Electrokinetic and hydrodynamic properties of charged-particles systems: From small electrolyte ions to large colloids

Dynamic processes in dispersions of charged spherical particles are of importance both in fundamental science, and in technical and bio-medical applications. There exists a large variety of charged-particles systems, ranging from nanometer-sized electrolyte ions to micron-sized charge-stabilized colloids. We review recent advances in theoretical methods for the calculation of linear transport coefficients in concentrated particulate systems, with the focus on hydrodynamic interactions and electrokinetic effects. Considered transport properties are the dispersion viscosity, self- and collective diffusion coefficients, sedimentation coefficients, and electrophoretic mobilities and conductivities of ionic particle species in an external electric field. Advances by our group are also discussed, including a novel mode-coupling-theory method for conduction-diffusion and viscoelastic properties of strong electrolyte solutions. Furthermore, results are presented for dispersions of solvent-permeable particles, and particles with non-zero hydrodynamic surface slip. The concentration-dependent swelling of ionic microgels is discussed, as well as a far-reaching dynamic scaling behavior relating colloidal long- to short-time dynamics

Adaptive Algorithms and Collusion via Coupling

We develop a theoretical model to study strategic interactions between adaptive learning algorithms. Applying continuous-time techniques, we uncover the mechanism responsible for collusion between Artificial Intelligence algorithms documented by recent experimental evidence. We show that spontaneous coupling between the algorithms' estimates leads to periodic coordination on actions that are more profitable than static Nash equilibria. We provide a sufficient condition under which this coupling is guaranteed to disappear, and algorithms learn to play undominated strategies. We apply our results to interpret and complement experimental findings in the literature and to the design of learning-robust strategy-proof mechanisms. We show that ex-post feedback provision guarantees robustness to the presence of learning agents. We fully characterize the optimal learning-robust mechanisms: they are menu mechanisms.Comment: 57 pages, 13 figure

Sensibilidad de estados críticos en inestabilidad estructural via perturbaciones singulares

En este trabajo presentamos un método directo para obtener la relación entre la carga crítica, las coordenadas críticas y el parámetro de imperfección. En la presente propuesta suponemos las expansiones para la carga crítica y las coordenadas correspondientes en términos de potencias arbitrarias del parámetro de imperfección. Luego aplicando el principio de menor degeneración, se determinan los exponentes y los coeficientes de las expansiones. La técnica desarrollada corresponde a perturbaciones singulares e incluye un esquema para identificar los exponentes posibles de las expansiones para estados críticos generales. En la teoría general de estabilidad elástica la clasificación de estados críticos se obtiene a partir del estado crítico y de la trayectoria postcrítica inicial. En este trabajo se demuestra que el mismo esquema de clasificación puede obtenerse a partir de investigar la sensibilidad del estado crítico sin necesidad de entrar en la trayectoria postcrítica.In this work, we describe a direct procedure for obtaining the relationships between the critical loads, the critical coordinates, and the amplitude of the imperfection. In the present approach we assume the expansions for the critical loads and correspon ding coordinates in terms of arbitrary powers of the imperfections parameter. Then by the principle of least degeneracy, we determine the exponents and the coefficients of the expansions. The technique developed in this work employs singular perturbations and includes a methodology to identify the set of exponents for general cases of critical states. The classification of critical states in the general theory of elastic stability is obtained from the critical and the initial post-critica1 states. We show that the some type of classification can be obtained from a detailed investigation of the sensitivity of the critical states, without making use of the post-critica1 path.Peer Reviewe

Domain size polydispersity effects on the structural and dynamical properties in lipid monolayers with phase coexistence

In lipid monolayers with phase coexistence, domains of the liquid-condensed phase always present size polydispersity. However, very few theoretical works consider size distribution effects on the monolayer properties. Because of the difference in surface densities, domains have excess dipolar density with respect to the surrounding liquid expanded phase, originating a dipolar inter-domain interaction. This interaction depends on the domain area, and hence the presence of a domain size distribution is associated with interaction polydispersity. Inter-domain interactions are fundamental to understanding the structure and dynamics of the monolayer. For this reason, it is expected that polydispersity significantly alters monolayer properties. By means of Brownian dynamics simulations, we study the radial distribution function (RDF), the average mean square displacement and the average time-dependent self-diffusion coefficient, D(t), of lipid monolayers with normally distributed size domains. For this purpose, we vary the relevant system parameters, polydispersity and interaction strength, within a range of experimental interest. We also analyze the consequences of using a monodisperse model to determine the interaction strength from an experimental RDF. We find that polydispersity strongly affects the value of the interaction strength, which is greatly underestimated if polydispersity is not considered. However, within a certain range of parameters, the RDF obtained from a polydisperse model can be well approximated by that of a monodisperse model, by suitably fitting the interaction strength, even for 40% polydispersities. For small interaction strengths or small polydispersities, the polydisperse systems obtained from fitting the experimental RDF have an average mean square displacement and D(t) in good agreement with that of the monodisperse system.Fil: Rufeil Fiori, Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Banchio, Adolfo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentin

