Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “luminance”

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.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Parafoveal Target Detectability Reversal Predicted by Local Luminance and Contrast Gain Control

This project is part of a program to develop image discrimination models for the prediction of the detectability of objects in a range of backgrounds. We wanted to see if the models could predict parafoveal object detection as well as they predict detection in foveal vision. We also wanted to make our simplified models more general by local computation of luminance and contrast gain control. A signal image (0.78 x 0.17 deg) was made by subtracting a simulated airport runway scene background image (2.7 deg square) from the same scene containing an obstructing aircraft. Signal visibility contrast thresholds were measured in a fully crossed factorial design with three factors: eccentricity (0 deg or 4 deg), background (uniform or runway scene background), and fixed-pattern white noise contrast (0%, 5%, or 10%). Three experienced observers responded to three repetitions of 60 2IFC trials in each condition and thresholds were estimated by maximum likelihood probit analysis. In the fovea the average detection contrast threshold was 4 dB lower for the runway background than for the uniform background, but in the parafovea, the average threshold was 6 dB higher for the runway background than for the uniform background. This interaction was similar across the different noise levels and for all three observers. A likely reason for the runway background giving a lower threshold in the fovea is the low luminance near the signal in that scene. In our model, the local luminance computation is controlled by a spatial spread parameter. When this parameter and a corresponding parameter for the spatial spread of contrast gain were increased for the parafoveal predictions, the model predicts the interaction of background with eccentricity.

Ahumada, Albert J., Jr.↗
NASA NTRS2010

Luminous Efficiency of Hypervelocity Meteoroid Impacts on the Moon Derived from the 2006 Geminids, 2007 Lyrids, and 2008 Taurids

Since early 2006 the Meteoroid Environment Office at NASA's Marshall Space Flight Center has been consistently monitoring the Moon for impact flashes produced by meteoroids striking the lunar surface. During this time, several meteor showers have produced multiple impact flashes on the Moon. The 2006 Geminids, 2007 Lyrids, and 2008 Taurids were observed with average rates of 5.5, 1.2, and 1.5 meteors/hr, respectively, for a total of 12 Geminid, 11 Lyrid, and 12 Taurid lunar impacts. These showers produced a sufficient, albeit small sample of impact flashes with which to perform a luminous efficiency analysis similar to that outlined in Bellot Rubio et al. for the 1999 Leonids. An analysis of the Geminid, Lyrid, and Taurid lunar impacts is carried out herein in order to determine the luminous efficiency in the 400-900 nm wavelength range for each shower. Using the luminous efficiency, the kinetic energies and masses of these lunar impactors can be calculated.

Moser, D. E.↗
NASA NTRS2010

Luminous Efficiency of Hypervelocity Meteoroid Impacts on the Moon Derived from the 2006 Geminids, 2007 Lyrids, and 2008 Taurids

Since early 2006 the Meteoroid Environment Office (MEO) at NASA s Marshall Space Flight Center has been consistently monitoring the Moon for impact flashes produced by meteoroids striking the lunar surface. During this time, several meteor showers have produced multiple impact flashes on the Moon. The 2006 Geminids, 2007 Lyrids, and 2008 Taurids were observed with average rates of 5.5, 1.2, and 1.5 meteors/hr, respectively, for a total of 12 Geminid, 12 Lyrid, and 12 Taurid lunar impacts. These showers produced a sufficient, albeit small sample of impact flashes with which to perform a luminous efficiency analysis similar to that outlined in Bellot Rubio et al. (2000) for the 1999 Leonids. An analysis of the Geminid, Lyrid, and Taurid lunar impacts is carried out herein in order to determine the luminous efficiency in the 400-800 nm wavelength range for each shower. Using the luminous efficiency, the kinetic energies and masses of these lunar impactors can be calculated.

Moser, D. E.↗
NASA NTRS2011

Luminous Efficiency of Hypervelocity Meteoroid Impacts on the Moon Derived from the 2006 Geminids, 2007 Lyrids, and 2008 Taurids

Since early 2006, NASA s Marshall Space Flight Center has been routinely monitoring the Moon for impact flashes produced by meteoroids striking the lunar surface. During this time, several meteor showers have produced multiple impact flashes on the Moon. The 2006 Geminids, 2007 Lyrids, and 2008 Taurids were observed with average rates of 5.5, 1.2, and 1.5 meteors/hr, respectively, for a total of 12 Geminid, 12 Lyrid, and 12 Taurid lunar impacts. These showers produced a sufficient, albeit small sample of impact flashes with which to perform a luminous efficiency analysis similar to that outlined in Bellot Rubio et al. (2000a, b) for the 1999 Leonids. An analysis of the Geminid, Lyrid, and Taurid lunar impacts is carried out herein in order to determine the luminous efficiency in the 400-800 nm wavelength range for each shower. Using the luminous efficiency, the kinetic energies and masses of these lunar impactors can be calculated from the observed flash intensity.

