1. Department of Electrical, Electronic and Information Engineering Guglielmo Marconi, University of Bologna, I 40136 Bologna, Italy
2. Faculté de Pharmacie, Université de Montréal, Montréal, Québec H3T 1J4, Canada
3. Centre de recherches mathématiques, Université de Montréal, Montréal, Québec H3T 1J4, Canada
4. Centre for Applied Mathematics in Bioscience and Medicine (CAMBAM), McGill University, Montréal, Québec H3G 1Y6, Canada