the National Natural Science Foundation of Chinaunder Grant No.60674016(国家自然科学基金);the National High-Tech Research and Development Plan of Chinaunder Grant No.2006AA04Z172(国家高技术研究发展计划(863));the National Science Fund for Distinguished Young Scholars of Chinaunder Grant No.60425310(国家杰出青年科学基金);the Natural Science Foundation of Hu’nan Province of Chinaunder Grant No.05JJ40118(湖南省自然科学基金)