Affiliation: | College of Mathematics and Physics, Chongqing University, Chongqing 400030, P. R. China;College of Mathematics and Physics, Chongqing University, Chongqing 400030, P. R. China;College of Mathematics and Physics, Chongqing University, Chongqing 400030, P. R. China;College of Mathematics and Physics, Chongqing University, Chongqing 400030, P. R. China;College of Mathematics and Physics, Chongqing University, Chongqing 400030, P. R. China |