1. KLASMOE and School of Mathematics and Statistics, Northeast Normal University, 5268 Peoples Road, 130024 Changchun, China
2. Department of Statistics and Applied Probability, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore
3. School of Mathematics, Jilin University, 2699 Qianjin Street, 130012 Changchun, China
4. School of Mathematics and Statistics, Northeast Normal University, 5268 Peoples Road, 130024 Changchun, China