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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 559 records · Page 31

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NASA NTRS1986

Albedo maps of Comets P/Giacobini-Zinner and P/Halley

Near-simultaneous infrared and visual maps of P/Giacobini-Zinner (P/G-Z) and P/Halley are combined to create maps of the spatial variation of geometric albedo. Giacobini-Zinner shows a minimum in albedo near 0.07 with an increase of a factor of 2 over 30 arcsec. The lowest albedos are offset from the nucleus in the antisunward direction, coincident with a dust tail observed in the IR. The P/Halley albedos are higher than those for P/G-Z and range from 0.2 to 0.4, but the trend of darker albedo in the antisunward direction (along the tail) is the same. The albedo distribution is attributed to large, dark, fluffy grains confined to the orbital plane close to the nucleus. The high albedo values in P/Halley may be due to enhanced flux in the visual image because of the comet's very small phase angle.

Hammel, H. B.↗

NASA NTRS1987

Structure in the nucleus of NGC 1068 at 10 microns

New 8-13 micron array camera images of the central kiloparsec of Seyfert 2 galaxy NGC 1068 resolve structure that is similar to that observed at visible and radio wavelengths. The images reveal an infrared source which is extended and asymmetric, with its long axis oriented at P.A. 33 deg. Maps of the spatial distribution of 8-13 micron color temperature and warm dust opacity are derived from the multiwavelength infrared images. The results suggest that there exist two pointlike luminosity sources in the central region of NGC 1068, with the brighter source at the nucleus and the fainter one some 100 pc to the northeast. This geometry strengthens the possibility that the 10 micron emission observed from grains in the nucleus is powered by a nonthermal source. In the context of earlier visible and radio studies, these results considerably strengthen the case for jet-induced star formation in NGC 1068.

Tresch-Fienberg, R.↗

NASA NTRS1987

Atmospheric lateral and longitudinal turbulent length scales (measured at 600 to 800 meters above grade level)

NASA's Airborne Doppler Lidar System has been used to obtain a detailed 'instantaneous' mapping of horizontal spatial wind fields at 600-800 m elevations on the east side of the San Gorgonio Pass in California, in the form of checkerboard-fashion horizontal wind vectors spaced at 300 m intervals along and normal to the flight path. Spatial autocorrelations for the lateral and longitudinal components are ensemble-averaged, and integral turbulent length scales are computed for the wind fields' longitudinal and lateral directions. The flow in the region studied does not appear to be isotropic.

Cliff, W. C.↗

NASA NTRS1987

Studies of isolated neutron stars, pulsars and pulsar-driven nebulae with the advanced X-ray astrophysics facility (AXAF)

The AXAF will signal a revolution in the understanding of neutron stars, pulsars, and Crab Nebula-type supernova remnants. The mission will provide vital and detailed observational data relevant to the physics of superdense matter inside neutron stars, to the acceleration and radiation of nonthermal particles in their magnetospheres, and to the processes whereby these relativistic particles and magnetic fields fuel the surrounding synchrotron nebulosities on scales of parsecs. Highlights of the results should include (1) detection of thermal surface emission from neutron stars, (2) greatly enlarged samples of pulsars that emit magnetospheric (nonthermal) X-rays, and (3) high resolution (spatial and spectral) maps of the nebulae powered by slowing pulsars. The AXAF will extend these studies to external galaxies, being capable of detection of young pulsars and remnants in normal galaxies like M31, in starburst systems like M82, and probably even in galaxies as distant as the Virgo cluster.

Wilson, A. S.↗

NASA NTRS1988

AVIRIS performance during the 1987 flight season: An AVIRIS project assessment and summary of the NASA-sponsored performance evaluation

Results are presented of the assessment of AVIRIS performance during the 1987 flight season by the AVIRIS project and the earth scientists who were chartered by NASA to conduct an independent data quality and sensor performance evaluation. The AVIRIS evaluation program began in late June 1987 with the sensor meeting most of its design requirements except for signal-to-noise ratio in the fourth spectrometer, which was about half of the required level. Several events related to parts failures and design flaws further reduced sensor performance over the flight season. Substantial agreement was found between the assessments by the project and the independent investigators of the effects of these various factors. A summary of the engineering work that is being done to raise AVIRIS performance to its required level is given. In spite of degrading data quality over the flight season, several exciting scientific results were obtained from the data. These include the mapping of the spatial variation of atmospheric precipitable water, detection of environmentally-induced shifts in the spectral red edge of stressed vegetation, detection of spectral features related to pigment, leaf water and ligno-cellulose absorptions in plants, and the identification of many diagnostic mineral absorption features in a variety of geological settings.

