Wang, Shumeng
Wang, Xingdong
Yao, Bing
Zhang, Baohua
Ding, Junqiao
Xie, Zhiyuan
Wang, Lixiang
Article History
Received: 9 March 2015
Accepted: 30 June 2015
First Online: 24 July 2015
Competing interests
: The authors declare no competing financial interests.