18,953 research outputs found
Mechanical component screening for scanner
The critical mechanical components of the scan mirror mechanism are described and their evaluation and screening procedures are discussed. A bumper/damper unit is used in the design to reverse motion of the mirror and effect scan and retrace cycles. A wear evaluation was conducted on the bumper impact surfaces that established nylon 6-10 as an acceptable material. The elastomeric dampers were subjected to thermal vacuum tests for condensables and outgassing as well as parametric life tests. The flexure pivots that support the mirror were tested to establish a curve of stress plotted as a function of cycles to failure for rotational operation. The pivots met the life requirement of 150,000,000 cycles at a + or - 2.9 deg amplitude during fatigue testing. Screening procedures were established for dampers and flexure pivots to obtain flight quality components
Plasma Sterilization Technology for Spacecraft Applications
The application of plasma gas technology to sterilization and decontamination of spacecraft components is considered. Areas investigated include: effective sterilizing ranges of four separate gases; lethal constituents of a plasma environment; effectiveness of plasma against a diverse group of microorganisms; penetrating efficiency of plasmas for sterilization; and compatibility of spacecraft materials with plasma environments. Results demonstrated that plasma gas, specifically helium plasma, is a highly effective sterilant and is compatible with spacecraft materials
Remote sensing of changes in morphology and physiology of trees under stress
Measurements on foliage samples collected from several drought and salt treated plants revealed that leaf thickness decreased with increasing severity of the drought treatment and increased with increasing severity of treatment with NaCl, but remained essentially unaffected by treatment with CaCl2. Airborne data collected by multispectral scanner indicated that false color images provide selective enhancement of a diseased area. Comparison of simulated and actual aerial color and color IR photography revealed that the color renditions of the MSS simulations agreed closely with those of the actual photography
Remote sensing applications in forestry - Remote sensing of changes in morphology and physiology of trees under stress Annual progress report
Remote sensing of changes in morphology and physiology of trees under stres
Point Defect Dynamics in Two-Dimensional Colloidal Crystals
We study the topological configurations and dynamics of individual point
defect vacancies and interstitials in a two-dimensional colloidal crystal. Our
Brownian dynamics simulations show that the diffusion mechanism for vacancy
defects occurs in two phases. The defect can glide along the crystal lattice
directions, and it can rotate during an excited topological transition
configuration to assume a different direction for the next period of gliding.
The results for the vacancy defects are in good agreement with recent
experiments. For the interstitial point defects, which were not studied in the
experiments, we find several of the same modes of motion as in the vacancy
defect case along with two additional diffusion pathways. The interstitial
defects are more mobile than the vacancy defects due to the more
two-dimensional nature of the diffusion of the interstitial defects.Comment: 8 pages, 9 postscript figures. Version to appear in Phys. Rev.
On the origin of the reversed vortex ratchet motion
We experimentally demonstrate that the origin of multiply reversed rectified
vortex motion in an asymmetric pinning landscape is a consequence not only of
the vortex-vortex interactions but also essentially depends on the ratio
between the characteristic interaction distance and the period of the
asymmetric pinning potential. Our system consists of an Al film deposited on
top of a square array of size-graded magnetic dots with a constant lattice
period a=2\mu m. Four samples with different periods of the size gradient d
were investigated. For large d the dc voltage Vdc recorded under a sinusoidal
ac excitation indicates that the average vortex drift is from bigger to smaller
dots for all explored positive fields. As d is reduced a series of sign
reversals in the dc response are observed as a function of field. We show that
the number of sign reversals increases as d decreases. These findings are in
agreement with recent computer simulations and illustrate the relevance of the
different characteristic lengths for the vortex rectification effects.Comment: accepted in Phys. Rev. Let
Resolution enhancement of multichannel microwave imagery from the Nimbus-7 SMMR for maritime rainfall analysis
A restoration of the 37, 21, 18, 10.7, and 6.6 GHz satellite imagery from the scanning multichannel microwave radiometer (SMMR) aboard Nimbus-7 to 22.2 km resolution is attempted using a deconvolution method based upon nonlinear programming. The images are deconvolved with and without the aid of prescribed constraints, which force the processed image to abide by partial a priori knowledge of the high-resolution result. The restored microwave imagery may be utilized to examined the distribution of precipitating liquid water in marine rain systems
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