1. Department of Mathematics and Statistics, McMaster University, Hamilton L8S 4K1, Ontario, Canada
2. The Faraday Institution, Quad One, Becquerel Avenue, Harwell Campus, Didcot OX11 0RA, U.K.
3. School of Mathematics and Physics, University of Portsmouth, Lion Terrace, Portsmouth, Hampshire PO1 2UP, U.K.
4. Department of Chemistry, McMaster University, Hamilton L8S 4L8, Ontario, Canada