T.V. Yakunina – Senior Lecturer, Department of Fundamental Training, Sayan-Shushenskiy Branch of Siberian Federal University (Sayanogorsk)
E-mail: tatav19@mail.ru
V.N. Udodov – Dr.Sc. (Phys.-Math.), Professor,
Engineering and Technology Institute, N.F. Katanov Khakas State University (Abakan)
E-mail: udodov@khsu.ru