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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Solar Irradiance Observed from PVO and Inferred Solar Rotation

Solar irradiance in the extreme ultraviolet flux (EUV) has been monitored for 11 years by the Pioneer Venus Orbiter (PVO). Since the experiment moves around the Sun with the orbital rate of Venus rather than that of Earth, the measurement gives us a second viewing location from which to begin unravelling which irradiance variations are intrinsic to the Sun, and which are merely rotational modulations whose periods depend on the motion of the observer. Researchers confirm an earlier detection, made with only 8.6 years of data, that the EUV irradiance is modulated by rotation rates of two families of global oscillation modes. One family is assumed to be r-modes occupying the convective envelope and sharing its rotation, while the other family (g-modes) lies in the radiative interior which as a slower rotation. Measured power in r-modes of low angular harmonic number indicates that the Sun's envelope rotated about 0.7 percent faster near the last solar maximum (1979 thru 1982) than it did during the next rise to maximum (1986 to 1989). No change was seen in the g-mode family of lines, as would be expected from the much greater rotational inertia of the radiative interior.

Wolff, Charles L.↗
NASA NTRS2011

Origin and Evolution of Prebiotic Organic Matter as Inferred from the Tagish Lake Meteorite

The complex suite of organic materials in carbonaceous chondrite meteorites probably originally formed in the interstellar medium and/or the solar protoplanetary disk, but was subsequently modified in the meteorites' asteroidal parent bodies. The mechanisms of formation and modification are still very poorly understood. We carried out a systematic study of variations in the mineralogy, petrology, and soluble and insoluble organic matter in distinct fragments of the Tagish Lake meteorite. The variations correlate with indicators of parent body aqueous alteration and at least some molecules of pre-biotic importance formed during the alteration.

Herd, Christopher D.↗
DOE OSTI2024

Atacama Cosmology Telescope: High-resolution component-separated maps across one third of the sky

Observations of the millimeter sky contain valuable information on a number of signals, including the blackbody cosmic microwave background (CMB), Galactic emissions, and the Compton-y distortion due to the thermal Sunyaev-Zel’dovich (tSZ) effect. Extracting new insight into cosmological and astrophysical questions often requires combining multiwavelength observations to spectrally isolate one component. Here, in this work, we present a new arc-minute-resolution Compton-y map, which traces out the line-of-sight-integrated electron pressure, as well as maps of the CMB in intensity and E-mode polarization, across a third of the sky (around 13,000 deg 2 ). We produce these through a joint analysis of data from the Atacama Cosmology Telescope (ACT) data release 4 and 6 at frequencies of roughly 93, 148, and 225 GHz, together with data from the Planck satellite at frequencies between 30 and 545 GHz. We present detailed verification of an internal linear combination pipeline implemented in a needlet frame that allows us to efficiently suppress Galactic contamination and account for spatial variations in the ACT instrument noise. These maps provide a significant advance, in noise levels and resolution, over the existing Planck component-separated maps and will enable a host of science goals including studies of cluster and galaxy astrophysics, inferences of the cosmic velocity field, primordial non-Gaussianity searches, and gravitational lensing reconstruction of the CMB.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

Auroral energy deposition and neutral composition changes observed simultaneously by ESRO 4 and AE-C at different altitudes

Neutral composition data obtained simultaneously from ESRO 4 and AE-C during geomagnetically disturbed conditions at different altitudes (160 and 230 km) are used to investigate the atmospheric response to geomagnetic storms and to infer information regarding the excitation mechanism. The data are compared with a theoretical model that estimates the composition effects in terms of wind induced diffusion. A parametric study was conducted bearing on the influence of energy deposition at different altitudes and with varying latitudinal extent. In one of the observed events the composition effects at 160 km are substantially smaller than at 230 km for which we inferred by comparison with the theory that the energy mainly was deposited at 150 km altitude over a wide latitude range. Another event required energy deposition at somewhat lower altitudes near 120 km with a more localized energy source. Significant variations of the turbopause level were not necessary to explain the observed variations.

