1. Department of Computer Science, The University of Sheffield, Regent Court, 211 Portobello St., S1 4DP, Sheffield, UK
2. Department of Computer Science and Mathematics, University of Pitesti, Str Targu din Vale 1, 0300, Pitesti, Romania
3. Department of Electronic & Electrical Engineering, The University of Sheffield, Mappin St., S1 3JD, Sheffield, UK