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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Report of the Joint Scientific Mission Definition Team for an infrared astronomical satellite

The joint effort is reported of scientists and engineers from the Netherlands, the United Kingdom, and the United States working as a team for the purpose of exploring the possibility of a cooperative venture. The proposed mission builds upon experience gained from the successful Astronomical Netherlands Satellite (ANS). This satellite will be in a polar orbit at an altitude of 900 km. It will carry an 0.6 m diameter telescope cooled with helium to a temperature near 10K. An array of approximately 100 detectors will be used to measure the infrared flux in four wavelength bands centered at 10, 20, 50, and 100 microns. Sources will be located on the sky with positional accuracy of 1/2 arcminute. The instrument should be able to investigate the structure of extended sources with angular scales up to 1.0 deg. The entire sky will be surveyed and the full lifetime of the mission of about one year will be necessary to complete the survey. Special observational programs will also be incorporated into the mission.

Source record↗
NASA NTRS1978

Nonthermal galactic emission below 10 megahertz

The Radio Astronomy Explorer 2 (RAE 2) lunar-orbiting satellite has provided measurements of the nonthermal galactic radio emission at frequencies below 10 MHz. Measurements of the emission spectra are presented for the center, anticenter, north polar, and south polar directions at 22 frequencies between 0.25 and 9.18 MHz. Survey maps of the spatial distribution of the observed low-frequency Galactic emission at 1.31, 2.20, 3.93, 4.70, 6.55, and 9.18 MHz are presented. The observations were obtained with the 229-m traveling-wave V antenna on this lunar-orbiting spacecraft. The improved frequency coverage offers additional insights into the structure of the local Galactic neighborhood.

Milky Way↗
NASA NTRS1978

An advanced structural analysis/synthesis capability - ACCESS 2

An advanced automated design procedure for minimum weight design of structures (ACCESS 2) is reported. Design variable linking, constraint deletion, and explicit constraint approximation are used to effectively combine finite element and nonlinear mathematical programming techniques. The approximation concepts approach to structural synthesis is extended to problems involving fiber composite structure, thermal effects and natural frequency constraints in addition to the usual static stress and displacement limitations. Sample results illustrating these new features are given.

Schmit, L. A.↗
NASA NTRS1982

Ion current in a magnetic neutral region - Generation of an incipient magnetopause

The current contributed by ions trapped in the vicinity of a magnetic X line is calculated. The three dimensional configuration of the neutral region is found to be critical in determining the current in that the escape mechanism and trapping times depend on the three-dimensional aspects. A trapping criterion is defined. In the neutral region the ions can gain substantial kinetic energy, and the current will change the X line configuration in such a way that there will be a positive feedback effect, rapidly forming an extended magnetopauselike structure for even very small incident plasma densities.

Whipple, E. C.↗
NASA NTRS1983

Tool for Replacing Bushings

Centerlines of original bushings maintained. Tool frame extends around structure that holds bushings to be removed. Floating bushings of tool positioned with jig pin that slides snugly in old bushing and floating tool bushings. Floating bushings then clamped to tool frame.

Bird, R. G.↗
NASA NTRS1984

The nature of the filaments northeast of the supernova remnant IC 443

New optical spectrophotometry of the faint filaments northeast of the bright supernova remnant IC 443 show emission-line ratios very similar to those seen in the bright filaments of IC 443 and other supernova remnants. This suggests that these northeastern filaments also represent shock-heated interstellar gas and are not simply the southern boundary of the neighboring H II region S249 as previously suspected. If these filaments are associated with IC 443, they then reveal a much more extended remnant structure than previously assumed and permit a relatively accurate determination of IC 443's distance via its interaction with S249.

Fesen, R. A.↗
NASA NTRS1984

The 1982 eclipse of 31 Cygni

UBV photometry and optical-UV spectroscopy of the primary eclipse of the long period Zeta Aurigae-like system 31 Cygni are reported. The precise timings made possible by the photometry imply that the spectral features could be due to an accretion shock associated with a hot star embedded in an extended chromosphere surrounding the red supergiant. The data also suggest an extended clumpy structure to the atmosphere of the late-type supergiant in the binary.

