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 mass profile measured directly in the STEM. This has been used in many projects involving cylindrical or spherical symmetry-An automatic program (""""""""AutoMass"""""""") was developed for particle location, classification, alignment, and mass analysis with spherical or cylindrical density analysis, where appropriate, and is used extensively for analyzing STEM 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 multancously 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 nonlinearities in STEM signals can be corrected before or during processing. We have adapted these programs to run on a standard personal computer (PCMass). This cost and makes analysis available to many of our users who do not have image processing facilities. A second Pc program imports 3-D x-ray structures from the Protein Data Bank, projects these in various directions and compares these pixel by pixel with a STEM image, while viewing the differ~nce image and computing'the RMS difference. Small-angle scattering curves can be computed for comparison to neutron or x-ray data. STEM images for the past year are archived on our server and available over Internet or on optical disk. The PCMass program also provides a convenient viewer for these remote files and is provided along with image data.
Showing the most recent 10 out of 101 publications
