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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Chemistry of the moon's surface

The chemical composition of the lunar surface is discussed on the basis of analyses of Apollo samples. Three new minerals, armalcolite, pyroxferroite and tranquillityite, high abundances of Ti, Zr, Sr, Y, Nb, U and Th, and a predominance of radiogenic isotopes of Pb are noted as the prominent features unraveled by sample analysis. Evidence is indicated to support the conclusion that the lunar rocks investigated are products of partial fusion and magmatic crystallization modified in much of the material by mechanical breakup and shock melting, and containing a small amount of meteoritic material. It is inferred from the results that the surface rocks are igneous in origin and that the moon has been a passive object since 3000 million years ago.

Mason, B.↗
NASA NTRS1992

Flow diagnostics of an arcjet using laser-induced fluorescence

A diagnostic has been developed to measure velocity and translational temperature in the plume of an arcjet thruster. Laser induced fluorescence with a narrowband CW laser is used to probe the Balmer alpha transition of excited atomic hydrogen. The velocity is determined from the Doppler shift of the fluorescence excitation spectrum while temperature is inferred from its shape. Analysis shows that while Doppler broadening is the only significant broadening mechanism, the fine structure of the transition must be accounted for. Near the exit plane, axial velocities vary from 4 to 14 km/s; radial velocities vary from 0 to 4 km/s; and swirl velocities are shown to be relatively small. Temperatures from 1000 to 5000 K indicate high dissociation fractions.

Liebeskind, John G.↗
NASA NTRS1993

The distant future of solar activity: A case study of Beta Hydri. III - Transition region, corona, and stellar wind

The paper investigates the secular decay of solar-type activity through a detailed comparison of the present sun with the very old solar-type star, Beta Hyi, taken as a proxy of the future sun. Analyses of successive atmospheric layers are presented, with emphasis of the outermost parts. The FUV emission lines for the transition zone are among the faintest so far seen in any solar-type star. The coronal soft X-ray spectrum was measured through different filters on EXOSAT and compared to simulated X-ray observations of the sun seen as a star. The flux from Beta Hyi is weaker than that from the solar corona and has a different spectrum. It is inferred that a thermally driven stellar wind can no longer be supported, which removes the mechanism from further rotational braking of the star through a magnetic stellar wind.

Dravins, D.↗
NASA NTRS1985

A knowledge based software engineering environment testbed

The Carnegie Group Incorporated and Boeing Computer Services Company are developing a testbed which will provide a framework for integrating conventional software engineering tools with Artifical Intelligence (AI) tools to promote automation and productivity. The emphasis is on the transfer of AI technology to the software development process. Experiments relate to AI issues such as scaling up, inference, and knowledge representation. In its first year, the project has created a model of software development by representing software activities; developed a module representation formalism to specify the behavior and structure of software objects; integrated the model with the formalism to identify shared representation and inheritance mechanisms; demonstrated object programming by writing procedures and applying them to software objects; used data-directed and goal-directed reasoning to, respectively, infer the cause of bugs and evaluate the appropriateness of a configuration; and demonstrated knowledge-based graphics. Future plans include introduction of knowledge-based systems for rapid prototyping or rescheduling; natural language interfaces; blackboard architecture; and distributed processing

Gill, C.↗
NASA NTRS1983

Broad-band gain in optically pumped S2

The broad fluorescence spectrum and Franck-Condon shift of the B-X system of S2 are exploited in broad-band-gain experiments using the absorption of 308-nm XeCl excimer radiation to pump the level (upsilon-prime = 4) in an S2 vapor with and without Ar. The fluorescence spectra are examined to determine the effects of gas collisions, and the intense near-UV and visible bands are attributed to the redistribution of the population among the upsilon-prime levels resulting from S2-Ar collisions. Broad-band gain is observed on the rare-gas relaxation bands (2,17) (about 475 nm) and (3,18) (480 nm), while absorption is found in the (0,6), (0,7), and (0,8) near-UV (about 360-380-nm) bands where a transient population cascading down the X-state manifold fills the lower levels. It is inferred from the achievement of gain over much of the S2 fluorescence bandwidth that nonselective pumping mechanisms like discharges, solar energy, or flashlamps can be used with S2 as the tunable, chemically stable 'dye'.

Epler, J. E.↗
NASA NTRS1989

Redshifts derived from gamma-ray burst spectra are inconclusive

If the reported large widths of the 'annihilation' features in gamma-ray burst spectra are real, the inferred value of the redshift can be as high as z = 0.8, depending on the emission mechanism. A model is presented in which a broad annihilation line peaking at 400 keV corresponds to a Doppler blueshift of the emitting region of z = -0.3. The prevalent view that the observed line centers of burst annihilation features imply emission from the surface of a nonrotating neutron star is not supported by the available data. However, emission from rapidly rotating neutron stars is a viable possibility.

