A.M. Bobreshov - Dr. Sc. (Phys.-Math.), Professor, Dean of Faculty of Physics, Voronezh State University. E-mail: bobreshov@phys.vsu.ru A.S. Zhabin - Assistant, Faculty of Physics, Voronezh State University. E-mail: zhabin@phys.vsu.ru V.A. Stepkin - Ph. D. (Phys.-Math.), Associate Professor, Faculty of Physics, Voronezh State University. E-mail: stepkin@phys.vsu.ru G.K. Uskov - Dr. Sc. (Phys.-Math.), Associate Professor, Faculty of Physics, Voronezh State University. E-mail: uskov@phys.vsu.ru