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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Theoretical and numerical studies of inverse source problem for the linear parabolic equation with sparse boundary measurements

We consider the inverse source problem in the parabolic equation, where the unknown source possesses the semi-discrete formulation. Theoretically, we prove that the flux data from any nonempty open subset of the boundary can uniquely determine the semi-discrete source. This means the observed area can be extremely small, and that is the reason we call it sparse boundary data. For the numerical reconstruction, we formulate the problem from the Bayesian sequential prediction perspective and conduct the numerical examples which estimate the space-time-dependent source state by state. To better demonstrate the method’s performance, we solve two common multiscale problems from two models with a long source sequence. The numerical results illustrate that the inversion is accurate and efficient.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2022

Trade Study of DEM Software

Review of Open-source Discrete Element Method Softwares: Three open-source solutions have been investigated for integration into OceanWATERS: Yade, EsysParticle, and ProjectChrono.

DEM↗
NASA NTRS1993

Detection of the N II 122 and 205 micron lines - Densities in G333.6-0.2

Measurements of the G333.6-0.2 H II region which include the first detection of the N II 122 micron forbidden line in an astronomical force and the first measurement of the N II 205 micron forbidden line in a discrete source are presented. Also considered are fine structure lines of forbidden S III, forbidden Fe III, forbidden Si II, forbidden Ne III, forbidden O III, forbidden N III, forbidden O I, and forbidden C II from 19 to 206 microns. It is concluded that the N II 122 and 205 microns forbidden line pair in a discrete astronomical source was detected for the first time. The emission in transitions is produced largely by low-ioninzation, low-density material not easily probed by other lines. Other FIR line pairs generally originate in higher density regions closer to the exciting force.

Colgan, Sean W. J.↗
DOE OSTI2024

Constraints on the origin of the radio synchrotron background via angular correlations

ABSTRACT The origin of the radio synchrotron background (RSB) is currently unknown. Its understanding might have profound implications in fundamental physics or might reveal a new class of radio emitters. In this work, we consider the scenario in which the RSB is due to extragalactic radio sources and measure the angular cross-correlation of Low-Frequency Array (LOFAR) images of the diffuse radio sky with matter tracers at different redshifts, provided by galaxy catalogues and cosmic microwave background lensing. We compare these measured cross-correlations to those expected for models of RSB sources. We find that low-redshift populations of discrete sources are excluded by the data, while higher redshift explanations are compatible with available observations. We also conclude that at least 20 per cent of the RSB surface brightness level must originate from populations tracing the large-scale distribution of matter in the Universe, indicating that at least this fraction of the RSB is of extragalactic origin. Future measurements of the correlation between the RSB and tracers of high-redshift sources will be crucial to constraining the source population of the RSB.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

High-energy gamma-ray astronomy

The subject of gamma-ray astronomy is discussed with emphasis on celestial gamma rays with energies in excess of 10 MeV. Early observations of such gamma rays are reviewed, a gamma-ray spark-chamber telescope is described together with a gas Cerenkov-counter telescope, and the gamma-ray sky is delineated. It is shown that the diffuse high-energy gamma radiation from the galactic plane probably results primarily from cosmic-ray interactions with interstellar matter. Mechanisms for gamma-ray production are identified, and it is noted that the general galactic radiation may prove to be of great value in studies of galactic structure. Possible sources are considered for the diffuse celestial radiation, and discrete sources are described, including the Crab pulsar, the Vela remnant, the Cygnus region, and Gould's Belt. Future developments in gamma-ray astronomy are considered.

Fichtel, C.↗
NASA NTRS1994

Cygnus A -- John Bolton's first cosmic source

Using a sea interferometer, Bolton and Stanley isolated Cygnus A as a discrete source in 1948. It is a prime example of a powerful radio galaxy and, in the last decade, has also been studied extensively in X-rays. In this paper I summarize the results from a ROSAT X-ray image.

