Search NASA⌕ Search

SEARCH · Search NASA

Results for “source region”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Location of the radio emitting regions of interplanetary shocks

Twenty interplanetary type II radio bursts are analyzed to determine the location of the type II source region relative to the interplanetary shock. The first determination of a density-distance relationship (density model) appropriate for interplanetary type II source regions is reported. To determine source location, densities in type II source regions, derived from observed type II emission frequencies, are compared to ambient solar wind densities to determine whether source regions are in the ambient, upstream solar wind or in the compressed plasma behind the shock. Densities in the ambient solar wind upstream of each shock are computed by using a simple model to extrapolate solar wind plasma densities measured at 1 AU back to the shock front. Densities in the type II source regions are found to be enhanced relative to densities in the ambient solar wind by a factor which is close to the average shock density compression ratio. The simplest interpretation of this result is that the source is located in the compressed plasma within or behind the shock. Although it is possible that the emission is produced in enhanced density regions of the upstream solar wind, it is argued that the weight of evidence favors the compressed postshock plasma as the source site.

Lengyel-Frey, D.↗
NASA NTRS1999

Effect of Directional Array Size on the Measurement of Airframe Noise Components

A study was conducted to examine the effects of overall size of directional (or phased) arrays on the measurement of aeroacoustic components. An airframe model was mounted in the potential core of an open-jet windtunnel, with the directional arrays located outside the flow in an anechoic environment. Two array systems were used; one with a solid measurement angle that encompasses 31.6 deg.of source directivity and a smaller one that encompasses 7.2 deg. The arrays, and sub-arrays of various sizes, measured noise from a calibrator source and flap edge model setups. In these cases, noise was emitted from relatively small, but finite size source regions, with intense levels compared to other sources. Although the larger arrays revealed much more source region detail, the measured source levels were substantially reduced due to finer resolution compared to that of the smaller arrays. To better understand the measurements quantitatively, an analytical model was used to define the basic relationships between array to source region sizes and measured output level. Also, the effect of noise scattering by shear layer turbulence was examined using the present data and those of previous studies. Taken together, the two effects were sufficient to explain spectral level differences between arrays of different sizes. An important result of this study is that total (integrated) noise source levels are retrievable and the levels are independent of the array size as long as certain experimental and processing criteria are met. The criteria for both open and closed tunnels are discussed. The success of special purpose diagonal-removal processing in obtaining integrated results is apparently dependent in part on source distribution. Also discussed is the fact that extended sources are subject to substantial measurement error, especially for large arrays.

Brooks, Thomas F.↗
NASA NTRS1988

Description of substorms in the tail incorporating boundary layer and neutral line effects

A description of the substorm expansion phase that includes the formation of a neutral line in the relatively near-earth portion of the tail plasma sheet and phenomena observed in the plasma sheet boundary layer (PSBL) is proposed. Specifically, it is proposed that substorm onset results from the formation of a neutral line within the preexisting source region for the PSBL. The source region is presumably the tail current sheet, which is suggested to extend well earthward of 80 earth radii. Both before and after the neutral line forms, auroral field-aligned currents and large ion flows remain confined to the PSBL earthward of the source region.

Lyons, L. R.↗
NASA NTRS1998

Galileo Direction Finding of Jovian Radio Emissions

The Galileo spacecraft, in orbit about Jupiter, has observed distinct spin modulation of plasma wave emissions near the Ganymede (G1 and G2) encounters in the frequency range from about 100 kHz to approximately 6 MHz. Assuming circularly polarized, transverse electromagnetic radiation, we have used the spin modulation of the sweep-frequency receivers of the electric dipole antenna over many spins to estimate the source location in the spin plane of the spacecraft. Hectometric (HOM) and decametric (DAM) emission is observed by Galileo as a general and continuous background with frequent bursts that last tens of minutes and can be separated by minutes or hours. We have analyzed HOM and DAM emissions observed near Jupiter just after the GI and G2 encounters, including two HOM/DAM "arc" signatures observed after the G2 encounter. These latter appear to be low-frequency extensions of DAM arcs, with source regions along either the Io or the Ganymede flux tube. While the uncertainties associated with the data analysis do not allow a precise source location, the HOM/DAM emission observed near the G1 and G2 encounters is consistent with a gyroresonant source region, but it is necessary to require refraction due to the Io torus to understand the results. To explain emission from apparent source regions above a gyroresonant source region, wave refraction from asymmetries in the Io plasma torus that extend along magnetic field lines is postulated. Alternatively, if such torus density asymmetries do not exist, emission with sources above a gyroresonant source region would require another free-energy source such as energetic plasma beams in the presence of density gradients or temperature anisotropies.

