1. School of Science, Nanjing University of Science and Technology, Nanjing, People's Republic of China
2. Department of Applied Mathematics, University of Waterloo, Waterloo, Canada
3. School of Automation and Electrical Engineering, Linyi University, Linyi, People's Republic of China
4. School of Mathematics and Computer Science, Yunnan Minzu University, Kunming, People's Republic of China
5. Department of Mathematics, Huaibei Normal University, Huaibei, People's Republic of China