Pyatigorsk ChomaevZaurА.Pyatigorsk State University, 9 Kalinina Ave, Pyatigorsk 357532, Russiazaurak1976@mail.ru Read more about Zaur A. Chomaev AkopyanViktorZ.Pyatigorsk State University, 9 Kalinina Ave, Pyatigorsk 357532, Russiazaven2005@yandex.ru Read more about Viktor Z. Akopyan