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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Thermal desorption of metals from tungsten single crystal surfaces

After a short review of experimental methods used to determine desorption energies and frequencies the assumptions underlying the theoretical analysis of experimental data are discussed. Recent experimental results on the flash desorption of Cu, Ag, and Au from clean, well characterized W (110) and (100) surfaces are presented and analyzed in detail with respect to the coverage dependence. The results obtained clearly reveal the limitations of previous analytical methods and of the experimental technique per se (such as structure and phase changes below and in the temperature region in which desorption occurs).

Bauer, E.↗
NASA NTRS1976

Chemical fractionations in meteorites. IX - C3 chondrites

Radiochemical neutron activation is applied to the analysis of four C3V chondrites and three C3O chondrites for 17 trace elements (U, Re, Ir, Ni, Au, Sb, Ge, Ag, Rb, Cs, Bi, Tl, Br, Se, Te, In, and Cd). It is shown that both classes exhibit a typical chondritic step pattern, reflecting loss of volatiles during chondrule formation. It appears that the H2S/H2 ratio is the key variable to account for the condensation of chalcophile elements as a function of H2S. C3O's seem to have condensed in a region where enough metallic Fe was present to buffer the H2S pressure, whereas C3V's condensed in a more oxidized region where H2S was in excess. Accretion temperatures for both subclasses is determined. Sb and Au show variable depletion, presumably reflecting variable loss during chondrule formation.

Anders, E.↗
NASA NTRS1976

Recent advances in shell theory

The results reviewed are divided into two categories: those that relate two-dimensional shell theory to three-dimensional elasticity theory and those concerned with shell theory per se. In the second category results for general elastic systems that carry over, by specialization or analogy, to shells and results that are unique to shell theory itself are considered.

Simmonds, J. G.↗
NASA NTRS1976

Crystal growth from the vapour phase (ASTP experiment MA-085)

The positive effects of microgravity on crystal quality and fundamental properties of the vapor transport reaction were established by analyzing the results of three transport experiments on multi-component systems performed during the Apollo Soyuz Test Project (ASTP) mission. The systems employed were GeSe(0.99)Te(0.01) - GeI4 (A), GeS(0.98)Se(0.02) - GeCl4 (B), and GeS - GeCl4-Ar (C). The crystallographic analysis is based on a direct comparison of space and ground-based (prototype) crystals, employing X-ray diffraction, microprobe, microscopic, and chemical etching techniques. The results demonstrate a considerable improvement of the space-grown crystals in terms of chemical and crystalline homogeneity, surface morphology, and bulk perfection relative to ground specimens. The confirmation of greater mass transport rates than predicted for micro-gravity by present vapor transport models is of basic scientific and practical importance for the improvement of transport models and techniques on earth and for the development of a transport model for space conditions. The internal consistency and agreement between ASTP and Skylab results obtained for different compounds, transport agents, and temperature gradients strongly support the validity of these observations. The combined findings of improved crystal quality and high mass transport rates are of technological significance for space-processing applications.

Wiedemeier, H.↗
NASA NTRS1976

Remote sensing of wetlands, marshes, and shorelines in Michigan including St. John's Marsh

Remote sensing data are used to show the strategic relationship of the endangered marsh to population centers of SE Michigan. The potential ecological consequences and the impact of past development and changing lake levels are discussed. Applications of remote sensing are presented showing its usefulness for preparing statewide infrared wetland and forest mapping.

Lowe, D. S.↗
NASA NTRS1976

University resources sharing using the CTS

NASA-Ames Research Center and Stanford University in California, and Carleton University in Ottawa, Canada, are designing a curriculum-sharing experiment which will use compressed digital television. The experiment will permit evaluation of the potential of curriculum sharing by two universities which are geographically distant, but capable of transmitting and receiving television signals. The evaluation of the curriculum sharing per se will include inputs from faculty, staff and students at both institutions. Accessibility to and acceptability of each other's curriculum will be studied and recorded. Adjustments to differences in academic terms, class meeting times, teaching styles and similar issues will be closely monitored. It is hoped that this experiment will provide long-range planners the kind of information which they will need when designing large-scale educational telecommunications systems for the future.

Down, K. S.↗
NASA NTRS1977

Some physiological effects of alternation between zero gravity and one gravity

The anatomy and physiology of the healthy vestibular system and the history of its study, maintenance of muskuloskeletal fitness under low-gravity conditions, tests of motion sickness, and data and techniques on testing subjects in a slow rotation room, are covered. Components of the inner ear labyrinth and their behavior in relation to equilibrium, gravity and inertial forces, motion sickness, and dizziness are discussed. Preventive medicine, the biologically effective force environment, weightlessness per se, activity in a weightless spacecraft, exercizing required to maintain musculoskeletal function, and ataxia problems are dealt with.

Graybiel, A.↗
NASA NTRS1977

'Mysterite' - A late condensate from the solar nebula

An attempt is made to clarify the nature of 'mysterite', a material that had been postulated to explain the overabundance of Tl, Bi, and Ag in certain chondrites. Four dark clasts and a vein sample from the H6 chondrite Supuhee were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Rb, Re, Sb, Se, Te, Tl, and Zn. One of the clasts is enriched in all volatile elements, while the other four samples are enriched only in the siderophile volatiles Ag, Bi, and Tl. The enrichments range up to 100 times typical H6 chondrite abundances. The proportions of Ag, Bi, and Tl suggest the presence of at least two, Tl-rich and Tl-poor, varieties of mysterite. The former seems to dominate in Supuhee and Krymka, and the latter in Mezo-Madaras. Apparently mysterite is a late condensate from the solar nebula that collected volatiles left behind by earlier generations of chondrites. It was incorporated in Supuhee and perhaps in other chondrites (mainly of low petrologic types) during brecciation events.

Higuchi, H.↗
NASA NTRS1978

Spraylon fluorocarbon encapsulation for silicon solar cell arrays, phase 3

The liquid transparent film-forming, fluorocarbon, Spraylon, a protective coating for terrestrial solar cell modules was evaluated. Two modules were completed and field tested. Problems developed early in the field testing which led to the shortened test period, specifically, lifting of the antireflection coating, followed in some areas by complete film delamination. It is believed that although these problems were certainly induced by the presence of the SPRAYLON film, they were not failures of the material per se. Instead, assembly procedures, module design, and cell coating quality should be evaluated to determine cause of failure.

Naes, L. G.↗
NASA NTRS1977

Earth-satellite path attenuation statistics influenced by orientation of rain cells

It is examined whether there may be preferred azimuths for earth-satellite paths along which fading and space diversity statistics are influenced differently than along other azimuths. Such preferred directions may exist if individual rain cells are statistically elongated along them for the given climatological region. The analysis is performed using the rain reflectivity data base obtained at Wallops Island during June, July and August 1973 using a high resolution radar. It is found that in the vicinity of Wallops Island increased attenuation and poorer diversity gains exist along paths whose azimuths and base lines lie in the NE-SW quadrants as compared to the NW-SE sectors. This result suggests the dominance of the major axis of rain cells in these quadrants.

Goldhirsh, J.↗
NASA NTRS1977

Stabilization of n-type semiconductors to photoanodic dissolution by competitive electron transfer processes

The behavior of n-type CdX (X = S, Se, Te) and GaP, GaAs, and InP in alkaline electrolytes containing X(--) and X sub n(--) ions is reviewed. Of the 18 combinations of electrode and electrolyte, 12 alliances are completely stable to photoanodic dissolution of the n-type photoanode. In each case the oxidation of the chalcogenide species at the photoanode is reversed at the cathode to complete an electrochemical cycle involving no net chemical change. The best system in terms of light-to-electric energy conversion seems to be the CdTe-based cell employing the Te(--)/Te2(--) electrolyte, with roughly 10% efficiency at an output voltage of 0.35 V for monochromatic 633 nm input optical energy at about 25 mW/sq cm.

Wrighton, M. S.↗
NASA NTRS1978

Differences in radar return from ice-covered North Slope Lakes

Comparisons are made between L and X band synthetic aperture radar images of frozen lakes on the North Slope of Alaska and ground truth observations of the nature of their ice covers. It is shown that the differences in radar backscatter observed on different areas of a lake can be correlated with whether or not the lake is frozen completely to the bottom at the site in question. This explanation is reasonable inasmuch as the reflection coefficient associated with the high-dielectric contrast ice/water interface is significantly higher than that associated with a low-contrast ice/soil interface. However, the presence of the ice/water interface cannot be the only condition required for the higher backscatter because the ice/water interface per se would be specular at X and L band frequencies, causing the energy returned from the interface to be reflected away from the radar receiver. The other principal factor contributing to the return of energy from the ice/water interface to the receiver is believed to be the presence in the ice of numerous vertically elongated air bubbles which would act as scatters.

