基金Many thanks are due to Dr. Liu Jiang and Prof. Cui Yuanlai for their great contribution to the English translation of the paper. This research was supported by funding from the National Key Project for Basic Research of P.R.China (Grand No. 2003CB415105), National Key Project for Science and Technology Advance of P.R.China (Grand No. 2002BA901A22), and the National Natural Science Foundation of China (Grand No. 40261001).