P.V. Lotorev - Post-graduate Student, South-West State University (Kursk). E-mail: pashik_email@mail.ru A.G. Kurochkin - Post-graduate Student, South-West State University (Kursk). E-mail: ak76@kursk.ru A.V. Grivachev - Post-graduate Student, South-West State University (Kursk). E-mail: Garpun-22@mail.ru