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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Zirconium and hafnium abundances in some lunar materials and implications of their ratios

A new rapid and precise analytical procedure for Zr and Hf has been applied to the study of lunar materials. The results indicate that the Zr/Hf ratios in lunar materials vary in a narrow range from 36.6 to 51.3 while their respective contents vary by a factor of 40. There is a strong Zr, Hf, and major element correlation. This correlation and the Zr and Hf systematics suggest that lunar materials fall into two groups. One group characterized by high Zr and Hf contents and higher Zr/Hf ratios corresponds to materials with a high KREEP content; the other characterized by low Zr and Hf contents and lower Zr/Hf ratios corresponds to materials with high Ti, Fe, Mn, and Mg contents. We believe that the modest Zr and Hf fractionation we observe is related to the extent of stabilization of the metals in the early titanium minerals and a charge disparity under extremely reduced conditions in which Zr exists as 3+, while Hf remains as 4+.

Chyi, L. L.↗
NASA NTRS1991

Two-dimensional model calculation of fluorine-containing reservoir species in the stratosphere

Two-dimensional model calculations have been carried out of the distributions of the fluorine-containing reservoir species HF, CF2O, and CFClO. HF constitutes the largest fluorine reservoir in the stratosphere, but CF2O also makes an important contribution to the inorganic fluorine budget. CFClO amounts are most important in the tropical lower stratosphere. HF amounts increase with altitude throughout the stratosphere, while those of CF2O and CFClO fall off above their mixing ratio peaks due to photolysis. The model is in good qualitative agreement with observed vertical profiles of HF and CF2O but tends to underestimate the total column of HF. The calculated CFClO distribution is in good agreement with the very limited data. The disagreement in the HF columns is likely due to small inaccuracies in the model's treatment of lower stratospheric photolysis of chlorofluorocarbons. The model results support the suggestion that CF2O may be heterogeneously converted to HF on the surface of polar stratospheric cloud particles. The model results also suggest that the quantum yield for photolysis of CF2O is near unity.

Kaye, Jack A.↗
NASA NTRS1999

Blood flow dynamics in heart failure

BACKGROUND: Exercise intolerance in heart failure (HF) may be due to inadequate vasodilation, augmented vasoconstriction, and/or altered muscle metabolic responses that lead to fatigue. METHODS AND RESULTS: Vascular and metabolic responses to rhythmic forearm exercise were tested in 9 HF patients and 9 control subjects (CTL) during 2 protocols designed to examine the effect of HF on the time course of oxygen delivery versus uptake (protocol 1) and on vasoconstriction during exercise with 50 mm Hg pressure about the forearm to evoke a metaboreflex (protocol 2). In protocol 1, venous lactate and H+ were greater at 4 minutes of exercise in HF versus CTL (P<0.05) despite similar blood flow and oxygen uptake responses. In protocol 2, mean arterial pressure increased similarly in each group during ischemic exercise. In CTL, forearm blood flow and vascular conductance were similar at the end of ischemic and ambient exercise. In HF, forearm blood flow and vascular conductance were reduced during ischemic exercise compared with the ambient trial. CONCLUSIONS: Intrinsic differences in skeletal muscle metabolism, not vasodilatory dynamics, must account for the augmented glycolytic metabolic responses to moderate-intensity exercise in class II and III HF. The inability to increase forearm vascular conductance during ischemic handgrip exercise, despite a normal pressor response, suggests that enhanced vasoconstriction of strenuously exercising skeletal muscle contributes to exertional fatigue in HF.

NASA Discipline Cardiopulmonary↗
NASA NTRS1993

A diminished aortic-cardiac reflex during hypotension in aerobically fit young men

