Stavropol Польская СветланаАнатольевнаNorth-Caucasus Federal University, 1 Puskina St., Stavropol 355017, Russiapolskaya-sa@yandex.ru Read more about Польская Светлана Анатольевна Krasnova Irina A.North-Caucasus Federal University, 1 Puskina St., Stavropol 355017, Russiagorward_@mail.ru Read more about Irina A. Krasnova