Bai, Guoyin
Zhang, Ji
Zhao, Chongsi
Wang, Yan
Qi, Yanmin
Zhang, Bing
Article History
Received: 21 January 2016
Revised: 19 July 2016
Accepted: 19 July 2016
First Online: 8 September 2016
Competing interests
: The authors declare no conflict of interest.
Free to read: This content has been made available to all.