Xu, W
Chen, Q
Wang, Q
Sun, Y
Wang, S
Li, A
Xu, S
Røe, O D
Wang, M
Zhang, R
Yang, L
Zhou, J
Article History
Received: 7 June 2014
Revised: 8 October 2014
Accepted: 29 October 2014
First Online: 4 December 2014
Competing interests
: The authors declare no conflict of interest.