- Tiren Huang: Department of Mathematics, Zhejiang Sci-Tech University, Hangzhou, 310018 China.
- Shenyang Tan: Taizhou Institute of Sci. & Tech., NUST, Taizhou, 225300 China.
- Xiaohui Zhang: Department of Mathematics, Zhejiang Sci-Tech University, Hangzhou, 310018 China.