1. University of Nis, Faculty of Electronic Engineering, Nis, Serbia
2. University of K.Mitrovica, Faculty of Teachers Education, Leposavic, Serbia
3. University of Belgrade, Institute of Technical Sciences, Serbian Academy of Sciences and Arts, Belgrade, Serbia
4. North Carolina Central University (NCCU), Durham, NC 27707, USA
5. Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan