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Search Results: 1 - 10 of 210079 matches for " Ga?l Raoul "
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Dynamics of a kinetic model describing protein exchanges in a cell population
Pierre Magal,Gal Raoul
Mathematics , 2015,
Abstract: We consider a cell population structured by a positive real number, describing the number of P-glycoproteins carried by the cell. We are interested in the effect of those proteins on the growth of the population: those proteins are indeed involve in the resistance of cancer cells to chemotherapy drugs. To describe this dynamics, we introduce a kinetic model. We then introduce a rigorous hydrodynamic limit, showing that if the exchanges are frequent, then the dynamics of the model can be described by a system of two coupled differential equations. Finally, we also show that the kinetic model converges to a unique limit in large times. The main idea of this analysis is to use Wasserstein distance estimates to describe the effect of the kinetic operator, combined to more classical estimates on the macroscopic quantities.
Existence and qualitative properties of travelling waves for an epidemiological model with mutations
Quentin Griette,Gal Raoul
Mathematics , 2014,
Abstract: In this article, we are interested in a non-monotone system of logistic reaction-diffusion equations. This system of equations models an epidemics where two types of pathogens are competing, and a mutation can change one type into the other with a certain rate. We show the existence of minimal speed travelling waves, that are usually non monotonic. We then provide a description of the shape of those constructed travelling waves, and relate them to some Fisher-KPP fronts with non-minimal speed.
Local stability of perfect alignment for a spatially homogeneous kinetic model
Pierre Degond,Amic Frouvelle,Gal Raoul
Physics , 2014, DOI: 10.1007/s10955-014-1062-3
Abstract: We prove the nonlinear local stability of Dirac masses for a kinetic model of alignment of particles on the unit sphere, each point of the unit sphere representing a direction. A population concentrated in a Dirac mass then corresponds to the global alignment of all individuals. The main difficulty of this model is the lack of conserved quantities and the absence of an energy that would decrease for any initial condition. We overcome this difficulty thanks to a functional which is decreasing in time in a neighborhood of any Dirac mass (in the sense of the Wasserstein distance). The results are then extended to the case where the unit sphere is replaced by a general Riemannian manifold.
Confinement by biased velocity jumps: aggregation of Escherichia coli
Vincent Calvez,Gal Raoul,Christian Schmeiser
Mathematics , 2014,
Abstract: We investigate a linear kinetic equation derived from a velocity jump process modelling bacterial chemotaxis in the presence of an external chemical signal centered at the origin. We prove the existence of a positive equilibrium distribution with an exponential decay at infinity. We deduce a hypocoercivity result, namely: the solution of the Cauchy problem converges exponentially fast towards the stationary state. The strategy follows [J. Dolbeault, C. Mouhot, and C. Schmeiser, Hypocoercivity for linear kinetic equations conserving mass, Trans. AMS 2014]. The novelty here is that the equilibrium does not belong to the null spaces of the collision operator and of the transport operator. From a modelling viewpoint it is related to the observation that exponential confinement is generated by a spatially inhomogeneous bias in the velocity jump process.
The effect of climate shift on a species submitted to dispersion, evolution, growth and nonlocal competition
Matthieu Alfaro,Henri Berestycki,Gal Raoul
Mathematics , 2015,
Abstract: We consider a population structured by a spacevariable and a phenotypical trait, submitted to dispersion,mutations, growth and nonlocal competition. We introduce theclimate shift due to {\it Global Warming} and discuss the dynamicsof the population by studying the long time behavior of thesolution of the Cauchy problem. We consider three sets ofassumptions on the growth function. In the so-called {\it confinedcase} we determine a critical climate change speed for theextinction or survival of the population, the latter case taking place by "strictly following the climate shift". In the so-called {\itenvironmental gradient case}, or {\it unconfined case}, we additionally determine the propagation speedof the population when it survives: thanks to a combination of migration and evolution, it can here be different from the speed of the climate shift. Finally, we consider {\it mixed scenarios}, that are complex situations, where thegrowth function satisfies the conditions of the confined case on the right, and the conditions of the unconfined case on the left.The main difficulty comes from the nonlocal competition term that prevents the use of classical methods based on comparison arguments. This difficulty is overcome thanks to estimates on the tails of the solution, and a careful application of the parabolic Harnack inequality.
