1. College of Science, North China University of Technology, Beijing 100144, China
2. School of Mathematics, University of Manchester, Manchester M13 9PL, UK
3. Department of Physics, Astronomy and Mathematics, School of Physics, Engineering & Computer Science, University of Hertfordshire, Hatfield AL10 9EU, UK
4. Department of Mathematics, College of Engineering, Design and Physical Sciences Brunel University, Uxbridge UB8 3PH, UK
5. School of Business and Economics, Humboldt-Universität zu Berlin, 10117 Berlin, Germany
6. School of Statistics and Mathematics, Shanghai Lixin University of Accounting and Finance, Shanghai 201620, China
7. Center for Applied Statistics, School of Statistics, Renmin University of China, Beijing 100872, China