1. Graduate School of Natural and Applied Sciences, Dokuz Eylül University, Tınaztepe Kampüsü, Buca, İzmir, Turkey + Department of Mathematics, Faculty of Arts and Sciences, Istanbul Technical University, Maslak, İstanbul, Turkey
2. Department of Computer Science, Rice University, Houston, Texas, USA
3. Department of Mathematics and Statistics, University of Houston-Downtown, Houston, Texas , USA