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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Extragalactic X-ray sources.

The extended X-ray sources associated with the Virgo, Perseus, and Coma clusters of galaxies can best be explained as a result of the Compton scattering of relativistic electrons (generated in the radio sources which are present in each of these clusters) on the microwave background radiation. The same physical process involving microwave infrared or optical photons generated in the nuclei of active galaxies may account for the more compact X-ray sources. Thermal bremsstrahlung of hot gas in clusters of galaxies is a less likely source of X-rays.

Brecher, K.↗
NASA NTRS1973

Applying high-emittance and solar-absorptance coating to aluminum

Coated surface withstands space environment with negilgible change in radiation characteristics and physical properties. Process can be used with any porous substance, as long as pores are large enough to allow molecules of reacting solutions to enter and yet not so large as to allow nickel sulfide to be leached out of pores before sealing.

Progar, D. J.↗
NASA NTRS1973

A dynamical model of the ejection of planetary nebulae

In order to study the ejection of planetary nebulae, the present work considers a star evolving up the red giant branch a second time. The star has a carbon oxygen core surrounded by a helium-burning shell source, a helium shell, and a hydrogen-rich shell. The mathematical model consists of a He shell and a hydrogen-rich shell overlying a hard core. It is concluded that the pulsation of long-period variables and the ejection of planetary nebulae are due to the same physical process: namely, radiation momentum and energy transfer to the gas. Furthermore, planetary nebulae ejection appears to be preceded by long-period variability.

Sparks, W. M.↗
NASA NTRS1974

Light scattering in planetary atmospheres

This paper reviews scattering theory required for analysis of light reflected by planetary atmospheres. Section 1 defines the radiative quantities which are observed. Section 2 demonstrates the dependence of single-scattered radiation on the physical properties of the scatterers. Section 3 describes several methods to compute the effects of multiple scattering on the reflected light.

Hansen, J. E.↗
NASA NTRS1975

Evolution of rotating interstellar clouds. I - Numerical techniques

A method is described for the numerical calculation of the hydrodynamic evolution of a self-gravitating configuration in two space dimensions with assumed axial symmetry. The calculation is formulated in cylindrical coordinates with respect to a moving Eulerian grid and is solved using explicit hydrodynamics combined with implicit radiative transfer. The physics included is appropriate for calculation of the collapse of a rotating protostellar cloud. The gravitational field is obtained by means of an alternating-direction iterative technique. Numerical tests to demonstrate the correctness of the method are presented for special cases.

Black, D. C.↗
NASA NTRS1975

Combined environmental effects on polymers

A series of space simulation tests on FEP Teflon and other polymeric thermal control coatings was conducted using UV, electrons, protons and Lyman-alpha wavelength vacuum UV radiation. Interest was centered on simulating synchronous altitude radiation environment conditions. Physical changes in materials included loss of specularity and introduction of a high density of photographable tracking defects on a microscopic scale. An example shows the discharge of trapped electrons when dielectric strength is exceeded. This leaves a portion of the Teflon volume no longer clear, but diffusely transmitting and reflecting. Thermophysical changes included degradation of solar absorptance coefficients as much as five-fold. The situation that prevails for earth orbit contrasted with polymer performance in the solar wind. It is suggested that conductive overcoatings be developed for polymers and other flexible materials, comparable or superior to those available for fused silica SSMs.

Fogdall, L. B.↗
NASA NTRS1976

Atoms in astronomy

Aspects of electromagnetic radiation and atomic physics needed for an understanding of astronomical applications are explored. Although intended primarily for teachers, this brochure is written so that it can be distributed to students if desired. The first section, Basic Topics, is suitable for a ninth-grade general science class; the style is simple and repetitive, and no mathematics or physics background is required. The second section, Intermediate and Advanced Topics, requires a knowledge of the material in the first section and assumes a generally higher level of achievement and motivation on the part of the student. These latter topics might fit well into junior-level physics, chemistry, or earth-science courses. Also included are a glossary, a list of references and teaching aids, class exercises, and a question and answer section.