Vane, Gregg↗

NASA NTRS1989

Images of the 10-micron source in the Cygnus 'Egg'

Mid-IR images of AFGL 2688, the Egg nebula, obtained with a 16 x 16 pixel array camera (field of view 12.5 x 12.5 arcsec) resolve the central source. It appears as a centrally peaked ellipsoid with major axis of symmetry parallel to the axis of the visible nebulosity. This is contrary to the expected extension perpendicular to this axis implied by proposed dust-toroid models of the IR source. Maps of the spatial distribution of 8-13 micron color temperature and warm dust opacity derived from the multiwavelength images further characterize the IR emission. The remarkable flatness of the color temperature conflicts with the radial temperature gradient expected across a thick shell of material with a single heat source at its center. The new data suggest instead that the source consists of a central star surrounded by a dust shell that is too thin to provide a detectable temperature gradient and too small to permit the resolution of limb brightening.

Jaye, D.↗

NASA NTRS1989

Spectroscopic images of NGC 7027 in the near-infrared dust emission features

Isophote maps derived from spatially resolved moderate spectral resolution images of the planetary nebula NGC 7027 in the 3.28-micron and 3.4-micron 'unidentified' emission features, and in the Br-alpha hydrogen recombination line are presented. Comparison of these images clearly shows that the 3.28-micron emission is spatially more extended than the ionized gas. Analysis and modeling of the spatial distribution of the 3.28-micron feature strength suggest that roughly equal amounts of feature emission appear to come from within the H II region and from a shell outside the H II region. The spatial distribution of the 3.4-micron feature emission is found to be similar to that of the 3.28-micron feature emission.

Woodward, C. E.↗

NASA NTRS1989

The 100 and 160 micron maps of the dust reemission from the nucleus and inner-arm regions of NGC 6946

Dust reemission from the Scd galaxy NGC 6946 has been measured at 100 and 160 microns with the 32-channel University of Chicago Far-Infrared Camera. Researchers present fully sampled maps of the nucleus and inner spiral arms at 45 seconds resolution. The far-infrared morphology of the galaxy is a bright peak centered on a diffuse disk, where the peak occurs about 24 seconds NE of the Dressel and Condon optical center. The 100/160 micron color temperature is correlated with the H alpha surface brightness. Assuming the distance from Earth to the galaxy is 10.1 Mpc, researchers determine that Tc is 32 K at the nucleus and at radius 5.4 kpc, where there is a concentration of H II regions. In the intermediate annulus of relatively low H alpha surface brightness, the temperature drops to a local minimum of 25 K at radius 3 kpc. The ratio of reradiated to transmitted stellar luminosity is approx. 3.0 at the nucleus and approx. 0.9 for the disk. The optical depth at 100 micron increases from .0005 at the edges of our map to .0035 at the far infrared radiation (FIR) peak. Combining our observations with a fully sampled map of similar spatial extent in CO(1 greater than 0), researchers determine that the ratio F sub IR/I sub CO at the center of the galaxy is almost twice that for the disk, where the value is more or less constant.

Engargiola, Gregory↗

NASA NTRS1991

Reconstruction of the Hubble Space Telescope mirror figure from out-of-focus stellar images

Both the amplitude and the phase of the incoming wave front viewed from the focal plane are reconstructed from the illumination recorded in defocused stellar images taken in flight by the HST. The reconstructed wavefront surface shows very little aberration. Compared to geometrical optics methods, the technique produces high spatial resolution wavefront maps with images taken closer to the telescope's focal plane. For the HST, the quality of the wavefront reconstruction is limited by the telescope jitter. The technique cannot be applied to ground-based telescopes at optical wavelength where the image is heavily blurred by the atmosphere. It is argued to be promising as a diagnostic tool for optical telescopes in space.

Roddier, C.↗

NASA NTRS1991

The Next Generation Space Telescope - A large UV-IR successor to HST

Attention is given to the science goals of the Next Generation Space Telescope (NGST), namely, detection and spectroscopy of gas giant planets to earthlike planets around nearby stars, study of nearby star-forming complexes with resolutions of 5-50 AU in the visible and IR, measurement of stellar populations in a variety of environments, spatial resolution and mapping of complex structures in the inner narrow line regions for AGN and QSOs, and investigation of the structure and evolution of galaxies at redshifts greater than 1. The NGST characteristics, milestones, long-term strategy, and launch capability are also discussed.

