1. Department of Computer Science, University of Bradford, Bradford, BD7 1DP, U.K.
2. Interdisciplinary Computing and Complex Biosystems Research Group, Newcastle University, Newcastle, NE1 7RU, U.K.
3. Department of Computer Science, University of Warwick, Coventry, CV4 7AL, U.K.
4. School of Computer Science, University of Nottingham, Nottingham, NG8 1BB, U.K.
5. Department of Computer Science, Stanford University, Stanford, California 94305, United States