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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

SAGE III Aerosol Extinction Validation in the Arctic Winter: Comparisons with SAGE II and POAM III

The use of SAGE III multiwavelength aerosol extinction coefficient measurements to infer PSC type is contingent on the robustness of both the extinction magnitude and its spectral variation. Past validation with SAGE II and other similar measurements has shown that the SAGE III extinction coefficient measurements are reliable though the comparisons have been greatly weighted toward measurements made at mid-latitudes. Some aerosol comparisons made in the Arctic winter as a part of SOLVE II suggested that SAGE III values, particularly at longer wavelengths, are too small with the implication that both the magnitude and the wavelength dependence are not reliable. Comparisons with POAM III have also suggested a similar discrepancy. Herein, we use SAGE II data as a common standard for comparison of SAGE III and POAM III measurements in the Arctic winters of 2002/2003 through 2004/2005. During the winter, SAGE II measurements are made infrequently at the same latitudes as these instruments. We have mitigated this problem through the use potential vorticity as a spatial coordinate and thus greatly increased the number of coincident events. We find that SAGE II and III extinction coefficient measurements show a high degree of compatibility at both 1020 nm and 450 nm except a 10-20% bias at both wavelengths. In addition, the 452 to 1020-nm extinction ratio shows a consistent bias of approx. 30% throughout the lower stratosphere. We also find that SAGE II and POAM III are on average consistent though the comparisons show a much higher variability and larger bias than SAGE II/III comparisons. In addition, we find that the two data sets are not well correlated below 18 km. Overall, we find both the extinction values and the spectral dependence from SAGE III are robust and we find no evidence of a significant defect within the Arctic vortex.

Thomason, L. W.↗
NASA NTRS2016

Holocene Accumulation and Ice Flow near the West Antarctic Ice Sheet Divide Ice Core Site

The West Antarctic Ice Sheet Divide Core (WDC) provided a high-resolution climate record from near the Ross-Amundsen Divide in Central West Antarctica. In addition, radar-detected internal layers in the vicinity of the WDC site have been dated directly from the ice core to provide spatial variations in the age structure of the region. Using these two data sets together, we first infer a high-resolution Holocene accumulation-rate history from 9.2 thousand years of the ice-core timescale and then confirm that this climate history is consistent with internal layers upstream of the core site. Even though the WDC was drilled only 24 kilometers from the modern ice divide, advection of ice from upstream must be taken into account. We evaluate histories of accumulation rate by using a flowband model to generate internal layers that we compare to observed layers. Results show that the centennially averaged accumulation rate was over 20 percent lower than modern at 9.2 thousand years before present (B.P.), increased by 40 percent from 9.2 to 2.3 thousand years B.P., and decreased by at least 10 percent over the past 2 thousand years B.P. to the modern values; these Holocene accumulation-rate changes in Central West Antarctica are larger than changes inferred from East Antarctic ice-core records. Despite significant changes in accumulation rate, throughout the Holocene the regional accumulation pattern has likely remained similar to today, and the ice-divide position has likely remained on average within 5 kilometers of its modern position. Continent-scale ice-sheet models used for reconstructions of West Antarctic ice volume should incorporate this accumulation history.

ice↗
NASA NTRS2004

Meridional Variations of C2H2 and C2H6 in Jupiter's Atmosphere from Cassini CIRS Infrared Spectra

The abundances of hydrocarbons such as acetylene (C2H2) and ethane (C2H6) in Jupiter's atmosphere are important physical quantities, constraining our models of the chemical and dynamical processes. However, our knowledge of these quantities and their vertical and latitudinal variations has remained sparse. The flyby of the Cassini spacecraft with Jupiter at the end of 2000 provided an excellent opportunity to observe the infrared spectrum with the Composite Infrared Spectrometer (CIRS) instrument, mapping the spatial variation of emissions from 10-1400 cm-1. CIRS spectra taken at the highest resolution (0.5 cm-1) in early December 2000 have been analysed to infer atmospheric temperatures in the stratosphere at 0.5-20 mbar via the v4 of CH4, and in the troposphere at 100-400 mbar, via the hydrogen collision-induced continuum absorption at 600-800 cm. Simultaneously, we have searched for meridional abundance variations in C2H2 and C2H6 via the v5 and vg bands respectively. Tropospheric absorption and stratospheric emission are highly anti-correlated at the CIM resolution, introducing a non-uniqueness into the retrievals, which means that vertical gradient and column abundance cannot be simultaneously found without additional constraints. If we assume the profile shapes from photochemical model calculations, we show that the column abundance of C2H2 must decrease sharply towards the poles, while C2H6 is constant or slightly increasing. The relevance of these results to current photochemical and dynamical knowledge of Jupiter's atmosphere is discussed.

