作者机构:[1]College of Mathematics and Computing Sciences, Changsha University of Science and Technology, Changsha 410004, China, [2]Universite de Bretagne-Sud, UMR 6205, LMBA, F-56000 Vannes, France, [3]School of Mathematical Sciences, Beijing Normal University, Beijing 100875, China
相关基金:Acknowledgements This work was partially supported by the National Natural Science Foundation of China (Grant Nos. 11171044, 11101039) and the Natural Science Foundation of Hunan Province (Grant No. 11JJ2001).