1. School of Mathematics and Physics, China University of Geosciences, Wuhan 430074, P. R. China
2. Division of Dynamics, Technical University of Lodz, Lodz, Stefanowskiego 1/15, 90-924, Poland
3. College of Mechanical Engineering, Beijing University of Technology, Beijing 100124, P. R. China
4. Mathematical Institute, University of Oxford, Oxford, OX2 6GG, England
5. Department of Applied Sciences, Xijing University, Xi’an 710123, P. R. China
6. Department of Physics, University of Wisconsin, Madison, WI 53706, USA