Acoustic gaps in a chain of magnetic spheres.

Acoustic gaps are normally observed in granular inhomogeneous structures made of composite materials. The modulation of the elastic properties in such media creates the coherent effects of scattering and interference that ultimately lead to frequency intervals where sound propagation is forbidden. Contrastingly, we report here an experimental observation of acoustic gaps in homogeneous media; specifically, in granular chains. The beads used in our study are magnetic. Therefore, instead of modulating the elastic properties of the chain, we modulate the magnetization (i.e., the contact forces). We also observe that the propagation speed of acoustic signals through the magnetic chains used in this study is at odds with the speed predicted by Hertz's law.

Transport properties of the diluted Lorentz slab.

We study the behavior of a point particle incident on a slab of a randomly diluted triangular array of circular scatterers. Various scattering properties, such as the reflection and transmission probabilities and the scattering time are studied as a function of thickness and dilution. We show that a diffusion model satisfactorily describes the mentioned scattering properties. We also show how some of these quantities can be evaluated exactly and their agreement with numerical experiments. Our results exhibit the dependence of these scattering data on the mean free path. This dependence again shows excellent agreement with the predictions of a Brownian motion model.

Nature of phase transitions in a probabilistic cellular automaton with two absorbing states.

We present a probabilistic cellular automaton with two absorbing states, which can be considered a natural extension of the Domany-Kinzel model. Despite its simplicity, it shows a very rich phase diagram, with two second-order and one first-order transition lines that meet at a bicritical point. We study the phase transitions and the critical behavior of the model using mean field approximations, direct numerical simulations and field theory. The second-order critical curves and the kink critical dynamics are found to be in the directed percolation and parity conservation universality classes, respectively. The first-order phase transition is put in evidence by examining the hysteresis cycle. We also study the "chaotic" phase, in which two replicas evolving with the same noise diverge, using mean field and numerical techniques. Finally, we show how the shape of the potential of the field-theoretic formulation of the problem can be obtained by direct numerical simulations.

[Transcultural approach to non-francophone patients originating from Southeast Asia in the psychiatric service network of the XIIIth district of Paris]. / Approche transculturelle des patients non francophones originaires du Sud-est asiatique dans le dispositif psychiatrique du XIIIe arrondissement de Paris.

Following the political upheaval that shook the Indochinese peninsula in the middle of the 1970s, many refugees originating from Southeast Asia re-established themselves in France. Since 1976, many of these refugees have formed a large Asian community in the XIIIth arrondissement of Paris. As a result, the arrondissement's psychiatric services, which cover the entire Asian neighborhood, have been confronted with the arrival of increasing numbers of non francophone patients from this ethnic minority. In this article, the authors present the steps that were taken by the psychiatric services to meet the very particular historical, cultural and psychopathological needs of this population.