Blanchard, P. A.↗
NASA NTRS1981

Inference of precipitation through thermal infrared measurements of soil moisture

The physics of microwave radiative transfer is well understood so that causal models can be assembled which relate the observed brightness temperatures to assumed distributions of hydrometeors (both liquid and ice), non-precipitating clouds, water vapor oxygen, and surface conditions. Present models assume a Marshall Palmer size distribution of liquid hydrometers from the surface to the freezing level (near the 0 C isotherm) and a variable thickness of frozen hydrometeors above that with various reasonable distribution of the other relevant constituents. The validity of such models is discussed. All uncertainties in the rain rate retrieval algorithms can be expressed in terms of specific model uncertainties which can be addressed through appropriate measurements. Those factors which must be known to achieve umambiguous results can be identified so that rainfall measuring algorithms can be developed and improved. The emissivity of the underlying surface significantly affects the contrast that may be measured between areas covered by rain and those which are dry. Sensing strategies for measuring rain over the ocean and rain over land are reviewed.

Wetzel, P. J.↗
NASA NTRS1984

Water vapor profile retrieval simulation studies for the HIRS/MSU and AMTS/MSU sounders

A combined physical statistical method for the retrieval of atmospheric water vapor column densities has been developed at the Goddard Laboratory for Atmospheric Sciences. In this method differences between observed and calculated clear column brightness temperatures are used in a regression formalism to obtain estimates of integrated column densities in given atmospheric layers. The physics of the radiative transfer problem is contained in the calculated clear column brightness temperatures and in accounting for the effects of clouds on the observed radiances. The regression matrix is equivalent to a set of empirical sensitivity factors.

Reuter, D.↗
NASA NTRS1985

Natural environment design criteria for the Space Station definition and preliminary design

The natural environment design criteria for the Space Station Program (SSP) definition and preliminary design are presented. Information on the atmospheric, dynamic and thermodynamic environments, meteoroids, radiation, magnetic fields, physical constants, etc. is provided with the intension of enabling all groups involved in the definition and preliminary design studies to proceed with a common and consistent set of natural environment criteria requirements. The space station program elements (SSPE) shall be designed with no operational sensitivity to natural environment conditions during assembly, checkout, stowage, launch, and orbital operations to the maximum degree practical.

Vaughan, W. W.↗
NASA NTRS1986

Present state of knowledge of the upper atmosphere: An assessment report; processes that control ozone and other climatically important trace gases

The state of knowledge of the upper atmosphere was assessed as of January 1986. The physical, chemical, and radiative processes which control the spatial and temporal distribution of ozone in the atmosphere; the predicted magnitude of ozone perturbations and climate changes for a variety of trace gas scenarios; and the ozone and temperature data used to detect the presence or absence of a long term trend were discussed. This assessment report was written by a small group of NASA scientists, was peer reviewed, and is based primarily on the comprehensive international assessment document entitled Atmospheric Ozone 1985: Assessment of Our Understanding of the Processes Controlling Its Present Distribution and Change, to be published as the World Meteorological Organization Global Ozone Research and Monitoring Project Report No. 16.

Watson, R. T.↗
NASA NTRS1986

Estimation of vegetation cover at subpixel resolution using LANDSAT data

The present report summarizes the various approaches relevant to estimating canopy cover at subpixel resolution. The approaches are based on physical models of radiative transfer in non-homogeneous canopies and on empirical methods. The effects of vegetation shadows and topography are examined. Simple versions of the model are tested, using the Taos, New Mexico Study Area database. Emphasis has been placed on using relatively simple models requiring only one or two bands. Although most methods require some degree of ground truth, a two-band method is investigated whereby the percent cover can be estimated without ground truth by examining the limits of the data space. Future work is proposed which will incorporate additional surface parameters into the canopy cover algorithm, such as topography, leaf area, or shadows. The method involves deriving a probability density function for the percent canopy cover based on the joint probability density function of the observed radiances.

