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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Studying the kinetics of magnetization in high Tc superconductors

We report the first microscopic maps of magnetic induction in YBa2Cu3O(7-x) crystals which directly show the dependence of flux flow on twin density, polytwin block, and twin boundary orientation. These maps were obtained by means of a recently-improved magneto-optical imaging technique. Pinning was lowest in untwinned regions and increasing with increasing twin density. Anisotropy in twin boundary pinning, defined as the ratio of the magnetic induction gradient across twin boundaries to that along twin boundaries, was 10 at 17 K; this ratio increased with increasing temperature. In polycrystals, twin boundaries also had a strongly anisotropic effect on flux flow into a grain from a grain boundary.

Source record↗
NASA NTRS1992

Gas-Grain Simulation Facility (GGSF)

The goal of the Gas-Grain Simulation Facility project is to provide a microgravity laboratory to facilitate research relevant to exobiology (the study of the origin and evolution of life in the universe). Such a facility will also be useful in other areas of study important to NASA including planetary science, biology, atmospheric science, astrophysics, chemistry, and physics. To achieve this goal, the project will develop and support the GGSF, a modular facility-class payload planned for inclusion on Space Station Freedom. The GGSF will consist of the following: an experiment chamber(s) supported by subsystems that provide chamber environment regulation and monitoring capabilities; sample generation, injection, positioning, and retrieval capabilities; and computer control, data acquisition, and housekeeping capabilities. The facility will also provide analytical tools such as light-scattering measurement systems, aerosol size-spectrum measurement devices, and optical imaging systems.

Greenwald, Ken↗
NASA NTRS1993

Studying the kinetics of magnetization in high Tc superconductors

The first microscopic maps of magnetic induction in YBa2Cu3O(7-x) crystals which directly show the dependence of flux flow on twin density and polytwin block and twin boundary orientation are reported. These maps were obtained by means of a recently-improved magneto-optical imaging technique. Pinning was lowest in untwinned regions and increased with increasing twin density. An isotropy in twin boundary pinning, defined as the ratio of the magnetic induction gradient across twin boundaries to that along twin boundaries, was 10 at 17 K; this ratio increased with increasing temperature. In polycrystals, twin boundaries also had a strongly anisotropic effect on flux flow into a grain from a grain boundary.

Turchinskaya, Marina↗
NASA NTRS1992

The synchrotron bays of the Crab Nebula - A magnetic structure associated with a presupernova circumstellar disk

We investigate the nature of two large conical indentations in the Crab Nebula's synchrotron emission, commonly known as the east and west 'bays'. Optical images spanning nearly nine decades (1899-1988) reveal the bays to be long-lasting remnant features. Proper motions of the bays away from the remnant's center of expansion are consistent with their locations near the SN progenitor site in A.D. 1054. Based on their morphologies and polarization properties, the bays appear to be portions of a torus encircling the remnant's center of expansion. The nebular magnetic field wrapped around this torus blocks the pulsar's relativistic particles, resulting in the observed lack of synchrotron emission. We propose that this torus is the result of a presupernova disklike ejection not less than 0.1 solar mass by the Crab progenitor, similar to the ring around SN 1987 A. A 0.5 solar mass disk of He-rich filaments along the equatorial plane is probably also related to presupernova mass loss, which might explain the wide range of abundances seen among filaments.

Fesen, Robert A.↗
NASA NTRS1992

The BL Lacertae object PKS 1413 + 135 - Is it within or behind a spiral galaxy?

New observations of the very red quasar or BL Lac object PKS 1413 + 135 are presented. Optical imaging and spectroscopy confirm the claim that the host galaxy to this BL Lac is a spiral, and H-band imaging shows the point source centered in the galaxy to within 0.1 arcsec. A reanalysis of Einstein X-ray data finds evidence for an extremely large column density in this source. While the astrometric evidence supports the hypothesis that PKS 1413 + 135 is the very unusual case of a BL Lac object in a spiral galaxy, a highly extincted nuclear source would produce other observable features in this galaxy that are not observed: narrow emission-line region and large thermal IR flux. Their absence argues for this source being background to the spiral.

