1. School of Mathematics and Statistics & Guizhou University of Finance and Economics, Guiyang, People's Republic of China
2. School of Mathematics and Statistics, Central China Normal University, Wuhan, People's Republic of China
3. Hubei Key Laboratory of Mathematical Sciences, Central China Normal University, Wuhan, People's Republic of China
4. School of Mathematical Sciences & Guizhou Normal University, Guiyang, People's Republic of China