Modeling the structure and thermodynamics of multicomponent and polydisperse hard-sphere dispersions with continuous potentials.

A model system of identical particles interacting via a hard-sphere potential is essential in condensed matter physics; it helps to understand in and out of equilibrium phenomena in complex fluids, such as colloidal dispersions. Yet, most of the fixed time-step algorithms to study the transport properties of those systems have drawbacks due to the mathematical nature of the interparticle potential. Because of this, mapping a hard-sphere potential onto a soft potential has been recently proposed [Báez et al., J. Chem. Phys. 149, 164907 (2018)]. More specifically, using the second virial coefficient criterion, one can set a route to estimate the parameters of the soft potential that accurately reproduces the thermodynamic properties of a monocomponent hard-sphere system. However, real colloidal dispersions are multicomponent or polydisperse, making it important to find an efficient way to extend the potential model for dealing with such kind of many-body systems. In this paper, we report on the extension and applicability of the second virial coefficient criterion to build a description that correctly captures the phenomenology of both multicomponent and polydisperse hard-sphere dispersions. To assess the accuracy of the continuous potentials, we compare the structure of soft polydisperse systems with their hard-core counterpart. We also contrast the structural and thermodynamic properties of soft binary mixtures with those obtained through mean-field approximations and the Ornstein-Zernike equation for the two-component hard-sphere dispersion.

Layering and packing in confined colloidal suspensions.

Confinement modifies the properties of a fluid. The particle density is no longer uniform but depends on the distance from the walls; parallel to the walls, layers with different particle densities form. This affects the particle packing in the layers. We investigated colloidal fluids with volume fractions between 0.19 and 0.32 confined between rough walls. The particle-particle interactions were dominated by hard-sphere interactions but also contained some electrostatic interactions. The particle locations were determined using confocal microscopy and served to calculate the density profile, radial distribution function, anisotropic and generalized structure factors but also to characterize the arrangement of the wall particles leading to the roughness of the walls. The experiments are complemented by molecular dynamics simulations and fundamental-measure theory. While the particle arrangements are mainly controlled by hard-core interactions, electrostatic interactions become more important as the volume fraction decreases. Furthermore, the structure of the rough walls was varied and found to have a significant effect on the fluid structure. An appropriate representation of the rough walls in the simulations is thus crucial to successfully mimic the experiments.

Using the second virial coefficient as physical criterion to map the hard-sphere potential onto a continuous potential.

In the same sense as in the extended law of corresponding states [M. Noro and D. Frenkel, J. Chem. Phys. 113, 2941 (2000)], we propose the use of the second virial coefficient to map the hard-sphere potential onto a continuous potential. We show that this criterion provides accurate results when the continuous potential is used, for example, in computer simulations to reproduce the physical properties of systems with hard-core interactions. We also demonstrate that this route is straightforwardly applicable to any spatial dimension, does not depend on the particle density and, from a numerical point of view, is easy to implement.

A Brownian dynamics algorithm for colloids in curved manifolds.

The many-particle Langevin equation, written in local coordinates, is used to derive a Brownian dynamics simulation algorithm to study the dynamics of colloids moving on curved manifolds. The predictions of the resulting algorithm for the particular case of free particles diffusing along a circle and on a sphere are tested against analytical results, as well as with simulation data obtained by means of the standard Brownian dynamics algorithm developed by Ermak and McCammon [J. Chem. Phys. 69, 1352 (1978)] using explicitly a confining external field. The latter method allows constraining the particles to move in regions very tightly, emulating the diffusion on the manifold. Additionally, the proposed algorithm is applied to strong correlated systems, namely, paramagnetic colloids along a circle and soft colloids on a sphere, to illustrate its applicability to systems made up of interacting particles.

Prevalencia de gérmenes causantes de faringoamigdalitis en niños. Sensibilidad y respuesta terapéutica a la ampicilina- / Prevalence of germs causing pharyngotonsillitis in children. Sensiativity and therapeutic response to ampicillin

Este estudio fue realizado para analizar la prevalencia de gérmenes aislados en pacientes pediátricos con faringoamigdalitis bacteriana en la consulta privada a nivel de la comunidad, y al mismo tiempo evaluar la respuesta clínica al tratamiento con ampicilina. Material y métodos. Se incluyó a 516 pacientes de 12 ciudades de México, con diagnóstico de faringoamigdalitis bacteriana. Se practicaron exudados faríngeos antes y después del tratamiento con ampicilina y se probó la susceptibilidad in vitro a varios antibióticos (incluida la ampicilina). Resultados. El patógeno más aislado fue el estreptococo betahemolítico del grupo A de Lancefield (S. pyogenes), con 26.6 por ciento de prevalencia. En dichos cultivos la sensibilidad in vitro a ampicilina fue de 100 por ciento para el estreptococo grupo A betahemolítico. La respuesta global a ampicilina fue satisfactoria en 95 por ciento de los pacientes. Conclusiones. Los resultados de este estudio confirman datos anteriormente reportados en población pediátrica a nivel de la comunidad en México y otros países en vías de desarrollo; contrastan con los obtenidos en países del primer mundo y confirman la utilidad del tratamiento de las faringoamigdalitis bacterianas con ampicilina en países en vías de desarrollo.

Los factores genéticos determinantes de la resistencia a la infección por VIH y del control de la progresión al SIDA: Implicaciones sobre la patogénesis y las estrategias terapéuticas para la erradicación del VIH. Una revisión

Esta revisión describe y discute los factores genéticos que al menos en parte, determinan la resistencia a la infección y que controlan el curso progresivo de la enfermedad en las personas infectadas por el virus de la inmunodeficiencia humana. Los factores genéticos podrían explicar la no progresión o la progresión lenta de la enfermedad, de una proporción de individuos infectados por VIH denominados no progresores a largo plazo. En general, este grupo permanece sin síntomas durante más de 10 años, mantiene estable sus niveles circulantes de cT CD4+ y habitualmente tiene baja carga viral. No obstante que los fenómenos de la no progresión y de la progresión rápida son aún incomprendidos, es probable que ciertos alelos de clase I y clase II del complejo principal de histocompatibilidad se asocien con un riesgo menor o mayor para desarrollar el síndrome de inmunodeficiencia adquirida...