1992 Research Highlights
1. NanoManipulator?A Virtual Reality Interface for Interactive Control of a Scanning Tunneling Microscope
The UNC Molecular Graphics Research Resource, in collaboration with with Prof. Stanley Williams of the UCLA Department of Chemistry, has developed a real-time graphics and force-feedback interface for scanning tunneling microscopes, atomic force microscopes, etc. The chemist uses a head-mounted display, flying and viewing controls, and head position sensing, so that he can scale himself down to nearatomic scale and see the surface features as if he were walking or flying over it. We use our GROPE force-display arm to allow the user to probe the surface shape, feeling the shape as well as seeing it. The scanned surface is treated as a virtual world for viewing, and for manipulation. The user can change the lighting, especially the lighting angle, on the surface. The effect is to scale the chemist down by about 108, put him on the surface, and let him move about in real-time, viewing, feeling by probing, and firing pulses of energy at spots he selects on the surface.
We have succeeded in making location-controlled surface modifications to gold samples using gold tips. These humps appear to be deposits from the tip to the sample. They anneal away under repeated imaging. A new result concerns pulse length. Taylor finds that pulses of about 20 ns. duration are necessary for surface modification, with shorter pulses having no effect and longer pulses not moving significantly more material. Most previous work seems to have used substantially longer pulses. This work is an important step towards human-controlled fabrication of quantum-scale devices.
2. SCULPT?Interactive Constrained Manipulation with Concurrent Energy Minimization
The SCULPT system is designed to let a chemist deform virtual protein molecules interactively, while the molecules continue to obey the physical constraints on bond length, bond angle, and dihedral angles, and while they maintain a conformational energy minimum. Ph.D. student Mark Surles built the first prototype of SCULPT, completing and demonstrating it this year. He showed that the running time of his continual energy minimizer is linear in the number of atoms in the molecular system being manipulated. For Felix, a protein designed by the Richardsons at Duke, the system updates the position of all atoms in the deforming molecule, taking one step toward the Lennard-Jones energy minimum, about 3 times a second, running on a Silicon Graphics Iris 4D/240 system, using all four 25 Mhz. processors.
The UNC team has ported the SCULPT interface from the Silicon Graphics monitor and mouse to our large-screen videoprojector and the Argonne ARM. Chemists can now operate SCULPT while viewing the molecule in stereo on the 4?x6? screen, and feeling the deformation forces they are applying. This tool radically speeds up the exploration of possible folding patterns for proteins.