Low Earth orbital atomic oxygen environmental simulation facility for space materials evaluation

Simulation of low Earth orbit atomic oxygen for accelerated exposure in ground-based facilities is necessary for the durability evaluation of space power system component materials for Space Station Freedom (SSF) and future missions. A facility developed at the National Aeronautics and Space Administrations's (NASA) Lewis Research Center provides accelerated rates of exposure to a directed or scattered oxygen beam, vacuum ultraviolet (VUV) radiation, and offers in-situ optical characterization. The facility utilizes an electron-cyclotron resonance (ECR) plasma source to generate a low energy oxygen beam. Total hemispherical spectral reflectance of samples can be measured in situ over the wavelength range of 250 to 2500 nm. Deuterium lamps provide VUV radiation intensity levels in the 115 to 200 nm range of three to five equivalent suns. Retarding potential analyses show distributed ion energies below 30 electron volts (eV) for the operating conditions most suited for high flux, low energy testing. Peak ion energies are below the sputter threshold energy (approximately 30 eV) of the protective coatings on polymers that are evaluated in the facility, thus allowing long duration exposure without sputter erosion. Neutral species are expected to be at thermal energies of approximately .04 eV to .1 eV. The maximum effective flux level based on polyimide Kapton mass loss is 4.4 x 10 exp 6 atoms/((sq. cm)*s), thus providing a highly accelerated testing capability

The effects of simulated low Earth orbit environments on spacecraft thermal control coatings

Candidate Space Station Freedom radiator coatings including Z-93, YB-71, anodized aluminum and SiO(x) coated silvered Teflon have been characterized for optical properties degradation upon exposure to environments containing atomic oxygen, vacuum ultraviolet (VUV) radiation, and/or silicone contamination. YB-71 coating showed a blue-gray discoloration, which has not been observed in space, upon exposure in atomic oxygen facilities which also provide exaggerated VUV radiation. This is evidence that damage mechanisms occur in these ground laboratory facilities which are different from those which occur in space. Radiator coatings exposed to an electron cyclotron resonance (ECR) atomic oxygen source in the presence of silicone-containing samples showed severe darkening from the intense VUV radiation provided by the ECR and from silicone contamination. Samples exposed to atomic oxygen from the ECR source and to VUV lamps, simultaneously, with in situ reflectance measurement, showed that significantly greater degradation occurred when samples received line-of-site ECR beam exposure than when samples were exposed to atomic oxygen scattered off of quartz surfaces without line-of-site view of the ECR beam. For white paints, exposure to air following atomic oxygen/VUV exposure reversed the darkening due to VUV damage. This illustrates the importance of in situ reflectance measurement

Exchange Bias Induced by the Fe3O4 Verwey transition

We present a study of the exchange bias in different configurations of V2O3 thin films with ferromagnetic layers. The exchange bias is accompanied by a large vertical shift in the magnetization. These effects are only observed when V2O3 is grown on top of Ni80Fe20 permalloy. The magnitude of the vertical shift is as large as 60% of the total magnetization which has never been reported in any system. X-Ray diffraction studies show that the growth conditions promote the formation of a ferrimagnetic Fe3O4 interlayer. The change in the easy magnetization axis of Fe3O4 across the Verwey transition at 120 K is correlated with the appearance of exchange bias and vertical shift in magnetization. Both phenomena disappear above 120 K, indicating for the first time a direct relationship between the magnetic signature of the Verwey transition and exchange bias.Comment: Accepted for publication Physical Review

Experimental demonstration of a suspended diffractively coupled optical cavity

All-reflective optical systems are under consideration for future gravitational wave detector topologies. One approach in proposed designs is to use diffraction gratings as input couplers for Fabry–Perot cavities. We present an experimental demonstration of a fully suspended diffractively coupled cavity and investigate the use of conventional Pound–Drever–Hall length sensing and control techniques to maintain the required operating condition

