国家自然科学基金No.51108177;湖南省自然科学基金No.10JJ4040.湖南工业大学自科基金项目No.2012HZX20,No.2013HZX09.This work was supported by the National Natural Science Foundation of China51108177,the Natural Science Foundation of Hunan Province10JJ4040 and the Natural Science Foundation of Hunan University of Technology 2012HZX20,2013HZX09.