作者机构:[1]College of Mathematics and Software Science, Sichuan Normal University, Chengdu 610066,P. R. China
相关基金:Project supported by the National Natural Science Foundation of China (Nos. 10771151 and 10901115), the Scientific Research Fund of Sichuan Provincial Education Department (No. 2006A063), and the Scientific Research Fund of Science and Technology Bureau of Sichuan Province (No. 07JY029-012)