1. Department of Applied Mathematics, Kuban State University, 149 Stavropolskaya st., Krasnodar 350040, Russia, Fachhochschule Wiesbaden, University of Applied Sciences, Kurt-Schumaher-Ring 18, D-65197 Wiesbaden, Germany, and Physical Chemistry Department, Kuban State University, 149 Stavropolskaya st., Krasnodar 350040, Russia