Peng, X
Gong, F
Chen, Y
Jiang, Y
Liu, J
Yu, M
Zhang, S
Wang, M
Xiao, G
Liao, H
Article History
Received: 1 January 2014
Revised: 6 May 2014
Accepted: 27 May 2014
First Online: 14 August 2014
Competing interests
: The authors declare no conflict of interest.