STEM mass measurements have been a mainstay of our program. Several years ago A. Steven developed a set of programs to compute radial density profiles from the projected niass profile measured directly in the STEM. This has been used in many projects involving cylindrical or spherical symmetry. We also have J. Frank's Spider program package and collaborate with A. Steven or T. Baker for virus analysis. An automatic program ("AutoMass't) was developed for particle location, classification, alignment, and mass analysis with spherical or cylindrical density analysis, where appropriate, and is used extensively for analyzing SThM data. Several factors motivated this effort. Particle selection can be by mathematical rather than subjective criteria. Coarse sampling in STEM images creates problems with some programs, degrading the resolution, but can be handled easily in a custom program. Using two or more channels of data recorded simultaneously from the same pixel may create bookkeeping problems (e.g., large angle minus small angle signals with appropriate thickness corrections to give hydrogen mapping). Various small non-linearities in STEM signals can be corrected before or during processing. We are adapting these programs to run on a standard personal computer (')CMass). This mininlizes cost and makes analysis available to many of our users who do not have image processing facilities. An additional features is the ability to import 3-') x-ray structures from the Protein Data Bank, project these in various directions and compare these pixel by pixel with the STEM image, while viewing the difference image and computing the RMS difference. Small angle scattering curves can be computed for comparison to neutron or x-ray data obtained at Brookhaven. STEM images for the past year are archived on our server and available over Internet. The PCMass program also provides a convenient viewer for these remote files.
NIH ExPorter
NIH ExPorter