longitudinal and diary designs that include teams and supervisor levels are necessary.
Large-scale citizen science provides high-resolution nitrogen dioxide values and health impact while enhancing community knowledge and collective action
Perelló J., Cigarini A., Vicens J., Bonhoure I., Rojas-Rueda D., Nieuwenhuijsen M.J., Cirach M., Daher C., Targa J., Ripoll A.
Science of the Total Environment
789
(2021)
We present outcomes from a large-scale air quality citizen science campaign (xAire, 725 measurements) to demonstrate its positive contribution in the interplay between advances in exposure assessment and developments in policy or collective action. A broad partnership with 1,650 people from communities around 18 primary schools across Barcelona provided the capacity to obtain unprecedented high-resolution NO2 levels and an updated asthma Health Impact Assessment. It is shown that NO2 levels vary considerably with at some cases very high levels. More than a 1,000 new cases of childhood asthma could be prevented each year by lowering NO2 levels. Representativity of site selection and the minimal number of samplers for land use regression modelling are considered. Enhancement of community knowledge and attitudes towards collective response were observed and identified as key drivers for successful large-scale monitoring campaigns. The results encourage strengthening collaboration with local communities when exploring environmental health issues.
Data set from large-scale citizen science provides high-resolution nitrogen dioxide values for enhancing community knowledge and collective action to related health issues
Perelló J., Cigarini A., Vicens J., Bonhoure I., Rojas-Rueda D., Nieuwenhuijsen M.J., Cirach M., Daher C., Targa J., Ripoll A.
Data in Brief
37
(2021)
Dataset from a large-scale air quality citizen science campaign is presented (xAire, 725 measurements, see Ref. [1]). A broad partnership with 1650 citizens from communities around 18 primary schools across Barcelona (Spain) provided the capacity to obtain unprecedented high-resolution NO2 levels which had in turn the capacity to provide an updated asthma Health Impact Assessment. Nitrogen dioxide levels being obtained in a 4-week period during February and March 2018 with Palmes’ diffusion samplers are herein provided. Dataset includes NO2 levels from outdoor locations n=671, playgrounds n=31, and inside school buildings (mostly classrooms) n=23. Data was calibrated and annualized with concentration levels from automatic reference stations. It is shown that NO2 levels vary considerably with at some cases very high levels. Strong differences might also however be explained by the fact that ambient air pollution is reduced exponentially with distance from an emission source like traffic meaning that two samplers located about 100 m away can measure a tenfold difference concentration level.
Healthy teleworking: Towards personalized exercise recommendations
Almarcha M., Balagué N., Torrents C.
Sustainability (Switzerland)
13
(2021)
Home-based teleworking, associated with sedentary behavior, may impair self-reported adult health status. Current exercise recommendations, based on universal recipes, may be insufficient or even misleading to promote healthy teleworking. From the Network Physiology of Exercise perspective, health is redefined as an adaptive emergent state, product of dynamic interactions among multiple levels (from genetic to social) that cannot be reduced to a few dimensions. Under such a perspective, fitness development is focused on enhancing the individual functional diversity potential, which is better achieved through varied and personalized exercise proposals. This paper discusses some myths related to ideal or unique recommendations, like the ideal exercise or posture, and the contribution of recent computer technologies and applications for prescribing exercise and assessing fitness. Highlighting the need for creating personalized working environments and strengthening the active contribution of users in the process, new recommendations related to teleworking posture, home exercise counselling, exercise monitoring and to the roles of healthcare and exercise professionals are proposed. Instead of exercise prescribers, professionals act as co-designers that help users to learn, co-adapt and adequately contextualize exercise in order to promote their somatic awareness, job satisfaction, productivity, work–life balance, wellbeing and health.
Metastable coordination dynamics of collaborative creativity in educational settings
Torrents C., Balagué N., Hristovski R., Almarcha M., Scott Kelso J.A.
Sustainability (Switzerland)
13
1 16
(2021)
Educational systems consider fostering creativity and cooperation as two essential aims to nurture future sustainable citizens. The cooperative learning approach proposes different pedagogical strategies for developing creativity in students. In this paper, we conceptualize collaborative creativity under the framework of coordination dynamics and, specifically, we base it on the formation of spontaneous multiscale synergies emerging in complex living systems when interacting with cooperative/competitive environments. This conception of educational agents (students, teachers, institutions) changes the understanding of the teaching/learning process and the traditional roles assigned to each agent. Under such an understanding, the design and co-design of challenging and meaningful learning environments is a key aspect to promote the spontaneous emergence of multiscale functional synergies and teams (of students, students and teachers, teachers, institutions, etc.). According to coordination dynamics, cooperative and competitive processes (within and between systems and their environments) are seen not as opposites but as complementary pairs, needed to develop collaborative creativity and increase the functional diversity potential of teams. Adequate manipulation of environmental and personal constraints, nested in different level and time scales, and the knowledge of their critical (tipping) points are key aspects for an adequate design of learning environments to develop synergistic creativity.
A Semi-Deterministic Random Walk with Resetting
Villarroel, J., Montero, M., & Vega, J. A.
Entropy
23
825
(2021)
We consider a discrete-time random walk (xt) which, at random times, is reset to the starting position and performs a deterministic motion between them. We show that the quantity Pr(xt+1=n+1|xt=n),n→∞ determines if the system is averse, neutral or inclined towards resetting. It also classifies the stationary distribution. Double barrier probabilities, first passage times and the distribution of the escape time from intervals are determined.
Integrating collaboration and leadership in conversational group recommender systems
Contreras, D., Salamó, M., & Boratto, L.
ACM Transactions on Information Systems
39
4
(2021)
Recent observational studies highlight the importance of considering the interactions between users in the group recommendation process, but to date their integration has been marginal. In this article, we propose a collaborative model based on the social interactions that take place in a web-based conversational group recommender system. The collaborative model allows the group recommender to implicitly infer the different roles within the group, namely, collaborative and leader user(s). Moreover, it serves as the basis of several novel collaboration-based consensus strategies that integrate both individual and social interactions in the group recommendation process. A live-user evaluation confirms that our approach accurately identifies the collaborative and leader users in a group and produces more effective recommendations.
Children building and having fun while they learn geometry.
Puig, A., Rodríguez, I., Baldeón, J., & Múria, S.
Computer Applications in Engineering Education
(2021)
Geometry is a basic discipline in STEM education. Recent educational reports, however, suggest that geometry is one of the subjects that sees the lowest levels of performance in the math curriculum. This paper presents a gamified itinerary through digital activities designed to teach geometry. Our aim is to attract Primary School children into the world of geometry. First, we scaffold geometry outcomes to take students progressively from basic geometric shapes to a stronger understanding of complex three-dimensional (3D) properties. Second, we use gamification to introduce fun into the learning process. Third, we propose digital activities in virtual environments, with which students can, in particular, develop 3D spatial perception. Concretely, children are immersed in a two-dimensional (2D)–3D world in which they play the role of architects who manipulate 2D and 3D shapes to create buildings. Results obtained in the evaluation of the system with 60 children showed an improvement in both their learning and their interest in math. Both children and teachers rated the experience very positively.
Enabling cross-continent provider fairness in educational recommender systems
Gómez, E., Zhang, C. S., Boratto, L., Salamó, M., & Ramos, G.
Future Generation Computer Systems
127
435 447
(2021)
With the widespread diffusion of Massive Online Open Courses (MOOCs), educational recommender systems have become central tools to support students in their learning process. While most of the literature has focused on students and the learning opportunities that are offered to them, the teachers behind the recommended courses get a certain exposure when they appear in the final ranking. Underexposed teachers might have reduced opportunities to offer their services, so accounting for this perspective is of central importance to generate equity in the recommendation process. In this paper, we consider groups of teachers based on their geographic provenience and assess provider (un)fairness based on the continent they belong to. We consider measures of visibility and exposure, to account (i) in how many recommendations and (ii) wherein the ranking of the teachers belonging to different groups appear. We observe disparities that favor the most represented groups, and we overcome these phenomena with a re-ranking approach that provides each group with the expected visibility and exposure, thus controlling fairness of providers coming from different continents (cross-continent provider fairness). Experiments performed on data coming from a real-world MOOC platform show that our approach can provide fairness without affecting recommendation effectiveness.
Provider fairness across continents in collaborative recommender systems
Gómez, E., Boratto, L., & Salamó, M.
Information Processing & Management
59
1
(2021)
When a recommender system suggests items to the end-users, it gives a certain exposure to the providers behind the recommended items. Indeed, the system offers a possibility to the items of those providers of being reached and consumed by the end-users. Hence, according to how recommendation lists are shaped, the experience of under-recommended providers in online platforms can be affected. To study this phenomenon, we focus on movie and book recommendation and enrich two datasets with the continent of production of an item. We use this data to characterize imbalances in the distribution of the user–item observations and regarding where items are produced (geographic imbalance). To assess if recommender systems generate a disparate impact and (dis)advantage a group, we divide items into groups, based on their continent of production, and characterize how represented is each group in the data. Then, we run state-of-the-art recommender systems and measure the visibility and exposure given to each group. We observe disparities that favor the most represented groups. We overcome these phenomena by introducing equity with a re-ranking approach that regulates the share of recommendations given to the items produced in a continent (visibility) and the positions in which items are ranked in the recommendation list (exposure), with a negligible loss in effectiveness, thus controlling fairness of providers coming from different continents. A comparison with the state of the art shows that our approach can provide more equity for providers, both in terms of visibility and of exposure.
Perturbation of the normalized Laplacian matrix for the prediction of missing links in real networks
Aliakbarisani, R., Ghasemi, A., & Serrano, M. Á.
IEEE Transactions on Network Science and Engineering
(2021)
The problem of predicting missing links in real-world networks is an active and challenging research area in both science and engineering. The goal is to model the process of link formation in a complex network based on its observed structure to unveil lost or unseen interactions. In this paper, we use perturbation theory to develop a general link prediction procedure, called Laplacian Perturbation Method (LPM), that relies on relevant structural information encoded in the normalized Laplacian matrix of the network. We implement a general algorithm for our perturbation method valid for different Laplacian-based link prediction schemes that successfully surpass the prediction accuracy of their standard non-perturbed versions in real-world and model networks. The suggested LPM for link prediction also exhibits higher accuracy compared to other extensively used local and global state-of-the-art techniques and, in particular, it outperform the Structural Perturbation Method (SPM), a popular procedure that perturbs the adjacency matrix of a network for inferring missing links, in many real-world and in synthetic networks. Taken together, our results show that perturbation methods can significantly improve Laplacian-based link prediction techniques, and feeds the debate on which representation, Laplacian or adjacency, better represents structural information for link prediction tasks in networks.
Osmotic pressure of suspensions comprised of charged microgels
Scotti, A., Pelaez-Fernandez, M., Gasser, U., & Fernandez-Nieves, A.
Physical Review E
103
3
(2021)
We determine the osmotic pressure of microgel suspensions using membrane osmometry and dialysis, for microgels with different softnesses. Our measurements reveal that the osmotic pressure of solutions of both ionic and neutral microgels is determined by the free ions that leave the microgel periphery to maximize their entropy and not by the translational degrees of freedom of the microgels themselves. Furthermore, up to a given concentration it is energetically favorable for the microgels to maintain a constant volume without appreciable deswelling. The concentration where deswelling starts weakly depends on the crosslinker concentration, which affects the microgel dimension; we explain this by considering the dependence of the osmotic pressure and the microgel bulk modulus on the particle size.
Internal structure of ultralow-crosslinked microgels: From uniform deswelling to phase separation.
Tennenbaum, M., Anderson, C., Hyatt, J. S., Do, C., & Fernandez-Nieves, A.
Physical Review E
103
2
(2021)
We perform small angle neutron scattering on ultralow-crosslinked microgels and find that while in certain conditions both the particle size and the characteristic internal length scale change in unison, in other instances this is not the case. We show that nonuniform deswelling depends not only on particle size, but also on the particular way the various contributions to the free energy combine to result in a given size. Only when polymer-solvent demixing strongly competes with ionic or electrostatic effects do we observe nonuniform behavior, reflecting internal microphase separation. The results do not appreciably depend on particle number density; even in concentrated suspensions, we find that at relatively low temperature, where demixing is not very strong, the deswelling behavior is uniform, and that only at sufficiently high temperature, where demixing is very strong, does the microgel structure change akin to internal microphase separation.
A Conceptual Probabilistic Framework for Annotation Aggregation of Citizen Science Data.
Cerquides, J., Mülâyim, M. O., Hernández-González, J., Ravi Shankar, A., & Fernandez-Marquez, J. L.
Mathematics
9
8
(2021)
Over the last decade, hundreds of thousands of volunteers have contributed to science by collecting or analyzing data. This public participation in science, also known as citizen science, has contributed to significant discoveries and led to publications in major scientific journals. However, little attention has been paid to data quality issues. In this work we argue that being able to determine the accuracy of data obtained by crowdsourcing is a fundamental question and we point out that, for many real-life scenarios, mathematical tools and processes for the evaluation of data quality are missing. We propose a probabilistic methodology for the evaluation of the accuracy of labeling data obtained by crowdsourcing in citizen science. The methodology builds on an abstract probabilistic graphical model formalism, which is shown to generalize some already existing label aggregation models. We show how to make practical use of the methodology through a comparison of data obtained from different citizen science communities analyzing the earthquake that took place in Albania in 2019.
Collective hydrodynamic transport of magnetic microrollers
Junot, G., Cebers, A., & Tierno, P.
Soft Matter
17
38
(2021)
We investigate the collective transport properties of microscopic magnetic rollers that propel close to a surface due to a circularly polarized, rotating magnetic field. The applied field exerts a torque to the particles, which induces a net rolling motion close to a surface. The collective dynamics of the particles result from the balance between magnetic dipolar interactions and hydrodynamic ones. We show that, when hydrodynamics dominate, i.e. for high particle spinning, the collective mean velocity linearly increases with the particle density. In this regime we analyse the clustering kinetics, and find that hydrodynamic interactions between the anisotropic, elongated particles, induce preferential cluster growth along a direction perpendicular to the driving one, leading to dynamic clusters that easily break and reform during propulsion.
Unified analysis of topological defects in 2D systems of active and passive disks
Digregorio, P., Levis, D., Cugliandolo, L. F., Gonnella, G., & Pagonabarraga, I.
Soft Matter
18
3
(2021)
We provide a comprehensive quantitative analysis of localized and extended topological defects in the steady state of 2D passive and active repulsive Brownian disk systems. We show that, both in and out-of-equilibrium, the passage from the solid to the hexatic is driven by the unbinding of dislocations, in quantitative agreement with the KTHNY singularity. Instead, extended clusters of defects largely dominate below the solid–hexatic critical line. The latter percolate in the liquid phase very close to the hexatic–liquid transition, both for continuous and discontinuous transitions, in the homogeneous liquid regime. At critical percolation the clusters of defects are fractal with statistical and geometric properties that are independent of the activity and compatible with the universality class of uncorrelated critical percolation. We also characterize the spatial organization of point-like defects and we show that the disclinations are not free, but rather always very near more complex defect structures. At high activity, the bulk of the dense phase generated by Motility-Induced Phase Separation is characterized by a density of point-like defects, and statistics and morphology of defect clusters, set by the amount of activity and not the packing fraction. Hexatic domains within the dense phase are separated by grain-boundaries along which a finite network of topological defects resides, interrupted by gas bubbles in cavitation. This structure is dynamic in the sense that the defect network allows for an unzipping mechanism that leaves free space for gas bubbles to appear, close, and even be released into the dilute phase.
PRD1 as a nanoscaffold for drug loading
Duyvesteyn, H. M., Santos-Pérez, I., Peccati, F., Martinez-Castillo, A., Walter, T. S., Reguera, D., ... & Abrescia, N. G.
Bacteriophage Nanoscale
13
47
(2021)
Viruses are very attractive biomaterials owing to their capability as nanocarriers of genetic material. Efforts have been made to functionalize self-assembling viral protein capsids on their exterior or interior to selectively take up different payloads. PRD1 is a double-stranded DNA bacteriophage comprising an icosahedral protein outer capsid and an inner lipidic vesicle. Here, we report the three-dimensional structure of PRD1 in complex with the antipsychotic drug chlorpromazine (CPZ) by cryo-electron microscopy. We show that the jellyrolls of the viral major capsid protein P3, protruding outwards from the capsid shell, serve as scaffolds for loading heterocyclic CPZ molecules. Additional X-ray studies and molecular dynamics simulations show the binding modes and organization of CPZ molecules when complexed with P3 only and onto the virion surface. Collectively, we provide a proof of concept for the possible use of the lattice-like organisation and the quasi-symmetric morphology of virus capsomers for loading heterocyclic drugs with defined properties.
Oxytocin variation and brain region-specific gene expression in a domesticated avian species
Tobari, Y., Theofanopoulou, C., Mori, C., Sato, Y., Marutani, M., Fujioka, S., ... & Okanoya, K.
Genes, Brain and Behavior
21
2
(2021)
The Bengalese finch was domesticated more than 250 years ago from the wild white-rumped munia (WRM). Similar to other domesticated species, Bengalese finches show a reduced fear response and have lower corticosterone levels, compared to WRMs. Bengalese finches and munias also have different song types. Since oxytocin (OT) has been found to be involved in stress coping and auditory processing, we tested whether the OT sequence and brain expression pattern and content differ in wild munias and domesticated Bengalese finches. We sequenced the OT from 10 wild munias and 11 Bengalese finches and identified intra-strain variability in both the untranslated and protein-coding regions of the sequence, with all the latter giving rise to synonymous mutations. Several of these changes fall in specific transcription factor-binding sites, and show either a conserved or a relaxed evolutionary trend in the avian lineage, and in vertebrates in general. Although in situ hybridization in several hypothalamic nuclei did not reveal significant differences in the number of cells expressing OT between the two strains, real-time quantitative PCR showed a significantly higher OT mRNA expression in the cerebrum of the Bengalese finches relative to munias, but a significantly lower expression in their diencephalon. Our study thus points to a brain region-specific pattern of neurochemical expression in domesticated and wild avian strains, which could be linked to domestication and the behavioral changes associated with it.
Heat sink avalanche dynamics in elastocaloric Cu-Al-Ni single crystal detected by infrared calorimetry and Gaussian filtering
Capellera, G., Ianniciello, L., Romanini, M., & Vives, E.
Applied Physics Letters
119
15
(2021)
The physics behind the cooling process occurring in an elastocaloric Cu–Al–Ni wire during the martensite to austenite transition after stress release is studied. A previous experiment using infrared imaging determined the temperature map evolution of the sample surface and obtained the qualitative evolution of heat sinks by reversing the Fourier heat equation. The results were only qualitative due to the data smoothing algorithm that was used to correct the experimental noise. We analyze the original data by using a more appropriate Gaussian filter to reject the noise without smoothing the sharp martensite-austenite interfaces. Results show a much better spatial resolution that enables us to obtain new physical variables characterizing the discontinuous, avalanche-like, cooling process: the sink width, the sink cooling power, and the sink velocity.
Thermo-magnetic characterization of phase transitions in a Ni-Mn-In metamagnetic shape memory alloy
Romero, F. J., Martín-Olalla, J. M., Blázquez, J. S., Gallardo, M. C., Soto-Parra, D., Vives, E., & Planes, A.
Journal of Alloys and Compounds
887
161395
(2021)
The partially overlapped ferroelastic/martensitic and para-ferromagnetic phase transitions of a Ni50.53Mn33.65In15.82 metamagnetic shape memory alloy have been studied from calorimetric, magnetic and acoustic emission measurement. We have taken advantage of the existence of thermal hysteresis of the first order ferroelastic/martensitic phase transition (~2.5 K) to discriminate the latent heat contribution ΔHt=7.2115kJkg-1 and the specific heat contribution ΔHc=2161Jkg-1to the total excess enthalpy of the phase transition. The specific heat was found to follow a step-like behavior at this phase transition. The intermittent dynamics of the ferroelastic/martensitic transition has been characterized as a series of avalaches detected both from acoustic emission and calorimetric measurements. The energy distribution of these avalanche events was found to follow a power law with a characteristic energy exponent ε≅2 which is in agreement with the expected value for a system undergoing a symmetry change from cubic to monoclinic. Finally, the critical behavior of the para-ferromagnetic austenite phase transition that takes place at ~311 K has been studied from the behavior of the specific heat. A critical exponent α≅0.09 has been obtained, which has been shown to be in agreement with previous values reported for Ni-Mn-Ga alloys but different from the critical divergence reported for pure Ni.
THE EFFECT OF SECOND-GENERATION ANTIDEPRESSANT TREATMENT ON THE EXECUTIVE FUNCTIONS OF PATIENTS WITH MAJOR DEPRESSIVE DISORDER: A META-ANALYSIS STUDY WITH STRUCTURAL EQUATION MODELS
Gudayol-Ferré E., Duarte-Rosas P., Peró-Cebollero M., Guàrdia-Olmos J.
Psychiatry Research
296
(2021)
Major depressive disorder (MDD) has been linked to executive functions (EF) deficits that can be improved after pharmacological treatment, but it is unclear whether there is a class of antidepressants that is more effective than others to ameliorate these deficits in MDD. Additionally, the possible effects of clinical and demographic variables on the improvement of MDD EF deficits after pharmacological treatment are currently unknown. Our aim was to study the possible neuropsychological effects of second-generation antidepressant classes on the EF of MDD patients and the potential influence of clinical and demographic variables as moderators of these effects through a meta-analytic approach. Twenty-one papers were included in our study. A structural equation model meta-analysis was performed. The improvement of EF after pharmacological treatment is clinically relevant, but it is incomplete. This effect is influenced by age and years of education of the patients. Selective serotonin reuptake inhibitors (SSRIs) and dual inhibitors are the drugs causing the greatest improvement in EF of MDD patients. Antidepressant class is an important variable linked to EF improvement after MDD treatment, but the degree of improvement in these cognitive functions is strongly influenced by some clinical and demographic variables of patients with depression.
Acoustic and prosodic information for home monitoring of bipolar disorder
Farrús, M.; Codina-Filbà, J.; Escudero, J.
Health Informatics Journal
27
1
(2021)
Epidemiological studies suggest that bipolar disorder has a prevalence of about 1% in European countries, becoming one of the most disabling illnesses in working age adults, and often long-term and persistent with complex management and treatment. Therefore, the capacity of home monitoring for patients with this disorder is crucial for their quality of life. The current paper introduces the use of speech-based information as an easy-to-record, ubiquitous and non-intrusive health sensor suitable for home monitoring, and its application in the framework on the NYMPHA-MD project. Some preliminary results also show the potential of acoustic and prosodic features to detect and classify bipolar disorder, by predicting the values of the Hamilton Depression Rating Scale (HDRS) and the Young Mania Rating Scale (YMRS) from speech.
Aphasia and acquired reading impairments: What are the high‐tech alternatives to compensate for reading deficits?
Cistola, G., Farrús, M., van der Meulen, I.
International Journal of Language & Communication Disorders
56
1
(2021)
People with aphasia (PWA) frequently present impairments in reading comprehension. Such impairments can be particularly debilitating due to the limitations and constraints they impose on everyday life. Recent technological advancements in the field of information and communication technologies offer many compensative tools for PWA. However, most technological tools are designed for patients with speech production impairments. Instruments addressing reading impairments associated with aphasia remain scarce and underrepresented in the scientific literature.
Resting-state default mode network connectivity in young individuals with Down syndrome
Figueroa-Jimenez M.D., Cañete-Massé C., Carbó-Carreté M., Zarabozo-Hurtado D., Peró-Cebollero M., Salazar-Estrada J.G., Guàrdia-Olmos J.
Brain and Behavior
11
1
(2021)
Down syndrome (DS) is a chromosomal disorder that causes intellectual disability. Few studies have been conducted on functional connectivity using resting-state fMRI (functional magnetic resonance imaging) signals or more specifically, on the relevant structure and density of the default mode network (DMN). Although data on this issue have been reported in adult DS individuals (age: >45 years), the DMN properties in young DS individuals have not been studied. The aim of this study was to describe the density and structure of the DMN network from fMRI signals in young DS (age: <36 years).
Spontaneous Functional Recovery after Focal Damage in Neuronal Cultures
Teller, S ; Estevez-Priego, E; Granell, C ; Tornero, D; Andilla, J ; Olarte, OE; Loza-Alvarez, P; Arenas, A; Soriano, J
ENEURO
7
1
(2020)
Damage in biological neuronal networks triggers a complex functional reorganization whose mechanisms are still poorly understood. To delineate this reorganization process, here we investigate the functional alterations of in vitro rat cortical circuits following localized laser ablation. The analysis of the functional network configuration before and after ablation allowed us to quantify the extent of functional alterations and the characteristic spatial and temporal scales along recovery. We observed that damage precipitated a fast rerouting of information flow that restored network's communicability in about 15 min. Functional restoration was led by the immediate neighbors around trauma but was orchestrated by the entire network. Our in vitro setup exposes the ability of neuronal circuits to articulate fast responses to acute damage, and may serve as a proxy to devise recovery strategies in actual brain circuits. Moreover, this biological setup can become a benchmark to empirically test network theories about the spontaneous recovery in dynamical networks.
Glutamate receptors in domestication and modern human evolution
O'Rourke, T ; Boeckx, C
NEUROSCIENCE AND BIOBEHAVIORAL REVIEWS
341 357
(2020)
There has been a recent resurgence of interest in the hypothesis that anatomically modern humans and domesticated species have followed convergent evolutionary paths. Here, we review results from domestication and modern-human evolutionary studies in order to evaluate evidence for shared changes to neurotransmission across these species. We compare genomic and, where available, brain-expression differences across 488 neurotransmitter receptor genes in 14 domesticated species and modern humans relative to their wild and archaic counterparts. This analysis highlights prevalent changes to glutamate - most notably kainate and metabotropic - receptor genes. We review evidence for these genes' expression and their respective receptor functions in the central nervous system, as well as phenotypes commonly associated with alterations to them. This evidence suggests an important role for kainate and metabotropic receptors in regulating hypothalamic-pituitary-adrenal axis excitation, and we provide a mechanistic account of their actions in attenuating the stress response. We assess the explanatory potential of such actions in contributing to the emergence of the (self-)domesticated phenotype, in particular to reduced reactive aggression.
Functional interactions in patients with hemianopia: A graph theory-based connectivity study of resting fMRI signal
Caterina A. Pedersini, Joan Guàrdia-Olmos, Marc Montalà-Flaquer, Nicolò Cardobi, Javier Sanchez-Lopez, Giorgia Parisi, Silvia Savazzi, Carlo A. Marzi
PLOS ONE
15
(2020)
The assessment of task-independent functional connectivity (FC) after a lesion causing hemianopia remains an uncovered topic and represents a crucial point to better understand the neural basis of blindsight (i.e. unconscious visually triggered behavior) and visual awareness. In this light, we evaluated functional connectivity (FC) in 10 hemianopic patients and 10 healthy controls in a resting state paradigm. The main aim of this study is twofold: first of all we focused on the description and assessment of density and intensity of functional connectivity and network topology with and without a lesion affecting the visual pathway, and then we extracted and statistically compared network metrics, focusing on functional segregation, integration and specialization. Moreover, a study of 3-cycle triangles with prominent connectivity was conducted to analyze functional segregation calculated as the area of each triangle created connecting three neighboring nodes. To achieve these purposes we applied a graph theory-based approach, starting from Pearson correlation coefficients extracted from pairs of regions of interest. In these analyses we focused on the FC extracted by the whole brain as well as by four resting state networks: The Visual (VN), Salience (SN), Attention (AN) and Default Mode Network (DMN), to assess brain functional reorganization following the injury. The results showed a general decrease in density and intensity of functional connections, that leads to a less compact structure characterized by decrease in functional integration, segregation and in the number of interconnected hubs in both the Visual Network and the whole brain, despite an increase in long-range inter-modules connections (occipito-frontal connections). Indeed, the VN was the most affected network, characterized by a decrease in intra- and inter-network connections and by a less compact topology, with less interconnected nodes. Surprisingly, we observed a higher functional integration in the DMN and in the AN regardless of the lesion extent, that may indicate a functional reorganization of the brain following the injury, trying to compensate for the general reduced connectivity. Finally we observed an increase in functional specialization (lower between-network connectivity) and in inter-networks functional segregation, which is reflected in a less compact network topology, highly organized in functional clusters. These descriptive findings provide new insight on the spontaneous brain activity in hemianopic patients by showing an alteration in the intrinsic architecture of a large-scale brain system that goes beyond the impairment of a single RSN.
Gender-based pairings influence cooperative expectations and behaviours
Anna Cigarini, Julián Vicens , Josep Perelló
SCIENTIFIC REPORTS
10
1
(2020)
The study explores the expectations and cooperative behaviours of men and women in a lab-in-the-field experiment by means of citizen science practices in the public space. It specifically examines the influence of gender-based pairings on the decisions to cooperate or defect in a framed and discrete Prisoner’s Dilemma game after visual contact. Overall, we found that when gender is considered behavioural differences emerge in expectations of cooperation, cooperative behaviours, and their decision time depending on whom the partner is. Men pairs are the ones with the lowest expectations and cooperation rates. After visual contact women infer men’s behaviour with the highest accuracy. Also, women take significantly more time to defect than to cooperate, compared to men. Finally, when the interacting partners have the opposite gender they expect significantly more cooperation and they achieve the best collective outcome. Together, the findings suggest that non verbal signals may influence men and women differently, offering novel interpretations to the context-dependence of gender differences in social decision tasks.
Two-dimensional telegraphic processes and their fractional generalizations
Masoliver, J; Lindenberg, K
PHYSICAL REVIEW E
101
1
(2020)
We study the planar motion of telegraphic processes. We derive the two-dimensional telegrapher's equation for isotropic and uniform motions starting from a random walk model which is the two-dimensional version of the multistate random walk with a continuum number of states representing the spatial directions. We generalize the isotropic model and the telegrapher's equation to include planar fractional motions. Earlier, we worked with the one-dimensional version [Masoliver, Phys. Rev. E 93, 052107 (2016)] and derived the three-dimensional version [Masoliver, Phys. Rev. E 96, 022101 (2017)]. An important lesson is that we cannot obtain the two-dimensional version from the three-dimensional or the one-dimensional one from the two-dimensional result. Each dimension must be approached starting from an appropriate random walk model for that dimension.
Curvature Corrections Remove the Inconsistencies of Binary Classical Nucleation Theory.
Aasen, Ailo; Reguera, David; Wilhelmsen, Oivind
Physical review letters
124
4
(2020)
The study of nucleation in fluid mixtures exposes challenges beyond those of pure systems. A striking example is homogeneous condensation in highly surface-active water-alcohol mixtures, where classical nucleation theory yields an unphysical, negative number of water molecules in the critical embryo. This flaw has rendered multicomponent nucleation theory useless for many industrial and scientific applications. Here, we show that this inconsistency is removed by properly incorporating the curvature dependence of the surface tension of the mixture into classical nucleation theory for multicomponent systems. The Gibbs adsorption equation is used to explain the origin of the inconsistency by linking the molecules adsorbed at the interface to the curvature corrections of the surface tension. The Tolman length and rigidity constant are determined for several water-alcohol mixtures and used to show that the corrected theory is free of physical inconsistencies and provides accurate predictions of the nucleation rates. In particular, for the ethanol-water and propanol-water mixtures, the average error in the predicted nucleation rates is reduced from 11-15 orders of magnitude to below 1.5. The curvature-corrected nucleation theory opens the door to reliable predictions of nucleation rates in multicomponent systems, which are crucial for applications ranging from atmospheric science to research on volcanos.
Collective Directional Locking of Colloidal Monolayers on a Periodic Substrate
Stoop, RL ; Straube, AV ; Johansen, TH; Tierno, P
PHYSICAL REVIEW LETTERS
124
5
(2020)
We investigate the directional locking effects that arise when a monolayer of paramagnetic colloidal particles is driven across a triangular lattice of magnetic bubbles. We use an external rotating magnetic field to generate a two-dimensional traveling wave ratchet forcing the transport of particles along a direction that intersects two crystallographic axes of the lattice. We find that, while single particles show no preferred direction, collective effects induce transversal current and directional locking at high density via a spontaneous symmetry breaking. The colloidal current may be polarized via an additional bias field that makes one transport direction energetically preferred.
Navigable maps of structural brain networks across species.
Allard, Antoine; Serrano, M Angeles
PLoS computational biology
16
2
(2020)
Connectomes are spatially embedded networks whose architecture has been shaped by physical constraints and communication needs throughout evolution. Using a decentralized navigation protocol, we investigate the relationship between the structure of the connectomes of different species and their spatial layout. As a navigation strategy, we use greedy routing where nearest neighbors, in terms of geometric distance, are visited. We measure the fraction of successful greedy paths and their length as compared to shortest paths in the topology of connectomes. In Euclidean space, we find a striking difference between the navigability properties of mammalian and non-mammalian species, which implies the inability of Euclidean distances to fully explain the structural organization of their connectomes. In contrast, we find that hyperbolic space, the effective geometry of complex networks, provides almost perfectly navigable maps of connectomes for all species, meaning that hyperbolic distances are exceptionally congruent with the structure of connectomes. Hyperbolic maps therefore offer a quantitative meaningful representation of connectomes that suggests a new cartography of the brain based on the combination of its connectivity with its effective geometry rather than on its anatomy only. Hyperbolic maps also provide a universal framework to study decentralized communication processes in connectomes of different species and at different scales on an equal footing.
From Language shift to language revitalization and sustainability. A complexity approach to linguistic ecology
Albert Bastardas-Boada
Edicions UB
(2020)
This book aims to contribute to the overall, integrated understanding of the processes of language contact and their evolution, be they the result of political or economic (dis)integrations or migrations or for technological reasons. Via an interdisciplinary, holistic approach, it also aims to support the theoretical grounding of a unified, common sociolinguistic paradigm, based on an ecological and complexity perspective. This approach built on the fact that linguistic structures do not live in isolation from their social functions and must be situated in relation to the sub-and supra-systems that determine their existence if we are to understand their fortunes. It is a useful contribution to understanding and promoting the processes of linguistic revitalization in the world, combining at the same time the maintenance and development of diversity while ensuring the intercommunication of human species.
Impact of targeted attack on the spontaneous activity in spatial and biologically-inspired neuronal networks
Faci-Lazaro, S; Soriano, J; Gomez-Gardenes, J
CHAOS
29
8
(2020)
We study the structural and dynamical consequences of damage in spatial neuronal networks. Inspired by real in vitro networks, we construct directed networks embedded in a two-dimensional space and follow biological rules for designing the wiring of the system. As a result, synthetic cultures display strong metric correlations similar to those observed in real experiments. In its turn, neuronal dynamics is incorporated through the Izhikevich model adopting the parameters derived from observation in real cultures. We consider two scenarios for damage, targeted attacks on those neurons with the highest out-degree and random failures. By analyzing the evolution of both the giant connected component and the dynamical patterns of the neurons as nodes are removed, we observe that network activity halts for a removal of 50% of the nodes in targeted attacks, much lower than the 70% node removal required in the case of random failures. Notably, the decrease of neuronal activity is not gradual. Both damage scenarios portray "boosts" of activity just before full silencing that are not present in equivalent random (Erdos-Renyi) graphs. These boosts correspond to small, spatially compact subnetworks that are able to maintain high levels of activity. Since these subnetworks are absent in the equivalent random graphs, we hypothesize that metric correlations facilitate the existence of local circuits sufficiently integrated to maintain activity, shaping an intrinsic mechanism for resilience. Published under license by AIP Publishing.
The use of the past tense aspect in Spanish by study At-Home and Study-Abroad Chinese learners in semi-guided written tasks
Sun Yuliang, Lourdes Díaz, Mariona Taulé (2020).
Círculo de Lingüística Aplicada a la Comunicación (CLAC), Ediciones Complutense
81
301 318
(2020)
Este estudio se centra en cómo los contextos de adquisición influyen en la competencia del español de los aprendices chinos. Elegimos el uso de pretérito indefinido y pretérito imperfecto como punto de partida para analizar su producción en tres redacciones semi-guiadas. Los resultados muestran que los diferentes objetivos de enseñanza promueven un desarrollo diferente en la competencia de español de los aprendices chinos: los aprendices de At-Home tienen un patrón de uso más cerca a hablantes nativos cuando se tiene en cuenta el factor al nivel discursivo; mientras que los aprendices de Study-Aboard muestran un patrón más cerca a hablantes nativos cuando se tiene en cuenta el factor al nivel de léxico. Sin embargo, los patrones del uso de los tiempos aspectuales del pasado en español en ambos contextos de adquisición muestran una tendencia tanto a la asociación prototípica al nivel discursivo como la al nivel léxico.
A comparative study of the acquisition of Spanish aspectual past tenses by Mandarin Chinese learners using guided and semi-guided written productions',
Sun Yuliang, Lourdes Díaz, Mariona Taulé
Strategies and Analyses of Language and Communication in Multilingual and International Contexts
Chapter 4
39 48
(2020)
"A comparative study of the acquisition of Spanish aspectual past tenses by Mandarin Chinese learners using guided and semi-guided written productions", is included within "Strategies and Analyses of Language and Communication in Multilingual and International Contexts" book.
Covering a variety of themes and subject areas related to language and communication in international and multilinguistic contexts, this book offers an insight into the latest research in applied linguistics and language acquisition. Aimed at both scholars and language practitioners, it presents empirical findings from researchers from more than 10 countries. Rather than limiting its focus to one language and context as a source of research, the collection reports and applies findings from various languages and communities.
Evaluating the effect of gamification on the deployment of digital cultural probes for children
Rodriguez, I ; Puig, A ; Tellols, D; Samso, K
INTERNATIONAL JOURNAL OF HUMAN-COMPUTER STUDIES
137
UNSP 102395
(2020)
This research proposes a digital Cultural Probe (CP) for children in the context of energy use and awareness. A CP is a user research method that allows participants to self-report by means of tools, artefacts, and tasks that they complete at their own pace. Our CP aims to gather data about the energy related habits and knowledge of the children and their families and also aims to provoke reflection and raise their awareness of energy and environmental issues. It is well known that the main drawback of CPs is their low completion rate and the consequent lack of gathered data. Based on the impact of gamification on users' motivation and engagement, we aim to test the hypothesis that "Gamification may encourage an active and fruitful participation of children in Cultural Probes". CP consists of four tasks designed to gather information about the children and their families' electric consumption and saving habits. We developed the CP as an Android app which was evaluated with children from two primary schools in Barcelona, who interacted with two different app versions (gamified and non-gamified). We designed a comparative experiment that gathered data on CP completion rate, CP task completion rate, and the time required to complete the CP. To our surprise, we found a slight difference in favour of the non-gamified app in all of these measures, though this difference was not statistically significant. However, the difference in the children's awareness of and attitude to energy consumption before and after the realisation of the CP was significant as measured by the Wilcoxon signed-rank test. This was not the case for the effect on energy awareness of the children's relatives. The lessons we learned, which may also prove to be useful for researchers that aim to design cultural probes, are that user research methods for children can be effective enough when designed to be interactive and dynamic (i.e. digital CPs) and that the number of CP tasks may also be a factor to take into account. When the number of tasks is low, the CP is likely to achieve a high completion rate and the additional effort of gamifying the application may be not worthwhile. Then, gamification may support a CP with a large number of tedious tasks. When designers want children to reflect on key issues, the CP should be thoughtfully designed because it is not easy to foster children's reflection and reasoning.
Emergent collective colloidal currents generated via exchange dynamics in a broken dimer state
Massana-Cid, H ; Ortiz-Ambriz, A ; Vilfan, A ; Tierno, P
Science Advances
6 (10)
eaaz2257
(2020)
Controlling the flow of matter down to micrometer-scale confinement is of central importance in material and environmental sciences, with direct applications in nano and microfluidics, drug delivery, and biotechnology. Currents of microparticles are usually generated with external field gradients of different nature (e.g., electric, magnetic, optical, thermal, or chemical ones), which are difficult to control over spatially extended regions and samples. Here, we demonstrate a general strategy to assemble and transport polarizable microparticles in fluid media through combination of confinement and magnetic dipolar interactions. We use a homogeneous magnetic modulation to assemble dispersed particles into rotating dimeric state and frustrated binary lattices, and generate collective currents that arise from a novel, field-synchronized particle exchange process. These dynamic states are similar to cyclotron and skipping orbits in electronic and molecular systems, thus paving the way toward understanding and engineering similar processes at different length scales across condensed matter.
Self-Propulsion of Active Colloids via Ion Release: Theory and Experiments
De Corato, M ; Arque, X ; Patino, T; Arroyoe, M ; Sanchez, S ; Pagonabarraga, I
Physical Review Letters
124 (10)
108001
(2020)
We study the self-propulsion of a charged colloidal particle that releases ionic species using theory and experiments. We relax the assumptions of thin Debye length and weak nonequilibrium effects assumed in classical phoretic models. This leads to a number of unexpected features that cannot be rationalized considering the classic phoretic framework: an active particle can reverse the direction of motion by increasing the rate of ion release and can propel even with zero surface charge. Our theory predicts that there are optimal conditions for self-propulsion and a novel regime in which the velocity is insensitive to the background electrolyte concentration. The theoretical results quantitatively capture the salt-dependent velocity measured in our experiments using active colloids that propel by decomposing urea via a surface enzymatic reaction.
Universal scaling of active nematic turbulence
Alert, R ; Joanny, JF ; Casademunt, J
NATURE PHYSICS
(2020)
A landmark of turbulence is the emergence of universal scaling laws, such as Kolmogorov's E(q) similar to q(-5/3) scaling of the kinetic energy spectrum of inertial turbulence with the wavevector q. In recent years, active fluids have been shown to exhibit turbulent-like flows at low Reynolds number. However, the existence of universal scaling properties in these flows has remained unclear. To address this issue, here we propose a minimal defect-free hydrodynamic theory for two-dimensional active nematic fluids at vanishing Reynolds number. By means of large-scale simulations and analytical arguments, we show that the kinetic energy spectrum exhibits a universal scaling E(q) similar to q(-1) at long wavelengths. We find that the energy injection due to activity has a peak at a characteristic length scale, which is selected by a nonlinear mechanism. In contrast to inertial turbulence, energy is entirely dissipated at the scale where it is injected, thus precluding energy cascades. Nevertheless, the non-local character of the Stokes flow establishes long-range velocity correlations, which lead to the scaling behaviour. We conclude that active nematic fluids define a distinct universality class of turbulence at low Reynolds number.
A multilevel analytical framework for studying cultural evolution in prehistoric hunter-gatherer societies
Romano, V ; Lozano, S; de Pablo, JFL
BIOLOGICAL REVIEWS
(2020)
Over the past decade, a major debate has taken place on the underpinnings of cultural changes in human societies. A growing array of evidence in behavioural and evolutionary biology has revealed that social connectivity among populations and within them affects, and is affected by, culture. Yet the interplay between prehistoric hunter-gatherer social structure and cultural transmission has typically been overlooked. Interestingly, the archaeological record contains large data sets, allowing us to track cultural changes over thousands of years: they thus offer a unique opportunity to shed light on long-term cultural transmission processes. In this review, we demonstrate how well-developed methods for social structure analysis can increase our understanding of the selective pressures underlying cumulative culture. We propose a multilevel analytical framework that considers finer aspects of the complex social structure in which regional groups of prehistoric hunter-gatherers were embedded. We put forward predictions of cultural transmission based on local- and global-level network metrics of small-scale societies and their potential effects on cumulative culture. By bridging the gaps between network science, palaeodemography and cultural evolution, we draw attention to the use of the archaeological record to depict patterns of social interactions and transmission variability. We argue that this new framework will contribute to improving our understanding of social interaction patterns, as well as the contexts in which cultural changes occur. Ultimately, this may provide insights into the evolution of human behaviour.
Comparing spatial networks: A one-size-fits-all efficiency-driven approach
Morer, I ; Cardillo, A ; Diaz-Guilera, A ; Prignano, L ; Lozano, S
Physical Review E
101 (4)
042301
(2020)
Spatial networks are a powerful framework for studying a large variety of systems belonging to a broad diversity of contexts: from transportation to biology, from epidemiology to communications, and migrations, to cite a few. Spatial networks can be described in terms of their total cost (i.e. the total amount of resources needed for building or traveling their connections). Here, we address the issue of how to gauge and compare the quality of spatial network designs (i.e. efficiency vs. total cost) by proposing a two-step methodology. Firstly, we assess the network's design by introducing a quality function based on the concept of network's efficiency. Second, we propose an algorithm to estimate computationally the upper bound of our quality function for a given network. Complementarily, we provide a universal expression to obtain an approximated upper bound to any spatial network, regardless of its size. Smaller differences between the upper bound and the empirical value correspond to better designs. Finally, we test the applicability of this analytic tool-set on spatial network data-sets of different nature.
Reputation-Based Maintenance in Case-Based Reasoning
Nakhjiri, N ; Salamo, M ; Sanchez-marre, M
KNOWLEDGE-BASED SYSTEMS
193
105283
(2020)
Case Base Maintenance algorithms update the contents of a case base in order to improve case-based reasoner performance. In this paper, we introduce a new case base maintenance method called Reputation-Based Maintenance (RBM) with the aim of increasing the classification accuracy of a Case-Based Reasoning system while reducing the size of its case base. The proposed RBM algorithm calculates a case property called Reputation for each member of the case base, the value of which reflects the competence of the related case. Based on this case property, several removal policies and maintenance methods have been designed, each focusing on different aspects of the case base maintenance. The performance of the RBM method was compared with well-known state-of-the-art algorithms. The tests were performed on 30 datasets selected from the UCI repository. The results show that the RBM method in all its variations achieves greater accuracy than a baseline CBR, while some variations significantly outperform the state-of-the-art methods. We particularly highlight the RBM_ACBR algorithm, which achieves the highest accuracy among the methods in the comparison to a statistically significant degree, and the RBMcr algorithm, which increases the baseline accuracy while removing, on average, over half of the case base. (c) 2019 Published by Elsevier B.V.
Electrophoretic origin of long-range repulsion of colloids near water/Nafion interfaces
Esplandiu, MJ ; Reguera, D ; Fraxedas, J
Soft Matter
16
15
(2020)
One of the most striking properties of Nafion is the formation of a long-range solute exclusion zone (EZ) in contact with water. The mechanism of formation of this EZ has been the subject of a controversial and long-standing debate. Previous studies by Schurr et al. and Florea et al. root the explanation of this phenomenon in the ion-exchange properties of Nafion, which generates ion diffusion and ion gradients that drive the repulsion of solutes by diffusiophoresis. Here we have evaluated separately the electrophoretic and chemiphoretic contributions to multi-ionic diffusiophoresis using differently charged colloidal tracers as solutes to identify better their contribution in the EZ formation. Our experimental results, which are also supported by numerical simulations, show that the electric field, built up due to the unequal diffusion coefficients of the exchanged ions, is the dominant parameter behind such interfacial phenomenon in the presence of alkali metal chlorides. The EZ formation depends on the interplay of the electric field with the zeta potential of the solute and can be additionally modulated by changing ion diffusion coefficients or adding salts. As a consequence, we show that not all solutes can be expelled from the Nafion interface and hence the EZ is not always formed. This study thus provides a more detailed description of the origin and dynamics of this phenomenon and opens the door to the rational use of this active interface for many potential applications.
