A.A. Teplykh – Ph.D.(Phys.-Math.), Senior Research Scientist, Saratov branch of Kotel'nikov IRE of RAS E-mail: teplykhaa@mail.ru

B.D. Zaitsev – Dr.Sc.(Phys.-Math.), Professor, Head of Laboratory, Saratov branch of Kotel'nikov IRE of RAS E-mail: zai-boris@yandex.ru

A.P. Semenov – Ph.D.(Phys.-Math.), Senior Research Scientist, Saratov branch of Kotel'nikov IRE of RAS E-mail: alex-sheih@yandex.ru

I.A. Borodina – Ph.D.(Phys.-Math.), Senior Research Scientist, Saratov branch of Kotel'nikov IRE of RAS E-mail: borodinaia @yandex.ru