1. School of Mathematics and Computing Science, Hunan University of Science and Technology, Xiangtan, Hunan 411201, People’s Republic of China
2. Department of Mathematical Sciences, The University of Texas at Dallas, Richardson, Texas 75080, USA
3. LMAM, School of Mathematical Sciences, Peking University, Beijing 100871, People’s Republic of China
4. Center for Statistical Science, Peking University, Beijing 100871, People’s Republic of China