Supported by the National Natural Science Foundation of China under Grant Nos.60673022, 60273026, 60473060 (国家自然科学基金); the National High-Tech Research and Development Plan of China under Grant Nos.2004AA1Z2100, 2005AA113140 (国家高技术研究发展计划(863)); the One-Hundred-People Program of the Chinese Academy of Sciences under Grant No.BCK35873 (中国科学院百人计划); the Chinese Academy of Sciences and the Royal Society of the United Kingdom Project under Grant Nos.20030389, 20032006 (中国科学院与英国皇家学会联合资助项目)