Noyau, résolvante et valeurs propres d'une classe d'opérateurs elliptiques et dégénérés
Observability properties of a semi-discrete 1d wave equation derived from a mixed finite element method on nonuniform meshes
The goal of this article is to analyze the observability properties for a space semi-discrete approximation scheme derived from a mixed finite element method of the 1d wave equation on nonuniform meshes. More precisely, we prove that observability properties hold uniformly with respect to the mesh-size under some assumptions, which, roughly, measures the lack of uniformity of the meshes, thus extending the work [Castro and Micu, Numer. Math.102 (2006) 413–462] to nonuniform meshes. Our results...
On an embedding criterion for interpolation spaces and application to indefinite spectral problems.
On counting the number of eigenvalues in the right half-plane for spectral problems connected with hyperbolic systems. II: Differential equations.
On diamagnetism and de Haas-van Alphen effect
On nodal lines of Neumann eigenfunctions.
On nodal sets and nodal domains on and
We discuss possible topological configurations of nodal sets, in particular the number of their components, for spherical harmonics on . We also construct a solution of the equation in that has only two nodal domains. This equation arises in the study of high energy eigenfunctions.
On nonlinear eigenvaule problems.
On some new spectral estimates for Schrödinger-like operators
We prove the analog of the Cwikel-Lieb-Rozenblum estimate for a wide class of second-order elliptic operators by two different tools: Lieb-Thirring inequalities for Schrödinger operators with matrix-valued potentials and Sobolev inequalities for warped product spaces.
On spectral properties of adiabatically perturbed Schroedinger operators with periodic potentials
On the asymptotic distribution of the eigenvalue branches of the Schrödinger operator H... W in a spectral gap of H.
On the asymptotics of scattering phases for the Schrödinger equation
On the best observation of wave and Schrödinger equations in quantum ergodic billiards
This paper is a proceedings version of the ongoing work [20], and has been the object of the talk of the second author at Journées EDP in 2012.In this work we investigate optimal observability properties for wave and Schrödinger equations considered in a bounded open set , with Dirichlet boundary conditions. The observation is done on a subset of Lebesgue measure , where is fixed. We denote by the class of all possible such subsets. Let . We consider first the benchmark problem of maximizing...
On the Bethe-Sommerfeld conjecture
We consider the operator in , of the form with a function periodic with respect to a lattice in . We prove that the number of gaps in the spectrum of is finite if . Previously the finiteness of the number of gaps was known for . Various approaches to this problem are discussed.
On the curvature and torsion effects in one dimensional waveguides
We consider the Laplace operator in a thin tube of with a Dirichlet condition on its boundary. We study asymptotically the spectrum of such an operator as the thickness of the tube's cross section goes to zero. In particular we analyse how the energy levels depend simultaneously on the curvature of the tube's central axis and on the rotation of the cross section with respect to the Frenet frame. The main argument is a Γ-convergence theorem for a suitable sequence of quadratic energies.
On the double-well problem for Dirac operators
On the Eigenvalue of a Class of Hypoelliptic Operators.
On the error term in Weyl's law for Heisenberg manifolds
On the essential spectrum and eigenvalue asymptotics of certain Schrödinger operators
On the existence of multiple principal eigenvalues for some indefinite linear eigenvalue problems.
We study the existence of principal eigenvalues for differential operators of second order which are not necessarily in divergence form. We obtain results concerning multiplicity of principal eigenvalues in both the variational and the general case. Our approach uses systematically the Krein-Rutman theorem and fixed point arguments for the inverse of the spectral radius of some associated problems. We also use a variational characterization for both the self-adjoint and the general case.