1. School of Science, Tianjin University of Commerce, Tianjin 300134, P. R. China
2. School of Mathematics and Information Science, Henan Polytechnic University, Jiaozuo 454000, P. R. China
3. State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo 454003, P. R. China
4. School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, P. R. China
5. Collaborative Innovation Center of Coal Safety Production of Henan Province, Jiaozuo 454003, P. R. China