1. School of Mathematics, Yunnan Normal University, Kunming, People's Republic of China
2. Department of Mathematical Sciences, University of South Dakota, Vermillion, SD, USA
3. Department of Mathematics, Indian Institute of Technology Patna, Patna, India
4. Department of Statistics, St. Anthony's College, Shillong, India
5. Center of Statistical Research, School of Statistics, Southwestern University of Finance and Economics, Chengdu, People's Republic of China