E.Y. Krylova - Ph.D. (Phys.-Math.), Associate Professor, National Research Saratov State University n.a. N.G. Chernyshevsky E-mail: kat.krylova@bk.ru I.E. Kutepov - Ph.D. (Phys.-Math.), Yuri Gagarin Saratov State Technical University E-mail: ilyakutepov@yandex.ru I.V. Papkova - Ph.D. (Phys.-Math.), Associate Professor, Yuri Gagarin Saratov State Technical University E-mail: ikravzova@mail.ru V.A. Krysko - Dr.Sc. (Eng.), Professor, Head of the Department, Yuri Gagarin Saratov State Technical University E-mail: tak@san.ru