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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

A convergence metric for counting statistics in time-resolved small angle neutron scattering

Here, this work introduces a model-independent, dimensionless metric for predicting optimal measurement duration in time-resolved small-angle neutron scattering using early-time data. Built on a Gaussian process regression framework, the method reconstructs scattering profiles with quantified uncertainty, even from sparse or noisy measurements. Demonstrated on the EQ-SANS instrument at the Spallation Neutron Source, the approach generalizes to general SANS instruments with a two-dimensional detector. A key result is the discovery of a dimensionless convergence metric revealing a universal power-law scaling in profile evolution across soft matter systems. When time is normalized by a system-specific characteristic time t*, the variation in inferred profiles collapses onto a single curve with an exponent between −2 and −1. This trend emerges within the first ten time steps, enabling early prediction of measurement sufficiency. The method supports real-time experimental optimization and is especially valuable for maximizing efficiency in low-flux environments such as compact accelerator-based neutron sources.

Tung, Chi-Huan [Oak Ridge National Laboratory (ORN↗
DOE OSTI2012

EXTREME CORONAL LINE EMITTERS: TIDAL DISRUPTION OF STARS BY MASSIVE BLACK HOLES IN GALACTIC NUCLEI?

Tidal disruption of stars by supermassive black holes at the centers of galaxies is expected to produce unique emission-line signatures, which have not yet been explored adequately. Here we report the discovery of extremely strong coronal lines from [Fe X] up to [Fe XIV] in a sample of seven galaxies (including two recently reported cases), which we interpret as such signatures. This is the first systematic search for objects of this kind, by making use of the immense database of the Sloan Digital Sky Survey. The galaxies, which are non-active as evidenced by the narrow line ratios, show broad emission lines of complex profiles in more than half of the sample. Both the high-ionization coronal lines and the broad lines are fading on timescales of years in objects observed with spectroscopic follow-ups, suggesting their transient nature. Variations of inferred non-stellar continua, which have absolute magnitudes of at least -16 to -18 mag in the g band, are also detected in more than half of the sample. The coronal line emitters reside in sub-L{sub *} disk galaxies (-21.3 < M{sub i} < -18.5) with small stellar velocity dispersions. The sample seems to form two distinct types based on the presence or absence of the [Fe VII] lines, with the latter having relatively low luminosities of [O III], [Fe XI], and the host galaxies. These characteristics can most naturally be understood in the context of transient accretion onto intermediate-mass black holes at galactic centers following tidal disruption of stars in a gas-rich environment. We estimate the incidence of such events to be around 10{sup -5} yr{sup -1} for a galaxy with -21.3 < M{sub i} < -18.5.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

LARGER PLANET RADII INFERRED FROM STELLAR ''FLICKER'' BRIGHTNESS VARIATIONS OF BRIGHT PLANET-HOST STARS

Most extrasolar planets have been detected by their influence on their parent star, typically either gravitationally (the Doppler method) or by the small dip in brightness as the planet blocks a portion of the star (the transit method). Therefore, the accuracy with which we know the masses and radii of extrasolar planets depends directly on how well we know those of the stars, the latter usually determined from the measured stellar surface gravity, log g. Recent work has demonstrated that the short-timescale brightness variations ({sup f}licker{sup )} of stars can be used to measure log g to a high accuracy of ∼0.1-0.2 dex. Here, we use flicker measurements of 289 bright (Kepmag < 13) candidate planet-hosting stars with T {sub eff} = 4500-6650 K to re-assess the stellar parameters and determine the resulting impact on derived planet properties. This re-assessment reveals that for the brightest planet-host stars, Malmquist bias contaminates the stellar sample with evolved stars: nearly 50% of the bright planet-host stars are subgiants. As a result, the stellar radii, and hence the radii of the planets orbiting these stars, are on average 20%-30% larger than previous measurements had suggested.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Estimating fluid-induced stress change from observed deformation

