1. Faculty of Natural Sciences and Mathematics, Institute of Physics, Ss. Cyril and Methodius University in Skopje, Arhimedova 3, 1000 Skopje, Macedonia
2. Research Center for Computer Science and Information Technologies, Macedonian Academy of Sciences and Arts, Boulevard Krste Misirkov 2, 1000 Skopje, Macedonia
3. Institute of Physics and Astronomy, University of Potsdam, D-14776 Potsdam-Golm, Germany
4. Departamento de Fisica, Universidade Estadual de Ponta Grossa, Avenida Carlos Cavalcanti 4748, Ponta Grossa 84030-900, PR, Brazil