Age, poverty and alcohol use as HIV risk factors for women in Mongu, Zambia

Background: Age, poverty and alcohol use are seen as risk factors for HIV among women in sub-Saharan Africa. Objective: The objective of this study was to understand the influence of socioeconomic factors (including age and poverty) as well as alcohol use on risky sexual behaviors among women in Mongu, Zambia. Methods: This study examines these factors in the local context of Mongu, Zambia using the Priorities for Local AIDS Control Efforts (PLACE) methodology. This methodology allows for the study of risky behaviors while taking into consideration local factors. The two outcome variable studied were transactional sex in the past year and having two or more sexual partners in the past year. Results: In this study age was not a significant factor, but alcohol use and poverty/desire for economic advancement were significant factors. Conclusion: Programs and policies need to address the influence of alcohol on risky sexual behaviors and also the important but complex influence of poverty

Effect of prolonged ingestion of polychlorinated biphenyls on the rat

On a fair consommer a des rats, pendant 2, 4 et 6 mois et a raison de 0,5 et 25 ppm de leur regime alimentaire,de l'Aroclor 1242, melange commercial de biphenyles polychlores. Des augmentations significatives de l'excretion urinaire de coproporphyrine, des lipides hepatiques et de l'activite de l'hydroxylase microsomique hepatique ont ete observees chez les animaux qui avaient consomme 25 ppm pendant 2 mois. L'excretion urinaire de coproporphyrine, le poids du foie, sa teneur en lipides et l'activite de son hydroxylase microsomique etaient plus eleves chez les rats soumis pendant 4 ou 6 mois aux regimes a 5 ou a 25 ppm que chez les animaux temoins. A l'examen histopathologique on a constate une vacuolation des lipides et une proliferation de reticulum endoplasmique dans les hepatocytes des animaux traites. Ces constatations signifient que l'ingestion prolongee de faibles doses d'Aroclor 1242 peut modifier un certain nombre de parametres biologiques.AbstractAroclor 1242, a commercial polychlorinated biphenyl mixture, was fed to rats at dietary levels of 0, 5 and 25 ppm for 2, 4 and 6 months. Significant elevations of urinary coproporphyrin excretion, hepatic lipid and hepatic microsomal-hydroxylase activity were observed in rats ingesting 25 ppm for 2 months. In rats given the 5 or 25 ppm regimens for 4 or 6 months, urinary coproporphyrin excretion and liver weight, lipid content and microsomal-hydroxylase activity were higher than in controls. Histopathological examination revealed lipid vacuolation and proliferation of smooth endoplasmic reticulum in the hepatocytes of treated animals. These findings indicate that long-term, low-level ingestion of Aroclor 1242 may result in changes in a variety of biological parameters.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22345/1/0000791.pd

Biological responses of the rat to polychlorinated biphenyls

A commercial polychlorinated biphenyl mixture (PCBs), Aroclor 1242, was administered to rats po by intubation in order to determine toxic manifestations of acute and subacute ingestion. In addition, the effect of PCBs on hepatic microsomal enzyme systems in rats was evaluated. The oral, 14-day LD50 was determined to be approximately 4.25 g/kg. Major toxic signs observed upon administration of high doses of PCBs included diarrhea, chromodacryorrhea, loss of body weight, unusual stance and gait, lack of response to pain stimuli, and terminal ataxia. Progressive dehydration and CNS depression appeared to be contributing factors in each fatality. Histopathologic alterations were evident only in the liver and kidneys, manifest as foci of sudanophilic vacuolation. Rats maintained on an oral dosage regimen of 100 mg/kg every other day for 3 weeks exhibited similar histopathologic changes, but no overt signs of toxicity. Serum GOT activities were elevated over controls in both the acute and subacute groups. A single ip injection (100 mg/kg) increased liver weight, total hepatic microsomal enzyme activity (measured as hydroxylation of acetanilide and N-demethylation of aminopyrine), and hepatic cytochrome P450 and b5 levels. Hepatic microsomal enzyme activity remained elevated 10 days after a single dose of PCBs, suggesting that PCBs may play an important role in altering biologic responses of mammals subjected to environmental chemical stress.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33934/1/0000201.pd