1. Research Associate, Dept. of Civil Engineering, Stellenbosch Univ., Stellenbosch 7600, South Africa; Senior Technical Staff Member, Dept. of Multiscale Science, Sandia National Laboratories, Albuquerque, NM 87185 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Houston, Houston, TX 77204.
3. Principal Technical Staff Member, Dept. of Thermal and Fluid Sciences and Engineering, Sandia National Laboratories, Albuquerque, NM 87185-0836.