[熊岳山] College of Sciences, National Univ. of Defense Technology, Changsha 410073, China
School of Mathematics and Physics, Nanhua University, Hengyang 421001, China
Changsha University, Changsha 410003, China
[蔡放] College of Sciences, National Univ. of Defense Technology, Changsha 410073, China, Changsha University, Changsha 410003, China
[王礼广] College of Sciences, National Univ. of Defense Technology, Changsha 410073, China, School of Mathematics and Physics, Nanhua University, Hengyang 421001, China