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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 OSTI2023

Radio-bright versus radio-dark gamma-ray bursts – more evidence for distinct progenitors

ABSTRACT We analyse two distinct samples of gamma-ray bursts (GRBs), with and without radio afterglow emission. We use an updated sample of 211 GRBs and find, in agreement with previous results (although with a sample that is almost twice as large), that the intrinsic gamma-ray duration (Tint) and isotropic equivalent energy (Eiso) distributions between these two populations appear to be significantly different. This implies that the radio-bright GRBs are more energetic and last longer than radio-dark GRBs. The two samples’ redshift distributions (z) are not statistically different. We analyse several correlations between variables (Eiso, Tint, jet opening angle, and z), accounting for selection effects and redshift evolution using the Efron–Petrosian method. We find a statistically significant anticorrelation between the jet opening angle and redshift, as well as between Tint and redshift, for both radio-bright and radio-dark GRBs. Finally, in agreement with previous work, we find that very high energy (0.1–100 GeV) extended emission is present only in the radio-bright GRB sample. Our work supports the possibility that the radio-bright and radio-dark GRBs originate from different progenitors.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Machine-learning-based, online estimation of ceramic’s microstructure upon the laser spot brightness during laser sintering

The ceramic microstructure strongly influences its properties. During manufacturing, the online monitoring of microstructure is critical to ensure the desired material properties. So far, the microstructure on the relevant scale is usually characterized offline using scanning electron microscopy (SEM), which is time and cost-consuming. In this work, we demonstrate a cost-effective, machine learning (ML)-based approach to simulate the SEM micrographs in real-time from the laser spot brightness. We experimentally observed a strong correlation between the laser spot brightness and the corresponding microstructure at the exact locations. The brightness values obtained from thermal emission images and the corresponding SEM micrographs were used in the training datasets. The ML algorithm was a style-based conditional generative adversarial network (CGAN). After training, the ML model could generate high-fidelity microstructure images within 0.1 seconds based on in-situ captured brightness at the laser sintering spot. We used the average grain sizes as the metric to evaluate the accuracy of the ML-predicted micrographs. Here, the ML-predicted microstructures were in good agreement, with less than 5% in difference from the real SEM images. In conclusion, we demonstrate the cost-effective, online microstructure estimation during laser sintering with a simple setup (a camera, a regular computer, and the ML model).

08 HYDROGEN↗
DOE OSTI2023

Opportunities for Bright Beam Generation at the Argonne Wakefield Accelerator (AWA)

Bright electron beams have played a critical role in many recent advances in accelerator technology. Producing bright beams via photo-emission is ultimately limited by the mean transverse energy (MTE), which is determined by the photocathode. This paper discusses the opportunity to generate bright electron beams using an upgraded version of the Argonne Wakefield Accelerator (AWA) photo-injector. The focus of this study is to examine the optimal configurations of the AWA photo-injector to produce 100 pC with a ∼100 nm transverse emittance (corresponding to a 5D brightness B5≥1015 A·m−2). The numerical optimization of the AWA photo-injector operating point, including realistic electromagnetic field maps, is presented for the different types of photocathodes under consideration.

Frame, Emily↗
DOE OSTI2021

Shadows in the Dark: Low-surface-brightness Galaxies Discovered in the Dark Energy Survey

We present a catalog of 23,790 extended low-surface-brightness galaxies (LSBGs) identified in $\sim 5000\,{\deg }^{2}$ from the first three years of imaging data from the Dark Energy Survey (DES). Based on a single-component Sérsic model fit, we define extended LSBGs as galaxies with g-band effective radii ${R}_{\mathrm{eff}}(g)\gt 2\buildrel{\prime\prime}\over{.} 5$ and mean surface brightness ${\bar{\mu }}_{\mathrm{eff}}(g)\gt 24.2\,\mathrm{mag}\,{\mathrm{arcsec}}^{-2}$. We find that the distribution of LSBGs is strongly bimodal in (g-r) versus (g-i) color space. We divide our sample into red (g- i ≥ 0.60) and blue (g- i < 0.60) galaxies and study the properties of the two populations. Redder LSBGs are more clustered than their blue counterparts and are correlated with the distribution of nearby (z < 0.10) bright galaxies. Red LSBGs constitute ~33% of our LSBG sample, and $\sim 30 \% $ of these are located within 1° of low-redshift galaxy groups and clusters (compared to ~8% of the blue LSBGs). For nine of the most prominent galaxy groups and clusters, we calculate the physical properties of associated LSBGs assuming a redshift derived from the host system. In these systems, we identify 41 objects that can be classified as ultradiffuse galaxies, defined as LSBGs with projected physical effective radii ${R}_{\mathrm{eff}}\gt 1.5\,\mathrm{kpc}$ and central surface brightness ${\mu }_{0}(g)\gt 24.0\,\mathrm{mag}\,{\mathrm{arcsec}}^{-2}$. The wide-area sample of LSBGs in DES can be used to test the role of environment on models of LSBG formation and evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

The night sky brightness at McDonald Observatory

Baseline observations of the night sky brightness in B and V are presented for McDonald Observatory. In agreement with earlier work by Elvey and Rudnick (1937) and Elvey (1943), significant night-to-night and same-night variations in sky brightness are found. Possible causes for these variations are discussed. The largest variation in sky brightness found during a single night is approximately a factor of two, a value which corresponds to a factor-of-four variation in airglow brightness. The data are used to comment on the accuracy of previously published surface photometry of M 81.

Kalinowski, J. K.↗
NASA NTRS1976

On the surface brightness and geometric albedo of some Martian areas

High-quality photographs of Mars (red, yellow, green, and blue) are used to analyze the surface, limb, and south-polar-cap brightness of Mars. The surface brightness can be fitted with the Lommel-Seeliger reflection law. For the limb and polar-cap brightness, the method suggested by Lumme (1974) has been used to correct for smearing effects. It is found that the brightness increases noticeably when approaching the limb, that the upper limit to optical thickness of the atmosphere in the blue is 0.16, and that the corresponding single-scattering albedo is 0.55, both with uncertainties of about 15%. Values for the geometric albedo and the phase function (at 37-deg phase angle) are also obtained for both the atmosphere and the ground for a central meridian of 0 deg. The south polar cap in September 1973 was nearly circular, with a radius of about 8 deg (heliocentric longitude of 0 deg) and geometric albedos of 0.68 (red), 0.68 (yellow), 0.60 (green), and 0.53 (blue).

Lumme, K.↗
NASA NTRS1976

The solar brightness temperature at millimeter wavelengths

Measurements of the brightness temperature of the sun near 36 GHz and 93 GHz were made using the new moon as a calibration source. Provided the brightness temperature of the moon is known and all measurements are reduced to the same zenith angle, a simple expression can be used for the sun-to-new moon ratio which is independent of antenna gain, atmospheric absorption and reemission, and radiometer calibration constants. This ratio was measured near 36 GHz and at two frequencies near 93 GHz with a Dicke switched superheterodyne radiometer system and a 2.4 m Cassegrain antenna. The slopes of the solar brightness temperature spectrum based on these ratios were measured. The absolute solar brightness spectrum derived from all current available measurements supplemented by the present ones is also plotted and discussed.

Kuseski, R. A.↗
NASA NTRS1977

The brightness temperatures of Saturn and its rings at 39 microns

The relative rings-to-disk brightness (specific intensity) of Saturn at 39 microns was resolved using a 224-cm telescope, and the total flux of Saturn relative to Jupiter in the same bandpass was measured from the NASA Learjet Observatory. These two measurements, which were made with Saturn's rings near maximum inclination, determine the disk and average ring (A and B) brightness in terms of an absolute flux calibration of Jupiter in the same bandpass. While present uncertainties in Jupiter's absolute calibration make it impossible to compare existing measurements unambiguously, it is nevertheless possible to conclude the following: (1) observations between 20 and 40 microns are all compatible (within 2 sigmas) with a disk brightness temperature of 94 K and do not agree with the radiative equilibrium models of Trafton (1967); (2) the rings at large tilt contribute a flux component comparable to that of the planet itself for wavelengths not exceeding about 40 microns; and (3) there is a decrease of approximately 22% in the relative ring:disk brightness between effective wavelengths of 33.5 and 39 microns.

Nolt, I. G.↗
NASA NTRS1978

Effects of cloud size and cloud particles on satellite-observed reflected brightness

Satellite observations allowed obtaining data on the visible brightness of cumulus clouds over South Park, Colorado, while aircraft observations were made in cloud to obtain the drop size distributions and liquid water content of the cloud. Attention is focused on evaluating the relationship between cloud brightness, horizontal dimension, and internal microphysical structure. A Monte Carlo cloud model for finite clouds was run using different distributions of drop sizes and numbers, while varying the cloud depth and width to determine how theory would predict what the satellite would view from its given location in space. Comparison of these results to the satellite observed reflectances is presented. Theoretical results are found to be in good agreement with observations. For clouds of optical thickness between 20 and 60, monitoring cloud brightness changes in clouds of uniform depth and variable width gives adequate information about a cloud's liquid water content. A cloud having a 10:1 width to depth ratio is almost reaching its maximum brightness for a specified optical thickness.

Reynolds, D. W.↗
NASA NTRS1978

A measurement of the brightness temperature of Saturn's rings at 8-mm wavelength

The brightness temperature of Saturn's rings has been measured at 8-mm wavelength using a millimeter-wavelength interferometer. A ring brightness temperature of 12.7 + or -2 K is obtained with the assumption that the rings are of uniform brightness and the region of emission coincides with the visible A and B rings. This result is higher than comparable results obtained at centimeter wavelengths and may indicate a small increase in the thermal emission from the rings at 8 mm. The low brightness temperature places significant constraints on the nature of the ring particles and implies that they must be either highly metallic or of limited size and composed of a low-loss dielectric material such as water ice.

Janssen, M. A.↗
NASA NTRS1978

Io may have a bright dawn terminator

A test of the thermoluminescence properties of Io is proposed which can be performed with the unique optical observations programmed for Voyager 1's close flyby of that Jovian satellite. It is suggested that if Io's surface is thermoluminescent with a characteristic post-eclipse-brightening time of the order of 10 min, there should be a characteristic bright rim on the sunlit side of the satellite's dawn terminator. It is noted that the spatial resolution of six-color pictures to be taken by Voyager 1 should be sufficiently adequate to reveal the bright dawn terminator if it exists and is bright enough. A mathematical model illustrating the bright-dawn-terminator effect is presented.

Forman, M.↗
NASA NTRS1980

IR brightness and eclipse cooling of Saturn's rings

Equatorial scans of Saturn at 20 microns wavelength, obtained with the Mayall 4-m telescope in 1978-79, show a continuing decrease in the specific brightness of the A and B rings as the ring plane projection approaches and edge-on apparition. The decreased brightness of the previously dominant B ring reveals more clearly a large difference in brightness between the east and west ansae portions of the C ring, in contrast to a barely discernible difference for the other ring ansae. The amount of eclipse cooling is compatible with a C ring particle size of about 1 cm. It is proposed here that the B ring brightness variation could partially result from a decrease of absorbed insolation by a modest amount of visible scattering.

Nolt, I. G.↗
NASA NTRS1980

The 20-micron brightness temperature of the unilluminated side of Saturn's rings

Observations of the 20-micron brightness temperature of the unilluminated (north) side of Saturn's rings are presented and discussed in terms of models of B ring heating. Observations centered on the B ring ansae were made at 19.8 microns by the 3-m IR telescope facility on Mauna Kea during a period when the unilluminated side of the rings could be observed from earth. Flux measurements indicate a 20-micron brightness temperature of 56 + or - 1 K, in agreement with that measured at 45 microns by Pioneer 11. Under the assumptions that the emission of the Cassini division is negligible and that the ring brightness temperature is close to the actual temperature, it is shown that the brightness temperature can be accounted for by heating by the disk of Saturn, and is proportional to the sine of the Saturnicentric declination of the sun.

