国家自然科学基金项目No.U1361204, No.51408613;中国神华集团科研专项No.SHGF-14-55;中国铁路总公司原铁道部重大课题No.2013G004-A-2.This work was supported by the National Natural Science Foundation of China U1361204 and 51408613, the Special Research Projects of Shenhua Group Corporation Limited of China SHGF-14-55 and the Major Projects of China Railway Corporation 2013G004-A-2.