Funding for this research was provided by:
Natural Science Foundation of Hebei Province (C2017209103)
China-Hebei 100 Scholars Supporting Project (E2013100003)
Doctoral Scientific Research Foundation of North China University of Science and Technology
Text and Data Mining valid from 2018-05-09
Received: 4 November 2017
Accepted: 30 April 2018
First Online: 9 May 2018
Ethics approval and consent to participate
: Not applicable.
: The authors declare that they have no competing interests.