Development of two-photon polymerised scaffolds for optical interrogation and neurite guidance of human iPSC-derived cortical neuronal networks
Crowe, JA; El-Tamer, A ; Nagel, D; Koroleva, AV; Madrid-Wolff, J ; Olarte, OE; Sokolovsky, S; Estevez-Priego, E ; Ludl, AA ; Soriano, J; Loza-Alvarez, P; Chichkov, BN ; Hill, EJ; Parri, HR; Rafailov, EU
LAB ON A CHIP
20
10
(2020)
Recent progress in the field of human induced pluripotent stem cells (iPSCs) has led to the efficient production of human neuronal cell models for in vitro study. This has the potential to enable the understanding of live human cellular and network function which is otherwise not possible. However, a major challenge is the generation of reproducible neural networks together with the ability to interrogate and record at the single cell level. A promising aid is the use of biomaterial scaffolds that would enable the development and guidance of neuronal networks in physiologically relevant architectures and dimensionality. The optimal scaffold material would need to be precisely fabricated with submicron resolution, be optically transparent, and biocompatible. Two-photon polymerisation (2PP) enables precise microfabrication of three-dimensional structures. In this study, we report the identification of two biomaterials that support the growth and differentiation of human iPSC-derived neural progenitors into functional neuronal networks. Furthermore, these materials can be patterned to induce alignment of neuronal processes and enable the optical interrogation of individual cells. 2PP scaffolds with tailored topographies therefore provide an effective method of producing defined in vitro human neural networks for application in influencing neurite guidance and complex network activity.
Precision as a measure of predictability of missing links in real networks
Garcia-Perez, G; Aliakbarisani, R; Ghasemi, A; Serrano, MA
PHYSICAL REVIEW E
101
052318
(2020)
Predicting missing links in real networks is an important open problem in network science to which considerable efforts have been devoted, giving as a result a vast plethora of link prediction methods in the literature. In this work, we take a different point of view on the problem and focus on predictability instead of prediction. By considering ensembles defined by well-known network models, we prove analytically that even the best possible link prediction method, given by the ensemble connection probabilities, yields a limited precision that depends quantitatively on the topological properties-such as degree heterogeneity, clustering, and community structure-of the ensemble. This suggests an absolute limitation to the predictability of missing links in real networks, due to the irreducible uncertainty arising from the random nature of link formation processes. We show that a predictability limit can be estimated in real networks, and we propose a method to approximate such a bound from real-world networks with missing links. The predictability limit gives a benchmark to gauge the quality of link prediction methods in real networks.
Deficits in coordinated neuronal activity and network topology are striatal hallmarks in Huntington's disease
Fernandez-Garcia, S ; Orlandi, JG ; Barriga, GAGD; Rodriguez, MJ ; Masana, M; Soriano, J; Alberch, J
BMC BIOLOGY
18
58
(2020)
Background Network alterations underlying neurodegenerative diseases often precede symptoms and functional deficits. Thus, their early identification is central for improved prognosis. In Huntington's disease (HD), the cortico-striatal networks, involved in motor function processing, are the most compromised neural substrate. However, whether the network alterations are intrinsic of the striatum or the cortex is not fully understood. Results In order to identify early HD neural deficits, we characterized neuronal ensemble calcium activity and network topology of HD striatal and cortical cultures. We used large-scale calcium imaging combined with activity-based network inference analysis. We extracted collective activity events and inferred the topology of the neuronal network in cortical and striatal primary cultures from wild-type and R6/1 mouse model of HD. Striatal, but not cortical, HD networks displayed lower activity and a lessened ability to integrate information. GABA(A) receptor blockade in healthy and HD striatal cultures generated similar coordinated ensemble activity and network topology, highlighting that the excitatory component of striatal system is spared in HD. Conversely, NMDA receptor activation increased individual neuronal activity while coordinated activity became highly variable and undefined. Interestingly, by boosting NMDA activity, we rectified striatal HD network alterations. Conclusions Overall, our integrative approach highlights striatal defective network integration capacity as a major contributor of basal ganglia dysfunction in HD and suggests that increased excitatory drive may serve as a potential intervention. In addition, our work provides a valuable tool to evaluate in vitro network recovery after treatment intervention in basal ganglia disorders.
Dynamic response of a compressible binary fluid mixture
Lombard, J; Pagonabarraga, I; Poire, EC
PHYSICAL REVIEW FLUIDS
5
064201
(2020)
Binary fluids are present in a wide variety of systems at microscales, such as microfluidic devices containing drops, fluids with air bubbles trapped in them, and devices designed to mix fluids or to make two fluid substances react. Microfluidics devices are often, intentionally or unintentionally, subject to pulsatile forces due to the passing of drops. We demonstrate that when a binary fluid is subject to a pulsatile forcing, the compressibility of the lower viscosity phase is so important that it is able to generate resonances in the dynamic permeability of the whole system. This implies that the flow amplitude of a binary-fluid system in a zero-mean flow could be optimized at certain frequencies. The dynamic permeability is a powerful concept to describe the dynamics of the system, in the regime where the flow and the pressure gradient are related linearly in the frequency domain. We find two regimes for the frequency at which the resonance occurs: one dominated by a characteristic frequency of the system, related to the compressibility of the lower viscosity phase; and another one dominated by a more complex frequency, involving both the characteristic viscous frequency of the lower viscosity phase and a characteristic frequency related to the compressibility. In order to guide potential experiments, we calculate relevant quantities for two sets of binary fluids in standard microfluidic setups. Our calculations imply that for systems of typical microfluidic dimensions, involving a compressible fluid, the existence of the compressibility-induced resonance has to be contemplated for a correct description of the dynamics.
Topology Restricts Quasidegeneracy in Sheared Square Colloidal Ice
Oguz, EC; Ortiz-Ambriz, A; Shem-Tov, H; Babia-Soler, E; Tierno, P; Shokef, Y
PHYSICAL REVIEW LETTERS
124
238003
(2020)
Recovery of ground-state degeneracy in two-dimensional square ice is a significant challenge in the field of geometric frustration with far-reaching fundamental implications, such as realization of vertex models and understanding the effect of dimensionality reduction. We combine experiments, theory, and numerical simulations to demonstrate that sheared square colloidal ice partially recovers the ground-state degeneracy for a wide range of field strengths and lattice shear angles. Our method could inspire engineering a novel class of frustrated microstructures and nanostructures based on sheared magnetic lattices in a wide range of soft- and condensed-matter systems.
Stokes layers in oscillatory flows of viscoelastic fluids
Ortin, J
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
378
20190521
(2020)
Oscillatory flows of viscoelastic fluids are studied from the perspective of Stokes viscoelastic layers. We identify the governing dimensionless variables, and study the flows in a general way for fluids with linear rheology. Nonlinearities can be treated perturbatively to account for reported flow instabilities.
Grafted human pluripotent stem cell-derived cortical neurons integrate into adult human cortical neural circuitry
Hansen, MG ; Laterza, C ; Palma-Tortosa, S ; Kvist, G ; Monni, E ; Tsupykov, O; Tornero, D; Uoshima, N; Soriano, J; Bengzon, J; Martino, G; Skibo, G; Lindvall, O; Kokaia, Z
STEM CELLS TRANSLATIONAL MEDICINE
(2020)
Several neurodegenerative diseases cause loss of cortical neurons, leading to sensory, motor, and cognitive impairments. Studies in different animal models have raised the possibility that transplantation of human cortical neuronal progenitors, generated from pluripotent stem cells, might be developed into a novel therapeutic strategy for disorders affecting cerebral cortex. For example, we have shown that human long-term neuroepithelial-like stem (lt-NES) cell-derived cortical neurons, produced from induced pluripotent stem cells and transplanted into stroke-injured adult rat cortex, improve neurological deficits and establish both afferent and efferent morphological and functional connections with host cortical neurons. So far, all studies with human pluripotent stem cell-derived neurons have been carried out using xenotransplantation in animal models. Whether these neurons can integrate also into adult human brain circuitry is unknown. Here, we show that cortically fated lt-NES cells, which are able to form functional synaptic networks in cell culture, differentiate to mature, layer-specific cortical neurons when transplanted ex vivo onto organotypic cultures of adult human cortex. The grafted neurons are functional and establish both afferent and efferent synapses with adult human cortical neurons in the slices as evidenced by immuno-electron microscopy, rabies virus retrograde monosynaptic tracing, and whole-cell patch-clamp recordings. Our findings provide the first evidence that pluripotent stem cell-derived neurons can integrate into adult host neural networks also in a human-to-human grafting situation, thereby supporting their potential future clinical use to promote recovery by neuronal replacement in the patient's diseased brain.
Cooperation and competition of viscoelastic fluids and elastomeric microtubes subject to pulsatile forcing
Rojas, AMT ; Poire, EC
PHYSICAL REVIEW FLUIDS
5
063303
(2020)
We analyze the dynamic behavior of viscoelastic fluids in elastic tubes subject to pulsatile pressure gradients. In particular, we study the dynamic permeability, a response function that relates linearly flow and pressure gradient in frequency domain. We have found resonances that can be associated to the elasticity of the tube and resonances that can be associated to the elasticity of the fluid. There is a rich phenomenology that includes cooperation and competition of both elasticities. Tuning of the system parameters allows for the excitation of the different modes in the system, sometimes giving responses that are larger than the ones of the corresponding systems with elasticity in only one of its elements. This behavior is similar to the one of two coupled oscillators. Our results are relevant for small confining geometries with low Young moduli. For example, for a microtube with a radius of a few hundred microns with the elasticity of polydimethylsiloxane (PDMS), in which a viscoelastic fluid, with the rheological parameters of blood, is driven by a pulsatile pressure gradient, resonance frequencies on the sound range are predicted. In a wide frequency range, the dynamic permeability is much lower than the one of the same fluid flowing in a poly(methyl methacrilate) (PMMA) tube. Our results are potentially useful for tailoring composite laboratory-on-a-chip devices, where introducing materials with different parameters in a device would induce an increase or decrease of the amplitude of the longitudinally averaged flow. We demonstrate that the magnitude of the dynamic permeability for a composite tube, at a given frequency of the driving pressure drop, determines the amplitude of the average flow along the composite tube.
Propulsion and energetics of a minimal magnetic microswimmer
Calero, C ; Garcia-Torres, J ; Ortiz-Ambriz, A ; Sagues, F ; Pagonabarraga, I ; Tierno, P
SOFT MATTER
16
28
(2020)
In this manuscript we describe the realization of a minimal hybrid microswimmer, composed of a ferromagnetic nanorod and a paramagnetic microsphere. The unbounded pair is propelled in water upon application of a swinging magnetic field that induces a periodic relative movement of the two composing elements, where the nanorod rotates and slides on the surface of the paramagnetic sphere. When taken together, the processes of rotation and sliding describe a finite area in the parameter space, which increases with the frequency of the applied field. We develop a theoretical approach and combine it with numerical simulations, which allow us to understand the dynamics of the propeller and explain the experimental observations. Furthermore, we demonstrate a reversal of the microswimmer velocity by varying the length of the nanorod, as predicted by the model. Finally, we determine theoretically and in experiments the Lighthill's energetic efficiency of this minimal magnetic microswimmer.
Dynamics and clogging of colloidal monolayers magnetically driven through a heterogeneous landscape
Leyva, SG; Stoop, RL; Tierno, P; Pagonabarraga, I
Soft Matter
16
30
(2020)
We combine experiments and numerical simulations to investigate the emergence of clogging in a system of interacting paramagnetic colloidal particles driven against a disordered landscape of larger obstacles. We consider a single aperture in a landscape of immobile silica particles which are irreversibly attached to the substrate. We use an external rotating magnetic field to generate a traveling wave potential which drives the magnetic particles against these obstacles at a constant and frequency tunable speed. Experimentally we find that the particles display an intermittent dynamics with power law distributions at high frequencies. We reproduce these results by using numerical simulations and show that clogging in our system arises at large frequency, when the particles desynchronize with the moving landscape. Further, we use the model to explore the hidden role of flexibility in the obstacle displacements and the effect of hydrodynamic interactions between the particles. We also consider numerically the situation of a straight wall and investigate the range of parameters where clogging emerges in such case. Our work provides a soft matter test-bed system to investigate the effect of clogging in driven microscale matter.
Geometric renormalization unravels self-similarity of the multiscale human connectome
Muhua Zheng, Antoine Allard, Patric Hagmann, Yasser Alemán-Gómez, and M. Ángeles Serrano
PNAS
117
33
(2020)
The architecture of the human brain underlies human behavior and is extremely complex with multiple scales interacting with one another. However, research efforts are typically focused on a single spatial scale. We explored the spatial multiscale organization of the human brain by using two high-quality datasets with connectomes at five anatomical resolutions for 84 healthy subjects. We found that the zoomed-out layers remain self-similar and that a geometric network model, where distances are not Euclidean, predicts the observations by application of a renormalization protocol. Our results prove that the same principles organize brain connectivity at different scales and lead to efficient decentralized communication. Implications extend to debates, like criticality in the brain, and applications, including tools for brain simulation.
Self-Assembly of Microscopic Rods Due to Depletion Interaction
Calero, C ; Pagonabarraga, I
ENTROPY
22
10
(2020)
In this article, using numerical simulations we investigate the self-assembly of rod-like particles in suspension due to depletion forces which naturally emerge due to the presence of smaller spherical depletant particles. We characterize the type of clusters that are formed and the evolution of aggregation departing from a random initial configuration. We show that eventually the system reaches a thermodynamic equilibrium state in which the aggregates break and reform dynamically. We investigate the equilibrium state of aggregation, which exhibits a strong dependence on depletant concentration. In addition, we provide a simple thermodynamic model inspired on the theory of self-assembly of amphiphilic molecules which allows us to understand qualitatively the equilibrium aggregate size distributions that we obtain in simulation.
Unravelling the role of phoretic and hydrodynamic interactions in active colloidal suspensions
Scagliarini, A; Pagonabarraga, I
SOFT MATTER
16
38
(2020)
Active fluids comprise a variety of systems composed of elements immersed in a fluid environment which can convert some form of energy into directed motion; as such they are intrinsically out-of-equilibrium in the absence of any external force. A fundamental problem in the physics of active matter concerns the understanding of how the characteristics of autonomous propulsion and agent-agent interactions determine the collective dynamics of the system. We study numerically the suspensions of self-propelled diffusiophoretic colloids, in (quasi)-2d configurations, accounting for both dynamically resolved solute-mediated phoretic interactions and solvent-mediated hydrodynamic interactions. Our results show that the system displays different scenarios at changing the colloid-solute affinity and it develops a cluster phase in the chemoattractive case. We study the statistics of cluster sizes and cluster morphologies for different magnitudes of colloidal activity. Finally, we provide evidences that hydrodynamics plays a relevant role in the aggregation kinetics and cluster morphology, significantly hindering cluster growth.
Network temporality can promote and suppress information spreading
Xue, XY; Pan, LM; Zheng, MH; Wang, W
CHAOS
30
113136
(2020)
Temporality is an essential characteristic of many real-world networks and dramatically affects the spreading dynamics on networks. In this paper, we propose an information spreading model on temporal networks with heterogeneous populations. Individuals are divided into activists and bigots to describe the willingness to accept the information. Through a developed discrete Markov chain approach and extensive numerical simulations, we discuss the phase diagram of the model and the effects of network temporality. From the phase diagram, we find that the outbreak phase transition is continuous when bigots are relatively rare, and a hysteresis loop emerges when there are a sufficient number of bigots. The network temporality does not qualitatively alter the phase diagram. However, we find that the network temporality affects the spreading outbreak size by either promoting or suppressing, which relies on the heterogeneities of population and of degree distribution. Specifically, in networks with homogeneous and weak heterogeneous degree distribution, the network temporality suppresses (promotes) the information spreading for small (large) values of information transmission probability. In networks with strong heterogeneous degree distribution, the network temporality always promotes the information spreading when activists dominate the population, or there are relatively fewer activists. Finally, we also find the optimal network evolution scale, under which the network information spreading is maximized.
Epidemic spreading under infection-reduced-recovery
Zhang, XY; Ruan, ZY ; Zheng, MH; Barzel, B; Boccaletti, S
CHAOS SOLITONS & FRACTALS
140
110130
(2020)
The pandemic transition is a hallmark of current epidemiological models, predicting a continuous shift from a healthy to a pandemic state, whose critical point is driven by the parameters of the disease, e.g., its infection, recovery or mortality rates. These parameters, characterizing the disease cycle, are tuned by the biological characteristics of the pathogen, capturing its natural time-scales, often considered independent of the state of the spread itself. If, however, the disease gains a population-wide impact, its prevalence may exceed the health-care system capacity, resulting in sub-optimal treatment, and hence a potential feedback mechanism, in which the disease cycle is no longer decoupled from the state of the spread. Such dependence was demonstrated during the spread of COVID-19, for instance, where hard-hit places showed elevated mortality rates, likely due to an over-stressed health-care system. We therefore introduce an infection-reduced recovery mechanism, linking an individual's rate of recovery to the prevalence of the disease. The outcome, we show, may have dramatic consequences on the observed patterns of spread. For instance, under rather broad conditions, the pandemic transition becomes discontinuous, exhibiting an abrupt shift from a healthy to a pandemic state. In some cases the disease reaches population-wide coverage even below the classically predicted critical transition point. We also observe a potential multi-stability and hysteresis, capturing an irreversible pandemic transition, in which overcoming the disease requires us to quench infection rates significantly below the critical threshold. These findings not only provide hints on the current difficulties to contain COVID-19, but more broadly, they set the bar for sustaining a stably functioning treatment capacity in the face of population-wide demand. (c) 2020 Elsevier Ltd. All rights reserved.
Dynamical modes of sheared confined microscale matter
Gerloff, S; Ortiz-Ambriz, A; Tierno, P; Klapp, SHL
SOFT MATTER
16
41
(2020)
Based on (overdamped) Stokesian dynamics simulations and video microscopy experiments, we study the non equilibrium dynamics of a sheared colloidal cluster, which is confined to a two-dimensional disk. The experimental system is composed of a mixture of paramagnetic and non magnetic polystyrene particles, which are held in the disk by time shared optical tweezers. The paramagnetic particles are located at the center of the disk and are actuated by an external, rotating magnetic field that induces a magnetic torque. We identify two different steady states by monitoring the mean angular velocities per ring. The first one is characterized by rare slip events, where the inner rings momentarily depin from the outer ring, which is kept static by the set of optical traps. For the second state, we find a bistability of the mean angular velocities, which can be understood from the analysis of the slip events in the particle trajectories. We calculate the particle waiting- and jumping time distributions and estimate a time scale between slips, which is also reflected by a plateau in the mean squared azimuthal displacement. The dynamical transition is further reflected by the components of the stress tensor, revealing a shearthinning behavior as well as shear stress overshoots. Finally, we briefly discuss the observed transition in the context of stochastic thermodynamics and how it may open future directions in this field.
Integrating a cognitive assistant within a critique-based recommender system
Guell, M ; Salamo, M; Contreras, D; Boratto, L
COGNITIVE SYSTEMS RESEARCH
64
1 14
(2020)
Recommender systems are cognitive computing systems designed to support humans in their decision-making processes through convincing, timely product suggestions. In the field of recommender systems, critique-based recommenders have been widely applied as an effective approach for guiding users through a product space in pursuit of suitable products. To date, no critique-based approach has included an assistant that support users in their search in a pleasant way. In this paper, we describe how we integrate an assistant within a critique-based recommender. We consider the proposed assistant to be cognitive because its reasoning process when recommending products is based on a cognitively-inspired clustering algorithm. The proposal is evaluated by users and compared with a non-assistant approach. The results of this research demonstrate that the integration of a cognitive assistant within the recommender improves the user experience and increases the performance of the recommendation process, i.e., users need fewer cycles to achieve the desired product or service. (C) 2020 Published by Elsevier B.V.
Functional strengthening through synaptic scaling upon connectivity disruption in neuronal cultures
Estevez-Priego, E; Teller, S; Granell, C; Arenas, A; Soriano, J
NETWORK NEUROSCIENCE
4
4
(2020)
Author Summary Neuronal circuits exhibit homeostatic plasticity mechanisms to cope with perturbations or damage. A central mechanism is 'synaptic scaling,' a self-organized response in which the strength of neurons' excitatory synapses is adjusted to compensate for activity variations. Here we present experiments in which the excitatory connectivity of in vitro cortical networks is progressively weakened through chemical action. The spontaneous activity and effective connectivity of the whole network is monitored as degradation progresses, and the capacity of the network for broad information communication is quantified through the global efficiency. We observed that the network responded to the perturbation by strengthening the effective connectivity, reaching a hyperefficient state for moderate perturbations. The study proves the importance of 'synaptic scaling' as a driver for functional reorganization and network-wide resilience.
An elusive phenomenon in network neuroscience is the extent of neuronal activity remodeling upon damage. Here, we investigate the action of gradual synaptic blockade on the effective connectivity in cortical networks in vitro. We use two neuronal cultures configurations-one formed by about 130 neuronal aggregates and another one formed by about 600 individual neurons-and monitor their spontaneous activity upon progressive weakening of excitatory connectivity. We report that the effective connectivity in all cultures exhibits a first phase of transient strengthening followed by a second phase of steady deterioration. We quantify these phases by measuring G(EFF), the global efficiency in processing network information. We term hyperefficiency the sudden strengthening of G(EFF) upon network deterioration, which increases by 20-50% depending on culture type. Relying on numerical simulations we reveal the role of synaptic scaling, an activity-dependent mechanism for synaptic plasticity, in counteracting the perturbative action, neatly reproducing the observed hyperefficiency. Our results demonstrate the importance of synaptic scaling as resilience mechanism.
Modification of lipid membrane compressibility induced by an electric field
Prathyusha, KR; Pagonabarraga, I; Kumar, PBS
PHYSICAL REVIEW E
102
062413
(2020)
Changes in membrane deformation and compressibility, induced by an external electric field, are investigated using coarse-grained MARTINI force field simulations in a salt-free environment. We observe changes in the area of the membrane above a critical electric field. Below this value, the membrane compressibility modulus is found to decrease monotonically. For higher electric fields, the membrane projected area remains constant while the net interfacial area increases, with the corresponding compressibility moduli, show the opposite behavior. We find that the mechanical parameters, surface tension and bending modulus, of a freely floating membrane in the absence of explicit ions, are unaffected by the presence of the electric field. We believe these results have a bearing on our understanding of the electroformation of uncharged lipids in a salt-free environment.
Spontaneous polarization and locomotion of an active particle with surface-mobile enzymes
De Corato, M; Pagonabarraga, I; Abdelmohsen, LKEA; Sanchez, S; Arroyo, M
PHYSICAL REVIEW FLUIDS
5
122001
(2020)
We examine a mechanism of locomotion of active particles whose surface is uniformly coated with mobile enzymes. The enzymes catalyze a reaction that drives phoretic flows but their homogeneous distribution forbids locomotion by symmetry. We find that the ability of the enzymes to migrate over the surface combined with self-phoresis can lead to a spontaneous symmetry-breaking instability whereby the homogeneous distribution of enzymes polarizes and the particle propels. The instability is driven by the advection of enzymes by the phoretic flows and occurs above a critical Peclet number. The transition to polarized motile states occurs via a supercritical or subcritical pitchfork bifurcations, the latter of which enables hysteresis and coexistence of uniform and polarized states.
Geometric detection of hierarchical backbones in real networks
Ortiz, E; Garcia-Perez, G; Serrano, MA
PHYSICAL REVIEW RESEARCH
2
033519
(2020)
Hierarchies permeate the structure of real networks, whose nodes can be ranked according to different features. However, networks are far from treelike structures and the detection of hierarchical ordering remains a challenge, hindered by the small-world property and the presence of a large number of cycles, in particular clustering. Here, we use geometric representations of undirected networks to achieve an enriched interpretation of hierarchy that integrates features defining the popularity of nodes and similarity between them, such that the more similar a node is to a less popular neighbor the higher the hierarchical load of the relationship. The geometric approach allows us to measure the local contribution of nodes and links to the hierarchy within a unified framework. Additionally, we propose a link filtering method, the similarity filter, able to extract hierarchical backbones containing the links that represent statistically significant deviations with respect to the maximum entropy null model for geometric heterogeneous networks. We applied our geometric approach to the detection of similarity backbones of real networks in different domains and found that the backbones preserve local topological features at all scales. Interestingly, we also found that similarity backbones favor cooperation in evolutionary dynamics modeling social dilemmas.
Unfolding the prospects of computational (bio)materials modeling
Sevink, GJA; Liwo, JA ; Asinari, P; MacKernan, D; Milano, G; Pagonabarraga, I
JOURNAL OF CHEMICAL PHYSICS
153
100901
(2020)
In this perspective communication, we briefly sketch the current state of computational (bio)material research and discuss possible solutions for the four challenges that have been increasingly identified within this community: (i) the desire to develop a unified framework for testing the consistency of implementation and physical accuracy for newly developed methodologies, (ii) the selection of a standard format that can deal with the diversity of simulation data and at the same time simplifies data storage, data exchange, and data reproduction, (iii) how to deal with the generation, storage, and analysis of massive data, and (iv) the benefits of efficient "core" engines. Expressed viewpoints are the result of discussions between computational stakeholders during a Lorentz center workshop with the prosaic title Workshop on Multi-scale Modeling and are aimed at (i) improving validation, reporting and reproducibility of computational results, (ii) improving data migration between simulation packages and with analysis tools, (iii) popularizing the use of coarse-grained and multi-scale computational tools among non-experts and opening up these modern computational developments to an extended user community.
Landau theory for cellular patterns driven by lateral inhibition interaction
Sancho, JM; Ibanes, M
PHYSICAL REVIEW E
102
032056
(2020)
Populations of mobile agents-animal groups, robot swarms, or crowds of people-self-organize into a large diversity of states as a result of information exchanges with their surroundings. While in many situations of interest the motion of the agents is driven by the transmission of information from neighboring peers, previous modeling efforts have overlooked the feedback between motion and information spreading. Here we show that such a feedback results in contagion enhanced by flocking. We introduce a reference model in which agents carry an internal state whose dynamics is governed by the susceptible-infected-susceptible (SIS) epidemic process, characterizing the spread of information in the population and affecting the way they move in space. This feedback triggers flocking, which is able to foster social contagion by reducing the epidemic threshold with respect to the limit in which agents interact globally. The velocity of the agents controls both the epidemic threshold and the emergence of complex spatial structures, or swarms. By bridging together soft active matter physics and modeling of social dynamics, we shed light upon a positive feedback mechanism driving the self-organization of mobile agents in complex systems.
Impact of Physical Obstacles on the Structural and Effective Connectivity ofin silicoNeuronal Circuits
Ludl, AA ; Soriano, J
FRONTIERS IN COMPUTATIONAL NEUROSCIENCE
14
77
(2020)
Scaffolds and patterned substrates are among the most successful strategies to dictate the connectivity between neurons in culture. Here, we used numerical simulations to investigate the capacity of physical obstacles placed on a flat substrate to shape structural connectivity, and in turn collective dynamics and effective connectivity, in biologically-realistic neuronal networks. We considered mu-sized obstacles placed in mm-sized networks. Three main obstacle shapes were explored, namely crosses, circles and triangles of isosceles profile. They occupied either a small area fraction of the substrate or populated it entirely in a periodic manner. From the point of view of structure, all obstacles promoted short length-scale connections, shifted the in- and out-degree distributions toward lower values, and increased the modularity of the networks. The capacity of obstacles to shape distinct structural traits depended on their density and the ratio between axonal length and substrate diameter. For high densities, different features were triggered depending on obstacle shape, with crosses trapping axons in their vicinity and triangles funneling axons along the reverse direction of their tip. From the point of view of dynamics, obstacles reduced the capacity of networks to spontaneously activate, with triangles in turn strongly dictating the direction of activity propagation. Effective connectivity networks, inferred using transfer entropy, exhibited distinct modular traits, indicating that the presence of obstacles facilitated the formation of local effective microcircuits. Our study illustrates the potential of physical constraints to shape structural blueprints and remodel collective activity, and may guide investigations aimed at mimicking organizational traits of biological neuronal circuits.
Motility-Induced Microphase and Macrophase Separation in a Two-Dimensional Active Brownian Particle System
Caporusso, CB; Digregorio, P; Levis, D; Cugliandolo, LF; Gonnella, G
PHYSICAL REVIEW LETTERS
125
178004
(2020)
As a result of nonequilibrium forces, purely repulsive self-propelled particles undergo macrophase separation between a dense and a dilute phase. We present a thorough study of the ordering kinetics of such motility-induced phase separation (MIPS) in active Brownian particles in two dimensions, and we show that it is generically accompanied by microphase separation. The growth of the dense phase follows a law akin to the one of liquid-gas phase separation. However, it is made of a mosaic of hexatic microdomains whose size does not coarsen indefinitely, leaving behind a network of extended topological defects from which microscopic dilute bubbles arise. The characteristic length of these finite-size structures increases with activity, independently of the choice of initial conditions.
A story-writing based study on the acquisition of aspect in Spanish by Mandarin Chinese learners
Sun, Y., Rodríguez, L.D., Taulé, M.
Revista Española de Lingüística Aplicada
33
2
(2020)
In this paper, we analyze the acquisition of Spanish past tense aspect by Mandarin Chinese learners of Spanish by means of three semi-guided writing tests. Specifically, we analyze the choice of pretérito indefinido and pretérito imperfecto, taking into account lexical aspect, grounding information, and the combination of both as variables. Moreover, we analyze whether transfer from Mandarin Chinese, the students' first language (L1), occurs in the acquisition process. Our results partly support the Lexical Aspect Hypothesis (Andersen, 1991; Andersen & Shirai, 1996) and the Discourse Hypothesis (Bardovi-Harlig, 1994). According to these hypotheses, verbal properties and grounding information play a role in the selection of pretérito indefinido or pretérito imperfecto. Finally, our data support the existence of L1 transfer at the semantic level only. © 2020 John Benjamins Publishing Company. All rights reserved.
The origin of hysteresis and memory of two-phase flow in disordered media
Holtzman, R., Dentz, M., Planet, R., Ortín, J.
Communications Physics
3
1
(2020)
Cyclic fluid-fluid displacements in disordered media feature hysteresis, multivaluedness, and memory properties in the pressure-saturation relationship. Quantitative understanding of the underlying pore-scale mechanisms and their extrapolation across scales constitutes a major challenge. Here we find that the capillary action of a single constriction in the fluid passage contains the key features of hysteresis. This insight forms the building block for an ab initio model that provides the quantitative link between the microscopic capillary physics, spatially-extended collective events (Haines jumps) and large-scale hysteresis. The mechanisms identified here apply to a broad range of problems in hydrology, geophysics and engineering.
Quantifying Human Engagement into Playful Activities
Reguera, D., Colomer-de-Simón, P., Encinas, I., Sort, M., Wedekind, J., Boguñá, M.
Scientific Reports
10
1 7
(2020)
Engaging in playful activities, such as playing a musical instrument, learning a language, or performing sports, is a fundamental aspect of human life. We present a quantitative empirical analysis of the engagement dynamics into playful activities. We do so by analyzing the behavior of millions of players of casual video games and discover a scaling law governing the engagement dynamics. This power-law behavior is indicative of a multiplicative (i.e., “happy- get-happier”) mechanism of engagement characterized by a set of critical exponents. We also find, depending on the critical exponents, that there is a phase transition between the standard case where all individuals eventually quit the activity and another phase where a finite fraction of individuals never abandon the activity. The behavior that we have uncovered in this work might not be restricted only to human interaction with videogames. Instead, we believe it reflects a more general and profound behavior of how humans become engaged in challenging activities with intrinsic rewards.
A robust solution to variational importance sampling of minimum variance
Hernández-González, J., Cerquides, J.
Entropy
22
12
(2020)
Importance sampling is a Monte Carlo method where samples are obtained from an alternative proposal distribution. This can be used to focus the sampling process in the relevant parts of space, thus reducing the variance. Selecting the proposal that leads to the minimum variance can be formulated as an optimization problem and solved, for instance, by the use of a variational approach. Variational inference selects, from a given family, the distribution which minimizes the divergence to the distribution of interest. The Rényi projection of order 2 leads to the importance sampling estimator of minimum variance, but its computation is very costly. In this study with discrete distributions that factorize over probabilistic graphical models, we propose and evaluate an approximate projection method onto fully factored distributions. As a result of our evaluation it becomes apparent that a proposal distribution mixing the information projection with the approximate Rényi projection of order 2 could be interesting from a practical perspective
Evolutionary Dynamics Do Not Motivate a Single-Mutant Theory of Human Language
de Boer, B., Thompson, B., Ravignani, A., Boeckx, C.
Scientific Reports
10
1
(2020)
One of the most controversial hypotheses in cognitive science is the Chomskyan evolutionary conjecture that language arose instantaneously in humans through a single mutation. Here we analyze the evolutionary dynamics implied by this hypothesis, which has never been formalized before. The hypothesis supposes the emergence and fixation of a single mutant (capable of the syntactic operation Merge) during a narrow historical window as a result of frequency-independent selection under a huge fitness advantage in a population of an effective size no larger than ~15 000 individuals. We examine this proposal by combining diffusion analysis and extreme value theory to derive a probabilistic formulation of its dynamics. We find that although a macro-mutation is much more likely to go to fixation if it occurs, it is much more unlikely a priori than multiple mutations with smaller fitness effects. The most likely scenario is therefore one where a medium number of mutations with medium fitness effects accumulate. This precise analysis of the probability of mutations occurring and going to fixation has not been done previously in the context of the evolution of language. Our results cast doubt on any suggestion that evolutionary reasoning provides an independent rationale for a single-mutant theory of language
Training or Synergizing? Complex Systems Principles Change the Understanding of Sport Processes
Pol, R., Balagué, N., Ric, A., Torrents, C., Kiely, J., Hristovski, R.
Sports Medicine
6
1 13
(2020)
There is a need to update scientific assumptions in sport to promote the critical thinking of scientists, coaches, and practitioners and improve their methodological decisions. On the basis of complex systems science and theories of biological evolution, a systematization and update of theoretical and methodological principles to transform the understanding of sports training is provided. The classical focus on learning/acquiring skills and fitness is replaced by the aim of increasing the diversity/unpredictability potential of teams/athletes through the development of synergies. This development is underpinned by the properties of hierarchical organization and circular causality of constraints, that is, the nestedness of constraints acting at different levels and timescales. These properties, that integrate bottom-up and top-down all dimensions and levels of performance (from social to genetic), apply to all types of sport, ages, or levels of expertise and can be transferred to other fields (e.g., education, health, management). The team as the main training unit of intervention, the dynamic concept of task representativeness, and the co-adaptive and synergic role of the agents are some few practical consequences of moving from training to synergizing
Benchmarking seeding strategies for spreading processes in social networks: an interplay between influencers, topologies and sizes
Montes, F., Jaramillo, A.M., Meisel, J.D., Diaz-Guilera, A., Valdivia, J.A., Sarmiento, O.L., Zarama, R.
Scientific Reports
10
3666
(2020)
The explosion of network science has permitted an understanding of how the structure of social networks affects the dynamics of social contagion. In community-based interventions with spill-over effects, identifying influential spreaders may be harnessed to increase the spreading efficiency of social contagion, in terms of time needed to spread all the largest connected component of the network. Several strategies have been proved to be efficient using only data and simulation-based models in specific network topologies without a consensus of an overall result. Hence, the purpose of this paper is to benchmark the spreading efficiency of seeding strategies related to network structural properties and sizes. We simulate spreading processes on empirical and simulated social networks within a wide range of densities, clustering coefficients, and sizes. We also propose three new decentralized seeding strategies that are structurally different from well-known strategies: community hubs, ambassadors, and random hubs. We observe that the efficiency ranking of strategies varies with the network structure. In general, for sparse networks with community structure, decentralized influencers are suitable for increasing the spreading efficiency. By contrast, when the networks are denser, centralized influencers outperform. These results provide a framework for selecting efficient strategies according to different contexts in which social networks emerge.
Behavior and mechanics of dense microgel suspensions
Nikolov, S.V., Fernandez-Nieves, A., Alexeev, A.
Proceedings of the National Academy of Sciences of the United States of America
117
44
(2020)
Suspensions of soft and highly deformable microgels can be concentrated far more than suspensions of hard colloids, leading to their unusual mechanical properties. Microgels can accommodate compression in suspensions in a variety of ways such as interpenetration, deformation, and shrinking. Previous experiments have offered insightful, but somewhat conflicting, accounts of the behavior of individual microgels in compressed suspensions. We develop a mesoscale computational model to probe the behavior of compressed suspensions consisting of microgels with different architectures at a variety of packing fractions and solvent conditions. We find that microgels predominantly change shape and mildly shrink above random close packing. Interpenetration is only appreciable above space filling, remaining small relative to the mean distance between cross-links. At even higher packing fractions, microgels solely shrink. Remarkably, irrespective of the single-microgel properties, and whether the suspension concentration is changed via changing the particle number density or the swelling state of the particles, which can even result in colloidal gelation, the mechanics of the suspension can be quantified in terms of the single-microgel bulk modulus, which thus emerges as the correct mechanical measure for these type of soft-colloidal suspensions. Our results rationalize the many and varied experimental results, providing insights into the relative importance of effects defining the mechanics of suspensions comprising soft particles. © 2020 National Academy of Sciences. All rights reserved.
A privacy-preserving routing protocol using mix networks in opportunistic networks
Chen, D., Borrego, C., Navarro-Arribas, G.
Electronics
9
11
(2020)
This paper focuses on the problem of providing anonymous communications in opportunistic networks. To that end, we propose an approach using Mix networks that enables a relatively simple solution. Opportunistic networks present some constraints that make the deployment of typical network anonymity solutions difficult or infeasible. We show, utilizing simulations on the basis of real mobility traces, that the proposed solution is feasible for some scenarios by introducing a tolerable penalty in terms of message delay and delivery. To investigate the impact of routing strategies, we offer two different methods to select Mix nodes. From the experiment results, we show the trade-off between network performance and security.
Relationship between quality of life and the complexity of default mode network in resting state functional magnetic resonance image in down syndrome
Carbó-Carreté, M., Cañete-Massé, C., Figueroa-Jiménez, M.D., Peró-Cebollero, M., Guàrdia-Olmos, J.
International Journal of Environmental Research and Public Health
17
9
(2020)
The study of the Default Mode Network (DMN) has been shown to be sensitive for the recognition of connectivity patterns between the brain areas involved in this network. It has been hypothesized that the connectivity patterns in this network are related to different cognitive states. Purpose: In this study, we explored the relationship that can be estimated between these functional connectivity patterns of the DMN with the Quality-of-Life levels in people with Down syndrome, since no relevant data has been provided for this population. Methods: 22 young people with Down syndrome were evaluated; they were given a large evaluation battery that included the Spanish adaptation of the Personal Outcome Scale (POS). Likewise, fMRI sequences were obtained on a 3T resonator. For each subject, the DMN functional connectivity network was studied by estimating the indicators of complexity networks. The variability obtained in the Down syndrome group was studied by taking into account the Quality-of-Life distribution. Results: There is a negative correlation between the complexity of the connectivity networks and the Quality-of-Life values. Conclusions: The results are interpreted as evidence that, even at rest, connectivity levels are detected as already shown in the community population and that less intense connectivity levels correlate with higher levels of Quality of Life in people with Down syndrome. © 2020 by the authors.
Decreased coupling among respiratory variables with effort accumulation
Zebrowska, M., Garcia-Retortillo, S., Sikorski, K., Balagué, N., Hristovski, R., Casimiro, J., Petelczyc, M.
EPL
132
2
(2020)
We applied symbolic transfer entropy (STE) for the detection of directed couplings between pulmonary variables registered during repeated progressive and maximal cardiopulmonary exercise tests (CPET). We verified the hypothesis whether effort accumulation has an impact on the decrease of the level of coupling between ventilation (VEbtps), fraction of expired oxygen (FeO2) and carbon dioxide (FeCO2). A group of 10 volunteers performed two consecutive CPET (T1 and T2) on a cycle ergometer. STE values obtained for T1 are higher than for T2, which indicates that the interaction of these variables is sensitive to effort accumulation. The difference of the STE between signals corresponds to the dominating direction of the coupling and indicates that FeO2 and FeCO2 drives the VEbtps.
Suppression of acoustic emission during superelastic tensile cycling of polycrystalline Ni50.4Ti49.6
Nataf, G.F., Romanini, M., Vives, E., ŽuŽek, B., Planes, A., Tušek, J., Moya, X.
Physical Review Materials
4
9
(2020)
We investigate acoustic emission (AE) that arises during the martensitic transition in a polycrystalline specimen of the prototypical superelastic/elastocaloric alloy Ni50.4Ti49.6 (at. %) driven using tensile strain. We use two independent AE sensors in order to locate AE events, and focus on contributions to the AE that arise away from the grips of the mechanical testing machine. Significant AE activity is present during the first mechanical loading primarily due to nucleation and growth of wide Lüders-like bands during the forward martensitic transition (imaged using visible light and infrared radiation) that lead to persistent changes in intergranular interactions. AE activity is suppressed during the subsequent reverse martensitic transition on unloading, and in successive loading/unloading cycles, for which the Lüders-like bands narrow and modify intergranular interactions to a much smaller extent. After the first loading, we find that the AE activity associated with the martensitic transition is weak, and we suggest that this is because the elastic anisotropy and strain incompatibility in Ni-Ti are low. We also find that the AE activity becomes weaker on mechanical cycling due to increased retained martensite
Theory of Cooperative-Competitive Intelligence: Principles, Research Directions, and Applications
Hristovski, R., Balagué, N.
Frontiers in Psychology
11
2220
(2020)
We present a theory of cooperative-competitive intelligence (CCI), its measures, research program, and applications that stem from it. Within the framework of this theory, satisficing sub-optimal behavior is any behavior that does not promote a decrease in the prospective control of the functional action diversity/unpredictability (D/U) potential of the agent or team. This potential is defined as the entropy measure in multiple, context-dependent dimensions. We define the satisficing interval of behaviors as CCI. In order to manifest itself at individual or team level, this capacity harnesses properties such as degeneracy, pleiotropy (pluri-potentiality), synergies, and metastability. Intelligence is embodied because intelligent behavior is deeply dependent on body functionalities, defined as entropy measures. We base our theory on three principles: (a) relativity of functional entropy/information in agent (team)-environment systems, (b) tendency toward the satisficing level of D/U potential, and (c) tendency toward the non-decreasing D/U potential. The conjunction of these three principles provides existence of sub-optimal behaviors associated with CCI. First, we deal with the problem of how to reduce multidimensional behavior to a concept that accounts for the vast set of scenarios in which CCI is manifested. Secondly, we define and discuss the three interacting principles that underpin CCI behavior as well as providing an outline for a future CCI research program supported by agent-based modeling and empirical research. Finally, we provide some preliminary practical issues that stem from the theory.
MISMIS: Misinformation and Miscommunication in social media: Aggregating information and analysing language
Rosso, P., Casacuberta, F., Gonzalo, J., Plaza, L., Carrillo, J., Amigó, E., Verdejo, M.F., Taulé, M., Salamó, M., Martí, M.A.
Procesamiento de Lenguaje Natural
65
101 104
(2020)
The general objectives of the project are to address and monitor misinformation (biased and fake news) and miscommunication (aggressive language and hate speech) in social media, as well as to establish a high quality methodological standard for the whole research community (i) by developing rich annotated datasets, a data repository and online evaluation services; (ii) by proposing suitable evaluation metrics; and (iii) by organizing evaluation campaigns to foster research on the above issues.
Optimising data diffusion while reducing local resources consumption in Opportunistic Mobile Crowdsensing
Hernández-Orallo, E., Borrego, C., Manzoni, P., Marquez-Barja, J.M., Cano, J.C., Calafate, C.T.
Pervasive and Mobile Computing
67
101201
(2020)
The combination of Mobile Crowdsensing (MCS) with Opportunistic Networking (OppNet) allows mobile users to share sensed data easily and conveniently without the use of fixed infrastructure. OppNet is based on intermittent connectivity among wireless mobile devices, in which mobile nodes may store, carry and forward messages (sensing information) by taking advantage of wireless ad hoc communication opportunities. A common approach for the diffusion of this sensing data in OppNet is the epidemic protocol, which carries out a fast data diffusion at the expense of increasing the usage of local buffers on mobile nodes and also the number of transmissions, thereby limiting scalability. A way to reduce this consumption of local resources is to set a message expiration time that forces the removal of old messages from local buffers. Since dropping messages too early may reduce the speed of information diffusion, we propose a dynamic expiration time setting to limit this effect. Moreover, we introduce an epidemic diffusion model for evaluating the impact of the expiration time. This model allows us to obtain optimal expiration times that achieve performances similar to those other approaches where no expiration is considered, with a significant reduction of local buffer and network usage. Furthermore, in our proposed model, the buffer utilisation remains steady with the number of nodes, whereas in other approaches it increases sharply. Finally, our approach is evaluated and validated in a mobile crowdsensing scenario, where students collect and broadcast information regarding a university campus, showing a significant reduction on buffer usage and nodes message transmissions, and therefore, decreasing battery consumption.
Network change point detection in resting-state functional connectivity dynamics of mild cognitive impairment patients
Mancho-Fora, N., Montalà-Flaquer, M., Farràs-Permanyer, L., Zarabozo-Hurtado, D., Gallardo-Moreno, G.B., Gudayol-Farré, E., Peró-Cebollero, M., Guàrdia-Olmos, J.
International Journal of Clinical and Health Psychology
20
3
(2020)
Background/Objective: This study aims to characterize the differences on the short-term temporal network dynamics of the undirected and weighted whole-brain functional connectivity between healthy aging individuals and people with mild cognitive impairment (MCI). The Network Change Point Detection algorithm was applied to identify the significant change points in the resting-state fMRI register, and we analyzed the fluctuations in the topological properties of the sub-networks between significant change points. Method: Ten MCI patients matched by gender and age in 1:1 ratio to healthy controls screened during patient recruitment. A neuropsychological evaluation was done to both groups as well as functional magnetic images were obtained with a Philips 3.0T. All the images were preprocessed and statistically analyzed through dynamic point estimation tools. Results: No statistically significant differences were found between groups in the number of significant change points in the functional connectivity networks. However, an interaction effect of age and state was detected on the intra-participant variability of the network strength. Conclusions: The progression of states was associated to higher variability in the patient's group. Additionally, higher performance in the prospective and retrospective memory scale was associated with higher median network strength.
