A.M. Bobreshov - Dr. Sc. (Phys.-Math.), Professor, Dean of Faculty of Physics, Voronezh State University. E-mail: bobreshov@phys.vsu.ru P.A. Kretov - Post-graduate Student, Assistant, , Faculty of Physics, Voronezh State University. E-mail: kretov@phys.vsu.ru N.S. Sbitnev - Student, Voronezh State University. E-mail: nikita.sbitnev@yandex.ru G.K. Uskov - Dr. Sc. (Phys.-Math.), Associate Professor, Faculty of Physics, Voronezh State University. E-mail: uskov@phys.vsu.ru