Jasinski, Michael F.↗
NASA NTRS1987

Simultaneous 2 and 6 centimeter wavelength observations of a solar flare using the VLA

VLA observations of a solar active region and a flare are discussed. The event was observed at wavelengths of 2 and 6 cm simultaneously. Radio maps prior to the flare delineate the most important magnetic structures in the region. Interaction between these structures apparently led to preheating of plasma above the active region some 30 minutes prior to the flare. The 2 and 6 cm flare positions were coincident, and the time profiles of the burst at the two wavelengths were almost identical, implying that the same population of electrons was responsible for emission at the two wavelengths. Emission was probably nonthermal gyrosynchrotron radiation, and the physical conditions in the burst source are derived using this assumption.

Kundu, M. R.↗
NASA NTRS1990

FIRE Cirrus on October 28, 1986: LANDSAT; ER-2; King Air; theory

A simultaneous examination was conducted of cirrus clouds in the FIRE Cirrus IFO-I on 10/28/86 using a multitude of remote sensing and in-situ measurements. The focus is cirrus cloud radiative properties and their relationship to cloud microphysics. A key element is the comparison of radiative transfer model calculations and varying measured cirrus radiative properties (emissivity, reflectance vs. wavelength, reflectance vs. viewing angle). As the number of simultaneously measured cloud radiative properties and physical properties increases, more sharply focused tests of theoretical models are possible.

Wielicki, Bruce A.↗
NASA NTRS1992

Kennedy Space Center environmental health program

The Kennedy Space Center's environmental health organization is responsible for programs which assure its employees a healthful workplace under diverse and varied working conditions. These programs encompass the disciplines of industrial hygiene, radiation protection (health physics), and environmental sanitation/pollution control. Activities range from the routine, such as normal office work, to the highly specialized, such as the processing of highly toxic and hazardous materials.

Marmaro, G. M.↗
NASA NTRS1993

Scientific goals of the Cooperative Multiscale Experiment (CME)

Mesoscale Convective Systems (MCS) form the focus of CME. Recent developments in global climate models, the urgent need to improve the representation of the physics of convection, radiation, the boundary layer, and orography, and the surge of interest in coupling hydrologic, chemistry, and atmospheric models of various scales, have emphasized the need for a broad interdisciplinary and multi-scale approach to understanding and predicting MCS's and their interactions with processes at other scales. The role of mesoscale systems in the large-scale atmospheric circulation, the representation of organized convection and other mesoscale flux sources in terms of bulk properties, and the mutually consistent treatment of water vapor, clouds, radiation, and precipitation, are all key scientific issues concerning which CME will seek to increase understanding. The manner in which convective, mesoscale, and larger scale processes interact to produce and organize MCS's, the moisture cycling properties of MCS's, and the use of coupled cloud/mesoscale models to better understand these processes, are also major objectives of CME. Particular emphasis will be placed on the multi-scale role of MCS's in the hydrological cycle and in the production and transport of chemical trace constituents. The scientific goals of the CME consist of the following: understand how the large and small scales of motion influence the location, structure, intensity, and life cycles of MCS's; understand processes and conditions that determine the relative roles of balanced (slow manifold) and unbalanced (fast manifold) circulations in the dynamics of MCS's throughout their life cycles; assess the predictability of MCS's and improve the quantitative forecasting of precipitation and severe weather events; quantify the upscale feedback of MCS's to the large-scale environment and determine interrelationships between MCS occurrence and variations in the large-scale flow and surface forcing; provide a data base for initialization and verification of coupled regional, mesoscale/hydrologic, mesoscale/chemistry, and prototype mesoscale/cloud-resolving models for prediction of severe weather, ceilings, and visibility; provide a data base for initialization and validation of cloud-resolving models, and for assisting in the fabrication, calibration, and testing of cloud and MCS parameterization schemes; and provide a data base for validation of four dimensional data assimilation schemes and algorithms for retrieving cloud and state parameters from remote sensing instrumentation.