Hopkins, J. L.↗
NASA NTRS1984

Absorption features in the 5-8 micron spectra of protostars

High signal-to-noise ratio spectra in the range of 5-8 microns of four sources embedded in molecular clouds are examined using low-temperature laboratory measurements of the 5-8-micron spectra of simple molecules and their mixtures. The absorption, apparent in all four sources, is characterized by highly distinct features ranging from two relatively narrow bands at 6.0 and 6.8 microns in W33A to a broad, shallow, and partially structured feature extending from 5.2 to 7.8 microns in Mon R2-IRS2, BN, and NGC2264. The first feature (W33A) is explained by the OH bending mode in H2O and the CH deformation modes in saturated hydrocarbons; while the second feature (Mon R2-IRS2-type) is explained by the presence of a mixture of saturated and unsaturated hydrocarbons possibly containing strongly electronegative groups.

Tielens, A. G. G. M.↗
NASA NTRS1985

Multifrequency radio images of L1551 IRS 5

L1551 IRS 5 has been observed at 15 GHz, 5 GHz, and 1.5 GHz with the VLA, and the findings are discussed. At 15 GHz, the central core is well resolved into two pointlike sources surrounded by weaker extended emission. The northern, brighter source is coincident with the peak at 5 GHz. The jet seen at 5 GHz is barely detected at 15 GHz. There is clearcut evidence for a much flatter spectral index in the extended (jet) structure than in either of the two point sources. The observed length-to-width ratio in the jet is greater than ten. It is suggested that L1551 IRS 5 is a binary system whose orbital plane coincides with the CS molecular toroid. A model of the jet is summarized in which the jet contains small clumps which dominate the 15 GHz emission.

Bieging, J. H.↗
NASA NTRS1986

Accretion disks and periodic outbursts of active galactic nuclei

The local thermal stability of accretion disks around supermassive black holes in active galactic nuclei is examined. Such disks are unstable at radii where the surface temperature is several thousand degrees. Supermassive disks therefore should undergo limit-cycle outbursts similar to those believed to occur in dwarf novae. Operating on a time scale of about 10,000 to 10 million yr and at radii of about 10 to the 15th to 10 to the 16th cm, this mechanism will result in alternating periods of higher and lower accretion rate onto the black hole and, consequently, higher and lower luminosity. Quasi-periodic outbursts on this time scale may be recorded in the structure of extended radio sources, a possible example being 4C 29.47. For accretion rates greater than 0.1 solar masses/yr, the situation is complicated by instabilities caused by self-gravitation and by the dominance of radiation pressure and electron scattering opacity.

Lin, D. N. C.↗
NASA NTRS1987

On singular cases in the design derivative of Green's functional

The author's prior development of a general abstract representation for the design sensitivities of Green's functional for linear structural systems is extended to the case where the structural stiffness vanishes at an internal location. This situation often occurs in the optimal design of structures. Most optimality criteria require that optimally designed beams be statically determinate. For clamped-pinned beams, for example, this is possible only if the flexural stiffness vanishes at some intermediate location. The Green's function for such structures depends upon the stiffness and the location where it vanishes. A precise representation for Green's function's sensitivity to the location of vanishing stiffness is presented for beams and axisymmetric plates.

Reiss, Robert↗
NASA NTRS1986

Comets and three-dimensional solar wind structure

The use of comet observations to characterize three-dimensional solar-wind structure is discussed, including the plasma-tail orientations, the Lyman-alpha emission contours from the hydrogen cloud, and periodic disconnection of the plasma tail. Models based on observations of plasma-tail orientations produce solar-wind radial speeds in the 400-420 km/s range, and azimuthal speeds of 5-7 km/s. Studies of disconnection events indicate that the sector structure can extend to solar latitudes of greater than 45 deg for much of a solar cycle, and that the tilt angles could be quite high.

Brandt, J. C.↗
NASA NTRS1989

Solar coronal loop heating by cross-field wave transport

Solar coronal arches heated by turbulent ion-cyclotron waves may suffer significant cross-field transport by these waves. Nonlinear processes fix the wave-propagation speed at about a tenth of the ion thermal velocity, which seems sufficient to spread heat from a central core into a large cool surrounding cocoon. Waves heat cocoon ions both through classical ion-electron collisions and by turbulent stochastic ion motions. Plausible cocoon sizes set by wave damping are in roughly kilometers, although the wave-emitting core may be only 100 m wide. Detailed study of nonlinear stabilization and energy-deposition rates predicts that nearby regions can heat to values intermediate between the roughly electron volt foot-point temperatures and the about 100 eV core, which is heated by anomalous Ohmic losses. A volume of 100 times the core volume may be affected. This qualitative result may solve a persistent problem with current-driven coronal heating; that it affects only small volumes and provides no way to produce the extended warm structures perceptible to existing instruments.