Nixon, C. A.↗
NASA NTRS2002

REE in Shergottite Augites and Whole Rocks

Redox variations have been reported among the shergottites. Eu and Gd were used in partitioning experiments designed for the LEW86010 angrite, to infer a range of fO2 for the shergottites. Inferred fO2 using equilibria between Fe-Ti oxides was used. There is fairly good agreement between the Fe- Ti oxide determinations and the estimates from Eu anomalies in terms of which meteorites are more or less oxidized. The Eu anomaly technique and the Fe-Ti oxide technique both essentially show the same trend, with Shergotty and Zagami being the most oxidized and QUE94201 and DaG 476 being the most reduced. Thus, the variation in fO2 appears to be both real and substantive. However, although the redox trends indicated by the two techniques are similar, there is as much as a two log unit offset between the results of presented. One explanation for this offset is that the Eu calibration used for the shergottites was actually designed for the LEW86010 angrite, a silica-undersaturated basalt whose pyroxene (diopside) compositions are rather extreme. To correct this, a set of experiments were conducted on the redox relationship of Eu partitioning relative to Sm and Gd for pyroxene and melt compositions more relevant to Martian meteorites. We have taken the experimentally determined relationship between (Sm,Eu,Gd) and fO2 and applied it to augite Eu and Gd data for the basaltic Shergottites as well as previously unreported augite Sm data.

Musselwhite, D. S.↗
NASA NTRS2007

An Alternative Interpretation of the Relationship between the Inferred Open Solar Flux and the Interplanetary Magnetic Field

Photospheric observations at the Wilcox Solar Observatory (WSO) represent an uninterrupted data set of 32 years and are therefore unique for modeling variations in the magnetic structure of the corona and inner heliosphere over three solar cycles. For many years, modelers have applied a latitudinal correction factor to these data, believing that it provided a better estimate of the line-of-sight magnetic field. Its application was defended by arguing that the computed open flux matched observations of the interplanetary magnetic field (IMF) significantly better than the original WSO correction factor. However, no physically based argument could be made for its use. In this Letter we explore the implications of using the constant correction factor on the value and variation of the computed open solar flux and its relationship to the measured IMF. We find that it does not match the measured IMF at 1 AU except at and surrounding solar minimum. However, we argue that interplanetary coronal mass ejections (ICMEs) may provide sufficient additional magnetic flux to the extent that a remarkably good match is found between the sum of the computed open flux and inferred ICME flux and the measured flux at 1 AU. If further substantiated, the implications of this interpretation may be significant, including a better understanding of the structure and strength of the coronal field and I N providing constraints for theories of field line transport in the corona, the modulation of galactic cosmic rays, and even possibly terrestrial climate effects.

Riley, Pete↗
NASA NTRSDate not supplied

Use of Design of Experiments in Determining Neural Network Architectures for Loss of Control Detection

Abstract—We describe empirical methods for selecting a neural network architecture to implement belief state inference on generic commercial transport aircraft. We highlight a case study on the planning, execution, and analysis of a set of experiments to determine the configurations of a conditional variational autoencoder (CVAE). Our main contribution is the application of a structured method that can be used for machine learning in many aerospace applications. This method optimizes the structure and training parameters of a neural network for belief state inference, using Design of Experiments (DOE) statistical methodologies. The motivation for this specific DOE analysis was to identify the appropriate hyperparameters for measuring the CVAE reconstruction probability and latent space, such that the measurements can be used to infer qualitative state changes for the aircraft. We demonstrate that this process yields information about a trained neural network’s utility for this specific application, along with a quantifiable range of certainty. We execute 84 experiments using loss-of-control flight maneuver data from the NASA T-2 aircraft, demonstrating that this empirical process allows us to construct cheap and simple models with specific attributes amenable to belief state inference in aerospace applications.

neural networks↗
NASA NTRS1990

A tomographic glimpse of the upper mantle source of magmas of the Jemez lineament, New Mexico

In this study, the lateral variations of the P wave velocity as a function of depth were examined for the regions of the Rio Grande rift and the Jemez lineament, to infer spatial distributions of partial melt in the upper mantle source zones for the rift and the lineament. The method involved measurements of teleismic P wave delays at a 22-station network followed by performing a damped least-squares three-dimensional inversion for these lateral variations. Results indicate that, directly beneath the Jemez lineament (but not beneath the Rio Grande rift), there is a 100-km-wide 1-2-percent low-P-wave-velocity feature in the depth range of 50-160 km. This implies that the volcanic potential of the Jemez lineaments continues to greatly exceed that of the Rio Grande rift.

