[1] Univ Belgrade, Inst Phys, Zemun 11080, Serbia
[2] Fac Sci, Banja Luka, Bosnia & Herceg
[3] Univ Nacl Autonoma Mexico, Inst Ciencias Fis, Cuernavaca 62251, Morelos, Mexico
[4] Univ Autonoma Metropolitana Azcapotzalco, Unidad Ciencias Basicas, Mexico City 02200, DF, Mexico
[5] Univ Autonoma Metropolitana Azcapotzalco, Dept Energia, Mexico City 02200, DF, Mexico