Funding for this research was provided by:
the National Natural Science Foundation of China (71761025)
the Humanities and Social Science Research Foundation of Education of China (12YJC630100)
Lanzhou Jiaotong University and Tianjin University Joint Innovation Fund Project of China (2019058)
Article History
Received: 11 December 2018
Accepted: 4 July 2019
First Online: 9 July 2019