V.I. Anisimkin - Dr. Sc. (Phys.-Math.), Main Research Scientist, Kotel\'nikov IRE of RAS (Moscow). E-mail: anis@cplire.ru I.I. Pyataikin - Ph. D. (Phys.-Math.), Senior Research Scientist, Kotel\'nikov IRE of RAS (Moscow). E-mail: iip@cplire.ru