Rheology of capillary foams
Okesanjo, O., Tennenbaum, M., Fernandez-Nieves, A., Meredith, J.C., Behrens, S.H.
Soft Matter
16
29
(2020)
Aqueous foams are ubiquitous; they appear in products and processes that span the cosmetics, food, and energy industries. The versatile applicability of foams comes as a result of their intrinsic viscous and elastic properties; for example, foams are exploited as drilling fluids in enhanced oil recovery for their high viscosity. Recently, so-called capillary foams were discovered: a class of foams that have excellent stability under static conditions and whose flow properties have so far remained unexplored. The unique architecture of these foams, containing oil-coated bubbles and a gelled network of oil-bridged particles, is expected to affect foam rheology. In this work, we report the first set of rheological data on capillary foams. We study the viscoelastic properties of capillary foams by conducting oscillatory and steady shear tests. We compare our results on the rheological properties of capillary foams to those reported for other aqueous foams. We find that capillary foams, which have low gas volume fractions, exhibit long lasting rheological stability as well as a yielding behavior that is reminiscent of surfactant foams with high gas volume fractions.
Kinetics of active water/ethanol Janus droplets
Li, M., Hosseinzadeh, M., Pagonabarraga, I., Seemann, R., Brinkmann, M., Fleury, J.-B.
Soft Matter
16
29
(2020)
Droplets made of a water/ethanol mixture spontaneously self-propel in an oil/surfactant solution and, depending on the initial ethanol concentration at the time of production, may evolve in up to three stages. Upon self-propulsion the droplets absorb surfactant molecules during their continuous motion in the oily phase. In combination with the continuous loss of ethanol this mass exchange with the ambient phase may lead to a spontaneous phase separation of the water/ethanol mixture, and eventually to the formation of characteristic Janus droplets. Supported by experimental evidence, we propose a simple model that is able to explain the propulsion velocity and its scaling with the droplet radius in the last stage of the droplet evolution.
Defining Collective Identities in Technopolitical Interaction Networks
Barandiaran, X.E., Calleja-López, A., Cozzo, E.
Frontiers in Psychology
11
1549
(2020)
We are currently witnessing the emergence of new forms of collective identities and a redefinition of the old ones through networked digital interactions, and these can be explicitly measured and analyzed. We distinguish between three major trends on the development of the concept of identity in the social realm: (1) an essentialist sense (based on conditions and properties shared by members of a group), (2) a representational or ideational sense (based on the application of categories by oneself or others), and (3) a relational and interactional sense (based on interaction processes between actors and their environments). The interactional approach aligns with current empirical and methodological progress in social network analysis. Moreover, it has been argued that, within the network society, the notion of collective identity (Melucci, 1995) in the political field must be rethought as technologically mediated and interactive. We suggest that collective identities should be understood as recurrent, cohesive, and coordinated communicative interaction networks. We here propose that such identities can be depicted by: (a) mapping and filtering a relevant interaction network, (b) delimiting a set of communities, (c) determining the strongly connected component(s) of such communities (the core identity) in a directed graph, and (d) defining the identity audiences and sources within the community. This technical graph–theoretical characterization is explained and justified in detail through a toy model and applied to three empirical case studies to characterize political identities in party politics (communicative interaction in Twitter during the Spanish elections in 2018), contentious politics in confrontation (in Twitter during the Catalan strike for independence 2019), and the multitudinous identity of Spanish Indignados/15 social movement (in Facebook fan pages 2011). We discuss how the proposed definition is useful to delimit and characterize the internal structure of collective identities in technopolitical interaction networks, and we suggest how the proposed methods can be improved and complemented with other approaches. We finally draw the theoretical implications of understanding collective identities as emerging from interaction networks in a progressive platformization of social interactions in a digital world.
Activity effects on the nonlinear mechanical properties of fire-ant aggregations
Tennenbaum, M., Fernandez-Nieves, A.
Physical Review E
102
1
(2020)
Individual fire ants are inherently active as they are living organisms that convert stored chemical energy into motion. However, each individual ant is not equally disposed to motion at any given time. In an active aggregation, most of the constituent ants are active, and vice versa for an inactive aggregation. Here we look at the role activity plays on the nonlinear mechanical behavior of the aggregation through large amplitude oscillatory shear measurements. We find that the level of viscous nonlinearity can be decreased by increasing the activity or by increasing the volume fraction. In contrast, the level of elastic nonlinearity is not affected by either activity or volume fraction. We interpret this in terms of a transient network with equal rates of linking and unlinking but with varying number of linking and unlinking events.
Complexation of Pluronic L62 (EO6)-(PO34)-(EO6)/aerosol-OT (sodium bis(2-ethylhexyl)sulfosuccinate) in aqueous solutions investigated by small angle neutron scattering
Zhou, B., Fernandez-Nieves, A., Chen, W.-R., Kim, T.-H., Do, C.
Physical Chemistry Chemical Physics
22
22
(2020)
We investigate the phase behaviours of Pluronic L62 in aqueous solution in the presence of aerosol-OT (AOT) molecules by small angle neutron scattering (SANS). The presence of AOT significantly changes the micellization phenomenon of L62 micelles in aqueous solution, including their critical micelle temperature (CMT), global size, and asphericity. The origin of these observations is attributed to the complexation between the neutral L62 surfactants and the ionic AOT molecules, which additionally provides charge to the mixed micelles: we analyse the data and extract meaningful information using the Ornstein-Zernike integral formalism. As a result, we observe that the co-micellization of L62 and AOT is very stable across a wide temperature range.
Coherence-enhanced diffusion filtering applied to partially-ordered fluids
Ellis, P.W., Nambisan, J., Fernandez-Nieves, A.
Molecular Physics
118
e1725167
(2020)
Due to the increased interest in directly visualising partially-ordered fluids, there is a need for techniques that enable determining the associated director field from intensity images in robust and precise ways. Coherence-enhanced diffusion filtering (CEDF) is a computer vision technique designed to determine the local direction along which the intensity fluctuates the least. We pedagogically illustrate how CEDF can be applied to such partially-ordered systems using a microtubule-based active nematic as an example. In this system, the local microtubule orientation is visible using fluoresence microscopy. We illustrate how to choose parameters in the analysis, and demonstrate the technique is robust by applying it to data corresponding to an active nematic in flat space and an active nematic confined to the surface of a torus. Lastly, we show how to leverage topology to calculate the error in the analysis and find that in the examples presented, the influence of errors is negligible.
Citizen science and sustainability transitions
Sauermann, H., Vohland, K., Antoniou, V., Balázs, B., Göbel, C., Karatzas, K., Mooney, P., Perelló, J., Ponti, M., Samson, R., Winter, S.
Research Policy
49
5
(2020)
Citizen Science (CS) projects involve members of the general public as active participants in research. While some advocates hope that CS can increase scientific knowledge production (“productivity view”), others emphasize that it may bridge a perceived gap between science and the broader society (“democratization view”). We discuss how an integration of both views can allow Citizen Science to support complex sustainability transitions in areas such as renewable energy, public health, or environmental conservation. We first identify three pathways through which such impacts can occur: (1) Problem identification and agenda setting; (2) Resource mobilization; and (3) Facilitating socio-technical co-evolution. To realize this potential, however, CS needs to address important challenges that emerge especially in the context of sustainability transitions: Increasing the diversity, level, and intensity of participation; addressing the social as well as technical nature of sustainability problems; and reducing tensions between CS and the traditional institution of academic science. Grounded in a review of academic literature and policy reports as well as a broad range of case examples, this article contributes to scholarship on science, innovation, and sustainability transitions. We also offer insights for actors involved in initiating or institutionalizing Citizen Science efforts, including project organizers, funding agencies, and policy makers.
Human Pluripotent Stem Cell-Derived Neurons Are Functionally Mature In Vitro and Integrate into the Mouse Striatum Following Transplantation
Comella-Bolla, A., Orlandi, J.G., Miguez, A., Straccia, M., García-Bravo, M., Bombau, G., Galofré, M., Sanders, P., Carrere, J., Segovia, J.C., Blasi, J., Allen, N.D., Alberch, J., Soriano, J., Canals, J.M.
Molecular Neurobiology
57
6
(2020)
Human pluripotent stem cells (hPSCs) are a powerful tool for modelling human development. In recent years, hPSCs have become central in cell-based therapies for neurodegenerative diseases given their potential to replace affected neurons. However, directing hPSCs into specific neuronal types is complex and requires an accurate protocol that mimics endogenous neuronal development. Here we describe step-by-step a fast feeder-free neuronal differentiation protocol to direct hPSCs to mature forebrain neurons in 37 days in vitro (DIV). The protocol is based upon a combination of specific morphogens, trophic and growth factors, ions, neurotransmitters and extracellular matrix elements. A human-induced PSC line (Ctr-Q33) and a human embryonic stem cell line (GEN-Q18) were used to reinforce the potential of the protocol. Neuronal activity was analysed by single-cell calcium imaging. At 8 DIV, we obtained a homogeneous population of hPSC-derived neuroectodermal progenitors which self-arranged in bi-dimensional neural tube-like structures. At 16 DIV, we generated hPSC-derived neural progenitor cells (NPCs) with mostly a subpallial identity along with a subpopulation of pallial NPCs. Terminal in vitro neuronal differentiation was confirmed by the expression of microtubule associated protein 2b (Map 2b) by almost 100% of hPSC-derived neurons and the expression of specific-striatal neuronal markers including GABA, CTIP2 and DARPP-32. HPSC-derived neurons showed mature and functional phenotypes as they expressed synaptic markers, voltage-gated ion channels and neurotransmitter receptors. Neurons displayed diverse spontaneous activity patterns that were classified into three major groups, namely “high”, “intermediate” and “low” firing neurons. Finally, transplantation experiments showed that the NPCs survived and differentiated within mouse striatum for at least 3 months. NPCs integrated host environmental cues and differentiated into striatal medium-sized spiny neurons (MSNs), which successfully integrated into the endogenous circuitry without teratoma formation. Altogether, these findings demonstrate the potential of this robust human neuronal differentiation protocol, which will bring new opportunities for the study of human neurodevelopment and neurodegeneration, and will open new avenues in cell-based therapies, pharmacological studies and alternative in vitro toxicology.
Tracking the dynamics of power sources and sinks during the martensitic transformation of a Cu-Al-Ni single crystal
Ianniciello, L., Romanini, M., Mañosa, L., Planes, A., Engelbrecht, K., Vives, E.
Applied Physics Letters
116
18
(2020)
We have tracked the dynamics of the martensitic transformation in a Cu-Al-Ni single crystal by means of acoustic emission and infrared imaging techniques. A Fourier equation-based post-processing of temperature maps has enabled us to reveal the inhomogeneous and discontinuous character of heat power sources and sinks during the transition. A good correlation between the dynamics of thermal and mechanical energy release has been evidenced. It has also been shown that the merging of martensitic interfaces results in an enhanced heat absorption.
Polarized epifluorescence microscopy and the imaging of nematic liquid crystals in highly curved geometries
Ellis, P.W., Klaneček, S., Fernandez-Nieves, A.
Physical Review E
101
5
(2020)
We develop polarized epifluorescence microscopy (PFM), a technique to qualitatively determine a director field, even when refraction effects are too strong to use optical polarized microscopy. We present the basic theory behind the technique and cover in detail the experimental setup. We validate PFM on the well-studied cases of a planar nematic cell, spherical nematic droplets, and a cylindrical capillary filled with nematic liquid crystal. Last, we use nematic capillary bridges to demonstrate that PFM can indeed provide measurements of the director field, even when refraction effects are large.
Forwarding in opportunistic information-centric networks: An optimal stopping approach
Borrego, C., Amadeo, M., Molinaro, A., Mendes, P., Sofia, R.C., Magaia, N., Borrell, J.
IEEE Communications Magazine
58
5
(2020)
By natively supporting in-network caching and name-based forwarding, ICN brings in features that are relevant to better support data transmission in opportunistic wireless networks. Such environments are highly challenged because of the node mobility and intermittent contacts. Therefore, forwarding packets to the right node at the right moment is critical to data retrieval performance. This article proposes a novel ICN forwarding strategy that leverages notable metrics, such as centrality and reliability, and the optimal stopping theory to statistically select the best next-hop forwarders and the time to perform the forwarding decision. Simulations with realistic mobility traces show that the proposed forwarding strategy outperforms other state-of-the-art solutions by guaranteeing shorter retrieval time and less overhead in terms of packet replicas.
Modern human changes in regulatory regions implicated in cortical development
Moriano, J., Boeckx, C.
BMC Genomics
21
1 10
(2020)
Recent paleogenomic studies have highlighted a very small set of proteins carrying modern human-specific missense changes in comparison to our closest extinct relatives. Despite being frequently alluded to as highly relevant, species-specific differences in regulatory regions remain understudied. Here, we integrate data from paleogenomics, chromatin modification and physical interaction, and single-cell gene expression of neural progenitor cells to identify derived regulatory changes in the modern human lineage in comparison to Neanderthals/Denisovans. We report a set of genes whose enhancers and/or promoters harbor modern human single nucleotide changes and are active at early stages of cortical development. Results: We identified 212 genes controlled by regulatory regions harboring modern human changes where Neanderthals/Denisovans carry the ancestral allele. These regulatory regions significantly overlap with putative modern human positively-selected regions and schizophrenia-related genetic loci. Among the 212 genes, we identified a substantial proportion of genes related to transcriptional regulation and, specifically, an enrichment for the SETD1A histone methyltransferase complex, known to regulate WNT signaling for the generation and proliferation of intermediate progenitor cells. Conclusions: This study complements previous research focused on protein-coding changes distinguishing our species from Neanderthals/Denisovans and highlights chromatin regulation as a functional category so far overlooked in modern human evolution studies. We present a set of candidates that will help to illuminate the investigation of modern human-specific ontogenetic trajectories.
Statistical analysis and stochastic interest rate modeling for valuing the future with implications in climate change mitigation
Perelló, J., Montero, M., Masoliver, J., Farmer, J.D., Geanakoplos, J.
Journal of Statistical Mechanics: Theory and Experiment
4
043210
(2020)
High future discounting rates favor inaction on present expending while lower rates advise for a more immediate political action. A possible approach to this key issue in global economy is to take historical time series for nominal interest rates and inflation, and to construct then real interest rates and finally obtaining the resulting discount rate according to a specific stochastic model. Extended periods of negative real interest rates, in which inflation dominates over nominal rates, are commonly observed, occurring in many epochs and in all countries. This feature leads us to choose a well-known model in statistical physics, the Ornstein-Uhlenbeck model, as a basic dynamical tool in which real interest rates randomly fluctuate and can become negative, even if they tend to revert to a positive mean value. By covering 14 countries over hundreds of years we suggest different scenarios and include an error analysis in order to consider the impact of statistical uncertainty in our results. We find that only 4 of the countries have positive long-run discount rates while the other ten countries have negative rates. Even if one rejects the countries where hyperinflation has occurred, our results support the need to consider low discounting rates. The results provided by these fourteen countries significantly increase the priority of confronting global actions such as climate change mitigation. We finally extend the analysis by first allowing for fluctuations of the mean level in the Ornstein-Uhlenbeck model and secondly by considering modified versions of the Feller and lognormal models. In both cases, results remain basically unchanged thus demonstrating the robustness of the results presented.
Capillary jumps of fluid-fluid fronts across an elementary constriction in a model open fracture
Planet, R., Díaz-Piola, L., Ortín, J.
Physical Review Fluids
5
4
(2020)
We study experimentally the quasistatic displacement of an oil-air front across a localized constriction in a model open fracture. The front experiences capillary jumps at one end of the constriction in both imbibition and drainage, leading to a microscale pressure-saturation hysteresis cycle. At the other end the front is reversibly pinned. A condition of local mechanical equilibrium between the restoring elasticity of the front and the distortion produced by the local change in aperture captures all we measure quantitatively, in terms of material and geometrical properties only.
Shape selection and mis-assembly in viral capsid formation by elastic frustration
Mendoza, C.I., Reguera, D.
eLife
9
e52525
(2020)
The successful assembly of a closed protein shell (or capsid) is a key step in the replication of viruses and in the production of artificial viral cages for bio/nanotechnological applications. During self-assembly, the favorable binding energy competes with the energetic cost of the growing edge and the elastic stresses generated due to the curvature of the capsid. As a result, incomplete structures such as open caps, cylindrical or ribbon-shaped shells may emerge, preventing the successful replication of viruses. Using elasticity theory and coarse-grained simulations, we analyze the conditions required for these processes to occur and their significance for empty virus self-assembly. We find that the outcome of the assembly can be recast into a universal phase diagram showing that viruses with high mechanical resistance cannot be self-assembled directly as spherical structures. The results of our study justify the need of a maturation step and suggest promising routes to hinder viral infections by inducing mis-assembly.
Resting-State Functional Connectivity Dynamics in Healthy Aging: An Approach Through Network Change Point Detection
Mancho-Fora, N., Montalà-Flaquer, M., Farràs-Permanyer, L., Bartrés-Faz, D., Vaqué-Alcázar, L., Peró-Cebollero, M., Guàrdia-Olmos, J.
Brain Connectivity
10
3
(2020)
This study aims at assessing the impact of age on the short-term temporal dynamics of the topological properties of the undirected and weighted whole-brain functional connectivity (FC) networks. We studied the association between the participant's age and the number of significant change points detected through the Network Change Point Detection algorithm. Secondary, we defined state as the resting-state functional magnetic resonance imaging (rs-fMRI) subsequence between two significant change points, obtaining the FC network in each state and participant and characterized their network topological properties. The data comprise the rs-fMRI sequences of 114 healthy individuals combined from 3 different studies conducted at the Department of Medicine, School of Medicine and Health Sciences, University of Barcelona. Participants were healthy people in the absence of any pathology that could interfere with the scanning procedures, as well as any chronic illness that implied a short-lived situation. Topological properties of everyone's FC networks were characterized by their network strength, transitivity, characteristic path length, and small-worldness, analyzing the effect of age in those observed distributions. To that effect, we constructed a mixed linear model for each network topological property with age, state, and state duration as the linear predictors. Several statistically significant relationships have been estimated between the indicators of the FC networks that show a certain regular pattern of change in the networks during the time of registration at the resting fMRI paradigm. These dynamic changes seem to be related to the age of each group studied. Healthy aging could be characterized by FC dynamics patterns.
Vocal learning: Beyond the continuum
Martins, P.T., Boeckx, C.
PLoS Biology
18
3
(2020)
Vocal learning is the ability to modify vocal output on the basis of experience. Traditionally, species have been classified as either displaying or lacking this ability. A recent proposal, the vocal learning continuum, recognizes the need to have a more nuanced view of this phenotype and abandon the yes–no dichotomy. However, it also limits vocal learning to production of novel calls through imitation, moreover subserved by a forebrain-to-phonatory-muscles circuit. We discuss its limitations regarding the characterization of vocal learning across species and argue for a more permissive view.
Capillary-Based Microfluidics—Coflow, Flow-Focusing, Electro-Coflow, Drops, Jets, and Instabilities
Guerrero, J., Chang, Y.-W., Fragkopoulos, A.A., Fernandez-Nieves, A.
Small
16
9
(2020)
Capillary-based microfluidics is a great technique to produce monodisperse and complex emulsions and particulate suspensions. In this review, the current understanding of drop and jet formation in capillary-based microfluidic devices for two primary flow configurations, coflow and flow-focusing is summarized. The experimental and theoretical description of fluid instabilities is discussed and conditions for controlled drop breakup in different modes of drop generation are provided. Current challenges in drop breakup with low interfacial tension systems and recent progress in overcoming drop size limitations using electro-coflow are addressed. In each scenario, the physical mechanisms for drop breakup are revisited, and simple scaling arguments proposed in the literature are introduced.
Motility and morphodynamics of confined cells
Lavi, I., Meunier, N., Voituriez, R., Casademunt, J.
Physical Review E
101
2
(2020)
We introduce a minimal hydrodynamic model of polarization, migration, and deformation of a biological cell confined between two parallel surfaces. In our model, the cell is driven out of equilibrium by an active cytsokeleton force that acts on the membrane. The cell cytoplasm, described as a viscous droplet in the Darcy flow regime, contains a diffusive solute that actively transduces the applied cytoskeleton force. While fairly simple and analytically tractable, this quasi-two-dimensional model predicts a range of compelling dynamic behaviours. A linear stability analysis of the system reveals that solute activity first destabilizes a global polarization-translation mode, prompting cell motility through spontaneous symmetry breaking. At higher activity, the system crosses a series of Hopf bifurcations leading to coupled oscillations of droplet shape and solute concentration profiles. At the nonlinear level, we find traveling-wave solutions associated with unique polarized shapes that resemble experimental observations. Altogether, this model offers an analytical paradigm of active deformable systems in which viscous hydrodynamics are coupled to diffusive force transducers.
Unraveling the hidden complexity of quasideterministic ratchets: Random walks, graphs, and circle maps
Blanch-Mercader, C., Orlandi, J.G., Casademunt, J.
Physical Review E
101
1
(2020)
Brownian ratchets are shown to feature a nontrivial vanishing-noise limit where the dynamics is reduced to a stochastic alternation between two deterministic circle maps (quasideterministic ratchets). Motivated by cooperative dynamics of molecular motors, here we solve exactly the problem of two interacting quasideterministic ratchets. We show that the dynamics can be described as a random walk on a graph that is specific to each set of parameters. We compute point by point the exact velocity-force V(f) function as a summation over all paths in the specific graph for each f, revealing a complex structure that features self-similarity and nontrivial continuity properties. From a general perspective, we unveil that the alternation of two simple piecewise linear circle maps unfolds a very rich variety of dynamical complexity, in particular the phenomenon of piecewise chaos, where chaos emerges from the combination of nonchaotic maps. We show convergence of the finite-noise case to our exact solution.
Design and evaluation of gamification experiences in computer science studies
Rodríguez, I., Salamó, M., Puig, A.
International Conference on Higher Education Advances
1137 1145
(2020)
This paper presents two gamification experiences developed in the Computer Science (CS) degree at the University of Barcelona. Usually, the CS degree suffers from low class attendance, which impacts the participation of students in in-class programming activities. Additionally, this degree includes a basic course related to human computer interaction that, despite of being valuable for the formation of students, they feel as boring and useless, far from their - heavily computer focused - interests. Then we decided to gamify a basic course of programming skills and the mentioned HCI course. We decided to use two different formats, online and physical. First, one experience was performed in “Human Factors in Computing” course of third year of studies, with 70 enrolled students. First, students attended to a 3D online theoretical class related to emotional design in “The education district” (TED) platform, which is a 3D Virtual World (VW) for educational purposes, developed by Virtway corporation. Afterwards, they participated in the 'Game of thrones' gamified activity where they evaluated the usability of TED. Second, we designed 'physical' gamified classes to increase attendance to Data Structures course, and in consequence, augment the number of programming exercises that students perform and the assistance they receive from the teacher. During the gamified sessions, the 120 enrolled students enhanced their skills in solving programming problems. The experience consisted of three kinds of challenges (with easy, medium, and hard difficulty level) solved in large, medium, and low-sized groups of students, respectively. The results of both experiences were satisfactory as evidenced by the percentage of students (>=66,7%) that rated the activities between 6 and 10 (in a 0 to 10 scale).
Early Holocene Socio-Ecological Dynamics in the Iberian Peninsula: A Network Approach
Lozano, S., Prignano, L., Gómez-Puche, M., de Pablo, J.F.-L.
Springer Proceedings in Complexity
287 290
(2020)
Late Glacial and Early Holocene environmental changes affected different domains of human demography, settlement, and subsistence patterns. The variable spatial patterning produced by the prehistoric hunter-gatherers’ archaeological record demands new approaches for analysing the multi-scalar nature of human-environmental interactions. In this contribution, we presented part of a long-term research programme aimed to cover this gap in the context the Iberian Peninsula from the Late Magdalenian to the end of the Late Mesolithic. PALEODEM (“Late Glacial and Postglacial Population History and Cultural Transmission in Iberia (c.15,000–8,000 cal BP)”) is a Consolidator Grant ERC project that addresses the role of human population levels and geographical distribution over the relationship between climatic events and cultural dynamics in our context of study. To do so, it will develop a three-level (micro-regional, regional, and macro-regional) analysis. In this contribution, we will focus on the macro-regional scale, which is addressed through a combination of network analysis and computational modelling.
Focus of negation: Its identification in Spanish
Taulé, M., Nofre, M., González, M., Martí, M.A.
Natural Language Engineering
1 22
(2020)
This article describes the criteria for identifying the focus of negation in Spanish. This work involved an in-depth linguistic analysis of the focus of negation through which we identified some 10 different types of criteria that account for a wide variety of constructions containing negation. These criteria account for all the cases that appear in the NewsCom corpus and were assessed in the annotation of this corpus. The NewsCom corpus consists of 2955 comments posted in response to 18 different news articles from online newspapers. The NewsCom corpus contains 2965 negative structures with their corresponding negation marker, scope, and focus. This is the first corpus annotated with focus in Spanish and it is freely available. It is a valuable resource that can be used both for the training and evaluation of systems that aim to automatically detect the scope and focus of negation and for the linguistic analysis of negation grounded in real data.
Decomposing and comparing meaning relations: Paraphrasing, textual entailment, contradiction, and specificity
Kovatchev, V., Gold, D., Antònia Martí, M., Salamó, M., Zesch, T.
LREC 2020 - 12th International Conference on Language Resources and Evaluation, Conference Proceedings
5782 5791
(2020)
In this paper, we present a methodology for decomposing and comparing multiple meaning relations (paraphrasing, textual entailment, contradiction, and specificity). The methodology includes SHARel - a new typology that consists of 26 linguistic and 8 reason-based categories. We use the typology to annotate a corpus of 520 sentence pairs in English and we demonstrate that unlike previous typologies, SHARel can be applied to all relations of interest with a high inter-annotator agreement. We analyze and compare the frequency and distribution of the linguistic and reason-based phenomena involved in paraphrasing, textual entailment, contradiction, and specificity. This comparison allows for a much more in-depth analysis of the workings of the individual relations and the way they interact and compare with each other. We release all resources (typology, annotation guidelines, and annotated corpus) to the community.
Random walk with hyperbolic probabilities
Montero, M.
Journal of Statistical Mechanics: Theory and Experiment
2020
1
(2020)
The random walk with hyperbolic probabilities that we are introducing is an example of stochastic diffusion in a one-dimensional heterogeneous media. Although driven by site-dependent one-step transition probabilities, the process retains some of the features of a simple random walk, shows other traits that one would associate with a biased random walk and, at the same time, presents new properties not related to either of them. In particular, we show how the system is not fully ergodic, as not every statistic can be estimated from a single realization of the process. We further give a geometric interpretation for the origin of these irregular transition probabilities
Functionability in complex networks: Leading nodes for the transition from structural to functional networks through remote asynchronization
Rosell-Tarragó, G., Díaz-Guilera, A.
Chaos
30
1
(2020)
Complex networks are essentially heterogeneous not only in the basic properties of the constituent nodes, such as their degree, but also in the effects that these have on the global dynamical properties of the network. Networks of coupled identical phase oscillators are good examples for analyzing these effects, since an overall synchronized state can be considered a reference state. A small variation of intrinsic node parameters may cause the system to move away from synchronization, and a new phase-locked stationary state can be achieved. We propose a measure of phase dispersion that quantifies the functional response of the system to a given local perturbation. As a particular implementation, we propose a variation of the standard Kuramoto model in which the nodes of a complex network interact with their neighboring nodes, by including a node-dependent frustration parameter. The final stationary phase-locked state now depends on the particular frustration parameter at each node and also on the network topology. We exploit this scenario by introducing individual frustration parameters and measuring what their effect on the whole network is, measured in terms of the phase dispersion, which depends only on the topology of the network and on the choice of the particular node that is perturbed. This enables us to define a characteristic of the node, its functionability, that can be computed analytically in terms of the network topology. Finally, we provide a thorough comparison with other centrality measures.
Applications in security and evasions in machine learning: A survey
Sagar, R., Jhaveri, R., Borrego, C.
Electronics
9
1
(2020)
In recent years, machine learning (ML) has become an important part to yield security and privacy in various applications. ML is used to address serious issues such as real-time attack detection, data leakage vulnerability assessments and many more. ML extensively supports the demanding requirements of the current scenario of security and privacy across a range of areas such as real-time decision-making, big data processing, reduced cycle time for learning, cost-efficiency and error-free processing. Therefore, in this paper, we review the state of the art approaches where ML is applicable more effectively to fulfill current real-world requirements in security. We examine different security applications’ perspectives where ML models play an essential role and compare, with different possible dimensions, their accuracy results. By analyzing ML algorithms in security application it provides a blueprint for an interdisciplinary research area. Even with the use of current sophisticated technology and tools, attackers can evade the ML models by committing adversarial attacks. Therefore, requirements rise to assess the vulnerability in the ML models to cope up with the adversarial attacks at the time of development. Accordingly, as a supplement to this point, we also analyze the different types of adversarial attacks on the ML models. To give proper visualization of security properties, we have represented the threat model and defense strategies against adversarial attack methods. Moreover, we illustrate the adversarial attacks based on the attackers’ knowledge about the model and addressed the point of the model at which possible attacks may be committed. Finally, we also investigate different types of properties of the adversarial attacks. © 2020 by the authors.
Using fMRI to assess brain activity in people with down syndrome: A systematic review
Carbó-Carreté, M., Cañete-Massé, C., Peró-Cebollero, M., Guàrdia-Olmos, J.
Frontiers in Human Neuroscience
14
147
(2020)
In the last few years, many investigations have focused on brain activity in general and in populations with different pathologies using non-invasive techniques such as electroencefalography (EEG), positron emission tomography (PET), functional magnetic resonance imaging (fMRI) and magnetic resonance imaging (MRI). However, the use of non-invasive techniques to detect brain signals to evaluate the cognitive activity of people with Down syndrome (DS) has not been sufficiently addressed. The objective of this study is to describe the state-of-the-art in fMRI techniques for recording brain signals in people with DS. Method: A systematic review was performed based on PRISMA recommendations; only nine papers on this topic have been published. Three independent researchers selected all relevant information from each paper. Analyses of information concordance showed a high value of agreement between researchers. Results: Although few relevant works have been published, the use of fMRI in people with DS is becoming an appropriate option to study brain function in this population. Of the nine identified papers, five used task designs, and four used resting-state paradigms. Conclusion: Thus, we emphasize the need to incorporate rigorous cognitive activity procedures in evaluations of the DS population. We suggest several factors (such as head correction movements and paired sample techniques) that must be considered when designing an fMRI study with a task or a resting-state paradigm in a DS population.
Patient-Specific iPSC-Derived Astrocytes Contribute to Non-Cell-Autonomous Neurodegeneration in Parkinson's Disease
di Domenico, A ; Carola, G ; Calatayud, C ; Pons-Espinal, M ; Munoz, JP ; Richaud-Patin, Y; Fernandez-Carasa, I ; Gut, M ; Faella, A ; Parameswaran, J ; Soriano, J ; Ferrer, I ; Tolosa, E ; Zorzano, A; Cuervo, AM ; Raya, A; Consiglio, A
STEM CELL REPORTS
12
2
(2019)
Parkinson's disease (PD) is associated with the degeneration of ventral midbrain dopaminergic neurons (vmDAns) and the accumulation of toxic alpha-synuclein. A non-cell-autonomous contribution, in particular of astrocytes, during PD pathogenesis has been suggested by observational studies, but remains to be experimentally tested. Here, we generated induced pluripotent stem cell-derived astrocytes and neurons from familial mutant LRRK2 G2019S PD patients and healthy individuals. Upon co-culture on top of PD astrocytes, control vmDAns displayed morphological signs of neurodegeneration and abnormal, astrocyte-derived alpha-synuclein accumulation. Conversely, control astrocytes partially prevented the appearance of disease-related phenotypes in PD vmDAns. We additionally identified dysfunctional chaperone-mediated autophagy (CMA), impaired macroautophagy, and progressive alpha-synuclein accumulation in PD astrocytes. Finally, chemical enhancement of CMA protected PD astrocytes and vmDAns via the clearance of alpha-synuclein accumulation. Our findings unveil a crucial non-cell-autonomous contribution of astrocytes during PD pathogenesis, and open the path to exploring novel therapeutic strategies aimed at blocking the pathogenic cross talk between neurons and glial cells.
Telegraphic processes with stochastic resetting
Masoliver, J
PHYSICAL REVIEW E
99
012121
(2019)
We investigate the effects of resetting mechanisms on random processes that follow the telegrapher's equation instead of the usual diffusion equation. We thus study the consequences of a finite speed of signal propagation, the landmark of telegraphic processes. Likewise diffusion processes where signal propagation is instantaneous, we show that in telegraphic processes, where signal propagation is not instantaneous, random resettings also stabilize the random walk around the resetting position and optimize the mean first-arrival time. We also obtain the exact evolution equations for the probability density of the combined process and study the limiting cases.
Enhancing Nanoparticle Diffusion on a Unidirectional Domain Wall Magnetic Ratchet
Stoop, RL; Straube, AV ; Tierno, P
NANO LETTERS
19
1
(2019)
The performance of nanoscale magnetic devices is often limited by the presence of thermal fluctuations, whereas in micro- and nanofluidic applications the same fluctuations may be used to spread reactants or drugs. Here, we demonstrate the controlled motion and the enhancement of diffusion of magnetic nanoparticles that are manipulated and driven across a series of Bloch walls within an epitaxially grown ferrite garnet film. We use a rotating magnetic field to generate a traveling wave potential that unidirectionally transports the nanoparticles at a frequency tunable speed. Strikingly, we find an enhancement of diffusion along the propulsion direction and a frequency-dependent diffusion coefficient that can be precisely controlled by varying the system parameters. To explain the reported phenomena, we develop a theoretical approach that shows a fair agreement with the experimental data enabling an exact analytical expression for the enhanced diffusivity above the magnetically modulated periodic landscape. Our technique to control thermal fluctuations of driven magnetic nanoparticles represents a versatile and powerful way to programmably transport magnetic colloidal matter in a fluid, opening the doors to different fluidic applications based on exploiting magnetic domain wall ratchets.
Active wetting of epithelial tissues
Perez-Gonzalez, C ; Alert, R ; Blanch-Mercader, C ; Gomez-Gonzalez, M ; Kolodziej, T ; Bazellieres, E ; Casademunt, J ; Trepat, X
NATURE PHYSICS
15
1
(2019)
Development, regeneration and cancer involve drastic transitions in tissue morphology. In analogy with the behaviour of inert fluids, some of these transitions have been interpreted as wetting transitions. The validity and scope of this analogy are unclear, however, because the active cellular forces that drive tissue wetting have been neither measured nor theoretically accounted for. Here we show that the transition between two-dimensional epithelial monolayers and three-dimensional spheroidal aggregates can be understood as an active wetting transition whose physics differs fundamentally from that of passive wetting phenomena. By combining an active polar fluid model with measurements of physical forces as a function of tissue size, contractility, cell-cell and cell-substrate adhesion, and substrate stiffness, we show that the wetting transition results from the competition between traction forces and contractile intercellular stresses. This competition defines a new intrinsic length scale that gives rise to a critical size for the wetting transition in tissues, a striking feature that has no counterpart in classical wetting. Finally, we show that active shape fluctuations are dynamically amplified during tissue dewetting. Overall, we conclude that tissue spreading constitutes a prominent example of active wetting-a novel physical scenario that may explain morphological transitions during tissue morphogenesis and tumour progression.
Criticality in failure under compression: Acoustic emission study of coal and charcoal with different microstructures
Xu, YY ; Borrego, AG; Planes, A ; Ding, XD; Vives, E
PHYSICAL REVIEW E
99
3
(2019)
A systematic study of acoustic emission avalanches in coal and charcoal samples under slow uniaxial compression is presented. The samples exhibit a range of organic composition in terms of chemical elements as well as different degrees of heterogeneity in the microstructure. The experimental analysis focuses on the energies E of the individual acoustic emission events as well as on the time correlations between successive events. The studied samples can be classified into three groups. The more homogeneous samples (group I) with pores in the micro and nanoscales, with signatures of hardening effects in the stress-strain curves, exhibit the cleanest critical power-law behavior for the energy distributions g(E)dE similar to E(similar to epsilon)dE with a critical exponent epsilon = 1.4. The more heterogeneous samples with voids, macropores, and granular microstructures (group III), show signatures of weakening effects and a larger effective exponent close to the value epsilon = 1.66, but in some cases truncated by exponential damping factors. The rest of the samples (group II) exhibit a mixed crossover behavior still compatible with an effective exponent epsilon = 1.4 but clearly truncated by exponential factors. These results suggest the existence of two possible universality classes in the failure of porous materials under compression: one for homogeneous samples and another for highly heterogeneous samples. Concerning time correlations between avalanches, all samples exhibit very similar waiting time distributions although some differences for the Omori aftershock distributions cannot be discarded.
Assessing diversity in multiplex networks
Carpi, LC ; Schieber, TA ; Pardalos, PM; Marfany, G; Masoller, C; Diaz-Guilera, A ; Ravetti, MG
SCIENTIFIC REPORTS
9
4511
(2019)
Diversity, understood as the variety of different elements or configurations that an extensive system has, is a crucial property that allows maintaining the system's functionality in a changing environment, where failures, random events or malicious attacks are often unavoidable. Despite the relevance of preserving diversity in the context of ecology, biology, transport, finances, etc., the elements or configurations that more contribute to the diversity are often unknown, and thus, they can not be protected against failures or environmental crises. This is due to the fact that there is no generic framework that allows identifying which elements or configurations have crucial roles in preserving the diversity of the system. Existing methods treat the level of heterogeneity of a system as a measure of its diversity, being unsuitable when systems are composed of a large number of elements with different attributes and types of interactions. Besides, with limited resources, one needs to find the best preservation policy, i.e., one needs to solve an optimization problem. Here we aim to bridge this gap by developing a metric between labeled graphs to compute the diversity of the system, which allows identifying the most relevant components, based on their contribution to a global diversity value. The proposed framework is suitable for large multiplex structures, which are constituted by a set of elements represented as nodes, which have different types of interactions, represented as layers. The proposed method allows us to find, in a genetic network (HIV-1), the elements with the highest diversity values, while in a European airline network, we systematically identify the companies that maximize (and those that less compromise) the variety of options for routes connecting different airports.
Memory-induced complex contagion in epidemic spreading
Hoffmann, XR ; Boguna, M
NEW JOURNAL OF PHYSICS
21
033034
(2019)
Albeit epidemic models have evolved into powerful predictive tools for the spread of diseases and opinions, most assume memoryless agents and independent transmission channels. We develop an infection mechanism that is endowed with memory of past exposures and simultaneously incorporates the joint effect of multiple infectious sources. Analytic equations and simulations of the susceptible-infected-susceptible model in unstructured substrates reveal the emergence of an additional phase that separates the usual healthy and endemic ones. This intermediate phase shows fundamentally distinct characteristics, and the system exhibits either excitability or an exotic variant of bistability. Moreover, the transition to endemicity presents hybrid aspects. These features are the product of an intricate balance between two memory modes and indicate that non-Markovian effects significantly alter the properties of spreading processes.
Microscale Magneto-Elastic Composite Swimmers at the Air-Water and Water-Solid Interfaces Under a Uniaxial Field
Bryan, MT ; Garcia-Torres, J ; Martin, EL ; Hamilton, JK ; Calero, C; Petrov, PG ; Winlove, CP ; Pagonabarraga, I ; Tierno, P ; Sagues, F ; Ogrin, FY
PHYSICAL REVIEW APPLIED
11
4
(2019)
Self-propulsion of magneto-elastic composite microswimmers is demonstrated under a uniaxial field at both the air-water and the water-substrate interfaces. The microswimmers are made of elastically linked magnetically hard Co-Ni-P and soft Co ferromagnets, fabricated using standard photolithography and electrodeposition. Swimming speed and direction are dependent on the field frequency and amplitude, reaching a maximum of 95.1 mu m/s on the substrate surface. Fastest motion occurs at low frequencies via a spinning (air-water interface) or tumbling (water-substrate interface) mode that induces transient inertial motion. Higher frequencies result in low Reynolds number propagation at both interfaces via a rocking mode. Therefore, the same microswimmer can be operated as either a high or a low Reynolds number swimmer. Swimmer pairs agglomerate to form a faster superstructure that propels via spinning and rocking modes analogous to those seen in isolated swimmers. Microswimmer propulsion is driven by a combination of dipolar interactions between the Co and Co-Ni-P magnets and rotational torque due to the applied field, combined with elastic deformation and hydrodynamic interactions between different parts of the swimmer, in agreement with previous models.
Leap-frog transport of magnetically driven anisotropic colloidal rotors
Massana-Cid, H ; Navarro-Argemi, E; Levis, D ; Pagonabarraga, I ; Tierno, P
JOURNAL OF CHEMICAL PHYSICS
150
16
(2019)
In this article, we combine experiments and theory to investigate the transport properties of anisotropic hematite colloidal rotors that dynam ically assemble into translating clusters upon application of a rotating magnetic field. The applied field exerts a torque to the particles forcing rotation close to a surface and thus a net translational motion at a frequency tunable speed. When approaching, pairs of particles are observed to assemble into stable three-dimensional clusters that perform a periodic leap-frog type dynamics and propel at a faster speed. We analyze the cluster formation and its lifetime and investigate the role of particle shape in the propulsion speed and stability. We show that the dynamics of the system results from a delicate balance between magnetic dipolar interactions and hydrodynamics, and we introduce a theoretical model that qualitatively explains the observed phenomena.
Brassinosteroid signaling in plant development and adaptation to stress
Planas-Riverola, A ; Gupta, A ; Betegon-Putze, I ; Bosch, N ; Ibanes, M ; Cano-Delgado, AI
DEVELOPMENT
146
5
(2019)
Brassinosteroids (BRs) are steroid hormones that are essential for plant growth and development. These hormones control the division, elongation and differentiation of various cell types throughout the entire plant life cycle. Our current understanding of the BR signaling pathway has mostly been obtained from studies using Arabidopsis thaliana as a model. In this context, the membrane steroid receptor BRI1 (BRASSINOSTEROID INSENSITIVE 1) binds directly to the BR ligand, triggering a signal cascade in the cytoplasm that leads to the transcription of BR-responsive genes that drive cellular growth. However, recent studies of the primary root have revealed distinct BR signaling pathways in different cell types and have highlighted cell-specific roles for BR signaling in controlling adaptation to stress. In this Review, we summarize our current knowledge of the spatiotemporal control of BR action in plant growth and development, focusing on BR functions in primary root development and growth, in stem cell selfrenewal and death, and in plant adaption to environmental
Mapping individual behavior in financial markets: synchronization and anticipation
Gutierrez-Roig, M ; Borge-Holthoefer, J; Arenas, A ; Perello, J
EPJ DATA SCIENCE
8
10
(2019)
In this paper we develop a methodology, based on Mutual Information and Transfer of Entropy, that allows to identify, quantify and map on a network the synchronization and anticipation relationships between financial traders. We apply this methodology to a dataset containing 410,612 real buy and sell operations, made by 566 non-professional investors from a private investment firm on 8 different assets from the Spanish IBEX market during a period of time from 2000 to 2008. These networks present a peculiar topology significantly different from the random networks. We seek alternative features based on human behavior that might explain part of those 12,158 synchronization links and 1031 anticipation links. Thus, we detect that daily synchronization with price (present in 64.90% of investors) and the one-day delay with respect to price (present in 4.38% of investors) play a significant role in the network structure. We find that individuals reaction to daily price changes explains around 20% of the links in the Synchronization Network, and has significant effects on the Anticipation Network. Finally, we show how using these networks we substantially improve the prediction accuracy when Random Forest models are used to nowcast and predict the activity of individual investors.
Selection mechanism at the onset of active turbulence
Martinez-Prat, B ; Ignes-Mullol, J ; Casademunt, J ; Sagues, F
NATURE PHYSICS
15
4
(2019)
Active turbulence describes a flow regime that is erratic, and yet endowed with a characteristic length scale(1). It arises in animate soft-matter systems as diverse as bacterial baths(2), cell tissues(3) and reconstituted cytoskeletal preparations(4.) However, the way that these turbulent dynamics emerge in active systems has so far evaded experimental scrutiny. Here, we unveil a direct route to active nematic turbulence by demonstrating that, for radially aligned unconfined textures, the characteristic length scale emerges at the early stages of the instability. We resolve two-dimensional distortions of a microtubule-based extensile systems(5) in space and time, and show that they can be characterized in terms of a growth rate that exhibits quadratic dependence on a dominant wavenumber. This wavelength selection mechanism is justified on the basis of a continuum model for an active nematic including viscous coupling to the adjacent fluid phase. Our findings are in line with the classical pattern-formation studies in non-active systems(6), bettering our understanding of the principles of active self-organization, and providing potential perspectives for the control of biological fluids.
Competing orders in colloidal kagome ice: Importance of the in-trap motion of the particles
Le Cunuder, A ; Frerot, I ; Ortiz-Ambriz, A ; Tierno, P
PHYSICAL REVIEW B
99
14
(2019)
Artificial ice systems have been designed to replicate paradigmatic phenomena observed in frustrated spin systems. Here, we present a detailed theoretical analysis based on Monte Carlo simulations of the low-energy phases in an artificial colloidal ice system, a recently introduced ice system where an ensemble of repulsive colloids are two-dimensionally confined by gravity to a lattice of double wells at a one-to-one filling. Triggered by recent results obtained by Brownian dynamics simulations [A. Libal et al., Phys. Rev. Lett. 120, 027204 (2018)], we analyze the energetics and the phase transitions that occur in the honeycomb geometry (realizing the analog of a spin-ice system on a kagome lattice) when decreasing the temperature. When the particles are restricted to occupy the two minima of the potential well, we recover the same phase diagram as the dipolar spin-ice system, with a long-range-ordered chiral ground state. In contrast, when considering the particle motion and their relaxation within the traps, we observe ferromagnetic ordering at low temperature. This observation highlights the fundamental role played by the continuous motion of colloids in artificial ice systems.
Gems in Ancient Rome: Pliny's Vision
Pérez González, J.
