Scientific Reports 4, Article number: 4885 (2014); Published: 9 May 2014; Updated: 11 July 2014

The original version of this Article contained two typographical errors in the spelling of the authors Xinli Li and Jiuhong Xu, which were incorrectly given as LI-Xinli and XU-Jiuhong respectively. These have now been corrected in the PDF and HTML versions of the Article.