1. Department of Mathematics, School of Mathematics and Statistics; Southwest University; Chongqing 400715 People's Republic of China
2. Department of Electrical Engineering, Nonlinear Dynamics Group; Yeungnam University; Kyongsan 38541 Republic of Korea
3. Department of Mathematics; Southeast University; Nanjing 210096 Jiangsu People's Republic of China
4. Department of Mathematics, Faculty of Science; King Abdulaziz University; Jeddah 21589 Saudi Arabia