Chen, B
Yu, S
Ding, X
Jing, C
Xia, L
Wang, M
Matro, E
Rehman, F
Niu, Y
Li, G
Chang, C
Article History
Received: 22 March 2014
Revised: 9 July 2014
Accepted: 10 July 2014
First Online: 8 August 2014
Competing interests
: The authors declare no conflict of interest.