Acknowledgements
This work was supported by ERDF funds through the Competitiveness
Factors Operational Programme – COMPETE and
National Funds through FCT – Foundation for Science and Technology
[project number FCOMP-01-0124-FEDER-007189]. The author,
Pedro Silva, was supported by FCT and DST, S.A. [grant number
SFRH/BDE/15599/2006], which was co-financed by the Human
Potential Operational Programme of the European Union POPH –
NSRF – Type 4.1 –Advanced Training, shared by the European Social
Fund and national funds MCTES.