作者机构:[1]Department of Mathematics, Huzhou Teachers College, Huzhou 313000, China, [2]School of Mathematical Sciences, Fudan University, Shanghai 200433, China
相关基金:Supported-by the National Natural Science Foundation of China(11101140, 11301177), the China Post- doctoral Science Foundation (2011M500721, 2012T50391) and the Zhejiang Natural Science Foundation of China (Y6110775, Y6110789).