a Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, Moscow, 125047 Russia
b RUDN University, Moscow, 117198 Russia
c Moscow Institute of Physics and Technology (State University), Dolgoprudnyi, Moscow oblast, 141700 Russia
Correspondence to: *e-mail: vicveden@yahoo.com
Correspondence to: **e-mail: nurka.de@yandex.ru
Correspondence to: ***e-mail: vvorobyeva@yandex.ru
Received 1 February, 2018
DOI: 10.1134/S1064562418030171