100 research outputs found
A curved Brunn--Minkowski inequality on the discrete hypercube
We compare two approaches to Ricci curvature on non-smooth spaces, in the
case of the discrete hypercube . While the coarse Ricci curvature of
the first author readily yields a positive value for curvature, the
displacement convexity property of Lott, Sturm and the second author could not
be fully implemented. Yet along the way we get new results of a combinatorial
and probabilistic nature, including a curved Brunn--Minkowski inequality on the
discrete hypercube.Comment: Latest version: improved constants, minor correction
Amortissement Landau
10 pages -- version française de la note "Landau damping" hal-00383920Dans cette note nous prĂ©sentons les principaux rĂ©sultats du rĂ©cent travail hal-00376547/arXiv:0904.2760, oĂč le phĂ©nomĂšne d'amortissement Landau est pour la premiĂšre fois Ă©tabli dans un contexte non linĂ©aire. [In this note we present the main results from the recent work hal-00376547/arXiv:0904.2760, which for the first time establish Landau damping in a nonlinear context.
Tangent cut loci on surfaces
International audienceGiven a smooth compact Riemannian surface, we prove that if a suitable convexity assumption on the tangent focal cut loci is satisïŹed, then all injectivity domains are semiconvex
Nearly round spheres look convex
International audienceWe prove that a Riemannian manifold (M, g), close enough to the round sphere in the C4 topology, has uniformly convex injectivity domains so M appears uniformly convex in any exponential chart. The proof is based on the Ma-Trudinger-Wang nonlocal curvature tensor, which originates from the regularity theory of optimal transport
On the Ma-Trudinger-Wang condition on surfaces
International audienceWe investigate the properties of the Ma-Trudinger-Wang nonlocal curvature tensor in the case of surfaces. In particular, we prove that a strict form of the Ma-Trudinger-Wang condition is stable under C 4 perturbation if the nonfocal domains are uniformly convex; and we present new examples of positively curved surfaces which do not satisfy the Ma-Trudinger-Wang condition. As a corollary of our results, optimal transport maps on a "suïŹciently ïŹat" ellipsoid are in general nonsmooth
LâĂ©criture des mathĂ©maticiens
Cette note rĂ©sume et dĂ©veloppe certains sujets abordĂ©s lors de ma participation Ă la table ronde « les Ă©critures des mathĂ©maticiens et des physiciens », avec Patrick Flandrin et Jean Dhombres, dans le cadre du colloque Ăcritures : sur les traces de Jack Goody. En mathĂ©matiques, comme en physique thĂ©orique, le rĂŽle de lâĂ©criture prĂ©sente quelques caractĂšres distinctifs. Sans faire dâĂ©tude dĂ©taillĂ©e, et sans mise en perspective historique sĂ©rieuse, je me contenterai de dĂ©crire lâexistant, Ă la ..
Le ciel étoilé de Poincaré à la Fondation Cartier
Jean-Michel Alberola, Un ciel mathĂ©matique â Henri PoincarĂ© Vue de lâexposition MathĂ©matiques, un dĂ©paysement soudain, PrĂ©sentĂ©e du 21 octobre 2011 au 18 mars 2012 Ă la Fondation Cartier pour lâart contemporain, Paris. Photo © Olivier Ouadah. Vue dâartiste : Henri PoincarĂ©, cĂ©lĂšbre pour ses intuitions fulgurantes, brille au plus haut du firmament mathĂ©matique ; mais comment faire pour lui rendre hommage de maniĂšre Ă la fois rĂ©aliste et poĂ©tique ? Pour ce faire, lâartiste Jean-Michel Albero..
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