Cheboksary TrushinaL.E. Cheboksary Polytechnic Institute (branch) of Moscow State Open University, st. Karl Marx, 54, Cheboksary, Chuvash Republic, 428003 ltrushina@inbox.ru Read more about L.E. Trushina TrifonovG. F. Chuvash State University , 15, Moskovskiy Prospekt, Cheboksary, 428025, Russia gen-trifonov@yandex.ru Read more about G. F. Trifonov Osipov N. E. Chuvash State University , 15, Moskovskiy Prospekt, Cheboksary, 428025, Russia gen-trifonov@yandex.ru Read more about N. E. Osipov
