1. E. Downing is in the Mechanical Engineering Department, Stanford University, Stanford, CA 94305 and at 3D Technology Laboratories, Post Office Box 114, 200 Blossom Lane, Mountain View, CA 94042, USA.
2. L. Hesselink is in the Electrical Engineering Department, Stanford University, Stanford, CA 94305, USA.
3. J. Ralston is at SDL Corporation, 90 Rose Orchard Way, San Jose, CA 95134, USA.
4. R. Macfarlane is at IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA.