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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The application of the Wigner Distribution to wave type identification in finite length beams

The object of the research described in this paper was to develop a means of identifying the wave-types propagating between two points in a finite length beam. It is known that different structural wave-types possess different dispersion relations: i.e., that their group speeds and the frequency dependence of their group speeds differ. As a result of those distinct dispersion relationships, different wave-types may be associated with characteristic features when structural responses are examined in the time frequency domain. Previously, the time-frequency character of analytically generated structural responses of both single element and multi-element structures were examined by using the Wigner Distribution (WD) along with filtering techniques that were designed to detect the wave-types present in the responses. In the work to be described here, the measure time-frequency response of finite length beam is examined using the WD and filtering procedures. This paper is organized as follows. First the concept of time-frequency analysis of structural responses is explained. The WD is then introduced along with a description of the implementation of a discrete version. The time-frequency filtering techniques are then presented and explained. The results of applying the WD and the filtering techniques to the analysis of a transient response is then presented.

Wahl, T. J.↗
DOE OSTI2020

Determination of excited state molecular structures from time-resolved gas-phase X-ray scattering

We present a comprehensive investigation of a recently introduced method to determine transient structures of molecules in excited electronic states with sub-ångstrom resolution from time-resolved gas-phase scattering signals. The method, which is examined using time-resolved X-ray scattering data measured on the molecule N-methylmorpholine (NMM) at the Linac Coherent Light Source (LCLS), compares the experimentally measured scattering patterns against the simulated patterns corresponding to a large pool of molecular structures to determine the full set of structural parameters. In addition, we examine the influence of vibrational state distributions and find the effect negligible within the current experimental detection limits, despite that the molecules have a comparatively high internal vibrational energy. Here, the excited state structures determined using three structure pools generated using three different computational methods are in good agreement, demonstrating that the procedure is largely independent of the computational chemistry method employed as long as the pool is sufficiently expansive in the vicinity of the sought structure and dense enough to yield good matches to the experimental patterns.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Spatio-temporal electric field distributions in an atmospheric plasma jet impinging on a microchannel array surface

The electric field distribution in the ionization waves (IWs) propagating over a microchannel array dielectric surface, with the channels either empty or filled with distilled water, is measured by ps electric field induced second harmonic generation. The surface IW is initiated by the atmospheric pressure N 2 –Ar plasma jet impinging on the surface vertically and powered by ns pulse discharge bursts. The results show that the electric field inside the microchannels, specifically its horizontal component, is enhanced by up to a factor of 2. The field enhancement region is localized within the channels. The vertical electric field inside the channels lags in time compared to the field measured at the ridges, indicating the transient reversal of the IW propagation direction across the channels (toward the jet). This is consistent with the phase-locked plasma emission images and confirmed by the kinetic modeling predictions, which show that the IW ‘jumps’ over the empty channels and propagates into the channels only after the jump between the adjacent ridges. When the channels are filled with water, the wave speed increases by up to 50%, due to the higher effective dielectric constant of the surface. No evidence of a significant electric field enhancement near the dielectric surface (ceramic or water) has been detected, within the spatial resolution of the present diagnostic, ~100 μ m.

plasmas and liquids↗
NASA NTRS1997

The Decay of Optical Emission Form the Gamma-Ray Burst GRB 970228

The origin of gamma-ray bursts has been one of the great unsolved mysteries in high-energy astrophysics for almost 30 years. The recent discovery of fading sources at X-ray and optical wave-lengths coincident with the location of the gamma-ray burst GRB970228 therefore provides an unprecedented opportunity to probe the nature of these high-energy events. The optical counterpart appears to be a transient point source embedded in a region of extended nebulosity, the latter having been tentatively identified as a high-redshift galaxy. This would seem to favour models that place gamma-ray bursts at cosmological distances, although a range of mechanisms for producing the bursts is still allowed. A crucial piece of information for distinguishing between such models is how the brightness of the optical counterpart evolves with time. Here we re-evaluate the existing photometry of the optical counterpart of GRB970228 to construct an optical light curve for the transient event. We find that between 21 hours and six days after the burst, the R-band brightness decreased by a factor of approx. 50, with any subsequent decrease in brightness occurring at a much slower rate. As the point source faded, it also became redder. The initial behaviour of the source appears to be consistent with the 'fireball' model, in which the burst results from the merger of two neutron stars, but the subsequent decrease in the rate of fading may prove harder to explain. The gamma-ray burst of 28 February 1997, detected with the Gamma-Ray Burst Monitor on board the BeppoSAX satellite, and located with an approx. 3 feet radius position with the Wide Field Camera on the same satellite, was the first for which a fading X-ray and optical counterpart were discovered. The optical Counterpart was discovered from a comparison of V- and I-band images taken with the William Herschel Telescope (WHT) on February 28.99 UT, and the Isaac Newton Telescope (INT; V band) and the WHT (I band) on March 8.8 uT.

Galama, T.↗
DOE OSTI2021

Identification of dislocation-related and point-defects in III-As layers for silicon photonics applications

Abstract The aim of this paper is to identify, analyze and compare the defects present in III-As, as a function of dislocation density, and as a function of the presence/absence of quantum dots (QDs). Such materials are of fundamental importance for the development of lasers and photodiodes for silicon photonics. The study is based on an extensive deep-level transient spectroscopy investigation, carried out on GaAs pin diodes grown on Si and on GaAs (that differ in the dislocation density), with and without embedded QDs. The original results described in this paper demonstrate that: (a) we were able to identify four different defects within the device grown on Si (three electron and one hole traps) and one defect (hole trap) in the device on GaAs, common to both samples; (b) all the majority carrier traps identified are located near midgap, i.e. are efficient non-radiative recombination centers; (c) such defects are absent (or non-detectable) in the sample grown on GaAs substrate, having a very low dislocation density; (d) the presence of QDs does not result in additional defects within the semiconductor material; (e) the analysis of the capture kinetics revealed that two of the identified traps are related to point defects, whereas the other two traps can be associated with point defects located near a dislocation; (f) a comparison with previous reports indicate that the detected traps are related to native III-As defects, or to oxygen-related complexes.

Physics↗
NASA NTRS1984

Solar hard X-ray microflares

Using balloon-borne instrumentation of very high sensitivity, approximately 25 hard X-ray bursts with peak fluxes of above 7 x 10 to the -3rd/(sq cm s keV) at 20 keV have been detected, in 141 minutes of observation of the sun on June 27, 1980. These hard X-ray microflares last from a few seconds to several tens of seconds and have power-law energy spectra. They are generally accompanied by small soft X-ray bursts, but H-alpha flares and solar radio bursts are reported for only a few of these hard X-ray bursts. The integral number of events varies approximately as the inverse of the peak flux, down to the limits of the measurements. These observations suggest that even very small transient releases of energy by the sun may be primarily nonthermal in character. It is speculated that the energy released in accelerated electrons for these microflares, averaged over time, may contribute significantly to the heating of the active corona.

Lin, R. P.↗
NASA NTRS2000

The May 1997 SOHO-Ulysses Quadrature

We present results from the May 1997 SOHO-Ulysses quadrature, near sunspot minimum. Ulysses was at 5.1 AU, 100 north of the solar equator, and off the east limb. It was, by chance, also at the very northern edge of the streamer belt. Nevertheless, SWOOPS detected only slow, relatively smooth wind and there was no direct evidence of fast wind from the northern polar coronal hole or of mixing with fast wind. LASCO images show that the streamer belt at 10 N was narrow and sharp at the beginning and end of the two week observation interval, but broadened in the middle. A corresponding change in density, but not flow speed, occurred at Ulysses. Coronal densities derived from UVCS show that physical parameters in the lower corona are closely related to those in the solar wind, both over quiet intervals and in transient events on the limb. One small transient observed by both LASCO and UVCS is analyzed in detail.