Stocke, John T.↗
NASA NTRS1992

Achieving safe autonomous landings on Mars using vision-based approaches

Autonomous landing capabilities will be critical to the success of planetary exploration missions, and in particular to the exploration of Mars. Past studies have indicated that the probability of failure associated with open-loop landings is unacceptably high. Two approaches to achieving autonomous landings with higher probabilities of success are currently under analysis. If a landing site has been certified as hazard free, then navigational aids can be used to facilitate a precision landing. When only limited surface knowledge is available and landing areas cannot be certified as hazard free, then a hazard detection and avoidance approach can be used, in which the vehicle selects hazard free landing sites in real-time during its descent. Issues pertinent to both approaches, including sensors and algorithms, are presented. Preliminary results indicate that one promising approach to achieving high accuracy precision landing is to correlate optical images of the terrain acquired during the terminal descent phase with a reference image. For hazard detection scenarios, a sensor suite comprised of a passive intensity sensor and a laser ranging sensor appears promising as a means of achieving robust landings.

Pien, Homer↗
NASA NTRS1993

HST observations of NGC 4395, the least luminous Seyfert 1 nucleus - Evidence against the starburst hypothesis for broad-lined active galactic nuclei

The starburst hypothesis for broad-line AGN is examined here using ultraviolet spectra and optical images of NGC 4395, the least luminous Seyfert 1 nucleus. From the evidence it is concluded that the apparent activity in the Seyfert 1 nucleus of NGC 4395 probably cannot be explained in the context of the starburst hypothesis of Terlevich et al. (1992). The strongest piece of evidence is the absence of stellar absorption lines, especially in the UV and NIR spectra. Other relevant characteristics are the UV spectral index of roughly -1, small physical size, low luminosity, and lack of obvious variability.

Filippenko, Alexei V.↗
NASA NTRS1988

The Einstein Observatory extended medium sensitivity survey sample of BL Lacertae objects

We present new results on BL Lacertae Objects discovered in an extensive X-ray survey of the high galactic latitude sky performed by the Einstein satellite. While BL Lacs have been found primarily in high frequency radio surveys, we show that X-ray emission is an efficient new method for finding such objects and will offer an outstanding opportunity to find many of these objects in the near future using the ROSAT all-sky survey. It is also shown that X-ray selected BL Lac objects have somewhat different optical and radio properties than their radio selected counterparts. Using a complete, flux limited sample of 16 X-ray selected BL Lacs, we show that their number counts differ decisively from those of X-ray selected QSOs. Moreover, using the few red shifts available for these objects and limits on red shift determined from resolving the optical images of most of the remainder of the sample, a preliminary V/Vmax = 0.37 +/- 0.06. This value suggests an evolution in luminosity and/or density opposite in sense to that of QSOs.

Stocke, John T.↗
NASA NTRS1994

Diffractive Optics For Geostationary Earth Observatory

Report analyzes design of proposed Geostationary Earth Observatory (GEO) instruments and identifies potential applications within those instruments in which diffractive optics improve performance while reducing weight and cost. Applications include use of hybrid diffractive/refractive lenses in aft-optic imagers, and diffractive components compensating for aberrations in reflecting imaging systems and in grating spectrometers.

Morris, G. Michael↗
NASA NTRS1993

The GAMCIT gamma ray burst detector

The GAMCIT payload is a Get-Away-Special payload designed to search for high-energy gamma-ray bursts and any associated optical transients. This paper presents details on the design of the GAMCIT payload, in the areas of battery selection, power processing, electronics design, gamma-ray detection systems, and the optical imaging of the transients. The paper discusses the progress of the construction, testing, and specific design details of the payload. In addition, this paper discusses the unique challenges involved in bringing this payload to completion, as the project has been designed, constructed, and managed entirely by undergraduate students. Our experience will certainly be valuable to other student groups interested in taking on a challenging project such as a Get-Away-Special payload.

