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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

The Non-Stellar Infrared Continuum of Seyfert Galaxies

JHKL'M (1 - 5 micrometers) imaging of a sample of Seyfert 2 galaxies is presented. We have performed an accurate estimate of the near-infrared non-stellar nuclear fluxes. We confirm that the near-infrared nuclear continuum between 1 and 2.2microns of some Seyfert 2s is dominated by stellar emission, whereas the continuum emission at longer wavelengths (lambda = 3 - 5 micrometers) is almost entirely non-stellar in origin. The non-stellar spectral energy distributions (SED) in the infrared (up to 15 micrometers) of Seyfert galaxies show a variety of shapes, and they are well reproduced with the tapered disk models of Efstathiou & Rowan-Robinson (1995). We have used two models, one including an optically thin cone component found to fit the SED of NGC 1068, and a coneless model. Although our modelling of the SEDs does not allow us to favor either model to account for all the observed SEDs, we find that the viewing angle towards the central source is well constrained by both models. The galaxies in our sample have fitted values of the viewing angle in the range Theta(sub V) = 0 deg - 64 deg, for the assumed model parameters. We have also investigated non-stellar color-color diagrams (L' - M vs. H - M and L' - M vs. H - L'). The colors of the Seyfert galaxies with viewing angles Theta(sub v) less than 30 deg are better reproduced with the cone model. These diagrams provide a good means to separate Seyfert 2s with moderate obscuration (A(sub V) approx. less than 20 mag from hard X-ray observations) from those with high obscuration. The ground-based 4.8 microns and ISO 9.6 microns luminosities are well correlated with the hard X-ray luminosities of Seyfert ls and 2s. These continuum emissions appear as a good indicator of the AGN luminosity, at least in the cases of hard X-ray Compton-thin Seyfert galaxies (N(sub H) less than or = 10(exp 24)/sq cm). We finally stress the finding that some Compton thick galaxies show bright non-stellar emission at 5 microns This suggests that the near-infrared emission in Seyfert galaxies is produced in an extended component illuminated by the central source, that is more visible from all viewing angles, providing a good explanation for the differing N(sub H)/A(sub V) ratios found in some Seyfert 2s. We discuss possible implications of mid-infrared surveys for the search of counterparts of highly obscured hard X-ray sources.

Alonso-Herrero, Almudena↗
NASA NTRS1996

Simulations of Titan's brightness by a two-dimensional haze model

We have used a 2-D microphysics model to study the effects of atmospheric motions on the albedo of Titan's thick haze layer. We compare our results to the observed variations of Titan's brightness with season and latitude. We use two wind fields; the first is a simple pole-to-pole Hadley cell that reverses twice a year. The second is based on the results of a preliminary Titan GCM. Seasonally varying wind fields, with horizontal velocities of about 1 cm sec-1 at optical depth unity, are capable of producing the observed change in geometric albedo of about 10% over the Titan year. Neither of the two wind fields can adequately reproduce the latitudinal distribution of reflectivity seen by Voyager. At visible wavelengths, where only haze opacity is important, upwelling produces darkening by increasing the particle size at optical depth unity. This is due to the suspension of larger particles as well as the lateral removal of smaller particles from the top of the atmosphere. At UV wavelengths and at 0.89 micrometers the albedo is determined by the competing effects of the gas the haze material. Gas is bright in the UV and dark at 0.89 micrometers. Haze transport at high altitudes controls the UV albedo and transport at low altitude controls the 0.89 micrometers albedo. Comparisons between the hemispheric contrast at UV, visible, and IR wavelengths can be diagnostic of the vertical structure of the wind field on Titan.

NASA Discipline Exobiology↗
NASA NTRS1994

High-resolution imaging with a tip-tilt Cassegrain secondary

A prototype adaptive secondary mirror has been developed on a 2.3-m telescope to stabilize rapid motion caused by atmospheric turbulence. The instantaneous position of an image's centroid, or brightest speckle, is measured by a near-infrared camera system which enables the tip-tilt mirror to recenter the image. Correction is accomplished at closed-loop frequencies of less than or = 100 Hz on guide stars with K (2.2 micrometers) magnitudes less than or = 8. Image motion is reduced to less than 0.1 sec rms, removing over 90% of low-frequency (f less than or = 5 Hz) tilt power, leaving less than or = 1 rad exp 2 mean square wave front tilt phase error. In seeing conditions where D/r sub o approximately = 4, long exposures in the H band (1.6 micrometers) exhibit a nearly diffraction-limited resolution of 0.19 sec full width at half maximum (FWHM) (Strehl ratio aprroximately = 0.14)-a factor of 4 improvement over uncorrected images. Reduction of the present static optical errors will improve the Strehl ratio another factor of 2, leading to approximately 70% of the maximum possible Strehl ratio.