Menietti, J. D.↗
NASA NTRS2003

SNC Oxygen Fugacity Recorded in Pyroxenes and its Implications for the Oxidation State of the Martian Interior: An Experimental and Analytical Study

Knowledge of the oxidation state of a magma is critical as it is one of the parameters which controls the nature and composition of the resulting crystals. In terrestrial magmatic systems, oxygen fugacity (fo2) is known to vary by over nine orders of magnitude. With variations of this magnitude, understanding the compositional differences, phase changes, and crystallization sequence variations, caused by the magma fo2, is essential in deciphering the origin of all igneous rocks. Magmatic oxidation state is of great importance in that it reflects the degree of oxidation of the source region and can provide insight into magmatic processes, such as metasomatism, degassing, and assimilation, which may have changed them. Carmichael [1991] argues that most magmas are unlikely to have their redox states altered from those of their source region. This assumption allows for estimation of the oxidation state of planetary interiors. Conversely, it is known that the fo2 of the magma can be affected by other processes, which occur outside of the source region and therefore, the oxidation state may record those too. Processes which could overprint source region fugacities include melt dehydrogenation or other volatile loss, water or melt infiltration, or assimilation of oxidized or reduced wallrock. Understanding which of these processes is responsible for the redox state of a magma can provide crucial information regarding igneous processes and other forces active in the region. The composition of the SNC basalts and their widely varying proposed oxidation states raise some interesting questions. Do the SNC meteorites have an oxidized or reduced signature? What was the oxygen fugacity of the SNC source region at the time of melt generation? Is the fugacity calculated for the various SNC samples the fugacity of the magma source region or was it overprinted by later events? Are there different oxidation states in the Martian interior or a single one? This proposal seeks to address all of these questions.

McCanta, M. C.↗
DOE OSTI2021

Steep slope transistors with threshold switching devices

A steep-slope (SS) field effect transistor (FET) including a FET having a source region and a drain region, and a threshold switching device in direct contact with the source region or the drain region of the FET. Fabricating the steep-slope (SS) field effect transistor (FET) includes fabricating an AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) having a source region and a drain region, depositing a first electrode layer directly on the source region or the drain region, depositing a threshold switching layer directly on the first electrode layer, and depositing a second electrode layer directly on the threshold switching layer.

Huang, Xuanqi↗
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 NTRS1982

Theory of the fine structure of auroral kilometric radiation

Recent data from ISEE 1 show auroral kilometric radiation (AKR) with finely separated bands in frequency. The observation that the AKR fine structure frequency separation is about equal to the ion cyclotron frequency at the AKR source is strong evidence for the interaction of AKR and electrostatic ion cyclotron (EIC) waves in the source, as proposed by Grabbe et al. (1980) to explain the origin of AKR. It is pointed out that no other wave of frequency close to the band separation is known to exist in the auroral source region. The fine structure observed in the source region AKR is the first evidence for EIC waves in the lower source region (3000 - 5000 km attitude), as required in the theory of Grabbe et al.

Grabbe, C. L.↗
NASA NTRS1976

The problem of spiral galaxies and satellite radio sources

Regions 2-deg x 2-deg in area centered on four spiral galaxies were scanned with the Goldstone 64-m antenna in search of satellite radio sources at 2295 MHz. Four control regions of equal area but free of galaxies brighter than 13th magnitude were also scanned. No significant excess in the number density of sources with flux densities greater than 0.10 Jy relative to the control fields was found. A detailed comparison is made between the results of this program and the results of previous investigators. In particular, attention is directed to the potentially important implications of an investigation by Tovmasyan (1968), who searched a large number of spirals and found evidence that a small percentage of them apparently have radio satellites located up to 20 arcmin from the central galaxy. Fifteen sources selected from Tovmasyan's list of 43 satellite sources were measured. The present results confirm his positions and relative flux densities for each of the sources.

