[1] City Univ Hong Kong, Dept Math, Hong Kong, Hong Kong, Peoples R China
[2] Chinese Acad Sci, Wuhan Inst Phys & Math, Wuhan, Peoples R China
[3] Cent China Normal Univ, Dept Math, Wuhan, Peoples R China
[4] Cent China Normal Univ, Lab Nonlinear Anal, Wuhan, Peoples R China