Mccall, Benjamin J.↗
NASA NTRS1994

Advanced ballistic range technology

The research conducted supported two facilities at NASA Ames Research Center: the Hypervelocity Free-Flight Aerodynamic Facility and the 16-Inch Shock Tunnel. During the grant period, a computerized film-reading system was developed, and five- and six-degree-of-freedom parameter-identification routines were written and successfully implemented. Studies of flow separation were conducted, and methods to extract phase shift information from finite-fringe interferograms were developed. Methods for constructing optical images from Computational Fluid Dynamics solutions were also developed, and these methods were used for one-to-one comparisons of experiment and computations.

Yates, Leslie A.↗
NASA NTRS1993

A nonthermal superbubble in the irregular galaxy IC 10

We present synthesis radio continuum observations of the nearby irregular galaxy IC 10. These observations, at 6, 20, and 49 cm, allow us to measure the flux and spectral index of a number of resolved sources in IC 10. While most of these are easily identified as thermal emission from H II regions and a few are nonthermal background sources, one extended, nonthermal source appears to be a superbubble in IC 10. Its large size (about 250 pc) implies that it is most likely the product of several supernovae. Comparisons of these radio observations with Halpha, H I, and optical imaging observations reveal that the large nonthermal superbubble is associated with a region of star formation containing two of the most luminous H II regions and the most massive H I cloud in IC 10. We tentatively identify a stellar cluster with two Wolf-Rayet stars in the center of the superbubble. We propose that this superbubble in IC 10 represents a bridge between the giant H II regions and the H I shells and supershells observed in our Galaxy and external galaxies.

Yang, Hui↗
NASA NTRS1995

The distribution of far-infrared light in the 'Dusty Hand' galaxy NGC 2146

The Kuiper Airborne Observatory (KAO) has been used to obtain high spatial resolution 50 and 100 micrometers observations of the peculiar galaxy NGC 2146. We find that the far-infrared luminosity of NGC 2146 arises in a 21 arcsecs x less than or = 16 arcsecs (1.5 kpc x less than or equal 1.1 kpc) region (FWHM) elongated along the major axis. This limit is consistent with the size of the central radio continuum and (12)CO (1-0) sources. The far-infrared distribution is slightly more compact than that of the H-alpha; this difference is consistent with observed pattern of extinction in this galaxy. From a study of the energetics in this galaxy, we conclude that young massive stars are largely responsible for powering the far-infrared luminosity of NGC 2146. The far-infrared and CO (1-0) distributions differ from the reddening morphology as seen in optical images and in the Br-gamma/H-alpha ratio. The starlight and the ionized gas appear most highly reddened at the prominent dust lane 15 arcsecs to the west of the nucleus, while the CO and far-infrared emission peak near the nucleus. This result dust lane lies in front of the main body of the galaxy.

Smith, Beverly J.↗
NASA NTRS1995

A first determination of the surface density of galaxy clusters at very low x-ray fluxes

We present the first results of a serendipitous search for clusters of galaxies in deep ROSAT position sensitive proportional counter (PSPC) pointed observations at high Galactic latitude. The survey is being carried out using a wavelet-based detection algorithm which is not biased against extended, low surface brightness sources. A new flux-diameter limited sample of 10 cluster candidates has been created from approximately 3 deg(exp 2) surveyed area. Preliminary CCD observations have revealed that a large fraction of these candidates correspond to a visible enhancement in the galaxy surface density, and several others have been identified from other surveys. We believe these sources to be either low- to moderate-redshift groups or intermediate- to high-redshift clusters. We show X-ray and optical images of some of the clusters identified to date. We present, for the first time, the derived number density of the galaxy clusters to a flux limit of 1 x 10(exp -14) ergs cm(exp -2) s(exp -1) (0.5-2.0 keV). This extends the log N-log S of previous cluster surveys by more than one decade in flux. Results are compared to theoretical predictions for cluster number counts.

