Funding for this research was provided by:
Education Department of Hunan Province (18C0758)
National Natural Science Foundation of China (61903049)
HongKong Research Grants Council (PolyU 152151/17E)
Text and Data Mining valid from 2019-11-15
Received: 11 June 2019
Revised: 22 October 2019
Accepted: 5 November 2019
First Online: 15 November 2019
Compliance with ethical standards
: The authors do not have conflicts of interest.
: This research does not involve human participants and/or animals.