Zhang, P
Gao, K
Jin, X
Ma, J
Peng, J
Wumaier, R
Tang, Y
Zhang, Y
An, J
Yan, Q
Dong, Y
Huang, H
Yu, L
Wang, C
Article History
Received: 12 October 2014
Revised: 20 January 2015
Accepted: 21 January 2015
First Online: 12 March 2015
Competing interests
: The authors declare no conflict of interest.