1. School of Statistics and Mathematics, Shanghai Lixin University of Accounting and Finance, Shanghai, China;
2. School of Mathematics and Statistics, Henan University of Science and Technology, Luoyang, China;
3. School of Statistics, Renmin University of China, Beijing, China;
4. School of Statistics, Lanzhou University of Finance and Economics, Lanzhou, China;
5. Department of Mathematics and Statistics, Hang Seng University of Hong Kong, Hong Kong, China