Search NASA⌕ Search

SEARCH · Search NASA

Results for “energy band alignments”

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.

49 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Quantification of Error Associated with Using Misaligned Meshes in Continuum Damage Mechanics Material Models for Matrix Crack Growth Predictions in Composites

The ability of a material model to capture in-plane matrix mode I and mode II crack growth is an essential component for modeling ply level damage evolution in composite structures. Previous studies using a continuum damage mechanics (CDM) approach have shown success in satisfying benchmark solutions for mode I and II crack growth. However, success was shown using a fiber-aligned meshing strategy, which encourages matrix cracks to propagate in a single band of elements, along the fiber direction. Generating a fiber-aligned mesh becomes a highly involved process for laminates including off-axis (non 0° or 90°) plies. The objective of this study is to quantify the effect of non-fiber aligned mesh discretization on predictions of in-plane matrix crack propagation. The approach taken incrementally varies the mesh orientation angle relative to the fiber orientation; more specifically, misaligned meshes are used to quantify the effect of element angle orientation relative to the initial crack orientation on the energy released during matrix crack propagation simulations using a CDM method. CDM solutions obtained with the misaligned meshes are evaluated against known benchmarks for mode I and II matrix crack growth. The CDM solutions reveal a near-polynomial trend of increased predicted failure stress with increased mesh misalignment angle; hence implying a potential relationship between element orientation angle and apparent fracture toughness.

Justusson, Brian↗
NASA NTRS2020

On-Ground Calibration of the HaloSat Science Instrument

HaloSat is a CubeSat-class microsatellite sensitive in the0.4−7.0keV energy band and designed to survey the entire sky in search of soft X-ray emission from highly ionized oxygen residing in the halo of the Milky Way galaxy. Those observations will help constrain the mass and spatial distribution of the Milky Way halo and help us understand if hot galactic halos constitute a significant contribution to the overall cosmological baryon budget. In this paper we describe the science instrument calibration products, including channel-to-energy transformation, instrument energy resolution and instrument response, and the on-ground efforts that led to their creation. We also describe the alignment process used to obtain the field of view information for the HaloSat science instrument.

Anna Zajczyk↗
NASA NTRS1990

4C 41.17 - A radio galaxy at a redshift of 3.8

Observations, comprising radio imaging at three frequencies, optical broadband and narrow-band imaging, optical spectroscopy, and K-band IR imaging, of a distant radio source, 4C 41.17, are presented. It is shown that 4C 41.17 is associated with an extended source of optical and IR emission at a redshift of 3.8. The morphological similarities between the radio source and the ionized gas and optical/IR continua suggest that the radio source is interacting vigorously with the galaxy. Various mechanisms for producing the optical/IR emission in 4C 41.17 are considered. It is concluded that a large fraction of the spectral energy distribution is from stars, and that the star formation induced by the radio source is the likely mechanism to account for the radio/optical alignment.

Chambers, K. C.↗
NASA NTRS1989

Ionospheric dynamo theory for production of far ultraviolet emissions on Uranus

A model is presented to explain diffuse FUV emissions from the outer planets, specifically Uranus, in excess of those diffuse emissions that are currently explainable by scattering of sunlight and/or excitation by photoelectrons. These electroglow emissions in H Ly-alpha and H2 bands, which occur in the sunlit hemisphere slightly above the homopause, appear to require particle excitation in the 10- to 50-eV range. An in situ mechanism for accelerating photoelectrons (and ions is proposed, involving neutral wind dynamo generation of field-aligned currents analogous to what occurs in the earth's equatorial E and F regions. Sufficiently strong field-aligned currents are found in the model calculation for Uranus to produce a potential drop of about 100 eV or greater between the F peak and homopause, concentrated at lower altitudes, and capable in principle of accelerating photoelectrons (and ions) to the 10- to 50-eV energies required to explain the observed emissions. The fact that the excitation and ionization cross sections are larger than elastic scattering cross sections in an H2 atmosphere at these energies makes in situ acceleration feasible for the production of UV on the outer planets.

Hudson, M. K.↗
NASA NTRS1999

A Highly Doppler Blueshifted Fe-K Emission Line in the High-Redshift QSO PKS 2149-306

We report the results from an ASCA observation of the high-luminosity, radioloud quasar PKS 2149-306 (redshift 2.345), covering the approximately 1.7 - 30 keV band in the quasar-frame. We find the source to have a luminosity of approximately 6 x 10(exp 47) ergs/s in the 2 - 10 keV band (quasar frame). We detect an emission line centered at approximately 17 keV in the quasar frame. Line emission at this energy has not been observed in any other active galaxy or quasar to date. We present evidence rejecting the possibility that this line is the result of instrumental artifacts, or a serendipitous source. The most likely explanation is blueshifted Fe-K emission (the equivalent width, is EW approximately 300 +/- 200 eV, quasar frame). Bulk velocities of the order of 0.75c are implied by the data. We show that Fe-K line photons originating in an accretion disk and Compton-scattering off a leptonic jet aligned along the disk axis can account for the emission line. Curiously. if the emission-line feature recently discovered in another quasar (PKS 0637-752, z = 0.654) at 1.6 keV in the quasar frame, is due to blueshifted OVII emission, the Doppler blueshifting factor in both quasars is similar (approximately 2.7 - 2.8).

Yaqoob, Tahir↗
NASA NTRS2011

Development of the ASTRO-H Soft X-ray Telescope (SXT): Engineering Model Performance

The X-ray astronomy satellite ASTRO-H, being developed under the collaboration among JAXA, NASA's GSFC and ESA, will have two Soft X-ray Telescopes (SXTs), among other instuments onboard, with a sensitive energy band below 12 keV. One is for an X-ray micorocalorimeter detector and the other for a X-ray CCD detector. The SXT uses a conically approximated Wolter I grazing incidence optic implemented by thin aluminum foil substrates with thickness of 0.152, 0.229, and 0.305 mm. It is similar to the Suzaku XRT, but with larger diameter (45 cm) and longer focal length (5.6 m). Goal of the angular resolution and effective area are 1 arcmin and 390 cm$A2$ at 6 keV, respectively. We made serveral improvements from Suzaku to ASTRO-H, such as thicker substrates, more forming mandrels, thinner epoxy layer for replication, stiffer housings, precise alignment bars, etc. With all these changes, we have fabricated the engineering test unit of the SXT. In this paper, we will discuss all the changes made, their effects, and report X-ray performance of the SXT test unit. An angular resolution of the test unit was measured at new Goddard X-ray calibration facility (100 m X-ray beamline) and was found to be 1.1 arcmin. We will also discuss further improvements toward the flight unit to be delivered to JAXA in 2012.

Okajima, Takashi↗
NASA NTRS1995

The X-ray telescope on board ASCA

The Advanced Satellite for Cosmology and Astrophysics (ASCA) instrument uses identical conical foil X-ray mirrors for its four telescopes. One of the major advantages of ASCA's telescopes is the first time ever use of X-ray imaging over a broad energy band and high throughput for conducting astronomical spectroscopy. Nested thin foil reflectors make possible a large effective area up to 10 keV, even under the tight weight restriction of the ASCA spacecraft. The expected characteristics of the ASCA mirrors are summarized based on ray tracings and pre-flight calibrations. The total effective area of four telescopes at 1 and 7 keV are approximately 1200 and 600 sq cm, respectively. The image size (half power diameter: HPD) is about 3 min. The field of view is 24 min and 16 min full width at half maximum for 1 and 7 keV, respectively. Observations of several X-ray sources from space during the performance verification phase have confirmed those performances as well as the alignment of the optical systems.

Serlemitsos, Peter J.↗
NASA NTRS1991

UGC galaxies stronger than 25 mJy at 4.85 GHz

UGC galaxies in the declination band +5 to +75 deg were identified by position coincidence with radio sources stronger than 25 mJy on the Green Bank 4.85 GHz sky maps. Candidate identifications were confirmed or rejected with the aid of published aperture-synthesis maps and new 4.86 GHz VLA maps having 15 or 18 arcsec resolution, resulting in a sample of 347 nearby radio galaxies plus five new quasar-galaxy pairs. The radio energy sources in UGC galaxies were classified as 'starbursts' or 'monsters' on the basis of their infrared-radio flux ratios, infrared spectral indices, and radio morphologies. The rms scatter in the logarithmic infrared-radio ratio q is not more than 0.16 for starburst galaxies selected at 4.85 GHz. Radio spectral indices were obtained for nearly all of the UGC galaxies, and S0 galaxies account for a disproportionate share of the compact flat-spectrum (alpha less than 0.5) radio sources. The extended radio jets and lobes produced by monsters are preferentially, but not exclusively, aligned within about 30 deg of the optical minor axes of their host galaxies. The tendency toward minor-axis ejection appears to be independent of radio-source size and is strongest for elliptical galaxies.

Condon, J. J.↗
NASA NTRS2018

The Hitomi X-Ray Observatory, Part 2

When it was launched on 17 February 2016, the Hitomi X-ray Observatory carried four kinds of new-generation x-ray instruments—the Soft X-ray Spectrometer (SXS), the Soft X-ray Imager (SXI), the Hard X-ray Imager (HXI), and the Soft Gamma-ray Detector (SGD). All four instruments were turned on and were in the process of activation at the time of loss of contact on 26 March 2016. In the time it was operational, Hitomi was able to provide researchers with a trove of ground-breaking scientific results. Initial results demonstrated that the instruments were meeting or exceeding requirements and that Hitomi was on its way to pioneering a new era of broad-band and high-resolution x-ray spectroscopy. The results published here summarize the in-flight instrument performance, calibration, and data processing accomplishments of the observatory. Of the papers accepted for publication in this special section, 17 were presented in Part 1 in the January-March 2018 issue of JATIS (Journal of Astronomical Telescopes, Instruments, and Systems). Ten more papers are presented here as Part 2 in the April-June 2018 issue. These papers cover the detailed in-flight performance of the four state-of the-art instruments on-board the Hitomi X-Ray Observatory. These instruments were extremely diverse in their design and principles of operation, ranging from low temperature x-ray calorimeters for high-resolution spectroscopy, CCDs (Charge-Coupled Devices) for wide field imaging, high fill-factor grazing incidence x-ray optics, including multilayer x-ray optics and silicon strip and CdTe strip detectors for high-energy imaging, and a Si/CdTe Compton cameras for extending the bandpass out to 600 kiloelectronvolts. All of these instruments operated as expected and for sufficient time to validate their operating principles and carry out first light scientific investigations, published elsewhere. Collectively, these instruments, all co-aligned and operated simultaneously, provided a tool for astronomers with unprecedented resolution and broadband sensitivity for investigating high-energy processes throughout the universe. These papers serve as part of the Hitomi legacy and will guide the next generation of instruments planned for future missions.

Kelley, Richard L.↗
NASA NTRSDate not supplied

Assimilation of Soil Moisture Observations Over Land Improves Analysis and Prediction of Tropical Cyclone Idai

Soil moisture conditions can impact the circulation and structure of a tropical cyclone (TC) when part or all of the circulation is over land. Dry land surface conditions may lead to faster dissipation of a TC over land, whereas very wet conditions may lead to a prolonged maintenance of its intensity. While this relationship is relatively well understood in theory, applications of these findings in the context of numerical weather prediction (NWP) have been limited. Here we present a case study that explores the potential of improving TC predictions through an improved soil moisture initialization in an NWP framework. Specifically, we examine the impact of assimilating observations from the NASA Soil Moisture Active Passive (SMAP) mission into the NASA Goddard Earth Observing System (GEOS) global weather model on the prediction of South-West Indian Ocean TC Idai (2019). SMAP provides accurate L-band (1.4 GHz) brightness temperatures (Tb) observations that are sensitive to soil moisture globally and at high revisit times of 2-3 days. It has previously been shown that the assimilation of SMAP Tbs significantly improves modeled land surface states. Here we evaluate: (i) forecasts initialized from an analysis that is comparable to the GEOS operational analysis (without SMAP Tb assimilation) and (ii) forecasts initialized from an analysis that additionally assimilates SMAP Tb observations. We find that in the analysis with SMAP assimilation, the TC has a better-defined, more aligned vertical structure over land relative to the control run; moreover, the analyzed TC size, as measured by the wind speed radius, better matches the observed TC size. We further find significant reductions in the forecast intensity error and the forecast along-track error, measured against observations. The largest error reductions occur at lead times of 36 to 72 hours, suggesting that the land with its longer memory gains in importance as a source of predictability at this timescale. An investigation of the underlying mechanisms leading to the skill improvements from SMAP data assimilation revealed that the assimilation of SMAP leads to wetter soil moisture conditions and an increased latent heat flux in the SMAP analysis, which results in a TC with higher column-integrated total moisture content and total energy compared to the control analysis.

Jana Kolassa↗
NASA NTRS2013

The Nuclear Spectroscopic Telescope Array (NuSTAR) High-Energy X-ray Mission

High-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the 10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: (1) probe obscured active galactic nucleus (AGN) activity out to thepeak epoch of galaxy assembly in the universe (at z 2) by surveying selected regions of the sky; (2) study the population of hard X-ray-emitting compact objects in the Galaxy by mapping the central regions of the Milky Way; (3) study the non-thermal radiation in young supernova remnants, both the hard X-ray continuum and the emission from the radioactive element 44Ti; (4) observe blazars contemporaneously with ground-based radio, optical, and TeV telescopes, as well as with Fermi and Swift, to constrain the structure of AGN jets; and (5) observe line and continuum emission from core-collapse supernovae in the Local Group, and from nearby Type Ia events, to constrain explosion models. During its baseline two-year mission, NuSTAR will also undertake a broad program of targeted observations. The observatory consists of two co-aligned grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis stabilized spacecraft. Deployed into a 600 km, near-circular, 6 inclination orbit, the observatory has now completed commissioning, and is performing consistent with pre-launch expectations. NuSTAR is now executing its primary science mission, and with an expected orbit lifetime of 10 yr, we anticipate proposing a guest investigator program, to begin in late 2014.

