1. Mathematical Institute of the Serbian Academy of Sciences and Arts Belgrade Serbia
2. Department of Medical Research, China Medical University Hospital China Medical University Taichung 40402 Taiwan Republic of China
3. Faculty of Electrical Engineering Belgrade University Beograd Serbia
4. Department of Mathematical Sciences Appalachian State University Boone North Carolina
5. Faculty of Electrical Engineering and Communication, Department of Mathematics Brno University of Technology Brno Czech Republic