Supported by the Project of National Science Fund for Distinguished Young Scholars of China under Grant No.60225008(国家杰出青年基金);the National Natural Science Foundation of China under Grant No.60332010(国家自然科学基金);the Project for Young Scientists’ Fund of National Natural Science Foundation of China under Grant No.60303022(国家自然科学基金青年科学基金);the Natural Science Foundation of Beijing of China under Grant No.4052026 (北京市自然科学基金)