1. School of Mathematics and Statistics, Henan University of Science and Technology, Luoyang, People's Republic of China
2. School of Mathematics and Statistics, Northwest Normal University, LanZhou, People's Republic of China
3. School of Statistics and Mathematics, The Central University of Finance and Economics, Beijing, People's Republic of China
4. Department of Mathematics and Statistics, The Hang Seng University of Hong Kong, Hong Kong, Hong Kong
5. School of Statistics, Renmin University of China, Beijing, People's Republic of China