Weeks, W. F.↗
NASA NTRS1978

Rat growth during chronic centrifugation

Female weanling rats were chronically centrifuged at 4.15 G with controls at terrestrial gravity. Samples were sacrificed for body composition studies at 0, 28, 63, 105 and 308 days of centrifugation. The centrifuged group approached a significantly lower mature body mass than the controls (251 and 318g) but the rate of approach was the same in both groups. Retirement to 1G on the 60th day resulted in complete recovery. Among individual components muscle, bone, skin, CNS, heart, kidneys, body water and body fat were changed in the centrifuged group. However, an analysis of the growth of individual components relative to growth of the total fat-free compartment revealed that only skin (which increased in mass) was responding to centrifugation per se.

Pitts, G. C.↗
NASA NTRS1978

Evaporative water loss in man in a gravity-free environment

Daily evaporative water losses (EWL) during the three Skylab missions were measured indirectly using mass and water-balance techniques. The mean daily values of EWL for the nine crew members who averaged 1 hr of daily exercise were: preflight 1,750 + or - 37 (SE) ml or 970 + or - 20 ml/sq m and inflight 1,560 + or - 26 ml or 860 + or - 14 ml/sq m. Although it was expected the EWL would increase in the hypobaric environment of Skylab, an average decrease from preflight sea-level conditions of 11% was measured. The results suggest that weightlessness decreased sweat losses during exercise and possibly reduced insensible skin losses. The weightlessness environment apparently promotes the formation of an observed sweat film on the skin surface during exercise by reducing convective flow and sweat drippage, resulting in high levels of skin wettedness that favor sweat suppression.

Leach, C. S.↗
NASA NTRS1979

Structure and electrical activity of planar defects in EFG ribbons

Optical, electron beam induced current (EBIC), and transmission electron microscopy were used to study the structure and electrical activity of planar defects in EFG silicon. What appears to be twin boundaries by both optical microscopy plus etching, and by EBIC are in reality systems of microtwins, some of which are only a few atomic lattice planes thick. The electrical activity of planar defects appears to be correlated with emission of dislocations especially at termination points. Impurity effects may also play a role. Twin boundaries per se appear not to be electrically active.

Ast, D. G.↗
NASA NTRS1979

Trace element contents of selected antarctic meteorites, 1

Data are reported for volatile/mobile Ag, As, Au, Bi, Cd, Co, Cs, Cu, Ga, In, Rb, Sb, Se, Te, T1 and Zn in exterior and/or interior samples of four Antarctic meteorites: 77005 (unique achondrite); 77257 (unreilite); 77278 (L3); 77299 (H3). Exterior samples reflect contamination and/or leaching by weathering but trace element (ppm-ppt) contents in interior samples seem reasonable for representatives of these rare meteoritic types. The 77005 achondrite seems related to shergottites; other samples extend compositional ranges previously known for their types. With suitable precautions, Antarctic meteorite finds yield trace element data as reliable as those obtained from previously known falls.

Biswas, S.↗
NASA NTRS1979

Early space experiments in materials processing

A comprehensive survey of the flight experiments conducted in conjunction with the United States Materials Processing in Space Program is presented. Also included are a brief description of the conditions prevailing in an orbiting spacecraft and the research implications provided by this unique environment. What was done and what was learned are summarized in order to serve as a background for future experiments. It is assumed that the reader has some knowledge of the physical sciences but no background in spaceflight experimentation or in the materials science per se.

Naumann, R. J.↗
NASA NTRS1978

Quantitative mapping of particulate iron in an ocean dump using remotely sensed data

A remote sensing experiment was conducted at the industrial acid waste ocean dump site located approximately 38 n mi SE of Cape Henlopen, Delaware, to see if there was a relationship between aircraft remotely sensed spectral signatures and the iron concentration measured in the plume. Results are presented which show that aircraft remotely sensed spectral data can be used to quantify and map an acid waste dump in terms of its particulate iron concentration. A single variable equation using the ratio of band 2 (440-490 nm) radiance to band 4 (540-580 nm) radiance was used to quantify the acid plume and the surrounding water. The acid waste varied in age from freshly dumped to 3 1/2 hours old. Particulate iron concentrations in the acid waste were estimated to range up to 1.1 mg/liter at the 0.46 meter depth. A classification technique was developed to remove sunglitter-affected pixels from the data set.

Ohlhorst, C. W.↗