The Propagation of the Waves in Periodic Media Atlarge
نویسنده
چکیده
Asymptotics at large time of the Green function to the wave equation with periodic coeecients are found. A particular attention is given to its asymptotics near the wave front. It is shown that the spectral band (with number n = 0; 1; 2; ::) of the corresponding Hill operator is associated with a wave having the front velocity c n < 1. Estimates for c n in the terms of the gap lengths, the eeective masses of the Hill operator are proved (both with xed number n and their sums). Some extensions for more general cases (the Dirac operator with periodic coeecients, the Schrodinger operator with nite band potentials etc.) are also obtained.
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