Observed deformation is sensitive to a changing stress field within the Earth. There are, however, several impediments to a direct inversion of geodetic measurements for changes in stress. Estimating six independent components of stress change from a smaller number of displacement or strain components is inherently non-unique. The reliance upon surface measurements leads to a loss of resolution, due to the attenuation of higher spatial frequencies in the displacement field with distance from a source. Here, we adopt a technique suited to the estimation of stress changes due to the injection and/or withdrawal of fluids at depth. In this approach the surface displacement data provides an estimate of the volume change responsible for the deformation, rather than stress changes themselves. The inversion for volume change is constrained by the fluid fluxes into and out of the reservoir. The distribution of volume change is used to calculate the displacements in the region above the reservoir. Estimates of stress change follow from differentiating the displacement field in conjunction with a geomechanical model of the o verburden. We also apply the technique to Interferometric Synthetic Aperture Radar (InSAR) observations gathered over a petroleum reservoir in the San Joaquin Valley of California. An analysis of the InSAR range changes reveals that the stress field in the overburden varies rapidly both in space and in time. The inferred stress variations are found to be compatible with the documented failure of a well in the field.

58 GEOSCIENCES↗
DOE OSTI2024

Posterior Covariance Matrix Approximations

Here, the Davis equation of state (EOS) is commonly used to model thermodynamic relationships for high explosive (HE) reactants. Typically, the parameters in the EOS are calibrated, with uncertainty, using a Bayesian framework and Markov Chain Monte Carlo (MCMC) methods. However, MCMC methods are computationally expensive, especially for complex models with many parameters. This paper provides a comparison between MCMC and less computationally expensive Variational methods (Variational Bayesian and Hessian Variational Bayesian) for computing the posterior distribution and approximating the posterior covariance matrix based on heterogeneous experimental data. All three methods recover similar posterior distributions and posterior covariance matrices. This study demonstrates that for this EOS parameter calibration application, the assumptions made in the two Variational methods significantly reduce the computational cost but do not substantially change the results compared to MCMC.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

CONCURRENT, CONDENSED STEIN VARIATIONAL GRADIENT DESCENT FOR UNCERTAINTY QUANTIFICATION OF NEURAL NETWORKS

In this work, we propose a Stein variational gradient descent (SVGD) method to concurrently sparsify, train, and provide uncertainty quantification (UQ) of a complexly parameterized model, such as a neural network (NN). It employs a graph reconciliation and condensation process to reduce complexity and increase similarity in the Stein ensemble of parameterizations. Therefore, the proposed concurrent, condensed SVGD (ccSVGD) method can provide UQ on parameters, not just outputs. Furthermore, the parameter reduction speeds up the convergence of the Stein gradient descent as it reduces the combinatorial complexity by aligning and differentiating the sensitivity to parameters. These properties are demonstrated with an illustrative example and an application to a mechanical response representation problem in solid mechanics.

42 ENGINEERING↗
DOE OSTI2020

We Know Where We Don't Know: 3D Bayesian CNNs for Credible Geometric Uncertainty

Deep learning has been successfully applied to the segmentation of 3D Computed Tomography (CT) scans. Establishing the credibility of these segmentations requires uncertainty quantification (UQ) to identify untrustworthy predictions. Recent UQ architectures include Monte Carlo dropout networks (MCDNs), which approximate deep Gaussian processes, and Bayesian neural networks (BNNs), which learn the distribution of the weight space. BNNs are advantageous over MCDNs for UQ but are thought to be computationally infeasible in high dimension, and neither architecture has produced interpretable geometric uncertainty maps. We propose a novel 3D Bayesian convolutional neural network (BCNN), the first deep learning method which generates statistically credible geometric uncertainty maps and scales for application to 3D data. We present experimental results on CT scans of graphite electrodes and laser-welded metals and show that our BCNN outperforms an MCDN in recent uncertainty metrics. The geometric uncertainty maps generated by our BCNN capture distributions of sigmoid values that are interpretable as confidence intervals, critical for applications that rely on deep learning for high-consequence decisions.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Xenon in the Protoplanetary Disk (PPD), in Two Planets, and a Comet