Existence of self-accelerating fronts for a non-local reaction-diffusion equations
Nathana?l Berestycki,Clément Mouhot,Gal Raoul
Mathematics , 2015,
Abstract: We describe the accelerated propagation wave arising from a non-local reaction-diffusion equation. This equation originates from an ecological problem, where accelerated biological invasions have been documented. The analysis is based on the comparison of this model with a related local equation, and on the analysis of the dynamics of the solutions of this second model thanks to probabilistic methods.
Travelling waves in a nonlocal reaction-diffusion equation as a model for a population structured by a space variable and a phenotypical trait
Matthieu Alfaro,Jér?me Coville,Gal Raoul
Mathematics , 2012,
Abstract: We consider a nonlocal reaction-diffusion equation as a model for a population structured by a space variable and a phenotypical trait. To sustain the possibility of invasion in the case where an underlying principal eigenvalue is negative, we investigate the existence of travelling wave solutions. We identify a minimal speed $c^*>0$, and prove the existence of waves when $c\geq c^*$ and the non existence when $0\leq c
Asymptotic profile in selection-mutation equations: Gauss versus Cauchy distributions
àngel Calsina,Sílvia Cuadrado,Laurent Desvillettes,Gal Raoul
Mathematics , 2015,
Abstract: In this paper, we study the asymptotic (large time) behavior of a selection-mutation-competition model for a population structured with respect to a phenotypic trait, when the rate of mutation is very small. We assume that the reproduction is asexual, and that the mutations can be described by a linear integral operator. We are interested in the interplay between the time variable $t$ and the rate $\varepsilon$ of mutations. We show that depending on $\alpha > 0$, the limit $\varepsilon \to 0$ with $t = \varepsilon^{-\alpha}$ can lead to population number densities which are either Gaussian-like (when $\alpha$ is small) or Cauchy-like (when $\alpha$ is large).
Optimal Endogenous Tariffs with Implicit Campaign Contributions  [PDF]
Gal Lagadec
Theoretical Economics Letters (TEL) , 2014, DOI: 10.4236/tel.2014.44040

This article proposes a model of endogenous protection by integrating informed and non-informed voters in the population. The model also distinguishes between interest groups and pressure groups, by considering that the members of one interest group do not necessarily organize as a pressure group (lobby). The endogenous tariff stemming from the model is an increasing function of the relative influence of the lobby, and the aforementioned function itself increases in accordance with the part of non-informed voters. This framework avoids formalizing contributions. It also permits to show that the conditions of the lobbying’s efficiency depend on the nature of the free rider comportment of the interest group members.

Participatory Teaching and Happiness in Developed Nations  [PDF]
Gal Brulé
Advances in Applied Sociology (AASoci) , 2014, DOI: 10.4236/aasoci.2014.411028
Abstract: Average happiness differs considerably across nations. Much of this difference is in societal development, but average happiness differs also among developed nations. Much of that latter difference seems to be due to cultural factors and education is a main carrier of these. In that context we explored the effect of teaching styles on happiness. In a first study on the general public in 37 developed nations we found that people feel happier in the nations where participatory teaching prevailed. Much of this difference can be explained by the effect of teaching style on psychological autonomy. Participatory teaching fosters autonomy and autonomy adds to happiness. In a second study among high school pupils we found no correlation between average happiness and dominant teaching style in the nation, which fits the explanation that the effect of participatory teaching is in personality formation, with the consequences for happiness of which manifest in adulthood.
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