Liang, Gang
Ai, Qin
Yu, Diqiu
Article History
Received: 25 February 2015
Accepted: 19 May 2015
First Online: 2 July 2015
Change Date: 20 April 2020
Change Type: Correction
Change Details: An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Competing interests
: The authors declare no competing financial interests.