A fixed-point theorem for asymptotically contractive mappings

We present fixed point theorems for a nonexpansive mapping from a closed convex subset of a uniformly convex Banach space into itself under some asymptotic contraction assumptions. They generalize results valid for bounded convex sets or asymptotically compact sets.

     

Scattering poles for asymptotically hyperbolic manifolds

For a class of manifolds that includes quotients of real hyperbolic -dimensional space by a convex co-compact discrete group, we show that the resonances of the meromorphically continued resolvent kernel for the Laplacian on coincide, with multiplicities, with the poles of the meromorphically continued scattering operator for . In order to carry out the proof, we use Shmuel Agmon's perturbation theory of resonances to show that both resolvent resonances and scattering poles are simple for generic potential perturbations.

     

A sampling theorem on homogeneous manifolds

We consider a generalization of entire functions of spherical exponential type and Lagrangian splines on manifolds. An analog of the Paley-Wiener theorem is given. We also show that every spectral entire function on a manifold is uniquely determined by its values on some discrete sets of points.

The main result of the paper is a formula for reconstruction of spectral entire functions from their values on discrete sets using Lagrangian splines.

     

A theorem on contingents of hyperspaces in euclidean space

An attempt is made to carry out a deeper study of the contingent characterization of arbitrary sets in euclidean space ^m+1.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 11, pp. 1484–1490, November, 1992.     

A Morse-Sard theorem for the distance function on Riemannian manifolds

We prove that the set of critical values of the distance function from a submanifold of a complete Riemannian manifold is of Lebesgue measure zero. In this way, we extend a result of Itoh and Tanaka. Mathematics Subject Classification (2000):53C22, 28A78, 49J52     

A volume comparison theorem for Finsler manifolds

Let be a symmetric Finsler manifold, endowed with the Busemann volume form, and let be its unit disk bundle endowed with the canonical symplectic volume form. It is shown that , where is the volume of the unit disk in . Moreover, equality holds if and only if is Riemannian.

     

A Gauss-Bonnet-Chern theorem for complex Finsler manifolds

Using Chern’s method of transgression and the currents, we establish a Gauss-Bonnet-Chern theorem for general closed complex Finsler manifolds (M, F). This result extends the classical Gauss-Bonnet-Chern theorem for Hermitian manifolds. Furthermore, a simplified version of the Gauss-Bonnet-Chern theorem is obtained in the case of complex Berwald 1-manifolds.     

A topological splitting theorem for sub-Riemannian manifolds

We prove an analogue of the Cheeger–Gromoll splitting theorem for sub-Riemannian manifolds with the measure contraction property instead of the nonnegativity of the Ricci curvature. If such a sub-Riemannian manifold contains a straight line, then the manifold splits diffeomorphically, where the splitting is not necessarily isometric. We prove that such a sub-Riemannian manifold containing a straight line cannot split isometrically under some typical condition in sub-Riemannian geometry. Heisenberg groups are such examples.     

Concerning the Strauss conjecture on asymptotically Euclidean manifolds

In this paper we verify the Strauss conjecture for semilinear wave equations on asymptotically Euclidean manifolds when n=3,4. We also give an almost sharp lifespan for the subcritical case 2?p<pc when n=3. The main ingredients include a Keel-Smith-Sogge type estimate with 0<μ<1/2 and weighted Strichartz estimates of order two.