Arp, H.↗
NASA NTRS2014

Impacts of Intercontinental Transport of Anthropogenic Fine Particulate Matter on Human Mortality

Fine particulate matter with diameter of 2.5 microns or less (PM2.5) is associated with premature mortality and can travel long distances, impacting air quality and health on intercontinental scales. We estimate the mortality impacts of 20 % anthropogenic primary PM2.5 and PM2.5 precursor emission reductions in each of four major industrial regions (North America, Europe, East Asia, and South Asia) using an ensemble of global chemical transport model simulations coordinated by the Task Force on Hemispheric Transport of Air Pollution and epidemiologically-derived concentration-response functions. We estimate that while 93-97 % of avoided deaths from reducing emissions in all four regions occur within the source region, 3-7 % (11,500; 95 % confidence interval, 8,800-14,200) occur outside the source region from concentrations transported between continents. Approximately 17 and 13 % of global deaths avoided by reducing North America and Europe emissions occur extraregionally, owing to large downwind populations, compared with 4 and 2 % for South and East Asia. The coarse resolution global models used here may underestimate intraregional health benefits occurring on local scales, affecting these relative contributions of extraregional versus intraregional health benefits. Compared with a previous study of 20 % ozone precursor emission reductions, we find that despite greater transport efficiency for ozone, absolute mortality impacts of intercontinental PM2.5 transport are comparable or greater for neighboring source-receptor pairs, due to the stronger effect of PM2.5 on mortality. However, uncertainties in modeling and concentration-response relationships are large for both estimates.

human health↗
NASA NTRS2010

Variability of Springtime Transpacific Pollution Transport During 2000-2006: The INTEX-5 Mission in the Context of Previous Years

We analyze the transport of pollution across the Pacific during the NASA INTEX-B (Intercontinental Chemical Transport Experiment Part 8) campaign in spring 2006 and examine how this year compares to the time period for 2000 through 2006. In addition to aircraft measurements of carbon monoxide (CO) collected during INTEX-B, we include in this study multi-year satellite retrievals of CO from the Measurements of Pollution in the Troposphere (MOPITT) instrument and simulations from the chemistry transport model MOZART-4. Model tracers are used to examine the contributions of different source regions and source types to pollution levels over the Pacific. Additional modeling studies are performed to separate the impacts of inter-annual variability in meteorology and .dynamics from changes in source strength. interannual variability in the tropospheric CO burden over the Pacific and the US as estimated from the MOPITT data range up to 7% and a somewhat smaller estimate (5%) is derived from the model. When keeping the emissions in the model constant between years, the year-to-year changes are reduced (2%), but show that in addition to changes in emissions, variable meteorological conditions also impact transpacific pollution transport. We estimate that about 113 of the variability in the tropospheric CO loading over the contiguous US is explained by changes in emissions and about 213 by changes in meteorology and transport. Biomass burning sources are found to be a larger driver for inter-annual variability in the CO loading compared to fossil and biofuel sources or photochemical CO production even though their absolute contributions are smaller. Source contribution analysis shows that the aircraft sampling during INTEX-B was fairly representative of the larger scale region, but with a slight bias towards higher influence from Asian contributions.

Pfister, G. G.↗
DOE OSTI2025

Geometric Interpretation of the Cluster Location Problem Part I: Theory

We present a new framing of the seismic location problem using principles drawn from differential geometry. Our interpretation relies upon the common assumption that travel times observed across a network are continuous, differentiable functions of source location. In consequence, travel‐time functions constitute a differentiable map between the source region and a Riemannian manifold. The manifold is said to be the image of the source region embedded in a generally high‐dimension travel‐time vector space. A cluster of events in the source region has an image of discrete points on the manifold, that, except in the simplest cases, cannot be viewed directly. However, it is possible to project the image of a cluster into a tangent space of the manifold for direct visualization. The projection operator can be computed directly from the data without a velocity model, but produces a distorted rendering of the cluster geometry. With a model we can predict the distortions and correct them to estimate cluster geometry. We develop these points with the simplest possible example, one for which direct visualization of the manifold is possible, using the example as an introduction to the relevant concepts from differential geometry in a familiar setting. The tangent space, a local linearization of the manifold, plays a key role. We develop a metric to estimate the limits of linearization, that is, to determine when the curvature of the manifold invalidates the linear assumption. We also examine the interplay of model error, inadequate network geometry, and pick error. We then generalize our results from the simple case to the general case of 3D source regions observed by general networks. Although we do suggest a new “project and correct” method for location, we do not develop it into a practical algorithm. In conclusion, our intention rather is to highlight new analytical methods grounded in differential geometry.