Cotton, William↗
NASA NTRS1994

A uniform geometrical optics and an extended uniform geometrical theory of diffraction for evaluating high frequency EM fields near smooth caustics and composite shadow boundaries

A uniform geometrical optics (UGO) and an extended uniform geometrical theory of diffraction (EUTD) are developed for evaluating high frequency electromagnetic (EM) fields within transition regions associated with a two and three dimensional smooth caustic of reflected rays and a composite shadow boundary formed by the caustic termination or the confluence of the caustic with the reflection shadow boundary (RSB). The UGO is a uniform version of the classic geometrical optics (GO). It retains the simple ray optical expressions of classic GO and employs a new set of uniform reflection coefficients. The UGO also includes a uniform version of the complex GO ray field that exists on the dark side of the smooth caustic. The EUTD is an extension of the classic uniform geometrical theory of diffraction (UTD) and accounts for the non-ray optical behavior of the UGO reflected field near caustics by using a two-variable transition function in the expressions for the edge diffraction coefficients. It also uniformly recovers the classic UTD behavior of the edge diffracted field outside the composite shadow boundary transition region. The approach employed for constructing the UGO/EUTD solution is based on a spatial domain physical optics (PO) radiation integral representation for the fields which is then reduced using uniform asymptotic procedures. The UGO/EUTD analysis is also employed to investigate the far-zone RCS problem of plane wave scattering from two and three dimensional polynomial defined surfaces, and uniform reflection, zero-curvature, and edge diffraction coefficients are derived. Numerical results for the scattering and diffraction from cubic and fourth order polynomial strips are also shown and the UGO/EUTD solution is validated by comparison to an independent moment method (MM) solution. The UGO/EUTD solution is also compared with the classic GO/UTD solution. The failure of the classic techniques near caustics and composite shadow boundaries is clearly demonstrated and it is shown that the UGO/EUTD results remain valid and uniformly reduce to the classic results away from the transition regions. Mathematical details on the asymptotic properties and efficient numerical evaluation of the canonical functions involved in the UGO/EUTD expressions are also provided.

Constantinides, E. D.↗
NASA NTRS1994

Radio and X-ray observations of the gamma-ray bright quasar PKS 0528+134

We present a study of the z = 2.07 quasar PKS 0528+134, which has been detected as an extraordinarily luminous gamma-ray source. Its radio properties are highly variable in both total and polarized flux density. Milliarcsecond-scale maps from global very long base interferometry (VLBI) experiments, an X-ray spectrum from ROSAT Position Sensitive Proportional Counter (PSPC) observations, and light curves in total flux density and polarization are used to investigate the geometry, radiation mechanism, and physical environment of the emission region in the source. The VLBI images reveal a bent jet extending toward the northeast on parsec scales, with less intense knots of emission appearing on the opposite side of the brightest spot. The position of the core usually found in such sources is unclear. The polarization angle is stable despite strong variability in polarized flux density and indicates that the magnetic field is aligned with the jet axis as defined by our 8.4 GHz image. The ROSAT X-ray flux density of PKS 0528+134 in 1991 March is measured to be 1.6 micro Jy at 1 keV, with a very steep spectral (`energy') index sigma(sub x) approximately equal to 2.2. The X-ray observations reveal the presence of cold gas along the line of sight significantly in excess of that present in the Galaxy. A strong radio flare began within two months of the first observation of a high flux of gamma-rays from PKS 0528+134 by Hunter et al. Using the geometry and spectral chacateristics determined by our VLBI observations, a synchrotron self-Compton calculation indicates that relativistic bulk motion is required in PKS 0528+134, with an estimated Doppler beaming factor delta approximately greater than 4.3, similar to the value delta approximately greater than 7 required to explain the low optical depth of the gamma-rays to photon-photon pair production. We suggest that the core activity of PKS 0528+134 is sporadic in nature, with the nonthermal outburst starting in 1991 representing a violent period involving ejection of relativistic plasma along a compact jet pointed almost directly toward us.

Zhang, Yun Fei↗