Moisture Diffusion Analysis for Composite Microdamage

The absorption of moisture into fibrous polymeric meterials has been recognized as one of the major mechanisms in the strength degradation of such materials as reported by several workshops (1-3) and publications (4-7). The objective of the work reported here is to use nondestructive evaluation (NDE) techniques to determine the moisture content (profile) within a composite by measuring the w~isture diffusion rate and then subjecting the data to a statistical estimation analysis. This reveals the location of structural degradation and provides a sensitive inspection method for the serviceability of composites. Hydrothermal aging effects on cured graphite-epoxy composites were determined using: (1) acoustic attenuation, αL, (2) ultrasonic velocity, cL, and (3) thickness measurements of the composites. Results showed that while ultrasonic acoustic properties, sample thickness and moisture diffusion profiles are highly sensitive to structural degradation, ultrasonic inspection becomes insensitive in areas of extensive internal damage, probably due to high acoustic attenuation which results in loss of signals. Moisture diffusion analysis (MDA), in this case, becomes highly sensitive as a quantitative detection tool. Presently, analytical methods are developed to quantify the depth profile of moisture penetration in graphite-epoxy composites. Measurement of effusion kinetics over a range of time intervals followed by application of statistical estimation theory enables the depth concentration of moisture at initial time t=0 to be calculated. For a particular model in which the sample is assumed to be exposed to periodically changing environments, the model predicts large fluctuations in moisture concentration near the surfaces while the interior concentration is relatively constant

Prelaunch absolute radiometric calibration of LANDSAT-4 protoflight Thematic Mapper

Results are summarized and analyzed from several prelaunch tests with a 122 cm integrating sphere used as part of the absolute radiometric calibration experiments for the protoflight TM sensor carried on the LANDSAT-4 satellite. The calibration procedure is presented and the radiometric sensitivity of the TM is assessed. The internal calibrator and dynamic range after calibration are considered. Tables show dynamic range after ground processing, spectral radiance to digital number and digital number to spectral radiance values for TM bands 1, 2, 3, 4, 5, 7 and for channel 4 of band 6

Prelaunch absolute radiometric calibration of the reflective bands on the LANDSAT-4 protoflight Thematic Mapper

The results of the absolute radiometric calibration of the LANDSAT 4 thematic mapper, as determined during pre-launch tests with a 122 cm integrating sphere, are presented. Detailed results for the best calibration of the protoflight TM are given, as well as summaries of other tests performed on the sensor. The dynamic range of the TM is within a few per cent of that required in all bands, except bands 1 and 3. Three detectors failed to pass the minimum SNR specified for their respective bands: band 5, channel 3 (dead), band 2, and channels 2 and 4 (noisy or slow response). Estimates of the absolute calibration accuracy for the TM show that the detectors are typically calibrated to 5% absolute error for the reflective bands; 10% full-scale accuracy was specified. Ten tests performed to transfer the detector absolute calibration to the internal calibrator show a 5% range at full scale in the transfer calibration; however, in two cases band 5 showed a 10% and a 7% difference

Radiometric calibration and processing procedure for reflective bands on LANDSAT-4 protoflight Thematic Mapper

The radiometric subsystem of NASA's LANDSAT-4 Thematic Mapper (TM) sensor is described. Special emphasis is placed on the internal calibrator (IC) pulse shapes and timing cycle. The procedures for the absolute radiometric calibration of the TM channels with a 122-centimeter integrating sphere and the transfer of radiometric calibration from the channels to the IC are reviewed. The use of the IC to calibrate TM data in the ground processing system consists of pulse integration, pulse averaging, IC state identification, linear regression analysis, and histogram equalization. An overview of the SCROUNGE-era (before August 1983) method is presented. Procedural differences between SCROUNGE and the TIPS-era (after July 1983) and the implications of these differences are discussed

Characterization of radiometric calibration of LANDSAT-4 TM reflective bands

Prelaunch and postlaunch internal calibrator, image, and background data is to characterize the radiometric performance of the LANDSAT-4 TM and to recommend improved procedures for radiometric calibration. All but two channels (band 2, channel 4; band 5, channel 3) behave normally. Gain changes relative to a postlaunch reference for channels within a band vary within 0.5 percent as a group. Instrument gain for channels in the cold focal plane oscillates. Noise in background and image data ranges from 0.5 to 1.7 counts. Average differences in forward and reverse image data indicate a need for separate calibration processing of forward and reverse scans. Precision is improved by increasing the pulse integration width from 31 to 41 minor frames, depending on the band

Impact of the Desert dust on the summer monsoon system over Southwestern North America

The radiative forcing of dust emitted from the Southwest United States (US) deserts and its impact on monsoon circulation and precipitation over the North America monsoon (NAM) region are simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem) for 15 years (1995–2009). During the monsoon season, dust has a cooling effect (−0.90 W m<sup>−2</sup>) at the surface, a warming effect (0.40 W m<sup>−2</sup>) in the atmosphere, and a negative top-of-the-atmosphere (TOA) forcing (−0.50 W m<sup>−2</sup>) over the deserts on 24-h average. Most of the dust emitted from the deserts concentrates below 800 hPa and accumulates over the western slope of the Rocky Mountains and Mexican Plateau. The absorption of shortwave radiation by dust heats the lower atmosphere by up to 0.5 K day<sup>−1</sup> over the western slope of the Mountains. Model sensitivity simulations with and without dust for 15 summers (June-July-August) show that dust heating of the lower atmosphere over the deserts strengthens the low-level southerly moisture fluxes on both sides of the Sierra Madre Occidental. It also results in an eastward migration of NAM-driven moisture convergence over the western slope of the Mountains. These monsoonal circulation changes lead to a statistically significant increase of precipitation by up to ~40 % over the eastern slope of the Mountains (Arizona-New~Mexico-Texas regions). This study highlights the interaction between dust and the NAM system and motivates further investigation of possible dust feedback on monsoon precipitation under climate change and the mega-drought conditions projected for the future

Comments on Neutrino Tests of Special Relativity

We point out that the assumption of Lorentz noninvariance examined recently by Coleman and Glashow leads to neutrino flavor oscillations which are phenomenologically equivalent to those obtained by assuming the neutrinos violate the principle of equivalence. We then comment on the limits on Lorentz noninvariance which can be derived from solar, atmospheric, and accelerator neutrino experiments.Comment: 5 pages, Revte