Suess, Steven T.↗
NASA NTRS2001

GLAST: Exploring Nature's Highest Energy Processes with the Gamma-ray Large Area Space Telescope

The Gamma-ray Large Area Space Telescope (GLAST) is an international and multi-agency space mission that will study the cosmos in the energy range 10 keV-300 GeV. Several successful exploratory missions in gamma-ray astronomy led to the Energetic Gamma Ray Experiment Telescope (EGRET) instrument on the Compton Gamma Ray Observatory (CGRO). Launched in 1991, EGRET made the first complete survey of the sky in the 30 MeV-10 GeV range. EGRET showed the high-energy gamma-ray sky to be surprisingly dynamic and diverse, with sources ranging from the sun and moon to massive black holes at large redshifts. Most of the gamma-ray sources detected by EGRET remain unidentified. In light of the discoveries with EGRET, the great potential of the next generation gamma-ray telescope can be appreciated. GLAST will have an imaging gamma-ray telescope vastly more capable than instruments flown previously, as well as a secondary instrument to augment the study of gamma-ray bursts. The main instrument, the Large Area Telescope (LAT), will have superior area, angular resolution, field of view, and deadtime that together will provide a factor of 30 or more advance in sensitivity, as well as provide capability for study of transient phenomena. The GLAST Burst Monitor (GBM) will have a field of view several times larger than the LAT and will provide spectral coverage of gamma-ray bursts that extends from the lower limit of the LAT down to 10 keV. The basic parameters of the GBM are compared to those of the Burst and Transient Source Experiment (BATSE) instrument on CGRO in Table 1-2. With the LAT and GBM, GLAST will be a flexible observatory for investigating the great range of astrophysical phenomena best studied in high-energy gamma rays. NASA plans to launch GLAST in late 2005.

Digel, Seth↗
NASA NTRS1983

Ultraviolet observations of the transient X-ray sources A0535 + 26 and A0620-00

Observations of A0535+26 (HDE 245770) by the ANS in September 1975 and March 1976 when it was at the X-ray low state are discussed. Also observed were 58 early-type stars lying within 10 deg of HDE 245770; these stars are used to derive a localized extinction curve. On the basis of the depth of the 2200 A interstellar absorption feature observed in the ANS flux distribution of HDE 245770 and the shape of the localized extinction curve, an E(B-V) = 0.72 is derived for HDE 245770. Observations were made of this system during its X-ray flare-up (October 1980) and quiescent (November 1981) states by the IUE. It is noted that the fine error sensor on board the IUE detected an increase in the optical brightness of HDE 245770 during the X-ray outburst. This greatly corroborates the identification of HDE 245770 as the optical counterpart of A0535+26. No significant change in the absorption-line profiles during the X-ray high and low periods is found, indicating that there was no significant increase in the stellar wind density when the X-ray flare-up occurred. The UV continuum level increased by less than 6 percent when it was near peak X-ray luminosity. The UV spectrum of HDE 245770 suggests that it is a B0 V or a B0 III star with its dereddened continuum slope slightly in favor of being a giant.