Illingworth, Garth↗

NASA NTRS1992

Structural-acoustic coupling in aircraft fuselage structures

Results of analytical and experimental investigations of structural-acoustic coupling phenomenon in an aircraft fuselage are described. The structural and acoustic cavity modes of DC-9 fuselage were determined using a finite element approach to vibration analysis. Predicted structural and acoustic dispersion curves were used to determine possible occurrences of structural-acoustic coupling for the fuselage. An aft section of DC-9 aircraft fuselage, housed in an anechoic chamber, was used for experimental investigations. The test fuselage was excited by a shaker and vibration response and interior sound field were measured using accelerometer and microphone arrays. The wavenumber-frequency structural and cavity response maps were generated from the measured data. Analysis and interpretation of the spatial plots and wavenumber maps provided the required information on modal characteristics, fuselage response and structural-acoustic coupling.

Mathur, Gopal P.↗

NASA NTRS1994

High-resolution mid-infrared observations of NGC 7469

We present a high-resolution 11.7 micrometer image of the starburst/Seyfert hybrid galaxy NGC 7469 using the Hale 5 m telescope at Palomar Observatory. Our map, with diffraction limited spatial resolution of 0.6 sec, shows a 3 sec diameter ring of emission around an unresolved nucleus. The map is similar to the Very Large Array (VLA) 6 cm map of this galaxy made with 0.4 sec resolution by Wilson et al. (1991). About half of the mid-infrared flux in our map emerges from the unresolved nucleus. We also present spatially resolved low resolution spectra that show that the 11.3 micrometer polycyclic aromatic hydrocarbon (PAH) feature comes from the circumnuclear ring but not from the nucleus of the galaxy.

Miles, J. W.↗

NASA NTRS1996

Mesospheric response to impacting relativistic electrons

Daily maps of the spatial distributions of precipitating energetic electrons were produced for the period 10-20 May 1992. These data will serve as the input for potential changes in upper atmosphere composition.

Chenette, D. L.↗

NASA NTRS1996

Mesospheric Response to Impacting Relativistic Electrons

Chenette, D. L.↗

NASA NTRS1997

Mid-Infrared Observations of the Galactic Center

Under this grant, Susan Stolovy completed her thesis work and performed an analysis of the galactic center. For her thesis Susan analyzed observations of the galactic center obtained with the KAO using the KEGS spectrograph, built at Cornell. These observations present a study of the distribution and kinematics of the atomic gas in the inner few parsecs of the Galaxy as traced by the forbidden [SiII] line at 34.814 microns. The integrated [SiII] emission peaks near Sgr A* and extends past the inner edge of the Circumnuclear Disk (CND), passing through a gap in the dense molecular material to the northwest. The [SiII] maps have a spatial resolution of 15" and a spectral resolution of 50 km/s. The spectra, which are characterized by broad linewidths of order 100 km/s, are kinematically consistent with the CND rotation to the southwest but not to the north. The northern extension may be experiencing shocks and is likely to be infalling along the Northern Arm. Observations of high [Sill]/ [OI] and [SiII]/dust continuum ratios support the conjecture that turbulent motions and shocks in the inner few parsecs of the Galaxy are destroying dust grains, thus elevating the abundance of atomic silicon.

Stolovy, Susan↗

NASA NTRS2003

Tensor Fields for Use in Fractional-Order Viscoelasticity

To be able to construct viscoelastic material models from fractional0order differentegral equations that are applicable for 3D finite-strain analysis requires definitions for fractional derivatives and integrals for symmetric tensor fields, like stress and strain. We define these fields in the body manifold. We then map them ito spatial fields expressed in terms of an Eulerian or Lagrangian reference frame where most analysts prefer to solve boundary problems.

Freed, Alan D.↗

NASA NTRS2006

Plasma Characteristics Measured in the Plume of a NEXT Multi-Thruster Array

Plasma properties in the plume produced by a 3+1 NEXT thruster array operating at full power were mapped using a series of planar Langmuir probes. The Langmuir probes were swept across the diameters of each thruster as well as the centerline of the array at multiple downstream axial locations to produce a plasma map of the plume produced by the array. Such maps yielded the spatial distribution of the plasma density, the electron temperature and the plasma potential in the near field of the array. This spatial information provides insight into local plasma particle flow. Flow direction is particularly important from both an array lifetime and spacecraft-plume plasma interaction standpoint. The variation in the plume plasma parameters tended to vary in a manner consistent with both plume shape and overlap of adjacent plumes.

Foster, John E.↗

NASA NTRS1995

Surface Displacement of the May 17, 1993 Eureka Valley, California, Earthquake

Satellite synthetic aperture radar (SAR) interferometry shows that the magnitude 6.1 Eureka Valley earthquake of 17 May 1993 produced an elongated subsidence basin oriented north-northwest, parallel to the trend defined by the aftershock distribution, whereas the source mechanism of the earthquake implies a north-northeast-striking normal fault. The ±3-millimeter accuracy of the radar-observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event. These observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west-dipping, north-northeast fault plane, reactivating the largest escarpment in the Saline Range.

Gilles Peltzer↗