Funding for this research was provided by:
National Planning Office of Philosophy and Social Science (14ZDB145)
State Key Laboratory of Coal Resources and Safe Mining (SKLCRSM 15KF06)
Excellent Young Talents Fund Program of Higher Education Institutions of Hebei Province (BJ2016010)
University Natural Science Research Project of Anhui Province (KJ2018A0002)
Article History
Received: 13 December 2018
Accepted: 13 April 2019
First Online: 29 April 2019