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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

The Gum nebula and related problems

Papers were presented in conference sessions on the Gum nebula, the Vela X remnant, the hot stars gamma Velorum and zeta Puppis, the B associations in the Vela-Puppis complex, and pulsars. Ground-based optical and radio astronomy; rocket and satellite observations in the radio, visible, ultraviolet, and X-ray regions; and theoretical problems in the physical state of the interstellar medium, stellar evolution, and runaway star dynamics were considered.

Maran, S. P.↗
NASA NTRS1972

Plasma physics abstracts

Abstracts of publications in plasma physics are presented including theoretical and ionospheric research.

Montgomery, D. C.↗
NASA NTRS1975

Cosmic ray intensity gradients in the solar system

Recent progress in the determination of cosmic-ray intensity gradients is reviewed. Direct satellite measurements of the integral gradient are described together with various types of indirect measurements, including measurements of the Ar-37/Ar-39 ratio in samples from the Lost City meteorite, studies of anisotropies in neutron-monitor counting rates, and analysis of the sidereal diurnal anisotropy observed at a single point on earth. Nucleonic radial gradients and electron gradients measured by satellites in differential energy windows are discussed, and theoretical studies of the physical processes involved in these gradients are summarized. Observations of intensity gradients in heliographic latitude are reported.

Mckibben, R. B.↗
NASA NTRS1975

Ultraviolet studies of the interstellar gas

Sounding-rocket and satellite UV observations of interstellar gas clouds are reviewed with major attention given to Copernicus observations of interstellar absorption lines. Analysis of typical absorption-line data is outlined, and observations are reviewed for atomic hydrogen as well as interstellar H2, HD, and CO molecules. Investigations of atomic abundances in H I regions are summarized, measurements of atomic deuterium abundances in the interstellar gas are examined, and the properties of ionized interstellar gas are described. Theoretical analyses of the physical state of the interstellar gas are summarized with respect to ionization by energetic radiation, cool H I clouds, and the intercloud medium. The data obtained thus far are shown to indicate mean temperatures of about 80 K, particle densities between 10 and 1000 per cu cm, and a depletion of heavy elements that becomes greatly enhanced with increasing condensation temperature for those H I regions with strong H2 lines.

Spitzer, L., Jr.↗
NASA NTRS1981

Cosmic plasma

Attention is given to experimental and theoretical approaches to plasma physics, plasma phenomena in laboratory and space, field and particle aspects of plasmas, the present state of the classical theory, boundary conditions and circuit dependence, and cosmology. Electric currents in space plasmas are considered, taking into account dualism in physics, particle-related phenomena in plasma physics, magnetic field lines, filaments, local plasma properties and the circuit, electric double layers, field-aligned currents as 'cables', an expanding circuit, different types of plasma regions, the cellular structure of space, and the fine structure of active plasma regions. Other topics discussed are related to circuits, the theory of cosmic plasmas, the origin of the solar system, the coexistence of matter and antimatter, annihilation as a source of energy, the Hubble expansion in a Euclidean space, and a model for the evolution of the Metagalaxy.

Alfven, H.↗
NASA NTRS1982

Solar microwave bursts - A review

Observational and theoretical results on the physics of microwave bursts that occur in the solar atmosphere are reviewed. Special attention is given to the advances made in burst physics over the last few years with the great improvement in spatial and time resolution, especially with instruments like the NRAO three-element interferometer, the Westerbork Synthesis Radio Telescope, and more recently the Very Large Array. Observations made on the preflare build-up of an active region at centimeter wavelengths are reviewed. Three distinct phases in the evolution of cm bursts, namely the impulsive phase, the post-burst phase, and the gradual rise and fall, are discussed. Attention is also given to the flux density spectra of centimeter bursts. Descriptions are given of observations of fine structures with temporal resolution of 10-100 ms in the intensity profiles of cm-wavelength bursts. High spatial resolution observations are analyzed, with special reference to the one- and two-dimensional maps of cm burst sources.

Kundu, M. R.↗
NASA NTRS1984

Experiments to test theoretical models of the polarization of light by rough surfaces

A number of attempts have been made to provide theoretical models of the physical processes involved in the polarization of light scattered by a rough surface, such as the regolith of an atmosphereless planet. Some laboratory experiments designed to test different aspects of these models are described. It is concluded that double Fresnel reflection is usually the dominant process in producing negative polarization, but that diffraction effects may play a significant part in double events involving small-scale surface features.

