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Structures de contact sur les fibrés principaux en cercles de dimension trois

Robert Lutz (1977)

Annales de l'institut Fourier

On construit et classifie à conjugaison équivariante près toutes les formes de contact invariantes sur un fibré principal en cercles M 3 B 2 ( M compact). Si M ˜ = S 3 , les formes obtenues induisent sur S 3 des formes de contact dans chaque classe d’homotopie de 1-formes sans zéros : on en déduit que M admet une infinité de structures de contact non isomorphes.

Structures lisses

Claude Albert (1974)

Annales de l'institut Fourier

Une variété lisse est une variété C dont le fibré tangent est muni d’une structure de fibré en algèbres de Lie localement définie par un crochet de champs de vecteurs. On définit les notions de G -structures et de pseudo-groupe de Lie adaptées, qui recouvrent les notions usuelles de G -structures et pseudogroupes plats.

Strutture subriemanniane in alcuni problemi di Analisi

Ermanno Lanconelli (2005)

Bollettino dell'Unione Matematica Italiana

Vengono presentati alcuni problemi, idee e tecniche sorte nell'ambito della teoria delle equazioni alle derivate parziali del secondo ordine, con forma caratteristica semidefinita positiva e con soggiacenti strutture sub-riemanniane. Se ne traccia lo sviluppo a partire dalla classica teoria delle funzioni armoniche e caloriche, attraverso la teoria del potenziale negli spazi armonici astratti e la teoria della regolarità locale delle soluzioni.

Submanifold averaging in Riemannian and symplectic geometry

Marco Zambon (2006)

Journal of the European Mathematical Society

We give a canonical construction of an “isotropic average” of given C 1 -close isotropic submanifolds of a symplectic manifold. For this purpose we use an improvement (obtained in collaboration with H. Karcher) of Weinstein’s submanifold averaging theorem and apply “Moser’s trick”. We also present an application to Hamiltonian group actions.

Submanifolds and the Hofer norm

Michael Usher (2014)

Journal of the European Mathematical Society

In [Ch00], Chekanov showed that the Hofer norm on the Hamiltonian diffeomorphism group of a geometrically bounded symplectic manifold induces a nondegenerate metric on the orbit of any compact Lagrangian submanifold under the group. In this paper we consider the orbits of more general submanifolds. We show that, for the Chekanov–Hofer pseudometric on the orbit of a closed submanifold to be a genuine metric, it is necessary for the submanifold to be coisotropic, and we show that this condition is...

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