SUN Wei-Hua:School of Mathematics and Statistics, Shandong University at Weihai,Weihai 264209, Shandong, China; GUO Hong-Feng:. School of Statistics and Mathematics, Shandong University of Finace, Jinan 250014, Shandong, China; Zhang-Xin: School of Statistics and Mathematics, Shandong Economic University, Jinan 250014, Shandong, China