Rosati, Piero↗
NASA NTRS1995

The far-infrared distribution in the Dusty Hand Galaxy NGC 2146

Our high spatial resolution 50 and 100 micro m observations of the peculiar galaxy NGC 2146 show that the FIR emission arises in a 21 arc-sec x is less than 16 arc-sec (1.5 kpc x is less than 1.1 kpc) region (FWHM) elongated along the major axis. This size limit is similar to that of the radio continuum, the (12)CO (1 - 0), and the H alpha. From an investigation of the energetics in this galaxy, we conclude that young massive stars are largely responsible for powering the FIR luminosity of this galaxy. The FIR and CO (1 - 0) distributions differ from the extinction morphology as seen in optical images and in the Br gamma/H alpha ratio. The starlight and the ionized gas are most highly reddened at the prominent dust lane 15 arc-sec to the west of the nucleus, while the CO and FIR emission peak near the nucleus. This result can be explained by either a high proportion of cold dust and gas at the dust lane, or a geometry in which the dust lane lies in front of the main body of the galaxy.

Smith, Beverly J.↗
NASA NTRS1997

Achromatic Emission Velocity Measurements in Luminous Flows

A new velocity measurement instrument for luminous flows was developed by Science Research Laboratory for NASA. The SIEVE (Segmented Image Emission VElocimeter) instrument uses broadband light emitted by the flow for the velocity measurement. This differs from other velocimetry techniques in that it does not depend on laser illumination and/or light scattering from particles in the flow. The SIEVE is a passive, non-intrusive diagnostic. By moving and adjusting the imaging optics, the SIEVE can provide three-dimensional mapping of a flow field and determine turbulence scale size. A SIEVE instrument was demonstrated on an illuminated rotating disk to evaluate instrument response and noise and on an oxy-acetylene torch to measure flame velocities. The luminous flow in rocket combustors and plumes is an ideal subject for the SIEVE velocity measurement technique.

Schneider, S. J.↗
NASA NTRS1997

The Extragalactic X-ray Background in the 0.2 - 2 keV Range

We made the first measurement of the extragalactic 0.7 keV background. We detected the X-ray shadow of a neutral gas cloud in the Magellanic Bridge. We further constrained the point-like source contribution based on the mean spectrum of detected sources and on our early autocorrelation function analysis of the background. We find that our measurement extragalactic background intensity is significantly greater than the total point-like source contribution expected if sources are responsible for all the observed background intensity in the 1-2 keV range. For a further confirmation of the theoretical prediction of the hot intergalactic medium, we have conducted a pilot project to search for enhanced X-ray-emitting features near rich clusters of galaxies. We have reported the discovery of an elongated complex of extended X-ray-emitting objects in and around the galaxy cluster A2125, based on an archival deep ROSAT/PSPC observation. Using multicolor optical imaging of galaxies in the field, we find that this complex represents a hierarchical superstructure spanning approx. 11 Mpc at the redshift approx. 0.247. The multiple peak X-ray morphology and large blue galaxy fraction of A2125 indicate that the cluster is undergoing a coalescence of subunits. The superstructure contains two additional clusters, projected at distances of only 3 and 4.3 Mpc from A2125. The most interesting feature is, however, the low-surface-brightness X-ray emission from a moderate galaxy concentration away from individual clusters. The emission likely arises in a hot (approx. 10(exp 7) K) intergalactic medium, as predicted in N-body/hydro simulations of structure formation. These results demonstrate the potential of X-ray observations as a powerful tool to study the large-scale structure of the universe.

Wang, Q. Daniel↗
NASA NTRS1998

Exploring the Full Range of Properties of Quasar Spectral Distributions

The aim of this work is to support our ISO, far-infrared (IR) observing program of quasars and active galaxies. We have obtained, as far as possible, complete spectral energy distributions (radio-X-ray) of the ISO sample in order to fully delineate the continuum shapes and to allow detailed modelling of that continuum. This includes: ground-based optical, near-IR and mm data, the spectral ranges closest to the ISO data, within 1-2 years of the ISO observations themselves. ISO was launched in Nov 1995 and is currently observing routinely. It has an estimated lifetime is 2 years. All near-IR and optical imaging and spectroscopy are now in hand and in the process of being reduced, mm data collection and proposal writing continues.

Wilkes, B.↗