Scripta Classica Israelica
(2019)
Greco-Roman culture classified a great variety of gems. Authors such as
Theophrastus, Plutarch and Pliny the Elder dealt with the subject. To now which gems were most highly valued in ancient Rome, it is essential to consult book 37 of Pliny the Elder. Book 37 of Pliny’s Natural History is one of the few accounts on precious stones, gems and amber that collects information from various sources of antiquity, which in many cases have survived only thanks to Pliny’s transcription. He catalogued the most prestigious gems, and discussed their origin, their exploitation techniques, their properties and their etymology. This corpus collects a total of 240 different variants of gems, of which, in 93 cases, its place of origin is known. In order to know to what extent the words of Pliny reflect the reality of the Roman market, we have analyzed as examples ten catalogs of modern collections of gems from various places and compared them with Pliny’s comments. This analysis confirms the fact that the urban Roman elites valued precious stones extracted from the territories beyond the Roman Empire, especially those of the East. The ten catalogues contain more than 4000 different gems and glasses. It compares the information in Pliny’s book on gems with ten current catalogs of various museums, adding more than 4000 analyzed copies. Both of these sources similar results and therefore confirms the interest of the Romans for these productions.
The value of the distant future: The process of discount in random environments
Masoliver, J.
ESTUDIOS DE ECONOMIA APLICADA
37
2
(2019)
We analyze how future costs must be balanced against present costs. This is traditionally done using an exponential function with a constant discount rate. The choice of discount rate can dramatically e_ect the question on what is the value of the future. This is specially critical for environmental problems such as global warming, and it has generated a controversy as to the urgency for immediate action (Stern, 2006; Nordhaus, 2007a,b). We briey review the issue for the nonspecialist and take into account the randomness of the economic evolution by studying the discount function of three widely used processes for the dynamics of interest rates: Ornstein-Uhlenbeck, Feller and log-normal.We also outline our previous empirical survey on 9 stable countries (countries that have not su_ered periods of destabilizing ination) over time spans ranging up to more than 300 years (Farmer et. al. 2014). We estimate the parameters of one of the models studied (the Ornstein-Uhlenbeck process) and obtain the long-run discount rate for all these countries. The long-run discount obtained supports the low discounting rate proposed by Stem (2006) over higher rates that have been advocated by others (Nordhaus, 2007a,b).
Modelling terrestrial route networks to understand inter-polity interactions (southern Etruria, 950-500 BC)
Prignano, L ; Morer, I ; Fulminante, F ; Lozano, S
JOURNAL OF ARCHAEOLOGICAL SCIENCE
105
46 58
(2019)
Ancient regional routes were vital for interactions between settlements and deeply influenced the development of past societies and their "complexification". At the same time, since any transportation infrastructure needs some level of inter-settlement cooperation to be established, they can also be regarded as an epiphenomenon of social interactions at the regional scale. Here, we propose to analyze ancient pathway networks to understand the organization of cities and villages located in a certain territory, attempting to clarify whether such organization existed and if so, how it functioned. To address such a question, we chose a quantitative approach. Adopting network science as a general framework, by means of formal models, we try to identify how the collective effort that produced the terrestrial infrastructure was directed and organized. We selected a paradigmatic case study: Iron Age southern Etruria, a very well-studied context, with detailed archaeological information about settlement patterns and an established tradition of studies on terrestrial transportation routes, perfectly suitable for testing new techniques. The results of the modelling suggest that a balanced coordinated decision-making process was shaping, the route network in Etruria, a scenario which correlates well with the picture elaborated by different scholars using a more traditional technique.
Geometric randomization of real networks with prescribed degree sequence
Starnini, M ; Ortiz, E ; Serrano, MA
NEW JOURNAL OF PHYSICS
21
053039
(2019)
We introduce a model for the randomization of complex networks with geometric structure. The geometric randomization (GR) model assumes a homogeneous distribution of the nodes in a hidden similarity space and uses rewirings of the links to find configurations that maximize a connection probability akin to that of the popularity-similarity geometric network models. The rewiring preserves exactly the original degree sequence, thus preventing fluctuations in the degree cutoff. The GR model is manifestly simple as it relies upon a single free parameter controlling the clustering of the rewired network, and it does not require the explicit estimation of hidden degree variables. We demonstrate the applicability of GR by implementing it as a null model for the analysis of community structure. As a result, we find that geometric and topological communities detected in real networks are consistent, while topological communities are also detected in randomized counterparts as an effect of structural constraints.
Tunable self-healing of magnetically propelling colloidal carpets
Massana-Cid, H ; Meng, FL ; Matsunaga, D ; Golestanian, R ; Tierno, P
NATURE COMMUNICATIONS
10
2444
(2019)
The process of crystallization is difficult to observe for transported, out-of-equilibrium systems, as the continuous energy injection increases activity and competes with ordering. In emerging fields such as microfluidics and active matter, the formation of long-range order is often frustrated by the presence of hydrodynamics. Here we show that a population of colloidal rollers assembled by magnetic fields into large-scale propelling carpets can form perfect crystalline materials upon suitable balance between magnetism and hydrodynamics. We demonstrate a field-tunable annealing protocol based on a controlled colloidal flow above the carpet that enables complete crystallization after a few seconds of propulsion. The structural transition from a disordered to a crystalline carpet phase is captured via spatial and temporal correlation functions. Our findings unveil a novel pathway to magnetically anneal clusters of propelling particles, bridging driven systems with crystallization and freezing in material science.
Orientational order and morphology of clusters of self-assembled Janus swimmers
Alarcon, F; Navarro-Argemi, E ; Valeriani, C ; Pagonabarraga, I
PHYSICAL REVIEW E
99
062602
(2019)
Due to the combined effect of anisotropic interactions and activity, Janus swimmers are capable to self-assemble in a wide variety of structures, many more than their equilibrium counterpart. This might lead to the development of novel active materials capable of performing tasks without any central control. Their potential application in designing such materials endows trying to understand the fundamental mechanism in which these swimmers self-assemble. In the present work, we study a quasi-two-dimensional semidilute suspensions of two classes of amphiphilic spherical swimmers whose direction of motion can be tuned: either swimmers propelling in the direction of the hydrophobic patch or swimmers propelling in the opposite direction (toward the hydrophilic side). In both systems we have systematically tuned swimmers' hydrophobic strength and signature and observed that the anisotropic interactions, characterized by the angular attractive potential and its interaction range, in competition with the active stress, pointing toward or against the attractive patch gives rise to a rich aggregation phenomenology.
Role of Substrate Stiffness in Tissue Spreading: Wetting Transition and Tissue Durotaxis
Alert, R ; Casademunt, J
LANGMUIR
35
23
(2019)
Living tissues undergo wetting transitions: On a surface, they can either form a dropletlike cell aggregate or spread as a monolayer of migrating cells. Tissue wetting depends not only on the chemical but also on the mechanical properties of the substrate. Here, we study the role of substrate stiffness in tissue spreading, which we describe by means of an active polar fluid model. Taking into account that cells exert larger active traction forces on stiffer substrates, we predict a tissue wetting transition at a critical substrate stiffness that decreases with tissue size. On substrates with a stiffness gradient, we find that the tissue spreads faster on the stiffer side. Furthermore, we show that the tissue can wet the substrate on the stiffer side while dewetting from the softer side. We also show that, by means of viscous forces transmitted across the tissue, the stiffer-side interface can transiently drag the softer-side interface toward increasing stiffness, against its spreading tendency. These two effects result in directed tissue migration up the stiffness gradient. This phenomenon-tissue durotaxis-can thus emerge both from dewetting on the soft side and from hydrodynamic interactions between the tissue interfaces. Overall, our work unveils mechanisms whereby substrate stiffness impacts the collective migration and the active wetting properties of living tissues, which are relevant in development, regeneration, and cancer.
2D melting and motility induced phase separation in Active Brownian Hard Disks and Dumbbells
Digregorio, P ; Levis, D ; Suma, A ; Cugliandolo, LF ; Gonnella, G ; Pagonabarraga, I
INTERNATIONAL CONFERENCE ON COMPUTER SIMULATION IN PHYSICS AND BEYOND
1163
(2019)
Recently, we characterized the complete phase transition diagram in the phi-Pe parameter space for two models of active brownian particles in two dimensions. These models are composed of hard disks and dumbbells, respectively, the former being isotropic and the latter anisotropic. Here, we want to outline all the most significant features of these two paradigmatic models and compare them.
Remarkably, the phase diagrams of the two models are affected differently by the introduction of activity. Disks present a two-stage melting scenario from Pe=0 to about Pe=3, with a first order phase transition between liquid and hexatic and a Berezinskii-Kosterlitz-Thouless transition between hexatic and solid. At higher activities, the three phases are still observed, but the transition between liquid and hexatic becomes a BKT transitions without a distinguishable coexistence region. Dumbbells, instead, present a macroscopic coexistence between hexatically ordered regions and disordered ones, over a finite interval of packing fractions, for all activities, included Pe=0, without any observable discontinuity in the behavior upon increasing Pe.
Simultaneous phase separation and pattern formation in chiral active mixtures
Levis, D ; Liebchen, B
PHYSICAL REVIEW E
100
1
(2019)
Chiral active particles, or self-propelled circle swimmers, from sperm cells to asymmetric Janus colloids, form a rich set of patterns, which are different from those seen in linear swimmers Such patterns have mainly been explored for identical circle swimmers, while real-world circle swimmers typically possess a frequency distribution. Here we show that even the simplest mixture of (velocity-aligning) circle swimmers with two different frequencies hosts a complex world of superstructures: The most remarkable example comprises a microflock pattern, formed in one species, while the other species phase separates and forms a macrocluster, coexisting with a gas phase. Here one species microphase separates and selects a characteristic length scale, whereas the other one macrophase separates and selects a density. A second notable example, here occurring in an isotropic system, are patterns comprising two different characteristic length scales, which are controllable via frequency and swimming speed of the individual particles.
Confinement-controlled rectification in a geometric nanofluidic diode
Dal Cengio, S ; Pagonabarraga, I
JOURNAL OF CHEMICAL PHYSICS
151
4
(2019)
Recent experiments with electrolytes driven through conical nanopores give evidence of strong rectified current response. In such devices, the asymmetry in the confinement is responsible for the non-Ohmic response, suggesting that the interplay of entropic and enthalpic forces plays a major role. Here, we propose a theoretical model to shed light on the physical mechanism underlying ionic current rectification. By use of an effective description of the ionic dynamics, we explore the system's response in different electrostatic regimes. We show that the rectification efficiency, as well as the channel selectivity, is driven by the surface-to-bulk conductivity ratio Dukhin length rather than the electrical double layer overlap.
Co-assembly of Janus nanoparticles in block copolymer systems
Diaz, J ; Pinna, M ; Zvelindovsky, A ; Pagonabarraga, I
SOFT MATTER
15
31
(2019)
Block copolymer are ideal matrices to control the localisation of colloids. Furthermore, anisotropic nanoparticles such as Janus nanoparticles possess an additional orientational degree of freedom that can play a crucial role in the formation of highly ordered materials made of block copolymers. This work presents a mesoscopic simulation method to assert the co-assembly of Janus nanoparticles in a block copolymer mixture, finding numerous instances of aggregation and formation of ordered configurations. Comparison with chemically homogeneous neutral nanoparticles shows that Janus nanoparticles are less prone to induce bridging along lamellar domains, thus being a less destructive way to segregate nanoparticles at interfaces. The combination of asymmetric block copolymer and asymmetric Janus nanoparticles can result in assembly of colloids with an even number of layers within the minority domain.
Intermittency of Deformation and the Elastic Limit of an Icosahedral Virus under Compression
Mercedes Hernando-Pérez, Cheng Zeng, M. Carmen Miguel,and Bogdan Dragnea
ACS Nano
13
7842 7849
(2019)
Viruses undergo mesoscopic morphological changes as they
interact with host interfaces and in response to chemical cues. The
dynamics of these changes, over the entire temporal range relevant to
virus processes, are unclear. Here, we report on creep compliance
experiments on a small icosahedral virus under uniaxial constant stress.
We find that even at small stresses, well below the yielding point and
generally thought to induce a Hookean response, strain continues to
develop in time via sparse, randomly distributed, relatively rapid plastic
events. The intermittent character of mechanical compliance only appears
above a loading threshold, similar to situations encountered in granular
flows and the plastic deformation of crystalline solids. The threshold load
is much smaller for the empty capsids of the brome mosaic virus than for
the wild-type virions. The difference highlights the involvement of RNA in
stabilizing the assembly interface. Numerical simulations of spherical crystal deformation suggest intermittency is
mediated by lattice defect dynamics and identify the type of compression-induced defect that nucleates the transition to
plasticity.
Kinetics of empty viral capsid assembly in a minimal model
Reguera, D ; Hernandez-Rojas, J ; Llorente, JMG
SOFT MATTER
15
36
(2019)
The efficient construction of a protective protein shell or capsid is one of the most crucial steps in the replication cycle of a virus. The formation of the simplest capsid typically proceeds by the spontaneous assembly of identical building blocks. This process can also be achieved in vitro even in the absence of genetic material, thus opening the door to the production of artificial viral cages for a myriad of applications. In this work, we analyze the efficiency and the kinetic peculiarities of this self-assembly process using Brownian Dynamics simulations. We use a minimal model that considers identical assembly units and is able to reproduce successfully the correct final architecture of spherical capsids. The selection of a specific size and structure is achieved by changing a single parameter that imposes an angular anisotropy on the interaction. We analyze how the geometrical constraints of the interaction affect the efficiency of the assembly. We find that the optimal conditions for an efficient assembly from a kinetic point of view strongly depart from the lowest capsid energy corresponding to the minimum of the potential energy landscape. Our work illustrates the important differences between the equilibrium and dynamic characteristics of viral self-assembly, and provides important insights on how to design specific interactions for a successful assembly of artificial viral cages.
Anomalous diffusion under stochastic resettings: A general approach
Masoliver, J ; Montero, M
PHYSICAL REVIEW E
100
4
(2019)
We present a general formulation of the resetting problem which is valid for any distribution of resetting intervals and arbitrary underlying processes. We show that in such a general case, a stationary distribution may exist even if the reset-free process is not stationary, as well as a significant decreasing in the mean first-passage time. We apply the general formalism to anomalous diffusion processes which allow simple and explicit expressions for Poissonian resetting events.
The interconnected wealth of nations: Shock propagation on global trade-investment multiplex networks
Starnini, M ; Boguna, M ; Serrano, MA
SCIENTIFIC REPORTS
9
(2019)
The increasing integration of world economies, which organize in complex multilayer networks of interactions, is one of the critical factors for the global propagation of economic crises. We adopt the network science approach to quantify shock propagation on the global trade-investment multiplex network. To this aim, we propose a model that couples a spreading dynamics, describing how economic distress propagates between connected countries, with an internal contagion mechanism, describing the spreading of such economic distress within a given country. At the local level, we find that the interplay between trade and financial interactions influences the vulnerabilities of countries to shocks. At the large scale, we find a simple linear relation between the relative magnitude of a shock in a country and its global impact on the whole economic system, albeit the strength of internal contagion is country-dependent and the inter-country propagation dynamics is non-linear. Interestingly, this systemic impact can be associated to intra-layer and inter-layer scale factors that we name network multipliers, that are independent of the magnitude of the initial shock. Our model sets-up a quantitative framework to stress-test the robustness of individual countries and of the world economy.
Driving an electrolyte through a corrugated nanopore
Malgaretti, P; Janssen, M; Pagonabarraga, I ; Rubi, JM
JOURNAL OF CHEMICAL PHYSICS
151
8
(2019)
We characterize the dynamics of a z - z electrolyte embedded in a varying-section channel. In the linear response regime, by means of suitable approximations, we derive the Onsager matrix associated with externally enforced gradients in electrostatic potential, chemical potential, and pressure, for both dielectric and conducting channel walls. We show here that the linear transport coefficients are particularly sensitive to the geometry and the conductive properties of the channel walls when the Debye length is comparable to the channel width. In this regime, we found that one pair of off-diagonal Onsager matrix elements increases with the corrugation of the channel transport, in contrast to all other elements which are either unaffected by or decrease with increasing corrugation. Our results have a possible impact on the design of blue-energy devices as well as on the understanding of biological ion channels through membranes. Published under license by AIP Publishing.
Guidance of active particles at liquid-liquid interfaces near surfaces
Palacios, LS ; Katuri, J ; Pagonabarraga, I; Sanchez, S
SOFT MATTER
15
32
(2019)
Artificial microswimmers have the potential for applications in many fields, ranging from targeted cargo delivery and mobile sensing to environmental remediation. In many of these applications, the artificial swimmers will operate in complex media necessarily involving liquid-liquid interfaces. Here, we experimentally study the motion of chemically powered phoretic active colloids close to liquid-liquid interfaces while swimming next to a solid substrate. In a system involving this complex geometry, we find that the active particles have an alignment interaction with both the neighbouring solid and liquid interfaces, allowing for a robust guiding mechanism along the liquid interface. We compare with minimal active Brownian simulations to show that these phoretically active particles stay along the interfaces for much longer times and lengths than expected for standard active Brownian particles. We also track the propulsion speeds of these particles and find a reduced speed close to the liquid-liquid interface. We report an interesting non-linear dependence of this reduction on the particle's bulk speed.
Scalar model of flocking dynamics on complex social networks
Miguel, MC ; Pastor-Satorras, R
PHYSICAL REVIEW E
100
4
(2019)
We investigate the effects of long-range social interactions in flocking dynamics by studying the dynamics of a scalar model of collective motion embedded in a complex network representing a pattern of social interactions, as observed in several social species. In this scalar model we find a phenomenology analogous to that observed in the classic Vicsek model: In networks with low heterogeneity, a phase transition separates an ordered from a disordered phase. At high levels of heterogeneity, instead, the transition is suppressed, and the system is always ordered. This observation is backed up analytically by the solution of a modified scalar model within an heterogeneous mean-field approximation. Our work extends the understanding of the effects of social interactions in flocking dynamics and opens the path to the analytical study of more complex topologies of social ties.
Direct measurement of Lighthill's energetic efficiency of a minimal magnetic microswimmer
Calero, C; Garcia-Torres, J ; Ortiz-Ambriz, A ; Sagues, F ; Pagonabarraga, I; Tierno, P
NANOSCALE
11
40
(2019)
The realization of artificial microscopic swimmers able to propel in viscous fluids is an emergent research field of fundamental interest and vast technological applications. For certain functionalities, the efficiency of the microswimmer in converting the input power provided through an external actuation into propulsive power output can be critical. Here we use a microswimmer composed by a self-assembled ferromagnetic rod and a paramagnetic sphere and directly determine its swimming efficiency when it is actuated by a swinging magnetic field. Using fast video recording and numerical simulations we fully characterize the dynamics of the propeller and identify the two independent degrees of freedom which allow its propulsion. We then obtain experimentally the Lighthill's energetic efficiency of the swimmer by measuring the power consumed during propulsion and the energy required to translate the propeller at the same speed. Finally, we discuss how the efficiency of our microswimmer could be increased upon suitable tuning of the different experimental parameters.
ESPACIO, TIEMPO Y FORMA
José Remesal Rodríguez, Lluis Pons Pujol, Jordi Pérez González, Juan Manuel Bermúdez Lorenzo
Revistas Espacio, Tiempo y Forma. Series I-VII Espacio, Tiempo y Forma, Serie II, Historia Antigua
(2019)
Language evolution and complexity considerations: The no half-Merge fallacy
Pedro Tiago Martins , Cedric Boeckx
PLoS Biol
17
11
(2019)
Recently, prominent theoretical linguists have argued for an explicit scenario for the evolution of the human language capacity on the basis of its computational properties. Concretely, the simplicity of a minimalist formulation of the operation Merge, which allows humans to recursively compute hierarchical relations in language, has been used to promote a sudden-emergence, single-mutation scenario. In support of this view, Merge is said to be either fully present or fully absent: one cannot have half-Merge. On this basis, it is inferred that the emergence of our fully fledged language capacity had to be sudden. Thus, proponents of this view draw a parallelism between the formal complexity of the operation at the computational level and the number of evolutionary steps it must imply. Here, we examine this argument in detail and show that the jump from the atomicity of Merge to a single-mutation scenario is not valid and therefore cannot be used as justification for a theory of language evolution along those lines.
1283. Arqueologia i col·leccionisme: Gabriel de Molina i els inicis de les excavacions d'Empúries (català)
Lluís Buscató Somoza, Lluís Pons Pujol
Revista Bibliográfica de Geografía y Ciencias Sociales
24
(2019)
L’any 2008 se celebrà el primer centenari de l’inici de les excavacions arqueològiques a l’antiga ciutat grecorromana d’Empúries. Sense voler negar la importància cultural i simbòlica d’aquest fet, a través de les següents pàgines exposarem que, en realitat, els precedents de les intervencions en aquest jaciment són molt anteriors i en ells hi tingué un paper destacat, entre d’altres personatges avui quasi oblidats, el funcionari Gabriel de Molina Ramos. Raó per la qual creiem d’interès investigar qui era i per quin motiu se sentí atret per l’arqueologia. La base d’aquesta recerca són, en bona part, documents inèdits trobats en diferents arxius catalans i estatals. (Català)
Nonspherical Nanoparticles in Block Copolymer Composites: Nanosquares, Nanorods, and Diamonds
Diaz, J ; Pinna, M ; Zvelindovsky, AV ; Pagonabarraga, I
MACROMOLECULES
52
21
(2019)
A hybrid two-dimensional block copolymer (BCP) nanocomposite computational model is proposed to study nanoparticles (NPs) with a generalized shape including square, rectangle, and rhombus. Simulations are used to study the role of anisotropy in the assembly of colloids within BCPs, ranging from NPs that are compatible with one phase to neutral NPs. The ordering of squarelike NPs into grid configurations within a minority BCP domain was investigated, as well as the alignment of nanorods in a lamellar-forming BCP, comparing the simulation results with experiments of mixtures of nanoplates and polystyrene-b-poly(methyl methacrylate) BCP. The assembly of rectangular NPs at the interface between domains resulted in alignment along the interface. The aspect ratio is found to play a key role in the aggregation of colloids at the interface, which leads to a distinct co-assembly behavior for low- and high-aspect-ratio NPs.
Spontaneous functional recovery after focal damage in neuronal cultures
Teller, Sara; Estevez-Priego, Estefania; Granell, Clara; Tornero, Daniel; Andilla, Jordi; Olarte, Omar E; Loza-Alvarez, Pablo; Arenas, Alex; Soriano, Jordi
eNeuro
(2019)
Damage in biological neuronal networks triggers a complex functional reorganization whose mechanisms are still poorly understood. To delineate this reorganization process, here we investigate the functional alterations of in vitro rat cortical circuits following localized laser ablation. The analysis of the functional network configuration before and after ablation allowed us to quantify the extent of functional alterations and the characteristic spatial and temporal scales along recovery. We observed that damage precipitated a fast rerouting of information flow that restored network's communicability in about 15 min. Functional restoration was led by the immediate neighbors around trauma but was orchestrated by the entire network. Our in vitro setup exposes the ability of neuronal circuits to articulate fast responses to acute damage, and may serve as a proxy to devise recovery strategies in actual brain circuits. Moreover, this biological setup can become a benchmark to empirically test network theories about the spontaneous recovery in dynamical networks.Significance Statement Given the sheer size of the brain, in vitro models in the form of neuronal cultures have emerged as a promising tool to investigate dynamic and network alterations in detail upon physical damage. Here we present a new experimental paradigm based on the combination of laser microsurgery and calcium fluorescence imaging to analyze network functional alterations after a focal lesion. We show that the network is not only able to cope with damage but that the regions around the lesion core actively participate in recovery, restoring the initial network activity levels in just 15 min. Our approach offers interesting perspectives for modeling network functional loss and recovery in a number of damage actions, from stroke to degenerative disorders.
Universality of power-law exponents by means of maximum-likelihood estimation
Navas-Portella, V ; Gonzalez, A ; Serra, I ; Vives, E ; Corral, A
PHYSICAL REVIEW E
100
6
(2019)
Power-law-type distributions are extensively found when studying the behavior of many complex systems. However, due to limitations in data acquisition, empirical datasets often only cover a narrow range of observation, making it difficult to establish power-law behavior unambiguously. In this work we present a statistical procedure to merge different datasets, with two different aims. First, we obtain a broader fitting range for the statistics of different experiments or observations of the same system. Second, we establish whether two or more different systems may belong to the same universality class. By means of maximum likelihood estimation, this methodology provides rigorous statistical information to discern whether power-law exponents characterizing different datasets can be considered equal among them or not. This procedure is applied to the Gutenberg-Richter law for earthquakes and for synthetic earthquakes (acoustic emission events) generated in the laboratory: labquakes. Different earthquake catalogs have been merged finding a Gutenberg-Richter law holding for more than eight orders of magnitude in seismic moment. The value of the exponent of the energy distribution of labquakes depends on the material used in the compression experiments. By means of the procedure proposed in this manuscript, we find that the Gutenberg-Richter law for earthquakes and charcoal labquakes can be characterized by the same power-law exponent, whereas Vycor labquakes exhibit a significantly different exponent.
Linear Response Theory and Green-Kubo Relations for Active Matter
Dal Cengio, S ; Levis, D ; Pagonabarraga, I
PHYSICAL REVIEW LETTERS
123
23
(2019)
We address the question of how interacting active systems in a nonequilibrium steady state respond to an external perturbation. We establish an extended fluctuation-dissipation theorem for active Brownian particles (ABP), which highlights the role played by the local violation of detailed balance due to activity. By making use of a Markovian approximation we derive closed Green-Kubo expressions for the diffusivity and mobility of ABP and quantify the deviations from the Stokes-Einstein relation. We compute the linear response function to an external force using unperturbed simulations of ABP and compare the results with the analytical predictions of the transport coefficients. Our results show the importance of the interplay between activity and interactions in the departure from equilibrium linear response.
Large scale three dimensional simulations of hybrid block copolymer/nanoparticle systems
Diaz, J ; Pinna, M ; Zvelindovsky, AV ; Pagonabarraga, I
SOFT MATTER
15
45
(2019)
Block copolymer melts self-assemble in the bulk into a variety of nanostructures, making them perfect candidates to template the position of nanoparticles. The morphological changes of block copolymers are studied in the presence of a considerable filling fraction of colloids. Furthermore, colloids can be found to assemble into ordered hexagonally close-packed structures in a defined number of layers when softly confined within the phase-separated block copolymer. A high concentration of interface-compatible nanoparticles leads to complex long-lived block copolymer morphologies depending on the polymeric composition. Macrophase separation between the colloids and the block copolymer can be induced if colloids are unsolvable within the matrix. This leads to the formation of ellipsoid-shaped polymer-rich domains elongated along the direction perpendicular to the interface between block copolymer domains.
Colloquium: Ice rule and emergent frustration in particle ice and beyond
Ortiz-Ambriz, A ; Nisoli, C ; Reichhardt, C; Reichhardt, CJO; Tierno, P
REVIEWS OF MODERN PHYSICS
91
4
(2019)
Geometric frustration and the ice rule are two concepts that are intimately connected and widespread across condensed matter. The first refers to the inability of a system to satisfy competing interactions in the presence of spatial constraints. The second, in its more general sense, represents a prescription for the minimization of the topological charges in a constrained system. Both can lead to manifolds of high susceptibility and nontrivial, constrained disorder where exotic behaviors can appear and even be designed deliberately. This Colloquium describes the emergence of geometric frustration and the ice rule in soft condensed matter. It excludes the extensive developments of mathematical physics within the field of geometric frustration, but rather focuses on systems of confined microscopic or mesoscopic particles that emerge as a novel paradigm exhibiting spin degrees of freedom. In such systems, geometric frustration can be engineered artificially by controlling the spatial topology and geometry of the lattice, the position of the individual particle units, or their relative filling fraction. These capabilities enable the creation of novel and exotic phases of matter and also potentially lead toward technological applications related to memory and logic devices that are based on the motion of topological defects. The rapid progress in theory and experiments is reviewed and the intimate physical connections with other frustrated systems at different length scales are discussed.
Asymmetric and long range interactions in shaken granular media
Codina, J ; Pagonabarraga, I
JOURNAL OF CHEMICAL PHYSICS
151
16
(2019)
We use a computational model to investigate the emergence of interaction forces between pairs of intruders in a horizontally vibrated granular fluid. The time evolution of a pair of particles shows a maximum of the likelihood to find the pair at contact in the direction of shaking. This relative interaction is further studied by fixing the intruders in the simulation box where we identify effective mechanical forces and torques between particles and quantify an emergent long range attractive force as a function of the shaking relative angle, the amplitude, and the packing density of grains. We determine the local density and kinetic energy profiles of granular particles along the axis of the dimer to find no gradients in the density fields and additive gradients in the kinetic energies. Published under license by AIP Publishing.
Adenovirus major core protein condenses DNA in clusters and bundles, modulating genome release and capsid internal pressure
Martin-Gonzalez, N ; Hernando-Perez, M ; Condezo, GN ; Perez-Illana, M; Siber, A; Reguera, D; Ostapchuk, P; Hearing, P; San Martin, C; de Pablo, PJ
NUCLEIC ACIDS RESEARCH
47
17
(2019)
Some viruses package dsDNA together with large amounts of positively charged proteins, thought to help condense the genome inside the capsid with no evidence. Further, this role is not clear because these viruses have typically lower packing fractions than viruses encapsidating naked dsDNA. In addition, it has recently been shown that the major adenovirus condensing protein (polypeptide VII) is dispensable for genome encapsidation. Here, we study the morphology and mechanics of adenovirus particles with (Ad5-wt) and without (Ad5-VII-) protein VII. Ad5-VII- particles are stiffer than Ad5-wt, but DNA-counterions revert this difference, indicating that VII screens repulsive DNA-DNA interactions. Consequently, its absence results in increased internal pressure. The core is slightly more ordered in the absence of VII and diffuses faster out of Ad5-VII-than Ad5-wt fractured particles. In Ad5-wt unpacked cores, dsDNA associates in bundles interspersed with VII-DNA clusters. These results indicate that protein VII condenses the adenovirus genome by combining direct clustering and promotion of bridging by other core proteins. This condensation modulates the virion internal pressure and DNA release from disrupted particles, which could be crucial to keep the genome protected inside the semi-disrupted capsid while traveling to the nuclear pore.
The acquisition of aspect in Spanish by Chinese learners
Sun, YL; Gonzalez, P; Couto, MDP; Mauder, E; Child, MW; Diaz, L; Taule, M
CIRCULO DE LINGUISTICA APLICADA A LA COMUNICACION
78
287 316
(2019)
This work focuses on the acquisition of the preterito indefinido and the preterito imperfecto in Spanish by Chinese learners. Based on previous research, we predict that the differences in the aspectual systems of Mandarin Chinese and Spanish may prove challenging for Chinese learners in their use and comprehension of aspect in their inter-language. Moreover, we believe that the acquisition of aspect may not be synchronized at the morphological and semantic levels. By means of a grammatical task and a comprehension task, we found that the differences in the aspectual systems of the L1 and the L2 do cause difficulty for our learners. Additionally, our data support the claim that the acquisition of aspect at the morphological level occurs earlier than at semantic level.
Estimation of Brain Functional Connectivity in Patients with Mild Cognitive Impairment
Farras-Permanyer, L ; Mancho-Fora, N ; Montala-Flaquer, M ; Gudayol-Ferre, E; Gallardo-Moreno, GB; Zarabozo-Hurtado, D; Villuendas-Gonzalez, E; Pero-Cebollero, M; Guardia-Olmos, J
BRAIN SCIENCES
9
350
(2019)
Mild cognitive impairment is defined as greater cognitive decline than expected for a person at a particular age and is sometimes considered a stage between healthy aging and Alzheimer's disease or other dementia syndromes. It is known that functional connectivity patterns change in people with this diagnosis. We studied functional connectivity patterns and functional segregation in a resting-state fMRI paradigm comparing 10 MCI patients and 10 healthy controls matched by education level, age and sex. Ninety ROIs from the automated anatomical labeling (AAL) atlas were selected for functional connectivity analysis. A correlation matrix was created for each group, and a third matrix with the correlation coefficient differences between the two matrices was created. Functional segregation was analyzed with the 3-cycle method, which is novel in studies of this topic. Finally, cluster analyses were also performed. Our results showed that the two correlation matrices were visually similar but had many differences related to different cognitive functions. Differences were especially apparent in the anterior default mode network (DMN), while the visual resting-state network (RSN) showed no differences between groups. Differences in connectivity patterns in the anterior DMN should be studied more extensively to fully understand its role in the differentiation of healthy aging and an MCI diagnosis.
Mercator: uncovering faithful hyperbolic embeddings of complex networks
Garcia-Perez, G; Allard, A; Serrano, MA; Boguna, M
NEW JOURNAL OF PHYSICS
21
12
(2019)
We introduce Mercator, a reliable embedding method to map real complex networks into their hyperbolic latent geometry. The method assumes that the structure of networks is well described by the popularity x similarity S1/H2<i static geometric network model, which can accommodate arbitrary degree distributions and reproduces many pivotal properties of real networks, including self-similarity patterns. The algorithm mixes machine learning and maximum likelihood (ML) approaches to infer the coordinates of the nodes in the underlying hyperbolic disk with the best matching between the observed network topology and the geometric model. In its fast mode, Mercator uses a model-adjusted machine learning technique performing dimensional reduction to produce a fast and accurate map, whose quality already outperforms other embedding algorithms in the literature. In the refined Mercator mode, the fast mode embedding result is taken as an initial condition in a ML estimation, which significantly improves the quality of the final embedding. Apart from its accuracy as an embedding tool, Mercator has the clear advantage of systematically inferring not only node orderings, or angular positions, but also the hidden degrees and global model parameters, and has the ability to embed networks with arbitrary degree distributions. Overall, our results suggest that mixing machine learning and ML techniques in a model-dependent framework can boost the meaningful mapping of complex networks.
Annotating and analyzing the interactions between meaning relations
Gold, D., Kovatchev, V., & Zesch, T.
Proceedings of the 13th Language Annotation Workshop.
(2019)
Pairs of sentences, phrases, or other text pieces can hold semantic relations such as paraphrasing, textual entailment, contradiction, specificity, and semantic similarity. These relations are usually studied in isolation and no dataset exists where they can be compared empirically. Here we present a corpus annotated with these relations and the analysis of these results. The corpus contains 520 sentence pairs, annotated with these relations. We measure the annotation reliability of each individual relation and we examine their interactions and correlations. Among the unexpected results revealed by our analysis is that the traditionally considered direct relationship between paraphrasing and bi-directional entailment does not hold in our data
Effects of two channels on explosive information spreading
Wu, J., Zheng, M., Xu, K., & Gu, C.
Nonlinear Dynamics
99
3
(2019)
Information spreading has been studied for decades, but the underlying mechanism why the information can be accepted by a large number of people overnight is still under debate, especially in the aspects of two-channel effects for information transmission and theoretical analysis. In this study, based on a susceptible-accepted-recovered (SAR) model, we examine the effects of two channels represented by a two-layered network, in which one channel is the intra-links within the same layer and the other is inter-links between layers. Different with the case of one single channel on a one-layered network, in the case of two channels, the spreading can be speeded up by the increase in the coupling strength, i.e., average node degree and transmission probability between the two layers. Strikingly, even if the parameter (social reinforcement) is small, the strongly coupling strength can induce explosive transition in the information spreading process. Additionally, a big gap closed to the critical point for the explosive transition was found in the phase space of theoretical analysis, which indicates the emergency of a global large-scope outbreak. These findings may be of significance on the understanding and controlling explosive information spreading in modern society.
Lessons learned from supplementing archaeological museum exhibitions with virtual reality
Puig, A., Rodríguez, I., Arcos, J. L., Rodríguez- Aguilar, J. A., Cebrián, S., Bogdanovych, A., & Piqué, R.
Virtual Reality
1 16
(2019)
Archaeological excavations provide us with important clues about the past. Excavated artefacts represent an important connection to civilisations that no longer exist and help us understand some of their customs, traditions and common practices. With the help of academics and practitioners from various disciplines, the results of archaeological excavations can be analysed and a body of knowledge about the corresponding society can be created and shared with members of the general public. Museums have traditionally served the purpose of communicating this knowledge and backing it up with the help of the excavated artefacts. Many museum visitors, however, find it difficult to develop a coherent understanding of the corresponding society only based on the artefacts and annotations shown in museums. Effective modern techniques that have high potential in helping museum visitors with better understanding of the past are 3D reconstruction and virtual reality. 3D reconstruction offers a cost-effective way of recreating historical settlements in a computer-generated virtual environment, while virtual reality helps with immersing people into such environments and reaching a high degree of realism. With the help of these technologies, it becomes possible to relive history, imagine yourself being a part of the reconstructed society and learn about its culture firsthand. The combination of 3D reconstruction and virtual reality represents a very powerful learning tool; however, this tool has been rarely used in a museum setting and its correct use has not been properly investigated. In this paper, we present a study into using virtual reality in itinerant archaeological exhibitions. We discuss the lessons we have learned from developing an interactive virtual reality simulation of the Neolithic settlement of La Draga. These lessons feature our analysis of qualitative and quantitative feedback of museum visitors, as well as what we have learned from analysing their navigation and interaction patterns.
A Polypropylene Carbonate-Based Adaptive Buffer Layer for Stable Interfaces of Solid Polymer Lithium Metal Batteries
Yang, H., Zhang, Y., Tennenbaum, M. J., Althouse, Z., Ma, Y., He, Y., ... & Huang, Y.
ACS applied materials & interfaces
11
31
(2019)
Solid polymer electrolytes (SPEs) have the potential to enhance the safety and energy density of lithium batteries. However, poor interfacial contact between the lithium metal anode and SPE leads to high interfacial resistance and low specific capacity of the battery. In this work, we present a novel strategy to improve this solid–solid interface problem and maintain good interfacial contact during battery cycling by introducing an adaptive buffer layer (ABL) between the Li metal anode and SPE. The ABL consists of low molecular-weight polypropylene carbonate , poly(ethylene oxide) (PEO), and lithium salt. Rheological experiments indicate that ABL is viscoelastic and that it flows with a higher viscosity compared to PEO-only SPE. ABL also has higher ionic conductivity than PEO-only SPE. In the presence of ABL, the interface resistance of the Li/ABL/SPE/LiFePO4 battery only increased 20% after 150 cycles, whereas that of the battery without ABL increased by 117%. In addition, because ABL makes a good solid–solid interface contact between the Li metal anode and SPE, the battery with ABL delivered an initial discharge specific capacity of >110 mA·h/g, which is nearly twice that of the battery without ABL, which is 60 mA·h/g. Moreover, ABL is able to maintain electrode–electrolyte interfacial contact during battery cycling, which stabilizes the battery Coulombic efficiency.
Activity induced synchronization: Mutual flocking and chiral self-sorting
Levis, D., Pagonabarraga, I., & Liebchen, B.
Physical Review Research
1
2
(2019)
Synchronization, the temporal coordination of coupled oscillators, allows fireflies to flash in unison, neurons to fire collectively, and human crowds to fall in step on the London millenium bridge. Here, we interpret active (or self-propelled) chiral microswimmers with a distribution of intrinsic frequencies as motile oscillators and show that they can synchronize over very large distances, even for local coupling in two dimensions (2D). This opposes canonical nonactive oscillators on static or time-dependent networks, leading to synchronized domains only. A consequence of this activity-induced synchronization is the emergence of a “mutual flocking phase,” where particles of opposite chirality cooperate to form superimposed flocks moving at a relative angle to each other, providing a chiral active matter analogue to the celebrated Toner-Tu phase. The underlying mechanism employs a positive feedback loop involving the two-way coupling between oscillators' phase and self-propulsion and could be exploited as a design principle for synthetic active materials and chiral self-sorting techniques.
Capillary-Based Microfluidics—Coflow, Flow- Focusing, Electro-Coflow, Drops, Jets, and Instabilities
Guerrero, J., Chang, Y. W., Fragkopoulos, A. A., & Fernandez-Nieves, A.
Small
1904344
(2019)
Capillary‐based microfluidics is a great technique to produce monodisperse and complex emulsions and particulate suspensions. In this review, the current understanding of drop and jet formation in capillary‐based microfluidic devices for two primary flow configurations, coflow and flow‐focusing is summarized. The experimental and theoretical description of fluid instabilities is discussed and conditions for controlled drop breakup in different modes of drop generation are provided. Current challenges in drop breakup with low interfacial tension systems and recent progress in overcoming drop size limitations using electro‐coflow are addressed. In each scenario, the physical mechanisms for drop breakup are revisited, and simple scaling arguments proposed in the literature are introduced.
Collective dynamics and conformal ordering in electrophoretically driven nematic colloids
Straube, A. V., Pagès, J. M., Tierno, P., Ignés- Mullol, J., & Sagués, F.
Physical Review Research
1
2
(2019)
We present a theoretical framework to understand the collective dynamics of an ensemble of electrophoretically driven colloidal particles that are forced to assemble around a single topological defect in a nematic liquid crystal by an alternating current electric field. Our generic model combines phoretic propulsion with electrostatic interactions and liquid-crystal-mediated hydrodynamics, which are effectively cast into a long-range interparticle repulsion, while nematic elasticity plays a subdominant role. Simulations based on this model fully capture the collective organization process observed in the experiments and other striking effects as the emergence of conformal ordering and a nearly frequency-independent repulsive interaction above 10Hz. Our results demonstrate the importance of hydrodynamic interactions on the assembly of driven microscale matter in anisotropic media.
Curved boundaries and chiral instabilities–two sources of twist in homeotropic nematic tori
McInerney, J. P., Ellis, P. W., Rocklin, D. Z., Fernandez-Nieves, A., & Matsumoto, E. A.
Soft Matter
15
6
(2019)
Many liquid crystalline systems display spontaneous breaking of achiral symmetry, as achiral molecules aggregate into large chiral domains. In confined cylinders with homeotropic boundary conditions, chromonic liquid crystals – which have a twist elastic modulus which is at least an order of magnitude less than their splay and bend counter parts – adopt a twisted escaped radial texture (TER) to minimize their free energy, whilst 5CB – which has all three elastic constants roughly comparable – does not. In a recent series of experiments, we have shown that 5CB confined to tori and bent cylindrical capillaries with homeotropic boundary conditions also adopts a TER structure resulting from the curved nature of the confining boundaries [P. W. Ellis et al., Phys. Rev. Lett., 2018, 247803]. We shall call this microscopic twist, as the twisted director organization not only depends on the confinement geometry but also on the values of elastic moduli. Additionally, we demonstrate theoretically that the curved geometry of the boundary induces a twist in the escaped radial (ER) texture. Moving the escaped core of the structure towards the center of the torus not only lowers the splay and bend energies, but lowers the energetic cost of this distinct source for twist that we shall call geometric twist. As the torus becomes more curved, the ideal location for the escaped core approaches the inner radius of the torus.
Emission modes in electro co-flow
Guerrero, J., Hijano, A.J., Lobato, M.A., Higuera, F.J., Loscertales, I.G., & Fernandez-Nieves, A.
Physics of Fluids
31
8
(2019)
We apply an electric field to a moderately conducting liquid surrounded by another co-flowing liquid, all inside a glass-based microfluidic device, and study and classify the resulting emission modes. The viscosity and flow rate of the co-flowing liquid affect the number of modes observed in classical electrospray as well as their geometrical characteristics. In particular, we observe a two-dimensional whipping mode not described before. We also provide a qualitative description of some of the modes, including dripping, electrodripping, microdripping, the cone-jet mode, and both the two- and three-dimensional whipping modes.
Multifractal intermittency in granular flow through bottlenecks
Gella, D., Zuriguel, I., & Ortín, J.
Physical Review Letters
123
21
(2019)
We experimentally analyze the intermittent nature of granular silo flow when the discharge is controlled by an extracting belt at the bottom. We discover the existence of four different scenarios. For low extraction rates, the system is characterized by an on-off intermittency. When the extraction rate is increased the structure functions of the grains velocity increments, calculated for different lag times, reveal the emergence of multifractal intermittency. Finally, for very high extraction rates that approach the purely gravitational discharge, we observe that the dynamics become dependent on the outlet size. For large orifices the behavior is monofractal, whereas for small ones, the fluctuations of the velocity increments deviate from Gaussianity even for very large time lags.
Phagocyte-inspired smart microcapsules
Nikolov, S., Fernandez-Nieves, A., & Alexeev, A.
ACS Macro Letters
8
4
(2019)
Phagocytes protect the organism by ingesting harmful foreign particles and cells. We use mesoscale computer simulations to design a phagocyte-inspired active microcapsule that is capable of selectively capturing nanoparticles dispersed in solvent. Our fully synthetic microdevice is actuated by a temperature-sensitive microgel enclosed inside a perforated spherical shell. The shell pores are decorated with a copolymer brush that regulates the transport of solutes into the capsule interior. When exposed to an external stimulus, the microgel swells, expanding through the shell pores to make contact with the nanoparticle-rich solution surrounding the capsule. Upon removal of the external stimulus, the gel retracts back into the shell, bringing along with it captured nanoparticles. We probe how periodic application of the stimulus combined with nanoparticle-microgel adhesion enable selectivity and enhance capturing efficiency of our nature-inspired microdevice.
Simulating optical polarizing microscopy textures using Jones calculus: a review exemplified with nematic liquid crystal tori
Ellis, P. W., Pairam, E., & Fernández-Nieves, A.
Journal of Physics D: Applied Physics
52
21
(2019)
Simulated optical polarizing microscopy (OPM) textures can be used to help compare a director ansatz with an associated experimental OPM texture. Here, we present a pedagogical treatmement of a simulation formalism based on the method of Jones matrices. We focus on toroidal geometries as an example and perform computer simulations of the nematic textures seen between crossed-polarizers. For tangentially-anchored nematic tori, we compare qualitative and quantitative features between experimental and simulated OPM textures and discuss the influence of twist in the director field. In addition, we quantify the effect of averaging over multiple wavelengths, the effect of voxel size, how refraction affects the comparison between experimental and simulated OPM textures, and the effect of deviations from the toroidal shape. For homeotropically-anchored nematic tori, we adapt the classic escaped-radial director field found in homeotropically-anchored capillaries to a toroidal geometry to produce simulated OPM textures. Lastly, we show that the same signatures of twist in the tangentially-anchored nematic toroids persist in the homeotropically-anchored nematic toroids.
Spontaneous deswelling of microgels controlled by counterion clouds
Gasser, U., Scotti, A., & Fernandez-Nieves, A.
