1. a Department of Accounting and Financial Management , Baskent University , 06810 Ankara , Turkey
2. b Institute of Applied Mathematics, Middle East Technical University , 06531 Ankara , Turkey
3. c Fachbereich Mathematik, TU Kaiserslautern , 67653 Kaiserslautern , Germany
4. d Fraunhofer ITWM , Fraunhofer Platz 1, 67663 Kaiserslautern , Germany