1. Institute of Applied Mathematics and Department of Mathematics, University of British Columbia, 121–1984 Mathematics Road, Vancouver, British Columbia, V6T 1Z2, Canada
2. 2Nonlinear Systems Group, Department of Aeronautical and Astronautical Engineering, University of Illinois at Urbana-Champaign, 306 Talbot Laboratory, 104 South Wright Street, Urbana, IL 61801–2935, USA