Trinks, H.↗
NASA NTRS1987

Evidence for turbulence in H II regions

The results of extensive velocity mapping across the face of Galactic H II regions are used to make an accurate determination of velocity dispersions and structure functions for a number of nebulae. A dependence of random velocities upon scale, indicating the presence of turbulence, is found. These relationships are compared with the predictions of models for Kolmogorov turbulence in H II regions, and poor agreement is found. A more general formulation shows that there is no single power law for the velocity-distance relation that fits the observations. From the variations in the shape of the observed structure function, it is concluded that the turbulent energy enters the nebulae at several different scales. It is also found that velocity broadening of the observed lines is significantly greater than would be inferred from the velocity scatter across the face of the nebulae.

O'Dell, C. R.↗
NASA NTRS1991

Remanent magnetic properties of unbrecciated eucrites

This study examines the remanent magnetic properties of five unbrecciated eucrites, ranging from the coarse-grained cumulate Moore County to the quenched melt rock ALH 81001 in order to assess the strength of the magnetic field associated with their parent body during their formation. Two of the meteorites are judged as unlikely to have preserved their primary thermal remanence because of large variations in subsample remanence intensity and direction (Ibitira), and lack of NRM resistance to AF and thermal demagnetization (PCA 82502). The lack of a strong (greater than 0.01 mT) magnetizing field during their cooling on the eucrite parent body is inferred from the low normalized NRM intensities for subsamples of ALH 81001 and Yamato 791195.

Cisowski, Stanley M.↗
DOE OSTI2022

Amazonian terrestrial water balance inferred from satellite-observed water vapor isotopes

Atmospheric humidity and soil moisture in the Amazon forest are tightly coupled to the region’s water balance, or the difference between two moisture fluxes, evapotranspiration minus precipitation (ET-P). However, large and poorly characterized uncertainties in both fluxes, and in their difference, make it challenging to evaluate spatiotemporal variations of water balance and its dependence on ET or P. Here, we show that satellite observations of the HDO/H 2 O ratio of water vapor are sensitive to spatiotemporal variations of ET-P over the Amazon. When calibrated by basin-scale and mass-balance estimates of ET-P derived from terrestrial water storage and river discharge measurements, the isotopic data demonstrate that rainfall controls wet Amazon water balance variability, but ET becomes important in regulating water balance and its variability in the dry Amazon. Changes in the drivers of ET, such as above ground biomass, could therefore have a larger impact on soil moisture and humidity in the dry (southern and eastern) Amazon relative to the wet Amazon.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1999

The Role of Gravity Waves in Generating Equatorial Oscillations in Modulating Atmospheric Tides

We discuss a Numerical Spectral Mode (NSM) that extends from the ground up into the thermosphere and incorporates Hines' Doppler spread parameterization (DSP) for small scale gravity waves (GW). This model is applied to describe the seasonal variations in the mean zonal circulation, the semi-annual and quasi-biennial oscillations (SAO and QBO), as well as the tides and planetary waves in the middle atmosphere. Initial results showed that this model can reproduce the salient features observed, including the QBO extending into the upper mesosphere inferred from UARS measurements. The model has now been extended to simulate also: (a) the zonal circulation of the lower stratosphere and upper troposphere, and (b) the upwelling at equatorial latitudes associated with the Brewer Dobsen circulation that affects the dynamics significantly as pointed out by Dunkerton. Upward vertical winds increase the period of the QBO observed from the ground. To compensate for that, one needs to increase in the model the eddy diffusivity and the GW momentum flux, bringing the latter closer to values recommended in the DSP. This development is conducive to extending the QBO and SAO to higher latitudes through global scale momentum redistribution. Multi-year interannual oscillations are generated through wave filtering by the solar driven annual oscillation in the zonal circulation. In a 3D version of the model, wave momentum is absorbed and dissipated by tides and planetary waves. A somewhat larger GW source (well within the DSP range) is then required to generate realistic QBO and SAO amplitudes. Since GW momentum is deposited in the altitude regime of increasing winds, the amplitude of the diurnal tide is amplified and its vertical wavelength is reduced at altitudes between 70 and 120 km. Wave filtering by the mean zonal circulation causes the GW flux to peak during equinox, and this produces a large semi-annual variation in the tide that has been observed on UARS. Without the diurnal tide, the semidiurnal tide would also be modulated in this way. But the diurnal tide filters out the GW preferentially during equinox, so that the semidiurnal tide tends to peak during solstice. Under the influence of GW, the tides are modulated significantly by planetary waves that are generated preferentially during solstice in part due to baroclinic instability.

