1. Department of Mathematics, Harbin Institute of Technology, Harbin 150001, P. R. China
2. Department of Mathematics, Southern University of Science and Technology, Shenzhen 518055, P. R. China
3. Department of Mathematics, North Carolina State University, Raleigh, NC 27695, USA
4. Department of Mathematics, International Center for Mathematics, Southern University of Science and Technology, Shenzhen 518055, P. R. China
5. Department of Mathematics, International Center for Mathematics, Guangdong Provincial Key Laboratory of Computational Science and Material Design, Southern University of Science and Technology, Shenzhen 518055, P. R. China
6. Department of Mathematics, Guangdong Provincial Key Laboratory of Computational Science and Material Design, National Center for Applied Mathematics (Shenzhen), Southern University of Science and Technology, Shenzhen 518055, P. R. China