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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Herschel - PACS Survey Of Protoplanetary Disks In Taurus - Auriga Observations Of [O I] And [C Ii], And Far-Infrared Continuum

The Herschel Space Observatory was used to observe approx. 120 pre-main-sequence stars in Taurus as part of the GASPS Open Time Key project. Photodetector Array Camera and Spectrometer was used to measure the continuum as well as several gas tracers such as [O I] 63 micron, [O I] 145 micron, [C II] 158, micron OH, H2O, and CO. The strongest line seen is [O I] at 63 micron. We find a clear correlation between the strength of the [O I] 63 micron line and the 63 micron continuum for disk sources. In outflow sources, the line emission can be up to 20 times stronger than in disk sources, suggesting that the line emission is dominated by the outflow. The tight correlation seen for disk sources suggests that the emission arises from the inner disk (<50 AU) and lower surface layers of the disk where the gas and dust are coupled. The [O I] 63 micron is fainter in transitional stars than in normal Class II disks. Simple spectral energy distribution models indicate that the dust responsible for the continuum emission is colder in these disks, leading to weaker line emission. [C II] 158 micron emission is only detected in strong outflow sources. The observed line ratios of [O I] 63 micron to [O I] 145 micron are in the regime where we are insensitive to the gas-to-dust ratio, neither can we discriminate between shock or photodissociation region emission. We detect no Class III object in [O I] 63 micron and only three in continuum, at least one of which is a candidate debris disk.

GASPS Open Time Key project↗
NASA NTRS2019

Intensity Mapping in the Presence of Foregrounds and Correlated Continuum Emission

Intensity mapping has attracted significant interest as an approach to measuring the properties of the interstellar medium in typical galaxies at high redshift. Intensity mapping measures the statistics of surface brightness as a function of frequency, making it sensitive to not only all line emission of interest but also radiation from all other sources. Significant effort has gone into developing approaches that reject foreground contamination. Additionally, the target galaxies have multiple sources of emission that can complicate the interpretation of the line brightness.We describe the problem of jointly estimating correlated continuum emission and cleaning uncorrelated continuum emission, such as from the Milky Way. We apply these considerations to a cross-correlation of Planck data with BOSS quasars for a determination of [C II] for 2 < z < 3.2. Intensity mapping surveys with few bands have unique challenges for treating foregrounds and avoiding bias from correlated continuum emission. We show how a future intensity mapping survey with many bands can separate line from continuum emission in cross-correlation.

Switzer, E. R.↗
DOE OSTI2026

Seamlessly joining length scales: From atomistic thermal graphs to anisotropic continuum conductivity

Thermal transport in complex solids is governed by local structure, defects, and anisotropy, yet most continuum models still rely on oversimplified and homogenized conductivities. Here, we bridge atomistic and continuum descriptions by building finite element (FE) models directly from the site-projected thermal conductivity (SPTC), an atomic-level decomposition of the Green–Kubo thermal conductivity. We introduce a toolkit, the “Simulator Collection for Atomic-to-Continuum Scales (SCACS)”, which uses a graph neural network to predict SPTC on large atomic structures, coarse-grains these fields into anisotropic conductivity tensors, and embeds them into the heat-flow FE equation with a customized, anisotropy-aware adaptive mesh refinement scheme. Applied to silicon nanostructures, the resulting FE models act as representative volume elements, reproduce bulk conductivities, and capture interfacial and defect-driven anisotropy while maintaining thermodynamic consistency. Additionally, SCACS predicts experimental conductance trends and fields. This work demonstrates a general route for transferring atomistic transport information into device-scale thermal simulations with physics-based approximations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2013