Isotopic anomalies in several elements, as recently observed in meteorites, are generally interpreted to indicate nonequilibrium environments in the protoplanetary disk (PPD). Here we study reported Xe isotopic compositions on planets Earth and Mars, in a comet, and in meteorites for precursor discrepancies. Abundance variations of inferred presolar nano-diamonds, the carrier phase of the Xe-HL component, appear to be the primary source of nonuniformity of Xe precursors in the PPD, together with mechanisms of mass-dependent fractionation. While planet Mars kept a record of initial solar Xe isotopic abundances, such a record is missing for planet Earth. Xe isotopic abundances in paleo-atmospheres of both planets represent secondary reservoirs that show mass-dependent fractionation effects, but the inferred compositions of their PPD precursors differ: Mars atmospheric precursor Xe had solar isotopic composition, while Earth’s Xe precursor is consistent with a PPD reservoir of low nano-diamond abundance. Strong mass-dependent fractionation effects are observed in Xe components of IAB irons and in Yamato carbonaceous (CY) chondrites, and show that fractionation mechanisms are not restricted to planetary atmospheres. These records show that Xe isotopes in solar system reservoirs are useful tracers of evolutionary processes and of nonequilibrated presolar components in the PPD.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

SQUID Readout of a High-$Q$ Superconducting $LC$ Resonator

We demonstrate the readout of a superconducting $LC$ resonator, with $Q \approx 2 \times 10^{6}$ at approximately 250 kHz, using a dc SQUID followed by a SQUID series-array amplifier readout chain. We find that $Q$ depends on the SQUID flux-bias point, increasing near the shallow-slope point of the SQUID modulation curve and decreasing near the steep-slope point, consistent with the previously observed SQUID damping effects. From this variation, we infer the SQUID effective input impedance. We further infer the effective temperature of the resonator circuit from the resonance peak in the noise spectrum and show that it also depends on the SQUID flux-bias point, suggesting a possible contribution from SQUID back-action noise. This system provides a working prototype for future experiments based on lumped-element resonators with SQUID readout, in particular low-mass axion searches within the DMRadio program.

FOS: Physical sciences↗
NASA NTRS1972

Compositional characteristics of some Apollo 14 clastic materials.

Eighty-two subsamples of Apollo 14 materials have been analyzed by instrumental neutron activation analysis techniques for as many as 25 elements. In many cases, it was necessary to develop new procedures to allow analyses of small specimens. Compositional relationships among Apollo 14 materials indicate that there are small but systematic differences between regolith from the valley terrain and that from Cone Crater ejecta. Fragments from 1-2 mm size fractions of regolith samples may be divided into compositional classes, and the 'soil breccias' among them are very similar to valley soils. Multicomponent linear mixing models have been used as interpretive tools in dealing with data on regolith fractions and subsamples from breccia 14321. These mixing models show systematic compositional variations with inferred age for Apollo 14 clastic materials.

Lindstrom, M. M.↗
NASA NTRS1976

Ion chemistry of N2/+/ and the solar ultraviolet flux in the thermosphere

We have analyzed daytime composition measurements in the thermosphere from Atmosphere Explorer-C by use of a theory of the ion chemistry. Predicted and measured N2(+) densities are compared to infer global variation of the solar ionizing flux. Results indicate that the solar flux of Hinteregger measured on Atmosphere Explorer-C provides an adequate basis for the calculation of solar ultraviolet photoionization rates. The role of metastable species is examined, and theoretical O+(2D) densities are presented.