Mayr, H. G.↗
NASA NTRS1983

Venus - Global surface radio emissivity

Observations of thermal radio emission from the surface of Venus, made by the Pioneer Venus radar mapper at a wavelength of 17 cm, show variations that are dominated by changes in surface emissivity. The regions of lowest emissivity (0.54 + or - 0.05 for the highland areas of Aphrodite Terra and Theia Mons) correspond closely to regions of high radar reflectivity reported earlier. These results support the inference of inclusions of material with high electrical conductivity in the surface rock of these areas.

Ford, P. G.↗
NASA NTRS1987

Rayleigh lidar observations of gravity wave activity in the stratosphere and lower mesosphere

Forty-two monochromatic gravity wave events were observed in the 25 to 55 km altitude region during 16 nights of Rayleigh lidar measurements at Poker Flat, Alaska and Urbana, Illinois. The measured wave parameters were compared to previous radar and lidar measurements of gravity wave activity. Vertical wavelengths, lambda(z), between 2 and 11.5 km with vertical phase velocities, c(z), between 0.1 and 1 m/s were observed. Measured values of lambda(z) and c(z) were used to infer observed wave periods, T(ob), between 50 and 1000 minutes and horizontal wavelengths, lambda(x), from 25 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No seasonal variations were evident in the observed wave parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with T(ob), which is consistent with recent sodium lidar studies of monochromatic wave events near the mesopause. Measured power law relationships between the wave parameters were lambda(z) varies as T(ob) sup 0.96, lambda(x) varies as T(ob) sup 1.8, and c(z) varies as T(ob) sup -0.85. The kinetic energy calculated for the monochromatic wave events varied as k(z) sup -2, k(x) sup -1, and f(ob) sup -1.7. The atmospheric scale heights calculated for each observation date range from 6.5 to 7.6 km with a mean value of 7 km. The increase of rms wind perturbations with altitude indicated an amplitude growth length of 20.9 km. The altitude profile of kinetic energy density decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.

Miller, M. S.↗
NASA NTRS1988

H2 spectroscopy and a diurnally changing cloud on Jupiter

Spectroscopic observations of H2 in specific longitude regions of Jupiter as they rotate from limb to limb are reported. Data obtained in the 3-0 S(0) and S(1) lines using a CCD detector and a spectrograph with either echelle or plane gratings at the Cassegrain focus of the 24-inch telescope at Whipple Observatory during April-June 1983 are presented in extensive tables and graphs and analyzed in detail, modeling spatial and temporal variations at seven latitudes. An east-to-west increase in the equivalent line widths is attributed to the combined action of internal and solar heating of a convective layer, resulting in diurnal changes in the vertical cloud structure. It is inferred that the hydrogen observed is mainly in an equilibrium thermodynamic state, with small amounts of nonequilibrium hydrogen at high altitudes.

