1. Jie Zhou is Associate Professor, School of Mathematics, Capital Normal University, Beijing, 100048, P.R. China
2. Xiao-Hua Zhou is Chair Professor, Department of Biostatistics, School of Public Health, and Beijing International Center for Mathematical Research, Peking University, Beijing, 100871, P.R. China
3. Liuquan Sun is Professor, Institute of Applied Mathematics, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing, 100190, P.R. China