Some stochastic models for structured populations : scaling limits and long time behavior

The first chapter concerns monotype population models. We first study general birth and death processes and we give non-explosion and extinction criteria, moment computations and a pathwise representation. We then show how different scales may lead to different qualitative approximations, either ODEs or SDEs. The prototypes of these equations are the logistic (deterministic) equation and the logistic Feller diffusion process. The convergence in law of the sequence of processes is proved by tightness-uniqueness argument. In these large population approximations, the competition between individuals leads to nonlinear drift terms. We then focus on models without interaction but including exceptional events due either to demographic stochasticity or to environmental stochasticity. In the first case, an individual may have a large number of offspring and we introduce the class of continuous state branching processes. In the second case, catastrophes may occur and kill a random fraction of the population and the process enjoys a quenched branching property. We emphasize on the study of the Laplace transform, which allows us to classify the long time behavior of these processes. In the second chapter, we model structured populations by measure-valued stochastic differential equations. Our approach is based on the individual dynamics. The individuals are characterized by parameters which have an influence on their survival or reproduction ability. Some of these parameters can be genetic and are inheritable except when mutations occur, but they can also be a space location or a quantity of parasites. The individuals compete for resources or other environmental constraints. We describe the population by a point measure-valued Markov process. We study macroscopic approximations of this process depending on the interplay between different scalings and obtain in the limit either integro-differential equations or reaction-diffusion equations or nonlinear super-processes. In each case, we insist on the specific techniques for the proof of convergence and for the study of the limiting model. The limiting processes offer different models of mutation-selection dynamics. Then, we study two-level models motivated by cell division dynamics, where the cell population is discrete and characterized by a trait, which may be continuous. In 1 particular, we finely study a process for parasite infection and the trait is the parasite load. The latter grows following a Feller diffusion and is randomly shared in the two daughter cells when the cell divides. Finally, we focus on the neutral case when the rate of division of cells is constant but the trait evolves following a general Markov process and may split in a random number of cells. The long time behavior of the structured population is then linked and derived from the behavior a well chosen SDE (monotype population)

Speed of coming down from infinity for birth and death processes

We finely describe the speed of "coming down from infinity" for birth and death processes which eventually become extinct. Under general assumptions on the birth and death rates, we firstly determine the behavior of the successive hitting times of large integers. We put in light two different regimes depending on whether the mean time for the process to go from $n+1$ to $n$ is negligible or not compared to the mean time to reach $n$ from infinity. In the first regime, the coming down from infinity is very fast and the convergence is weak. In the second regime, the coming down from infinity is gradual and a law of large numbers and a central limit theorem for the hitting times sequence hold. By an inversion procedure, we deduce that the process is a.s. equivalent to a non-increasing function when the time goes to zero. Our results are illustrated by several examples including applications to population dynamics and population genetics. The particular case where the death rate varies regularly is studied in details.Comment: 30 pages. arXiv admin note: text overlap with arXiv:1310.740

Shear induced normal stress differences in aqueous foams

A finite simple shear deformation of an elastic solid induces unequal normal stresses. This nonlinear phenomenon, known as the Poynting effect, is governed by a universal relation between shear strain and first normal stresses difference, valid for non-dissipative elastic materials. We provide the first experimental evidence that an analog of the Poynting effect exists in aqueous foams where besides the elastic stress, there are significant viscous or plastic stresses. These results are interpreted in the framework of a constitutive model, derived from a physical description of foam rheology

User Centered and Ontology Based InformationRetrieval System for Life Sciences

Because of the increasing number of electronic data, designing efficient tools to retrieve and exploit documents is a major challenge. Current search engines suffer from two main drawbacks: there is limited interaction with the list of retrieved documents and no explanation for their adequacy to the query. Users may thus be confused by the selection and have no idea how to adapt their query so that the results match their expectations. 
This talk describes a request method and an environment based on aggregating models to assess the relevance of documents annotated by concepts of ontology. The selection of documents is then displayed in a semantic map to provide graphical indications that make explicit to what extent they match the user’s query; this man/machine interface favors a more interactive exploration of data corpus.
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Espaces publics touristiques urbains et développement durable : principes d'aménagement, usages et tensions. Une analyse à partir du cas de Barcelone (Espagne)

International audienceThe expansion of tourism reflects a more general growth of the service sector in the major cities of the Western world. Towns and cities typically seek to develop a unique image to bolster their attractiveness in highly competitive markets, particularly by remodelling public spaces. Since the early 1980s, Barcelona - a Mediterranean metropolis with a population of over 3.1 million people and an increasingly popular tourist destination - has invested significantly in public spaces. This has helped to foster an image of Barcelona as a modern city opene d to the world and focussed on practicing long-term sustainable development. This paper questions whether the public spaces policy implemented in Barcelona represents a full and adequate response to the demands of economic, environmental and social sustainability.L'expansion du tourisme accompagne le processus de tertiarisation de l'économie des grandes métropoles du monde occidental. Pour conforter leur attractivité dans un marché très concurrentiel, les villes tentent de se créer une image singulière à travers, notamment, le remodelage des espaces publics. Métropole méditerranéennede plus de 3,1 millions d'habitants et destination touristique de plus en plus prisée, Barcelone a accordé une attention toute particulière aux espaces publics dès le début des années 1980. Ceux-ci ont contribué à façonner l'image d'une ville moderne, ouverte au monde et soucieuse de s'inscrire dans une logique de durabilité. Cependant, la politique barcelonaise en matière d'espaces publics parvient-elle à répondre pleinement aux exigences de durabilité économique, environnementale et sociale

Cultures juvéniles à l\u27ère de la globalisation : une approche par le cosmopolitisme esthético-culturel (Les)

Les œuvres et contenus culturels circulent de manière croissante dans le monde et contribuent à façonner des répertoires et des goûts juvéniles désormais internationalisés. Ainsi la série Game of Thrones, qui a battu tous les records d’audience, Waka waqua, l’hymne de la Coupe du monde de football en Afrique du Sud en 2010 interprété par Shakira, chanteuse colombienne qui fait carrière aux États-Unis ou encore Naruto, personnage de manga japonais, sont-ils devenus des références partagées par les jeunes Français aujourd’hui, aux côtés d’icônes nationales comme Astérix ou David Guetta