[1] Univ Trieste, Dipartimento Fis, I-34148 Trieste, Italy
[2] Ist Nazl Fis Nucl, Sez Trieste, I-34148 Trieste, Italy
[3] Univ Strathclyde, Dept Math & Stat, Glasgow G1 1XH, Lanark, Scotland
[4] Univ Verona, Dipartimento Biotecnol, I-37134 Verona, Italy
[5] Univ Trieste, Dipartimento Fis, I-34127 Trieste, Italy