Kluzniak, Wlodzimierz↗
NASA NTRS1988

Magnetospheric ULF waves observed during the major magnetospheric compression of November 1, 1984

The magnetospheric ULF waves observed during the magnetospheric compression event of November 1, 1984, were investigated using the magnetic field and medium-energy ion data obtained by the AMPTE Charge Composition Explorer. The electric field of ULF waves was inferred from the particle data, using a method developed on the basis of the gyration acceleration mechanism. Three types of waves were found: (1) a 10-15-min wave with perturbations in the magnetic field intensity and in the flux of ions; (2) a 3-5-min standing Alfven wave with perturbations in the azimuthal magnetic field component and in the radial component of the electric field; and (3) a 2-5-min irregular disturbance near the magnetopause, which involves all components of the magnetic field and the intensity of the ion flux. The origins of these waves are discussed.

Takahashi, K.↗
NASA NTRS1989

Nonlocal thermodynamic equilibrium effects in stratospheric HF by collisional energy transfer from electronically excited O2 and implications for infrared remote sensing

A possible nonlocal thermodynamic equilibrium (non-LTE) effect involving stratospheric HF arising from the direct photochemical excitation of vibrationally excited HF by collisional energy transfer from electronically excited O2 is presented. Although this non-LTE effect is smaller that one associated with the direct solar excitation of both HF(nv = 1) and HF(nv = 2), calculations show that inclusion of the mechanism into retrieval algorithms is necessary if correct daytime upper stratosphere HF profiles are to be inferred in future IR thermal emission measurements.

Kaye, Jack A.↗
NASA NTRS1992

Dark material in the polar layered deposits on Mars

The Martian polar layered deposits probably record periodic variations in the deposition of dust and ice caused by climate changes over the past 10 to 100 million years. The polar layered deposits appear to be the source of dark, saltating material that has been distributed over the surface of Mars, but the mechanisms by which this material is incorporated and eroded from the layered deposits is unknown. These mechanisms must be understood before the processes that formed and modified the layered deposits can be inferred and related to Martian climate changes. In summary, weathering of the Martian layered deposits by sublimation of water ice may account for the geologic relationships observed in the Martian polar regions. The non-volatile components of the layered deposits appears to consist mainly of bright red dust, with small amounts of dark dust or sand. Alternatively, dark sand-sized basaltic particles may occasionally be transported onto the layered deposits, forming thin layers. Once eroded, particles of either type may saltate to form the dark dunes found in both polar regions.

Herkenhoff, Ken↗
NASA NTRS1999

Relaxation from Steady States Far from Equilibrium and the Persistence of Anomalous Shock Behavior in Weakly Ionized Gases

The decay of anomalous effects on shock waves in weakly ionized gases following plasma generator extinction has been measured in the anticipation that the decay time must correlate well with the relaxation time of the mechanism responsible for the anomalous effects. When the relaxation times cannot be measured directly, they are inferred theoretically, usually assuming that the initial state is nearly in thermal equilibrium. In this paper, it is demonstrated that relaxation from any steady state far from equilibrium, including the state of a weakly ionized gas, can proceed much more slowly than arguments based on relaxation from near equilibrium states might suggest. This result justifies a more careful analysis of the relaxation times in weakly ionized gases and suggests that although the experimental measurements of relaxation times did not lead to an unambiguous conclusion, this approach to understanding the anomalous effects may warrant further investigation.

Rubinstein, Robert↗
NASA NTRS2003

Volatile Cycling and Layering on Mars: Observations, Theory and Modeling

With the release of Mars Odyssey Gamma Ray Spectrometer (GRS) results, which indicate the presence of vast reservoirs of near-surface ice in the martian polar regions, we are presented with an exquisite dilemma. These deposits, which are present as far down as 60 deg. latitude in both hemispheres, are consistent with the suggestion of thermal models that ice will be best protected in these extended regions during periods of higher obliquity. However, the current paradigm regarding the placement of these deposits, i.e., diffusive deposition of water vapor, appears to be inconsistent with the large volume mixing ratios (approx. 70%) inferred from the GRS data. This apparent conflict argues that diffusion alone cannot be the primary mechanism for the creation of these reservoirs, and that an alternate, large-scale process should be considered.

