Funding for this research was provided by:
National Natural Science Foundation of China (11171221)
Doctoral Program Foundation of Institutions of Higher Education of China (20123120110004)
Text and Data Mining valid from 2018-08-29
Received: 30 March 2018
Accepted: 13 August 2018
First Online: 29 August 2018
: The authors declare that they have no competing interests.