[1] Kunming Univ Sci & Technol, Sch Sci, Ctr Nonlinear Sci Studies, Kunming 650093, Yunnan, Peoples R China
[2] Zhejiang Normal Univ, Dept Math, Jinhua 321004, Zhejiang, Peoples R China
[3] Binzhou Univ, Dept Math, Binzhou 256603, Shandong, Peoples R China