Affiliation: | 1.School of Mathematics, Southwest Jiaotong University, 610031, 111 N 1st Section, 2nd Ring Rd, Sha Xi Mei Shi Yi Tiao Jie, Jinniu District, Chengdu, Sichuan, P. R. China ;2.College of Mathematics, Hunan Institute of Science and Technology, Xueyuan Rd, 414006, Yueyang, Hunan, P. R. China ; |