Nuclear↗
NASA NTRS1994

Hubble Space Telescope Planetary Camera observations of Arp 220

Planetary Camera images of peculiar galaxy Arp 220 taken with V, R, and I band filters reveal a very luminous object near the position of the western radio continuum source, assumed to be the major nucleus, ans seven lesser objects within 2 sec of this position. The most luminous object is formally coincident with the radio source to within the errors of Hubble Space Telescope (HST) pointing accuracy, but we have found an alternate, more compelling alignment of maps in which the eastern radio source coincides with one of the lesser objects and the OH radio sources reside near the surfaces of other optical objects. The proposed centering places the most luminous object 150 pc (0.4 sec) away from the western radio source. We explore the possibilities that the objects are either holes in the dense dust distribution, dusty clouds reflecting a hidden bright nucleus, or associations of bright young stars. We favor the interpretation that at least the brightest two objects are massive young star associations with luminosities 10(exp 9) to 10(exp 11) solar luminosity, but highly extinguished by intervening dust. These massive associations should fall into the nucleus on a time scale of 10(exp 8) yr. About 10% of the enigmatic far-IR flux arises from the observed objects. In addition, if the diffuse starlight out to a radius of 8 sec is dominated by stars with typical ages of order 10(exp 8) yr (the time since the alleged merger of two galaxies), as indicated by the blue colors at larger radius, then the lower limit to the reradiation of diffuse starlight contributes 3 x 10(exp 11) solar luminosity to the far-infrared flux, or greater than or equal to 25% of the total far-IR flux. Three additional bright objects (M(sub V) approximately equals -13) located about 6 sec from the core are likely young globular clusters, but any of these could be recently exploded supernovae instead. The expected supernovae rate, if the dominant energy source is young stars, is about one per month for the region where the intense far-infrared flux originates. Also, individual giant dust clouds are visible in these images. Their typical size is 300 pc (1 sec).

Shaya, Edward J.↗
NASA NTRS1995

Coronagraphic imaging of pre-main-sequence stars: Remnant evvelopes of star formation seen in reflection

We have obtained R- and I-band coronagraphic images of the vicinities of 11 pre-main sequence (PMS) stars to search for faint, small-scale reflection nebulae. The inner radius of the search and the field of view are 1.9 arcsec and 1x1 arcmin, respectively. Reflection nebulae were imaged around RY Tau, T Tau,DG Tau, SU Aur, AB Aur, FU Ori, and Z CMa. No nebulae were detected around HBC 347, GG Tau, V773 Tau, and V830 Tau. Categorically speaking, most of the classical T Tauri program stars and all the FU Orionis-type program stars are associated with the reflection nebulae, while none of the weak-line T Tauri program stars are associated with nebulae. The detected nebulae range in size from 250 to 37 000 AU. From the brightness ratios of the stars and nebulae, we obtain a lower limit to the visual extinction of PMS star light through the nebulae of (A(sub V))(sub neb) = 0.1. The lower limits of masses and volume densities of the nebulae associated with the classical T Tauri stars are 10(exp-6) Solar mass and N(sub H) = 10(exp 5)/cu cm, respectively. Lower limits for the nebulae around FU Orionis stars are 10(exp -5) Solar mass and n(sub H) = 10 (exp 5)/cu cm, respectively. Some reflection nebulae may trace the illuminated surfaces of the optically thick dust nebulae, so these mass estimates are not stringent. All the PMS stars with associated nebulae are strong far-infrared emitters. Both the far-infrared emission and the reflection nebulae appear to originate from the remnant envelopes of star formation. The 100 micrometers emitting regions of SU Aur and FU Ori are likely to be cospatial with the reflection nebulae. A spatial discontinuity between FU Ori and its reflection nebula may explain the dip in the far-infrared spectral energy distribution at 60 micrometers. The warped, disk-like nebulae around T Tau and Z CMa are aligned with and embrace the inner star/circumstellar disk systems. The arc-shaped nebula around DG Tau may be in contact with the coaligned inner star/disk system. These three-reflection nebulae may trace the surfaces of pseudodisks from which matter accretes onto the stars or the inner circumstellar disks. 19 stellar objects brighter than I = 19 were detected around 9 program stars. Using a color-magnitude diagram, we have identified three new PMS candidates aroun Z CMa and one previously known PMS candidate, GG Tau/c.

Nakajima, Tadashi↗