[1] Univ Siena, Dipartimento Ingn Informaz & Sci Matemat DIISM, I-53100 Siena, Italy
[2] Univ Cambridge, Dept Comp Sci & Technol, Cambridge CB3 0FD, England
[3] Univ Florence, Magnet Resonance Ctr CERM, I-50019 Florence, Italy
[4] Univ Florence, Dept Chem Ugo Schiff, I-50019 Florence, Italy
[5] Consorzio Interuniv Risonanze Magnet Met Prot CIR, I-50019 Florence, Italy