1. School of Science, East China Jiaotong University, Nanchang 330013, P. R. China
2. School of Mechatronic Engineering, East China Jiaotong University, Nanchang 330013, P. R. China
3. School of Mathematics and Statistics, Wuhan Institute of Technology in Wuhan, Wuhan 430072, P. R. China
4. School of Mathematics and Statistics, Wuhan University, Wuhan 430072, P. R. China