18 mai 2017

 
Remise des Palmes Académiques à Thierry Ramond

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Résumé : Thierry Ramond sera décoré des palmes académiques pour services éminents rendus à l’Education Nationale. Un pot festif aura lieu à cette occasion. Félicitations Thierry !
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Remise des Palmes Académiques à Thierry Ramond  Version PDF

Kathryn Mann (Berkeley)
Ordering groups and group actions on 1-manifolds

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Lieu : Bâtiment 425, salle 121-123

Résumé : Given a group G, and a manifold M, can one describe all the ways that G acts on M ? This is a remarkably rich question even in the case where M is the line or the circle, and is connected to problems in dynamics, topology, and foliation theory.
This talk will describe one very useful way to capture such an action, namely, through the algebraic data of a left-invariant linear or circular order on a group. I’ll explain new work (joint with C. Rivas) that describes the space of orders on a group, and relates its topology to the moduli space of actions of G on the line or circle. As an application we’ll see new rigidity phenomena for actions, and the answers to some older algebraic questions about orderings.

Notes de dernières minutes : Café culturel à 13h par Frédéric Paulin

Ordering groups and group actions on 1-manifolds  Version PDF

Cristina Toninelli  (LPMA)
Bootstrap percolation and kinetically constrained spin models : critical time and lengths scales

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Résumé : Recent years have seen a great deal of progress in understanding the behavior of bootstrap percolation models, a particular class of monotone cellular automata. In the two dimensional lattice there is now a quite satisfactory understanding of their evolution starting from a random initial condition, with a strikingly beautiful universality picture for their critical behavior.
Much less is known for their non-monotone stochastic counterpart, namely kinetically constrained models (KCM). In KCM each vertex is resampled (independently) at rate one by tossing a p-coin iff it can be infected in the next step by the bootstrap model. In particular infection can also heal, hence the non-monotonicity.
Besides the connection with bootstrap percolation, KCM have an interest in their own : when p->0 they display some of the most striking features of the liquid/glass transition, a major and still largely open problem in condensed matter physics.
In this talk I will discuss some recent results on the characteristic time scales of KCM as p → 0 and the connection with the critical behavior of the corresponding bootstrap models.

Bootstrap percolation and kinetically constrained spin models : critical time and lengths scales  Version PDF

Jun Kitagawa (Michigan State University)
Multi-marginal optimal partial transport and partial barycenter problems

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Lieu : Bât 425, salle 113-115

Résumé : The classical two-marginal optimal transport problem can be interpreted as the coupling of two probability distributions subject to an optimality criterion, determined by a “cost function” defined on the domains. Recently, there has been much activity on two generalizations of this problem. The first is the partial transport problem, where the total masses of the two distributions to be coupled may not match, and one is forced to choose submeasures of the constraints for coupling. The other generalization is the multi-marginal transport problem, where there are 3 or more probability distributions to be coupled together in an optimal manner. By combining the above two generalizations we obtain a natural extension : the multi-marginal optimal partial transport problem. In joint work with Brendan Pass (University of Alberta), we have obtained uniqueness of solutions (under hypotheses analogous to the two-marginal partial transport problem given by Figalli) by relating the problem to what we call the “partial barycenter problem” for finite measures. A notable difference is that in some cases, solutions can exhibit significantly different qualitative behavior compared to those of the two marginal case.

Multi-marginal optimal partial transport and partial barycenter problems  Version PDF

Felipe Linares (IMPA)
On the fractional KP equation

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Lieu : Bât 425, salle 113-115

Résumé : In this talk we will discuss local well-posedness issues for the Cauchy problem associated to the fractional Kadomtsev-Petviashvili (fKP) equations. We will present positive and negative results.
This is a joint work with D. Pilod (UFRJ, Brazil) and J-C. Saut (Orsay).

On the fractional KP equation  Version PDF

mai 2017 :

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