Supported by the National Natural Science Foundation of China under Grant No.60573097(国家自然科学基金);the Research Foundation of National Science and Technology Plan Project of China under Grant No.2004BA721A02(国家科技计划);the Research Foundation of Disciplines Leadingto Doctorate Degree of Chinese Universities under Grant No.20050558017(高等学校博士学科点专项科研基金);the Natural Science Foundation of Guangdong Province of China under Grant Nos.05200302,04300462(广东省自然科学基金);the Research Foundation of Science and Technology Plan Project in Guangdong Province of China under Grant No.2005B10101032(广东省科技计划项目)