5 années de mutualisation des ressources en calcul scientifique au PSMN de l'ENS-Lyon

The PSMN (Pôle Scientifique de Modélisation Numérique) was founded in 1993. Since 2007, the PSMN has supported thepooling of resources dedicated to scientific computing at ENS-Lyon. After a brief history describing the evolution of thePSMN structure since its founding in 1993, I will develop its evolution since 2007. I will focus specifically on the description ofthe highlights of its functioning (involvement of all participants and flexibility) illustrated by some examples of research andpublications this operation has made possible. I will conclude with the objectives to achieve in order to sustain the structure

Examples of the influence of the geometry on the propagation of progressive waves

International audienceIn this paper, we give examples of the influence of the domain of propagation on progressive waves. More precisely, we numerically investigate the propagation of reaction diffusion waves in cylinders with variable radius. We show that, when the radius rapidly expands from a very small radius to a larger one, depending on the viscosity and the nonlinearity, the travelling wave may be blocked. The aim of this paper is to give numerical illustrations and quantifications of this effect, and to propose some conjectures which could be interesting subjects for further mathematical investigations. This work is linked to the study of spreading depression (SD), a propagative mechanism in brain and various tissues which has been observed in vivo and in vitro in many species since their discovery in 1944 by Leao. As a matter of fact, their direct observation in Man is still controversial. The complex structure of gray and white matter in humans may block the propagation of SD over large distances in brain and thus explain the difficulty of observing it. Medical consequences of the current numerical studies are detailed in [M.A. Dronne, et al., Influence of brain geometry on spreading depressions: a computationnal study, Progress in Biophysics and Molecular Biology 97 (1) (2008) 54-59] and a first mathematical approach given in [M.A. Dronne, E. Grenier, H. Gilquin, Modelization of spreading depressions following Nedergaard, preprint, 2003]

Construction de plans répliqués à partir de séquences de Sobol'

International audienceIn the perspective of estimating main effects of model inputs, two approaches are studied to iteratively construct replicated designs based on Sobol' sequences. Space-filling properties of the resulting designs are studied based on two criteria.Dans l'objectif d'estimer les effets principaux des paramètres d'un modèle, nous proposons d'étudier deux approches pour construire itérativement des plans répliqués à partir de séquences de Sobol'. Les propriétés de remplissement de l'espace des plans construits sont étudiées sur la base de deux critères

A global phenomenological model of ischemic stroke with stress on spreading depressions.

International audienceIn this paper, we establish a new global phenomenological model of ischemic stroke. It takes into account local ischemia, energy reduction, propagation of spreading depressions (SD), damages to the cells and cellular death by apoptosis or necrosis. The spatial diffusion of the ions in the extracellular space which triggers the propagation of SD is a central point here. First we expose the various biological hypotheses that we have made in this model, and then we explain how to determine the parameters and solve the system of equations that we obtain. Next we present some results of this model: we simulate a KCl injection and then a local ischemia. Finally we discuss results and propose some improvements for this model

A numerical study of the blocking of migraine by Rolando sulcus.

International audienceMigraine with aura is a complex phenomena, which remains still not completely understood. A striking fact is that its clinical manifestations may change from one patient to another. Migraine with aura may only consist in visual hallucinations, but may as well go on to temporary aphasy. However, for all the patients it always stops before it goes from area 3 to area 4, thus just before crossing Rolando sulcus. In this paper, we give arguments showing that the detailed geometry of Rolando sulcus in human cortex may by itself explain that migraine attack never crosses Rolando sulcus