Abstracts

These are the Abstracts of the talks in order of appearance.

Binary mixtures at critical concentration: a playground of the Fluctuation-Induced Forces

Ignacio.A.Martínez.UCM The dynamics and energetics of the small systems are dominated by the thermal fluctuations. In recent years, a plethora of toy models based in micromanipulation techniques have been proposed and experimentally built in order to ground the framework of stochastic thermodynamics. However, the control of the fluctuations is experimentally limited to the case of white Gaussian noise or active media. Here, we will discuss about the use of critical media to easily manage the correlation length and time of the thermal fluctuations by slight changes of the fluid temperature over the room conditions. Specifically, binary liquid mixtures at critical concentration represent a perfect target since they allow applying photonics techniques such as optical tweezers to measure the forces induced by the media as well as its microrheological properties. Finally, we will discuss the possibility to use this experimental model for the study of the work and heat exchanges between colloids once we confine these fluctuations.

Public Goods Games revisited: scale and information effects on cooperation

María.Pereda.UPM The problem of public good provision is central in economics and touches upon many challenging societal issues, ranging from climate change mitigation to vaccination schemes. However, results which are supposed to be applied to a societal scale have only been obtained with small groups of people, with a maximum group size of 100 being reported in the literature. This work presents the first experiment until date where the Public Goods Game is scaled to a thousand people, all of them playing simultaneously within a single group, and a detailed comparison with experiments of size 100. Moreover, we study the effects of information on the cooperative endeavour of contributing to a public good.

El modelo Netflix llega a las aulas: una experiencia docente

Mario.Castro.UPC El modelo docente actual es eficaz porque permite la economía de recursos (1 profesor/N alumnos) y escalable (vale para 30, 100 ó 300 alumnos por aula). No obstante, también presenta varios problemas entre ellos: 1) un porcentaje alto de los alumnos está en modo zombie, 2) otro porcentaje simplemente no recibe el mensaje adecuado en el aula porque no tiene los prerrequisitos necesarios, 3) la capacidad de mantener la concentración por periodos prolongados de tiempo ha disminuido en la última década (quizá provocado por las tecnologías móviles) y, 4) el modelo no fomenta los aspectos sociales del aprendizaje ni el "aprender enseñando". Del mismo modo que pocos usuarios jóvenes ven la televisión "en tiempo real" (vs Netflix u otras plataformas similares), la educación puede aprovechar este modelo. En los últimos años se ha extendido el uso de una metodología llamada "flipped classroom" en la que la teoría se imparte en casa "a través de vídeos" y el tiempo en el aula se dedica a la resolución de problemas y de dudas con el profesor. En esta charla se discuten los resultados de aplicar esta metodología a un curso de Física para 1º de Ingeniería.

Study of cavitation through simulation

Ignacio.Sánchez.UCM Estudio del fenómeno de la cavitación por simulación mediante el método del seeding y comparativa entre disitntos colectivos.

Ice Ih vs ice III along the homogeneous nucleation line

Ángel.Luis.Díez.López.UCM El agua pura en estado líquido puede subenfriarse notablemente por debajo de la temperatura de fusión, manteniéndose en estado metaestable. Las presiones y temperaturas a las que el agua se congela cuando es enfriada a una determinada velocidad definen la llamada línea de nucleación homogénea. La pendiente de esta curva medida experimentalmente pasa de ser negativa a positiva al aumentar la presión. Este cambio de tendencia se ha investigado empleando simulaciones con el método de Dinámica Molecular, utilizando el modelo TIP4P/ICE para el agua. Encontramos, conforme a hipótesis previas, que el cambio de signo en la pendiente se debe a un cambio en el polimorfo del hielo que nuclea, desde hielo Ih hasta hielo III.

Latent heat in ice nucleation

Cintia.Pulido.UCM Estudio de como afecta el calor latente desprendido al crecimiento del hielo, y nucleación heterogénea de hielo sobre diferentes sustratos.

Effect of nanoconfinement on structural and transport properties of water

Alberto.Zaragoza.UCM In this work we present a molecular dynamics simulation study for TIP4P/2005 water model under two different nano confinements. We have carried out our simulations at wide range of temperatures (243 K - 298 K). Structural properties (density profiles and hydrogen bond distribution) and transport properties ( diffusion and shear viscosity) have been obtained for these systems and are compared with their bulk analogue.

Can information be recovered from thermal equilibrium?

Carlos.Morales.UCM We show that it is possible to recover information from the initial state of a quantum system after it has reached thermal equilibrium providing the process is done slowly enough. To do so, we perform a numerical simulation of a closed cycle bringing the system very slowly to a chaotic region where we let it reach thermal equilibrium and where the erasure of information would be expected. Next, we bring the system back to where it started very slowly. We obtain that the average expected value of macroscopic observables after the whole process depends on the initial conditions, therefore allowing the recovery of information about the initial state. We simulate the process using the Hamiltonian of the Dicke model through two different procedures, obtaining the same result.