Oppenheimer, M.↗
NASA NTRS1978

On the supposed anticorrelation of solar polar and equatorial rotation rates

The anticorrelation between two of the three parameters used to calculate the angular velocity of the sun's differential rotation is here said to be due to numerical coupling. A computer simulation technique shows that the relationship between the two parameters is caused by the effect of noise on the least-squares analysis used to obtain the three parameters used to determine the angular velocity in terms of the heliographic latitude. The computer simulation technique is described. The supposed anticorrelation had been used to infer that variations of the sun's polar and equatorial rotation rates are anticorrelated.

Duvall, T. L., Jr.↗
NASA NTRS1979

Alteration in CM carbonaceous chondrites inferred from modal and chemical variations in matrix

The modal abundance of matrix in CM chondrites appears to vary from 57-85 vol%. The concentrations of volatile elements that should occur in matrix remain approximately constant despite differences in the proportions of matrix, suggesting that the differing matrix contents may not be real primary variations but are optical effects due to aqueous alteration processes that make other petrologic components unrecognizable. Apparent matrix content can be used as a qualitative measure of the degree of alteration experienced by each CM chondrite. Fe/Si ratios in matrices decrease progressively with increasing alteration due to the formation of new phyllosilicate phases with higher Mg/Fe ratios and optically recognizable opaque minerals that are not counted as matrix. The aqueous alteration process in CM chondrites appears to have been largely isochemical if the bulk meteorites are considered as the reacting systems, although depletion patterns and isotopic anomalies indicate open-system behavior for a few highly mobile components.

Mcsween, H. Y., Jr.↗
NASA NTRS1980

Monitoring snowpack properties by passive microwave sensors on board of aircraft and satellites

Snowpack properties such as water equivalent and snow wetness may be inferred from variations in measured microwave brightness temperatures. This is because the emerged microwave radiation interacts directly with snow crystals within the snowpack. Using vertically and horizontally polarized brightness temperatures obtained from the multifrequency microwave radiometer (MFMR) on board a NASA research aircraft and the electrical scanning microwave radiometer (ESMR) and scanning multichannel microwave radiometer (SMMR) on board the Nimbus 5, 6, and 7 satellites, linear relationships between snow depth or water equivalent and microwave brightness temperature were developed. The presence of melt water in the snowpack generally increases the brightness temperatures, which can be used to predict snowpack priming and timing of runoff.

Chang, A. T. C.↗
NASA NTRS1983

11-year cycle solar modulation of cosmic ray intensity inferred from C-14 content variation in dated tree rings

A liquid scintillation-photomultiplier tube counter system was used to measure the Delta-C-14 values of 60 tree rings, dating from 1866 to 1925, that were taken from a white spruce grown in Canada at 68 deg N, 130 deg W. A 10-percent variation is found which is anticorrelated with sunspot numbers, although the amplitude of the variation is 2-3 times higher than expected in trees grown at lower latitudes. A large dip in the data at about 1875 suggests an anomalously large modulation of cosmic ray intensity during the 1867-1878 AD solar cycle, which was the most active of the 19th century.

Fan, C. Y.↗
NASA NTRS1985

Evidence for a thermospheric source of stratospheric NOx

Analyses of a three-year time series of rocket ozone measurements at Wallops Island, VA, a set of rocket ozone soundings across the Southern Hemisphere, and rocket soundings at Fort Churchill, Manitoba are reported. Evidence is obtained that the NOx budget is not simply explained by oxidation of biospheric nitrous oxide. I 1-D time-dependent photochemical model is used to compute the amount of NO2 required to maintain odd oxygen in a steady state after accounting for Chapman, odd hydrogen, and odd chlorine reactions. At Wallops Island, a mid-latitude station, the inferred seasonal variation of NOx is small with the fall and winter mixing ratios about 20 percent greater than the spring and summer values. The soundings at Fort Churchill require about the same NOx amount as at Wallops Island in the spring and summer months but more than twice this amount in late fall and winter. Results indicate that the nitrous oxide source of NOx is supplemented by a polar source during the fall and winter months. This is consistent with the descent of thermospheric air with its high nitric oxide content during the period of strong cooling in the polar night.

Krueger, A. J.↗