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Extended Shelf Life for PMR Polyimide Resins and Prepregs

Secondary alcohols are used in place of primary alcohols. An improved class of formulations for PMR polyimide resins retards the imidization that undesirably occurs during handling and storage. While imidization is desired at the final (deliberate polymerization) stage of production of a polyimide, imidization results in premature aging when it occurs during earlier stages of synthesis, shipping, prepregging, and fabrication layup. By retarding imidization at storage and handling temperatures, the improved class of formulations increases both shelf life and the upper limit of allowable temperature for handling and storage prior to final polymerization.

Posted in: Briefs, TSP, Materials, Performance upgrades, Storage, Resins, Durability

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Silica-Filled EPDM Rubbers as Ablative Insulating Materials

These materials are intended to replace other materials that will soon be unavailable. Silica-filled polymers made from ethylene propylene diene monomer (EPDM) have been found to be useful as ablative thermal-insulation materials. These polymers have been investigated as candidates to replace some previously developed polymeric ablative rocket-engine insulating materials that will soon become commercially unavailable. Although these materials have been developed specifically for use in and on solid-fuel rocket motors, they may also be useful in terrestrial applications in which there are requirements for protection against high temperatures for short times.

Posted in: Briefs, Materials, Elastomers, Heat resistant materials, Insulation, Rocket engines

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Statistical Sampling of Tide Heights Study

The goal of the study was to determine if it was possible to reduce the cost of verifying computational models of tidal waves and currents. Statistical techniques were used to determine the least number of samples required, in a given situation, to remain statistically significant, and thereby reduce overall project costs. Commercial, academic, and Federal agencies could benefit by applying these techniques, without the need to “touch” every item in the population. For example, the requirement of this project was to measure the heights and times of high and low tides at 8,000 locations for verification of computational models of tidal waves and currents. The application of the statistical techniques began with observations to determine the correctness of submitted measurement data, followed by some assumptions based on the observations.

Posted in: Briefs, Materials, Computational fluid dynamics, Mathematical models, Statistical analysis, Water, Marine vehicles and equipment

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Wafer-Level Lens Alignment

Over one billion cell phones with cameras are sold every year, and this number has been increasing annually at a rate of about 15 percent for the past 7 years. Approximately 80 percent of cell phones now have embedded cameras, with about 20 percent of new cell phones having two cameras – one on the back for taking photographs and one on the front for videoconferencing.

Posted in: Application Briefs, Imaging, Photonics

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Multiparallel Three-Dimensional Optical Microscopy

Lyndon B. Johnson Space Center, Houston, Texas Multiparallel three-dimensional optical microscopy is a method of forming an approximate three-dimensional image of a microscope sample as a collection of images from different depths through the sample. The imaging apparatus includes a single microscope plus an assembly of beam splitters and mirrors that divide the output of the microscope into multiple channels. An imaging array of photodetectors in each channel is located at a different distance along the optical path from the microscope, corresponding to a focal plane at a different depth within the sample. The optical path leading to each photodetector array also includes lenses to compensate for the variation of magnification with distance so that the images ultimately formed on all the photodetector arrays are of the same magnification.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Microscopy

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Sub-Aperture Interferometers

Multiple target sub-beams are derived from the same measurement beam. NASA’s Jet Propulsion Laboratory, Pasadena, California Sub-aperture interferometers — also called wavefront-split interferometers — have been developed for simultaneously measuring displacements of multiple targets. The terms “sub-aperture” and “wavefront-split” signify that the original measurement light beam in an interferometer is split into multiple sub-beams derived from non-overlapping portions of the original measurement- beam aperture. Each measurement sub-beam is aimed at a retroreflector mounted on one of the targets. The splitting of the measurement beam is accomplished by use of truncated mirrors and masks, as shown in the example below.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Mirrors, Measurements, Optics

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Vacuum-Compatible Wideband White Light and Laser Combiner Source System

NASA’s Jet Propulsion Laboratory, Pasadena, California For the Space Interferometry Mission (SIM) Spectrum Calibration Development Unit (SCDU) testbed, wideband white light is used to simulate starlight. The white light source mount requires extremely stable pointing accuracy (hts were coupled to a photonic crystal fiber (PCF).

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Lasers, Fibers, Test equipment and instrumentation

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