[1] Xinjiang Univ, Coll Math & Syst Sci, Urumqi 830046, Peoples R China
[2] Huzhou Univ, Dept Math, Huzhou 313000, Zhejiang, Peoples R China
[3] Shanghai Normal Univ, Dept Math, Shanghai 200234, Peoples R China
[4] Jiangsu Univ, Inst Appl Syst Anal, Zhenjiang 212013, Jiangsu, Peoples R China
[5] Wilfrid Laurier Univ, Dept Math, Waterloo, ON N2L 3C5, Canada
[6] Hebei Normal Teachers Univ, Sch Math Sci, Shijiazhuang 050016, Hebei, Peoples R China