Spence, William↗
NASA NTRS1975

OGO-6 observations of 5577 A

A brief review is given of the data obtained by the horizon-scanning 5577-A airglow photometer flown aboard OGO 6. Data are presented which show the contributions to the 5577-A emission from the F-1 region and the Chapman airglow layer. Emission rates are calculated for both regions on the basis of the dissociative-recombination and Chapman reactions, and the atomic oxygen density and downward flux are inferred from the emission rates and several assumptions concerning the temperature dependence of the rate constants. Latitude variations in the emission rates are discussed along with variations in the altitude of the 5577-A airglow. It is shown that there is a large semiannual variation in the average effective transport properties of the lower thermosphere, that the atomic oxygen profiles near 110 km suggest a maximum in eddy diffusion at about that altitude, and that systematic variations in the altitude of the atomic oxygen maximum probably do not exceed 2 km.

Donahue, T. M.↗
NASA NTRS1983

A study of the atmosphere and ionosphere using satellite observations of 300-1400 Ang airglow

A study of the O(+) ion distribution reveals that the OII 834 A emission can be used to infer the O(+) density as a function of altitude. The ion temperature was obtained from these measurements. Variations of the ion density distributions were obtained as a function of latitude. Daytime observations show that the OII 834 A emissions contain the signature of the Appleton anomary. Analysis of the 300 to 900 A auroral spectra reveals a large number of OII features. Several pairs of OII features with a common upper state were used to obtain their branching ratios and compared with laboratory observations and theoretical calculations. Evidence for OIII emissions were also found in an aurora.

Chakrabarti, S.↗
NASA NTRS1985

Effects of breaking gravity waves on the chemical composition of the mesosphere and lower thermosphere

Eddy diffusion and momentum forcing in the mesosphere and lower thermosphere arise principally from the effects of breaking gravity and waves. The propagation and dissipation of gravity waves depend strongly on season and latitude because of its relationship to the background zonal wind. These processes have significant effects on the transport of chemical species in that region, so that observations of variations in chemical constituents provide useful tracers for dynamical theory. A parameterization of gravity wave propagation and dissipation was incorporated in the coupled dynamical-chemical model to study these effects. Several easily observable airglow features of the mesosphere-thermosphere region are shown to provide sensitive indications of gravity wave influence. In particular, theoretical predictions of large seasonal and latitudinal variations in the atomic oxygen green line, the Meinal bands of excited OH, and the O3 densities inferred from O2 (delta supra 1 sub g) emission at altitudes from 75 to 90 km are shown to be in remarkably good agreement with observations. Implications of these sensitive chemical tracers for the dynamics of the mesosphere-lower thermosphere region and its relationship to gravity waves are discussed.

Solomon, S.↗
NASA NTRS2012

Origins of GEMS Grains

Interplanetary dust particles (IDPs) collected in the Earth s stratosphere contain high abundances of submicrometer amorphous silicates known as GEMS grains. From their birth as condensates in the outflows of oxygen-rich evolved stars, processing in interstellar space, and incorporation into disks around new stars, amorphous silicates predominate in most astrophysical environments. Amorphous silicates were a major building block of our Solar System and are prominent in infrared spectra of comets. Anhydrous interplanetary dust particles (IDPs) thought to derive from comets contain abundant amorphous silicates known as GEMS (glass with embedded metal and sulfides) grains. GEMS grains have been proposed to be isotopically and chemically homogenized interstellar amorphous silicate dust. We evaluated this hypothesis through coordinated chemical and isotopic analyses of GEMS grains in a suite of IDPs to constrain their origins. GEMS grains show order of magnitude variations in Mg, Fe, Ca, and S abundances. GEMS grains do not match the average element abundances inferred for ISM dust containing on average, too little Mg, Fe, and Ca, and too much S. GEMS grains have complementary compositions to the crystalline components in IDPs suggesting that they formed from the same reservoir. We did not observe any unequivocal microstructural or chemical evidence that GEMS grains experienced prolonged exposure to radiation. We identified four GEMS grains having O isotopic compositions that point to origins in red giant branch or asymptotic giant branch stars and supernovae. Based on their O isotopic compositions, we estimate that 1-6% of GEMS grains are surviving circumstellar grains. The remaining 94-99% of GEMS grains have O isotopic compositions that are indistinguishable from terrestrial materials and carbonaceous chondrites. These isotopically solar GEMS grains either formed in the Solar System or were completely homogenized in the interstellar medium (ISM). However, the chemical compositions of GEMS grains are extremely heterogeneous and seem to rule out this possibility. Based on their solar isotopic compositions and their non-solar elemental compositions we propose that most GEMS grains formed in the nebula as late-stage non-equilibrium condensates.