Wu, C.-C.↗
DOE OSTI2023

Natural gas odorants: A scoping review of health effects

Organosulfur compounds are intentionally added to natural gas as malodorants with the intent of short-term nasal inhalation to aid in leak detection. Regulatory exposure limits have not been established for all commonly used natural gas odorants, and recent community-level exposure events and growing evidence of indoor natural gas leakage have raised concerns associated with natural gas odorant exposures. We conducted a scoping review of peer-reviewed scientific publications on human exposures and animal toxicological studies of natural gas odorants to assess toxicological profiles, exposure potential, health effects and regulatory guidelines associated with commonly used natural gas odorants. We identified only 22 studies which met inclusion criteria for full review. Overall, there is limited evidence of both transient nonspecific health symptoms and clinically diagnosed causative neurotoxic effects associated with prolonged odorant exposures. Across seven community-level exposure events and two occupational case reports, consistent symptom patterns included: headache, ocular irritation, nose and throat irritation, respiratory complaints such as shortness of breath and asthma attacks, and skin irritation and rash. Of these, respiratory inflammation and asthma exacerbations are the most debilitating, whereas the high prevalence of ocular and dermatologic symptoms suggest a non-inhalation route of exposure. The limited evidence available raises the possibility that organosulfur odorants may pose health risks at exposures much lower than presently understood, though additional dose-response studies are needed to disentangle specific toxicologic effects from nonspecific responses to noxious organosulfur odors. Numerous recommendations are provided including more transparent and prescriptive natural gas odorant use practices.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2021

The Dark Energy Survey supernova programme: modelling selection efficiency and observed core-collapse supernova contamination

ABSTRACT The analysis of current and future cosmological surveys of Type Ia supernovae (SNe Ia) at high redshift depends on the accurate photometric classification of the SN events detected. Generating realistic simulations of photometric SN surveys constitutes an essential step for training and testing photometric classification algorithms, and for correcting biases introduced by selection effects and contamination arising from core-collapse SNe in the photometric SN Ia samples. We use published SN time-series spectrophotometric templates, rates, luminosity functions, and empirical relationships between SNe and their host galaxies to construct a framework for simulating photometric SN surveys. We present this framework in the context of the Dark Energy Survey (DES) 5-yr photometric SN sample, comparing our simulations of DES with the observed DES transient populations. We demonstrate excellent agreement in many distributions, including Hubble residuals, between our simulations and data. We estimate the core collapse fraction expected in the DES SN sample after selection requirements are applied and before photometric classification. After testing different modelling choices and astrophysical assumptions underlying our simulation, we find that the predicted contamination varies from 7.2 to 11.7 per cent, with an average of 8.8 per cent and an r.m.s. of 1.1 per cent. Our simulations are the first to reproduce the observed photometric SN and host galaxy properties in high-redshift surveys without fine-tuning the input parameters. The simulation methods presented here will be a critical component of the cosmology analysis of the DES photometric SN Ia sample: correcting for biases arising from contamination, and evaluating the associated systematic uncertainty.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Statistics and sensitivity of axion wind detection with the homogeneous precession domain of superfluid helium-3

The homogeneous precession domain (HPD) of superfluid He 3 has recently been identified as a detection medium which might provide sensitivity to the axion-nucleon coupling g a N N competitive with, or surpassing, existing experimental proposals. In this work, we make a detailed study of the statistical and dynamical properties of the HPD system in order to make realistic projections for a full-fledged experimental program. We include the effects of clock error and measurement error in a concrete readout scheme using superconducting qubits and quantum metrology. This work also provides a more general framework to describe the statistics associated with the axion gradient coupling through the treatment of a transient resonance with a nonstationary background in a time-series analysis. Incorporating an optimal data-taking and analysis strategy, we project a sensitivity approaching g a N N ∼ 10 − 12 GeV − 1 across a decade in axion mass. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2008

Broadband X-Ray Spectra of GX 339-4 and the Geometry of Accreting Black Holes in the Hard State