Moser, D. E.↗
NASA NTRS2017

Luminous Efficiency of Hypervelocity Meteoroid Impacts on the Moon Derived from the 2015 Geminid Meteor Shower

Since early 2006 the Meteoroid Environment Office (MEO) at NASA's Marshall Space Flight Center has routinely monitored the Moon for impact flashes produced by meteoroids striking the lunar surface. Activity from the Geminid meteor shower (EM) was observed in 2015, resulting in the detection of 45 lunar impact flashes (roughly 10% of the NASA dataset), in about 10 hours of observation with peak R magnitudes ranging from 6.5 to 11. A subset of 30 of these flashes, observed 14-15 December, was analyzed in order to determine the luminous efficiency, the ratio of emitted luminous energy to the meteoroid's kinetic energy. The resulting luminous efficiency, found to range between n = 1.8 x 10(exp -4) and 3.3 x 10(exp -3), depending on the assumed mass index and flux, was than applied to calculate the masses of Geminid meteoroids striking the Moon in 2015.

Moser, D. E.↗
NASA NTRS2018

The Fast, Luminous Ultraviolet Transient AT2018cow: Extreme Supernova, or Disruption of a Star by an Intermediate-Mass Black Hole?

Wide-field optical surveys have begun to uncover large samples of fast (trise <~ 5 d), luminous (Mpeak < −18), blue transients. While commonly attributed to the breakout of a supernova shock into a dense wind, the great distances to the transients of this class found so far have hampered detailed investigation of their properties. We present photometry and spectroscopy from a comprehensive worldwide campaign to observe AT 2018cow (ATLAS 18qqn), the first fast-luminous optical transient to be found in real time at low redshift. Our first spectra (<2 days after discovery) are entirely featureless. A very broad absorption feature suggestive of near relativistic velocities develops between 3 and 8 days, then disappears. Broad emission features of H and He develop after >10 days. The spectrum remains extremely hot throughout its evolution, and the photospheric radius contracts with time (receding below R < 1014 cm after 1 month). This behaviour does not match that of any known supernova, although a relativistic jet within a fallback supernova could explain some of the observed features. Alternatively, the transient could originate from the disruption of a star by an intermediate-mass black hole, although this would require long-lasting emission of highly super-Eddington thermal radiation. In either case, AT 2018cow suggests that the population of fast luminous transients represents a new class of astrophysical event. Intensive follow-up of this event in its late phases, and of any future events found at comparable distance, will be essential to better constrain their origins.

Black-hole↗
DOE OSTI2026

Structural interactions of TLP18.3 and Psb27-H1 to the luminal CP43 and Rubredoxin-ENH1 to the stromal side of Photosystem II in higher plants

TLP18.3 and Psb27 are known proteins on the luminal side of photosystem II. The structural locations of these two proteins are still absent in the currently available higher plant photosystem II cryo-EM structures. We interrogated the structural locations of these proteins using chemical cross-linking followed by liquid chromatography/tandem MS analysis. Structural mass spectrometry results then provided chemical restrains to direct structural modelling to determine the collective binding/stabilization of these two proteins to the luminal PSII CP43 protein. Using this pipeline, we also found the structural location of a Rubredoxin protein on the stromal side of PSII. Discovery of this redox active iron-sulfur protein in the vicinity of PSII subunit D1/D2 proteins, greatly showcases the importance of the redox processes that are potentially involved in PSII assembly or less known steady state functionality or photoprotection. This structural mass spectrometry platform high-lights its powerful applicability in protein complex discovery.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1973

Luminous efficiency measurements for silicon and aluminum simulated micrometeors

Laboratory measurements on simulated silicon and aluminum micrometeors in an air atmosphere have produced values for the elemental photographic luminous efficiencies of silicon over a velocity range 13-48 km/sec and of aluminum over a range 12-42 km/sec. The photographic luminous efficiency of both elements first increases with increasing velocity, then reaches a peak and declines. Supplementary measurements on Si and Al in atmospheres of O2 and N2 support the air results.

Becker, D. G.↗
NASA NTRS1975

Luminous stars in galactic supernova remnants

It is shown that luminous stars should be expected in the vicinity of supernova remnants. Luminous stars within the maximum optical areas of supernova remnants are tabulated from catalogs, and an excitation parameter is correlated with the spectral classification of such stars when their UV flux excites H II regions to produce nebular thermal bremsstrahlung. The correlations indicate that the presence of a ZAMS star of type 08 to 05 is necessary to produce thermal bremsstrahlung equal to the observed flux density at 1 GHz. Optical components of seven other supernova remnants are discussed, and it is concluded that gross uncertainties in the distance moduli of both stars and supernova remnants prevent any associations from being made.

Johnson, H. M.↗
NASA NTRS1976

A new interpretation of luminous blue stars

A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's (1976) radiative opacities are adopted in stellar models. Unlike earlier opacities, these exhibit a large 'bump' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot diffuse stellar envelopes. Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. The stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures for O stars and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than about 20 solar masses. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars.

Stothers, R.↗
NASA NTRS1987

Morphology of luminous IRAS galaxies: Summary talk

The author discusses the morphology of luminous Infrared Astronomy Satellite (IRAS) galaxies. A few comments are made about the direction to be taken in future observations of luminous IRAS galaxies.