Geake, J. E.↗
NASA NTRS1984

Soft X-ray polychromator for the Solar Maximum Mission

The XRP was designed to measure the following temporal and spatial properties of the active and flaring Sun: electron temperature, departures from steady state, ion kinetic temperatures, and electron density. The Bent Crystal Spectrometer (BCS) is capable of measuring the broadening and blue shifts often observed in the impulsive phase of flares. The six simultaneous line fluxes indicative of six different temperatures of formation observable by the Flat Crystal Spectrometer (FCS) allows the derivation of the differential emission measure of the plasma at each raster point. During the operational periods of the XRP hundreds of flares of C-level (GOES classification) were observed and brighter in both the FCS and BCS, including 5 X-flares. Associated theoretical work in atomic physics, stimulated in part by the promise of XRP measurements, has benefitted from the experimental data on solar plasmas which the XRP has provided in abundance.

Haisch, B. M.↗
NASA NTRS1985

N(+)-N long-range interaction energies and resonance charge exchange

The aerothermodynamic studies of proposed space missions require atmospheric charge-transfer data. N2(+) eigenstate energies are calculated with use of the complete-active-space self-consistent-field method with an extended Gaussian basis set. The N(+)-N charge-exchange cross section, determined from these energies, agrees with merged-beam measurements. This contradicts the previous theoretical conclusion. A simple physical description of the long-range interaction is presented and should expedite future charge-transfer studies.

Stallcop, J. R.↗
NASA NTRS1984

Wave approach to brightness temperature from a bounded layer of random discrete scatterers

By using the fluctuation-dissipation theorem, the strong fluctuation theory is applied to the calculation of brightness temperatures from a bounded layer of random discrete scatterers with the zeroth- and first-order approximations. Various functional dependences on wavelength, polarization, observation angle, medium depth, scatterer constituents, and other physical parameters are discussed. Theoretical results are favorably matched with experimental data for passive remote sensing of snowpacks.

Jin, Y.-Q.↗
NASA NTRS1987

Current loop coalescence model of solar flares

A computer simulation and theoretical study of the physical characteristics of the explosive coalescence of current-carrying loops is presented. Characteristics of the explosive coalescence include a large impulsive increase of the kinetic energies of electrons and ions, the simultaneous heating and acceleration of electrons and ions in high and low energy ranges, and a break in the energy spectra of electrons and ions. A characteristic double subpeak structure is found in the quasi-periodic oscillations found in the time profiles of the solar flares of June 7, 1980 and November 26, 1982 which can be explained in terms of the coalescence instability of two current loops.

Tajima, T.↗
NASA NTRS1987

Experimental studies on Goertler vortices

Goertler vortices arise in laminar boundary layers along concave walls due to an imbalance between pressure and centrifugal forces. In advanced laminar-flow control (LFC) supercritical airfoil designs, boundary-layer suction is primarily used to control Tollmien-Schlichting instability and cross-flow vortices in the concave region near the leading edge of the airfoil lower surface. The concave region itself is comprised of a number of linear segments positioned to limit the total growth of Goertler vortices. Such an approach is based on physical reasonings but rigorous theoretical justification or experimental evidence to support such an approach does not exist. An experimental project was initiated at NASA Langley to verify this concept. In the first phase of the project an experiment was conducted on an airfoil whose concave region has a continuous curvature distribution. Some results of this experiment were previously reported and significant features are summarized.

Mangalam, Siva M.↗
NASA NTRS1991

Guiding principles for vortex flow controls

In the practice of vortex flow controls, the most important factor is that the persistency and obstinacy of a concentrated vortex depend on its stability and dissipation. In this paper, the modern nonlinear stability theory for circulation-preserving flows is summarized, and the dissipation for general viscous flows is analyzed in terms of the evolution of total enstrophy. These analyses provide a theoretical base for understanding relevant physics of vortex flows, and lead to some guiding principles and methods for their controls. Case studies taken from various theoretical and/or experimental works of vortex controls, due to the present authors as well as others, confirm the feasibility of the recommended principles and methods.

