Scientific Reports 5: Article number: 8462; published online 16 February 2015; updated 30 June 2015

The Acknowledgements section in this Article is incomplete.

“This work has been supported by the European Union under FP7 in the DENFREE project and Fundação para Ciência e Tecnologia (FCT), Portugal.”

should read:

This work has been supported by the European Union under FP7 in the DENFREE project (grant 282378) and Fundação para Ciêcia e Tecnologia (FCT), Portugal, project PEst-OE/MAT/UI0209/2013