A.D. Usanov Ph.D. (Phis.-Math.), Associate Professor, Saratov State University named after N.G. Chernyshevsky. E-mail: aka_norton@mail.ru A.E. Postelga Ph.D. (Phis.-Math.), Associate Professor, Saratov State University named after N.G. Chernyshevsky. E-mail: sanyalace@list.ru D.G. Verkhov Post-graduate Student, Saratov State University named after N.G. Chernyshevsky. E-mail: werchowdg@mail.ru V.G. Rebrov Ph.D. (Biol.), Associate Professor, Saratov State University named after N.G. Chernyshevsky. E-mail: rebrovvg@yandex.ru