the National Natural Science Foundation of China under Grant Nos.60607010,60672125,60672126,60736043,60776795(国家自然科学基金);the Program for Cheung Kong Scholars and Innovative Research Team in University of China under Grant No.IRT0645(教育部长江学者和创新团队支持计划);the Natural Science Foundation of Hu'nan Province of China under Grant No.08JJ3123(湖南省自然科学基金)