Simulations and integral-equation theories for dipolar density interacting disks

Integral equation theories (IETs) based on the Ornstein-Zernike (OZ) relation can be used as an analytical tool to predict structural and thermodynamic properties and phase behavior of fluids with low numerical cost. However, there are no studies of the IETs for the dipolar density interaction potential in 2D systems, a relevant inter-domain interaction in lipid monolayers with phase coexistence. This repulsive interaction arises due to the excess dipole density of the domains, which are aligned perpendicular to the interface. This work studies the performance of three closures of the OZ equation for this novel system: Rogers-Young (RY), Modified Hypernetted Chain (MHNC), and Variational Modified Hypernetted Chain (VMHNC). For the last two closures the bridge function of a reference system is required, being the hard disk the most convenient reference system. Given that in 2D there is no analytical expressions for the hard disk correlation functions, two different approximations are proposed: one based on the Percus-Yevick approximation (PY), and the other based on an extension of the hard spheres Verlet-Weis-Henderson-Grundke parameterization (LB). The accuracy of the five approaches is evaluated by comparison of the pair correlation function and the structure factor with Monte Carlo simulation data. The results show that RY closure is only satisfactory for low-structured regimes. MHNC and VMHNC closures perform globally well and there are no significant differences between them. However, the reference system in some cases affects their performance; when the pair correlation function serves as the measure, the LB--based closures quantitatively outperform the PY ones. From the point of view of its applicability, LB--based closures do not have a solution for all studied interaction strength parameters, and, in general, PY--based closures are numerically preferable.Comment: 9 pages, 4 figure

Sensibilidad de estados críticos en inestabilidad estructural via perturbaciones singulares

En este trabajo presentamos un método directo para obtener la relación entre la carga crítica, las coordenadas críticas y el parámetro de imperfección. En la presente propuesta suponemos las expansiones para la carga crítica y las coordenadas correspondientes en términos de potencias arbitrarias del parámetro de imperfección. Luego aplicando el principio de menor degeneración, se determinan los exponentes y los coeficientes de las expansiones. La técnica desarrollada corresponde a perturbaciones singulares e incluye un esquema para identificar los exponentes posibles de las expansiones para estados críticos generales. En la teoría general de estabilidad elástica la clasificación de estados críticos se obtiene a partir del estado crítico y de la trayectoria postcrítica inicial. En este trabajo se demuestra que el mismo esquema de clasificación puede obtenerse a partir de investigar la sensibilidad del estado crítico sin necesidad de entrar en la trayectoria postcrítica.In this work, we describe a direct procedure for obtaining the relationships between the critical loads, the critical coordinates, and the amplitude of the imperfection. In the present approach we assume the expansions for the critical loads and correspon ding coordinates in terms of arbitrary powers of the imperfections parameter. Then by the principle of least degeneracy, we determine the exponents and the coefficients of the expansions. The technique developed in this work employs singular perturbations and includes a methodology to identify the set of exponents for general cases of critical states. The classification of critical states in the general theory of elastic stability is obtained from the critical and the initial post-critica1 states. We show that the some type of classification can be obtained from a detailed investigation of the sensitivity of the critical states, without making use of the post-critica1 path.Peer Reviewe

Reflexiones sobre el ejercicio de la autoridad municipal en el marco de un proceso de disputa público por ruidos molestos

En febrero de 2019, un conjunto de vecinos circundantes al parque municipal Eva Perón de la ciudad de Olavarría denunció, en el Honorable Concejo Deliberante, por contaminación acústica a una serie de agrupaciones de murga y comparsa. El conflicto que allí tomó estado público ha continuado su derrotero hasta la actualidad con una multiplicidad de particularidades derivadas del hecho de que el objeto de disputa constituye un bien público y de libre acceso por ser un parque público. Estas singularidades modelaron tanto las demandas que las facciones en disputa le han reclamado al Estado como las estrategias y modalidades de reclamar que los actores sociales involucrados desplegaron en distintas arenas de conflicto. La presente ponencia se enmarca en la investigación en curso. En particular, se buscará aquí dar cuenta de las diversas estrategias de demanda y reclamó que los actores sociales involucrados desplegaron problematizando los tipos de relaciones (de parentesco, de alianza, de vecindad, etc) que los mismos revisten. Se sostiene que los sentidos que las personas poseen en torno a estas relaciones es un aspecto central en la planificación, ejecución y publicización de los reclamos. Metodológicamente se ha trabajado desde un abordaje cualitativo y etnográfico privilegiando la mirada emic; en este sentido, el trabajo de campo realizado se basó en la observación directa y participante en conjunto con la elaboración de entrevistas y análisis de fuentes documentales.GT 73: La justicia en disputa: administración de conflictos, tramas locales, activismos sociales y de los Derechos Humanos en contextos de transformaciones sociales y reformas estatales.Universidad Nacional de La Plat

Diseño e implementación de front end analógico para SDR

Proyecto Integrador (IE)--FCEFN-UNC, 2017Diseña e Implementa un front end analògico para SDR (bloque de cadena de recepciòn encargado de filtrar, amplificar y trasladar en frecuencia la señal). El procesamiento es realizado mediante un bloque de programa basado en el software libre GNU Radio. La aplicaciòn ademàs es la encargada de enviar la informaciòn para la selecciòn del ancho de banda y frecuencias de trabajo al dispositiv