Close, L. M.↗
NASA NTRS2006

Applications of Microwave Photonics in Radio Astronomy and Space Communication

An overview of narrow band vs wide band signals is given. Topics discussed included signal transmission, reference distribution and photonic antenna metrology. Examples of VLA, ALMA, ATA and DSN arrays are given. . Arrays of small antennas have become more cost-effective than large antennas for achieving large total aperture or gain, both for astronomy and for communication. It is concluded that emerging applications involving arrays of many antennas require low-cost optical communication of both wide bandwidth and narrow bandwidth; development of round-trip correction schemes enables timing precision; and free-space laser beams with microwave modulation allow structural metrology with approx 100 micrometer precision over distances of 200 meters.

microwave↗
NASA NTRS2011

The Hyperspectral Thermal Emission Spectrometer (HyTES): Preliminary Results

The Hyperspectral Thermal Emission Spectrometer (HyTES) is being developed as part of the risk reduction activities associated with the Hyperspectral Infrared Imager (HyspIRI). HyspIRI is one of the Tier 2 Decadal Survey Missions. HyTES will provide information on how to place the filters on the HyspIRI Thermal Infrared Instrument (TIR) as well as provide antecedent science data. The pushbroom design has 512 spatial pixels over a 50-degree field of view and 256 spectral channels between 7.5 micrometers to 12 micrometers. HyTES includes many key enabling state-of-the-art technologies including a high performance convex diffraction grating, a quantum well infrared photodetector (QWIP) focal plane array, and a compact Dyson-inspired optical design. The Dyson optical design allows for a very compact and optically fast system (F/1.6). It also minimizes cooling requirements due to the fact it has a single monolithic prism-like grating design which allows baffling for stray light suppression. The monolithic configuration eases mechanical tolerancing requirements which are a concern since the complete optical assembly is operated at cryogenic temperatures ((is) approximately 100K). The QWIP allows for optimum spatial and spectral uniformity and provides adequate responsivity or D-star to allow 200mK noise equivalent temperature difference (NEDT) operation across the LWIR passband. Assembly of the system is nearly complete. After completion, alignment results will be presented which show low keystone and smile distortion. This is required to minimize spatial-spectral mixing between adjacent spectral channels and spatial positions. Predictions show the system will have adequate signal to noise for laboratory calibration targets.

Moon Mineralogical Mapper (M3).↗
NASA NTRS1996

The First Diffraction-Limited Images from the W. M. Keck Telescope

The first diffraction limited, 0.05s resolution, images on the W. M. Keck Telescope have been obtained at a wavelength of 2.2 micrometers. These images were part of an experiment to test the suitability of the Keck Telescope for speckle imaging. In order to conduct this test, it was necessary to modify the pixel scale of the Keck facility Near Infrared Camera (NIRC) to optimally sample the spatial frequencies made available by the Keck telescope. The design and implementation of the external reimaging optics, which convert the standard fl25 beam from the secondary mirror to fl182, are described here. Techniques for reducing speckle data with field rotation on an alt-az telescope are also described. Three binary stars were observed in this experiment with separations as small as 0.05s. With only 100 frames of data on each, a dynamic range of at least 3.5 mag was achieved in all cases. These observations imply that a companion as faint as 14.5 mag at 2.2 micrometers could be detected around an 11th magnitude point source.

Matthews, K.↗
NASA NTRS1973

Red clouds in reducing atmospheres

A dark reddish-brown high-molecular weight polymer is produced by long wavelength ultraviolet irradiation of abundant gases in reducing planetary atmospheres. The polymer is examined by paper chromatography, mass spectrometry, and infrared, visible, and ultraviolet spectroscopy. High carbon-number straight-chain alkanes with NH2 and, probably, OH and C = O groups are identified, along with amino acids. There are chemical similarities between this polymer and organic compounds recovered from carbonaceous chondrites and precambrian sediments. The visible and near-ultraviolet transmission spectrum of the polymer shows its absorption optical depth to be redder than lambda(-2) and perhaps similar in coloration to the clouds of Jupiter, Saturn, and Titan. The nitrile content is small, and the polymer should be semitransparent in the 5 micrometer atmospheric window. Such polymers may be a common constituent of clouds in the outer solar system and on the early earth.

