1. Assistant Professor, Dept. of Civil Engineering, Technical Univ. of Denmark, Kgs. Lyngby 2800, Denmark; formerly, Ph.D. Student, Dept. of Engineering Science, Univ. of Oxford, Oxford OX1 3JP, UK (corresponding author).
2. Associate Professor, Dept. of Engineering Science, Univ. of Oxford, Oxford OX1 3JP, UK.
3. Professor Emeritus, Dept. of Engineering Science, Univ. of Oxford, Oxford OX1 3JP, UK.