1. Department of Mathematics and Statistics, Dalhousie University, Halifax, NS B3H 4R2, Canada
2. Department of Physics and Astronomy, Bishop’s University, 2600 College Street, Sherbrooke, QC J1M 1Z7, Canada
3. Physics Department, Champlain College-Lennoxville, 2580 College Street, Sherbrooke, QC J1M 2K3, Canada