1. Faculty of Mathematics, Voronezh State University, Voronezh, Russia
2. Faculty of Physics and Mathematics, Voronezh State Pedagogical University, Voronezh, Russia
3. Center for Fundamental Science, and Research Center for Nonlinear Analysis and Optimization, Kaohsiung Medical University, Kaohsiung, Taiwan
4. Department of Medical Research, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan