Funding for this research was provided by:
Natural Science Foundation of Hebei Province (A2018208171)
the Foundation of Hebei Education Department (QN2018104)
Text and Data Mining valid from 2019-03-18
Received: 7 September 2018
Accepted: 25 February 2019
First Online: 18 March 2019
: The author declares that she has no competing interests.