[1] Inner Mongolia Univ Nationalities, Coll Math & Phys, Tongliao 028043, Inner Mongolia, Peoples R China
[2] Henan Polytech Univ, Inst Math, Jiaozuo 454010, Henan, Peoples R China
[3] Tianjin Polytech Univ, Sch Math Sci, Tianjin 300387, Peoples R China
[4] Univ Roma Tre, Dipartimento Matemat & Fis, Largo San Leonardo Murialdo 1, I-00146 Rome, Italy
[5] Int Telemat Univ UniNetturio, Sez Matemat, Corso Vittorio Emanuele II 39, I-00186 Rome, Italy