Funding for this research was provided by:
Shaanxi Provincial Science and Technology Department (2013K1117)
Xi'an Polytechnic University doctoral research start-up fund (20170914)
Text and Data Mining valid from 2019-08-13
Received: 10 April 2019
Accepted: 3 July 2019
First Online: 13 August 2019
: The authors declare that they have no competing financial interests.