Multi-wavelength Radio Continuum Emission Studies of Dust-free Red Giants

Multi-wavelength centimeter continuum observations of non-dusty, non-pulsating K spectral-type red giants directly sample their chromospheres and wind acceleration zones. Such stars are feeble emitters at these wavelengths, however, and previous observations have provided only a small number of modest signal-to-noise measurements slowly accumulated over three decades. We present multi-wavelength Karl G. Jansky Very Large Array thermal continuum observations of the wind acceleration zones of two dust-free red giants, Arcturus (alpha Boo: K2 III) and Aldebaran (alpha Tau: K5 III). Importantly, most of our observations of each star were carried out over just a few days, so that we obtained a snapshot of the different stellar atmospheric layers sampled at different wavelengths, independent of any long-term variability. We report the first detections at several wavelengths for each star including a detection at 10 cm (3.0 GHz: S band) for both stars and a 20 cm (1.5 GHz: L band) detection for alpha Boo. This is the first time single (non-binary) luminosity class III red giants have been detected at these continuum wavelengths. Our long-wavelength data sample the outer layers of alpha Boo's atmosphere where its wind velocity is approaching (or possibly has reached) its terminal value and the ionization balance is becoming frozen-in. For alpha Tau, however, our long-wavelength data are still sampling its inner atmosphere, where the wind is still accelerating probably due to its lower mass-loss rate. We compare our data with published semi-empirical models based on ultraviolet data, and the marked deviations highlight the need for new atmospheric models to be developed. Spectral indices are used to discuss the possible properties of the stellar atmospheres, and we find evidence for a rapidly cooling wind in the case of alpha Boo. Finally, we develop a simple analytical wind model for alpha Boo based on our new long-wavelength flux measurements.

chromospheres↗
DOE OSTI2024

Radiative and continuum dampings of reversed shear Alfvén eigenmodes and perturbative analysis limitations for tokamaks

A careful theoretical analysis of the excitation of Alfvén eigenmodes (AEs), such as TAE (toroidicity-induced AE) and RSAE (reversed shear AE), by superalfvenic energetic particles is required for reliable predictions of energetic ion relaxation in present day fusion experiments. This includes the evaluation of different AE damping mechanisms including radiative and continuum dampings which are the focus of this study. A recent comprehensive benchmark of different eigenmode solvers including gyrokinetic, gyrofluid and hybrid magenetohydrodynamics (MHD) has shown that employed models may have deficiencies when addressing some of them (Taimourzadeh et al., Nucl. Fusion, vol. 59, 2019, 066006). Here, in this paper, we are studying the radiative and continuum dampings of RSAEs in details which were missing in hybrid NOVA/NOVA-C calculations to prepare a NOVA-C package with a substantial upgrade. Both dampings require the finite Larmor radius (FLR) corrections to AE mode structures to be accounted for. Accurately calculating different damping rates and understanding their parametric dependencies, we resolve the limitation coming out of the perturbative approach. In particular, here, the radiative damping is included perturbatively, whereas the continuum damping is computed non-perturbatively. Our comparison leads to the conclusion that the non-perturbative treatment of the unstable RSAE modes is needed to find the agreement with the gyrokinetic calculations. We expect that the RSAE mode structure modification plays a dominant role in determining the RSAE stability.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Anisotropic interactions for continuum modeling of protein–membrane systems

In this work, a model for anisotropic interactions between proteins and cellular membranes is proposed for large-scale continuum simulations. The framework of the model is based on dynamic density functional theory, which provides a formalism to describe the lipid densities within the membrane as continuum fields while still maintaining the fidelity of the underlying molecular interactions. Within this framework, we extend recent results to include the anisotropic effects of protein–lipid interactions. As applications, we consider two membrane proteins of biological interest: a RAS–RAF complex tethered to the membrane and a membrane embedded G protein-coupled receptor. A strong qualitative and quantitative agreement is found between the numerical results and the corresponding molecular dynamics simulations. Combining the scope of continuum level simulations with the details from molecular level particle simulations enables research into protein–membrane behaviors at a more biologically relevant scale, which crucially can also be accessed via experiment.

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

Non-Hermitian quantum mechanics approach for extracting and emulating continuum physics based on bound-state-like calculations: Detailed description

Here, this work applies a reduced basis method to study the continuum physics of a finite quantum system—either few or many-body. Specifically, I develop reduced-order models, or emulators, for the underlying inhomogeneous Schrödinger equation and train the emulators against the equation's bound-state-like solutions at complex energies. The emulators rapidly and accurately interpolate and extrapolate the matrix elements of the Hamiltonian resolvent operator (Green's function) across a parameter space that includes both complex energy and other real-valued physical inputs in the Schrödinger equation. The spectra, discretized and compressed as the result of emulation, and the associated resolvent matrix elements (or amplitudes), have the defining characteristics of non-Hermitian quantum mechanics calculations, featuring complex eigenenergies with negative imaginary parts and branch cuts moved below the real axis in the complex energy plane. Therefore, one now has a method that extracts continuum physics from bound-state-like calculations and emulates those extractions in the input parameter space. Building on a prior Letter [Zhang, Phys. Rev. Lett. 135, 242501 (2025)], this article provides the full theoretical details, a comprehensive analysis of the method's performance, and a brief discussion of how it can be coupled with existing continuum approaches to perform emulations in their input parameter spaces.

