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Plateau-Stein manifolds

Misha Gromov (2014)

Open Mathematics

We study/construct (proper and non-proper) Morse functions f on complete Riemannian manifolds X such that the hypersurfaces f(x) = t for all −∞ < t < +∞ have positive mean curvatures at all non-critical points x ∈ X of f. We show, for instance, that if X admits no such (not necessarily proper) function, then it contains a (possibly, singular) complete (possibly, compact) minimal hypersurface of finite volume.

Poincaré-invariant structures in the solution manifold of a nonlinear wave equation.

Irving E. Segal (1986)

Revista Matemática Iberoamericana

The solution manifold M of the equation ⎯φ + gφ3 = 0 in Minkowski space is studied from the standpoint of the establishment of differential-geometric structures therein. It is shown that there is an almost Kähler structure globally defined on M that is Poincaré invariant. In the vanishing curvature case g = 0 the structure obtained coincides with the complex Hilbert structure in the solution manifold of the real wave equation. The proofs are based on the transfer of the equation to an ambient universal...

Quantum 4-sphere: the infinitesimal approach

F. Bonechi, M. Tarlini, N. Ciccoli (2003)

Banach Center Publications

We describe how the constructions of quantum homogeneous spaces using infinitesimal invariance and quantum coisotropic subgroups are related. As an example we recover the quantum 4-sphere of [2] through infinitesimal invariance with respect to q ( S U ( 2 ) ) .

Quantum ultrametrics on AF algebras and the Gromov-Hausdorff propinquity

Konrad Aguilar, Frédéric Latrémolière (2015)

Studia Mathematica

We construct quantum metric structures on unital AF algebras with a faithful tracial state, and prove that for such metrics, AF algebras are limits of their defining inductive sequences of finite-dimensional C*-algebras for the quantum propinquity. We then study the geometry, for the quantum propinquity, of three natural classes of AF algebras equipped with our quantum metrics: the UHF algebras, the Effrös-Shen AF algebras associated with continued fraction expansions of irrationals, and the Cantor...

Régularité des solutions d'équations aux dérivées partielles non linéaires associées à un système de champs de vecteurs

Chao-Jiang Xu (1987)

Annales de l'institut Fourier

Cet article considère des équations aux dérivées partielles non linéaires de la forme F ( x , X α u ) = 0 , | α | m , où les X 1 , ... , X p sont des champs de vecteur vérifiant la condition de Hörmander. Soit u une solution réelle de classe C 2 m + 1 ; on suppose que la localisation de l’opérateur linéarisé sur le groupe de Lie associé au système { X j } est hypoelliptique; nous démontrons sous ces hypothèses que u est de classe C .

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