A major question in the study of black hole binaries involves our understanding of the accretion geometry when the sources are in the "hard" state. In this state, the X-ray energy spectrum is dominated by a hard power-law component and radio observations indicate the presence of a steady and powerful "compact" jet. Although the common hard state picture is that the accretion disk is truncated, perhaps at hundreds of gravitational radii (R(sub g)) from the black hole, recent results for the recurrent transient GX 339-4 by Miller and co-workers show evidence for optically thick material very close to the black hole's innermost stable circular orbit. That work focused on an observation of GX 339-4 at a luminosity of about 5% of the Eddington limit (L(sub Edd)) and used parameters from a relativistic reflection model and the presence of a soft, thermal component as diagnostics. In this work, we use similar diagnostics, but extend the study to lower luminosities (2.3% and 0.8% L(sub Edd)) using Swift and RXTE observations of GX 339-4. We detect a thermal component with an inner disk temperature of approx.0.2 keV at 2.3% L(sub Edd). At 0.8% L(sub Edd), the spectrum is consistent with the presence of such a component, but the component is not required with high confidence. At both luminosities, we detect broad features due to iron Ka that are likely related to reflection of hard X-rays off the optically thick material. If these features are broadened by relativistic effects, they indicate that optically thick material resides within 10 R(sub g) down to 0.8% L(sub Edd), and the measurements are consistent with the inner radius of the disk remaining at approx.4 R(sub g) down to this level. However, we also discuss an alternative model for the broadening, and we note that the evolution of the thermal component is not entirely consistent with the constant inner radius interpretation. Finally, we discuss the results in terms of recent theoretical work by Liu and co-workers on the possibility that material may condense out of an Advection-Dominated Accretion Flow to maintain an inner optically thick disk.

Tomsick↗
NASA NTRS2000

Jovian Substorms: A Study of Processes Leading to Transient Behavior in the Jovian Magnetosphere

Solar system magnetospheres can be divided into two groups: induced and intrinsic. The induced magnetospheres are produced in the solar wind interaction of the magnetized solar wind with planetary obstacles. Examples of these magnetospheres are those of comets, Venus and Mars. Intrinsic magnetospheres are the cavities formed in the solar wind by the magnetic fields produced by dynamo current systems inside the planets: Mercury, Earth, Jupiter, Saturn, Uranus and Neptune are known to have intrinsic magnetospheres. Intrinsic magnetospheres can be further subdivided as to how the circulating plasma is driven by external or internal processes. The magnetospheres of Mercury and Earth are driven by the solar wind. The magnetospheres of Jupiter and possibly of Saturn are principally driven by internal processes. These processes provide the energy for the powerful jovian radio signals that can be detected easily on the surface of the Earth.

Russell, C. T.↗
DOE OSTI2022

On the Importance of Using Event-Specific Wave Diffusion Rates in Modeling Diffuse Electron Precipitation

A few to tens of keV electron precipitation that carries substantial energy source down to the upper atmosphere to create aurora is manifested as an important magnetosphere-ionosphere coupling process. The precipitation is usually caused by scattering processes associated with plasma waves in the magnetosphere. The scattering process is often quantified by wave diffusion rates that indicate how fast an electron is scattered. Global models commonly use diffusion coefficients that are derived from statistical wave models. However, due to the statistical nature, many localized, transient features could be smeared out. In this study, we investigate electron precipitation using event-specific diffusion coefficients that are obtained based on simultaneous in-situ measured/inferred, rather than statistical, chorus wave dynamics. We find that the application of the event-specific diffusion coefficients associated with a more dynamic and intense chorus wave model leads more electrons, particularly at several to tens of keV in the dawn-to-noon sector at L > 3, to precipitate than using statistical coefficients. Here, the new simulation roughly captures both the intensity and variability of the precipitating flux as detected by the NOAA/POES satellites. Ionospheric electron density in the lower E region (100–120 km) observed by the mid-latitude Millstone Hill radar is also much better reproduced, while the case using statistical diffusion coefficients underestimates the ionization rate. This study implies the importance of using event-specific diffusion rates in simulating the diffuse electron precipitation and understanding the magnetosphere-ionosphere coupling.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Ultrafast x-ray and electron scattering of free molecules: A comparative evaluation

