基金Research is supported by National Science Foundation (19970128) of ChinaNatural Science Foundations[(011438)(021073),(Z02017)]Guangdong Province,China.The author would like to express his appreciation to Professor Y.Q.Guo for his help
基金Research is supported by National Natural Science Foundation (No.19970128) of ChinaNatural Science Foundations of Guangdong Province China(No.011438,021073,Z02017).