Lipetsk State Pedagogical University of P.P.Semenov-Tyan-Shansky, Lipetsk 398020, the Russian Federation;
Lipetsk State Technical University, Lipetsk 398600, the Russian Federation;
Lipetsk State Pedagogical University of P.P.Semenov-Tyan-Shansky, Lipetsk 398020, the Russian Federation;