“…The results of the paper are applicable in electrodynamics of continuous media [34][35][36][37], in sound wave propagation theory [38][39][40], in describing the passage of electrons through heterostructures [46][47][48][49][50], in quantum chemistry [51], in hydrodynamics and plasma physics [52], etc. In particular, the issue of proving unitarity of the S-matrix in open channels arises in describing photon scattering by metamaterials with a large spatial dispersion.…”