We compared the aortic-cardiac baroreflex sensitivity in eight average fit (AF: VO2max = 44.7 +/- 1.3 ml.kg-1 x min-1) and seven high fit (HF: VO2max = 64.1 +/- 1.7 ml.min-1 x kg-1) healthy young men during hypotension elicited by steady state sodium nitroprusside (SN) infusion. During SN mean arterial pressure (MAP) was similarly decreased in AF (-12.6 +/- 1.0 mm Hg) and HF (-12.1 +/- 1.1 mm Hg). However, the increases in heart rate (HR) were less (P < 0.023) in HF (15 +/- 3 bpm) than AF (25 +/- 1 bpm). When sustained neck suction (NS, -22 +/- 1 torr in AF and -20 +/- 1 torr in HF, P > 0.05) was applied to counteract the decreased carotid sinus transmural pressure during SN, thereby isolating the aortic baroreceptors, the increased HR remained less (P < 0.021) in HF (8 +/- 2 bpm) than AF (16 +/- 2 bpm). During both SN infusion and SN+NS, the calculated gains (i.e., delta HR/delta MAP) were significantly greater in AF (2.1 +/- 0.3 and 1.3 +/- 0.2 bpm.mm Hg-1) than HF (1.2 +/- 0.2 and 0.6 +/- 0.2 bpm.mm Hg-1). However, the estimated carotid-cardiac baroreflex sensitivity (i.e., the gain difference between the stage SN and SN + NS) was not different between AF (0.7 +/- 0.2 bpm.mm Hg-1) and HF (0.6 +/- 0.1 bpm.mm Hg-1). These data indicated that the aortic-cardiac baroreflex sensitivity during hypotension was significantly diminished with endurance exercise training.

NASA Discipline Number 14-10↗
NASA NTRS2013

Empirical Study of the Multiaxial, Thermomechanical Behavior of NiTiHf Shape Memory Alloys

An empirical study was conducted to characterize the multiaxial, thermomechanical responses of new high temperature NiTiHf alloys. The experimentation included loading thin walled tube Ni(sub 50.3)Ti(sub 29.7)Hf(sub 20) alloy samples along both proportional and nonproportional axial-torsion paths at different temperatures while measuring surface strains using stereo digital image correlation. A Ni(sub 50.3)Ti(sub 33.7)Hf(sub 16) alloy was also studied in tension and compression to document the effect of slightly depleting the Hf content on the constitutive responses of NiTiHf alloys. Samples of both alloys were made from nearly texture free polycrystalline material processed by hot extrusion. Analysis of the data shows that very small changes in composition significantly alter NiTiHf alloy properties, as the austenite finish (Af) temperature of the 16-at Hf alloy was found to be approximately 60 C less than the 20-at Hf alloy (approximately 120 C vs. 180 C). In addition, the 16-at Hf alloy exhibited smaller compressive transformation strains (2 vs. 2.5 percent). Multi-axial characterization of the 20-at % Hf alloy showed that while the random polycrystal transformation strains in tension (4 percent) and compression (2.5 percent) are modest in comparison with binary NiTi (6 percent, 4 percent), the torsion performance is superior (7 vs. 4 shear strain width to the pseudoelastic plateau).

tensile deformation↗
NASA NTRS2016

Human Factors Checklist: Think Human Factors - Focus on the People

A quick-look Human Factors (HF) Checklist condenses industry and NASA Agency standards consisting of thousands of requirements into 14 main categories. With support from contractor HF and Safety Practitioners, NASA developed a means to share key HF messages with Design, Engineering, Safety, Project Management, and others. It is often difficult to complete timely assessments due to the large volume of HF information. The HF Checklist evolved over time into a simple way to consider the most important concepts. A wide audience can apply the checklist early in design or through planning phases, even before hardware or processes are finalized or implemented. The checklist is a good place to start to supplement formal HF evaluation. The HF Checklist was based on many Space Shuttle processing experiences and lessons learned. It is now being applied to ground processing of new space vehicles and adjusted for new facilities and systems.

Human Factors; Human Systems Integration↗
NASA NTRS1995

Estimating gravity wave parameters from oblique high-frequency backscatter: Modeling and analysis

A new technique for estimating electron density perturbation amplitudes of traveling ionospheric disturbances (TIDs), using HF radar data, is presented. TIDs are observed in HF radar data as enhancements of the ground-scattered power which propagate through the radar's field of view. These TIDs are the ionospheric manifestation of atmospheric acoustic-gravity waves. TID electron density perturbation amplitudes were estimated by simulating the radar returns, using HF ray tracing through a model ionosphere perturbed by a model gravity wave. The simulation determined the return power in the ground-scattered portion of the signal as a function of range, and this was compared to HF radar data from the Goose Bay HF radar at a time when evidence of gravity waves was present in the data. By varying the amplitude of the electron density perturbation in the model it was possible to estimate the perturbation of the actual wave. It was found that the perturbations that are observed by the Goose Bay HF radar are of the order of 20% to 35%. It was also found that the number of observable power enhancements, and the relative amplitudes of these enhancements, depended on the vertical thickness of the gravity wave's source region. From the simulations and observations it was estimated that the source region for the case presented here was approximately 20 km thick. In addition, the energy in the wave packet was calculated and compared to an estimate of the available energy in the source region. It was found that the wave energy was about 0.2% of the estimated available source region energy.

