Fan, H
Liu, F
Dong, G
Ren, D
Xu, Y
Dou, J
Wang, T
Sun, L
Hou, Y
Article History
Received: 27 March 2014
Revised: 30 July 2014
Accepted: 1 August 2014
First Online: 11 September 2014
Competing interests
: The authors declare no conflict of interest.