Curved planar quantum wires with Dirichlet and Neumann boundary   conditions
  We investigate the discrete spectrum of the Hamiltonian describing a quantum particle living in the two-dimensional curved strip. We impose the Dirichlet and Neumann boundary conditions on opposite sides of the strip. The existence of the discrete eigenvalue below the essential spectrum threshold depends on the sign of the total bending angle for the asymptotically straight strips. 
Jaroslav Dittrich, Jan Kriz