Khare, B. N.↗
NASA NTRS1995

Dust torus around Mars

We investigate the orbital dynamics of small dust particles generated via the continuous micrometeoroid bombardment of the Martian moons. In addition to Mar's oblateness, we also consider the radiation pressure perturbation that is complicated by the planet's eccentric orbit and tilted rotational axis. Considering the production rates and the lifetimes of dust grains, we show that particles from Deimos with radii of about 15 micrometers are expected to dominate the population of a permanently present and tilted dust torus. This torus has an estimated peak number density of approximately equals 5 x 10(exp -12)/cu cm and an optical depth of approximately equals 4 x 10(exp -8).

Juhasz, Antal↗
NASA NTRS1995

Dust Grains and the Luminosity of Circumnuclear Water Masers in Active Galaxies

In previous calculations for the luminosities of 22 GHz water masers, the pumping is reduced and ultimately quenched with increasing depth into the gas because of trapping of the infrared (approximately equals 30-150 micrometers), spectral line radiation of the water molecule. When the absorption (and reemission) of infrared radiation by dust grains is included, we demonstrate that the pumping is no longer quenched but remains constant with increasing optical depth. A temperature difference between the grains and the gas is required. Such conditions are expected to occur, for example, in the circumnuclear masing environments created by X-rays in active galaxies. Here, the calculated 22 GHz maser luminosities are increased by more than an order of magnitude. Application to the well-studied, circumnuclear masing disk in the galaxy NGC 4258 yields a maser luminosity near that inferred from observations if the observed X-ray flux is assumed to be incident onto only the inner surface of the disk.

Collison, Alan J.↗
NASA NTRS1994

10-micrometers images and spectra of T Tauri stars

T Tauri stars are young stars usually surrounded by dusty disks similar to the one from which we believe our own Solar System formed. Most T Tauri stars exhibit a broad emission or absorption band between 7.5 and 13.5 micrometers which is attributed to silicate grains in the circumstellar environment. We imaged three spatially resolved T Tauri binaries through a set of broadband filters which include the spectral region occupied by the silicate band. Two of these objects (T Tauri and Haro 6-10) are 'infrared companion' systems in which one component is optically much fainter but contributes strongly in the infrared. Both infrared companions exhibit a deep silicate absorption which is not present in their primaries, indicating that they suffer very strong local extinction whigh may be due to an edge-on circumstellar disk or to a dense shell. We also took low resolution spectra of the silicate feature of two unresolved T Tauris to look for narrow features in the silicate band which would indicate the presence of specific minerals such as olivine. We observed GK Tau, for which Cohen and Witteborn (1985) reported a narrow emission feature at 9.7 micrometers, but do not find evidence for this feature, and conclude that it is either time-dependent or an artifact of absorption by telluric ozone.

Van Cleve, J. E.↗
NASA NTRS2010

Low Power Consumption Lasers for Next Generation Miniature Optical Spectrometers for Major Constituent and Trace Gas Analysis

The air quality of any manned spacecraft needs to be continuously monitored in order to safeguard the health of the crew. Air quality monitoring grows in importance as mission duration increases. Due to the small size, low power draw, and performance reliability, semiconductor laser-based instruments are viable candidates for this purpose. The minimum instrument size requires lasers with emission wavelength coinciding with the absorption of the fundamental frequency of the target gases which are mostly in the 3.0-5.0 micrometers wavelength range. In this paper we report on our progress developing high wall plug efficiency type-I quantum-well GaSb-based diode lasers operating at room temperatures in the spectral region near 3.0-3.5 micrometers and quantum cascade (QC) lasers in the 4.0-5.0 micrometers range. These lasers will enable the development of miniature, low-power laser spectrometers for environmental monitoring of the spacecraft.

semiconductor lasers↗
NASA NTRS1976

Scanning radiometer for measurement of forward-scattered light to determine mean diameter of spray particles

A scanning radiometer is reported that measures forward-scattered light to determine the mean diameter of spray particles. An optical scanning method gives a continuous measurement of the light-scattering angle during spray nozzle tests. A method of calibration and a correction for background light are presented. Mean particle diameters of 10 to 500 micrometers can be measured.

