Funding for this research was provided by:
Hunan Philosophy and Social Science Fund Project grant (16YBA039)
Text and Data Mining valid from 2019-10-11
First Online: 11 October 2019
Compliance with Ethical Standards
: The author declares that he has no conflict of interest.
: All procedures performed in the study involving human participants were in accordance with the ethical standards of the ethics review board of Hengyang Normal University and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
: Informed consent was obtained from all individual participants included in the study.