Cunningham, Cindy C.↗
NASA NTRS1992

Ultraviolet observations of clusters of Wolf-Rayet stars in the SBm3 galaxy NGC 4214 and Ultraviolet and optical observations of LINER's

The purpose of the grant was to obtain and analyze IUE (UV) and ground-based (optical) spectra of the central bar of NGC 4214, which contains several bright H II regions, in order to further explore the properties of the Wolf-Rayet stars in this galaxy. Several spatially distinct regions, with widely different equivalent widths of optical Wolf-Rayet lines, could be sampled by the large IUE entrance aperture. By using newly developed extraction techniques, the spectra of these H II regions could be isolated, and differences in their stellar populations would be systematically studied. Data were obtained with IUE in late February and early March, 1992. Some of the shifts were successful, but a few were not -- apparently the blind offset from the nearby star did not work equally well in all cases. Thus, the signal-to-noise ratio is somewhat lower than we had hoped. This necessitated a more careful extraction of the spectra of individual H II regions from the two-dimensional spectra. (A program that models the point spread function in the spatial direction was used to deblend the distinct H II regions.) The IUE data are currently being analyzed in conjunction with ground-based optical spectra. There appear to be obvious variations in the stellar population over angular scales of only a few arc seconds. The second part of the research performed under this grant was a continuation of a project that uses IUE (UV) and ground-based (optical) spectra to infer the physical conditions in Low-Ionization Nuclear Emission-Line Regions (LINER's). We have obtained spectra of a few key objects that cover a representative range in LINER continuum and emission-line properties. The overall goals are to (1) separate the emission into spatially distinct components, (2) establish whether the observed nuclear ultraviolet continua indicate sufficient photoionizing fluxes to account for the emission lines, (3) determine whether the nuclear emission can be explained by hot stars alone, (4) detect and measure the strengths of UV emission lines, and (5) search for systematic differences in the UV spectra of LINER's whose other properties differ in some respects.

Filippenko, Alexei V.↗
NASA NTRS1994

Asymmetries in the Io plasma torus

Using Ulysses radio wave data taken during the 1992 Jupiter encounter, we conclude that there are significant large and small spatial scale azimuthal asymmetries at high latitudes in the Io plasma torus. During a period of time near perijove when the spacecraft motion was predominantly in the azimuthal direction and was relatively fixed in both latitude and radial distance, inferred electron densities depart significantly from the common assumption of longitudinal symmetry. Specifically, electron plasma concentrations near 0 deg system III longitude (and 0400 LT) are greater than those near 180 deg (and 0000 LT). Superposed on this large-scale variation are regularly spaced density depletions, 30-50% in magnitude, and having a spatial periodicity of about 17 deg. Some of these depletions may drive various known radio and plasma wave sources by means of large B parallel electric potentials. The observations are compared with recent models and with the in-situ Voyager observations.

Desch, M. D.↗
NASA NTRS2003

Fluid core size of Mars from detection of the solar tide

The solar tidal deformation of Mars, measured by its k2 potential Love number, has been obtained from an analysis of Mars Global Surveyor radio tracking. The observed k2 of 0.153 +/- 0.017 is large enough to rule out a solid iron core and so indicates that at least the outer part of the core is liquid. The inferred core radius is between 1520 and 1840 kilometers and is independent of many interior properties, although partial melt of the mantle is one factor that could reduce core size. Ice-cap mass changes can be deduced from the seasonal variations in air pressure and the odd gravity harmonic J3, given knowledge of cap mass distribution with latitude. The south cap seasonal mass change is about 30 to 40% larger than that of the north cap.

Mars↗
DOE OSTI2023

The Atacama Cosmology Telescope: High-resolution component-separated maps across one-third of the sky

Observations of the millimeter sky contain valuable information on a number of signals, including the blackbody cosmic microwave background (CMB), Galactic emissions, and the Compton-$y$ distortion due to the thermal Sunyaev-Zel'dovich (tSZ) effect. Extracting new insight into cosmological and astrophysical questions often requires combining multi-wavelength observations to spectrally isolate one component. In this work, we present a new arcminute-resolution Compton-$y$ map, which traces out the line-of-sight-integrated electron pressure, as well as maps of the CMB in intensity and E-mode polarization, across a third of the sky (around 13,000 sq.~deg.). We produce these through a joint analysis of data from the Atacama Cosmology Telescope (ACT) Data Release 4 and 6 at frequencies of roughly 93, 148, and 225 GHz, together with data from the \textit{Planck} satellite at frequencies between 30 GHz and 545 GHz. We present detailed verification of an internal linear combination pipeline implemented in a needlet frame that allows us to efficiently suppress Galactic contamination and account for spatial variations in the ACT instrument noise. These maps provide a significant advance, in noise levels and resolution, over the existing \textit{Planck} component-separated maps and will enable a host of science goals including studies of cluster and galaxy astrophysics, inferences of the cosmic velocity field, primordial non-Gaussianity searches, and gravitational lensing reconstruction of the CMB.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Sensitivity of gas filter correlation instrument to variations in optical balance

