[1] Univ Federico II, Dipartimento Sci Fis, INFN, Complesso Univ MS Angelo,Via Cintia 1, I-80126 Naples, Italy
[2] Ruhr Univ, Inst Theoretische Phys IV, Fak Phys & Astronome, D-44780 Bochum, Germany
[3] Univ Vale Rio dos Sinos, Dept Engn Mech, Unisinos, BR-9302200 Sao Leopoldo, Brazil
[4] Inst Phys, Belgrade 11001, Serbia
[5] Inst Nazionale Ottica CNR, I-80078 Pozzuoli, Italy