Bristow, W. A.↗
NASA NTRS1995

Radar investigation of barium releases over Arecibo Observatory, Puerto Rico

The NASA Combined Release and Radiation Effects Satellite (CRRES) El Coqui rocket campaign was successfully carried out in Puerto Rico during the period 18 May through 12 July 1992. This report describes five chemical release experiments in the upper ionosphere supported by Geospace Research, Inc. during the El Coqui campaign. Additional spin-off science is also discussed. The El Coqui releases are designated AA-1 (rocket 36-082), AA-2 (rocket 36-081), AA-3b (rocket 36-064), AA-4 (rocket 36-065), and AA-7 (rocket 36-083). Particular attention is paid to releases AA-2 and AA-4. These two experiments involved the illumination of ionospheric release regions with powerful high-frequency (HF) radio waves transmitted from the Arecibo HF facility. In the AA-2 experiment, microinstabilities excited by the HF wave in a Ba(+) plasma were examined. This release yielded a smooth plasma cloud that helped clarify several fundamental issues regarding the physics of wave plasma instabilities. During AA-2 extremely strong HF-induced Langmuir turbulence was detected with the Arecibo 430 MHz radar. CF3Br was released in the AA-4 study to create an ionospheric hole that focused the HF beam. This experiment successfully explored wave-plasma coupling in an O(+) ionosphere under conditions of very high HF electric field strengths.

Djuth, Frank T.↗
NASA NTRS2007

Toxicity and Radioprotective Effects of DF-1 and Carbon Nanotubes in Human Lung and Liver Cell Lines

The DF-1 compound, a sixty carbon fullerene derivative, has been shown to have antioxidant effects and is thought to possibly help mediate the effects of radiation on cells. While this is potentially useful, it is important to first understand the effect that the DF-1 has on the cells and the growth rate of the cells to determine if the material itself has any innate toxicity. A growth curve was established for both HF-19 cells, human fibroblasts, and HepG2 cells, liver tissue cells in the presence of two different concentrations of DF-1 and for untreated controls. The cells were plated in triplicate in 60mm dishes and were lifted and counted with a hemocytometer daily for one week. The growth curve data for the HF-19 cells show that while the low concentration of DF-1 had no apparent effect on the growth rate, the high concentration of DF-1 appeared to severely inhibit the growth of the HF-19 cells. The growth curve data for the HepG2 cells shows that the DF-1 compound had no significant effect on the rate at which the cells grew. A second growth curve study was performed plain carbon nanotubes, but with only 24 hour exposure to a high and low concentration of material. The carbon nanotubes are another carbon compound similar to DF-1, but in the shape of a tube, rather than a ball. We hypothesize that nanotubes may also mediate the effect of radiation on cells. This time, nanotubes did not showed any significant effect on the growth rate HF-19 or HepG2 cells. A third growth curve study is underway to further determine the effect of DF-1, nanotubes, and a derivatized nanotube (BHT-nanotubes). This derivatized nanotube has been modified with a compound that is known to be very effective at neutralizing free radicals. We expect that the high concentration of DF-1 and possibly the nanotubes and BHT-nanotubes may inhibit the growth of the HF-19 cells while the low concentration will resemble the growth of the control. We also hypothesize that there will be no significant effect on the growth of the HepG2 cells by the nanotubes, and BHT-nanotubes. In order to examine the usefulness of the DF-1, nanotubes, and BHT-nanotubes in mediating the effects of radiation a clonogenic assay is being performed. The HF-19 cells were plated in different concentrations of the various compounds and exposed to varying amounts of radiation. The cells are being allowed to grow in a small enough concentration so that the ability of each cell to divide can be seen by the development of cell clusters. By comparing the irradiated control to the un-irradiated control the effects of radiation alone can be seen. By comparing the compound treated irradiated cells to the irradiated control the usefulness of each compound can be seen. It is thought that Amifostine, the positive control, will have more regularly dividing cells then the irradiated control, as will DF-1 and hopefully both nanotube materials as well.

