1. a Faculty of Applied Science, Royal Melbourne Institute of Technology , Melbourne, Victoria, 3001, Australia
2. b Dept. of Physics , Univ. of Colorado , Boulder, CO, 80309-0390, USA
3. c Dept. of Electrical Engineering , Univ. of Colorado , Colorado Springs, CO, 80933-7150, USA
4. d Symetrix Corp. , Colorado Springs, CO, 80918, USA