Wang, N
Ding, H
Liu, C
Li, X
Wei, L
Yu, J
Liu, M
Ying, M
Gao, W
Jiang, H
Wang, Y
Article History
Received: 17 July 2014
Revised: 31 October 2014
Accepted: 21 November 2014
First Online: 26 January 2015
Competing interests
: The authors declare no conflict of interest.