Messenger, S.↗
NASA NTRS2019

Hydrogen Isotope Fractionation During Impact Degassing of Pyroxene and Maskelynite in Shergottite Larkman Nunatak 06319

Hydrogen in nominally anhydrous minerals (NAMs) in meteorites provides insight to mantle sources of indigenous water on differentiated bodies: e.g. Peslier et al. 2017 [1], including Mars [2-4]. However, all meteorite samples, including Martian shergottites, record impact events as fractures, deformation, silicate darkening, shock melt veins and pockets, etc. The effect of shock on hydrogen in NAMs is poorly constrained, and must be understood prior to using these data to infer planetary indigenous water. Here we present water contents and D/H ratios (calculated as dD, i.e. the variation of the D/H ratio relative to a standard, in this case sea water "SMOW") in pyroxene, olivine and maskelynite in the olivine-phyric shergottite Larkman Nunatak 06319 (LAR 06319) as a function of proximity to impact melt. While the results suggest impact may have a role in fractionating H isotopes, the magmatic signature of H2O in Mars can be preserved in some pyroxene.

Dudley, J. M.↗
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 NTRS1979

Basaltic volcanism - The importance of planet size

The volumetrically abundant basalts on the earth, its moon, and the eucrite parent planet all have chemical compositions that are controlled to a large extent by dry, low-pressure, crystal-liquid equilibria. Since this generalization is valid for these three planetary bodies, we infer that it may also apply to the other unsampled terrestrial planets. Other characteristics of basaltic volcanism show variations which appear to be related to planet size: the eruption temperatures, degrees of fractionation, and chemical variety of basalts and the endurance of basaltic volcanism all increase with planet size. Although the processes responsible for chemical differences between basalt suites are known, no simple systematization of the chemical differences between basalts from planet to planet has emerged.

Walker, D.↗
NASA NTRS1983

The large scale dust distribution in the inner galaxy

Initial results are presented from a new large-scale survey of the first quadrant of the galactic plane at wavelengths of 160, 260, and 300 microns. The submillimeter wavelength emission, interpreted as thermal radiation by dust grains, reveals an optically thin disk of angular width about 0.09 deg (FWHM) with a mean dust temperature of 23 K and significant variation of the dust mass column density. Comparison of the dust column density with the gas column density inferred from CO survey data shows a striking spatial correlation. The mean luminosity per hydrogen atom is found to be 2.5 x 10 to the -30th W/H, implying a radiant energy density in the vicinity of the dust an order of magnitude larger than in the solar neighborhood. The data favor dust in molecular clouds as the dominant submillimeter radiation source.

Hauser, M. G.↗
NASA NTRS1988

An experimental and theoretical study of the ice accretion process during artificial and natural icing conditions

Real-time measurements of ice growth during artificial and natural icing conditions were conducted using an ultrasonic pulse-echo technique. This technique allows ice thickness to be measured with an accuracy of + or - 0.5 mm; in addition, the ultrasonic signal characteristics may be used to detect the presence of liquid on the ice surface and hence discern wet and dry ice growth behavior. Ice growth was measured on the stagnation line of a cylinder exposed to artificial icing conditions in the NASA Lewis Icing Research Tunnel (IRT), and similarly for a cylinder exposed in flight to natural icing conditions. Ice thickness was observed to increase approximately linearly with exposure time during the initial icing period. The ice accretion rate was found to vary with cloud temperature during wet ice growth, and liquid runback from the stagnation region was inferred. A steady-state energy balance model for the icing surface was used to compare heat transfer characteristics for IRT and natural icing conditions. Ultrasonic measurements of wet and dry ice growth observed in the IRT and in flight were compared with icing regimes predicted by a series of heat transfer coefficients. The heat transfer magnitude was generally inferred to be higher for the IRT than for the natural icing conditions encountered in flight. An apparent variation in the heat transfer magnitude was also observed for flights conducted through different natural icing-cloud formations.

Kirby, Mark S.↗
NASA NTRS1989

VLF bursts in the night ionosphere of Venus - Estimates of the Poynting flux

Even though the Pioneer Venus plasma wave instrument returns a measure of only one component of the electric field due to waves, for the 100 Hz channel it is possible to calcualte an approximate Poynting flux of the waves by making several assumptions. When this is done the Poynting flux at lowest altitudes in a 30 Hz band centered on 100 Hz is found to be about 10 to the -7th W/sq m, independent of ionospheric conditions as indicated by the strength of the magnetic field. The local time variation of the approximate Poynting flux shows a maximum from about 2000 to 2200 LT in accord with inferences from the higher frequency channels. The observed wave energy flux is consistent with that expected from lightning given rates and flash strengths on Venus that are similar to or greater than that of the earth.

Russell, C. T.↗