Becklin, E. E.↗
NASA NTRS1988

Infrared spectroscopy of radio-luminous OH/IR stars

Low-resolution 1.5-2.5-micron spectra for 21 radio-luminous OH/IR stars are presented. These spectra divide into two broad classes. Those with very strong water-vapor absorption closely resemble the spectra of classical Mira variables and are classified Type VM. Those with weaker water-vapor absorption, but still showing strong CO absorption, resemble the spectra of true core-burning supergiants and are classified Type SG. Comparison of the classification of 30 radio-luminous OH/IR stars with their Delta(V)s and luminosities suggests this classification is a good indicator of the intrinsic nature of the underlying star. There is some evidence, however, that some true supergiants (massive main-sequence progenitors) develop the pulsation properties and photospheric characteristics of the Mira-like OH/IR stars when they become optically obscured OH/IR stars.

Jones, Terry Jay↗
NASA NTRS1988

21 centimeter survey of luminous infrared galaxies

This paper presents the results from a 21-cm Arecibo survey of the atomic hydrogen and radio continuum in the most luminous IRAS galaxies of the local universe. Ninety-two galaxies with FIR luminosities in the range of L(FIR) between the solar luminosity values of 2 x 10 to the 10th and 2 x 10 to the 12th were surveyed. Eighty eight of these were detected in the 21 cm line of atomic hydrogen; the radio continuum flux was determined for 80 galaxies. The data of this survey are compared the FIR and optical-wavelength band results. It is noted that luminous IR galaxies show a striking statistical trend for the optical radial velocities to be smaller than the systemic velocities derived from the 21 H I profiles.

Mirabel, I. F.↗
NASA NTRS1989

The ratio of molecular to atomic gas in infrared luminous galaxies

In infrared luminous galaxies the ratio of the CO(1 - 0) to H I integrated fluxes increases with the far-infrared excess, f(fir)/f(b). All infrared active galaxies with f(fir)/f(b) greater than 2 have molecular to atomic gas mass fractions greater than 0.5. Among the galaxies with the higher infrared excesses there are systems with strikingly small atomic mass fractions, where less than 15 percent of the total mass of interstellar gas is in atomic form. The optical morphology of luminous infrared galaxies indicates that the majority, if not all, of these objects are interacting systems. These observations suggest that the overall mass fraction of molecular to atomic gas, and the infrared luminosities per nucleon of interstellar gas are enhanced during galaxy-galaxy interactions.

Mirabel, I. F.↗
NASA NTRS1990

WRA 751, a candidate for a new luminous blue variable

Results are presened on spectroscopic observations (carried out with the ESO 1.52-m telescope at La Silla, Chile) and measurements made by the Infrared Astronomical Satellite on the star WRA 751. It is estimated that the T(eff) of this star is 30,000 K and its E(B-V) is 1.8 mag. Comparison with evolutionary tracks of Maeder and Meynet (1980) indicates that WRA 751 is located in the region of luminous blue variables at a lower limit of the initial mass of about 50 solar masses. Its other physical characteristics, such as the light variability, strong Fe II lines, and the extinction-free spectral energy distribution, suggest that WRA 751 is a candidate for a new luminous blue variable.

Hu, J. Y.↗
NASA NTRS1991

Evolution of luminous IRAS sources - CCD imaging

The paper presents optical imaging of a sample of 64 luminous IRAS galaxies which cover a wide range of IRAS spectra and luminosity and also include a range of optical types. The objects are almost all in current or recent tidal interaction. The connections between the strength and age of the interaction, the IR spectrum and luminosity, and the optical colors, and other properties of the galaxies are discussed. The principal result is that the powerful IR sources with steep IR spectra are stronger and dynamically younger interacting systems, while the flat IR spectrum objects are older. Star formation, dust obscuration, and the timescales for nuclear activity compared with IR and tidal events are discussed, and a self-consistent evolution scenario connecting the luminous IR sources is described.

Hutchings, J. B.↗
NASA NTRS1990

Nearby luminous blue galaxies

Some galaxies are comparable to spirals in terms of blue luminosities but show optical evidence (blue colors, strong emission lines) for large population I stellar components. These luminous blue galaxies provide examples of rapidly evolving large galaxies in the nearby universe. This paper discusses the evolutionary status of luminous blue galaxies and their possible relationships to the excess numbers of faint blue galaxies that are being found by deep surveys of galaxies.

Gallagher, John S., III↗
NASA NTRS1992

Evolution of luminous IRAS sources - Radio imaging

Observations of the compact radio morphology of 111 luminous IRAS-selected active galaxies covering a wide range of IR and optical properties are presented and discussed. Of these sources, 72 are observed for the first time with the VLA A configuration. The circumnuclear radio sources are generally small and weak, with 15 nondetections to a limit of about 0.4 mJy. Comparison with the IR and optical properties of the objects indicates that the radio sources turn on within 10 exp 8 yr of the tidal encounter that is presumed to generate the IR activity. However, the radio sources do not all appear at the same time. The radio observations are consistent with the evolution scenario for luminous IRAS galaxies suggested by Hutchings and Neff (1991).

Neff, S. G.↗