M A Mischna↗
NASA NTRS2003

Tether-Cutting Energetics of a Solar Quiet Region Prominence Eruption

We study the morphology and energetics of a slowly-evolving quiet region solar prominence eruption occurring on 1999 February 8-9 in the solar north polar crown region, using soft X-ray data from the soft X-ray telescope (SXT) on Yohkoh and Fe xv EUV 284 A data from the EUV Imaging Telescope (EIT) on SOHO. After rising at approx. 1 km/s for about six hours, the prominence accelerates to a velocity of approx. 10 km/s, leaving behind EUV and soft X-ray loop arcades of a weak flare in its source region. Intensity dimmings occur in the eruption region cospatially in EUV and soft X-rays, indicating that the dimmings result from a depletion of material. Over the first two hours of the prominence s rapid rise, flare-like brightenings occur beneath the rising prominence which may correspond to "tether cutting" magnetic reconnection. These brightenings have heating requirements of up to approx. 10(exp 28)-10(exp 29) ergs, and this is comparable to the mechanical energy required for the rising prominence over the same time period. If the ratio of mechanical energy to heating energy remains constant through the early phase of the eruption, then we infer that coronal signatures for the tether cutting may not be apparent at or shortly after the start of the fast phase in this or similar low-energy eruptions, since the plasma-heating energy levels would not exceed that of the background corona.

Sterling, Alphonse C.↗
NASA NTRS2003

Tether-Cutting Energetics of a Solar Quiet Region Prominence Eruption

We study the morphology and energetics of a slowly evolving quiet-region solar prominence eruption occurring on 1999 February 8-9 in the solar north polar crown region, using soft X-ray data from the soft X-ray telescope (SXT) on Yohkoh and Fexv EUV 284 Angstrom data from the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO). After rising at approximately equal to l kilometer per second for about six hours, the prominence accelerates to a velocity of approximately equal to 10 kilometers per second, leaving behind EUV and soft X-ray loop arcades of a weak flare in its source region. Intensity dimmings occur in the eruption region cospatially in EUV and soft X-rays, indicating that the dimmings result from a depletion of material. Over the first two hours of the prominences rapid rise, flare-like brightenings occur beneath the rising prominence that might correspond to tether-cutting magnetic reconnection. These brightenings have heating requirements of up to approximately 10(exp 28)-10(exp 29) ergs, and this is comparable to the mechanical energy required for the rising prominence over the same time period. If the ratio of mechanical energy to heating energy remains constant through the early phase of the eruption, then we infer that coronal signatures for the tether cutting may not be apparent at or shortly after the start of the fast phase in this or similar low-energy eruptions, since the plasma-heating energy levels would not exceed that of the background corona.

Sterling, Alphonse C.↗
NASA NTRS2004

Crustal Deformation and the Seismic Cycle across the Kodiak Islands, Alaska

The Kodiak Islands are located approximately 130 to 250 km from the Alaska-Aleutian Trench where the Pacific plate is underthrusting the North American plate at a rate of about 57 mm/yr. The southern extent of the 1964 Prince William Sound (${M-w}$ = 9.2) earthquake rupture occurred offshore and beneath the eastern portion of the Kodiak Islands. Here we report GPS results (1993-2001) from northern Kodiak Island that span the transition between the 1964 uplift region along the eastern coast and the region of coseismic subsidence further inland. The horizontal velocity vectors range from 22.9 $\pm$ 2.2 mm/yr at N26.3$\deg$W $\pm$ 2.5$\deg$, about 150 km from the trench, to 5.9 $\pm$ 1.3 mm/yr at N65.9$\deg$W $\pm$ 6.6$\deg$, about 190 km from the trench. Near the northeastern coast of Kodiak the velocity vector above the shallow, locked main thrust zone is between the orientation of PCFC-NOAM plate motion (N22$/deg$W) and the trench-normal (N3O$\deg$W). Further west, our geodetic results suggest the accumulation of shear strain that will be released eventually as left-lateral motion on upper plate faults such as the Kodiak Island fault. These results are consistent with the hypothesis that the difference between the Pacific-North American plate motion and the orientation of the down going slab would lead to 4-8 mm/yr of left-lateral slip. Short-term geodetic uplift rates range from 2 - 14 mm/yr, with the maximum uplift located near the axis of maximum subsidence during the 1964 earthquake. We evaluated alternate interseismic models for Kodiak to test the importance of various mechanisms responsible for crustal deformation rates. These models are based on the plate interface slip history inferred from earlier modeling of coseismic and post-seismic geodetic results. The horizontal (trench perpendicular) and vertical deformation rates across Kodiak are consistent with a model that includes the viscoelastic response to : (1) a downgoing Pacific plate interface that is locked at shallow depths,(2) coseismic slip in the 1964 and (3) interseismic creep below the seismogenic zone. The change in orientation of the horizontal velocity vector occurs down-dip from the locked main thrust zone. In southern Kodiak, the coseismic slip in the 1964 earthquake was smaller than in the northern Kodiak region; yet, the horizontal, interseismic velocities as a function of distance from the trench are comparable to those in northern Kodiak. Based on the earthquake history prior to, and following the 1964 earthquake, we hypothesize that the plate interface in southern Kodiak slips in more frequent large earthquakes than in northern Kodiak.

