[1] Nanjing Univ Posts & Telecommun, Tongda Coll, Yangzhou 225127, Jiangsu, Peoples R China
[2] Nanjing Normal Univ, Sch Math Sci, Nanjing 210023, Jiangsu, Peoples R China
[3] Nanjing Normal Univ, Inst Finance & Stat, Nanjing 210023, Jiangsu, Peoples R China
[4] Univ Bielefeld, Dept Math, D-33615 Bielefeld, Germany
[5] Nanjing Artillery Acad, Nanjing 211132, Jiangsu, Peoples R China
[6] Nanjing Xiaozhuang Univ, Sch Informat Engn, Nanjing 211171, Jiangsu, Peoples R China