Resolving gas phase molecular motions with simultaneous spatial and temporal resolution is rapidly coming within the reach of x-ray Free Electron Lasers (XFELs) and Mega-electron-Volt (MeV) electron beams. These two methods enable scattering experiments that have yielded fascinating new results, and while both are important methods for determining transient molecular structures in photochemical reactions, it is important to understand their relative merits. In the present study, we evaluate the respective scattering cross sections of the two methods and simulate their ability to determine excited state molecular structures in light of currently existing XFEL and MeV source parameters. Using the example of optically excited N-methyl morpholine and simulating the scattering patterns with shot noise, we find that the currently achievable signals are superior with x-ray scattering for equal samples and on a per-shot basis and that x-ray scattering requires fewer detected signal counts for an equal fidelity structure determination. Importantly, within the independent atom model, excellent structure determinations can be achieved for scattering vectors only to about 5 Å−1, leaving larger scattering vector ranges for investigating vibrational motions and wavepackets. Electron scattering has a comparatively higher sensitivity toward hydrogen atoms, which may point to applications where electron scattering is inherently the preferred choice, provided that excellent signals can be achieved at large scattering angles that are currently difficult to access.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Strong chemical tagging with APOGEE: 21 candidate star clusters that have dissolved across the Milky Way disc

ABSTRACT Chemically tagging groups of stars born in the same birth cluster is a major goal of spectroscopic surveys. To investigate the feasibility of such strong chemical tagging, we perform a blind chemical tagging experiment on abundances measured from APOGEE survey spectra. We apply a density-based clustering algorithm to the 8D chemical space defined by [Mg/Fe], [Al/Fe], [Si/Fe], [K/Fe], [Ti/Fe], [Mn/Fe], [Fe/H], and [Ni/Fe], abundances ratios which together span multiple nucleosynthetic channels. In a high-quality sample of 182 538 giant stars, we detect 21 candidate clusters with more than 15 members. Our candidate clusters are more chemically homogeneous than a population of non-member stars with similar [Mg/Fe] and [Fe/H], even in abundances not used for tagging. Group members are consistent with having the same age and fall along a single stellar-population track in log g versus Teff space. Each group’s members are distributed over multiple kpc, and the spread in their radial and azimuthal actions increases with age. We qualitatively reproduce this increase using N-body simulations of cluster dissolution in Galactic potentials that include transient winding spiral arms. Observing our candidate birth clusters with high-resolution spectroscopy in other wavebands to investigate their chemical homogeneity in other nucleosynthetic groups will be essential to confirming the efficacy of strong chemical tagging. Our initially spatially compact but now widely dispersed candidate clusters will provide novel limits on chemical evolution and orbital diffusion in the Galactic disc, and constraints on star formation in loosely bound groups.

Price-Jones, Natalie↗
NASA NTRS2007

Varicella Zoster Virus in Saliva of Patients With Herpes Zoster

Background. VZV DNA is present in saliva of healthy astronauts and patients with Ramsay Hunt syndrome (geniculate zoster). We hypothesized that a prospective analysis of patients with zoster would detect VZV in saliva independent of zoster location. Methods. We treated 54 patients with valacyclovir. On the first treatment day, 7- and 14-days later, pain was scored and saliva examined for VZV DNA. Saliva from six subjects with chronic pain and 14 healthy subjects was similarly studied. Results. Follow-up data was available for 50/54 patients. Pain decreased in 43/50 (86 percent), disappeared in 37 (74 percent), recurred after disappearing in three (6 percent) and increased in four (8 percent). VZV DNA was found in every patient the day treatment was started, decreased in 47/50 (94 percent), transiently increased in three (6 percent) before decreasing, increased in two (4 percent) and disappeared in 41 (82 percent). There was a positive correlation between the presence of VZV DNA and pain, as well as between the VZV DNA copy number and pain (P<0.0005). Saliva of two patients was cultured, and infectious VZV was isolated from one. VZV DNA was present in one patient before rash and in four patients after pain resolved, and not in any control subjects. Conclusion. VZV DNA is present in saliva of zoster patients.

Mehta, Satish K.↗