East Pacific Ocean Islands↗
NASA NTRS2000

Interactive Soil Dust Aerosol Model in the GISS GCM: Sensitivity of the Soil Dust Cycle to Radiative Properties of Soil Dust Aerosols - Part 1

The sensitivity of the soil dust aerosol cycle to the radiative forcing by soil dust aerosols is studied. Four experiments with the NASA/GISS atmospheric general circulation model, which includes a soil dust aerosol model, are compared, all using a prescribed climatological sea surface temperature as lower boundary condition. In one experiment, dust is included as dynamic tracer only (without interacting with radiation), whereas dust interacts with radiation in the other simulations. Although the single scattering albedo of dust particles is prescribed to be globally uniform in the experiments with radiatively active dust, a different single scattering albedo is used in those experiments to estimate whether regional variations in dust optical properties, corresponding to variations in mineralogical composition among different source regions, are important for the soil dust cycle and the climate state. On a global scale, the radiative forcing by dust generally causes a reduction in the atmospheric dust load corresponding to a decreased dust source flux. That is, there is a negative feedback in the climate system due to the radiative effect of dust. The dust source flux and its changes were analyzed in more detail for the main dust source regions. This analysis shows that the reduction varies both with the season and with the single scattering albedo of the dust particles. By examining the correlation with the surface wind, it was found that the dust emission from the Saharan/Sahelian source region and from the Arabian peninsula, along with the sensitivity of the emission to the single scattering albedo of dust particles, are related to large scale circulation patterns, in particular to the trade winds during Northern Hemisphere winter and to the Indian monsoon circulation during summer. In the other regions, such relations to the large scale circulation were not found. There, the dependence of dust deflation to radiative forcing by dust particles is probably dominated by physical processes with short time scales. The experiments show that dust radiative forcing can lead to significant changes both in the soil dust cycle and in the climate state. To estimate dust concentration and radiative forcing by dust more accurately, dust size distributions and dust single scattering albedo in the model should be a function of the source region, because dust concentration and climate response to dust radiative forcing are sensitive to dust radiative parameters.

Perlwitz, Jan↗
DOE OSTI2021

Aircraft-based inversions quantify the importance of wetlands and livestock for Upper Midwest methane emissions

Abstract. We apply airborne measurements across three seasons (summer, winter and spring 2017–2018) in a multi-inversion framework to quantify methane emissions from the US Corn Belt and Upper Midwest, a key agricultural and wetland source region. Combing our seasonal results with prior fall values we find that wetlands are the largest regional methane source (32 %, 20 [16–23] Gg/d), while livestock (enteric/manure; 25 %, 15 [14–17] Gg/d) are the largest anthropogenic source. Natural gas/petroleum, waste/landfills, and coal mines collectively make up the remainder. Optimized fluxes improve model agreement with independent datasets within and beyond the study timeframe. Inversions reveal coherent and seasonally dependent spatial errors in the WetCHARTs ensemble mean wetland emissions, with an underestimate for the Prairie Pothole region but an overestimate for Great Lakes coastal wetlands. Wetland extent and emission temperature dependence have the largest influence on prediction accuracy; better representation of coupled soil temperature–hydrology effects is therefore needed. Our optimized regional livestock emissions agree well with the Gridded EPA estimates during spring (to within 7 %) but are ∼ 25 % higher during summer and winter. Spatial analysis further shows good top-down and bottom-up agreement for beef facilities (with mainly enteric emissions) but larger (∼ 30 %) seasonal discrepancies for dairies and hog farms (with > 40 % manure emissions). Findings thus support bottom-up enteric emission estimates but suggest errors for manure; we propose that the latter reflects inadequate treatment of management factors including field application. Overall, our results confirm the importance of intensive animal agriculture for regional methane emissions, implying substantial mitigation opportunities through improved management.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Regional Source-Type Discrimination Using Nonlinear Alignment Algorithms

