Shang, Suiming
Bai, Zhanbing
Tian, Yu
Yue, Yue
Funding for this research was provided by:
Beijing University of Posts and Telecommunications teaching reform project (2017JY23)
Article History
Received: 26 June 2018
Accepted: 25 October 2018
First Online: 29 November 2018
Competing interests
: The authors declare that they have no competing interests.