Lao, Yan-Feng
Perera, A. G. Unil
Li, L. H.
Khanna, S. P.
Linfield, E. H.
Liu, H. C.
Article History
Received: 10 October 2013
Accepted: 11 March 2014
First Online: 13 April 2014
Competing interests
: The authors declare no competing financial interests.