Funding for this research was provided by:
Natural Science Foundation of Hebei Province (F2016203467, F2018203370)
National Natural Science Foundation of China (61673335)
Text and Data Mining valid from 2018-11-28
Received: 16 July 2018
Accepted: 15 October 2018
First Online: 28 November 2018
: The authors declare that they have no competing interests.