Ma, J
Lu, J
Huang, H
Teng, X
Tian, M
Yu, Q
Yuan, X
Jing, Y
Shi, C
Li, J
Article History
Received: 31 December 2014
Revised: 22 June 2015
Accepted: 8 July 2015
First Online: 16 July 2015
Competing interests
: The authors declare no conflict of interest.