Active Brownian Particles. From Individual to Collective Stochastic Dynamics

We review theoretical models of individual motility as well as collective dynamics and pattern formation of active particles. We focus on simple models of active dynamics with a particular emphasis on nonlinear and stochastic dynamics of such self-propelled entities in the framework of statistical mechanics. Examples of such active units in complex physico-chemical and biological systems are chemically powered nano-rods, localized patterns in reaction-diffusion system, motile cells or macroscopic animals. Based on the description of individual motion of point-like active particles by stochastic differential equations, we discuss different velocity-dependent friction functions, the impact of various types of fluctuations and calculate characteristic observables such as stationary velocity distributions or diffusion coefficients. Finally, we consider not only the free and confined individual active dynamics but also different types of interaction between active particles. The resulting collective dynamical behavior of large assemblies and aggregates of active units is discussed and an overview over some recent results on spatiotemporal pattern formation in such systems is given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte

New III-V transducers for optical microwave and millimeter wave conversion

Fiber optic radio communications will require devices able to convert an optical carrier into a millimeter wave carrier. After a brief recall of possible systems to be used, showing that in most cases, the transducer must associate the following functions : high speed photodetection, millimeter wave amplification, and mixing, we will discuss the properties of PIN-waveguide photodetectors, GaAs microwave monolithic integrated circuits with dual gate FETs, InP edge-coupled Heterojunction Bipolar Phototransistors to fulfill these requirements

Utilisation de lasers multi-electrodes en tant que mélangeur hyperfréquence

The purpose of this paper is to describe a new technological process for the fabrication of Fabry-Pérot multi-electrodes lasers. Only two masks are required and we use self-alignment technics and exclusively optical photolithography. We will precise the motivation of the different technological choices that have been done and we will present the first results of an original use of these components as a microwave mixer.Le but de cet article est de décrire une approche technologique améliorée, pour la fabrication de lasers multi-électrodes de type Fabry-Pérot pour des applications hyperfréquences. Seuls deux masques sont nécessaires, et nous utilisons exclusivement la photolitographie optique. Nous préciserons les motivations des différents choix technologiques et nous présenterons les premiers résultats d'une utilisation originale de ces lasers en tant que mélangeur hyperfréquence

Le programme AQUAE: rôle des aménagements d'origine anthropique (zones enherbées et fossés) dans le transfert et la rétention des produits phytosanitaires

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