基金The project supported by the Natural Science Foundation of Zhejiang Province under Grant No. Y604106, the Foundation of New Century 151 Talent Engineering of Zhejiang Province, the Scientific Research Foundation of Key Discipline of Zhejiang Province, and the Natural Science Foundation of Zhejiang LishuiThe authors are in debt to Profs. J.F. Zhang, Z.M. Sheng, and L.Q. Chen, Drs. Z.Y. Ma and W.H. Huang for their helpful suggestions and fruitful discussions, and express their sincere thanks to Prof. S.Y. Lou for his useful references.University under Grant No. KZ05010