1Department of Mathematics, Central South University Railway Campus, Changsha, Hunan, 410075, P.R. China.
2School of Mathematics, Shandong Institute of Business and Technology 191 Binhaizhong Road, Yantai, Shandong, 264005, P.R. China.
3College of Science, Nanjing University of Aeronautics & Astronautics, Nanjing, 210016, P.R. China
4School of Computer Science, Communication University of China Beijing 100024, P.R. China. e-mail: fenglh0163.com