A computer program was used to simulate the response of the Gas Filter Correlation Radiometer (GFCR) to changing pollutant levels of CO, SO2, CH4, and NH3 in two model atmospheres. Positive and negative deviations of tau sub alpha of magnitudes 0.01, 0.1, and 1 percent were imposed upon the simulation and the resulting deviations in inferred concentrations were determined. For the CO, CH4, and the higher pressure cell of the NH3 channel, the deviations are less than + or - 12 percent for deviations in tau sub alpha of + or - 0.1 percent, but increase to significantly higher values for larger deviations. For the lower pressure cell of NH3 and for SO2, the deviations in inferred concentration begin to rise sharply between 0.01 and 0.1 percent deviation in tau sub alpha, suggesting that a tighter control on tau sub alpha may be required for these channels.

Orr, H. D., III↗
DOE OSTI2025

Inverse design of cellular structures with the targeted nonlinear mechanical response

Advanced additive manufacturing capabilities have enabled a transformational ability to create sophisticated cellular structures using diverse materials. By altering the topology of the unit cell, the mechanical behavior, such as the stress-strain response during compression, can be modulated. Nevertheless, identifying a printable topology within an enormous design space that would precisely deliver the targeted nonlinear material response is challenging. We propose a data-driven generative framework based on a conditional variational autoencoder (cVAE) architecture that can inverse design the cellular structure based on the intended nonlinear stress-strain response. Trained on a dataset of structure-property pairs, the cVAE learns a compact and expressive latent space that enables efficient mapping from targets to feasible geometries. Two inference modes are explored: (1) decoder-only generation, which enables the exploration of diverse designs conditioned solely on the desired mechanical response, and (2) encoder-decoder generation, which further allows for the incorporation of desired topologies, ensuring the generated structure conforms to both mechanical properties and to desired-topology constraints. The results demonstrate that the model can generate structurally plausible and mechanically accurate designs, with the predicted stress-strain curves closely matching the targets. Even under joint conditioning, the model effectively balances geometric fidelity and functional performance.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Modern Monte Carlo methods for efficient uncertainty quantification and propagation: A survey

Uncertainty quantification (UQ) includes the characterization, integration, and propagation of uncertainties that result from stochastic variations and a lack of knowledge or data in the natural world. Monte Carlo (MC) method is a sampling-based approach that has widely used for quantification and propagation of uncertainties. However, the standard MC method is often time-consuming if the simulation-based model is computationally intensive. This article gives an overview of modern MC methods to address the existing challenges of the standard MC in the context of UQ. Specifically, multilevel Monte Carlo (MLMC) extending the concept of control variates achieves a significant reduction of the computational cost by performing most evaluations with low accuracy and corresponding low cost, and relatively few evaluations at high accuracy and corresponding high cost. Multifidelity Monte Carlo (MFMC) accelerates the convergence of standard Monte Carlo by generalizing the control variates with different models having varying fidelities and varying computational costs. Multimodel Monte Carlo method (MMMC), having a different setting of MLMC and MFMC, aims to address the issue of UQ and propagation when data for characterizing probability distributions are limited. Multimodel inference combined with importance sampling is proposed for quantifying and efficiently propagating the uncertainties resulting from small data sets. All of these three modern MC methods achieve a significant improvement of computational efficiency for probabilistic UQ, particularly uncertainty propagation. Finally, an algorithm summary and the corresponding code implementation are provided for each of the modern MC methods. The extension and application of these methods are discussed in detail.

97 MATHEMATICS AND COMPUTING↗