The discrimination problem in seismology aims to accurately classify different underground source types based on local, regional, and/or teleseismic observations of ground motion. Typical discriminant approaches are rooted in fundamental, physics-based differences in radiation pattern or wave excitation, which can be frequency-dependent and may not make use of the full waveform. In this article, we explore whether phase and amplitude distances derived from dynamic time warping (DTW) and elastic shape analysis (ESA) can inform event discrimination. We demonstrate the ability to distinguish underground point sources using synthetic waveforms calculated for a 1D Earth model and various source mechanisms. We then apply the method to recorded data from events in the Korean Peninsula, which includes declared nuclear explosions, a collapse event, and naturally occurring earthquakes. Phase and amplitude distances derived from DTW and ESA are then used to classify the event types via dendrogram and k-nearest-neighbor clustering analyses. Using information from the full waveform, we show how different underground sources can be distinguished at regional distances. We highlight the potential of these nonlinear alignment algorithms for discrimination and comment on ways we can extend the framework presented here.

58 GEOSCIENCES↗
NASA NTRSDate not supplied

The Significance of Helium in the Solar Wind: Insights from 1 AU

Doubly ionized helium is the 2nd most abundant element in the solar wind. The solar wind’s properties are a function of the source region on the Sun from which it emanates. This includesthe abundances of solar wind Helium and rarer, heavier elements. The speed of the solar wind, when observed near Earth, is also related to the type of source region from which the solar wind originated. Early solar wind models are unable to explain how the solar wind achieved the asymptotically fastest, non-transient speeds observed at 1 AU and the solar wind must be accelerated during transit through interplanetary space. Only recently have observations shown that the solar wind from different source regions is accelerated by different mechanisms. However, the solar wind speed is also known to be an insufficient for identifying the type of solar source from which it originated, likely because these different acceleration mechanisms accelerate the solar wind into two different speed regimes that overlap. Furthermore, the mechanism that provides the coronal plasma sufficient energy to accelerate into the solar wind is still undetermined. These mysteries are further complicated by the Sun’s evolution through its 11-year activity cycle and the impact of the solar cycle on in situ observations. Using solar wind observations of the helium abundance from the Wind spacecraft and heavy ion abundances from the Advanced Composition Explorer (ACE) along with observations of the Sunspot Number – a long-studied proxy for the Sun’s activity – we will discuss the imprint of different solar wind source regions on observations collected at 1 AU. We will draw inferences about the role of helium in the acceleration of coronal plasma into the solar wind. Using the Alfvénicity – a metric related to the solar wind acceleration that occurs during transit through interplanetary space – we will derive a solar wind classification scheme for near-Earth observations that is related to the differences in the source regions from which it emanates.

Benjamin Alterman↗
NASA NTRS1972

Role of gas surface interactions in the reduction of OGO-6 neutral gas particle mass spectrometer data

The gas-surface interaction effects observed by the quadrupole mass spectrometer are described, and the technique developed to account for them in determining ambient neutral densities is summarized. The total ion current and the ion currents for ions with molecular weights 2, 4, 16, 28, and 32 are sampled for 1.125 sec once every 9.216 sec, for 258 sec out of a 368 sec cycle. An equation is given for the number density of any constituent in the ion source region, and source density data are discussed. The mass 28 background gas is considered to be CO rather than N2, and a CO model is developed. A quasi-equilibrium model of the atomic oxygen interactions is constructed, and a set of surface parameters is determined which provides a reasonable fit to the mass 16 and 32 source densities consistent with the predicted ambient atomic oxygen.

Hedin, A. E.↗
NASA NTRS1979

Petrology and origin of the shergottite meteorites

The results of petrographic studies and 1 atmosphere melting experiments of Shergotty and Zagami shergottites, the origin and evolution of the shergottites, and the relationship of the shergottite parent body to the parent bodies of the other achondrites and to the earth are examined. Shergotty and Zagami differ in the proportions of cumulus pyroxenes and crystallized intercumulus liquid, but their compositions are similar. Shergottites can be distinguished from other achondrite groups by their mineralogies, crystallization sequences, and inferred source region compositions, but their source regions can be related to other achondrite types by addition or loss of volatile components. Shergottites and terrestrial basalts show similar oxidation states and minor element concentrations which may be accounted for by accretion of similar materials to produce the terrestrial upper mantle and the shergottite parent body, or by accretion of the earth's upper mantle from planetisimals similar to the shergottite parent body.

Stolper, E.↗