Hierarchies arise spontaneously in egalitarian societies

Pablo.Lozano.UC3M Human behaviour is affected by culturally transmitted norms and values, where certain norms are internalized, i.e. acting according to a norm becomes an end in itself. Humans’ capacity to internalize norms likely evolved to simplify certain social challenges. In our recent study, we resort to an agent-based model and we hypothesize that hierarchical relationships reflecting power asymmetries between individuals, will have a negative impact on human cooperation as it does in non-human primates. The model takes into account the ranking and payoffs of each individual, as well as their abilities to follow a social norm to cooperate in collective action. The model works at the individual level and includes also between-group selection. The results from the model resemble the characteristics of human societies.

Nitrogen-fixing cyanobacteria are tuned for evolvability

Victoria.Doldán.Martelli.CNB Cyanobacteria constitute a paradigmatic model organism of the transition between unicellular and multicellular living forms. The genus Anabaena forms colonies with cells arranged in one-dimensional filaments; under nitrogen-limiting conditions some cells can differentiate into nitrogen-fixing heterocysts, forming regular patterns to effectively provide nitrogen for the colony. By combining genetic, metabolic and morphological features, a mathematical model was recently proposed to understand the regulation of heterocyst differentiation in Anabaena PCC 7120 [1]. In this new project, we analyze a simplified version of [1], using the minimal gene regulatory mechanisms for heterocyst pattern formation at early stages. Bifurcation diagrams predict a bistable regime where pattern formation and non-pattern formation coexist. This regime would act as a buffer to retard the transition from both behaviors and it is supported by stochastic simulations with 50 cell-filaments. Furthermore, the analysis of our model for two-cell filament shows that the wild-type genotype is poised very close to a critical point in the parameter space, a so-called codimension 2 bifurcation. This result suggests that the regulatory machinery of heterocyst differentiation has optimized evolvability, in the sense that small changes in the genotype, that can be produced in different ways by small mutations, are enough to adapt the system to permanent changes in environmental conditions.

Efecto en la funcionalidad de los canales artificiales de membrana (Carbon Nanotube-CNT) en la interacción con la membrana lipídica.

José.Carlos.Ureña.UCM Los nanotubos de carbono (CNT) se utilizan cada vez más como canales artificiales transmembranales. Sin embargo, aún no está bien definida la interacción CNT-membrana, ni la orientación del CNT dentro de la bicapa lipídica. La correcta orientación de éste es básica para el establecimiento de un flujo de agua a través del CNT. Se ha comprobado que esta orientación está mediada por la funcionalización de los extremos del CNT. Nuestro proyecto se basa en el estudio por simulación molecular de la influencia de los grupos funcionales del CNT sobre su orientación dentro de una membrana lipídica.

Modelling the evolution of antibiotic resistance in E. coli

Pablo.Catalán.ExeterUniversity We evolved populations of Escherichia coli for a week under several concentration of the antibiotic erythromycin. These populations evolved resistance to the antibiotic at different rates, with an intermediate concentration of erythromycin being responsible for the fastest adaptation. Using fluorescent methods and genomic analyses, we found that the evolution of resistance was mostly due to the over-expression of the AcrB efflux pump. We here present a mathematical model that captures the main non-linearities in our experimental results.

Influence of Water Models on AQP1

Miguel.Ángel.González.UCM Membrane proteins are vital for the correct functioning of cells, being responsible for cell-cell communication and both active and passive transport of molecules across the membrane[1]. The latter include protein channels and pores, and constitute a large family whose members have different features depending on the nature of the transported molecules. Aquaporins (AQP) are protein pores enabling the passage of water [2] across the membrane, characterised by high selectivity and rates of permeability. Although they have been widely studied, key aspects of the mechanisms relevant for their function remain unclear. Molecular dynamics (MD) is powerful numerical tool for investigating the features of a membrane protein, simulating a full complex system consisting of the membrane protein, the bilayer lipid membrane, water molecules, and ions. In such a system, water plays a key role in the lipid-protein interaction, given that the lipid membrane structure is governed by hydrophobic-hydrophilic forces (as well as the protein structure). Hence, it is essential to properly describe both the water-protein and water-membrane interactions. However, so far in biological simulations, water models have been selected for their ability to reproduce the behaviour of biological molecules, for example how lipids assemble into a membrane or the dynamics of a protein [5]. In our work, we propose a different point of view: the choice of the water model might influence the predicted transport properties of aquaporins [6]). We will be focusing on newer water models, such as TIP4P/2005 [7] and OPC [8], known to reproduce and to predict the values of a huge range of thermodynamics properties [6]. We have carried out several simulations for AQP1 in combination with TIP3P [9], TIP4P/2005 and OPC as the water potential. We have calculated the water flux through the channel, the water molecule orientation into the channel and the water dipole moment for the three systems. Our preliminary results for all systems reproduce the molecular mechanism described by Tajkhorshid et al. [10]. However, the number of water molecules crossing the channel depends on the water model. The thermodynamic properties of the water potential in bulk are extremely different, thus modifying the protein behaviour.

