1. Instituto de Ciencia
de Materiales de Madrid, CSIC, Cantoblanco, ES-28049 Madrid, Spain
2. Department
of Mechanical Engineering, School of Engineering, University of Thessaly, 38334 Volos, Greece
3. Department
of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
4. Instituto
de Investigacións Tecnolóxicas, and Departamento de
Física Aplicada, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain
5. Departament
d’Electrònica and IN2UB, Universitat de Barcelona, Martí
i Franquès 1, 08028 Barcelona, Spain