Acknowledgements
This work is funded by FEDER through ‘Programa Operacional de Fatores de Competitividade’ – COMPETE and by national funds through FCT – Fundação para a Ciência e Tecnologia under the projects FCOMP-01-0124-FEDER-010248 (PTDC/EME-PME/103578/2008), FCOMP-01-0124-FEDER-015143 (PTDC/EME-PME/111305/2009) and FCOMP-01-0124-FEDER-015191 (PTDC/EME TME/113039/2009).