基金Acknowledgements： This work is supported by the National Research Foundation for the Doctoral Program of Higher Education of China under Grant No. 20020001015： the National Grand Fundamental Research 973 Program of China under Grant No.2002CB312000 the National Science Foundation of China under Grant No.60073016 and No.60203002+1 种基金 the National High Technology Development 863 Program under Grant No. 2002AA 135330, No. 2002AA 134030 and No. 2001AAI 13151 the Beijing Science Foundation under Grant No.4012007.
