Chen, F
Li, A
Gao, S
Hollern, D
Williams, M
Liu, F
VanSickle, E A
Andrechek, E
Zhang, C
Yang, C
Luo, R
Xiao, H
Article History
Received: 21 January 2014
Revised: 11 April 2014
Accepted: 17 April 2014
First Online: 22 May 2014
Competing interests
: The authors declare no conflict of interest.