I.V. Polyakov – Ph.D.(Phys.-Math.), Associate Professor, HSE (Moscow)

E-mail: ipolyakov@hse.ru

V.O. Polyakova – Student, HSE (Moscow)

E-mail: igorp86@mail.ru

A.A. Chepovskiy – Ph.D.(Phys.-Math.), Associate Professor, HSE (Moscow) E-mail: aachepovsky@hse.ru