1. Department of Mathematics, Zhejiang Normal University, Jinhua 321004, Zhejiang, P. R. China
2. Department of Mathematics, King Abdulaziz University, Jeddah 21598, Saudi Arabia
3. Department of Mathematics and Statistics, University of South Florida, Tampa, FL 33620-5700, USA
4. Material Science Innovation and Modelling, Department of Mathematical Sciences, North-West University, Mafikeng Campus, Mmabatho 2735, South Africa
5. School of Mathematics and Physics, North China Electric Power University, Beijing 102206, P. R. China
6. School of Sciences, Great Bay University, Dongguan 523000, Guangdong, P. R. China
7. College of Mathematics and Systems Science, Shandong University of Science and Technology, Qingdao 266590, Shandong, P. R. China
8. School of Science, Nanjing University of Science and Technology, Nanjing 210094, Jiangsu,P. R. China