Sauber, Jeanne↗
NASA NTRS2018

Element Abundance Ratios in the Quiet Sun Transition Region

Element abundance ratios of magnesium to neon (Mg/Ne) and neon to oxygen (Ne/O) in the transition region of the quiet Sun have been derived by re-assessing previously published data from the Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory in the light of new atomic data. The quiet Sun Mg/Ne ratio is important for assessing the effect of magnetic activity on the mechanism of the first ionization potential (FIP) effect, while the Ne/O ratio can be used to infer the solar photospheric abundance of neon, which cannot be measured directly. The average Mg/Ne ratio is found to be 0.52+/-0.11, which applies over the temperature region 0.2-0.7MK, and is consistent with the earlier study. The Ne/O ratio is, however, about 40%larger, taking the value 0.24+/-0.05 that applies to the temperature range 0.08-0.40MK. The increase is mostly due to changes in ionization and recombination rates that affect the equilibrium ionization balance. If the Ne/O ratio is interpreted as reflecting the photospheric ratio, then the photospheric neon abundance is 8.08+/-0.09 or 8.15+/-0.10 (on a logarithmic scale for which hydrogen is 12), according to whether the oxygen abundances of M.Asplund et al. or E.Caffau et al. are used. The updated photospheric neon abundance implies a Mg/Ne FIP bias for the quiet Sun of 1.6+/-0.6.

transition region↗
NASA NTRS2004

Deep Moonquakes: Remaining Problems

We have recently reexamined more than 9000 United States previously unidentified seismic events catalogued during the Apollo landing missions and positively identified for the first time about 30 deep moonquake nests on the far side of the Moon. Although only a few of them are currently locatable, the relative arrival times among stations for the rest and presence or absence of seismic signals at particular stations suggest that either (a) the region within about $40\deg$ of the antipode is aseismic or (b) the deep interior of the Moon severely attenuates or deflects seismic waves. Aside from the obvious question of how to distinguish between such hypothetical models, this effort raised several more general questions concerning the use of deep moonquake signals to infer the structure and dynamics of the deep interior of the Moon. Among more important ones are: (1) How reliable are the seismic arrival picks from which to compute the seismic velocity variations in the Moon? (2) How do the possible lateral variations in seismic velocity affect the computed radial variation in seismic velocity at depth? (3) Can we tell more about the distribution and mechanism of deep moonquakes from the newly expanded database of identified deep moonquakes? Questions (1) and (2) are especially important because the inferred deep internal structure of the Moon depends critically on their answers. Answering these questions may demand additional data collected on future lunar missions, but some may be resolved with further examination of the existing data.

Nakamura, Y.↗
NASA NTRS1973

Failure analysis of aluminum alloy components

Analysis of six service failures in aluminum alloy components which failed in aerospace applications is reported. Identification of fracture surface features from fatigue and overload modes was straightforward, though the specimens were not always in a clean, smear-free condition most suitable for failure analysis. The presence of corrosion products and of chemically attacked or mechanically rubbed areas here hindered precise determination of the cause of crack initiation, which was then indirectly inferred from the scanning electron fractography results. In five failures the crack propagation was by fatigue, though in each case the fatigue crack initiated from a different cause. Some of these causes could be eliminated in future components by better process control. In one failure, the cause was determined to be impact during a crash; the features of impact fracture were distinguished from overload fractures by direct comparisons of the received specimens with laboratory-generated failures.

Johari, O.↗
NASA NTRS1977

Diterpenoid compounds and other lipids in deep-sea sediments and their geochemical significance

Cyclic diterpenoid compounds have been found by various investigators in the geosphere (e.g., fossil resins, coals, soil, shale, and deep-sea sediments). These compounds occur in significant amounts only in higher plants and are therefore potential markers of terrigenous plant lipids. Diterpenoids with the abietane skeleton (mainly dehydroabietic acid) have been identified in the lipids of sediment samples from the northeast Pacific Ocean, Black Sea, and North Atlantic Ocean. The presence of these resin-derived compounds was correlated with the terrigenous clay components and with the presence of pollen. The presence of polycyclic diterpenoids was also correlated with the distribution patterns and inferred sources of other sediment lipid constituents. Potamic transport, followed by turbidite redistribution, is the probable input mechanism of these resin-derived compounds to the deep-sea sediments. These diterpenoids appear to be excellent biological markers of resinous higher plants.

Simoneit, B. R. T.↗