Harris, D. E.↗
NASA NTRS1978

High-resolution observations of X-ray sources at the galactic center

A region about 1 deg of arc in radius and centered on the galactic nucleus has been surveyed during a rocket flight, using X-ray detectors equipped with 10-arcmin by 4-deg (FWHM) collimators. The extended source 4U 1743-29 has been resolved into at least four discrete sources having luminosities (2-10 KeV) between 4 by 10 to the 36th power and 3.5 by 10 to the 37th power erg/s.

Cruddace, R. G.↗
NASA NTRS1987

The large-scale radio structure of R Aquarii

Radio continuum observations of the R Aqr symbiotic star system, using the compact D configuration of the VLA at 6-cm wavelength, reveal a large-scale about 2-arcmin structure engulfing the binary, which has long been known to have a similar optical nebula. This optical/radio nebula possesses about 4 x 10 to the 42nd ergs of kinetic energy which is typical of a recurrent nova outburst. Moreover, a cluster of a dozen additional 6-cm radio sources were observed in proximity to R Aqr, most of these discrete sources lie about 3 arcmin south and/or west of R Aqr and, coupled with previous 20-cm data, spectral indices limits suggest a thermal nature for some of these sources. If the thermal members of the cluster are associated with R Aqr, it may indicate a prehistoric eruption of the system's suspected recurrent nova. The nonthermal cluster members may be extragalactic background radio sources.

Hollis, J. M.↗
NASA NTRS1975

Infrared, X-ray, and XUV astrophysics

An observational program covering wavelengths from the near infrared to 1 millimeter is reviewed. The program of millimeter observations largely consisted of analyzing previous observations since the summer humidity was too high for new observations. Maps of millimeter emission from W3, Sgr B2, W49 and M42 were made. Five extragalactic sources were detected and are discussed. Energy distributions of several of the discrete sources at the Galactic Center were studied. A 5-year visual/infrared program on Markarian galaxies is discussed which showed the presence of both thermal and nonthermal infrared radiation sources and established correlations between the infrared sources and the emission line regions. The Nova Cygnus 1975, caught during its rise as well as subsequent dimming, is also discussed. Several other continuing programs are described, including studies of dark clouds and CO maser sources.

Source record↗
NASA NTRS1978

A ring-source model for jet noise

A model consisting of two ring sources was developed to study the direct radiation of jet noise in terms of correlation, coherence, and phase and also to aid in solving the inverse radiation problem of determining the noise source in terms of far-field measurements. The rings consist of discrete sources which are either monopoles or quadrupoles with Gaussian profiles. Only adjacent sources, both within the rings and between rings, are correlated. Results show that from the far-field information can be used to determine when the sources are compact or noncompact with respect to the acoustic wavelength and to distinguish between the types of sources. In addition, from the inverse radiation approach, the center of mass, the location and separation distance of the ring, and the diameters can be recovered.

Maestrello, L.↗
NASA NTRS1994

VLA stereoscopy of solar active regions. 2: Altitude, relative motion, and center-to-limb darkening of 20 centimeter emission

A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of q(sub A) approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin(exp 2)B)). 5. We find a statistical limb darkening, which can be described by the relation (T(sub B)(alpha))/T(sub B)(0)) = 0.4 + ((0.6(cos(exp 2) alpha)) for sources with T(sub B) greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance.

Aschwanden, Markus J.↗
DOE OSTI2024

A High-Performance Discrete-Element Framework for Simulating Flow and Jamming of Moisture Bearing Biomass Feedstocks

We developed and verified a high-performance open-source discrete element method (DEM) solver with simultaneously-supported feedstock-specific interaction models, including bonded-sphere, liquid bridge, cohesion, and non-linear contact models. Our solver uses parallel data structures on hybrid central and graphics processing unit (CPU/GPU) architectures, with favorable strong scaling performance observed for large problem sizes comprised of (100 M particles), and 4X single-node GPU speedup. The particles for corn stover feedstock were conceptualized and calibrated based on experimental measurements and results. Sensitivity analyses demonstrate that the mass flow rate from a wedge hopper is governed primarily by moisture content, friction coefficient, and cohesion energy density. The model is used to reproduce experimentally observed hopper jamming results, highlighting that the experimental no-flow trends can only be achieved by using non-spherical particles, liquid bridge and cohesion models, highlighting the importance of using concurrent feedstock specialized models for the effective representation of biomass material handling problems.

bioenergy↗
NASA NTRS1972

Upper limits to the soft X-ray emission of sources in Virgo.

