Funding for this research was provided by:
the Fundamental Research Funds for the Central Universities (2015ZD29)
the Higher School Science Research Funds of Hebei Province of China (Z2015137)
Text and Data Mining valid from 2019-04-11
Received: 26 April 2018
Accepted: 2 April 2019
First Online: 11 April 2019
: The authors declare that there is no conflict of interests regarding the publication of this paper.