1. Department of Mathematics and Physics, Nanjing Institute of Technology, Nanjing 211167, P. R. China
2. Key Laboratory of Mathematics and Interdisciplinary Sciences, Guangdong Higher Education Institutes, Guangzhou University, Guangzhou 510006, P. R. China
3. Department of Mathematics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P. R. China
4. State Key Laboratory of Information Security, Institute of Information Engineering, Chinese Academy of Sciences, Beijing 100093, P. R. China
5. School of Science, Shandong University of Technology, Zibo 255091, P. R. China