D.S. Gubsky - Ph. D. (Phys.-Math.), Associate Professor, Southern Federal University (Rostov-on-Don). E-mail: ds@sfedu.ru V.V. Zemlyakov - Ph. D. (Phys.-Math.), Associate Professor, Southern Federal University (Rostov-on-Don). E-mail: vvzem@yandex.ru D.V. Lonkina - Student, Southern Federal University (Rostov-on-Don). E-mail: lonkina.daria@yandex.ru G.P. Sinyavsky - Dr. Sc. (Phys.-Math.), Professor, Head of Department, Southern Federal University (Rostov-on-Don). E-mail: sinyavsky@sfedu.ru