ab initio calculations↗
DOE OSTI2024

New Measurements of the Lyα Forest Continuum and Effective Optical Depth with LyCAN and DESI Y1 Data

Abstract We present the Ly α Continuum Analysis Network (LyCAN), a convolutional neural network that predicts the unabsorbed quasar continuum within the rest-frame wavelength range of 1040–1600 Å based on the red side of the Ly α emission line (1216–1600 Å). We developed synthetic spectra based on a Gaussian mixture model representation of nonnegative matrix factorization (NMF) coefficients. These coefficients were derived from high-resolution, low-redshift ( z < 0.2) Hubble Space Telescope/Cosmic Origins Spectrograph (COS) quasar spectra. We supplemented this COS-based synthetic sample with an equal number of DESI Year 5 mock spectra. LyCAN performs extremely well on testing sets, achieving a median error in the forest region of 1.5% on the DESI mock sample, 2.0% on the COS-based synthetic sample, and 4.1% on the original COS spectra. LyCAN outperforms principal component analysis (PCA) and NMF-based prediction methods using the same training set by 40% or more. We predict the intrinsic continua of 83,635 DESI Year 1 spectra in the redshift range of 2.1 ≤ z ≤ 4.2 and perform an absolute measurement of the evolution of the effective optical depth. This is the largest sample employed to measure the optical depth evolution to date. We fit a power law of the form τ ( z ) = τ 0 ( 1 + z ) γ to our measurements and find τ 0 = (2.46 ± 0.14) × 10 −3 and γ = 3.62 ± 0.04. Our results show particular agreement with high-resolution, ground-based observations around z = 2, indicating that LyCAN is able to predict the quasar continuum in the forest region with only spectral information outside the forest.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

Performance of continuum gas viscoseals.

Viscoseals performance as predicted by three different analytical models is compared with experimental data for air as the continuum gas sealant. An experimental investigation has been conducted on two multiple-grooved two-inch diameter viscoseals up to shaft speeds of 35,000 rpm. The two seal geometries considered differ significantly insofar as groove aspect ratio is concerned. The results of this continuum investigation of sealing coefficient for the gas viscoseals suggest that the Boon and Tal model is a good design tool for the laminar continuum regime provided it is restricted to high aspect ratio groove applications.

Wilkerson, H. J.↗
NASA NTRS1972

Inhomogeneous structure of the solar chromosphere from Lyman-continuum data.

A new model of the chromosphere is described that is based on Lyman-continuum observations by Harvard spectrometers aboard the satellites OSO 4 and OSO 6. The temperature, gas pressure, electron pressure, particle densities, and hydrogen ground-state departure coefficient are calculated as a function of height in the chromosphere. The model reproduces the observed quiet-region intensities in the Lyman continuum. The inhomogeneous structures, believed to be spicules, are inferred to be optically thick in the Lyman continuum and to have a source function below that of the mean chromosphere.

Vernazza, J. E.↗
NASA NTRS1973

Photodissociation continuums of N2 and O2.

Dissociation continuum cross sections for N2 and O2 have been determined from previously measured total absorption and ionization cross sections. Several dissociation continuums were found for each molecule. Some of these continuums were attributed to specific dissociation products in which the dissociation products are in excited states. The upper-atmosphere emission rates resulting from these photodissociative excitation processes have been calculated for the N I 10,400-A and O I 1356-A lines. The results indicate, particularly for the oxygen line, that these photodissociative processes may be important in the dayglow.

Cook, G. R.↗
NASA NTRS1974

Vibrational intensity distributions for continuum photoionization of oxygen

Results from measurements of vibrational intensity distributions for continuum photoionization of O2 are reported. Measurements were made using the 584 and 304 A He lines. The photoionization cross section of O2 shows a substantial dip in magnitude over a 20 A band centered about 590 A; thus the possibility exists that a 584 A photoelectron spectrum of O2 includes an autoionized contribution and the vibrational intensity distributions may not correspond to those of continuum ionization. Oxygen photoionization cross section shows no structure around 304 A and purley continuum ionization is expected.

