1. School of Mathematics and Physics, China University of Geosciences, Wuhan 430074, China
2. School of Mathematics and Statistic, Changshu Institute of Technology, Changshu 215500, China
3. School of Mechanics and Aerospace Engineering, Southwest Jiaotong University, Chengdu 610031, China
4. Institute for Complex Systems and Mathematical Biology King's College, University of Aberdeen, Aberdeen AB24 3UE, UK