Effect of light and temperature in plant embryonic growth

Saúl.Ares.CNB Plants need to assess environmental cues to decide how much to grow after germination. Buried in the ground, the plant’s hypocotyl (its embryonic stem) must grow until it reaches the surface. Once this happens, the hypocotyl stops growing and the plant develops leaves to absorb sunlight. Many signals and mechanisms take part in this process. It is of particular interest to understand how the plants integrate light and temperature signals in this decision-making process. Using experimental data from our collaborators growing Arabidopsis plants under different light and temperature conditions, we build a mathematical model of hypocotyl growth. Somehow unexpectedly, we find that a gene so far relatively neglected by the field plays a crucial part in light and temperature integration.

Complex nonlinear optical dynamics of quantum dot supercrystals

Andrey.Malyshev.UCM We address theoretically the nonlinear optical dynamics of a regular 2D array of three level systems, such as semiconductor quantum dots. We show that the system can exhibit optical multi-stability, self-oscillations, dynamic chaos as well as operate as a tunable bistable mirror. The optical response of the super crystal is very sensitive to parameters of excitation, such as the power and detunings from optical transition frequencies, suggesting possibilities of control of the optical dynamics of the system by adjusting these key parameters.

Controlling topologically protected states by external fields and doping

Alvaro.Díaz.Fernández.UCM Topological materials often display topologically protected surface states with Dirac-like dispersions. Controlling their properties is desirable for their foreseen applications and a number of proposals have been put forward to this respect (e.g [1,2,3,4]). In this contribution, the system I will consider is a topological boundary. I will discuss how applying uniform electric and magnetic fields that preserve the symmetries lead to an anisotropic reduction of the Fermi velocity as the fields are increased. [5,6]. I will also show how a delta-layer of donor atoms at the boundary can lead to a coexistence of a two-dimensional electron gas with the topological surface states. Moreover, the linear optical response is markedly reshaped by the presence of the topological state [7].

Design of active Janus colloids. An in silico study.

Francisco.Alarcón.UCM Motivated for various experimental results of active particles, we have studied numerically the collective behavior that different models of active Janus particles could have in order to control the physical properties of the assembled active aggregates and shed light in the design of new materials, where self-propulsion can be exploited as a tunable driving force for self-assembly. In the one hand, we will show the Brownian amphiphilic Janus particles, where tuning the propulsion direction (towards or against the attractive patch), we observe that the morphology of the aggregates emerging from self-assembly depends on the patch size and the direction of the active forces, we compare with different models of amphiphilic Janus swimmers in order to study the effect of the hydrodynamic interactions in the self-assembly. On the other hand, we will show experiments of spherical metallodielectric Janus particles, immersed in an electrolytic solution and subjected to an alternating uniform electric field. Such particles self-propel and reconfigure into different collective states by introducing imbalanced interactions. These experiments are complemented with simulations of active dipolar Janus particles. Both studied systems, will show the potential of colloid science to enrich the newer field of active matter.

Gaussian statistics as an emergent symmetry far from equilibrium

Enrique.Rodríguez.Fernández.UC3M Symmetries play a conspicuous role in the large-scale behavior of critical systems. While in equilibrium they allow to classify asymptotics into different universality classes, out of equilibrium they can emerge, sometimes unexpectedly, as collective properties which are not explicit in the “bare” interactions. Here we elucidate the emergence of an up-down symmetry in the asymptotic behavior of the stochastic scalar Burgers equation in one and two dimensions, manifested by the occurrence of Gaussian fluctuations for the physical field. This robustness of Gaussian behavior contradicts naive expectations, due to the detailed relation —including the same set of symmetries— between Burgers equation and the Kardar-Parisi-Zhang equation, which paradigmatically displays non-Gaussian fluctuations described by Tracy-Widom distributions. We reach our conclusions via a dynamic renormalization group study of the field statistics, confirmed by direct evaluation of the field probability distribution function from numerical simulations of the dynamical equation. All odd-order cumulants cancel exactly, while the excess kurtosis vanishes for large systems, indeed consistent with Gaussian behavior.

Ecological multiplex interactions determine the role of species for parasite spread amplification

Alberto.Antonioni.UC3M Despite their potential interplay, multiple routes of many disease transmissions are often investigated separately. As a unifying framework for understanding parasite spread through interdependent transmission paths, we present the ‘ecomultiplex’ model, where the multiple transmission paths among a diverse community of interacting hosts are represented as a spatially explicit multiplex network. We adopt this framework for designing and testing potential control strategies for Trypanosoma cruzi spread in two empirical host communities. We show that the ecomultiplex model is an efficient and low data-demanding method to identify which species enhances parasite spread and should thus be a target for control strategies. We also find that the interplay between predator-prey and host-parasite interactions leads to a phenomenon of parasite amplification, in which top predators facilitate T. cruzi spread, offering a mechanistic interpretation of previous empirical findings. Our approach can provide novel insights in understanding and controlling parasite spreading in real-world complex systems.