1. College of Aerospace Engineering, State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, P. R. China
2. Key Laboratory of Low-grade Energy Utilization Technology & Systems, Ministry of Education, College of Power Engineering, Chongqing University, Chongqing 400030, P. R. China
3. Department of Earth and Environmental Engineering, Columbia University, NY 10027, USA