Tokunaga, A. T.↗
NASA NTRS1981

Spatial and temporal variations of EUV coronal bright points

This paper reports results of an analysis of Skylab observations of coronal bright points made in EUV spectral lines formed in the chromosphere, chromospheric-coronal transition region and corona. The most important result is that the observed bright points exhibited large variations in EUV emission over time scales as short as 5.5 min, the temporal resolution of the data. In most cases strong enhancements in the coronal line were accompanied by strong enhancements in the chromospheric and transition region lines. The intensity variations appear to take place within substructures of the bright points, which most likely consist of miniature loops evolving on time scales of a few minutes. Coronal cooling times derived from the data are consistent with an intermittent, impulsive coronal heating mechanism for bright points.

Habbal, S. R.↗
NASA NTRS1981

Lunar craters with radar bright ejecta

The properties of the 3.8-cm radar-bright halos observed around certain lunar impact craters are compiled and compared with 70-cm radar, thermal infrared and photogeological data in order to address the nature of the halos. Diameters, positions, and radar and IR signal strengths are presented for 120 radar-bright ejecta regions of size greater than 20 km and twice the diameter of the crater. The 3.8-cm halos are noted to range in size up to 30 times that of the crater itself, although the strength of the signal from the crater and rim lies in a narrow range, while the IR halos are smaller in extent and variable in signal strength. The radar-bright ejecta are found to have a range of optical properties, and to be associated with fresh primary impact craters. Data are thus consistent with craters having radar-bright ejecta deposits having ages of less than 10 million to 1 billion years, with the radar and infrared signatures of the ejecta deposits produced by combinations of enhanced blockiness and roughness.

Thompson, T. W.↗
NASA NTRS1981

Satellite-derived ice data sets no. 1: Antarctic monthly average microwave brightness temperatures and sea-ice concentrations, 1973 - 1976

A summary data set concerning 4 years of Antarctic sea-ice conditions was created and is available on magnetic tape. The data were derived from electrically scanning microwave radiometer brightness temperatures and were mapped into a polar stereographic grid enclosing the 50 deg S latitude circle. The grid size varies from about 32 by 32 sq km at the poles to about 28 by 28 sq km at 50 deg S. The microwave brightness temperatures of Antarctic sea ice are predominantly characteristic of first-year ice with an emissivity of 0.92 at 19 GHz frequency. Sea ice concentrations were calculated from the brightness temperature data for each grid element with an algorithm that uses an emissivity value of 0.92 and an ice physical temperature estimate from climatological surface air temperatures. Monthly, multiyear monthly, and yearly maps of brightness temperatures and sea ice concentrations were created for the 4 years, except for 7 months for which useable data were insufficient.

Zwally, H. J.↗
NASA NTRS1982

Effects of subsurface volume scattering on the lunar microwave brightness temperature spectrum

The effects of volumetric scattering on the lunar microwave brightness temperature are examined for a broad range of feasible lunar rock population distributions. Mie-scattering phase functions and the radiative transfer method are utilized. Surveyor and Apollo data relevant to lunar rock size distributions are discussed, and parameters are chosen for nine scattering models which liberally cover the range of studied rock population distributions. Scattering model brightness temperature predictions are analyzed in terms of the lunar disk center emission averaged over a lunation for wavelengths of 3-30 cm. The effects of scattering on the amplitude of disk center brightness temperature variations and resultant deductions of regolith electrical loss are examined. Constraints on the global scale variability of subsurface scatterers imposed by microwave brightness temperature maps are considered.

Keihm, S. J.↗
NASA NTRS1983

A model function for ocean microwave brightness temperatures

A relatively simple, yet accurate, relationship between the microwave brightness temperature of the ocean and conventional oceanographic and meteorological parameters is derived. The equation for the brightness temperature upwelling from the sea surface through the intervening atmosphere is obtained, considering radiative emission and scattering by the sea surface along with radiative absorption and emission by the atmosphere. A number of approximations are applied to the integral brightness temperature equation and its supporting equations in order to obtain a simple equation for the brightness temperature that does not contain integrals. Values for a number of atmospheric parameters are determined, including temperature sensitivities, oxygen opacity, water vapor and liquid water normalized absorption coefficients, and effective columnar height. The sea surface emissivity model is then considered, modelling the sea surface as a composite of foam-free rough water and foam patches.

Wentz, F. J.↗