1. CNR-SPIN, UOS Salerno, 84084 Fisciano, Italy
2. CNR-IOM, TASC Laboratory in Area Science Park, 34139 Trieste, Italy
3. Department of Physics, University of Milano, 20133 Milano, Italy
4. International Centre for Theoretical Physics (ICTP), 34151 Trieste, Italy
5. Elettra Sincrotrone Trieste, 34139 Trieste, Italy
6. Department of Information and Electrical Engineering and Applied Mathematics, University of Salerno, 84084 Fisciano, Italy
7. Department of Industrial Engineering, University of Salerno, 84084 Fisciano, Italy