Burgoyne, Madeline↗
NASA NTRS1973

Composition effects on mechanical properties of tungsten-rhenium-hafnium-carbon alloys

The mechanical properties of rod and sheet fabricated from arc melted W-4Re-Hf-C alloys containing up to about 0.8 mol percent hafnium carbide (HfC) were evaluated in the as-worked condition. The DBTT's of electropolished bend and tensile specimens were independent of HfC content in this range but dependent on excess Hf or C above that required for stoichiometric HfC. Low temperature ductility was a maximum at Hf contents slightly in excess of stoichiometric. Variations in high temperature strength were also dependent on excess Hf and C. Maximum creep strengthening also occurred at Hf contents in excess of stoichiometric. Analysis of extracted second phase particles indicated that creep strength was reduced by increasing WC content in the HfC particles.

Witzke, W. R.↗
NASA NTRS1975

Compositional effects on mechanical properties of hafnium-carbide-strengthened molybdenum alloys

The mechanical properties of swaged rod thermomechanically processed from arc melted Mo-2Re-Hf-C alloys containing as much as 0.9-mol% HfC were evaluated. The low-temperature ductilities of these alloys were not influenced by the amount of HfC present but by the amount of Hf in excess of stoichiometry. Maximum ductility occurred at 0.2- to 0.3-at.% excess Hf. At 0.3- to 0.5-mol% HfC, alloy strength varied directly with the Mo content of extracted carbide particles, both decreasing as the amount of excess Hf increased. Additions of 2-at.% Re had little effect on strength or ductility. Tensile and creep strengths of Mo-2Re-0.7Hf-0.5C alloy equaled or exceeded those of other high strength Mo alloys.

Witzke, W. R.↗
NASA NTRS1976

Composition effects on mechanical properties of HfC-strengthened molybdenum alloys

The mechanical properties of swaged rod thermomechanically processed from arc-melted Mo-2Re-Hf-C alloys containing as much as 0.9 mol pct HfC have been evaluated. The low temperature ductilities of these alloys were not influenced by the amount of HfC present but by the amount of Hf in excess of stoichiometry. Maximum ductility occurred at 0.2 to 0.3 at. pct excess Hf. At 0.3 to 0.5 mol pct HfC, alloy strength varied directly with the Mo content of extracted carbide particles, both decreasing as the amount of excess Hf increased. Additions of 2 at. pct Re had little effect on strength or ductility. Tensile and creep strengths of Mo-2Re-0.7Hf-0.5C alloy equaled or exceeded those of other high strength Mo alloys.

Witzke, W. R.↗
NASA NTRS1979

Material science and solid state physics studies with positive muon spin precession

The hyperfine field on the muon, B sub hf, at interstitial sites in dilute Fe(Al) alloys was measured for four different concentrations of Al and as a function of temperature by the muon spin rotation method. The magnitude of B sub hf, which is negative, decreases at rates ranging from 0.09 + or - 0.03% per at.% Al at 200 K to an asymptotic limit of 0.35 + or - far above 440 K. This behavior shows that sites near the Al impurity are weakly repulsive to the muon, with an interaction potential of 13 + or - 3 meV. In order to fit the temperature dependence of the hyperfine field, it is necessary to hypothesize the existence of a small concentration of unidentified defects, possibly dislocations, which are attractive to the muon. Although the Al impurity acts as a non-magnetic hole in the Fe lattice, the observed decrease in B sub hf is only 35% of the decrease in the bulk magnetization. It is concluded that B sub hf is determined mainly by the enhanced screening of conduction electrons in Fe and Fe(Al). Since the influence of the Al impurity on the neighboring Fe monents is very small, most of the change in B sub hf is therefore attributed to the increase in conduction electron polarization of the Al impurity.

