1. Professor, Dept. of Engineering Mathematics, Dalhousie Univ., 1340 Barrington St., Halifax, NS, Canada B3J 1Y9.
2. Professor, Dept. of Engineering Mathematics, Dalhousie Univ., 1340 Barrington St., Halifax, NS, Canada B3J 1Y9 (corresponding author).
3. Professor, Dept. of Civil and Resource Engineering, Dalhousie Univ., 1360 Barrington St., Halifax, NS, Canada B3J 1Z1.