School of Mathematics and Statistics and School of Pharmaceutical Sciences, Central South University, Changsha 410083, Peoples Republic of China.|School of Mathematics and Statistics and School of Pharmaceutical Sciences, Central South University, Changsha 410083, Peoples Republic of China.|School of Mathematics and Statistics and School of Pharmaceutical Sciences, Central South University, Changsha 410083, Peoples Republic of China.|School of Mathematics and Statistics and School of Pharmaceutical Sciences, Central South University, Changsha 410083, Peoples Republic of China.