作者机构:[1]Wuhan University, China, [2]School of Mathematics and StatisticsWuhan University, Wuhan, 430072 P. R. China
相关基金:Supported by National Natural Science Foundation of China (No. 10471107) and SF of Wuhan University (No. 20127004). Acknowledgements The author appreciates professors Jianke Lu and Jinyuan Du for their long-term helps. Many thanks to Profssor Jinyuan Du who provided me A. I. Kalandia's paper..