Wu, J. Z.↗
NASA NTRS1990

Cooling flows and X-ray emission in early-type galaxies

The X-ray properties of normal early-type galaxies and the limited theoretical understanding of the physics of the hot interstellar medium in these galaxies are reviewed. A number of simple arguments about the physical state of the gas are given. Steady-state cooling flow models for these galaxies are presented, and their time-dependent evolution is discussed. The X-ray emission found in early-type galaxies indicates that they contain significant amounts of hot interstellar gas, and that they are not the gas-poor systems they were previously thought to be. In the brighter X-ray galaxies, the amounts of hot gas observed are consistent with those expected given the present rates of stellar mass loss. The required rates of heating of the gas are consistent with those expected from the motions of gas-losing stars and supernovae. The X-ray observations are generally more consistent with a lower rate of Type I supernovae than was previously thought.

Sarazin, Craig L.↗
NASA NTRS1992

Convective flow analysis on the KC-135 aircraft

A study conducting bouyancy driven convective flow experiments on the NASA KC-135 aircraft is presented. The response of a contained fluid (with an imposed temperature gradient) to changing g-levels during parabolic flight was obtained. Models for both transient and steady state flows were developed utilizing PC-based CFD software. Comparisons between the theoretical models and the physical observations are quite good.

Workman, Gary L.↗
NASA NTRS1993

The International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas

This was the fourth in a series of colloquia begun at the University of Lund, Sweden in 1983 and subsequently held in Toledo, Ohio and Amsterdam, The Netherlands. The purpose of these meetings is to provide an international forum for communication between major users of atomic spectroscopic data and the providers of these data. These data include atomic wavelengths, line shapes, energy levels, lifetimes, and oscillator strengths. Speakers were selected from a wide variety of disciplines including astrophysics, laboratory plasma research, spectrochemistry, and theoretical and experimental atomic physics.

Sugar, J.↗
NASA NTRS1995

Development and applications of laser-induced incandescence

Several NASA-funded investigations focus on soot processes and radiative influences of soot in diffusion flames given their simplicity, practical significance, and potential for theoretical modeling. Among the physical parameters characterizing soot, soot volume fraction, f(sub v), a function of particle size and number density, is often of chief practical interest in these investigations, as this is the geometrical property that directly impacts radiative characteristics and the temperature field of the flame and is basic to understanding soot growth and oxidation processes. Diffusion flames, however, present a number of challenges to the determination of f(sub v) via traditional extinction measurements. Laser-induced incandescence (LII) possesses several advantages compared to line-of-sight extinction techniques for determination of f(sub v). Since LII is not a line-of-sight technique, similar to fluorescence, it possesses geometric versatility allowing spatially resolved measurements of f(sub v) in real time in nonaxisymmetric systems without using deconvolution techniques. The spatial resolution of LII is determined by the detector and imaging magnification used. Neither absorption by polycyclic aromatic hydrocarbons (PAH's) nor scattering contributes to the signal. Temporal capabilities are limited only by the laser pulse and camera gate duration, with measurements having been demonstrated with 10 ns resolution. Because of these advantages, LII should be applicable to a variety of combustion processes involving both homogeneous and heterogeneous phases. Our work has focussed on characterization of the technique as well as exploration of its capabilities and is briefly described.

Vanderwal, Randy L.↗
NASA NTRS2000

Particle Engulfment and Pushing Micro-Gravity Experiments and Mathematical Modeling

The phenomenon of interaction of particles with solid-liquid interfaces that results in particle engulfment or pushing (PEP) has been Studied since mid 1960's. While the original interest stemmed from geology applications (frost heaving in soil), it was recognized early that understanding particle behavior at solidifying interfaces mi ht yield 9 practical benefits in other fields. In metallurgical applications the issue is the location of particles with respect to grain boundaries at the end of solidification. Considerable amount of experimental and theoretical research was lately focused on applications to metal matrix composites produced by casting; or spray forming techniques. Another application of PEP is in the growing of Y1Ba2CU3O7-delta(123) superconductor crystals from an undercooled liquid. The oxide melt contains Y2Ba1CU1O5 (211) precipitates, which act as flux pinning sites. The paper presents results of PEP micro-gravity research performed by the authors on two shuttle missions using metallic and polymeric materials. In addition. a discussion on the theoretical aspects of the physics of PEP is offered. Analytical and numerical models for planar solidification interfaces developed by the authors are used to explain the experimental results. Shortcomings of steady-state models are emphasized. A numerical model that includes the effect of the solutal field and of natural convection is introduced. A discussion of phenomena associated with dendritic solidification based on experimental observations is also offered. A mechanism of engulfment is proposed.

Stefanescu, Doru M.↗