Physical Review E
99
4
(2019)
Concentrated poly(N-isopropylacrylamide) (pNIPAM) microgel suspensions at a fixed temperature below the deswelling transition of pNIPAM exhibit spontaneous particle deswelling. The microgels deswell before they are in direct contact and in polydisperse suspensions this deswelling is most pronounced for the largest microgel particles; as a consequence, the polydispersity of the suspension is reduced. Recently, we presented a model for this spontaneous deswelling that is based on the presence of counterions originating from charged groups on the surface of the pNIPAM microgels [A. Scotti et al., Proc. Natl. Acad. Sci. USA 113, 5576 (2016)]. Here we present numerical Poisson-Boltzmann calculations of the electrostatic potential and osmotic pressure inside and outside a pNIPAM microgel that could trigger the observed deswelling at high particle concentrations.
Swelling Thermodynamics and phase transitions of polymer gels
Dimitriyev, M. S., Chang, Y. W., Goldbart, P. M., & Fernández-Nieves, A.
Nano Futures
3
4
(2019)
We present a pedagogical review of the swelling thermodynamics and phase transitions of polymer gels. In particular, we discuss how features of the volume phase transition of the gel's osmotic equilibrium are analogous to other transitions described by mean-field models of binary mixtures, and the failure of this analogy at the critical point due to shear rigidity. We then consider the phase transition at fixed volume, a relatively unexplored paradigm for polymer gels that results in a phase-separated equilibrium consisting of coexisting solvent-rich and solvent-poor regions of gel. Again, the gel's shear rigidity is found to have a profound effect on the phase transition, here resulting in macroscopic shape change at constant volume of the sample, exemplified by the tunable buckling of toroidal samples of polymer gel. By drawing analogies with extreme mechanics, where large shape changes are achieved via mechanical instabilities, we formulate the notion of extreme thermodynamics, where large shape changes are achieved via thermodynamic instabilities, i.e. phase transitions.
A Brownian Ratchet Model Explains the Biased Sidestepping of Single-Headed Kinesin-3 KIF1A
Mitra, A., Suñé, M., Diez, S., Sancho, J. M., Oriola, D., & Casademunt, J.
Biophysical Journal
116
12
(2019)
The kinesin-3 motor KIF1A is involved in long-ranged axonal transport in neurons. To ensure vesicular delivery, motors need to navigate the microtubule lattice and overcome possible roadblocks along the way. The single-headed form of KIF1A is a highly diffusive motor that has been shown to be a prototype of a Brownian motor by virtue of a weakly bound diffusive state to the microtubule. Recently, groups of single-headed KIF1A motors were found to be able to sidestep along the microtubule lattice, creating left-handed helical membrane tubes when pulling on giant unilamellar vesicles in vitro. A possible hypothesis is that the diffusive state enables the motor to explore the microtubule lattice and switch protofilaments, leading to a left-handed helical motion. Here, we study the longitudinal rotation of microtubules driven by single-headed KIF1A motors using fluorescence-interference contrast microscopy. We find an average rotational pitch of ≃1.5≃1.5 μm, which is remarkably robust to changes in the gliding velocity, ATP concentration, microtubule length, and motor density. Our experimental results are compared to stochastic simulations of Brownian motors moving on a two-dimensional continuum ratchet potential, which quantitatively agree with the fluorescence-interference contrast experiments. We find that single-headed KIF1A sidestepping can be explained as a consequence of the intrinsic handedness and polarity of the microtubule lattice in combination with the diffusive mechanochemical cycle of the motor.
Active fingering instability in tissue spreading
Alert, R., Blanch-Mercader, C., & Casademunt, J.
Physical Review Letters
122
8
(2019)
During the spreading of epithelial tissues, the advancing tissue front often develops fingerlike protrusions. Their resemblance to traditional viscous fingering patterns in driven fluids suggests that epithelial fingers could arise from an interfacial instability. However, the existence and physical mechanism of such a putative instability remain unclear. Here, based on an active polar fluid model for epithelial spreading, we analytically predict a generic instability of the tissue front. On the one hand, active cellular traction forces impose a velocity gradient that leads to an accelerated front, which is, thus, unstable to long-wavelength perturbations. On the other hand, contractile intercellular stresses typically dominate over surface tension in stabilizing short-wavelength perturbations. Finally, the finite range of hydrodynamic interactions in the tissue selects a wavelength for the fingering pattern, which is, thus, given by the smallest between the tissue size and the hydrodynamic screening length. Overall, we show that spreading epithelia experience an active fingering instability based on a simple kinematic mechanism. Moreover, our results underscore the crucial role of long-range hydrodynamic interactions in the dynamics of tissue morphology.
Adaptación transcultural y características de la versión española de la escala COMFORT Behavior Scale en el paciente crítico pediátrico
Bosch-Alcaraz, A., Jordan, I., Olmos, J. G., & Falcó-Pegueroles, A.
Medicina Intensiva
(2019)
To determine the measurement properties of the Spanish version of the COMFORT Behavior Scale developed by van Dijk et al. (2000) in pediatric critical care patients.
Age-related decrease in resting-state functional connectivity in older adults
Farras-Permanyer, L., Mancho-Fora, N., Montalà-Flaquer, M., Bartrés-Faz, D., Vaqué- Alcázar, L., Peró-Cebollero, M., & Guàrdia- Olmos, J.
Neural Regeneration Research
14
9
(2019)
Age-related changes in the brain connectivity of healthy older adults have been widely studied in recent years, with some differences in the obtained results. Most of these studies showed decreases in general functional connectivity, but they also found increases in some particular regions and areas. Frequently, these studies compared young individuals with older subjects, but few studies compared different age groups only in older populations. The purpose of this study is to analyze whole-brain functional connectivity in healthy older adult groups and its network characteristics through functional segregation. A total of 114 individuals, 48 to 89 years old, were scanned using resting-state functional magnetic resonance imaging in a resting state paradigm and were divided into six different age groups (< 60, 60–64, 65–69, 70–74, 75–79, ≥ 80 years old). A partial correlation analysis, a pooled correlation analysis and a study of 3-cycle regions with prominent connectivity were conducted. Our results showed progressive diminution in the functional connectivity among different age groups and this was particularly pronounced between 75 and 79 years old. The oldest group (≥ 80 years old) showed a slight increase in functional connectivity compared to the other groups. This occurred possibly because of compensatory mechanism in brain functioning. This study provides information on the brain functional characteristics of every age group, with more specific information on the functional progressive decline, and supplies methodological tools to study functional connectivity characteristics. Approval for the study was obtained from the ethics committee of the Comisión de Bioética de la Universidad de Barcelona (approval No. PSI2012-38257) on June 5, 2012, and from the ethics committee of the Barcelona’s Hospital Clínic (approval No. 2009-5306 and 2011-6604) on October 22, 2009 and April 7, 2011 respectively.
Collective behavior of red blood cells in confined channels
Lázaro, G. R., Hernández-Machado, A., & Pagonabarraga, I.
The European Physical Journal E
42
4
(2019)
We study the flow properties of red blood cells in confined channels, when the channel width is comparable to the cell size. We focus on the case of intermediate concentrations when hydrodynamic interactions between cells play a dominant role. This regime is different to the case of low concentration in which the cells behave as hydrodynamically isolated. In this last case, the dynamic behavior is entirely controlled by the interplay between the interaction with the wall and the elastic response of the cell membrane. Our results highlight the different fluid properties when collective flow is present. The cells acquire a characteristic slipper shape, and parachute shapes are only observed at very large capillary numbers. We have characterized the spatial ordering and the layering by means of a pairwise correlation function. Focusing effects are observed at the core of the channel instead of at the lateral position typical of the single-train case. These results indicate that at these intermediate concentrations we observed at the microscale the first steps of the well-known macroscopic Fahraeus-Lindqvist effect. The rheological properties of the suspension are studied by means of the effective viscosity, with an expected shear-thinning behavior. Two main differences are obtained with respect to the single-train case. First, a large magnitude of the viscosity is obtained indicating a high resistance to flow. Secondly, the shear-thinning behavior is obtained at larger values of the capillary number respect to the single-train case. These results suggest that the phenomena of ordering in space and orientation occur at higher values of the capillary number.
CRISPR/Cas9-mediated generation of a tyrosine hydroxylase reporter iPSC line for live imaging and isolation of dopaminergic neurons
Calatayud, C., Carola, G., Fernández-Carasa, I., Valtorta, M., Jiménez-Delgado, S., Díaz, M., & Consiglio, A.
Scientific Reports
9
1
(2019)
Patient-specific induced pluripotent stem cells (iPSCs) are a powerful tool to investigate the molecular mechanisms underlying Parkinson’s disease (PD), and might provide novel platforms for systematic drug screening. Several strategies have been developed to generate iPSC-derived tyrosine hydroxylase (TH)-positive dopaminergic neurons (DAn), the clinically relevant cell type in PD; however, they often result in mixed neuronal cultures containing only a small proportion of TH-positive DAn. To overcome this limitation, we used CRISPR/Cas9-based editing to generate a human iPSC line expressing a fluorescent protein (mOrange) knocked-in at the last exon of the TH locus. After differentiation of the TH-mOrange reporter iPSC line, we confirmed that mOrange expression faithfully mimicked endogenous TH expression in iPSC-derived DAn. We also employed calcium imaging techniques to determine the intrinsic functional differences between dopaminergic and non-dopaminergic ventral midbrain neurons. Crucially, the brightness of mOrange allowed direct visualization of TH-expressing cells in heterogeneous cultures, and enabled us to isolate live mOrange-positive cells through fluorescence-activated cell sorting, for further differentiation. This technique, coupled to refined imaging and data processing tools, could advance the investigation of PD pathogenesis and might offer a platform to test potential new therapeutics for PD and other neurodegenerative diseases.
Impact of targeted attack on the spontaneous activity in spatial and biologically-inspired neuronal networks
Faci-Lázaro, S., Soriano, J., & Gómez-Gardeñes, J.
Chaos: An Interdisciplinary Journal of Nonlinear Science
29
8
(2019)
We study the structural and dynamical consequences of damage in spatial neuronal networks. Inspired by real in vitro networks, we construct directed networks embedded in a two-dimensional space and follow biological rules for designing the wiring of the system. As a result, synthetic cultures display strong metric correlations similar to those observed in real experiments. In its turn, neuronal dynamics is incorporated through the Izhikevich model adopting the parameters derived from observation in real cultures. We consider two scenarios for damage, targeted attacks on those neurons with the highest out-degree and random failures. By analyzing the evolution of both the giant connected component and the dynamical patterns of the neurons as nodes are removed, we observe that network activity halts for a removal of 50% of the nodes in targeted attacks, much lower than the 70% node removal required in the case of random failures. Notably, the decrease of neuronal activity is not gradual. Both damage scenarios portray “boosts” of activity just before full silencing that are not present in equivalent random (Erdös–Rényi) graphs. These boosts correspond to small, spatially compact subnetworks that are able to maintain high levels of activity. Since these subnetworks are absent in the equivalent random graphs, we hypothesize that metric correlations facilitate the existence of local circuits sufficiently integrated to maintain activity, shaping an intrinsic mechanism for resilience.
Using an Overlapping Time Interval Strategy to Study Diagnostic Instability in Mild Cognitive Impairment Subtypes
Facal, D., Guàrdia-Olmos, J., Pereiro, A. X., Lojo-Seoane, C., Peró, M., & Juncos-Rabadán, O.
Brain Sciences
9
9
(2019)
Background: Mild cognitive impairment (MCI) is a diagnostic label in which stability is typically low. The aim of this study was to examine temporal changes in the diagnosis of MCI subtypes by using an overlapping-time strategy; (2) Methods: The study included 435 participants aged over 50 years with subjective cognitive complaints and who completed at least one follow-up evaluation. The probability of transition was estimated using Bayesian odds ratios; (3) Results: Within the different time intervals, the controls with subjective cognitive complaints represented the largest proportion of participants, followed by sda-MCI at baseline and in the first five intervals of the follow-up, but not in the last eight intervals. The odds ratios indicated higher odds of conversion to dementia in sda-MCI and mda-MCI groups relative to na-MCI (e.g., interval 9–15 months—sda-MCI OR = 9 and mda-MCI OR = 3.36; interval 27–33—sda-MCI OR = 16 and mda-MCI = 5.06; interval 42–48—sda-MCI OR = 8.16 and mda-MCI = 3.45; interval 45–51—sda-MCI OR = 3.31 and mda-MCI = 1); (4) Conclusions: Notable patterns of instability consistent with the current literature were observed. The limitations of a prospective approach in the study of MCI transitions are discussed
A Comparison of Probabilistic Reasoning in Psychology Undergraduates in Italy and Spain: Seeking Cross-national Evidence
Agus, M., Peró, M., Guàrdia Olmos, J., Pessa, E., Figus, R., & Penna, M. P.
Eurasia Journal of Mathematics Science and Technology Education
15
10
(2019)
A cross-national comparison between Italy and Spain was conducted on probabilistic reasoning performance presented in verbal-numerical and graphical-pictorial formats. This study investigated the similarities and differences in Psychology undergraduates in these two countries (Italy n=290; Spain n=130) and attempted to identify aspects that might enhance the probability of a student belonging to one country. The findings underscored that Spanish students had higher levels of visuospatial abilities, more positive attitudes toward statistics, lower statistical anxiety, and higher confidence in the correctness of their responses. Additionally, they gave a higher number of correct responses to problems presented in a verbal-numerical format. These data suggest interesting insights and highlight the interactions among multiple layers of variables at the collective, contextual, and individual levels.
ARqueologia i col·leccionisme: Gabriel de Molina i els inicis de les excavacions a Empúries
Somoza, L. B., & Pujol, L. P.
Biblio 3w: Revista Bibliográfica de Geografía y Ciencias Sociales
1
(2019)
Archaeology and Collectionism: Gabriel de Molina and the beginning of the excavations at Empúries (Abastract) The year 2008 marked the centenary of the beginning of the archaeological excavations at the ancient Greco-Roman city of Empúries. Without wishing to deny the cultural and symbolic relevance of this anniversary, in the following pages we will explain that, in fact, the first interventions in this site are much older and, among other characters today almost forgotten, the civil servant Gabriel de Molina Ramos played an important role in them. Reason why we think of interest to investigate who he was and for what reason he was attracted to archaeology. This research is based on unpublished documents found in different Catalan and statewide archives. Keywords: Empúries, archaeology historigraphy, collectionism, liberalism, 19th Century
Brokers in a destination’s knowledge networks
Sanz-Ibáñez, C., Lozano, S., & Clavé, S. A.
Journal of destination marketing & management
11
120 129
(2019)
This paper applies a two-mode social network analysis approach to identify the brokers in knowledge networks resulting from interactions taking place at specialized seminars and courses organized in a tourism destination. Empirical findings show that technology and innovation centers can be the leading hub of ‘administered knowledge networks’ – understood as efficient knowledge governance arrangements – in which a wide variety of actors, including universities, private-sector associations, public organizations, and firms play complementary roles depending on the nature of the interactions (formal transfer versus informal exchange flows). These structures are found to be fundamental for the functioning of localized systems of learning.
Cognitive reserve and working memory in cognitive performance of adults with subjective cognitive complaints: longitudinal structural equation modelling
Lojo-Seoane, C., Facal, D., Guàrdia-Olmos, J., Pereiro, A. X., Campos-Magdaleno, M., Mallo, S. C., & Juncos-Rabadán, O.
International Psychogeriatrics
1 10
(2019)
To study the influence of cognitive reserve (CR) on cognitive performance of individuals with subjective cognitive complaints (SCCs) within a period of 36 months.
Development and initial validation of a theory of planned behaviour questionnaire to assess critical care nurses’ intention to use physical restraints
Via-Clavero, G., Guàrdia-Olmos, J., Gallart-Vivé, E., Arias-Rivera, S., Castanera-Duro, A., & Delgado-Hito, P.
Journal of Advanced Nursing
75
9
(2019)
To develop and psychometrically test a Theory of Planned Behaviour (TPB) questionnaire to assess nurses’ intention to use physical restraints (PRs) in intubated patients.
DISCOver: DIStributional approach based on syntactic dependencies for discovering COnstructions
Martí, M. A., Taulé, M., Kovatchev, V., & Salamó, M.
Corpus Linguistics and Linguistic Theory
(2019)
One of the goals in Cognitive Linguistics is the automatic identification and analysis of constructions, since they are fundamental linguistic units for understanding language. This article presents DISCOver, an unsupervised methodology for the automatic discovery of lexico-syntactic patterns that can be considered as candidates for constructions. This methodology follows a distributional semantic approach. Concretely, it is based on our proposed pattern-construction hypothesis: those contexts that are relevant to the definition of a cluster of semantically related words tend to be (part of) lexico-syntactic constructions. Our proposal uses Distributional Semantic Models for modelling the context taking into account syntactic dependencies. After a clustering process, we linked all those clusters with strong relationships and we use them as a source of information for deriving lexico-syntactic patterns, obtaining a total number of 220,732 candidates from a 100 million token corpus of Spanish. We evaluated the patterns obtained intrinsically, applying statistical association measures and they were also evaluated qualitatively by experts. Our results were superior to the baseline in both quality and quantity in all cases. While our experiments have been carried out using a Spanish corpus, this methodology is language independent and only requires a large corpus annotated with the parts of speech and dependencies to be applied.
Dosage analysis of the 7q1123 Williams region identifies BAZ1B as a major human gene patterning the modern human face and underlying self-domestication
Zanella, M., Vitriolo, A., Andirko, A., Martins, P. T., Sturm, S., O’Rourke, T., ... & Germain, P. L.
Science Advances
5
12
(2019)
We undertook a functional dissection of chromatin remodeler BAZ1B in neural crest (NC) stem cells (NCSCs) from a uniquely informative cohort of typical and atypical patients harboring 7q11.23 copy number variants. Our results reveal a key contribution of BAZ1B to NCSC in vitro induction and migration, coupled with a crucial involvement in NC-specific transcriptional circuits and distal regulation. By intersecting our experimental data with new paleogenetic analyses comparing modern and archaic humans, we found a modern-specific enrichment for regulatory changes both in BAZ1B and its experimentally defined downstream targets, thereby providing the first empirical validation of the human self-domestication hypothesis and positioning BAZ1B as a master regulator of the modern human face. In so doing, we provide experimental evidence that the craniofacial and cognitive/behavioral phenotypes caused by alterations of the Williams-Beuren syndrome critical region can serve as a powerful entry point into the evolution of the modern human face and prosociality
Ethical conflicts and their characteristics among critical care nurses
Lluch-Canut, T., Sequeira, C., Falcó-Pegueroles, A., Pinho, J. A., Rodrigues-Ferreira, A., Olmos, J. G., & Roldan-Merino, J.
Nursing Ethics
27
2
(2019)
Ethical conflict is a phenomenon that has been under study over the last three decades, especially the types moral dilemma and moral distress in the field of nursing care. However, ethical problems and their idiosyncrasies need to be further explored.
Food Storage among the Iberians of the Late Iron Age Northwest Mediterranean (ca 225-50 bc)
González Vázquez, M.
Journal of Mediterranean Archaeology
32
2
(2019)
Storage pits are one of the most common archaeological features of an area that comprises the Catalancoastal region and western Languedoc. Although some of these pits are found in the region from as earlyas the Neolithic period, it is not until the late Iron Age-early Roman period (ca. 225-50 bc) that theybecome pervasive in the archaeological record, and as such the prevailing tendency is to take these foodreserves as an indicator of increased social complexity, as evidence of the ability of the peasantry to producesurplus and as marking the completion of a diachronic process of sedentarisation, all three of which are traditionallylinked more generally to the practice of storage. Consequently, for the most part, this explanationgives a pivotal role to storage, but fails to address storage as an economic process in itself. With these scholarlymisconceptions in mind, I adopt a cross-cultural perspective in order to reconsider the role of storageas a crucial form of evidence for understanding economic structures, localised responses and the landscape.In connection with this, I suggest that the storage pits' function-to protect production from human (e.g.thieving) and natural threats-is an aspect of fundamental importance for any attempt to explain socialand cultural changes in Iberia from the beginning of Roman colonisation.
Formal modelling approaches to complexity science in Roman Studies: a manifesto
Brughmans, T., Hanson, J. W., Mandich, M. J., Romanowska, I., Rubio-Campillo, X., Carrignon, S., & Haas, T. D.
Theoretical Roman Archaeology Journal
2
1 19
(2019)
Complexity science refers to the theoretical research perspectives and the formal modelling tools designed to study complex systems. A complex system consists of separate entities interacting following a set of (often simple) rules that collectively give rise to unexpected patterns featuring vastly different properties than the entities that produced them. In recent years a number of case studies have shown that such approaches have great potential for furthering our understanding of the past phenomena explored in Roman Studies. We argue complexity science and formal modelling have great potential for Roman Studies by offering four key advantages: (1) the ability to deal with emergent properties in complex Roman systems; (2) the means to formally specify theories about past Roman phenomena; (3) the power to test aspects of these theories as hypotheses using formal modelling approaches; and (4) the capacity to do all of this in a transparent, reproducible, and cumulative scientific framework. We present a ten-point manifesto that articulates arguments for the more common use in Roman Studies of perspectives, concepts and tools from the broader field of complexity science, which are complementary to empirical inductive approaches. There will be a need for constant constructive collaboration between Romanists with diverse fields of expertise in order to usefully embed complexity science and formal modelling in Roman Studies.
Impact of supports and partnership on family quality of life
Balcells-Balcells, A., Giné, C., Guàrdia-Olmos, J., Summers, J. A., & Mas, J. M.
Research in Developmental Disabilities
85
50 60
(2019)
In recent decades, Family Quality of Life (FQOL) has emerged as a decisive construct, both to improve the living conditions of the families of people with disabilities and to assess the results on the services and supports that they receive.
The aim of this research is to determine the perception of the families regarding their support needs, the quality of their partnerships with professionals, and their FQOL and then identify to what extent the supports of early childhood intervention centers have a positive impact on the families’ FQOL while exploring whether the family–professional partnership has become a fundamental intervening factor of FQOL.
Impact of the intellectual disability severity in the Spanish Personal Outcomes Scale
Carbó-Carreté, M., Guàrdia-Olmos, J., Peró- Cebollero, M., & Giné, C.
Journal of Intellectual Disability Research
63
10
(2019)
The interest in measuring quality of life (QoL) in persons with intellectual disability (ID) has brought about a number of QoL measurements for this population. These measurements need to address two issues that have contributed to enhancing the current instruments. First, the necessity to develop measures with adequate psychometric properties, which has been discussed in recent studies, and second, the agreement between experts in analysing objective and subjective perspectives, as well as the use of self‐report to include the participation of the person with ID. The question that we set out to investigate in this paper is whether the measurements function properly for the person with ID, independent of their level of severity. We used the Spanish version of the Personal Outcomes Scale, as it is a psychometrically sound instrument and includes three sources of information (the person with ID, a professional and a family member).
Interrater agreement on behavioral executive function measures in adolescents with Attention Deficit Hyperactivity Disorder
Krieger, V., Amador-Campos, J. A., & Peró- Cebollero, M.
International Journal of Clinical and Health Psychology
19
2
(2019)
Though most children with Attention Deficit Hyperactivity Disorder (ADHD) show difficulties in behavioral measures of executive functions (EF), few studies have examined interrater agreement in these measures.Objective: To analyze the agreement between parents, teachers and self-reports of behavioral EF in adolescents with ADHD and controls. Method: A sample of 118 adolescents (75 with ADHD and 43 controls) was rated by parents, teachers and the adolescents themselves using the Comprehensive Executive Function Inventory. The intraclass correlation coefficient (ICC) and Bland and Altman methods were used to evaluate agreement. Results: The ICC between parents, teachers and self-report was poor or moderate in the group with ADHD; in the control group the agreement was fair to good. The Bland and Altman graphs show that, in the control group, most of the scores are below to the clinical cut-off point, while in the group with ADHD they are above. Conclusions: Agreement between all raters was low. Parents, teachers and adolescents agreed on the absence of deficits in behavioral EF in the control group, and on the presence of deficits in the group with ADHD, although they did not agree on the frequency of these deficits.
Las causas del absentismo de los estudiantes de Derecho según su propia opinión
Rubinat, M. T., Acedo, B. R., Chueca, P. A., i Ivern, X. M. T., Olmos, J. G., Presas, P., & Yarza, I. M.
Revista de educación y derecho. Education and law review
19
8
(2019)
El absentismo en las aulas de los estudiantes de Derecho se ha convertido recientemente en un lugar común de las preocupaciones del profesorado y de la administración universitaria. El objetivo del presente estudio, que cuenta con precedentes en los cursos 2007-2008 y 2009-2010, es identificar los motivos esgrimidos por los estudiantes del grado de Derecho de la UB para explicar las causas del fenómeno absentista. El trabajo, más allá de su vertiente científica, pretende convertirse en un instrumento para poder diseñar políticas, sobre todo docentes y académicas, para reducir el absentismo en aquellos ámbitos en que sea posible. El estudio se ha realizado a partir de la opinión recogida a una muestra de 577 estudiantes del grado durante la primavera del 2017, mediante un muestreo aleatorio simple y a través de un cuestionario con 18 preguntas cerradas sobre los motivos que llevan a los estudiantes a no asistir a clase, 5 variables sociodemográficas y una pregunta abierta final. Se ha realizado un análisis estadístico cuantitativo, un análisis factorial y un análisis cualitativo de las respuestas abiertas. Los resultados indican que los posibles factores vinculados con el absentismo tienen que ver, en un sentido amplio, con la metodología docente –en muchos casos todavía únicamente de tipo magistral– utilizada por los profesores; no son irrelevantes las causas debidas a la organización logística del estudiante, pero en todo caso son causas secundarias. Que los profesores dispongan de otros recursos metodológicos además de la clase magistral y saber otorgar valor añadido a las clases –desarrollando por tanto políticas docentes y formación del profesorado– se antojan como algunas de las soluciones a un fenómeno complejo y multicausal.
Lithic refits as a tool to reinforce postdepositional analysis
López-Ortega, E., Rodríguez-Álvarez, X. P., Ollé, A., & Lozano, S.
Archaeological and Anthropological Sciences
11
9
(2019)
Studies of archaeological assemblages recovered from palimpsests encounter difficulties related not only to their nature (the preservation of the remains), but also to the formation of the accumulation itself: the evidence of the different human occupations that the accumulation contains and its temporal resolution. Layer TD10.1 of Gran Dolina (Sierra de Atapuerca, Burgos, Spain) is a 1-m-thick palimpsest from which 48,000 faunal remains and more than 21,000 lithic artefacts have been recovered. Several interdisciplinary studies have shown that TD10.1 is not the result of an intense and long-term occupation of the cavity, but rather the consequence of several repeated occupation events. Additionally, micro-morphological analyses demonstrate that there were only minimal postdepositional disturbances of the sedimentary context containing the artefacts. This paper presents results obtained from the study of lithic refits in a sample from the TD10.1 assemblage, posing the hypothesis that the position and relative distance separating the refitted elements show that they were in fact found in primary position. While in other cases, “raw material units” have been used as a tool to distinguish activity areas and occupational episodes, in this study we use refits to learn about the possible movement—or lack thereof—of the artefacts within the area of the site due to postdepositional factors. The use of refits is proposed as a support or supplement to other kinds of analyses of the postdepositional processes that affect the formation of archaeological layers.
Los negocios de Caius Iuventius Albinus en la Bética
Remesal Rodríguez, J., & Díaz, J. M.
Journal of Roman Archaeology
32
224 249
(2019)
A orillas de los ríos Guadalquivir (Baetis) y Genil (Singilis), en el triángulo formado por las capitales de tres conventus de la Bética, Hispalis, Corduba y Astigi, se extienden los restos arqueológicos de casi un centenar de alfarerías productoras de ánforas del tipo Dressel 20 (fig. 1). Durante los tres primeros siglos d.C., el aceite de oliva producido en el interior de la Bética se comercializaba con estas ánforas globulares que fueron exportadas masivamente a todo el Imperio romano, siendo particularmente abundantes en Roma y en el limes germano/británico.
Neurofunctional activation patterns reflect differences in cognitive control associated with spelling skills in Spanish
Martínez-Ramos, A., Gómez-Velázquez, F. R., Peró-Cebollero, M., González-Garrido, A. A., Guàrdia-Olmos, J., Gudayol-Ferré, E., & Gallardo-Moreno, G. B.
Rev Mex Neuroci,
20
5
(2019)
On the Relationship between Subjective and Objective measures of VR experiences: a Case Study of a Serious Game for Museums International Symposium on Gamification and Games for Learning
I. Rodríguez, A. Puig, J.A. Rodríguez-Aguilar, JL. Arcos, S. Cebrián, A. Bogdanovych, N. Morera, R. Piqué, & A. Palomo.
CEUR-WS.org
2497
(2019)
In this paper we present a Virtual Reality game related to Cultural Heritage. We contribute with an analysis of subjective measures taken from questionnaires filled by users after the VR experience, and objective measures taken from logs during the VR game. Specifically, we were interested on study data globally and in groups of user behaviour. Analysing data globally we see a high value of users’ subjective perceptions. Nevertheless, we found differences of subjective measures when splitting the Novice group. Specifically, the subjective perception of Strugglers is considerably lower than the rest of groups, and this difference is significant. Then, we propose strategies to provide a better experience to Strugglers. We also found correlations between objective and subjective data when they were analysed globally (i.e. without using groups), but these measures did not correlate when they were analysed using behaviour groups
Palaeodemographic modelling supports a population bottleneck during the Pleistocene- Holocene transition in Iberia
de Pablo, J. F. L., Gutiérrez-Roig, M., Gómez- Puche, M., McLaughlin, R., Silva, F., & Lozano, S.
Nature Communications,
10
1
(2019)
Demographic change lies at the core of debates on genetic inheritance and resilience to climate change of prehistoric hunter-gatherers. Here we analyze the radiocarbon record of Iberia to reconstruct long-term changes in population levels and test different models of demographic growth during the Last Glacial-Interglacial transition. Our best fitting demographic model is composed of three phases. First, we document a regime of exponential population increase during the Late Glacial warming period (c.16.6-12.9 kya). Second, we identify a phase of sustained population contraction and stagnation, beginning with the cold episode of the Younger Dryas and continuing through the first half of the Early Holocene (12.9-10.2 kya). Finally, we report a third phase of density-dependent logistic growth (10.2-8 kya), with rapid population increase followed by stabilization. Our results support a population bottleneck hypothesis during the Last Glacial-Interglacial transition, providing a demographic context to interpret major shifts of prehistoric genetic groups in south-west Europe.
Qualitative Evaluation Framework for Paraphrase Identification
Kovatchev, V., Martí, M. A., Salamó, M. & Beltran, J.
Proceedings of the 12th Recent Advances in Natural Language Processing conference.
(2019)
In this paper, we present a new approach for the evaluation, error analysis, and interpretation of supervised and unsupervised Paraphrase Identification (PI) systems. Our evaluation framework makes use of a PI corpus annotated with linguistic phenomena to provide a better understanding and interpretation of the performance of various PI systems. Our approach allows for a qualitative evaluation and comparison of the PI models using human interpretable categories. It does not require modification of the training objective of the systems and does not place additional burden on the developers. We replicate several popular supervised and unsupervised PI systems. Using our evaluation framework we show that: 1) Each system performs differently with respect to a set of linguistic phenomena and makes qualitatively different kinds of errors; 2) Some linguistic phenomena are more challenging than others across all systems.
Sobre un esgrafiado cononomástica ibérica del Tossal de Cal Montblanc (Albesa, Lleida)
Revilla Calvo, V., & Velaza Frías, J.
Palaeohispanica. Revista Sobre Lenguas Y Culturas De La Hispania Antigua
19
189 195
(2019)
La excavación de un asentamiento rural cercano a Lleida ha permitido recuperar un importante contexto cerámico datado entre finales del siglo I e inicios del II d.C. El depósito incluye una amplia representación de terra sigillata y vajillas de uso culinario del periodo, generalmente con pocas señales de uso. Con todo, el interés del repertorio reside en la diversidad y cantidad de los esgrafiados conservados. Los textos se escribieron casi exclusivamente en latín, pero incluyen algún ejemplo en griego. Su contenido se limita a representaciones onomásticas (en latín, griego y autóctonas), aunque también se identifican indicaciones de propiedad y expresiones insultantes o jocosas. En este artículo se analiza uno de los fragmentos, perteneciente a una jarra en cerámica engobada (una producción característica del Alto Imperio en el territorio), que parece conservar una indicación onomástica ibérica y tal vez un teónimo. Esta hipótesis conferiría un carácter votivo a la inscripción. La composición y cronología del conjunto, procedente de un asentamiento situado en la periferia de un municipium romano, permite hacer algunas consideraciones sobre la evolución de la onomástica autóctona en época imperial, así como sobre el contexto cultural y religioso en el que se inserta esta onomástica.
The Animal Cancer Cachexia Score (ACASCO)
Betancourt, A., Busquets, S., Ponce, M., Toledo, M., Guàrdia-Olmos, J., Peró-Cebollero, M., & Argilés, J. M.
Animal models and experimental medicine
2
3
(2019)
None of the published studies involving cancer cachexia experimental models have included a measure of the severity of the syndrome like the scoring system previously developed for human subjects. The aim of the present investigation was to define and validate a cachexia score usable in both rat and mouse tumor models.
The Economy of Laetanian Wine: A Conceptual Framework to Analyse an Intensive/Specialized Winegrowing Production System and Trade (First Century BC to Third Century AD)
Martín Oliveras, A., & Revilla Calvo, V.
In Finding the Limits of the Limes
129 164
(2019)
The Roman economy has been defined as an agrarian regime, where wheat was mainly cultivated combined with livestock farming and intensive cash crops such as wine and olive oil. Possibilities for economic growth in a winegrowing area such as the Laetanian region in Hispania Citerior depended upon changes in agrarian productivity but were subject to agro-ecological and agroeconomic endowments that could affect the settlement patterns, the fluctuations in population, the forms of production related to the vineyard crop capacities, the spread of new techniques of cultivation and processing and the adoption of new technological advances. The combination of these factors explains how comparative advantages arose from other winegrowing territories, achieved through intensification and specialization processes that generated an increase of winemaking production surplus capable of being traded in different overseas markets.
The development of dynamicity in the acquisition of Spanish by Chinese learners
Sun, Y., Díaz, L., & Taulé, M.
ITL-International Journal of Applied Linguistics
170
1
(2019)
The acquisition of aspect in L2 is influenced by the properties of the lexical-aspectual class, coercion at the syntactic-pragmatic interface and grounding information (foreground and background) in discourse. This paper addresses how these linguistic functions influence the acquisition of Spanish aspectual past tenses (pretérito indefinido and pretérito imperfecto) by Mandarin Chinese learners. The results show that activities and accomplishments are more problematic for learners to acquire and that dynamicity, rather than telicity, plays a determinant role for Chinese learners. Moreover, factors concerning coercion – a pragmatic and discourse mechanismremain difficult to master at C1. Our results also support the Discourse Hypothesis, though showing different patterns of association (lexical and grammatical aspect) across levels. We conclude that an integrative perspective gives a better account of the acquisition process of Spanish aspectual tenses
A Sizer model for cell differentiation in Arabidopsis thaliana root growth
Pavelescu, Irina; Vilarrasa-Blasi, Josep; Planas-Riverola, Ainoa; Gonzalez-Garcia, Mary-Paz; Cano-Delgado, Ana I; Ibañes, Marta
MOLECULAR SYSTEMS BIOLOGY
14
e7687
(2018)
Plant roots grow due to cell division in the meristem and subsequent cell elongation and differentiation, a tightly coordinated process that ensures growth and adaptation to the changing environment. How the newly formed cells decide to stop elongating becoming fully differentiated is not yet understood. To address this question, we established a novel approach that combines the quantitative phenotypic variability of wild-type Arabidopsis roots with computational data from mathematical models. Our analyses reveal that primary root growth is consistent with a Sizer mechanism, in which cells sense their length and stop elongating when reaching a threshold value. The local expression of brassinosteroid receptors only in the meristem is sufficient to set this value. Analysis of roots insensitive to BR signaling and of roots with gibberellin biosynthesis inhibited suggests distinct roles of these hormones on cell expansion termination. Overall, our study underscores the value of using computational modeling together with quantitative data to understand root growth.
Redundancy and cooperation in Notch intercellular signaling
Luna-Escalante, Juan C; Formosa-Jordan, Pau; Ibañes, Marta
DEVELOPMENT
145
UNSP dev154807
(2018)
During metazoan development, Notch signaling drives spatially coordinated differentiation by establishing communication between adjacent cells. This occurs through either lateral inhibition, in which adjacent cells acquire distinct fates, or lateral induction, in which all cells become equivalent. Notch signaling is commonly activated by several distinct ligands, each of which drives signaling with a different efficiency upon binding to the Notch receptor of adjacent cells. Moreover, these ligands can also be distinctly regulated by Notch signaling. Under such complex circumstances, the overall spatial coordination becomes elusive. Here, we address this issue through both mathematical and computational analyses. Our results show that when two ligands have distinct efficiencies and compete for the same Notch receptor, they cooperate to drive new signaling states, thereby conferring additional robustness and evolvability to Notch signaling. Counterintuitively, whereas antagonistically regulated ligands cooperate to drive and enhance the response that is expected from the more efficient ligand, equivalently regulated ligands coordinate emergent spatial responses that are dependent on both ligands. Our study highlights the importance of ligand efficiency in multi-ligand scenarios, and can explain previously reported complex phenotypes.
Physical properties of voltage gated pores
Ramirez-Piscina, Laureano; Sancho, Jose M
EUROPEAN PHYSICAL JOURNAL B
91
(2018)
Experiments on single ionic channels have contributed to a large extent to our current view on the function of cell membrane. In these experiments the main observables are the physical quantities: ionic concentration, membrane electrostatic potential and ionic fluxes, all of them presenting large fluctuations. The classical theory of Goldman-Hodking-Katz assumes that an open channel can be well described by a physical pore where ions follow statistical physics. Nevertheless real molecular channels are active pores with open and close dynamical states. By skipping the molecular complexity of real channels, here we present the internal structure and calibration of two active pore models. These models present a minimum set of degrees of freedom, specifically ion positions and gate states, which follow Langevin equations constructed from a unique potential energy functional and by using standard rules of statistical physics. Numerical simulations of both models are implemented and the results show that they have dynamical properties very close to those observed in experiments of Na and K molecular channels. In particular a significant effect of the external ion concentration on gating dynamics is predicted, which is consistent with previous experimental observations. This approach can be extended to other channel types with more specific phenomenology.
A unified description of colloidal thermophoresis
Burelbach, Jerome; Frenkel, Daan; Pagonabarraga, Ignacio; Eiser, Erika
EUROPEAN PHYSICAL JOURNAL E
41
7
(2018)
We use the dynamic length and time scale separation in suspensions to formulate a general description of colloidal thermophoresis. Our approach allows an unambiguous definition of separate contributions to the colloidal flux and clarifies the physical mechanisms behind non-equilibrium motion of colloids. In particular, we derive an expression for the interfacial force density that drives single-particle thermophoresis in non-ideal fluids. The issuing relations for the transport coefficients explicitly show that interfacial thermophoresis has a hydrodynamic character that cannot be explained by a purely thermodynamic consideration. Our treatment generalises the results from other existing approaches, giving them a clear interpretation within the framework of non-equilibrium thermodynamics.
Effects of Heterogeneous Social Interactions on Flocking Dynamics
Carmen Miguel, M.; Parley, Jack T; Pastor-Satorras, Romualdo
PHYSICAL REVIEW LETTERS
120
068303
(2018)
Social relationships characterize the interactions that occur within social species and may have an important impact on collective animal motion. Here, we consider a variation of the standard Vicsek model for collective motion in which interactions are mediated by an empirically motivated scale-free topology that represents a heterogeneous pattern of social contacts. We observe that the degree of order of the model is strongly affected by network heterogeneity: more heterogeneous networks show a more resilient ordered state, while less heterogeneity leads to a more fragile ordered state that can be destroyed by sufficient external noise. Our results challenge the previously accepted equivalence between the static Vicsek model and the equilibrium XY model on the network of connections, and point towards a possible equivalence with models exhibiting a different symmetry.
Micro-flock patterns and macro-clusters in chiral active Brownian disks
Levis, Demian; Liebchen, Benno
JOURNAL OF PHYSICS-CONDENSED MATTER
30
084001
(2018)
Chiral active particles (or self-propelled circle swimmers) feature a rich collective behavior, comprising rotating macro-clusters and micro-flock patterns which consist of phase-synchronized rotating clusters with a characteristic self-limited size. These patterns emerge from the competition of alignment interactions and rotations suggesting that they might occur generically in many chiral active matter systems. However, although excluded volume interactions occur naturally among typical circle swimmers, it is not yet clear if macro-clusters and micro-flock patterns survive their presence. The present work shows that both types of pattern do survive but feature strongly enhance fluctuations regarding the size and shape of the individual clusters. Despite these fluctuations, we find that the average micro-flock size still follows the same characteristic scaling law as in the absence of excluded volume interactions, i.e. micro-flock sizes scale linearly with the single-swimmer radius.
Multiscale unfolding of real networks by geometric renormalization
G. García-Pérez, M. Boguñá i M. Á. Serrano
Nature Physics
(2018)
Symmetries in physical theories denote invariance under some transformation, such as self-similarity under a change of scale. The renormalization group provides a powerful framework to study these symmetries, leading to a better understanding of the universal properties of phase transitions. However, the small-world property of complex networks complicates application of the renormalization group by introducing correlations between coexisting scales. Here, we provide a framework for the investigation of complex networks at different resolutions. The approach is based on geometric representations, which have been shown to sustain network navigability and to reveal the mechanisms that govern network structure and evolution. We define a geometric renormalization group for networks by embedding them into an underlying hidden metric space. We find that real scale-free networks show geometric scaling under this renormalization group transformation. We unfold the networks in a self-similar multilayer shell that distinguishes the coexisting scales and their interactions. This in turn offers a basis for exploring critical phenomena and universality in complex networks. It also affords us immediate practical applications, including high-fidelity smaller-scale replicas of large networks and a multiscale navigation protocol in hyperbolic space, which betters those on single layers.
Quantitative account of social interactions in a mental health care ecosystem: cooperation, trust and collective action
Cigarini, Anna; Vicens, Julian; Duch, Jordi; Sanchez, Angel; Perello, Josep
SCIENTIFIC REPORTS
8
3794
(2018)
Mental disorders have an enormous impact in our society, both in personal terms and in the economic costs associated with their treatment. In order to scale up services and bring down costs, administrations are starting to promote social interactions as key to care provision. We analyze quantitatively the importance of communities for effective mental health care, considering all community members involved. By means of citizen science practices, we have designed a suite of games that allow to probe into different behavioral traits of the role groups of the ecosystem. The evidence reinforces the idea of community social capital, with caregivers and professionals playing a leading role. Yet, the cost of collective action is mainly supported by individuals with a mental condition - which unveils their vulnerability. The results are in general agreement with previous findings but, since we broaden the perspective of previous studies, we are also able to find marked differences in the social behavior of certain groups of mental disorders. We finally point to the conditions under which cooperation among members of the ecosystem is better sustained, suggesting how virtuous cycles of inclusion and participation can be promoted in a 'care in the community' framework.
Editorial for the topical issue on the Continuous Time Random Walk
Kutner, Ryszard; Masoliver, Jaume
EUROPEAN PHYSICAL JOURNAL B
91
40
(2018)
Contribution to the Topical Issue “Continuous Time Random Walk Still Trendy: Fifty-year History, Current State and Outlook”, edited by Ryszard Kutner and Jaume Masoliver.
Advances in colloidal manipulation and transport via hydrodynamic interactions
Martinez-Pedrero, F.; Tierno, P.
JOURNAL OF COLLOID AND INTERFACE SCIENCE
519
296 311
(2018)
In this review article, we highlight many recent advances in the field of micromanipulation of colloidal particles using hydrodynamic interactions (HIs), namely solvent mediated long-range interactions. At the micrsocale, the hydrodynamic laws are time reversible and the flow becomes laminar, features that allow precise manipulation and control of colloidal matter. We focus on different strategies where externally operated microstructures generate local flow fields that induce the advection and motion of the surrounding components. In addition, we review cases where the induced flow gives rise to hydrodynamic bound states that may synchronize during the process, a phenomenon essential in different systems such as those that exhibit self-assembly and swarming. (C) 2018 Elsevier Inc. All rights reserved.
Cuantificar las economías antiguas. Problemas y métodos.
Pérez González, J., Morvan M., Prignano, L., Morer, I., Díaz-Guilera, A., Bermúdez Lorenzo, J.M., Remesal Rodríguez, J.
INSTRUMENTA 60
251 280
(2018)
Reconstruir lo roto. Un método para vincular entre sí las inscripciones del Testaccio
Synchronization invariance under network structural transformations
Arola-Fernandez, L ; Diaz-Guilera, A; Arenas, A
PHYSICAL REVIEW E
97
060301
(2018)
Synchronization processes are ubiquitous despite the many connectivity patterns that complex systems can show. Usually, the emergence of synchrony is a macroscopic observable; however, the microscopic details of the system, as, e.g., the underlying network of interactions, is many times partially or totally unknown. We already know that different interaction structures can give rise to a common functionality, understood as a common macroscopic observable. Building upon this fact, here we propose network transformations that keep the collective behavior of a large system of Kuramoto oscillators invariant. We derive a method based on information theory principles, that allows us to adjust the weights of the structural interactions to map random homogeneous in-degree networks into random heterogeneous networks and vice versa, keeping synchronization values invariant. The results of the proposed transformations reveal an interesting principle; heterogeneous networks can be mapped to homogeneous ones with local information, but the reverse process needs to exploit higher-order information. The formalism provides analytical insight to tackle real complex scenarios when dealing with uncertainty in the measurements of the underlying connectivity structure.
Longitudinal Estimation of the Clinically Significant Change in the Treatment of Major Depression Disorder
Canete-Masse, C ; Pero-Cebollero, M ; Gudayol-Ferre, E; Guardia-Olmos, J
FRONTIERS IN PSYCHOLOGY
9
1406
(2018)
Background: Although major depressive disorder is usually treated with antidepressants, only 50-70% of the patients respond to this treatment. This study applied Jacobson and Truax's (1991) methodology (reliable change index, RCI) to a sample of depressive patients being treated with one of two antidepressants to evaluate their functioning and the effect of certain variables such as severity and age.
Method: Seventy-three depressive patients medicated with Escitalopram (n = 37) or Duloxetine (n = 36) were assessed using the Hamilton depression rating scale over a 24-week period.
Results: They indicate that the RCI stabilizes in an absolute way starting in week 16, and it is not until week 24 that all of the patients become part of the functional population. We found limited statistical significance with respect to the RCI and the external variables.
Conclusion: Our study suggests the need to accompany the traditional statistical methodology with some other clinical estimation systems capable of going beyond a simple subtraction between pre and posttreatment values. Hence, it is concluded that RCI estimations could be stronger and more stable than the classical statistical techniques.