Amendt, Peter↗
NASA NTRS1991

Locating very high energy gamma-ray sources with arcminute accuracy

The angular accuracy of gamma-ray detectors is intrinsically limited by the physical processes involved in photon detection. Although a number of pointlike sources were detected by the COS B satellite, only two have been unambiguously identified by time signature with counterparts at longer wavelengths. By taking advantage of the extended longitudinal structure of VHE gamma-ray showers, measurements in the TeV energy range can pinpoint source coordinates to arcminute accuracy. This has now been demonstrated with new data analysis procedures applied to observations of the Crab Nebula using Cherenkov air shower imaging techniques. With two telescopes in coincidence, the individual event circular probable error will be 0.13 deg. The half-cone angle of the field of view is effectively 1 deg.

Akerlof, C. W.↗
NASA NTRS1992

Locating very high energy gamma ray sources with arc minute accuracy

The angular accuracy of gamma-ray detectors is intrinsically limited by the physical processes involved in photon detection. Although a number of point-like sources were detected by the COS-B satellite, only two were unambiguously identified by time signature with counterparts at longer wavelengths. By taking advantage of the extended longitudinal structure of Very High Energy gamma-ray showers, measurements in the TeV energy range can pinpoint source coordinates to arc minute accuracy. This was demonstrated using Cerenkov air shower imaging techniques. With two telescopes in coincidence, the individual event circular probable error will be 0.13 deg. The half-cone angle of the field of view is effectively 1 deg.

Akerlof, C. W.↗
NASA NTRS1992

Time-dependent cosmic ray shocks with injection - A progress report

The study presents preliminary results of a two-fluid hydrodynamical simulation of cosmic-ray-modified shock structure by extending the steady-state calculations of Zank et al. (1991) to the time-dependent case. The present simulations model diffusive shock acceleration of the energetic particle component at planar shocks. A new model for the injection of cosmic ray particles is presented. The quadratic artificial viscosity algorithm is found to be numerically unstable and therefore unusable for strong cosmic ray shocks. There is visible ringing and overshoot in the various profiles. A large enhancement in the fluid density appears downstream of the subshock. This 'overcompression' results from the upstream fluid being compressed in the precursor, then traversing a strong shock with compression ratio near the adiabatic limit of four.

Donohue, D. J.↗
NASA NTRS1993

The dynamic interstellar medium in NGC 4438

We present multiwavelength observations of the interstellar medium in the disturbed galaxy NGC 4438. We find extended emission-line filaments, which are kinematically unrelated to the galaxy disk. For one of these features, an extended loop, we propose a scheme in which the 'bubble' seen at radio wavelengths has swept a clear path for outflowing material from the nucleus to ionize more distant material. Another radial emission-line feature might represent shocks in the disk along a gravitationally-defined caustic produced during a tidal encounter, or a 'searchlight beam' escaping the inner dusty regions of the galaxy. Energy-balance arguments favor the shock picture, but further study will be important in understanding this feature. Emission-line ratios indicate that shocks may be important in the energetics of the interstellar medium (ISM) through much of the disk of NGC 4438; the alternative is star formation in a uniformly very dense ISM. We use K-band data to locate the stellar peak of the galaxy, which is just outside the prominent radio-continuum loop or shell feature. The nucleus itself is at most a very weak radio source. However, the more extended radio structure shows that energetic events have taken place in the innermost few hundred parsees of NGC 4438. The interstellar medium of NGC 4438 may show at once the impact of nuclear energy input (from an AGN or cocooned starburst), perturbation by the companion NGC 4435, and interaction with the dense intergalactic medium in the Virgo core.

Keel, William C.↗
NASA NTRS1990

Efficient eigensolution reanalysis of nonclassically damped structures

Effective methods of approximate eigensolution reanalysis of modified nonclassically damped structures are developed. For structures with passive or active discrete damping devices or with damping treatment, the system becomes nonproportionally damped and the computation of its dynamic responses may require the use of complex modes. For larger systems, the computation of complex modes is very expensive. Thus it is desirable to have approximate reanalysis techniques for the efficient evaluation of the effect of design changes. In recent years, the assumed mode reanalysis method was successfully applied to minimum weight design of undamped structures with natural frequency constraints. The accuracy of the assumed mode reanalysis method can be improved dramatically if the global approximation function includes the normal modes of the original system and their derivatives. This approach was demonstrated to be effective even for a system with shape changes. The approach used by Noor et al. for eigensolution reanalysis of undamped structures is extended to treat a nonclassically damped system.

Wang, Bo Ping↗