[1] Politech Univ Marche, Dept Phys, I-60100 Ancona, Italy
[2] Politech Univ Marche, Dept Mat, I-60100 Ancona, Italy
[3] Politech Univ Marche, Dept Soil Engn, I-60100 Ancona, Italy
[4] INFM, Ancona Unit, I-60100 Ancona, Italy
[5] Politech Univ Marche, Inst Phys Sci, I-60131 Ancona, Italy