Scientific Reports 4, Article number: 5341 (2014); Published: 18 June 2014; Updated: 14 October 2014

The original version of this Article contained a typographical error in the spelling of the author Renke Yang, which was incorrectly given as Yinke Yang. In addition, the current address for author Renke Yang was omitted. These errors have been corrected in both the PDF and HTML versions of the Article.