Text and Data Mining valid from 2018-08-02
Received: 19 January 2018
Accepted: 21 July 2018
First Online: 2 August 2018
Compliance with ethical standards
: All authors have no conflict of interest.
: The study protocol was approved by the research office in Hunan Institute of Technology that is responsible for research ethics, and all procedures in this study were in accordance with the 1964 Helsinki declaration and later amendments.
: Written consent forms were obtained from all participants.