1. School of Mathematics and physics, Mianyang Teachers' College, Sichuan, People's Republic of China
2. School of Mathematical Sciences, Chongqing Normal University, Chongqing, People's Republic of China
3. School of Automation, Nanjing University of Science and Technology, Nanjing, People's Republic of China
4. College of Electronics and Information Engineering, Sichuan University, Chengdu, People's Republic of China