1. College of Mathematics and Statistics, Chongqing Jiaotong University, China
2. College of Mathematical Sciences, University of Electronic Science and Technology of China, China, and College of Mathematics and Statistics, Chongqing Jiaotong University, China
3. College of Mathematics and Statistics, Chongqing Jiaotong University, China, and College of Mathematics, Sichuan University, China
4. College of Mathematical Sciences, University of Electronic Science and Technology of China, China