Funding for this research was provided by:
Education Department of Hunan Province, China (18C0758)
Hong Kong Research Grants Council (PolyU 152151/17E)
Hunan Natural Science Foundation (2017JJ2291)
Text and Data Mining valid from 2019-05-30
Received: 29 November 2018
Revised: 28 April 2019
Accepted: 6 May 2019
First Online: 30 May 2019
Compliance with ethical standards
: The authors do not have conflicts of interest.
: This research does not involve human participants and/or animals.