1. Beijing Institute of Petro-Chemical Technology, Daxing, Beijing, 102617, P. R. China
2. Department of Integrated Arts and Science, Okinawa National College of Technology, Nago, Okinawa, 905-2192, Japan
3. Graduate School of Mathematics, Nagoya University, Nagoya, 464-8602, Japan
4. Department of Mathematics, China University of Mining and Technology, Beijing 100083, P. R. China