Buchele, D. R.↗
NASA NTRS1979

Observations of far-infrared fine structure lines: o III88.35 micrometer and oI 63.2 micrometer

Observations of the O III 88.35 micrometer line and the O I63.2 micrometer were made with a far infrared spectrometer. The sources M17, NGC 7538, and W51 were mapped in the O III line with 1 arc minute resolution and the emission is found to be quite widespread. In all cases the peak of the emission coincides with the maximum radio continuum. The far infrared continuum was mapped simultaneously and in M17, NGC 7538, and W51 the continuum peak is found to be distinct from the center of ionization. The O III line was also detected in W3, W49, and in a number of positions in the Orion nebula. Upper limits were obtained on NGS 7027, NGC 6572, DR21, G29.9-0.0 and M82. The 63.2 micrometer O I line was detected in M17, M42, and marginally in DR21. A partial map of M42 in this line shows that most of the emission observed arises from the Trapezium and from the bright optical bar to the southeast.

Storey, J. W. V.↗
NASA NTRS1981

Transport of infrared radiation in cuboidal clouds

The transport of infrared radiation in a single cuboidal cloud using a vertical two steam approximation was modeled. The emittance of the top face of the model cloud is always less than that for a plane parallel cloud of the same optical depth. The hemisphere flux escaping from the cloud top has a gradient from the center to the edges which brighten when the cloud is over warmer ground. Cooling rate calculations in the 8 to 13.6 micrometer region show that there is cooling from the sides of the cloud at all levels even when there is heating of the core from the ground below. The radiances exiting from model cuboidal clouds were computed by path integration over the source function obtained with the two stream approximation. It is suggested that the brightness temperature measured from finite clouds will overestimate the cloud top temperature.

HARSHVARDHAN↗
NASA NTRS1980

The clouds of Venus - A synthesis report

The results presented represent a synthesis of data from those Pioneer Venus experiments directed toward studying cloud problems. These orbiter and multiprobe experiments show the cloud system to consist of three altitude regions populated by cloud particles and smaller haze particles which extend above and below as well as coexist with the cloud particles. The optical properties derived are only consistent with the largest particles, having platelike morphology. The smallest particles are shown to require changes in chemical composition to explain observed behavior. The medium-sized H2SO4 droplets of 2 micrometers diameter appear to be the least volatile and are the best understood. The role of the cloud particles in precipitation dynamical processes, lightning, and radiation are all discussed.

Knollenberg, R.↗
NASA NTRS1992

Prediction of propellant behavior in spinning flow of a space motor

A model for 2-phase flow dynamics in a spinning spherical rocket motor, developed for the Ofeq satellite program, is based on the sectional approach to solution of the flow equations. An experimental model was built, to enable the motion of the aluminum/aluminum-oxide particles resulting from combustion within a solid-fuel motor to be simulated by injected paraffin droplets. The injected droplets included under-5 micrometer droplets which move with the gas stream and larger droplets, averaging 20 micrometer diameter, which simulate the motion of aluminum particles. The test chamber comprised a pair of cylindrical pyrex tubes with a sharp contraction in diameter, rotated at various speeds by a frequency-controllable motor. An optical system, based on a 5 W argon ion laser with a beam splitter and frequency shifter, mounted on a movable table, facilitated sectional measurements of the three velocity components and determination of size-velocity relationships. Preliminary results indicate that the effect of rotation on axial velocity is negligible, while its effect on tangential velocity approximates to solid-body rotation.