Stronach, C. E.↗
NASA NTRS1979

The distribution of zirconium and hafnium in terrestrial rocks, meteorites and the moon

It is shown that Zr and Hf are not always fractionated in terrestrial igneous differentiation or regional metamorphism. Data do support a Zr-Hf fractionation in the differentiation of the alkali olivine magma at St. Helena Island. A strong Zr-Hf fractionation exists among lunar rocks and minerals. Ilmenite is an excellent concentrator of Zr and Hf and always exhibits high Zr/Hf ratios. Chondritic meteorites exhibit rather uniform Zr abundances and Zr/Hf ratios but a distinct Zr-Hf fractionation is observed among the eucrite and diogenite achondrites.

Ehmann, W. D.↗
NASA NTRS1980

Hafnium isotope variations in oceanic basalts

Hafnium isotope ratios generated by the beta(-) decay of Lu-176 are investigated in volcanic rocks derived from the suboceanic mantle. Hf-176/Hf-177 and Lu/Hf ratios were determined to precisions of 0.01-0.04% and 0.5%, respectively, by routine, low-blank chemistry. The Hf-176/Hf-177 ratio is found to be positively correlated with the Nd-143/Nd-144 ratio and negatively correlated with the Sr-87/Sr-86 and Pb-206/Pb-204 ratios, and to increase southwards along the Iceland-Reykjanes ridge traverse. An approximate bulk earth Hf-176/Hf-177 ratio of 0.28295 is inferred from the bulk earth Nd-143/Nd-144 ratio, which requires a bulk earth Lu/Hf ratio of 0.25, similar to the Juvinas eucrite. Midocean ridge basalts are shown to account for 60% of the range of Hf isotope ratios, and it is suggested that Lu-Hf fractionation is decoupled from Sm-Nd and Rb-Sr fractionation in very trace-element-depleted source regions as a result of partial melting.

Patchett, P. J.↗
NASA NTRS1982

Phase perturbation measurements through a heated ionosphere

High frequency radiowaves incident on an overdense (i.e., HF-frequency penetration frequency) ionosphere produce electron density irregularities. The effect of such ionospheric irregularities on the phase of UHF-radiowaves was determined. For that purpose the phase of radiowaves originating from celestial radio sources was observed with two antennas. The radiosources were chosen such that the line of sight to at least one of the antennas (usually both) passed through the modified volume of the ionosphere. Observations at 430 MHz and at 2380 MHz indicate that natural irregularities have a much stronger effect on the UHF phase fluctuations than the HF-induced irregularities for presently achieved HF-power densities of 20-80 uW/sq m. It is not clear whether some of the effects observed are the result of HF-modification of the ionosphere. Upper limits on the phase perturbations produced by HF-modification are 10 deg at 2380 MHz and 80 deg at 430 MHz.

Frey, A.↗
NASA NTRS1983

A human factors methodology for real-time support applications

A general approach to the human factors (HF) analysis of new or existing projects at NASA/Goddard is delineated. Because the methodology evolved from HF evaluations of the Mission Planning Terminal (MPT) and the Earth Radiation Budget Satellite Mission Operations Room (ERBS MOR), it is directed specifically to the HF analysis of real-time support applications. Major topics included for discussion are the process of establishing a working relationship between the Human Factors Group (HFG) and the project, orientation of HF analysts to the project, human factors analysis and review, and coordination with major cycles of system development. Sub-topics include specific areas for analysis and appropriate HF tools. Management support functions are outlined. References provide a guide to sources of further information.

Murphy, E. D.↗
NASA NTRS1985

The temporal evolution of 3-m striations in the modified ionosphere

Experiments were performed at Arecibo, Puerto Rico, to investigate the evolution times of 3-m field-aligned striations produced in the ionosphere by powerful high-frequency (HF) radio waves. The results of this investigation are now summarized. First, the striations' rise times are dependent on the HF electric field. The E region data suggest that this dependence is nonlinear. Second, the threshold value of the HF electric field required to produce detectable striations was experimentally determined. At threshold the component of the HF electric field perpendicular to the geomagnetic field is calculated to be 0.09 V/m in the F region and 0.37 V/m in the E region. Third, both the E and the F region data verify theoretical predictions that the striations' decay times are directly proportional to the electron diffusion across B. Finally, a one-to-one correspondence between the growth of the 3-m striations and the decline of the HF-enhanced plasma line during overshoot is sometimes observed.

Coster, A. J.↗