V.I. Anisimkin - Dr. Sc. (Phys.-Math.), Kotel\'nikov IRE of RAS (Moscow). E-mail: anis@cplire.ru I.E. Kuznetsova - Dr. Sc. (Phys.-Math.), Associate Professor, Kotel\'nikov IRE of RAS (Moscow). E-mail: kuziren@yandex.ru B.D. Zajtsev - Dr. Sc. (Phys.-Math.), Professor, Saratov branch of Kotel\'nikov IRE of RAS. E-mail: zai-boris@yandex.ru