D.V. Kalyabin - Post-graduate Student, Moscow Institute of Physics and Technology; Trainee Researcher, Kotelnikov IRE RAS (Moscow). E-mail: dmitry.kalyabin@phystech.edu A.V. Sadovnikov - Ph.D. (Phys.-Math.), Junior Research Scientist, Saratov branch of Kotelnikov IRE RAS E.N. Beginin - Ph.D. (Phys.-Math.), Associate Professor, Saratov National Research State University named N.G. Chernyshevsky S.A. Nikitov - Dr.Sc. (Phys. Math.), Director, Kotelnikov IRE RAS (Moscow)