Yu.E. Korchagin − Dr.Sc. (Phys.-Math.), Associate Professor, Head of Department of Radiophysics,

Voronezh State University (Voronezh, Russia)

E-mail: korchagin@phys.vsu.ru

K.D. Titov − Ph,D. (Phys.-Math.), Assistant,

Voronezh State University (Voronezh, Russia)

E-mail: titovkd@gmail.com