1. Department of Mathematics, Xinxiang University, Xinxiang 453003, China
2. Department of Mathematics, South-Central University for Nationalities, Wuhan 430074, China
3. Laboratoire de Mathématiques Raphaaël Salem, UMR 6085 CNRS-Université de Rouen, avenue de l'Université, BP 12, 76801 Saint-Etienne-du-Rouvray, France