Scattering on compact manifolds with infinitely thin horns
  The quantum-mechanical scattering on a compact Riemannian manifold with semi-axes attached to it (hedgehog-shaped manifold) is considered. The complete description of the spectral structure of Schroedinger operators on such a manifold is done, the proof of existence and uniqueness of scattering states is presented, an explicit form for the scattering matrix is obtained and unitary nature of this matrix is proven. It is shown that the positive part of the spectrum of the Schroedinger operator on the initial compact manifold as well as the spectrum of a point perturbation of such an operator may be recovered from the scattering amplitude for one attached half-line. Moreover, the positive part of the spectrum of the initial Schroedinger operator is fully determined by the conductance properties of an "electronic device" consisting of the initial manifold and two "wires" attached to it. 
J. Bruening and V. Geyler