A Complex Network Framework to Model Cognition: Unveiling Correlation Structures from Connectivity
Rosell-Tarrago, G ; Cozzo, E ; Diaz-Guilera, A
COMPLEXITY
1918753
(2018)
Several approaches to cognition and intelligence research rely on statistics-based model testing, namely, factor analysis. In the present work, we exploit the emerging dynamical system perspective putting the focus on the role of the network topology underlying the relationships between cognitive processes. We go through a couple of models of distinct cognitive phenomena and yet find the conditions for them to be mathematically equivalent. We find a nontrivial attractor of the system that corresponds to the exact definition of a well-known network centrality and hence stresses the interplay between the dynamics and the underlying network connectivity, showing that both of the two are relevant. Correlation matrices evince there must be a meaningful structure underlying real data. Nevertheless, the true architecture regarding the connectivity between cognitive processes is still a burning issue of research. Regardless of the network considered, it is always possible to recover a positive manifold of correlations. Furthermore, we show that different network topologies lead to different plausible statistical models concerning the correlation structure, ranging from one to multiple factor models and richer correlation structures.
Magnetically tunable bidirectional locomotion of a self-assembled nanorod-sphere propeller
Garcia-Torres, J ; Calero, C ; Sagues, F; Pagonabarraga, I ; Tierno, P
NATURE COMMUNICATIONS
9
1663
(2018)
Field-driven direct assembly of nanoscale matter has impact in disparate fields of science. In microscale systems, such concept has been recently exploited to optimize propulsion in viscous fluids. Despite the great potential offered by miniaturization, using self-assembly to achieve transport at the nanoscale remains an elusive task. Here we show that a hybrid propeller, composed by a ferromagnetic nanorod and a paramagnetic microsphere, can be steered in a fluid in a variety of modes, from pusher to puller, when the pair is dynamically actuated by a simple oscillating magnetic field. We exploit this unique design to build more complex structures capable of carrying several colloidal cargos as microscopic trains that quickly disassemble at will under magnetic command. In addition, our prototype can be extended to smaller nanorods below the diffraction limit, but still dynamically reconfigurable by the applied magnetic field.
Laning, thinning and thickening of sheared colloids in a two-dimensional Taylor-Couette geometry
Ortiz-Ambriz, A ; Gerloff, S ; Klapp, SHL ; Ortin, J; Tierno, P
SOFT MATTER
14
24
(2018)
We investigate the dynamics and rheological properties of a circular colloidal cluster that is continuously sheared by magnetic and optical torques in a two-dimensional (2D) Taylor-Couette geometry. By varying the two driving fields, we obtain the system flow diagram and report the velocity profiles along the colloidal structure. We then use the inner magnetic trimer as a microrheometer, and observe continuous thinning of all particle layers followed by thickening of the third one above a threshold field. Experimental data are supported by Brownian dynamics simulations. Our approach gives a unique microscopic view on how the structure of strongly confined colloidal matter weakens or strengthens upon shear, envisioning the engineering of rheological devices at the microscales.
A SYSTEMATIC REVIEW OF SIMULATION PROCEDURES FOR fMRI CONNECTIVITY STUDIES
Pero-Cebollero, M; Guardia-Olmos, J ; Mancho-Fora, N
ADVANCES AND APPLICATIONS IN STATISTICS
53
1
(2018)
The strategies used to study functional or effective connectivity in fMRI data are mainly based on the application of correlation studies, structural equation models (SEM), dynamic causal modelling (DCM), or the Granger causality model (GCM), while some contributions focus their attention on simulation studies. Although the tradition is scarce, this increase of the latter studies has become steeper in the last five years. In this work, we present a systematic study and analysis of simulation studies with fMRI data for the analysis of brain connectivity. We conducted a search on the Web of Science (WoS) and PubMed and eventually we reviewed a total of 134 studies. The most remarkable finding is a lack of information on the simulation procedure. For example, 17 works did not specify the model used to generate the signal, 36 did not indicate the model's white noise addition in the signal generated, and 52 did not detail the design under which the data had been generated. Under these circumstances, it is difficult to compare the different contributions in order to identify the best strategies to simulate data for the study of brain connectivity in fMRI works. However, it is important to note the emergence of the so-called third-generation simulation models, which consider the brain as a complex, dynamical system model. This kind of model to simulate brain activity will change the state of the art in this matter, and it might be a good tool to assess the different analytical procedures to study effective connectivity.
Assembly and transport of nematic colloidal swarms above photo-patterned defects and surfaces
Straube, AV; Pages, JM ; Ortiz-Ambriz, A; Tierno, P ; Ignes-Mullol, J ; Sagues, F
NEW JOURNAL OF PHYSICS
20
075006
(2018)
We investigate the dynamic assembly and swarm translocation of anisometric colloidal particles dispersed in a nematic liquid crystal and driven above a photosensitive surface. We use liquid crystal-enabled electrophoresis to propel these particles via an alternating electric field perpendicular to the sample cell. By manipulating the anchoring conditions on one surface of the experimental cell, we obtain a spatially extended spiral pattern of the liquid crystal orientation that induces the dynamic assembly of a rotating colloidal mill. This structure can be transported by translocating the topological defect above the photosensitive surface. We complement our findings with a theoretical model that captures the basic physics of the process, by formulating an analytic equation for the director field above the surface. Our reconfigurable nematic assemblies may be used as a test bed for complex swarming behaviour in biological and artificial microscale systems.
A dynamic vaccination strategy to suppress the recurrent epidemic outbreaks
Chen, DD ; Zheng, MH; Zhao, M ; Zhang, Y
CHAOS SOLITONS & FRACTALS
113
108 114
(2018)
Efficient vaccination strategy is crucial for controlling recurrent epidemic spreading on networks. In this paper, based on the analysis of real epidemic data and simulations, it's found that the risk indicator of recurrent epidemic outbreaks could be determined by the ratio of the epidemic infection rate of the year to the average infected density of the former year. According to the risk indicator, the dynamic vaccination probability of each year can be designed to suppress the epidemic outbreaks. Our simulation results show that the dynamic vaccination strategy could effectively decrease the maximal and average infected density, and meanwhile increase the time intervals of epidemic outbreaks and individuals attacked by epidemic. In addition, our results indicate that to depress the influenza outbreaks, it is not necessary to keep the vaccination probability high every year; and adjusting the vaccination probability at right time could decrease the outbreak risks with lower costs. Our findings may present a theoretical guidance for the government and the public to control the recurrent epidemic outbreaks. (C) 2018 Elsevier Ltd. All rights reserved.
Metabolic plasticity in synthetic lethal mutants: Viability at higher cost
Massucci, FA ; Sagues, F ; Serrano, MA
PLOS COMPUTATIONAL BIOLOGY
14
e1005949
(2018)
The most frequent form of pairwise synthetic lethality (SL) in metabolic networks is known as plasticity synthetic lethality. It occurs when the simultaneous inhibition of paired functional and silent metabolic reactions or genes is lethal, while the default of the functional partner is backed up by the activation of the silent one. Using computational techniques on bacterial genome-scale metabolic reconstructions, we found that the failure of the functional partner triggers a critical reorganization of fluxes to ensure viability in the mutant which not only affects the SL pair but a significant fraction of other interconnected reactions, forming what we call a SL cluster. Interestingly, SL clusters show a strong entanglement both in terms of reactions and genes. This strong overlap mitigates the acquired vulnerabilities and increased structural and functional costs that pay for the robustness provided by essential plasticity. Finally, the participation of coessential reactions and genes in different SL clusters is very heterogeneous and those at the intersection of many SL clusters could serve as supertargets for more efficient drug action in the treatment of complex diseases and to elucidate improved strategies directed to reduce undesired resistance to chemicals in pathogens.
Epidemic spreading in modular time-varying networks
Nadini, M ; Sun, KY ; Ubaldi, E ; Starnini, M ; Rizzo, A ; Perra, N
SCIENTIFIC REPORTS
8
2352
(2018)
We investigate the effects of modular and temporal connectivity patterns on epidemic spreading. To this end, we introduce and analytically characterise a model of time-varying networks with tunable modularity. Within this framework, we study the epidemic size of Susceptible-Infected-Recovered, SIR, models and the epidemic threshold of Susceptible-Infected-Susceptible, SIS, models. Interestingly, we find that while the presence of tightly connected clusters inhibits SIR processes, it speeds up SIS phenomena. In this case, we observe that modular structures induce a reduction of the threshold with respect to time-varying networks without communities. We confirm the theoretical results by means of extensive numerical simulations both on synthetic graphs as well as on a real modular and temporal network.
Collective motion of active Brownian particles with polar alignment
Martin-Gomez, A ; Levis, D ; Diaz-Guilera, A ; Pagonabarraga, I
SOFT MATTER
14
14
(2018)
We present a comprehensive computational study of the collective behavior emerging from the competition between self-propulsion, excluded volume interactions and velocity-alignment in a two-dimensional model of active particles. We consider an extension of the active brownian particles model where the self-propulsion direction of the particles aligns with the one of their neighbors. We analyze the onset of collective motion (flocking) in a low-density regime (10% surface area) and show that it is mainly controlled by the strength of velocity-alignment interactions: the competition between self-propulsion and crowding effects plays a minor role in the emergence of flocking. However, above the flocking threshold, the system presents a richer pattern formation scenario than analogous models without alignment interactions (active brownian particles) or excluded volume effects (Vicsek-like models). Depending on the parameter regime, the structure of the system is characterized by either a broad distribution of finite-sized polar clusters or the presence of an amorphous, highly fluctuating, large-scale traveling structure which can take a lane-like or band-like form (and usually a hybrid structure which is halfway in between both). We establish a phase diagram that summarizes collective behavior of polar active brownian particles and propose a generic mechanism to describe the complexity of the large-scale structures observed in systems of repulsive self-propelled particles.
Rheological behavior of colloidal suspension with long-range interactions
Arietaleaniz, S ; Malgaretti, P ; Pagonabarraga, I ; Hidalgo, RC
PHYSICAL REVIEW E
98
042603
(2018)
In this work, we study the constitutive behavior of interacting colloidal suspensions for moderate and high concentrations. Specifically, using a lattice Boltzmann solver, we numerically examine suspensions flowing through narrow channels, and explore the significance of the interaction potential strength on the system's macroscopic response. When only a short-range interaction potential is considered, a Newtonian behavior is always recovered and the system's effective viscosity mostly depends on the suspension concentration. However, when using a Lennard-Jones potential we identify two rheological responses depending on the interaction strength, the volume fraction, and the pressure drop. Exploiting a model proposed in the literature we rationalize the simulation data and propose scaling relations to identify the relevant energy scales involved in these transport processes. Moreover, we find that the spatial distribution of colloids in layers parallel to the flow direction does not correlate with changes in the system macroscopic response; but, interestingly, the rheology changes do correlate with the spatial distribution of colloids within individual layers. Namely, suspensions characterized by a Newtonian response display a cubiclike structure of the colloids within individual layers, whereas for suspensions with non-Newtonian response colloids organize in a hexagonal structure.
Unraveling the Operational Mechanisms of Chemically Propelled Motors with Micropumps
Esplandiu, MJ ; Zhang, K ; Fraxedas, J ; Sepulveda, B ; Reguera, D
ACCOUNTS OF CHEMICAL RESEARCH
51
1921 1930
(2018)
CONSPECTUS: The development of effective autonomous micro- and nanomotors relies on controlling fluid motion at interfaces. One of the main challenges in the engineering of such artificial machines is the quest for efficient mechanisms to power them without using external driving forces. In the past decade, there has been an important increase of man-made micro- and nanomotors fueled by self-generated physicochemical gradients. Impressive proofs of concept of multitasking machines have been reported demonstrating their capabilities for a plethora of applications. While the progress toward applications is promising, there are still open questions on fundamental physicochemical aspects behind the mechanical actuation, which require more experimental and theoretical efforts. These efforts are not merely academic but will open the door for an efficient and practical implementation of such promising devices.
In this Account, we focus on chemically driven motors whose motion is the result of a complex interplay of chemical reactions and (electro)hydrodynamic phenomena. A reliable study of these processes is rather difficult with mobile objects like swimming motors. However, pumps, which are the immobilized motor counterparts, emerge as simple manufacturing and well-defined platforms for a better experimental probing of the mechanisms and key parameters controlling the actuation.
Here we review some recent studies using a new methodology that has turned out to be very helpful to characterize micropump chemomechanics. The aim was to identify the redox role of the motor components, to map the chemical reaction, and to quantify the relevant electrokinetic parameters (e.g., electric field and fluid flow). This was achieved by monitoring the velocity of differently charged tracers and by fluorescence imaging of the chemical species involved in the chemical reaction, for example, proton gradients. We applied these techniques to different systems of interest. First, we probed bimetallic pumps as counterparts of the pioneering bimetallic swimmers. We corroborated that fluid motion was due to a self-generated electro-osmotic mechanism driven by the redox decomposition of H2O2. In addition, we analyzed by simulations the key parameters that yield an optimized operation. Moreover, we accomplished a better assessment of the importance of surface chemistry on the metal electrochemical response, highlighting its relevance in controlling the redox role of the metals and motion direction.
Second, we focused on metallic and semiconductor micropumps to analyze light-controlled motion mechanisms through photoelectrochemical decomposition of fuels. These pumps were driven by visible light and could operate using just water as fuel. In these systems, we found a very interesting competition between two different mechanisms for fluid propulsion, namely, light-activated electro-osmosis and light-insensitive diffusio-osmosis, stemming from different chemical pathways in the fuel decomposition. In this case, surface roughness becomes a pivotal parameter to enhance or depress one mechanism over the other.
These examples demonstrate that pumps are practical platforms to explore operating mechanisms and to quantify their performance. Additionally, they are suitable systems to test novel fuels or motor materials. This knowledge is extensible to swimmers providing not only fundamental understanding of their locomotion mechanisms but also useful clues for their design and optimization.
Statistical Physics Approach to Thermophoresis of Colloids
Sancho, JM
JOURNAL OF STATISTICAL PHYSICS
172
6
(2018)
Brownian colloidal particles dispersed in a fluid with a temperature gradient experience a driving force which produces a large biased steady density profile. This phenomenon, named thermophoresis, is quantified by the Soret coefficient S-T. This problem is studied here within the Fokker-Planck formalism. Using the experimental observation of S-T it is possible to extract relevant analytical information about a temperature dependent nonequilibrium effective potential which can produce the thermophoresis force. It will be presented here a statistical physics derivation of this effective potential in terms of some physical parameters. Experimental data are analyzed within this theoretical scenario.
Full Phase Diagram of Active Brownian Disks: From Melting to Motility-Induced Phase Separation
Digregorio, P ; Levis, D ; Suma, A ; Cugliandolo, LF ; Gonnella, G ; Pagonabarraga, I
PHYSICAL REVIEW LETTERS
121
098003
(2018)
We establish the complete phase diagram of self-propelled hard disks in two spatial dimensions from the analysis of the equation of state and the statistics of local order parameters. The equilibrium melting scenario is maintained at small activities, with coexistence between active liquid and hexatic order, followed by a proper hexatic phase, and a further transition to an active solid. As activity increases, the emergence of hexatic and solid order is shifted towards higher densities. Above a critical activity and for a certain range of packing fractions, the system undergoes motility-induced phase separation and demixes into low and high density phases; the latter can be either disordered (liquid) or ordered (hexatic or solid) depending on the activity.
Double transition of information spreading in a two-layered network
Wu, J; Zheng, MH ; Wang, W ; Yang, HJ ; Gu, CG
CHAOS
28
083117
(2018)
A great deal of significant progress has been seen in the study of information spreading on populations of networked individuals. A common point in many of the past studies is that there is only one transition in the phase diagram of the final accepted size versus the transmission probability. However, whether other factors alter this phenomenology is still under debate, especially for the case of information spreading through many channels and platforms. In the present study, we adopt a two-layered network to represent the interactions of multiple channels and propose a Susceptible-Accepted-Recovered information spreading model. Interestingly, our model shows a novel double transition including a continuous transition and a following discontinuous transition in the phase diagram, which originates from two outbreaks between the two layers of the network. Furthermore, we reveal that the key factors are a weak coupling condition between the two layers, a large adoption threshold, and the difference of the degree distributions between the two layers. Moreover, we also test the model in the coupled empirical social networks and find similar results as in the synthetic networks. Then, an edge-based compartmental theory is developed which fully explains all numerical results. Our findings may be of significance for understanding the secondary outbreaks of information in real life. Published by AIP Publishing.
Impact of modular organization on dynamical richness in cortical networks
Yamamoto, Hideaki; Moriya, Satoshi; Ide, Katsuya; Hayakawa, Takeshi; Akima, Hisanao; Sato, Shigeo; Kubota, Shigeru; Tanii, Takashi; Niwano, Michio; Teller, Sara; Soriano, Jordi; Hirano-Iwata, Ayumi
Science Advances
4
11
(2018)
As in many naturally formed networks, the brain exhibits an inherent modular architecture that is the basis of its rich operability, robustness, and integration-segregation capacity. However, the mechanisms that allow spatially segregated neuronal assemblies to swiftly change from localized to global activity remain unclear. Here, we integrate microfabrication technology with in vitro cortical networks to investigate the dynamical repertoire and functional traits of four interconnected neuronal modules. We show that the coupling among modules is central. The highest dynamical richness of the network emerges at a critical connectivity at the verge of physical disconnection. Stronger coupling leads to a persistently coherent activity among the modules, while weaker coupling precipitates the activity to be localized solely within the modules. An in silico modeling of the experiments reveals that the advent of coherence is mediated by a trade-off between connectivity and subquorum firing, a mechanism flexible enough to allow for the coexistence of both segregated and integrated activities. Our results unveil a new functional advantage of modular organization in complex networks of nonlinear units.
Resource heterogeneity leads to unjust effort distribution in climate change mitigation
Vicens, J ; Bueno-Guerra, N ; Gutierrez-Roig, M ; Gracia-Lazaro, C ; Gomez-Gardenes, J ; Perello, J ; Sanchez, A ; Moreno, Y ; Duch, J
PLOS ONE
13
10
(2018)
Climate change mitigation is a shared global challenge that involves collective action of a set of individuals with different tendencies to cooperation. However, we lack an understanding of the effect of resource inequality when diverse actors interact together towards a common goal. Here, we report the results of a collective-risk dilemma experiment in which groups of individuals were initially given either equal or unequal endowments. We found that the effort distribution was highly inequitable, with participants with fewer resources contributing significantly more to the public goods than the richer -sometimes twice as much. An unsupervised learning algorithm classified the subjects according to their individual behavior, finding the poorest participants within two "generous clusters" and the richest into a "greedy cluster". Our results suggest that policies would benefit from educating about fairness and reinforcing climate justice actions addressed to vulnerable people instead of focusing on understanding generic or global climate consequences.
Clogging and jamming of colloidal monolayers driven across disordered landscapes
Stoop, RL; Tierno, P
COMMUNICATIONS PHYSICS
1
68
(2018)
Understanding microscale transport across heterogeneous landscapes is relevant for many phenomena in condensed matter physics, from pinning of vortices in dirty superconductors, to electrons on liquid helium, skyrmions, and active matter. Here, we experimentally investigate the clogging and jamming of field tunable interacting colloids driven through a quenched disordered landscape of fixed obstacles. We focus on the emergent phenomenon of clogging, that has been the matter of much investigation at the level of a single aperture in macroscopic and granular systems. With our colloidal system, we find that quenched disorder significantly alters the particle flow, and we provide the experimental observation of the "Faster is Slower" effect with quenched disorder, that occurs when increasing the particle speed. Further, we show that clogging events may be controlled by tuning the pair interactions during transport, such that the colloidal flow decreases for repulsive interactions, but it increases for anisotropic attraction.
Active apolar doping determines routes to colloidal clusters and gels
Massana-Cid, H ; Codina, J; Pagonabarraga, I; Tierno, P
PNAS
115
42
(2018)
Collections of interacting active particles, self-propelling or not, have shown remarkable phenomena including the emergence of dynamic patterns across different length scales, from animal groups to vibrated grains, microtubules, bacteria, and chemicalor field-driven colloids. Burgeoning experimental and simulation activities are now exploring the possibility of realizing solid and stable structures from passive elements that are assembled by a few active dopants. Here we show that such an elusive task may be accomplished by using a small amount of apolar dopants, namely synthetic active but not self-propelling units. We use blue light to rapidly assemble 2D colloidal clusters and gels via nonequilibrium diffusiophoresis, where microscopic hematite dockers form long-living interstitial bonds that strongly glue passive silica microspheres. By varying the relative fraction of doping, we uncover a rich phase diagram including ordered and disordered clusters, space-filling gels, and bicontinuous structures formed by filamentary dockers percolating through a solid network of silica spheres. We characterize the slow relaxation and dynamic arrest of the different phases via correlation and scattering functions. Our findings provide a pathway toward the rapid engineering of mesoscopic gels and clusters via active colloidal doping.
La presencia del aceite bético en Mauretania Tingitana. Nuevos métodos de análisis.
Lluís PONS PUJOL, Jordi PÉREZ GONZÁLEZ
Studia Antiqua et Archaeologica
24
2
(2018)
Next 2019 will be ten years since the publication of the book “La economía de la Mauretania Tingitana (s. I–III d.C.). Aceite, vino y salazones” (Pons 2009). There we discuss the economy of the province, emphasizing the peculiarities of its food supply (imports and exports). Since then, both the scientific production of the province, with the inclusion of new data, as well as the progress in the different methods of analysis, allows us to approach the subject again, redefining some of its aspects. To carry out the following analyses, we have used the information collected in the CEIPAC online database in the framework of the EPNET project. At this point, the discovery of new data and, above all, the application of different methods of analysis can help us when dealing with complex tasks. In the present work we intend to address a series of questions about the meaning of the interprovincial food supply in Tingitana, a territory sufficiently prolific for its own supply.
The ecology of Roman trade. Reconstructing provincial connectivity with similarity measures.
Rubio-Campillo, X., Montanier, J.-M. Rull, R., Bermúdez Lorenzo, J.M., Moros Díaz, J., Pérez González, J., Remesal Rodríguez, J.
Journal of Archaeological Science
92
37 47
(2018)
The creation of the Roman Empire promoted the connectivity of a vast area around the Mediterranean sea. Mobility and trade flourished over the Roman provinces as massive amounts of goods were shipped over thousands of kilometres through sea, rivers and road networks. Several works have explored these dynamics of interaction in specific case studies but there is still no consensus on the intensity of this connectivity beyond local trade.
We argue here that the debate on the degree of large-scale connectivity across the empire is caused by a lack of appropriate methods and proxies of economic activity. The last years have seen an improvement on the availability of evidence as a growing amount of datasets is collected and published. However, data does not equal knowledge and the methods used to analyse this evidence have not advanced at the same pace.
A new framework of connectivity analysis has been applied here to reveal the existence of distinctive trade routes through the provinces of the Western region of Rome. The amphora stamps collected over more than a thousand sites have been analysed using quantitative measures of similarity. The patterns that emerge from the analysis highlight the intense connectivity derived from factors such as the spatial closeness, presence of military units and the relevance of the Atlantic sea as a main shipping route.
Complex systems representing effective connectivity in patients with Type One diabetes mellitus.
Joan Guàrdia-Olmos , Esteve Gudayol-Ferré, Geisa B. Gallardo-Moreno, Mar Martínez-Ricart, Maribel Peró-Cebollero, Andrés A. González-Garrido
PLOS ONE
1 21
(2018)
Type 1 diabetes mellitus (T1D) affects the entire cellular network of the organism. Some patients develop cognitive disturbances due to the disease, but several authors have suggested that the brain develops compensatory mechanisms to minimize or prevent neuropsychological decline. The present study aimed to assess the effective connectivity underlying visuospatial working memory performance in young adults diagnosed with T1D using neuroimaging techniques (fMRI).
Fifteen T1D right-handed, young adults with sustained metabolic clinical stability and a control group matched by age, sex, and educational level voluntarily participated. All participants performed 2 visuospatial working memory tasks using a block design within an MRI scanner. Regions of interest and their signal values were obtained. Effective connectivity—by means of structural equations models—was evaluated for each group and task through maximum likelihood estimation, and the model with the best fit was chosen in each case.
Compared to the control group, the patient group showed a significant reduction in brain activity in the two estimated networks (one for each group and task). The models of effective connectivity showed greater brain connectivity in healthy individuals, as well as a more complex network. T1D patients showed a pattern of connectivity mainly involving the cerebellum and the red nucleus. In contrast, the control group showed a connectivity network predominantly involving brain areas that are typically activated while individuals are performing working memory tasks.
Our results suggest a specific effective connectivity between the cerebellum and the red nucleus in T1D patients during working memory tasks, probably reflecting a compensatory mechanism to fulfill task demands.
Continuous-time ballistic process with random resets
Villarroel, J ; Montero, M
JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT
123204
(2018)
We consider ballistic motion on the line with random velocity which at certain random epochs of time is reset to its starting position. The mobile then restarts from scratch with new velocity, sampled with a certain probability distribution, until the next reset occurs. The distribution for the hitting time to an arbitrary level is obtained. Inversion of the relevant Laplace transform is discussed under particular choices for the distribution of velocities and resets train and classified in terms of the weights of reset and velocities tails. The large time behavior of the running-maximum is considered.
Energetics and the ground state quest in an artificial triangular colloidal ice
Lee, DY; Tierno, P
PHYSICAL REVIEW MATERIALS
2
112601
(2018)
We perform experiments and numerical simulations to investigate the low energy states of a triangular colloidal ice, realized by confining repulsive paramagnetic colloids to a lattice of topographic double wells. We find that the collective interactions between the particles lead to a unique ground state characterized by vertices with three colloids pointing inward and three outwards, similar to what was predicted, but never observed, for artificial spin ice. We show that a bias force that magnetizes the system allows us to easily access the elusive GS via a structural martensiticlike transition characterized by the coherent sliding of one particle at each vertex.
Velocity alignment promotes motility-induced phase separation
Sese-Sansa, E; Pagonabarraga, I; Levis, D
EPL
124
30004
(2018)
We study the phase behavior of polar active Brownian particles moving in two-spatial dimensions and interacting through volume exclusion and velocity alignment. We combine particle-based simulations of the microscopic model with a simple mean-field kinetic model to understand the impact of velocity alignment on the motility-induced phase separation of self-propelled disks. We show that, as the alignment strength is increased, approaching the onset of collective motion from below, orientational correlations grow, rendering the diffusive reorientation dynamics slower. As a consequence, the tendency of particles to aggregate into isotropic clusters is enhanced, favoring the complete de-mixing of the system into a low and high-density phase. Copyright (C) EPLA, 2018
Soft Communities in Similarity Space
Garcia-Perez, G ; Serrano, MA; Boguna, M
JOURNAL OF STATISTICAL PHYSICS
173
775 782
(2018)
The S-1 model has been central in the development of the field of network geometry. It places nodes in a similarity space and connects them with a likelihood depending on an effective distance which combines similarity and popularity dimensions, with popularity directly related to the degrees of the nodes. The S-1 model has been mainly studied in its homogeneous regime, in which angular coordinates are independently and uniformly scattered on the circle. We now investigate if the model can generate networks with targeted topological features and soft communities, that is, inhomogeneous angular distributions. To that end, hidden degrees must depend on angular coordinates, and we propose a method to estimate them. We conclude that the model can be topologically invariant with respect to the soft-community structure. Our results expand the scope of the model beyond the independent hidden variables limit and can have an important impact in the embedding of real-world networks.
Psychometric Properties of the Spanish Version of the Self-Determination Inventory Student Self-Report: A Structural Equation Modeling Approach
Mumbardo-Adam, C ; Guardia-Olmos, J ; Gine, C ; Shogren, KA ; Sanchez, EV
123
123
6
(2018)
Instruments to measure self-determination have only been available in the Spanish language to date, for adolescents with intellectual disability (ID). However, given the development of a new measure of self-determination for youth with and without disabilities, the Self-Determination Inventory, there is a need to adapt and validate this tool in the Spanish language so as to provide practitioners with a psychometrically strong measure of self-determination. This study provides evidence of reliability and validity of the Spanish version of the scale, empirically tested with a sample of 620 youth with and without disabilities in Spain. Specifically, validity was evidenced through structural equation modeling approaches, confirming the instrument adequacy to measure self-determination in Spanish speaking youth. Future lines of research are suggested.
Citizen Social Lab: A digital platform for human behavior experimentation within a citizen science framework
Vicens, J ; Perello, J ; Duch, J
PLOS ONE
13
12
(2018)
Cooperation is one of the behavioral traits that define human beings, however we are still trying to understand why humans cooperate. Behavioral experiments have been largely conducted to shed light into the mechanisms behind cooperation-and other behavioral traits. However, most of these experiments have been conducted in laboratories with highly controlled experimental protocols but with limitations in terms of subject pool or decisions' context, which limits the reproducibility and the generalization of the results obtained. In an attempt to overcome these limitations, some experimental approaches have moved human behavior experimentation from laboratories to public spaces, where behaviors occur naturally, and have opened the participation to the general public within the citizen science framework. Given the open nature of these environments, it is critical to establish the appropriate data collection protocols to maintain the same data quality that one can obtain in the laboratories. In this article we introduce Citizen Social Lab, a software platform designed to be used in the wild using citizen science practices. The platform allows researchers to collect data in a more realistic context while maintaining the scientific rigor, and it is structured in a modular and scalable way so it can also be easily adapted for online or brick-and-mortar experimental laboratories. Following citizen science guidelines, the platform is designed to motivate a more general population into participation, but also to promote engaging and learning of the scientific research process. We also review the main results of the experiments performed using the platform up to now, and the set of games that each experiment includes. Finally, we evaluate some properties of the platform, such as the heterogeneity of the samples of the experiments, the satisfaction level of participants, or the technical parameters that demonstrate the robustness of the platform and the quality of the data collected.
An analytical framework to determine flow velocities within nanotubes from their vibration frequencies
Torres-Herrera, U ; Poire, EC
PHYSICS OF FLUIDS
30
122001
(2018)
We develop a theoretical framework to determine fluid velocities within nanotubes. We demonstrate that the fluid/tube dynamic coupling could be exploited to determine flow velocities based on knowledge of the bending frequency spectrum of a single nanotube. We develop an analytical methodology that allows one to associate any of the frequencies in the spectrum with a single value of the fluid velocity. We discuss the feasibility of experiments by state-of-the-art atomic force microscopy and perform numerical simulations to determine uncertainties in fluid velocities. These are below 5% for common nanotube sizes, which are considerably smaller than the ones reported in the literature for conventional methods. Published by AIP Publishing.
A Cognitively Inspired Clustering Approach for Critique-Based Recommenders
Contreras, D., Salamó, M.
Cognitive Computation
1 14
(2018)
The purpose of recommender systems is to support humans in the purchasing decision-making process. Decision-making is a human activity based on cognitive information. In the field of recommender systems, critiquing has been widely applied as an effective approach for obtaining users’ feedback on recommended products. In the last decade, there have been a large number of proposals in the field of critique-based recommenders. These proposals mainly differ in two aspects: in the source of data and in how it is mined to provide the user with recommendations. To date, no approach has mined data using an adaptive clustering algorithm to increase the recommender’s performance. In this paper, we describe how we added a clustering process to a critique-based recommender, thereby adapting the recommendation process and how we defined a cognitive user preference model based on the preferences (i.e., defined by critiques) received by the user. We have developed several proposals based on clustering, whose acronyms are MCP, CUM, CUM-I, and HGR-CUM-I. We compare our proposals with two well-known state-of-the-art approaches: incremental critiquing (IC) and history-guided recommendation (HGR). The results of our experiments showed that using clustering in a critique-based recommender leads to an improvement in their recommendation efficiency, since all the proposals outperform the baseline IC algorithm. Moreover, the performance of the best proposal, HGR-CUM-I, is significantly superior to both the IC and HGR algorithms. Our results indicate that introducing clustering into the critique-based recommender is an appealing option since it enhances overall efficiency, especially with a large data set.
A Platform for the Authoring of Educational Games
Baldeon, J., Puig, A., Rodriguez, I., & Zardain, L.
13th Iberian Conference on Information Systems and Technologies (CISTI). IEEE
1 6
(2018)
An Educational Game Authoring (EGA) tool is a software to assist teachers in the authoring of games. Game authoring can be approached from two different perspectives. The first, where the educator creates a game from scratch, and a second one, where specific game components of an existing game can be configured (edited) by the teacher, abstracting the technical aspects of game development for non-programmer users. Nevertheless, whatever the perspective, the authoring games in an easy way is still a challenge, and even more, there is a lack of works considering educational aspects like Intended Learning Outcomes (ILOs), students' learning and playing styles, and learning mechanics. This work takes the second perspective and proposes an EGA platform that although embraces both the game and educational domains, puts the emphasis on the educational one. The platform provides educators with a mean for configuring educational games, and so adapt game's educational content to lessons pacing and students' learning needs. This platform is conceived generic enough to serve those educational games that are adapted to interact with it using a given protocol and communication language. In this paper, we present the architecture of the EGA platform, the communication protocol and the Authoring Description Language (ADL). We show the approach with an example of a maths game.
A structural equation model estimation of the role of social vulnerability as a predictor of people's feelings of unsafety.
Valente, R.; Valera, S. & Guardia, J.
Social Research Indicators.
1 17
(2018)
People’s perception of insecurity is linked to a wide range of factors and up-to-date sources stress the impact of socially constructed concerns on feelings of unsafety. Building further on recent developments, the present research proposes a measure of social vulnerability focusing on future-oriented anxieties and self-perceived social exclusion as predictors of subjective perceptions of insecurity. Data gathered in a large-scale survey in Italy (N = 15,428) were analysed by implementing structural equation modeling in an attempt to address people’s vulnerability beyond the mere consideration of the likelihood of individuals’ involvement as the victims of a crime. The results provide evidence for the predictive role of social vulnerability on neighbourhood-based worries, victimization patterns and community cohesion. Moreover, the analysis show that health and financial precariousness, together with the perception of being marginalized or in some way excluded from society, may result in higher levels of subjective insecurity.
Acoustic emission avalanches during compression of granular manganites
Soto-Parra, D.; Vives, E.;. Botello-Zubiate, M. E ; Matutes-Aquino, J. A. ; and Planes, A.
Applied Physics Letters
112
25
(2018)
We have studied acoustic emission (AE) during compression of La0.8Ca0.28Sr0.08MnO2.7 manganites with different microstructures obtained by selected synthesis techniques. In ceramic samples with large grains obtained by a solid-state method, avalanche criticality is confirmed when grain fracture is the AE dominant mechanism. In samples synthesized by means of micro-wave and sol-gel techniques, grains are much smaller and the AE is mainly originated from friction effects associated with relative displacement of grains during deformation. In this case, significant deviations from avalanche criticality have been detected.
Analysis of spontaneous activity in neuronal cultures through recurrence plots: impact of varying connectivity
Tibau, E; Soriano, J.
The European Physical Journal Special Topics
227
10-11
(2018)
We analyzed spontaneous activity of cortical neuronal networks in vitro using recurrence plots (RPs). Our data encompasses fluorescence traces of average network activity from two experimental explorations, namely the development of connections during the maturation of the network and the gradual weakening of connections through chemical action. The dynamical richness of the networks in these connectivity-evolving scenarios was examined through recurrence quantification analysis. Measures such as determinism and laminarity were used to portray the degree of uniformity and periodicity of the spontaneous activity patterns. The analysis shows that RPs are a powerful tool to visualize and interpret neuronal networks dynamics, and pinpoint its hallmarks.
Arquitectura i hábitat al territorio d’Ilerda: La vil·la del Romeral (Albesa, la Noguera) entre els segles I i VI dC
Marí i Sala, LL.; Revilla Calvo, V.
Revista d’Arqueologia de Ponent
28
103 129
(2018)
La vil·la del Romeral és un establiment amb una complexa seqüència d’ocupació al llarg de l’època imperial. La primera fase correspon a un edifici de característiques poc definides que es basteix a inicis del segle I dC. Aquesta construcció és substituïda per un gran edifici, amb funció residencial
Beyond the Virtual Reconstruction of An Archaological Settlement.
S. Cebrián; N. Morera; Juan A. Barceló; I. Bogdanovic; O. López-Bultó; I. Campana; A. Palomo; R. Piqué; J. Revelles; X. Terradas; J. L. Arcos; J. A. Rodríguez-Aguilar; A. Bogdanovych; S. Simoff5; T. Trescak; I. Rodríguez; A. Puig.
Computer Applications and Quantitative Methods in Archaeology (CAA)
(2018)
In the frame of the research project undertaken in the site of La Draga, an Early Neolithic (ca. 5.300-4.800 cal BC) pile-dwelling settlement located at the North Eastern of the Iberian Peninsula, a virtual reconstruction of the settlement has been developed in order to show how did this Neolithic community live. This virtual reconstruction of the settlement has been made accessible to the public– since it is exhibited in a museum – as a 360o video, a virtual reality (VR) serious game, and a VR tour, hence offering different degrees of human-computer interaction. These technological results have been produced by means of a complex co-creation process involving archeologists, computer scientists, software developers, and designers. In this article, we present the methodology and tools employed to produce the 3D reconstruction of La Draga as well as the VR serious game and the VR tour. Furthermore, we also present some preliminary lessons on the role of VR and serious games that stem from analyzing the feedback provided by the museum audience. From this specific experience, we also extract some general conclusions towards the potential of VR and serious games as valuable technologies to engage children and teenagers in history and archaeology as sciences of the social past.
Biophysical properties of single rotavirus particles account for the functions of protein shells in a multilayered virus
Jimenez-Zaragoza, M.; Yubero, M.P.L.; Martin-Forero, E.; Caston, J.R.; Reguera, D.; Luque, D.; de Pablo, P.J.; Rodriguez, J.M.
eLife
7
e37295
(2018)
The functions performed by the concentric shells of multilayered dsRNA viruses require specific protein interactions that can be directly explored through their mechanical properties. We studied the stiffness, breaking force, critical strain and mechanical fatigue of individual Triple, Double and Single layered rotavirus (RV) particles. Our results, in combination with Finite Element simulations, demonstrate that the mechanics of the external layer provides the resistance needed to counteract the stringent conditions of extracellular media. Our experiments, in combination with electrostatic analyses, reveal a strong interaction between the two outer layers and how it is suppressed by the removal of calcium ions, a key step for transcription initiation. The intermediate layer presents weak hydrophobic interactions with the inner layer that allow the assembly and favor the conformational dynamics needed for transcription. Our work shows how the biophysical properties of the three shells are finely tuned to produce an infective RV virion.
Breaking waves and spectral analysis of the two-dimensional KdV-Bogoyavlenskii equation
Villarroel, J.; Montero, M.
Studies in Applied Mathematics
140
1
(2018)
We study here the initial value problem for a two‐dimensional Korteweg–de Vries (KdV) equation, first derived by Calogero and Bogoyavlenskii, by means of the inverse scattering transform. The dynamics of the discrete spectrum of an associated Schrödinger operator is far richer than that of KdV equation. Even for optimal eigenvalues, generic smooth solutions may develop shocks with multiple branches and/or cusp singularities in finite time. However, evolution may move poles of the transmission coefficient off the imaginary axis, destroy or even create them. We characterize conditions to prevent these pathologies before explosion time and describe ample classes of solutions, corresponding to both continuous and discrete spectrum. We also find that in certain conditions new eigenvalues might be created; in these cases a minimal set of initial spectral data must incorporate additionally the transmission coefficient 
on the entire plane. The previous results are applied to describe the Cauchy problem corresponding to initial data combinations of delta terms and derivatives and show that for long time the delta singularity may persist or be smoothed to a cusp‐discontinuity. Finally, we give conditions under which the evolution 
is reduced to the classical KdV.
CALLEGARIN, L.; KBIRI ALAOUI, M.; ICHKHAKH, A.; ROUZ, J-Cl., Rirha: site antique et médiévale du Maroc. I. Cadre historique et géographique géneral. Madrid: Casa de Velázquez, 2016.
Pons, L.
Indice Histórico Español
(2018)
Ressenya de la monografia: CALLEGARIN, L.; KBIRI ALAOUI, M.; ICHKHAKH, A.; ROUZ, J-Cl., Rirha: site antique et médiévale du Maroc. I. Cadre historique et géographique géneral. Madrid: Casa de Velázquez, 2016. Primer volumen de los cuatro en los que se publican las excavaciones llevadas a cabo por un equipo marroco-francés en Rirha (Sidi Slimane, N. de Marruecos) entre 2005 y 2012. Se presenta este primer volumen como una exposición general de las excavaciones, objetivos y metodología utilizada, destacando el potencial arqueológico e histórico del yacimiento.
Cardiorespiratory coordination in repeated maximal exercises.
Garcia, S., Javierre, C., Hristovski, R., Ventura, J.L., Balagué, N.
Frontiers in Physiology
8
387
(2018)
Increases in cardiorespiratory coordination (CRC) after training with no differences in performance and physiological variables have recently been reported using a principal component analysis approach. However, no research has yet evaluated the short-term effects of exercise on CRC. The aim of this study was to delineate the behavior of CRC under different physiological initial conditions produced by repeated maximal exercises. Fifteen participants performed 2 consecutive graded and maximal cycling tests. Test 1 was performed without any previous exercise, and Test 2 6 min after Test 1. Both tests started at 0 W and the workload was increased by 25 W/min in males and 20 W/min in females, until they were not able to maintain the prescribed cycling frequency of 70 rpm for more than 5 consecutive seconds. A principal component (PC) analysis of selected cardiovascular and cardiorespiratory variables (expired fraction of O2, expired fraction of CO2, ventilation, systolic blood pressure, diastolic blood pressure, and heart rate) was performed to evaluate the CRC defined by the number of PCs in both tests. In order to quantify the degree of coordination, the information entropy was calculated and the eigenvalues of the first PC (PC1) were compared between tests. Although no significant differences were found between the tests with respect to the performed maximal workload (Wmax), maximal oxygen consumption (VO2 max), or ventilatory threshold (VT), an increase in the number of PCs and/or a decrease of eigenvalues of PC1 (t = 2.95; p = 0.01; d = 1.08) was found in Test 2 compared to Test 1. Moreover, entropy was significantly higher (Z = 2.33; p = 0.02; d = 1.43) in the last test. In conclusion, despite the fact that no significant differences were observed in the conventionally explored maximal performance and physiological variables (Wmax, VO2 max, and VT) between tests, a reduction of CRC was observed in Test 2. These results emphasize the interest of CRC evaluation in the assessment and interpretation of cardiorespiratory exercise testing.
Coexistence of a well-determined kinetic law and a scale-invariant power law during the same physical process
Zreihan, N.; Faran,E.; Vives, E.; Planes,A.; and Shilo, D.
Physical Review B
97
1
(2018)
It is generally claimed that physical processes which display scale-invariant power-law distributions are subjected to a dynamic criticality that prohibits a well-defined kinetic law. In this paper, we demonstrate the coexistence of these two apparently contradicting behaviors during the same physical process—the motion of type-II twin boundaries in martensite Ni-Mn-Ga. The process is investigated by combined measurements of the temporal twin-boundary velocity and the acoustic emitted energy. Velocity values are extracted from high-resolution force measurements taken during displacement-driven mechanical tests, as well as from force-driven magnetic tests, and cover an overall range of six orders of magnitude. Acoustic emission (AE) is measured during mechanical tests. Velocity values follow a normal distribution whose characteristic value is determined by the material's kinetic relation, and its width scales with the average velocity. In addition, it is observed that velocity distributions are characterized by a heavy tail at the right (i.e., faster) end that exhibits a power law over more than one and a half orders of magnitude. At the same time, the AE signals follow a scale-invariant power-law distribution, which is not sensitive to the average twin-boundary velocity. The coexistence of these two different statistical behaviors reflects the complex nature of twin-boundary motion and suggests the possibility that the transformation proceeds through physical subprocesses that are close to criticality alongside other processes that are not.
Crossover from three-dimensional to two-dimensional systems in the nonequilibrium zero-temperature random-field Ising model
Spasojevic, D.; Mijatovic, S.; Navas-Portella, V.; Vives, E.
Physical Review E
97
1
(2018)
We present extensive numerical studies of the crossover from three-dimensional to two-dimensional systems in the nonequilibrium zero-temperature random-field Ising model with metastable dynamics. Bivariate finite-size scaling hypotheses are presented for systems with sizes L×L×l which explain the size-driven critical crossover from two dimensions (l=const, L→∞) to three dimensions (l∝L→∞). A model of effective critical disorder Reffc(l,L) with a unique fitting parameter and no free parameters in the Reffc(l,L→∞) limit is proposed, together with expressions for the scaling of avalanche distributions bringing important implications for related experimental data analysis, especially in the case of thin three-dimensional systems.
Cultura material y cultura escrita en la sociedad rural de Hispania en los siglos I-II d. C.: el conjunto cerámico y los grafitos del asentamiento de Cal Montblanc (Albesa, Lleida)
Marí Sala, L.; Revilla Calvo, V.
Archivo Español de Arqueología
91
217 242
(2018)
La excavación de un asentamiento rural cercano a Lleida permitió recuperar un importante contexto cerámico datado en los siglos I-II d. C. El repertorio cerámico recuperado incluye una amplia representación de vajillas de mesa romana; en especial, sigillata hispánica. Un gran número de vasos presenta grafitos con significados muy diferentes. La riqueza y diversidad del conjunto permite hacer algunas consideraciones sobre las condiciones de su formación y la función del lugar, así como sobre la difusión de la cultura escrita entre la población rural del periodo.
Data-driven decision making in critique-based recommenders: from a critique to social media data
Contreras, D.; Salamó, M.
Journal of Intelligent Information Systems
1 22
(2018)
In the last decade there have been a large number of proposals in the field of Critique-based Recommenders. Critique-based recommenders are data-driven in their nature since they use a conversational cyclical recommendation process to elicit user feedback. In the literature, the proposals made differ mainly in two aspects: in the source of data and in how this data is analyzed to extract knowledge for providing users with recommendations. In this paper, we propose new algorithms that address these two aspects. Firstly, we propose a new algorithm, called HOR, which integrates several data sources, such as current user preferences (i.e., a critique), product descriptions, previous critiquing sessions by other users, and users’ opinions expressed as ratings on social media web sites. Secondly, we propose adding compatibility and weighting scores to turn user behavior into knowledge to HOR and a previous state-of-the-art approach named HGR to help both algorithms make smarter recommendations. We have evaluated our proposals in two ways: with a simulator and with real users. A comparison of our proposals with state-of-the-art approaches shows that the new recommendation algorithms significantly outperform previous ones.