Gany, A.↗
NASA NTRS1988

The 2.5-12 micrometers spectrum of comet Halley from the IKS-VEGA experiment

The infrared instrument IKS flown on board the VEGA space probes was designed for the detection of emission bands of parent molecules, and for a measurement of the size and temperature of the thermal emitting nuclear region. The instrument had three channels with cooled detectors: an "imaging channel" designed to modulate the signal of the nucleus and two spectroscopic channels operating at 2.5-5 and 6-12 micrometers, respectively, equipped with circular variable filters of resolving power approximately 50. This paper presents and discusses the results from the spectral channels. On VEGA 1, usable spectra were obtained at distances D from the comet nucleus ranging from 250,000 to 40,000 km corresponding to fields of view 4000 and 700 km in diameter, respectively. The important internal background signal caused by the instrument itself, which could not be cooled, had to be eliminated. Since no sky chopping was performed, we obtain difference spectra between the current spectrum and a reference spectrum with little or no cometary signal taken at the beginning of the observing sequence (D approximately 200,000 km). Final discrimination between cometary signal and instrumental background is achieved using their different time evolution, since the instrumental background is proportional to the slow temperature drift of the instrument, and the cometary signal due to parent molecules or dust grains is expected to vary in first order as D-1. The 2.5-5 micrometers IKS spectra definitely show strong narrow signals at 2.7 and 4.25 micrometers, attributed to the nu 3 vibrational bands of H2O and CO2, respectively, and a broader signal in the region 3.2-3.5 micrometers, which may be attributed to CH-bearing molecules. All these signals present the expected D-1 intensity variation. Weaker emission features at 3.6 and 4.7 micrometers could correspond to the nu 1 and nu 5 bands of H2CO and the (1 - 0) band of CO, respectively. Molecular production rates are derived from the observed emissions, assuming that they are due to resonance fluorescence excited by the Sun's infrared radiation. For the strong bands of H2O and CO2, the rovibrational lines are optically thick, and radiative transfer is taken into account. We derive production rates, at the moment of the VEGA 1 flyby, of approximately 10(30) sec-1 for H2O, approximately 2.7 x 10(28) sec-1 for CO2, approximately 5 x 10(28) sec-1 for CO, and 4 x 10(28) sec-1 for H2CO, if attributions to CO and H2CO are correct. The production rate of carbon atoms in CH-bearing molecules is approximately 9 x 10(29) sec-1 assuming fluorescence of molecules in the gas phase, but could be much less if the 3.2-3.5 micrometers emission is attributed to C-H stretch in polycyclic aromatic hydrocarbons or small organic grains. In addition, marginal features are present at 4.85 and 4.45 micrometers, tentatively attributed to OCS and molecules with the CN group, respectively. Broad absorption at 2.8-3.0 micrometers, as well as a narrow emission at 3.15 micrometers, which follow well the D-1 intensity variation, might be due to water ice. Emission at 2.8 micrometers is also possibly present, and might be due to OH created in vibrationally excited states after water photodissociation. The 6-12 micrometers spectrum does not show any molecular emission, nor emission in the 7.5-micrometers region. The spectrum is dominated by silicate emission showing a double structure with maxima at 9.0 and 11.2 micrometers, which suggests the presence of olivine.

NASA Discipline Number 52-10↗
DOE OSTI2024

The nontrivial effects of annealing on superconducting properties of Nb single crystals

The effect of annealing on the superconducting properties of niobium single crystals was studied using optical, magnetic, and scanning tunneling microscopy (STM) methods. Pieces of the same crystal boule were studied before and after the annealing at 800 ${^\circ}\textrm{C}$, 1400 ${^\circ}\textrm{C}$, and near the melting point of niobium (2477 ${^\circ}\textrm{C}$). The initial samples had a high hydrogen content and low-temperature imaging revealed large hydrides (hundreds of micrometers) appearing below 190 K. The formation of these large precipitates is already completely suppressed by annealing at 800 ${^\circ}\textrm{C}$. However, the overall superconducting properties of the annealed samples did not improve and, in fact, worsened. In particular, the superconducting transition temperature decreased, the upper critical field increased, and the pinning strength increased. In the STM study, the sample was annealed initially at 400 ${^\circ}\textrm{C}$, measured, annealed at 1700 ${^\circ}\textrm{C}$, and measured again. The STM revealed a ‘dirty’ superconducting gap with a significant spatial variation in tunneling conductance after annealing at 400 ${^\circ}\textrm{C}$. The clean gap was recovered after annealing at 1700 ${^\circ}\textrm{C}$. This is likely due to oxygen redistribution near the surface, which is always covered by oxide layers in as-grown crystals. Our results indicate that vacuum annealing at least up to 1400 ${^\circ}\textrm{C}$, while removing a large percentage of hydrogen, introduces additional nanosized defects, likely hydride precipitates, that act as efficient pair-breaking and pinning centers. The dimensionless scattering rate is estimated to have increased from $\Gamma = 0.2$ to about $\Gamma = 0.4$ after annealing at 1400 ${^\circ}\textrm{C}$. These results on single crystals differ drastically from those obtained in polycrystalline bulk niobium (i.e. cut from superconducting radio-frequency cavities), where annealing is known to have a significant positive effect that is attributed to the improvement of the crystalline structure masking the more subtle influence of the hydrides.

43 PARTICLE ACCELERATORS↗