Discussion of the soft X-rays from Virgo observed with a scanning focusing collector from an Aerobee 170 rocket. The region included the center of the Virgo cluster of galaxies, a source of higher energies which had been previously identified with M87, and QSO 3C 273. No discrete sources in Virgo were observed.

Gorenstein, P.↗
NASA NTRS1974

Galactic X-ray sources

Data on galactic X-ray sources from rocket and balloon experiments and the UHURU satellite are reported. The outline emphasizes general discrete source models and begins with some a priori considerations about X-ray emission mechanisms and their applicability, after which contemporary data are interpreted according to these models. Topics covered include the production of X-rays by various mechanisms, source regimes, observational parameters, stellar distributions, individual stars, flare stars, supernovae and pulsars, the Crab nebula, old and young remnants, binary systems, and others.

Holt, S. S.↗
NASA NTRS2008

X-Ray Source Motions and Their Implications for Flare Models

RHESSI observations have revealed a downward contraction of solar flare loops followed by upward expansion. In some flares a pair of above-the-looptop sources is observed, one just above the top of the cooler flare loops and the other a discrete source well above the looptops characterized by an effective temperature gradient increasing toward lower altitudes. In one flare the higher, temperature-inverted coronal source sped outward at a speed consistent with that of a coronal mass ejection associated with the flare. In some flares with minimal preheating (early impulsive flares), nonthermal X-ray sources have been observed to propagate downward and then upward along the legs of the flare loop. I will discuss the implications of all of these X-ray source motions for flare models, and their use as diagnostics of the evolution of the physical conditions in flares.

Holman, Gordon D.↗
NASA NTRS2006

Multiwavelength Study of the Bright X-ray Source Population in the Interacting Galaxies NGC 5774/NGC 5775

The X-ray source population in the field of the interacting pair of galaxies NGC 5774/5775 is reported. A total of 49 discrete sources are detected, including 12 ultraluminous X-ray source candidates with lum inosities above 10(exp 39)erg/s in the 0.5 - 8.0 keV X-ray band. Several of these latter are transient X-ray sources that fall below detect ion levels in one of two X-ray observations spaced 15 months apart. X-ray source positions are mapped onto optical and radio images to sear ch for potential counterparts. Eleven sources have optically-bright c ounterparts. Optical colors are used to differentiate these sources, which are mostly located outside the optical extent of the interacting galaxies, as potential globular clusters (3 sources) and quasars (5) . Follow-up optical spectroscopy confirms two of the latter are background quasars.

Ghosh, Kajal K.↗
NASA NTRS1988

The contribution to the gamma-ray background from a superposition of 3C 273-like jet sources

Recent theories suggest that quasar jets may produce the gamma-ray emission observed in sources such as 3C 273. One of these theories is tested to see if it is consistent with observations of the gamma-ray background. Quasar jets are taken as the source of this radiation, each with the spectrum of the nearby quasar 3C 273, and with an evolution in time based on a model for the observed gamma-rays of 3C 273. In that model, a plasma jet interacts with the ambient intergalactic gas to produce (from nuclear collisions) secondary electrons which lead to isotropic bremsstrahlung gamma-rays, and ultimately to a double radio source. It is shown that the gamma-ray background can be modeled in general as a superposition of such discrete sources of various redshifts. The results are consistent with the observed background intensity and spectral form; of course, there are uncertain and adjustable parameters.

Sadun, Alberto C.↗