1. Research Center of Nonlinear Science, School of Mathematical and Physical Sciences,Wuhan Textile University, Wuhan 430200, P, R. China
2. Department of Mathematics, Michigan State University, East Lansing, Michigan 48824, United States
3. Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan 48824, United States
4. Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824, United States