Ma, Ming
Grey, François
Shen, Luming
Urbakh, Michael
Wu, Shuai
Liu, Jefferson Zhe
Liu, Yilun
Zheng, Quanshui
Article History
Received: 26 September 2014
Accepted: 1 June 2015
First Online: 6 July 2015
Competing interests
: The authors declare no competing financial interests.