Supported by National Natural Science Foundation of China (No.90608024 and 303707762);Key Science and Technology Project of Guangzhou (No.2006J1-C0111);Planned Science and Technology Project of Guangdong Province (No.2006B35502002);Key Program of Natural Science Foundation of Guangdong Province (No.36703);China Postdoctoral Science Foundation Funded Project (No.20080430845)~~