1. College of Science, China Three Gorges University, Yichang 443002, People’s Republic of China.
2. Department of Mathematics and Statistics, University of Strathclyde, Glasgow, G1 1XH, United Kingdom, and Centre for Mathematical Imaging Techniques, University of Liverpool, Liverpool L69 7ZL, United Kingdom.
3. Corresponding author. Department of Mathematics, Wuhan University of Technology, Wuhan 430070, People’s Republic of China.
4. School of Mathematical Sciences and LPMC, Nankai University, Tianjin 300071, People’s Republic of China.