Critical Phenomena in Quasi-Two-Dimensional Vibrated Granular Systems

The critical phenomena associated to the liquid to solid transition of quasi-two-dimensional vibrated granular systems is studied using molecular dynamics simulations of the inelastic hard sphere model. The critical properties are associated to the fourfold bond-orientational order parameter $\chi_4$, which measures the level of square crystallization of the system. Previous experimental results have shown that the transition of $\chi_4$, when varying the vibration amplitude, can be either discontinuous or continuous, for two different values of the height of the box. Exploring the amplitude-height phase space, a transition line is found, which can be either discontinuous or continuous, merging at a tricritical point and the continuous branch ends in an upper critical point. In the continuous transition branch, the critical properties are studied. The exponent associated to the amplitude of the order parameter is $\beta=1/2$, for various system sizes, in complete agreement with the experimental results. However, the fluctuations of $\chi_4$ do not show any critical behavior, probably due to crossover effects by the close presence of the tricritical point. Finally, in quasi-one-dimensional systems, the transition is only discontinuous, limited by one critical point, indicating that two is the lower dimension for having a tricritical point

Effective two-dimensional model for granular matter with phase separation

Granular systems confined in vertically vibrated shallow horizontal boxes (quasi two-dimensional geometry) present a liquid to solid phase transition when the frequency of the periodic forcing is increased. An effective model, where grains move and collide in two-dimensions is presented, which reproduces the aforementioned phase transition. The key element is that besides the two-dimensional degrees of freedom, each grain has an additional variable $\epsilon$ that accounts for the kinetic energy stored in the vertical motion in the real quasi two-dimensional motion. This energy grows monotonically during free flight, mimicking the energy gain by collisions with the vibrating walls and, at collisions, this energy is instantaneously transferred to the horizontal degrees of freedom. As a result, the average values of $\epsilon$ and the kinetic temperature are decreasing functions of the local density, giving rise to an effective pressure that can present van der Waals loops. A kinetic theory approach predicts the conditions that must satisfy the energy grow function to obtain the phase separation, which are verified with molecular dynamics simulations. Notably, the effective equation of state and the critical points computed considering the velocity--time-of-flight correlations differ only slightly from those obtained by simple kinetic theory calculations that neglect those correlations

Non-ideal rheology of semidilute bacterial suspensions

The rheology of semidilute bacterial suspensions is studied with the tools of kinetic theory, considering binary interactions, going beyond the ideal gas approximation. Two models for the interactions are considered, which encompass both the steric and short range interactions. In these, swimmers can either align polarly regardless of the state previous to the collision or they can align axially, being possible the end up antiparallel if the relative angle between directors is large. In both cases, it is found that an ordered phase develops when increasing the density, where the shear stress oscillates with large amplitudes, when a constant shear rate is imposed. This oscillation disappears for large shear rates in a continuous or discontinuous transition, depending if the aligning is polar or axial, respectively. For pusher swimmers these non-linear effects can produce an increase on the shear stress, contrary to the prediction of viscosity reduction made for the dilute regime with the ideal gas approximation

Effective two-dimensional model for granular matter with phase separation

Granular systems confined in vertically vibrated shallow horizontal boxes (quasi two-dimensional geometry) present a liquid to solid phase transition when the frequency of the periodic forcing is increased. An effective model, where grains move and collide in two-dimensions is presented, which reproduces the aforementioned phase transition. The key element is that besides the two-dimensional degrees of freedom, each grain has an additional variable $\epsilon$ that accounts for the kinetic energy stored in the vertical motion in the real quasi two-dimensional motion. This energy grows monotonically during free flight, mimicking the energy gain by collisions with the vibrating walls and, at collisions, this energy is instantaneously transferred to the horizontal degrees of freedom. As a result, the average values of $\epsilon$ and the kinetic temperature are decreasing functions of the local density, giving rise to an effective pressure that can present van der Waals loops. A kinetic theory approach predicts the conditions that must satisfy the energy grow function to obtain the phase separation, which are verified with molecular dynamics simulations. Notably, the effective equation of state and the critical points computed considering the velocity--time-of-flight correlations differ only slightly from those obtained by simple kinetic theory calculations that neglect those correlations

Las Redes de Petri y su Aplicacion en la Administracion de Empresas

99 p.El proyecto consiste en el estudio y aplicación de una herramienta de modelación de sistemas para la representación de procesos administrativos, las Redes de Petri. A la fecha han sido utilizadas, fundamentalmente, en el ámbito de los sistemas de tiempo real, tales como los sistemas de manufactura y otros caracterizados por la concurrencia de procesos, existiendo escasos antecedentes en materia de aplicación en el ámbito de la Administración de Empresas. Considerando que muchas de las actividades que se Ilevan a cabo dentro de una organización son de carácter repetitivo, condicionales y concurrentes de forma similar a los sistemas anteriormente señalados, el proyecto apunta a profundizar el estudio de las redes de Petri con el propósito de utilizarla como herramienta de apoyo para modelar estas actividades

Caracterización de la calidad de aire de material particulado – mercurio y modelo de dispersión de material particulado derivado de la actividad de minería pequeña y artesanal en la localidad de Secocha

En la primera parte del presente trabajo se realizó la caracterización de la calidad de aire mediante una metodología cuantitativa en la localidad de Secocha, la cual estuvo constituida por dos puntos de monitoreo, donde los parámetros a evaluar fueron: PM10, PM2.5 y Hg gaseoso durante un periodo de 24 horas; al realizar los monitoreos se obtuvieron los siguientes resultados: Para el punto de monitoreo AIR-1 las concentraciones más altas obtenidas de PM10, PM2.5 Y Hg gaseoso fueron, 152.8, 77.1, 0.201 μg/m3 respectivamente. Para el punto de monitoreo AIR-2 las concentraciones más altas obtenidas de PM10, PM2.5 Y Hg gaseoso fueron, 185.9, 92.5, 0.224 μg/m3 respectivamente. Asimismo, se utilizó una estación meteorológica portátil, la cual nos brinda los parámetros como temperatura, presión atmosférica, humedad relativa, dirección y velocidad de viento, estos se consideran como datos de alimentación para el desarrollo del software. Los resultados de los monitoreos realizados en lo referente al material particulado (PM10, PM2.5), superaron los ECA de aire para ambos puntos de monitoreo, en cuanto al Hg gaseoso no se mostraron concentraciones elevadas en comparación con los estándares correspondientes. En la segunda parte de este trabajo se desarrolla un modelo de dispersión para conocer la concentración de material particulado en el aire a diferentes distancias, para ello se utilizó el software de AERMOD. Se realizó una evaluación por área, ya que no se tiene fuentes puntuales de generación de material particulado, al correr el programa se obtuvieron concentraciones que validan los resultados obtenidos del monitoreo.Tesi