S.G. Alekseev, D.V. Samokotina
A.P. Zagorodnov - Post-graduate Student, Institute of Precision Mechanics and Control RAS (Saratov)
A.N. Yakunin - Dr. Sc. (Phys.-Math.), Senior Research Scientist, Head of Department, Institute of Precision Mechanics and Control RAS (Saratov). E-mail: anyakunin@mail.ru