Effects of Cognitive Reserve on Cognitive Performance in a Follow-Up Study in Older Adults With Subjective Cognitive Complaints. The Role of Working Memory.
Lojo, C.; Facal, D.; Guàrdia, J.; Pereiro, A.; Juncos, O.
Frontiers in Aging Neuroscience
10
189
(2018)
Objective: Analyze the effects of CR on cognitive performance in adults with subjective cognitive complaints at follow-up.
Method: We analyzed the factorial structure of the three constructs defined in cognitive performance (Episodic memory, Working memory, and General cognitive performance) separately to search for evidence of the invariance of the measurement model. We then developed four structural nested models to analyze the relationship between CR and cognitive performance, measured at baseline and after approximately 18 months, in 266 participants older than 50 years with subjective cognitive complaints.
Results: The nested models revealed the following main results: direct effects of CR on all cognitive constructs at baseline and also indirect effects on the same constructs at follow-up, and indirect effects of CR on other cognitive constructs at follow-up via working memory at follow-up.
Conclusion: The findings show that the proposed model is useful for measuring the influence of CR on cognitive performance in follow-up studies and that CR has a positive influence on cognitive performance at follow-up via working memory. CR may enhance mechanisms of information processing, favoring performance of tasks involving other cognitive constructs in older adults with subjective cognitive complaints.
Elaboración y comercialización de perfumes y ungüentos en Roma. Los unguentarii.
Pérez González, J.
Revista de Estudos Filosóficos e Históricos da Antiguidade
31
(2018)
Emergent hydrodynamic bound states between magnetically powered micropropellers
Martinez-Pedrero, F. ; Navarro-Argemi, E.; Pagonabarraga, I. ; Tierno, P.
Science Advances
4
1
(2018)
Hydrodynamic interactions (HIs), namely, solvent-mediated long-range interactions between dispersed particles, play a crucial role in the assembly and dynamics of many active systems, from swimming bacteria to swarms of propelling microrobots. We experimentally demonstrate the emergence of long-living hydrodynamic bound states between model microswimmers at low Reynolds numbers. A rotating magnetic field forces colloidal hematite microparticles to translate at a constant and frequency-tunable speed close to a bounding plane in a viscous fluid. At high driving frequency, HIs dominate over magnetic dipolar ones, and close propelling particles couple into bound states by adjusting their translational speed to optimize the transport of the pair. The physical system is described by considering the HIs with the boundary surface and the effect of gravity, providing an excellent agreement with the experimental data for all the range of parameters explored. Moreover, we show that in dense suspensions, these bound states can be extended to one-dimensional arrays of particles assembled by the sole HIs. Our results manifest the importance of the boundary surface in the interaction and dynamics of confined propelling microswimmers.
Employability of recent graduates. Opinions of Catalonian companies and institutions
Guàrdia-Olmos, J.; Peró-Cebollero, M.; Martínez-Ricart, M.; Cañete-Massé, C.; Turbany-Oset, J.; Berlanga-Silvente, V.
Educación XX1
21
2
(2018)
Introduction: Labor insertion for young people is probably more difficult nowadays than it was a few decades ago in all productive sectors and in academic education. A few decades ago, having a university degree was a guarantee of quick labor insertion, but nowadays, although having a university degree may somewhat alleviate the unemployment rate, it is still high among recent university graduates. In this paper, we show the differential profile of the companies who do hire recent graduates as compared to those who do not.
Methodology: We worked with a sample of 1,325 employers from the business world of Catalonia, who were administered the questionnaire prepared adhoc during 2014.
Results: The main results show that the more workers a company has, the higher the probability that they will hire recent graduates. Companies with a high percentage of graduated workers are more likely to hire recent graduates. Companies who are willing to work with Agency for the Quality of the University System of Catalonia hire more than those who are not. And finally, the service sector hires more than construction or industry.
Conclusions: In the present study we have shown a differential pattern between the companies that hire recent graduates or not, a very important aspect because this could help define university policies to facilitate the transition to the labor market.
Epigrafía lapidaria en la Era Digital
Pérez González, J.
Boletín Archivo Epigráfico, Directora
5
(2018)
EventAware: A mobile recommender system for events
Horowitz, D.; Contreras, D.; Salamó, M.
Pattern Recognition Letters
105
121 134
(2018)
Developing a recommender system for events raises several issues that are different from other domains. Events rapidly disappear, users’ preferences quickly change over time, and direct feedback does not exist for events that have not taken place. As the recommendations will not be further available, user’s context become a key factor for providing accurate recommendations. In this paper we introduce EventAware, a context-aware mobile recommender system to personalize the agenda of users attending to a congress. In particular, we first introduce the EventAware system, which includes an intuitive user interface with an attractive design to enhance user experience. EventAware incorporates some implicit contextual information, automatically initializes both the user’s profiles with minimal user interaction and the properties of the items and it uses a context-aware tag-based recommender algorithm. We demonstrate its usability through a live-user case-study in one of the biggest events of mobile technology in the world, held in Barcelona.
Experimental Evidence of Accelerated Seismic Release without Critical Failure in Acoustic Emissions of Compressed Nanoporous Materials
Baró,J.; Dahmen, K.A.; Davidsen, J.; Planes, A.; Castillo, P.O.; Nataf, G. F.; Salje, E. K. H. and Vives, E.
Physical Review Letters
120
24
(2018)
The total energy of acoustic emission (AE) events in externally stressed materials diverges when approaching macroscopic failure. Numerical and conceptual models explain this accelerated seismic release (ASR) as the approach to a critical point that coincides with ultimate failure. Here, we report ASR during soft uniaxial compression of three silica-based (SiO2) nanoporous materials. Instead of a singular critical point, the distribution of AE energies is stationary, and variations in the activity rate are sufficient to explain the presence of multiple periods of ASR leading to distinct brittle failure events. We propose that critical failure is suppressed in the AE statistics by mechanisms of transient hardening. Some of the critical exponents estimated from the experiments are compatible with mean field models, while others are still open to interpretation in terms of the solution of frictional and fracture avalanche models.
Exploratory data analysis of executive functions in children: A new assessment battery.
Richard's, M.; Vernucci, S.; Stelzer, F.; Introzzi, I.; Guardia, J.
Current Psychology
1 8
(2018)
Executive Functions (EF) are fundamental during childhood since they participate actively in such heterogeneous domains as mental and physical health, learning, school performance, and cognitive, social and psychological development. Their evaluation is of interest, both in the field of clinical practice and research. Several criticisms and discussions have been generated regarding the available resources for its measurement, so it is necessary to have evaluation tasks that present adequate psychometric properties and that allow to evaluate each EF with the least possible interference of other processes. This paper aims to present the Tareas de Autorregulación Cognitiva Battery (TAC), a computerized platform designed for independent measurement of inhibition, working memory and cognitive flexibility, as well as obtaining evidence of construct validity from a set of tasks that compose it. 103 children between 9 and 12 years of age from the city of Mar del Plata, Argentina, were assessed. The results of the factor analysis showed a solution of 3 factors, which significantly explain 52.79% of the variance. These results, together with the scientific evidence presented by previous studies, provide empirical support of the validity of the tasks analyzed in the present study. Thus, this study contributes to the literature by presenting a computerized battery for specific and independent assessment of the different executive processes, valid for its application in children.
Exploring the impact of disability on self-determination
Mumbardó, C.; Giné, C.; Guardia, J.
Research in Developmental Disabilities
78
27 34
(2018)
Background
Self-determination is a psychological construct that applies to both the general population and to individuals with disabilities that can be self-determined with adequate accommodations and opportunities. As the relevance of self-determination-related skills in life has been recently acknowledged, researchers have created a measure to assess self-determination in adolescents and young adults with and without disabilities. The Self-Determination Inventory: Student Report (Spanish interim version) is empirically being validated into Spanish.
Aims
As this scale is the first assessment addressed to all youth, further exploration of its psychometric properties is required to ensure the reliability of the self-determination measurement and gain further insight into the construct when applied to youth with and without disabilities.
Methods
More than 600 participants were asked to complete the scale. The impact of disability on the item response distributions across the dimensions of self-determination was explored.
Outcomes
Differential item functioning (DIF) was found in only 5 of the scale’s 45 items. Differences primary favored youth without disabilities.
Conclusions
The weak presence of DIF across the items supports the instrument’s psychometrical robustness when measuring self-determination in youth with and without disabilities and provides further understanding of the self-determination construct. Implications and future research directions are also discussed.
Flow of colloidal suspensions through small orifices
Hidalgo, R.C. ; Gori-Arana, A.; Hernandez-Puerta, A.; Pagonabarraga , I.
Physical Review e
97
1
(2018)
In this work, we numerically study a dense colloidal suspension flowing through a small outlet driven by a pressure drop using lattice-Boltzmann methods. This system shows intermittent flow regimes that precede clogging events. Several pieces of evidence suggest that the temperature controls the dynamic state of the system when the driving force and the aperture size are fixed. When the temperature is low, the suspension's flow can be interrupted during long time periods, which can be even two orders of magnitude larger than the system's characteristic time (Stokes). We also find that strong thermal noise does not allow the formation of stable aggregate structures avoiding extreme clogging events, but, at the same time, it randomizes the particle trajectories and disturbs the advective particle flow through the aperture. Moreover, examining the particle velocity statistics, we obtain that in the plane normal to the pressure drop the colloids always move as free particles regardless of the temperature value. In the pressure drop direction, at high temperature the colloids experience a simple balance between advective and diffusive transport, but at low temperature the nature of the flow is much more complex, correlating with the occurrence of very long clogging events.
Increasing power-law range in avalanche amplitude and energy distributions
Navas-Portella, V.; Serra, I.; Corral, A. and Vives, E.
Physical Review E
97
2
(2018)
Power-law–type probability density functions spanning several orders of magnitude are found for different avalanche properties. We propose a methodology to overcome empirical constraints that limit the range of truncated power-law distributions. By considering catalogs of events that cover different observation windows, the maximum likelihood estimation of a global power-law exponent is computed. This methodology is applied to amplitude and energy distributions of acoustic emission avalanches in failure-under-compression experiments of a nanoporous silica glass, finding in some cases global exponents in an unprecedented broad range: 4.5 decades for amplitudes and 9.5 decades for energies. In the latter case, however, strict statistical analysis suggests experimental limitations might alter the power-law behavior.
Inventando el pasado, incluso la geografía de estrechos y mares.
Pons Pujol, Ll.
GeocritiQ
392
(2018)
Kepler: una deuda pendiente
Sancho, J.M.
Revista Española de Física
32
1
(2018)
Si bien la mecánica de Newton es considerada como la primera gran contribución del método científico aplicado a la nueva ciencia de la dinámica de los cuerpos, queda bastante silenciado el papel relevante de Kepler en el progreso inicial de esta disciplina.
Este olvido está tan interiorizado que en los libros actuales de mecánica únicamente se mencionan sus tres leyes como enunciados curiosos y bien certeros, pero sin profundizar en la determinante importancia de los mismos. Tanto es así que está totalmente olvidado que Kepler resolvió analíticamente el problema cinemático de la posición de un planeta en función del tiempo (las ecuaciones horarias).
La administración subalterna en Raetia durante el Imperio Romano.
Bermúdez Lorenzo, J.M.
Studia Antiqua et Archaeologica
24
1
(2018)
This study deals with the positions and people of the subordinate administration of the province of Raetia since its creation, at the end of the 1st century BC, until the first half of the 3rd century AD. The data that we know of all of them is offered to obtain an overview of this administrative area that has often been forgotten.
El presente estudio trata los cargos y personajes de la administración subalterna de la provincia de Raetia desde su creación, a finales del s. I a. C., hasta la primera mitad del s. III. Se ofrecen los datos que conocemos de todos ellos para obtener una visión general de este ámbito administrativo que a menudo ha sido olvidado.
From micro- to macroscopic injuries: Applying the Complex Systems Dynamic Approach to Sports Medicine
Pol, R., Hristovski, R., Medina, D., Balagué, N.
British Journal of Sports Medicine
0
1 8
(2018)
A better understanding of how sports injuries occur in order to improve their prevention is needed for medical, economic, scientific and sports success reasons. This narrative review aims to explain the mechanisms that underlie the occurrence of sports injuries, and an innovative approach for their prevention on the basis of complex dynamic systems approach. First, we explain the multilevel organisation of living systems and how function of the musculoskeletal system may be impaired. Second, we use both, a constraints approach and a connectivity hypothesis to explain why and how the susceptibility to sports injuries may suddenly increase. Constraints acting at multiple levels and timescales replace the static and linear concept of risk factors, and the connectivity hypothesis brings an understanding of how the accumulation of microinjuries creates a macroscopic non-linear effect, that is, how a common motor action may trigger a severe injury. Finally, a recap of practical examples and challenges for the future illustrates how the complex dynamic systems standpoint, changing the way of thinking about sports injuries, offers innovative ideas for improving sports injury prevention.
Hàbitat rural, sistemes agraris i dinàmiques de la romanització a les terres de l'Ebre
Revilla Calvo, V.
Miscel· lània del Centre d'Estudis de la Ribera d'Ebre
28
247 262
(2018)
L’article analitza els trets fonamentals de l’organització del poblament rural al curs inferior de l’Ebre. Es defineixen la tipologia i distribució de l’hàbitat, amb particular atenció als exemples coneguts d’arquitectura residencial, i s’analitza la relació entre el model d’ocupació del territori i un sistema agrari definit per l’organització racional d’inversions i de recursos, la integració d’activitats complementàries a l’agricultura desenvolupat entre finals del segle I a.C i els segles I-II. Es valoren, igualment, aspectes de l’estructura de la propietat i la condició de certs grups socials.
Ice Rule Fragility via Topological Charge Transfer in Artificial Colloidal Ice
Libal, A.; Lee, D.-Y.; Ortiz-Ambriz, A.; Reichhardt, C.; Reichhardt, C. O.; Tierno, P.; Nisoli, C.
Nature Communications
9
1
(2018)
Artificial particle ices are model systems of constrained, interacting particles. They have been introduced theoretically to study ice-manifolds emergent from frustration, along with domain wall and grain boundary dynamics, doping, pinning-depinning, controlled transport of topological defects, avalanches, and memory effects. Recently such particle-based ices have been experimentally realized with vortices in nano-patterned superconductors or gravitationally trapped colloids. Here we demonstrate that, although these ices are generally considered equivalent to magnetic spin ices, they can access a novel spectrum of phenomenologies that are inaccessible to the latter. With experiments, theory and simulations we demonstrate that in mixed coordination geometries, entropy-driven negative monopoles spontaneously appear at a density determined by the vertex-mixture ratio. Unlike its spin-based analogue, the colloidal system displays a “fragile ice” manifold, where local energetics oppose the ice rule, which is instead enforced through conservation of the global topological charge. The fragile colloidal ice, stabilized by topology, can be spontaneously broken by topological charge transfer.
Identifying social learning between Roman amphorae workshops through morphometric similarity
Coto-Sarmiento, M.; Rubio-Campillo, X.; Remesal Rodríguez, J.
Journal of Archaeological Science
97
117 123
(2018)
The aim of this study is to identify dynamics of social learning between amphorae workshops during the the Roman Empire. The Baetica province developed a massive infrastructure of olive oil production that supplied the Western provinces of Rome for almost 300 years. The olive oil produced in this area was shipped through maritime and riverine transport networks in a standardized amphoric shape made in several workshops spread around the region. These workshops have generated a large amount of evidence but it is still difficult to understand through archaeological proxies how the production of amphorae was organized.
We apply here an evolutionary framework to find links between workshops through the morphometric similarities of the amphorae they produced. The suggested approach identifies how individual potters acquired and transmitted technical skills by exploring small yet statistical significant differences in the amphorae made in 5 different workshops. Multivariate methods are used to cluster a variety of amphorae based on morphometric measurements and the outcome shows that the analysis is useful even when a high degree of standardization exists, such as was the case for Roman amphorae (i.e. Dressel 20).
Results suggest that morphometric similarity is inversely correlated with spatial distance between workshops. This pattern suggests that pottery-making techniques were transmitted through oblique transmission with little or no movement of potters between distant workshops. The conclusion is that morphometric similarity may be an effective proxy to identify social learning dynamics even amongst workshops producing exactly the same amphoric type.
Idiosyncratic Pain Patterns during Exhaustive Exercise
Slapšinskaitė, A., Razon, S., Balagué, N., Ščiupokas, A., Hristovski, R., Tenenbaum, G.
Global Journal of Health Science
10
6
(2018)
The purpose of this study was to investigate the dynamical distribution of pain in constant cycling and running tasks up to the point of exhaustion. Ten participants (M = 20.8 years old, SD = ± 1.03) ran and cycled at a “hard” intensity level (e.g., Borg’s RPE (6–20) = 15). During task performance, participants reported their pain on a body map every 15s. Three distinct and consistent pain distribution patterns emerged: adders who added pain locations, jumpers who switched among pain locations, and adders-jumpers who both added and switched among pain locations throughout the effort. These distribution patterns had a significant effect (p < .001) on pain stability (i.e., the time spent within the same pain location) and on total number of changes in pain locations (p < 0.04); which differed between the adders and jumpers (p < .035). Task endurance was associated with the total number of changes of pain locations (r = .46, p < .04). Finally, a significant effect of time on the number of symmetric locations χ2 (10,4) = 16.17, p < .003 emerged in running. Idiosyncratic pain distribution patterns with more switching among pain locations throughout effort seemed to increase time on task. Further scientific evidence is needed for confirming the extent to which idiosyncratic pain distribution patterns account for and/or help pain management within clinical settings
La evaluación de la autodeterminación en jóvenes hispanohablantes con y sin discapacidad: adaptación de la escala de Autodeterminación AIR.
Mumbardó, C.; Guardia, J. Giné, C.
Psicothema
30
2
(2018)
Longitudinal estimation of the clinically significant change in the treatment of major depression disorder.
Cañete-Massé, C.; Peró-Cebollero, M.; Gudayol-Ferré, E.; Guàrdia-Olmos, J.
Frontiers in Psychology
9
1406
(2018)
Background: Although major depressive disorder is usually treated with antidepressants, only 50–70% of the patients respond to this treatment. This study applied Jacobson and Truax’s (1991) methodology (reliable change index, RCI) to a sample of depressive patients being treated with one of two antidepressants to evaluate their functioning and the effect of certain variables such as severity and age.
Method: Seventy-three depressive patients medicated with Escitalopram (n = 37) or Duloxetine (n = 36) were assessed using the Hamilton depression rating scale over a 24-week period.
Results: They indicate that the RCI stabilizes in an absolute way starting in week 16, and it is not until week 24 that all of the patients become part of the functional population. We found limited statistical significance with respect to the RCI and the external variables.
Conclusion: Our study suggests the need to accompany the traditional statistical methodology with some other clinical estimation systems capable of going beyond a simple subtraction between pre and posttreatment values. Hence, it is concluded that RCI estimations could be stronger and more stable than the classical statistical techniques.
Look who’s talking: bipartite networks as representations of a topic model of New Zealand parliamentary speeches.
B. Curran, K. Higham, E. Ortiz, D. Vasques
PLOS ONE
13
6
(2018)
Quantitative methods to describe the participation to debate of Members of Parliament and the parties they belong to are lacking. Here we propose a new approach that combines topic modeling with complex networks techniques, and use it to characterize the political discourse at the New Zealand Parliament. We implement a Latent Dirichlet Allocation model to discover the thematic structure of the government’s digital database of parliamentary speeches, and construct from it two-mode networks linking Members of the Parliament to the topics they discuss. Our results show how topic popularity changes over time and allow us to relate the trends followed by political parties in their discourses with specific social, economic and legislative events. Moreover, the community analysis of the two-mode network projections reveals which parties dominate the political debate as well as how much they tend to specialize in a small or large number of topics. Our work demonstrates the benefits of performing quantitative analysis in a domain normally reserved for qualitative approaches, providing an efficient way to measure political activity.
Meta-Analysis of the Structural Equation Models' Parameters for the Estimation of Brain Connectivity with fMRI.
Guàrdia-Olmos, J.; Peró-Cebollero, M.; Gudayol-Ferré, E
Frontiers in Behavioral Neuroscience
12
19
(2018)
Structural Equation Models (SEM) is among of the most extensively applied statistical techniques in the study of human behavior in the fields of Neuroscience and Cognitive Neuroscience. This paper reviews the application of SEM to estimate functional and effective connectivity models in work published since 2001. The articles analyzed were compiled from Journal Citation Reports, PsycInfo, Pubmed, and Scopus, after searching with the following keywords: fMRI, SEMs, and Connectivity.
Results: A 100 papers were found, of which 25 were rejected due to a lack of sufficient data on basic aspects of the construction of SEM. The other 75 were included and contained a total of 160 models to analyze, since most papers included more than one model. The analysis of the explained variance (R2) of each model yields an effect of the type of design used, the type of population studied, the type of study, the existence of recursive effects in the model, and the number of paths defined in the model. Along with these comments, a series of recommendations are included for the use of SEM to estimate of functional and effective connectivity models.
Modelado geográfico de la agricultura romana. Vegetación de ribera y viticultura en Hasta Regia
Martín-Arroyo Sánchez, D. J.; Remesal Rodríguez, J.
SPOAL
27
1
(2018)
Micro-flock patterns and macro-clusters in chiral active Brownian disks
Levis, D.; Liebchen, B.
Journal of Physics: Condensed Matter
30
8
(2018)
Chiral active particles (or self-propelled circle swimmers) feature a rich collective behavior, comprising rotating macro-clusters and micro-flock patterns which consist of phase-synchronized rotating clusters with a characteristic self-limited size. These patterns emerge from the competition of alignment interactions and rotations suggesting that they might occur generically in many chiral active matter systems. However, although excluded volume interactions occur naturally among typical circle swimmers, it is not yet clear if macro-clusters and micro-flock patterns survive their presence. The present work shows that both types of pattern do survive but feature strongly enhance fluctuations regarding the size and shape of the individual clusters. Despite these fluctuations, we find that the average micro-flock size still follows the same characteristic scaling law as in the absence of excluded volume interactions, i.e. micro-flock sizes scale linearly with the single-swimmer radius.
Neuronal spatial arrangement shapes effective connectivity traits of in vitro cortical networks
Tibau, E.; Ludl, A.A.; Rüdiger, S.; Orlandi, J.G.; Soriano, J.
IEEE Transactions on Network Science and Engineering
(2018)
We studied effective connectivity in rat cortical cultures with various degrees of spatial aggregation, ranging from homogeneous networks to highly aggregated ones. We considered small cultures 3 mm in diameter and that contained about 2000 neurons. Spatial inhomogeneity favored an increase of metric correlations and connectivity among neighboring neurons. Effective connectivity was determined from spontaneous activity recordings using calcium fluorescence imaging. We used generalized transfer entropy as tool to infer the effective connectivity. We carried out numerical simulations to build networks that mimicked the experimental ones and to test the reliability of the connectivity-inference algorithm. Effective connectivity traits were investigated during the development of the cultures over two weeks, and along the gradual blockade of excitatory connections through CNQX. We observed that the average effective connectivity rapidly increased during culture development. At DIV 15 the average excitatory in-degree was measured as k¯inE≃50 for homogeneous and semi aggregated networks, and k¯inE≃120 for aggregated ones, and with 20% inhibition. Aggregated cultures exhibited assortative traits and a high resilience to chemical damage, while the other cultures were dissassortative or neutral, and less resilient. Our work illustrates the role of metric correlations in spatially embedded networks in
Oxytocin and Vasopressin Receptor variants as a window onto the evolution of human prosociality.
Theofanopoulou, C.; Andirkó, A.; Boeckx, C.
bioRxiv
460584
(2018)
Modern humans’ lifestyle strongly depends on complex social skills like empathy, tolerance and cooperation. Variation in the oxytocin receptor (OXTR) and the arginine-vasopressin receptors (.AVPR1A, AVPR1B genes) has been widely associated with diverse facets of social cognition, but the extent to which these variants may have contributed to the evolution of human prosociality remains to be elucidated. In this study, we compared the OXTR, AVPR1A and AVPR1B DNA sequences of modern humans to those of our closest extinct and extant relatives, and then clustered the variants we identified based on their distribution in the species studied. This clustering, along with the functional importance retrieved for each variant and their frequency in different modern-human populations, is then used to determine if any of the OXTR, AVPR1A and AVPRIB-variants might have had an impact at different evolutionary stages. We report a total of 29 SNPs, associated with phenotypic effects ranging from clearly pro-social to mixed or antisocial. Regarding modern human-specific alleles that could correlate with a shift towards prosociality in modern-humans, we highlight one allele in AVPR1A (rs11174811), found at high frequency and linked to prosocial phenotypes in modern humans, while the ancestral allele is associated with antisocial phenotypes. We also report three sites of putatively convergent changes between modern humans and bonobos (rs237897(A), rs2228485(G) and rs1042615(A)), and note the absence of such a convergent pattern between modern humans and chimpanzees. Finally, we observe the high concentration of ‘modern human specific’ alleles in vasopressin receptors not paralleled in the oxytocin receptor.
Participatory design of citizen science experiments
Senabre, E.; Ferran-Ferrer, N.; Perelló, J.
Comunicar
26
54
(2018)
Este artículo describe y analiza el diseño colaborativo de un proyecto de investigación de ciencia ciudadana a través de la cocreación. Tres grupos de estudiantes de centros de educación secundaria y un equipo de científicos idearon de forma participada tres experimentos sobre comportamiento humano y capital social en espacios públicos y urbanos. El objetivo del estudio es abordar cómo pueden integrarse en una investigación científica el trabajo interdisciplinar y la atención a preocupaciones y necesidades sociales, así como la construcción colectiva de preguntas de investigación. Los 95 estudiantes participantes en el proyecto respondieron una encuesta para evaluar su percepción sobre las dinámicas y herramientas utilizadas en el proceso de cocreación de cada experimento, y los cinco científicos respondieron a una entrevista semiestructurada. Los resultados de las encuestas y entrevistas demuestran cómo la ciencia ciudadana puede alcanzar una modalidad «cocreada» más allá del paradigma habitual «contributivo», el cual únicamente suele implicar al público o amateurs en la recopilación de datos. Esta modalidad de ciencia más colaborativa con la ciudadanía fue posible gracias a la adecuación de materiales y mecanismos de facilitación, así como al fomento de aspectos clave en una investigación como pueden ser la confianza, la creatividad y la transparencia. Los resultados apuntan también hacia la posibilidad de adoptar estrategias similares de codiseño en otros contextos de colaboración científica y generación colaborativa de conocimiento
Perfil de la autopercepción en personas con esquizofrenia.
Ruiz-Pérez, M.; Llistar-Verdú, S.; Farràs-Permanyer, L.; Gómez-Hinojosa, T.
Revista de Enfermería y Salud Mental
11
5 12
(2018)
Periodic spiking by a pair of ionic channels
Ramírez-Piscina,L.; Sancho, J.M.
Physica A : Statistical Mechanics and its Application
505
345 354
(2018)
Neuronal cells present periodic trains of localized voltage spikes involving a large amount of different ionic channels. A relevant question is whether this is a cooperative effect or it could also be an intrinsic property of individual channels. Here we use a Langevin formulation for the stochastic dynamics of a pair of Na and K ionic channels. These two channels are simple gated pore models where a minimum set of degrees of freedom follow standard statistical physics. The whole system is totally autonomous without any external energy input, except for the chemical energy of the different ionic concentrations across the membrane. As a result it is shown that a unique pair of different ionic channels can sustain membrane potential periodic spikes. The spikes are due to the interaction between the membrane potential, the ionic flows and the dynamics of the internal parts (gates) of each channel structures. The spike involves a series of dynamical steps being the more relevant one the leak of Na ions. Missing spike events are caused by the altered functioning of specific model parts. The time dependent spike structure is comparable with experimental data.
Review de "Sinner, Alejandro G., La ceca de Ilduro, Archaeopress Publishing Ltd, Archaeopres Roman Archaeology 29"
Revilla Calvo, V.
Pyrenae: Revista de Prehistòria i Antiguitat de la Mediterrània OccidentalPyrenae: Revista de Prehistòria i Antiguitat de la Mediterrània Occidental
49
2
(2018)
SFU ReviewSP-NEG: a Spanish corpus annotated with negation for sentiment analysis. A typology of negation patterns
Jiménez-Zafra, S.M; Taulé, M.; Martín-Valdivia, M.T.; Martí, M.A.; Ureña López, LA.
Language Resources and Evaluation
52
2
(2018)
In this paper, we present SFU ReviewSP-NEG, the first Spanish corpus annotated with negation with a wide coverage freely available. We describe the methodology applied in the annotation of the corpus including the tagset, the linguistic criteria and the inter-annotator agreement tests. We also include a complete typology of negation patterns in Spanish. This typology has the advantage that it is easy to express in terms of a tagset for corpus annotation: the types are clearly defined, which avoids ambiguity in the annotation process, and they provide wide coverage (i.e. they resolved all the cases occurring in the corpus). We use the SFU ReviewSP as a base in order to make the annotations. The corpus consists of 400 reviews, 221,866 words and 9455 sentences, out of which 3022 sentences contain at least one negation structure.
Shopping Decisions Made in a Virtual World: Defining a State-Based Model of Collaborative and Conversational User-Recommender Interactions
Contreras, D.; Salamó, M.; Rodríguez, I.; Puig, A.
Ieee Consumer Electronics Magazine
7
4
(2018)
A three-dimensional (3-D) virtual world (VW) facilitates users? interactions as they immerse and engage themselves in a shared virtual space. This type of interface may be especially useful when consumers utilize home electronics for accessing personalized online services. Previous research has focused on a collaborative conversational recommender (CCR) framework, in which a synchronous online 3-D interface for multiple consumers integrates with a recommender. In this article, a state-based model of user-recommender interaction that allows users to move from different states of interaction (i.e., individual and collaborative) among users, is defined. It is then evaluated by users and compared with an individual approach. The results from this research demonstrate that the collaborative capacities proposed in the framework improve user experience and significantly increase the performance of the recommendation process, i.e., users take less time in achieving the desired service.
Spatio-temporal organization of correlated local activity within global avalanches in slowly driven interfaces
Planet, R.; López, J.M.; Santucci, S.; Ortín, J.
Physical Review Letters
121
3
(2018)
We study the jerky response of slowly driven fronts in disordered media, just above the depinning transition. We focus on how spatially disconnected clusters of internally correlated activity lead to large-scale velocity fluctuations in the form of global avalanches and identify three different ways in which local activity clusters may organize within a global avalanche, depending on the distance to criticality. Our analysis provides new scaling relations between the power-law exponents of the statistical distributions of sizes and durations of local bursts and global avalanches. Fluid fronts of imbibition in heterogeneous media are taken as a case study to validate these scaling relations.
SRGAP2 and the gradual evolution of the modern human language faculty
Martins, P. T.; Marí, M.; Boeckx, C.
Journal of Language Evolution
3
1
(2018)
In this article, we examine a new source of evidence that draws on data from archaic human genomes to support the hypothesis that vocal learning in Homo preceded the emergence of anatomically modern humans. We build our claim on the evolutionary history of the SLIT-ROBO GTPase 2 gene (SRGAP2). The SLIT-ROBO molecular pathway has been shown to have an important role in the context of vocal learning. Though the relevance of the SRGAP2 gene duplication in the emergence of some aspect of language has not gone completely unnoticed, recent results now allow us to articulate a mechanistic hypothesis of its role in the context of axon guidance. Specifically, SRGAP2C, a duplication of SRGAP2 crucially also found in Neanderthals and Denisovans, but not in extant mammals, inhibits the ancestral SRGAP2A, which in turn modulates the axon guidance function of the SLIT-ROBO molecular pathway. This, we claim, could have contributed to the establishment of the critical cortico-laryngeal connection of the vocal learning circuit. Our conclusions support the idea that complex vocal learning could already have been part of the arsenal of some of our extinct ancestors.
Synchronization invariance under network structural transformations
Arola-Fernandez, L.; Diaz-Guilera, A.; Arenas, A.
Physical Review E
97
6
(2018)
Synchronization processes are ubiquitous despite the many connectivity patterns that complex systems can show. Usually, the emergence of synchrony is a macroscopic observable; however, the microscopic details of the system, as, e.g., the underlying network of interactions, is many times partially or totally unknown. We already know that different interaction structures can give rise to a common functionality, understood as a common macroscopic observable. Building upon this fact, here we propose network transformations that keep the collective behavior of a large system of Kuramoto oscillators invariant. We derive a method based on information theory principles, that allows us to adjust the weights of the structural interactions to map random homogeneous in-degree networks into random heterogeneous networks and vice versa, keeping synchronization values invariant. The results of the proposed transformations reveal an interesting principle; heterogeneous networks can be mapped to homogeneous ones with local information, but the reverse process needs to exploit higher-order information. The formalism provides analytical insight to tackle real complex scenarios when dealing with uncertainty in the measurements of the underlying connectivity structure.
The Giant Elastocaloric Effect in a Cu–Zn–Al Shape-Memory Alloy: a Calorimetric Study
Gràcia-Condal,A.; Stern-Taulats, E.; Planes, A.; Vives, E.; and Mañosa, LL.
Physica status solidi (b)
255
2
(2018)
We study the giant elastocaloric effect in a Cu–Zn–Al shape‐memory alloy by means of simultaneous calorimetry and dilatometry measurements under applied uniaxial compression which have been carried out with a bespoke experimental setup. The output data allow a unique quasidirect and indirect characterization of the thermal response that provides accurate ΔS and ΔT values. We report a large thermal response of |ΔS| = 22 J K kg−1, |ΔT| = 12.3 K, and RC = 325 K kg−1 driven by moderate uniaxial compression changes of 32.2 MPa, which is comparable with the performance of the best magnetocaloric materials. In view of the hysteresis effects, the thermal response is predicted to exhibit reversible values for |Δσ| = 32 MPa.
The RNA-Binding Protein of a Double-Stranded RNA Virus Acts like a Scaffold Protein
Mata, C.P.; Mertens, J.; Fontana, J.; Luque, D.; Allende-Ballestero, C.; Reguera, D.; Trus, B.L.; Steven, A.C.; Carrascosa, J.L.; Caston, J.R.
Journal of Virology
92
19
(2018)
Infectious bursal disease virus (IBDV), a nonenveloped, double-stranded RNA (dsRNA) virus with a T=13 icosahedral capsid, has a virion assembly strategy that initiates with a precursor particle based on an internal scaffold shell similar to that of tailed double-stranded DNA (dsDNA) viruses. In IBDV-infected cells, the assembly pathway results mainly in mature virions that package four dsRNA segments, although minor viral populations ranging from zero to three dsRNA segments also form. We used cryo-electron microscopy (cryo-EM), cryo-electron tomography, and atomic force microscopy to characterize these IBDV populations. The VP3 protein was found to act as a scaffold protein by building an irregular, ∼40-Å-thick internal shell without icosahedral symmetry, which facilitates formation of a precursor particle, the procapsid. Analysis of IBDV procapsid mechanical properties indicated a VP3 layer beneath the icosahedral shell, which increased the effective capsid thickness. Whereas scaffolding proteins are discharged in tailed dsDNA viruses, VP3 is a multifunctional protein. In mature virions, VP3 is bound to the dsRNA genome, which is organized as ribonucleoprotein complexes. IBDV is an amalgam of dsRNA viral ancestors and traits from dsDNA and single-stranded RNA (ssRNA) viruses.
Treatment of metabolic syndrome and quality of life in patients with schizophrenia: a systematic review
Ruiz-Pérez, M.; Llistar-Verdú, S.; Farràs-Permanyer, L.; Gómez-Hinojosa, T.
Revista de Psicologia i Ciències de l'Educació i de l'Esport
36
1
(2018)
schizophrenia affects around 0.3–0.7% people at some point in their lives - or 24 million people worldwide. This review covers topics of broad general interest that have seen significant development or progress in recent years. This paper aims to review the scientific literature of the past 10 years on metabolic syndrome regarding the quality of life of people with schizophrenia and the interventions carried out. A bibliographical search was conducted on Web of Science and PsycINFO, using the keywords of this study. More than 90 publications were found, 70 of which met the requirements. The main topic was schizophrenia, metabolic syndrome and quality of life. Those that focused on the effects of drugs were excluded. Although the association between mental illness and physical health problems has been convincingly demonstrated, numerous studies support the existence of dual physical health care neglect of people with schizophrenia. On the other hand, the modifiable risk factors are clearly defined to improve the physical health of these patients as well as the aspects which should be included in any approach to improve metabolic syndrome in particular, physical health in general, and thus modify the self-perceived quality of life. The data on psychoeducational treatments for this population were insufficient. However, some studies show that the implementation of behavioral interventions in clinical practice can help patients improve their overall health and prevent chronic disease. There are few studies on the application of ehealth devices to schizophrenic patients.
Viral nanomechanics with a virtual atomic force microscope
Aznar, M.; Roca-Bonet, S.; Reguera, D.
Journal of Physics: Condensed Matter
30
26
(2018)
One of the most important components of a virus is the protein shell or capsid that encloses its genetic material. The main role of the capsid is to protect the viral genome against external aggressions, facilitating its safe and efficient encapsulation and delivery. As a consequence, viral capsids have developed astonishing mechanical properties that are crucial for viral function. These remarkable properties have started to be unveiled in single-virus nanoindentation experiments, and are opening the door to the use of viral-derived artificial nanocages for promising bio- and nano-technological applications. However, the interpretation of nanoindentation experiments is often difficult, requiring the support of theoretical and simulation analysis. Here we present a 'Virtual AFM' (VAFM), a Brownian Dynamics simulation of a coarse-grained model of virus aimed to mimic the standard setup of atomic force microscopy (AFM) nanoindentation experiments. Despite the heavy level of coarse-graining, these simulations provide valuable information which is not accessible in experiments. Rather than focusing on a specific virus, the VAFM will be used to analyze how the mechanical response and breaking of viruses depend on different parameters controlling the effective interactions between capsid's structural units. In particular, we will discuss the influence of adsorption, the tip radius, and the rigidity and shape of the shell on its mechanical response.
A new approach to international trade from Network Geometry. The World Trade Atlas 1870-2013
García-Pérez, G.; Boguñá, M.; Allard, A.; Serrano, M. Á.
Networks of International Trade and Investment: Understanding globalization through the lens of network analysis, Sara Gorgoni, Alessia Amighini, and Matthew Smith Eds. REGNE UNIT.
(2018)
Here, we present the World Trade Atlas 1870–2013, a collection of annual world trade maps in which distance combines economic size and the different dimensions that affect international trade beyond mere geography. Trade distances, based on a gravity model predicting the existence of significant trade channels, are such that the closer countries are in trade space, the greater their chance of becoming connected. The atlas provides us with information regarding the long-term evolution of the international trade system and demonstrates that, in terms of trade, the world is not flat but hyperbolic, as a reflection of its complex architecture. The departure from flatness has been increasing since World War I, meaning that differences in trade distances are growing and trade networks are becoming more hierarchical. Smaller-scale economies are moving away from other countries except for the largest economies; meanwhile those large economies are increasing their chances of becoming connected worldwide. At the same time, Preferential Trade Agreements do not fit in perfectly with natural communities within the trade space and have not necessarily reduced internal trade barriers. We discuss an interpretation in terms of globalization, hierarchization, and localization; three simultaneous forces that shape the international trade system.
ISBN: 978-1-62273-065-0
Complexity applications in language and communication sciences.
Massip-Bonet, À.; Bel-Enguix, G.; Bastardas- Boada, A.
Springer Nature.Switzerland. 2019
ISBN: 978-3-030-04596-8
(2018)
This book offers insights on the study of natural language as a complex adaptive system. It discusses a new way to tackle the problem of language modeling, and provides clues on how the close relation between natural language and some biological structures can be very fruitful for science. The book examines the theoretical framework and then applies its main principles to various areas of linguistics. It discusses applications in language contact, language change, diachronic linguistics, and the potential enhancement of classical approaches to historical linguistics by means of new methodologies used in physics, biology, and agent systems theory. It shows how studying language evolution and change using computational simulations enables to integrate social structures in the evolution of language, and how this can give rise to a new way to approach sociolinguistics. Finally, it explores applications for discourse analysis, semantics and cognition.
Active microrheology in corrugated channels
Puertas, A. M., Malgaretti, P., & Pagonabarraga, I.
The Journal of chemical physics
149
17
(2018)
We analyze the dynamics of a tracer particle embedded in a bath of hard spheres confined in a channel of varying section. By means of Brownian dynamics simulations, we apply a constant force on the tracer particle and discuss the dependence of its mobility on the relative magnitude of the external force with respect to the entropic force induced by the confinement. A simple theoretical one-dimensional model is also derived, where the contribution from particle-particle and particle-wall interactions is taken from simulations with no external force. Our results show that the mobility of the tracer is strongly affected by the confinement. The tracer velocity in the force direction has a maximum close to the neck of the channel, in agreement with the theory for small forces. Upon increasing the external force, the tracer is effectively confined to the central part of the channel and the velocity modulation decreases, which cannot be reproduced by the theory. This deviation marks the regime of validity of linear response. Surprisingly, when the channel section is not constant, the effective friction coefficient is reduced as compared to the case of a plane channel. The transversal velocity, which cannot be studied with our model, follows qualitatively the derivative of the channel section, in agreement with previous theoretical calculations for the tracer diffusivity in equilibrium.
Assembly and Transport of Microscopic Cargos via Reconfigurable Photoactivated Magnetic Microdockers
Martinez-Pedrero, Fernando; Massana-Cid, Helena; Tierno, Pietro
Small
13
1603449
(2017)
The realization of micromotors able to dock and transport microscopic objects in a fluid medium has direct applications toward the delivery of drugs and chemicals in small channels and pores, and the realization of functional wireless microrobots in lab-on-a-chip technology. A simple and general method to tow microscopic particles in water by using remotely controllable light-activated hematite microdockers is demonstrated. These anisotropic ferromagnetic particles can be synthesized in bulk and present the remarkable ability to be activated by light while independently manipulated via external fields. The photoactivation process induces a phoretic flow capable to attract cargos toward the surface of the propellers, while a rotating magnetic field is used to transport the composite particles to any location of the experimental platform. The method allows the assembling of small colloidal clusters of various sizes, composed by a skeleton of mobile magnetic dockers, which cooperatively keep, transport, and release the microscopic cargos. The possibility to easily reconfigure in situ the location of the docker above the cargo is demonstrated, which enables optimize transport and cargo release operations.
Noise focusing in neuronal tissues: Symmetry breaking and localization in excitable networks with quenched disorder
Orlandi, Javier G.; Casademunt, Jaume
Phys Rev E
95
052304
(2017)
We introduce a coarse-grained stochastic model for the spontaneous activity of neuronal cultures to explain the phenomenon of noise focusing, which entails localization of the noise activity in excitable networks with metric correlations. The system is modeled as a continuum excitable medium with a state-dependent spatial coupling that accounts for the dynamics of synaptic connections. The most salient feature is the emergence at the mesoscale of a vector field V(r), which acts as an advective carrier of the noise. This entails an explicit symmetry breaking of isotropy and homogeneity that stems from the amplification of the quenched fluctuations of the network by the activity avalanches, concomitant with the excitable dynamics. We discuss the microscopic interpretation of V(r) and propose an explicit construction of it. The coarse-grained model shows excellent agreement with simulations at the network level. The generic nature of the observed phenomena is discussed.
Noise-induced polarization switching in complex networks
Haerter, Jan O.; Diaz-Guilera, Albert; Angeles Serrano, M.
Phys Rev E
95
042305
(2017)
The combination of bistability and noise is ubiquitous in complex systems, from biology to social interactions, and has important implications for their functioning and resilience. Here we use a simple three-state dynamical process, in which nodes go from one pole to another through an intermediate state, to show that noise can induce polarization switching in bistable systems if dynamical correlations are significant. In large, fully connected networks, where dynamical correlations can be neglected, increasing noise yields a collapse of bistability to an unpolarized configuration where the three possible states of the nodes are equally likely. In contrast, increased noise induces abrupt and irreversible polarization switching in sparsely connected networks. In multiplexes, where each layer can have a different polarization tendency, one layer is dominant and progressively imposes its polarization state on the other, offsetting or promoting the ability of noise to switch its polarization. Overall, we show that the interplay of noise and dynamical correlations can yield discontinuous transitions between extremes, which cannot be explained by a simple mean-field description.
Stationary patterns in star networks of bistable units: Theory and application to chemical reactions
Nikos E. Kouvaris, Michael Sebek, Albert Iribarne, Albert Díaz-Guilera, and István Z. Kiss
Phys Rev E
95
042203
(2017)
We present theoretical and experimental studies on pattern formation with bistable dynamical units coupled in a star network configuration. By applying a localized perturbation to the central or the peripheral elements, we demonstrate the subsequent spreading, pinning, or retraction of the activations; such analysis enables the characterization of the formation of stationary patterns of localized activity. The results are interpreted with a theoretical analysis of a simplified bistable reaction-diffusion model. Weak coupling results in trivial pinned states where the activation cannot propagate. At strong coupling, a uniform state is expected with active or inactive elements at small or large degree networks, respectively. A nontrivial stationary spatial pattern, corresponding to an activation pinning, is predicted to occur at an intermediate number of peripheral elements and at intermediate coupling strengths, where the central activation of the network is pinned, but the peripheral activation propagates toward the center. The results are confirmed in experiments with star networks of bistable electrochemical reactions. The experiments confirm the existence of the stationary spatial patterns and the dependence of coupling strength on the number of peripheral elements for transitions between pinned and retreating or spreading fronts in forced network configurations (where the central or periphery elements are forced to maintain their states).
Equivalence between Non-Markovian and Markovian Dynamics in Epidemic Spreading Processes
Starnini, Michele; Gleeson, James P.; Boguna, Marian
Phys Rev Lett
118
128301
(2017)
A general formalism is introduced to allow the steady state of non-Markovian processes on networks to be reduced to equivalent Markovian processes on the same substrates. The example of an epidemic spreading process is considered in detail, where all the non-Markovian aspects are shown to be captured within a single parameter, the effective infection rate. Remarkably, this result is independent of the topology of the underlying network, as demonstrated by numerical simulations on two-dimensional lattices and various types of random networks. Furthermore, an analytic approximation for the effective infection rate is introduced, which enables the calculation of the critical point and of the critical exponents for the non-Markovian dynamics.
