Pan, Zhicheng
Liu, Zexian
Cheng, Han
Wang, Yongbo
Gao, Tianshun
Ullah, Shahid
Ren, Jian
Xue, Yu
Article History
Received: 20 August 2014
Accepted: 11 November 2014
First Online: 5 December 2014
Competing interests
: The authors declare no competing financial interests.