1. State Key Laboratory for Geo-Mechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China
2. Department of Mathematics and Statistics, University of Victoria, Victoria, British Columbia V8W 3R4, Canada
3. Department of Medical Research, China Medical University Hospital, China Medical University, Taichung 40402, Taiwan, Republic of China