Synchronization in Dynamical Networks of Locally Coupled Self-Propelled Oscillators
Levis, Demian; Pagonabarraga, Ignacio; Diaz-Guilera, Albert
Phys Rev X
7
011028
(2017)
The emergent cooperative behavior of mobile physical entities exchanging information with their neighborhood has become an important problem across disciplines, thus requiring a general framework to describe such a variety of situations. We introduce a generic model to tackle this problem by considering the synchronization in time-evolving networks generated by the stochastic motion of self-propelled physical interacting units. This framework generalizes previous approaches and brings a unified picture to understand the role played by the network topology, the motion of the agents, and their mutual interaction. This allows us to identify different dynamic regimes where synchronization can be understood from theoretical considerations. While for noninteracting particles, self-propulsion accelerates synchronization, the presence of excluded volume interactions gives rise to a richer scenario, where self-propulsion has a nonmonotonic impact on synchronization. We show that the synchronization of locally coupled mobile oscillators generically proceeds through coarsening, verifying the dynamic scaling hypothesis, with the same scaling laws as the 2D XY model following a quench. Our results shed light into the generic nature of synchronization in time-dependent networks, providing an efficient way to understand more specific situations involving interacting mobile agents.
Driven transport on open filaments with interfilament switching processes
Ghosh, Subhadip; Pagonabarraga, Ignacio; Muhuri, Sudipto
Phys Rev E
95
022417
(2017)
We study a two-filament driven lattice gas model with oppositely directed species of particles moving on two parallel filaments with filament-switching processes and particle inflow and outflow at filament ends. The filament-switching process is correlated with the occupation number of the adjacent site such that particles switch filaments with finite probability only when oppositely directed particles meet on the same filament. This model mimics some of the coarse-grained features observed in context of microtubule-(MT) based intracellular transport, wherein cellular cargo loaded and off-loaded at filament ends are transported on multiple parallel MT filaments and can switch between the parallel microtubule filaments. We focus on a regime where the filaments are weakly coupled, such that filament-switching rate of particles scale inversely as the length of the filament. We find that the interplay of (off-) loading processes at the boundaries and the filament-switching process of particles leads to some distinctive features of the system. These features includes occurrence of a variety of phases in the system with inhomogeneous density profiles including localized density shocks, density difference across the filaments, and bidirectional current flows in the system. We analyze the system by developing a mean field (MF) theory and comparing the results obtained from the MF theory with the Monte Carlo (MC) simulations of the dynamics of the system. We find that the steady-state density and current profiles of particles and the phase diagram obtained within the MF picture matches quite well with MC simulation results. These findings maybe useful for studying multifilament intracellular transport.
Fluidization and Active Thinning by Molecular Kinetics in Active Gels
Oriola, David; Alert, Ricard; Casademunt, Jaume
Phys Rev Lett
118
088002
(2017)
We derive the constitutive equations of an active polar gel from a model for the dynamics of elastic molecules that link polar elements. Molecular binding kinetics induces the fluidization of the material, giving rise to Maxwell viscoelasticity and, provided that detailed balance is broken, to the generation of active stresses. We give explicit expressions for the transport coefficients of active gels in terms of molecular properties, including nonlinear contributions on the departure from equilibrium. In particular, when activity favors linker unbinding, we predict a decrease of viscosity with activity-active thinning-of kinetic origin, which could explain some experimental results on the cell cortex. By bridging the molecular and hydrodynamic scales, our results could help understand the interplay between molecular perturbations and the mechanics of cells and tissues.
Effective viscosity and dynamics of spreading epithelia: a solvable model
Blanch-Mercader, C.; Vincent, R.; Bazellieres, E.; Serra-Picamal, X.; Trepat, X.; Casademunt, J.
Soft Matter
13
1235 1243
(2017)
Collective cell migration in spreading epithelia in controlled environments has become a landmark in our current understanding of fundamental biophysical processes in development, regeneration, wound healing or cancer. Epithelial monolayers are treated as thin layers of a viscous fluid that exert active traction forces on the substrate. The model is exactly solvable and shows a broad range of applicabilities for the quantitative analysis and interpretation of force microscopy data of monolayers from a variety of experiments and cell lines. In addition, the proposed model provides physical insights into how the biological regulation of the tissue is encoded in a reduced set of time-dependent physical parameters. In particular the temporal evolution of the effective viscosity entails a mechanosensitive regulation of adhesion. Besides, the observation of an effective elastic tensile modulus can be interpreted as an emergent phenomenon in an active fluid.
Morphology of clusters of attractive dry and wet self-propelled spherical particle suspensions
Alarcon, Francisco; Valeriani, Chantal; Pagonabarraga, Ignacio
Soft Matter
13
814 826
(2017)
In order to assess the effect of hydrodynamics in the assembly of active attractive spheres, we simulate a semi-dilute suspension of attractive self-propelled spherical particles in a quasi-two dimensional geometry comparing the case with and without hydrodynamics interactions. To start with, independent of the presence of hydrodynamics, we observe that depending on the ratio between attraction and propulsion, particles either coarsen or aggregate forming finite-size clusters. Focusing on the clustering regime, we characterize two different cluster parameters, i.e. their morphology and orientational order, and compare the case when active particles behave either as pushers or pullers (always in the regime where inter-particle attractions compete with self-propulsion). Studying cluster phases for squirmers with respect to those obtained for active Brownian disks (indicated as ABPs), we have shown that hydrodynamics alone can sustain a cluster phase of active swimmers (pullers), while ABPs form cluster phases due to the competition between attraction and self-propulsion. The structural properties of the cluster phases of squirmers and ABPs are similar, although squirmers show sensitivity to active stresses. Active Brownian disks resemble weakly pusher squirmer suspensions in terms of cluster size distribution, structure of the radius of gyration on the cluster size and degree of cluster polarity.
The geometric nature of weights in real complex networks
Allard, Antoine; Serrano, M. Angeles; Garcia-Perez, Guillermo; Boguna, Marian
Nature Communications
8
14103
(2017)
The topology of many real complex networks has been conjectured to be embedded in hidden metric spaces, where distances between nodes encode their likelihood of being connected. Besides of providing a natural geometrical interpretation of their complex topologies, this hypothesis yields the recipe for sustainable Internet's routing protocols, sheds light on the hierarchical organization of biochemical pathways in cells, and allows for a rich characterization of the evolution of international trade. Here we present empirical evidence that this geometric interpretation also applies to the weighted organization of real complex networks. We introduce a very general and versatile model and use it to quantify the level of coupling between their topology, their weights and an underlying metric space. Our model accurately reproduces both their topology and their weights, and our results suggest that the formation of connections and the assignment of their magnitude are ruled by different processes.
Quantification of network structural dissimilarities
Schieber, Tiago A.; Carpi, Laura; Diaz-Guilera, Albert; Pardalos, Panos M.; Masoller, Cristina; Ravetti, Martin G.
Nature Communications
8
13928
(2017)
Identifying and quantifying dissimilarities among graphs is a fundamental and challenging problem of practical importance in many fields of science. Current methods of network comparison are limited to extract only partial information or are computationally very demanding. Here we propose an efficient and precise measure for network comparison, which is based on quantifying differences among distance probability distributions extracted from the networks. Extensive experiments on synthetic and real-world networks show that this measure returns non-zero values only when the graphs are non-isomorphic. Most importantly, the measure proposed here can identify and quantify structural topological differences that have a practical impact on the information flow through the network, such as the presence or absence of critical links that connect or disconnect connected components.
Effect of verbal task complexity in a working memory paradigm in patients with type 1 diabetes. A fMRI study
J Guardia-Olmos, G.B. Gallardo-Moreno, E. Gudayol-Ferre, M. Pero-Cebollero, A.A. Gonzalez-Garrido
PLoS ONE
12
e0178172
(2017)
Type 1 diabetes (T1D) is commonly diagnosed in childhood and adolescence, and the developing brain has to cope with its deleterious effects. Although brain adaptation to the disease may not result in evident cognitive dysfunction, the effects of T1D on neurodevelopment could alter the pattern of BOLD fMRI activation. The aim of this study was to explore the neural BOLD activation pattern in patients with T1D versus that of healthy matched controls while performing two visuospatial working memory tasks, which included a pair of assignments administered through a block design. In the first task (condition A), the subjects were shown a trial sequence of 3 or 4 white squares positioned pseudorandomly around a fixation point on a black background. After a fixed delay, a second corresponding sequence of 3 or 4 red squares was shown that either resembled (direct, 50%) or differed from (50%) the previous stimulation order. The subjects were required to press one button if the two spatial sequences were identical or a second button if they were not. In condition B, the participants had to determine whether the second sequence of red squares appeared in inverse order (inverse, 50%) or not (50%) and respond by pressing a button. If the latter sequence followed an order distinct from the inverse sequence, the subjects were instructed to press a different button. Sixteen patients with normal IQ and without diabetes complications and 16 healthy control subjects participated in the study. In the behavioral analysis, there were no significant differences between the groups in the pure visuo-spatial task, but the patients with diabetes exhibited poorer performance in the task with verbal stimuli (p < .001). However, fMRI analyses revealed that the patients with T1D showed significantly increased activation in the prefrontal inferior cortex, subcortical regions and the cerebellum (in general p < .001). These different activation patterns could be due to adaptive compensation mechanisms that are devoted to improving efficiency while solving more complex cognitive tasks.
Dominance of Metric Correlations in Two-Dimensional Neuronal Cultures Described through a Random Field Ising Model
Hernandez-Navarro, L; Orlandi, JG; Cerruti, B; Vives, E; Soriano, J
Phys Rev Lett
118
208101
(2017)
We introduce a novel random field Ising model, grounded on experimental observations, to assess the importance of metric correlations in cortical circuits in vitro. Metric correlations arise from both the finite axonal length and the heterogeneity in the spatial arrangement of neurons. The experiments consider the response of neuronal cultures to an external electric stimulation for a gradually weaker connectivity strength between neurons, and in cultures with different spatial configurations. The model can be analytically solved in the metric-free, mean-field scenario. The presence of metric correlations precipitates a strong deviation from the mean field. Null models of the same networks that preserve the distribution of connections recover the mean field. Our results show that metric-inherited correlations in spatial networks dominate the connectivity blueprint, mask the actual distribution of connections, and may emerge as the asset that shapes network dynamics.
Geometric Correlations Mitigate the Extreme Vulnerability of Multiplex Networks against Targeted Attacks
Kaj-Kolja Kleineberg, Lubos Buzna, Fragkiskos Papadopoulos, Marián Boguñá, and M. Ángeles Serrano
Phys Rev Lett
118
218301
(2017)
We show that real multiplex networks are unexpectedly robust against targeted attacks on high-degree nodes and that hidden interlayer geometric correlations predict this robustness. Without geometric correlations, multiplexes exhibit an abrupt breakdown of mutual connectivity, even with interlayer degree correlations. With geometric correlations, we instead observe a multistep cascading process leading into a continuous transition, which apparently becomes fully continuous in the thermodynamic limit. Our results are important for the design of efficient protection strategies and of robust interacting networks in many domains.
Detecting the Significant Flux Backbone of Escherichia coli metabolism
Guell, Oriol; Sagues, Francesc; Serrano, Angeles
FEBS LETTERS
591
1437 1451
(2017)
The heterogeneity of computationally predicted reaction fluxes in metabolic networks within a single flux state can be exploited to detect their significant flux backbone. Here, we disclose the backbone of Escherichia coli, and compare it with the backbones of other bacteria. We find that, in general, the core of the backbones is mainly composed of reactions in energy metabolism corresponding to ancient pathways. In E. coli, the synthesis of nucleotides and the metabolism of lipids form smaller cores which rely critically on energy metabolism. Moreover, the consideration of different media leads to the identification of pathways sensitive to environmental changes. The metabolic backbone of an organism is thus useful to trace simultaneously both its evolution and adaptation fingerprints.
Continuous time persistent random walk: a review and some generalizations
Masoliver, Jaume; Lindenberg, Katja
EUROPEAN PHYSICAL JOURNAL B
90
107
(2017)
We review some extensions of the continuous time random walk first introduced by Elliott Montroll and George Weiss more than 50 years ago [E.W. Montroll, G.H. Weiss, J. Math. Phys. 6, 167 (1965)], extensions that embrace multistate walks and, in particular, the persistent random walk. We generalize these extensions to include fractional random walks and derive the associated master equation, namely, the fractional telegrapher's equation. We dedicate this review to our joint work with George H. Weiss (1930-2017). It saddens us greatly to report the recent death of George Weiss, a scientific giant and at the same time a lovely and humble man.
Quantum and random walks as universal generators of probability distributions
Montero, Miquel
PHYSICAL REVIEW A
95
062326
(2017)
Quantum walks and random walks bear similarities and divergences. One of the most remarkable disparities affects the probability of finding the particle at a given location: typically, almost a flat function in the first case and a bell-shaped one in the second case. Here I show how one can impose any desired stochastic behavior (compatible with the continuity equation for the probability function) on both systems by the appropriate choice of time-and site-dependent coins. This implies, in particular, that one can devise quantum walks that show diffusive spreading without losing coherence as well as random walks that exhibit the characteristic fast propagation of a quantum particle driven by a Hadamard coin.
Dynamical properties of the herding voter model with and without noise
Rozanova, Liudmila; Boguna, Marian
PHYSICAL REVIEW E
96
012310
(2017)
Collective leadership and herding may arise in standard models of opinion dynamics as an interplay of a strong separation of time scales within the population and its hierarchical organization. Using the voter model as a simple opinion formation model, we show that, in the herding phase, a group of agents become effectively the leaders of the dynamics while the rest of the population follow blindly their opinion. Interestingly, in some cases such herding dynamics accelerates the time to consensus, which then becomes size independent or, on the contrary, makes the consensus nearly impossible. These behaviors have important consequences when an external noise is added to the system that makes consensus (absorbing) states to disappear. We analyze this model, which shows an interesting phase diagram, with a purely diffusive phase, a herding (or two-states) phase, and mixed phases where both behaviors are possible.
Orientational dynamics of fluctuating dipolar particles assembled in a mesoscopic colloidal ribbon
Helena Massana-Cid, Fernando Martinez-Pedrero, Andrejs Cebers, and Pietro Tierno
PHYSICAL REVIEW E
91
012607
(2017)
We combine experiments and theory to investigate the dynamics and orientational fluctuations of ferromagnetic microellipsoids that form a ribbonlike structure due to attractive dipolar forces. When assembled in the ribbon, the ellipsoids display orientational thermal fluctuations with an amplitude that can be controlled via application of an in-plane magnetic field. We use video microscopy to investigate the orientational dynamics in real time and space. Theoretical arguments are used to derive an analytical expression that describes how the distribution of the different angular configurations depends on the strength of the applied field. The experimental data are in good agreement with the developed model for all the range of field parameters explored. Understanding the role of fluctuations in chains composed of dipolar particles is important not only from a fundamental point of view, but it may also help understanding the stability of such structures against thermal noise, which is relevant in microfluidics and laboratory-on-a-chip applications.
Collective Behavior of Chiral Active Matter: Pattern Formation and Enhanced Flocking
Liebchen, Benno; Levis, Demian
PHYSICAL REVIEW LETTERS
119
058002
(2017)
We generalize the Vicsek model to describe the collective behavior of polar circle swimmers with local alignment interactions. While the phase transition leading to collective motion in 2D (flocking) occurs at the same interaction to noise ratio as for linear swimmers, as we show, circular motion enhances the polarization in the ordered phase (enhanced flocking) and induces secondary instabilities leading to structure formation. Slow rotations promote macroscopic droplets with late time sizes proportional to the system size (indicating phase separation) whereas fast rotations generate patterns consisting of phase synchronized microflocks with a controllable characteristic size proportional to the average single-particle swimming radius. Our results defy the viewpoint that monofrequent rotations form a vapid extension of the Vicsek model and establish a generic route to pattern formation in chiral active matter with possible applications for understanding and designing rotating microflocks.
Three-dimensional telegrapher's equation and its fractional generalization
Masoliver, Jaume
PHYSICAL REVIEW E
96
022101
(2017)
We derive the three-dimensional telegrapher's equation out of a random walk model. The model is a three-dimensional version of the multistate random walk where the number of different states form a continuum representing the spatial directions that the walker can take. We set the general equations and solve them for isotropic and uniform walks which finally allows us to obtain the telegrapher's equation in three dimensions. We generalize the isotropic model and the telegrapher's equation to include fractional anomalous transport in three dimensions.
7,8-dihydroxyflavone ameliorates cognitive and motor deficits in a Huntington's disease mouse model through specific activation of the PLC gamma 1 pathway
Gerardo García-Díaz Barriga Albert Giralt Marta Anglada-Huguet Nuria Gaja-Capdevila Javier G. Orlandi Jordi Soriano Josep-Maria Canals Jordi Alberch
HUMAN MOLECULAR GENETICS
26
3144 3160
(2017)
Huntington’s disease (HD) is a fatal neurodegenerative disease with motor, cognitive and psychiatric impairment. Dysfunctions in HD models have been related to reduced levels of striatal brain-derived neurotrophic factor (BDNF) and imbalance between its receptors TrkB and p75(NTR). Thus, molecules with activity on the BDNF/TrkB/p75 system can have therapeutic potential. 7,8-Dihydroxyflavone (7,8-DHF) was described as a TrkB agonist in several models of neuro-degenerative diseases, however, its TrkB activation profile needs further investigation due to its pleiotropic properties and divergence from BDNF effect. To investigate this, we used in vitro and in vivo models of HD to dissect TrkB activation upon 7,8-DHF treatment. 7,8-DHF treatment in primary cultures showed phosphorylation of TrkBY816 but not TrkBY515 with activation of the PLCγ1 pathway leading to morphological and functional improvements. Chronic administration of 7,8-DHF delayed motor deficits in R6/1 mice and reversed deficits on the Novel Object Recognition Test (NORT) at 17 weeks. Morphological and biochemical analyses revealed improved striatal levels of enkephalin, and prevention of striatal volume loss. We found a TrkBY816 but not TrkBY515 phosphorylation recovery in striatum concordant with in vitro results. Additionally, 7,8-DHF normalized striatal levels of induced and neuronal nitric oxide synthase (iNOS and nNOS, respectively) and ameliorated the imbalance of p75/TrkB. Our results provide new insights into the mechanism of action of 7,8-DHF suggesting that its effect through the TrkB receptor in striatum is via selective phosphorylation of its Y816 residue and activation of PLCγ1 pathway, but pleiotropic effects of the drug also contribute to its therapeutic potential.
When do redundant fluidic networks outperform non-redundant ones?
Aimee M. Torres Rojas, R. D. M. Travasso, I. Pagonabarraga, and Eugenia Corvera Poiré
EPL (Europhysics Letters)
117
64002
(2017)
Redundancy constitutes a fundamental and intrinsic aspect of healthy vasculatures. Built-in redundancy might also be a desirable feature in man-made microfluidic devices. We show that redundant and non-redundant networks, built to have identical resistances to flow when unobstructed, allow for very different flows when they are occluded; redundant ones —densely occluded at a certain bifurcation level— allowing for larger flows than non-redundant ones —obstructed above relatively small thresholds. We also show that redundancy protects vessels against the large shear-rate gradients that occlusions would cause if it were not present. Our study allows one to quantify a network tolerance against blockage, provides guidance in the tailoring of microfluidic devices, and offers novel insights into why nature has selected intrinsic redundancy over thicker vessels to assure blood supply at key places of the organisms.
Effects of temporal correlations in social multiplex networks
Michele Starnini, Andrea Baronchelli & Romualdo Pastor-Satorras
Scientific Reports
7
8597
(2017)
Multi-layered networks represent a major advance in the description of natural complex systems, and their study has shed light on new physical phenomena. Despite its importance, however, the role of the temporal dimension in their structure and function has not been investigated in much detail so far. Here we study the temporal correlations between layers exhibited by real social multiplex networks. At a basic level, the presence of such correlations implies a certain degree of predictability in the contact pattern, as we quantify by an extension of the entropy and mutual information analyses proposed for the single-layer case. At a different level, we demonstrate that temporal correlations are a signature of a ‘multitasking’ behavior of network agents, characterized by a higher level of switching between different social activities than expected in a uncorrelated pattern. Moreover, temporal correlations significantly affect the dynamics of coupled epidemic processes unfolding on the network. Our work opens the way for the systematic study of temporal multiplex networks and we anticipate it will be of interest to researchers in a broad array of fields.
Interplay between social influence and competitive strategical games in multiplex networks
Amato, Roberta; Diaz-Guilera, Albert; Kleineberg, Kaj-Kolja
Scientific Reports
7
7087
(2017)
We present a model that takes into account the coupling between evolutionary game dynamics and social influence. Importantly, social influence and game dynamics take place in different domains, which we model as different layers of a multiplex network. We show that the coupling between these dynamical processes can lead to cooperation in scenarios where the pure game dynamics predicts defection. In addition, we show that the structure of the network layers and the relation between them can further increase cooperation. Remarkably, if the layers are related in a certain way, the system can reach a polarized metastable state. These findings could explain the prevalence of polarization observed in many social dilemmas.
Elastic and dynamic properties of membrane phase-field models
Lazaro, Guillermo R.; Pagonabarraga, Ignacio; Hernandez-Machado, Aurora
European Physical Journal E
40
77
(2017)
Phase-field models have been extensively used to study interfacial phenomena, from solidification to vesicle dynamics. In this article, we analyze a phase-field model that captures the relevant physical features that characterize biological membranes. We show that the Helfrich theory of elasticity of membranes can be applied to phase-field models, allowing to derive the expressions of the stress tensor, lateral stress profile and elastic moduli. We discuss the relevance and interpretations of these magnitudes from a phase-field perspective. Taking the sharp-interface limit we show that the membrane macroscopic equilibrium equation can be derived from the equilibrium condition of the phase-field interface. We also study two dynamic models that describe the behaviour of a membrane. From the study of the relaxational behaviour of the membrane we characterize the relevant dynamics of each model, and discuss their applications.
Continuous-time random walks with reset events
Montero, Miquel; Maso-Puigdellosas, Axel; Villarroel, Javier
EUROPEAN PHYSICAL JOURNAL B
90
176
(2017)
In this paper, we consider a stochastic process that may experience random reset events which relocate the system to its starting position. We focus our attention on a one-dimensional, monotonic continuous-time random walk with a constant drift: the process moves in a fixed direction between the reset events, either by the effect of the random jumps, or by the action of a deterministic bias. However, the orientation of its motion is randomly determined after each restart. As a result of these alternating dynamics, interesting properties do emerge. General formulas for the propagator as well as for two extreme statistics, the survival probability and the mean first-passage time, are also derived. The rigor of these analytical results is verified by numerical estimations, for particular but illuminating examples.
Contribution to the Topical Issue “Continuous Time Random Walk Still Trendy: Fifty-year History, Current State and Outlook”, edited by Ryszard Kutner and Jaume Masoliver.
Hydrodynamic instabilities, waves and turbulence in spreading epithelia
Blanch-Mercader, Carles; Casademunt, Jaume
Soft Matter
13
6913 6928
(2017)
We present a hydrodynamic model of spreading epithelial monolayers described as polar viscous fluids, with active contractility and traction on a substrate. The combination of both active forces generates an instability that leads to nonlinear traveling waves, which propagate in the direction of polarity with characteristic time scales that depend on contact forces. Our viscous fluid model provides a comprehensive understanding of a variety of observations on the slow dynamics of epithelial monolayers, remarkably those that seemed to be characteristic of elastic media. The model also makes simple predictions to test the non-elastic nature of the mechanical waves, and provides new insights into collective cell dynamics, explaining plithotaxis as a result of strong flow-polarity coupling, and quantifying the non-locality of force transmission. In addition, we study the nonlinear regime of waves deriving an exact map of the model into the complex Ginzburg–Landau equation, which provides a complete classification of possible nonlinear scenarios. In particular, we predict the transition to different forms of weak turbulence, which in turn could explain the chaotic dynamics often observed in epithelia.
Bistability, Oscillations, and Bidirectional Motion of Ensemble of Hydrodynamically Coupled Molecular Motors
Malgaretti, P.; Pagonabarraga, Ignacio; Joanny, Jean-F.
PHYSICAL REVIEW LETTERS
119
168101
(2017)
We analyze the collective behavior of hydrodynamically coupled molecular motors. We show that the local fluxes induced by motor displacement can induce the experimentally observed bidirectional motion of cargoes and vesicles. By means of a mean-field approach we show that sustained oscillations as well as bistable collective motor motion arise even for very large collection of motors, when thermal noise is irrelevant. The analysis clarifies the physical mechanisms responsible for such dynamics by identifying the relevant coupling parameter and its dependence on the geometry of the hydrodynamic coupling as well as on system size. We quantify the phase diagram for the different phases that characterize the collective motion of hydrodynamically coupled motors and show that sustained oscillations can be reached for biologically relevant parameters, hence, demonstrating the relevance of hydrodynamic interactions in intracellular transport.
Propulsion and hydrodynamic particle transport of magnetically twisted colloidal ribbons
Massana-Cid, Helena; Martinez-Pedrero, Fernando; Navarro-Argemí, Eloy; Pagonabarraga, Ignacio; and Pietro Tierno, Pietro;
New Journal of Physics
19
103031
(2017)
We describe a method to trap, transport and release microscopic particles in a viscous fluid using the hydrodynamic flow field generated by a magnetically propelled colloidal ribbon. The ribbon is composed of ferromagnetic microellipsoids that arrange with their long axis parallel to each other, a configuration that is energetically favorable due to their permanent magnetic moments. We use an external precessing magnetic field to torque the anisotropic particles forming the ribbon, and to induce propulsion of the entire structure due to the hydrodynamic coupling with the close substrate. The propulsion speed of the ribbon can be controlled by varying the driving frequency, or the amplitude of the precessing field. The latter parameter is also used to reduce the average inter particle distance and to induce the twisting of the ribbon due to the increase in the attraction between the rotating ellipsoids. Furthermore, non magnetic particles are attracted or repelled with the hydrodynamic flow field generated by the propelling ribbon. The proposed method may be used in channel free microfluidic applications, where the precise trapping and transport of functionalized particles via non invasive magnetic fields is required.
Continuous Time Random Walks with memory and financial distributions
Montero, Miquel; Masoliver, Jaume
EUROPEAN PHYSICAL JOURNAL B
90
207
(2017)
We study financial distributions from the perspective of Continuous Time Random Walks with memory. We review some of our previous developments and apply them to financial problems. We also present some new models with memory that can be useful in characterizing tendency effects which are inherent in most markets. We also briefly study the effect on return distributions of fractional behaviors in the distribution of pausing times between successive transactions.
Navigability of temporal networks in hyperbolic space
Ortiz, Elisenda; Starnini, Michele; Angeles Serrano, M.
SCIENTIFIC REPORTS
7
15054
(2017)
Information routing is one of the main tasks in many complex networks with a communication function. Maps produced by embedding the networks in hyperbolic space can assist this task enabling the implementation of efficient navigation strategies. However, only static maps have been considered so far, while navigation in more realistic situations, where the network structure may vary in time, remains largely unexplored. Here, we analyze the navigability of real networks by using greedy routing in hyperbolic space, where the nodes are subject to a stochastic activation-inactivation dynamics. We find that such dynamics enhances navigability with respect to the static case. Interestingly, there exists an optimal intermediate activation value, which ensures the best trade-off between the increase in the number of successful paths and a limited growth of their length. Contrary to expectations, the enhanced navigability is robust even when the most connected nodes inactivate with very high probability. Finally, our results indicate that some real networks are ultranavigable and remain highly navigable even if the network structure is extremely unsteady. These findings have important implications for the design and evaluation of efficient routing protocols that account for the temporal nature of real complex networks.
Active Brownian equation of state: metastability and phase coexistence
Levis, Demian; Codina, Joan; Pagonabarraga, Ignacio
SOCT MATTER
13
8113 8119
(2017)
As a result of the competition between self-propulsion and excluded volume interactions, purely repulsive self-propelled spherical particles undergo a motility-induced phase separation (MIPS). We carry out a systematic computational study, considering several interaction potentials, systems confined by hard walls or with periodic boundary conditions, and different initial conditions. This approach allows us to identify that, despite its non-equilibrium nature, the equations of state of Active Brownian Particles (ABP) across MIPS verify the characteristic properties of first-order liquid-gas phase transitions, meaning, equality of pressure of the coexisting phases once a nucleation barrier has been overcome and, in the opposite case, hysteresis around the transition as long as the system remains in the metastable region. Our results show that the equations of state of ABPs account for their phase behaviour, providing a firm basis to describe MIPS as an equilibrium-like phase transition.
Mixed-order phase transition in a colloidal crystal
Alert, Ricard; Tierno, Pietro; Casademunt, Jaume
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
114
12906 12909
(2017)
Mixed-order phase transitions display a discontinuity in the order parameter like first-order transitions yet feature critical behavior like second-order transitions. Such transitions have been predicted for a broad range of equilibrium and nonequilibrium systems, but their experimental observation has remained elusive. Here, we analytically predict and experimentally realize a mixed-order equilibrium phase transition. Specifically, a discontinuous solid-solid transition in a 2D crystal of paramagnetic colloidal particles is induced by a magnetic field H. At the transition field H-s, the energy landscape of the system becomes completely flat, which causes diverging fluctuations and correlation length xi proportional to vertical bar H-2 - H-s(2)vertical bar(-1/2). Mean-field critical exponents are predicted, since the upper critical dimension of the transition is d(u) = 2. Our colloidal system provides an experimental test bed to probe the unconventional properties of mixed-order phase transitions.
Influence of topology in the mobility enhancement of pulse-coupled oscillator synchronization
Beardo, A; Prignano, L; Sagarra, O; Diaz-Guilera, A
PHYSICAL REVIEW E
96
062306
(2017)
In this work we revisit the nonmonotonic behavior (NMB) of synchronization time with velocity reported for systems of mobile pulse-coupled oscillators (PCOs). We devise a control parameter that allows us to predict in which range of velocities NMB may occur, also uncovering the conditions allowing us to establish the emergence of NMB based on specific features of the connectivity rule. Specifically, our results show that if the connectivity rule is such that the interaction patterns are sparse and, more importantly, include a large fraction of nonreciprocal interactions, then the system will display NMB. We furthermore provide a microscopic explanation relating the presence of such features of the connectivity patterns to the existence of local clusters unable to synchronize, termed frustrated clusters, for which we also give a precise definition in terms of simple graph concepts. We conclude that, if the probability of finding a frustrated cluster in a system of moving PCOs is high enough, NMB occurs in a predictable range of velocities.
Resonances of Newtonian fluids in elastomeric microtubes
Torres Rojas, Aimee M.; Pagonabarraga, I.; Corvera Poire, E.
PHYSICS OF FLUIDS
29
122003
(2017)
We analyze the dynamic behavior of Newtonian fluids in elastic tubes subject to pulsatile pressure gradients and show that the interplay between the viscosity of the fluid, the elasticity of the wall, and the characteristic size of the confining media gives rise to a rich phenomenology that includes resonances. We find that these resonances are relevant for small confining geometries with low Young's moduli, typical of elastomeric materials in microfluidics. These resonances disappear beyond a certain tube radius, a certain Young's modulus, and below a certain fluid viscosity. In order to guide potential experiments, we present results for mineral oil flowing through polydimethylsiloxane microtubes and find resonances of the order of few tens of kHz. Published by AIP Publishing.
La recherche de terrain dans la nécropole d’Althiburos – massif du Ksour
Kallala, K.; Sanmartí, J.; Jornet, R.; Belarte, M. C.; Canela, J.; Chérif, S.; Campillo, J.; Montanero, D.; Cruz, I.; Miniaoui, S.; Bermúdez, X.; Fadrique, T.; Revilla, V.; Ramon, J.; Ben Moussa, M.
Universitat de Barcelona-Institut Català d’Arqueologia Clàssica, Documenta-30, Tarragona
25 58
(2017)
KALLALA, K.; SANMARTÍ, J.; JORNET, R.; BELARTE, M. C.; CANELA, J.; CHÉRIF, S.; CAMPILLO, J.; MONTANERO, D.; CRUZ, I.; MINIAOUI, S.; BERMÚDEZ, X.; FADRIQUE, T.; REVILLA, V.; RAMON, J.; BEN MOUSSA, M. 2017: “La recherche de terrain dans la nécropole d’Althiburos – massif du Ksour”, en N. Kallala, J. Sanmartí (dirs.), M. C. Belarte (ed.), Althiburos III. La nécropole protohistòrique d’Althiburos – massif du Ksour, Universitat de Barcelona-Institut Català d’Arqueologia Clàssica, Documenta-30, Tarragona, 2017, ISBN 978-84-946298-3-9. pp. 25-58.
Opinion competition dynamics on multiplex networks
Amato, R ; Kouvaris, NE ; San Miguel, M; Diaz-Guilera, A
NEW JOURNAL OF PHYSICS
19
123019
(2017)
Multilayer and multiplex networks represent a good proxy for the description of social phenomena where social structure is important and can have different origins. Here, we propose a model of opinion competition where individuals are organized according to two different structures in two layers. Agents exchange opinions according to the Abrams-Strogatz model in each layer separately and opinions can be copied across layers by the same individual. In each layer a different opinion is dominant, so each layer has a different absorbing state. Consensus in one opinion is not the only possible stable solution because of the interaction between the two layers. Anew mean field solution has been found where both opinions coexist. In a finite system there is a long transient time for the dynamical coexistence of both opinions. However, the system ends in a consensus state due to finite size effects. We analyze sparse topologies in the two layers and the existence of positive correlations between them, which enables the coexistence of inter-layer groups of agents sharing the same opinion.
Emergent structures and dynamics of cell colonies by contact inhibition of locomotion
Smeets, Bart; Alert, Ricard; Pesek, Jiri; Pagonabarraga, Ignacio; Ramon, Herman; Vincent, Romaric
Proc Nat Acad Sciences US
113
14621 14626
(2016)
Cells in tissues can organize into a broad spectrum of structures according to their function. Drastic changes of organization, such as epithelial-mesenchymal transitions or the formation of spheroidal aggregates, are often associated either to tissue morphogenesis or to cancer progression. Here, we study the organization of cell colonies by means of simulations of self-propelled particles with generic cell-like interactions. The interplay between cell softness, cell-cell adhesion, and contact inhibition of locomotion (CIL) yields structures and collective dynamics observed in several existing tissue phenotypes. These include regular distributions of cells, dynamic cell clusters, gel-like networks, collectively migrating monolayers, and 3D aggregates. We give analytical predictions for transitions between noncohesive, cohesive, and 3D cell arrangements. We explicitly show how CIL yields an effective repulsion that promotes cell dispersal, thereby hindering the formation of cohesive tissues. Yet, in continuous monolayers, CIL leads to collective cell motion, ensures tensile intercellular stresses, and opposes cell extrusion. Thus, our work highlights the prominent role of CIL in determining the emergent structures and dynamics of cell colonies.
Chimera states in a network-organized public goods game with destructive agents
Kouvaris, Nikos E.; Requejo, Ruben J.; Hizanidis, Johanne; Diaz-Guilera, Albert
Chaos
26
123108
(2016)
We found that a network-organized metapopulation of cooperators, defectors, and destructive agents playing the public goods game with mutations can collectively reach global synchronization or chimera states. Global synchronization is accompanied by a collective periodic burst of cooperation, whereas chimera states reflect the tendency of the networked metapopulation to be fragmented in clusters of synchronous and incoherent bursts of cooperation. Numerical simulations have shown that the system's dynamics switches between these two steady states through a first order transition. Depending on the parameters determining the dynamical and topological properties, chimera states with different numbers of coherent and incoherent clusters are observed. Our results present the first systematic study of chimera states and their characterization in the context of evolutionary game theory. This provides a valuable insight into the details of their occurrence, extending the relevance of such states to natural and social systems. Published by AIP Publishing.
Bidirectional particle transport and size selective sorting of Brownian particles in a flashing spatially periodic energy landscape
Martinez-Pedrero, Fernando; Massana-Cid, Helena; Ziegler, Till; Johansen, Tom H.; Straube, Arthur V.; Tierno, Pietro
Physical Chemistry Chemical Physics
18
26353 26357
(2016)
We demonstrate a size sensitive experimental scheme which enables bidirectional transport and fractionation of paramagnetic colloids in a fluid medium. It is shown that two types of magnetic colloidal particles with different sizes can be simultaneously transported in opposite directions, when deposited above a stripe-patterned ferrite garnet film subjected to a square-wave magnetic modulation. Due to their different sizes, the particles are located at distinct elevations above the surface, and they experience two different energy landscapes, generated by the modulated magnetic substrate. By combining theoretical arguments and numerical simulations, we reveal such energy landscapes, which fully explain the bidirectional transport mechanism. The proposed technique does not require pre-imposed channel geometries such as in conventional microfluidics or lab-on-a-chip systems, and permits remote control over the particle motion, speed and trajectory, by using relatively low intense magnetic fields.
Formation of metastable phases by spinodal decomposition
Alert, Ricard; Tierno, Pietro; Casademunt, Jaume
Nature Communications
7
13067
(2016)
Metastable phases may be spontaneously formed from other metastable phases through nucleation. Here we demonstrate the spontaneous formation of a metastable phase from an unstable equilibrium by spinodal decomposition, which leads to a transient coexistence of stable and metastable phases. This phenomenon is generic within the recently introduced scenario of the landscape-inversion phase transitions, which we experimentally realize as a structural transition in a colloidal crystal. This transition exhibits a rich repertoire of new phase-ordering phenomena, including the coexistence of two equilibrium phases connected by two physically different interfaces. In addition, this scenario enables the control of sizes and lifetimes of metastable domains. Our findings open a new setting that broadens the fundamental understanding of phase-ordering kinetics, and yield new prospects of applications in materials science.
Directed random walk with random restarts: The Sisyphus random walk
Montero, Miquel; Villarroel, Javier
Phys Rev E
94
032132
(2016)
In this paper we consider a particular version of the random walk with restarts: random reset events which suddenly bring the system to the starting value. We analyze its relevant statistical properties, like the transition probability, and show how an equilibrium state appears. Formulas for the first-passage time, high-water marks, and other extreme statistics are also derived; we consider counting problems naturally associated with the system. Finally we indicate feasible generalizations useful for interpreting different physical effects.
The hidden hyperbolic geometry of international trade: World Trade Atlas 1870-2013
Garcia-Perez, Guillermo; Boguna, Marian; Allard, Antoine; Angeles Serrano, M.
Scientific Reports
6
33441
(2016)
Here, we present the World Trade Atlas 1870-2013, a collection of annual world trade maps in which distance combines economic size and the different dimensions that affect international trade beyond mere geography. Trade distances, based on a gravity model predicting the existence of significant trade channels, are such that the closer countries are in trade space, the greater their chance of becoming connected. The atlas provides us with information regarding the long-term evolution of the international trade system and demonstrates that, in terms of trade, the world is not flat but hyperbolic, as a reflection of its complex architecture. The departure from flatness has been increasing since World War I, meaning that differences in trade distances are growing and trade networks are becoming more hierarchical. Smaller-scale economies are moving away from other countries except for the largest economies; meanwhile those large economies are increasing their chances of becoming connected worldwide. At the same time, Preferential Trade Agreements do not fit in perfectly with natural communities within the trade space and have not necessarily reduced internal trade barriers. We discuss an interpretation in terms of globalization, hierarchization, and localization; three simultaneous forces that shape the international trade system.
Synchronization of mobile chaotic oscillator networks
Fujiwara, Naoya; Kurths, Jurgen; Diaz-Guilera, Albert
Chaos
26
094824
(2016)
We study synchronization of systems in which agents holding chaotic oscillators move in a two-dimensional plane and interact with nearby ones forming a time dependent network. Due to the uncertainty in observing other agents' states, we assume that the interaction contains a certain amount of noise that turns out to be relevant for chaotic dynamics. We find that a synchronization transition takes place by changing a control parameter. But this transition depends on the relative dynamic scale of motion and interaction. When the topology change is slow, we observe an intermittent switching between laminar and burst states close to the transition due to small noise. This novel type of synchronization transition and intermittency can happen even when complete synchronization is linearly stable in the absence of noise. We show that the linear stability of the synchronized state is not a sufficient condition for its stability due to strong fluctuations of the transverse Lyapunov exponent associated with a slow network topology change. Since this effect can be observed within the linearized dynamics, we can expect such an effect in the temporal networks with noisy chaotic oscillators, irrespective of the details of the oscillator dynamics. When the topology change is fast, a linearized approximation describes well the dynamics towards synchrony. These results imply that the fluctuations of the finite-time transverse Lyapunov exponent should also be taken into account to estimate synchronization of the mobile contact networks. Published by AIP Publishing.
Growing networks of overlapping communities with internal structure
Young, Jean-Gabriel; Hebert-Dufresne, Laurent; Allard, Antoine; Dube, Louis J.
Phys Rev E
94
022317
(2016)
We introduce an intuitive model that describes both the emergence of community structure and the evolution of the internal structure of communities in growing social networks. The model comprises two complementary mechanisms: One mechanism accounts for the evolution of the internal link structure of a single community, and the second mechanism coordinates the growth of multiple overlapping communities. The first mechanism is based on the assumption that each node establishes links with its neighbors and introduces new nodes to the community at different rates. We demonstrate that this simple mechanism gives rise to an effective maximal degree within communities. This observation is related to the anthropological theory known as Dunbar's number, i.e., the empirical observation of a maximal number of ties which an average individual can sustain within its social groups. The second mechanism is based on a recently proposed generalization of preferential attachment to community structure, appropriately called structural preferential attachment (SPA). The combination of these two mechanisms into a single model (SPA+) allows us to reproduce a number of the global statistics of real networks: The distribution of community sizes, of node memberships, and of degrees. The SPA+ model also predicts (a) three qualitative regimes for the degree distribution within overlapping communities and (b) strong correlations between the number of communities to which a node belongs and its number of connections within each community. We present empirical evidence that support our findings in real complex networks.
Market Imitation and Win-Stay Lose-Shift Strategies Emerge as Unintended Patterns in Market Direction Guesses
Gutierrez-Roig, Mario; Segura, Carlota; Duch, Jordi; Perello, Josep
PLoS ONE
11
e0159078
(2016)
Decisions made in our everyday lives are based on a wide variety of information so it is generally very difficult to assess what are the strategies that guide us. Stock market provides a rich environment to study how people make decisions since responding to market uncertainty needs a constant update of these strategies. For this purpose, we run a lab-in-thefield experiment where volunteers are given a controlled set of financial information - based on real data from worldwide financial indices- and they are required to guess whether the market price would go "up" or "down" in each situation. From the data collected we explore basic statistical traits, behavioural biases and emerging strategies. In particular, we detect unintended patterns of behavior through consistent actions, which can be interpreted as Market Imitation and Win-Stay Lose-Shift emerging strategies, with Market Imitation being the most dominant. We also observe that these strategies are affected by external factors: the expert advice, the lack of information or an information overload reinforce the use of these intuitive strategies, while the probability to follow them significantly decreases when subjects spends more time to make a decision. The cohort analysis shows that women and children are more prone to use such strategies although their performance is not undermined. Our results are of interest for better handling clients expectations of trading companies, to avoid behavioural anomalies in financial analysts decisions and to improve not only the design of markets but also the trading digital interfaces where information is set down. Strategies and behavioural biases observed can also be translated into new agent based modelling or stochastic price dynamics to better understand financial bubbles or the effects of asymmetric risk perception to price drops.
Humans display a reduced set of consistent behavioral phenotypes in dyadic games
Poncela-Casasnovas, Julia; Gutierrez-Roig, Mario; Gracia-Lazaro, Carlos; Vicens, Julian; Gomez-Gardenes, Jesus; Perello, Josep; Moreno, Yamir; Duch, Jordi; Sanchez, Angel
Science Advances
2
e1600451
(2016)
Socially relevant situations that involve strategic interactions are widespread among animals and humans alike. To study these situations, theoretical and experimental research has adopted a game theoretical perspective, generating valuable insights about human behavior. However, most of the results reported so far have been obtained from a population perspective and considered one specific conflicting situation at a time. This makes it difficult to extract conclusions about the consistency of individuals' behavior when facing different situations and to define a comprehensive classification of the strategies underlying the observed behaviors. We present the results of a lab-in-thefield experiment in which subjects face four different dyadic games, with the aim of establishing general behavioral rules dictating individuals' actions. By analyzing our datawith an unsupervised clustering algorithm, we find that all the subjects conform, with a large degree of consistency, to a limited number of behavioral phenotypes (envious, optimist, pessimist, and trustful), with only a small fraction of undefined subjects. We also discuss the possible connections to existing interpretations based on a priori theoretical approaches. Our findings provide a relevant contribution to the experimental and theoretical efforts toward the identification of basic behavioral phenotypes in a wider set of contexts without aprioristic assumptions regarding the rules or strategies behind actions. From this perspective, our work contributes to a fact-based approach to the study of human behavior in strategic situations, which could be applied to simulating societies, policy-making scenario building, and even a variety of business applications.
A Tunable Magnetic Domain Wall Conduit Regulating Nanoparticle Diffusion
Tierno, Pietro; Johansen, Tom H.; Sancho, Jose M.
Nano Letters
16
5169 5175
(2016)
We demonstrate a general and robust method to confine on a plane strongly diffusing nanoparticles in water by using size tunable magnetic channels. These virtual conduits are realized with pairs of movable Bloch walls located within an epitaxially grown ferrite garnet film. We show that once inside the magnetic conduit the particles experience an effective local parabolic potential in the transverse direction, while freely diffusing along the conduit. The stiffness of the magnetic potential is determined as a function of field amplitude that varies the width of the magnetic channel. Precise control of the degree of confinement is demonstrated by tuning the applied field. The magnetic conduit is then used to realize single files of nonpassing particles and to induce periodic condensation of an ensemble of particles into parallel stripes in a completely controllable and reversible manner.
Active and reactive behaviour in human mobility: the influence of attraction points on pedestrians
Gutierrez-Roig, M.; Sagarra, O.; Oltra, A.; Palmer, J. R. B.; Bartumeus, F.; Diaz-Guilera, A.; Perello, J.
Royal Society Open Science
3
UNSP 160177
(2016)
Human mobility is becoming an accessible field of study, thanks to the progress and availability of tracking technologies as a common feature of smart phones. We describe an example of a scalable experiment exploiting these circumstances at a public, outdoor fair in Barcelona (Spain). Participants were tracked while wandering through an open space with activity stands attracting their attention. We develop a general modelling framework based on Langevin dynamics, which allows us to test the influence of two distinct types of ingredients on mobility: reactive or context-dependent factors, modelled by means of a force field generated by attraction points in a given spatial configuration and active or inherent factors, modelled from intrinsic movement patterns of the subjects. The additive and constructive framework model accounts for some observed features. Starting with the simplest model (purely random walkers) as a reference, we progressively introduce different ingredients such as persistence, memory and perceptual landscape, aiming to untangle active and reactive contributions and quantify their respective relevance. The proposed approach may help in anticipating the spatial distribution of citizens in alternative scenarios and in improving the design of public events based on a facts-based approach.