Gardner, J. L.↗
NASA NTRS1974

The earth as a radio source: The non-thermal continuum

A weak nonthermal continuum, radiated by the earth from energetic electrons in the outer radiation zone, is studied. It is shown that the frequency spectrum of the continuum radiation consists of two components, a trapped component, which is permanently trapped within the magnetosphere at frequencies below the solar wind plasma frequency, and an escaping component which propagates freely away from the earth at frequencies above the solar wind plasma frequency. Direction finding measurements and measurements of the spatial distribution of intensity for both components indicated that the continuum radiation is generated (1) in a broad region which extends through the morning and early afternoon immediately beyond the plasmapause boundary, and (2) over a broad range of latitudes, including the magnetic equator. Possible mechanisms by which this radiation is generated, including gyro-synchrotron radiation from energetic electrons in the outer radiation zone, are discussed.

Gurnett, D. A.↗
NASA NTRS1974

Solar radio continuum storms

Radio noise continuum emission observed in metric and decametric wave frequencies is discussed. The radio noise is associated with actively varying sunspot groups accompanied by the S-component of microwave radio emissions. It is shown that the S-component emission in microwave frequencies generally occurs several days before the emission of the noise continuum storms of lower frequencies. It is likely that energetic electrons, 10 to 100 Kev, accelerated in association with the variation of sunspot magnetic fields, are the sources of the radio emissions. A model is considered to explain the relation of burst storms on radio noise. An analysis of the role of energetic electrons on the emissions of both noise continuum and type III burst storms is presented. It is shown that instabilities associated with the electrons and their relation to their own stabilizing effects are important in interpreting both of these storms.

Source record↗
NASA NTRS1975

The earth as a radio source - The nonthermal continuum

It is shown that a weak nonthermal continuum is produced by the earth's magnetosphere extending over a very wide range of frequencies, from 500 Hz in the low-density regions of the magnetotail to above 100 kHz. The frequency spectrum of the continuum radiation consists of two components: a trapped component within the magnetosphere at frequencies below the solar wind plasma frequency and an escaping component propagating freely away from the earth at frequencies above the solar wind plasma frequency. It is also shown that the continuum radiation is generated in a broad region extending through the morning and early afternoon from about 4.0 to 14.0 hours local time immediately beyond the plasmapause boundary, at radial distances from 4.0 to 8.0 earth radii. Possible mechanisms underlying the generation of this radiation are discussed, including the gyrosynchrotron radiation from energetic electrons in the outer radiation zone.

Gurnett, D. A.↗
NASA NTRS1975

Growth of metric noise continuum storms and its relation to the source of microwave S-emissions

The relationship between metric noise continuum storms and the S-component of solar microwave emissions is examined by considering the properties of a solar active region and its relation to LF radio burst emissions observed by IMP 6. It is noted that the development of radio noise continuum sources in metric frequencies or less is usually preceded by the appearance of an S-emission source, which is formed in complex sunspot groups such as beta-gamma and gamma types. A model for the development of radio noise continuum sources in metric and decametric frequencies is proposed in which the development of relationships between emissions is closely connected to the growth of magnetic-field lines above associated sunspot groups into complex configurations.

Sakurai, K.↗
NASA NTRS1975

The solar-flare infrared continuum

Potential sources of infrared (1 micron to 1 mm) continuum in solar flares are considered. Several mechanisms should produce detectable fluxes: in the 350 micron window for ground-based observations, impulsive emission will arise in synchrotron radiation from 1-10 MeV electrons, and possibly thermal (free-free) continuum from the source of the white-light flare; the hot flare plasma responsible for soft X-ray emission will also emit detectable fluxes of free-free continuum in the largest flares. At shorter wavelengths the dominant infrared emission will come from the H alpha flare itself. Observations in the infrared wavelengths will help to complete the picture of flare structure in both the impulsive and gradual phases.

Ohki, K.↗
NASA NTRS1976

Solar radio continuum storms

The paper reviews the current status of research on solar radio continuum emissions from metric to hectometric wave frequencies, emphasizing the role of energetic electrons in the 10-100 keV range in these emissions. It is seen that keV-energy electrons generated in active sunspot groups must be the sources of radio continuum storm emissions for wide frequency bands. These electrons excite plasma oscillations in the medium, which in turn are converted to electromagnetic radiation. The radio noise continuum sources are usually associated with type III burst activity observed above these sources. Although the mechanism for the release of the energetic electrons is not known, it seems they are ejected from storm source regions in association with rapid variation of associated sunspot magnetic fields due to their growth into complex types. To explain some of the observed characteristics, the importance of two-stream instability and the scattering of ambient plasma ions on energetic electron streams is pointed out.

Sakurai, K.↗