V.P. Reutov - Dr.Sc. (Phys.-Math.), Leading Research Scientist, Department of Nonlinear Dynamics, Federal State Budgetary Scientific Institution «Federal Research Center The Institute of Applied Physics of the Russian Academy of Sciences» (IAP RAS) (Nizhny Novgorod). E-mail: reutov@appl.sci-nnov.ru G.V. Rybushkina - Ph.D. (Phys.-Math.), Senior Research Scientist, Department of Nonlinear Dynamics, Federal State Budgetary Scientific Institution «Federal Research Center The Institute of Applied Physics of the Russian Academy of Sciences» (IAP RAS) (Nizhny Novgorod). E-mail: ryb@appl.sci-nnov.ru