1. Department of Mathematics, Beijing University of Chemical Technology, Beijing 100029, China
2. Department of Mathematics and Statistics, University of South Florida, Tampa, FL 33620, USA
3. Department of Mathematical Sciences, International Institute for Symmetry Analysis and Mathematical Modelling, North-West University, Mafikeng Campus, Private Bag X2046, Mmabatho 2735, South Africa
4. Department of Applied Mathematics, University of Science and Technology Beijing, Beijing 100083, China
5. Institute of Nonlinear Science, Shaoxing University, Shaoxing, Zhejiang 312000, China