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Nombre de programmes trouvés : 888
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le (9m43s)

Enigma, ou comment les mathématiciens ont gagné la guerre 1939-45. (Partie 5)

Dans cet exposé, à la fois historique et technique, nous expliqueronstout d'abord comment les machines à chiffrer Enigma ont pu êtrecryptanalysées durant la deuxième guerre mondiale. Nous nousefforcerons ensuite de dégager les grands principes qui sont àl'oeuvre aussi bien dans l'analyse des machines à rotors historiquesque dans le chiffrement par blocs moderne.  Dans les deux cas ils'agit de constructions à base de combinaisons (non-commutatives!) depermutations et il existe un certain nombre de stratégies quipermettent de déjouer leur apparente complexité. Nous expliquerons lerôle majeur joué par certaines propriétés et théorèmes clés sur lespermutations, qui concernent, notamment, les involutions, les cyclescourts et ...
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Cours magistraux

le (1h29m10s)

Thomas Richard - Lower bounds on Ricci curvature, with a glimpse on limit spaces (Part 1)

The goal of these lectures is to introduce some fundamental tools in the study of manifolds with a lower bound on Ricci curvature. We will first state and prove the laplacian comparison theorem for manifolds with a lower bound on the Ricci curvature, and derive some important consequences : Bishop-Gromov inequality, Myers theorem, Cheeger-Gromoll splitting theorem. Then we will define the Gromov-Hausdorff distance between metric spaces which will allow us to consider limits of sequences of Riemannian manifolds, along the way we will prove ...
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Cours magistraux

le (1h16m48s)

Sylvain Maillot - An introduction to open 3-manifolds (Part 1)

W. Thurston's geometrization program has lead to manyoutstanding results in 3-manifold theory. Thanks to worksof G. Perelman, J. Kahn and V. Markovic, D. Wise, and I. Agol among others, compact 3-manifolds can now beconsidered to be reasonably well-understood.By contrast, noncompact 3-manifolds remainmuch more mysterious. There is a series of examples,beginning with work of L. Antoine and J. H. C. Whitehead,which show that open 3-manifolds can exhibit wildbehavior at infinity. No comprehensive structure theoryanalogous to geometrization à la Thurston is currently availablefor these objectsIn these lectures, we will focus on two aspects of the subject:(1) constructing interesting examples, and(2) finding sufficientconditions ...
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Cours magistraux

le (1h26m42s)

Thomas Richard - Lower bounds on Ricci curvature, with a glimpse on limit spaces (Part 2)

The goal of these lectures is to introduce some fundamental tools in the study of manifolds with a lower bound on Ricci curvature. We will first state and prove the laplacian comparison theorem for manifolds with a lower bound on the Ricci curvature, and derive some important consequences : Bishop-Gromov inequality, Myers theorem, Cheeger-Gromoll splitting theorem. Then we will define the Gromov-Hausdorff distance between metric spaces which will allow us to consider limits of sequences of Riemannian manifolds, along the way we will prove ...
Voir la vidéo
Cours magistraux

le (1h21m8s)

Thomas Richard - Lower bounds on Ricci curvature, with a glimpse on limit spaces (Part 3)

The goal of these lectures is to introduce some fundamental tools in the study of manifolds with a lower bound on Ricci curvature. We will first state and prove the laplacian comparison theorem for manifolds with a lower bound on the Ricci curvature, and derive some important consequences : Bishop-Gromov inequality, Myers theorem, Cheeger-Gromoll splitting theorem. Then we will define the Gromov-Hausdorff distance between metric spaces which will allow us to consider limits of sequences of Riemannian manifolds, along the way we will prove ...
Voir la vidéo
Cours magistraux

le (1h28m21s)

Sylvain Maillot - An introduction to open 3-manifolds (Part 2)

W. Thurston's geometrization program has lead to manyoutstanding results in 3-manifold theory. Thanks to worksof G. Perelman, J. Kahn and V. Markovic, D. Wise, and I. Agol among others, compact 3-manifolds can now beconsidered to be reasonably well-understood.By contrast, noncompact 3-manifolds remainmuch more mysterious. There is a series of examples,beginning with work of L. Antoine and J. H. C. Whitehead,which show that open 3-manifolds can exhibit wildbehavior at infinity. No comprehensive structure theoryanalogous to geometrization à la Thurston is currently availablefor these objectsIn these lectures, we will focus on two aspects of the subject:(1) constructing interesting examples, and(2) finding sufficientconditions ...
Voir la vidéo
Cours magistraux

le (1h26m53s)

Thomas Richard - Lower bounds on Ricci curvature, with a glimpse on limit spaces (Part 4)

The goal of these lectures is to introduce some fundamental tools in the study of manifolds with a lower bound on Ricci curvature. We will first state and prove the laplacian comparison theorem for manifolds with a lower bound on the Ricci curvature, and derive some important consequences : Bishop-Gromov inequality, Myers theorem, Cheeger-Gromoll splitting theorem. Then we will define the Gromov-Hausdorff distance between metric spaces which will allow us to consider limits of sequences of Riemannian manifolds, along the way we will prove ...
Voir la vidéo

 
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