A.S. Gonchenko - Ph.D. (Phys.-Math.), Junior Research Scientist, UNN, Nizhny Novgorod. E-mail: agonchenko@mail.ru S.V. Gonchenko - Dr. Sc. (Phys.-Math.), Head of Laboratory, UNN, Nizhny Novgorod. E-mail: sergey.gonchenko@mail.ru A.O. Kazakov - Ph.D. (Phys.-Math.), Junior Research Scientist, UNN, Nizhny Novgorod. E-mail: kazakovdz@yandex.ru