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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 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

The Chemical Composition and Gas-to-Dust Mass Ratio of Nearby Interstellar Matter

We use recent results on interstellar gas toward nearby stars and interstellar by-products within the solar system to select among the equilibrium radiative transfer models of the nearest interstellar material presented in Slavin & Frisch. For the assumption that O/H - 400 parts per million, models 2 and 8 are found to yield good fits to available data on interstellar material inside and outside of the heliosphere, with the exception of the Ne abundance in the pickup ion and anomalous cosmic-ray populations. For these models, the interstellar medium (ISM) at the entry point to the heliosphere has n(H(sup 0)) = 0.202-0.208/cu cm, n(He(sup 0) = 0.0137-0.0152/cu cm, and ionizations X(H) = 0.29-0.30, X(He) = 0.47-0.51. These best models suggest that the chemical composition of the nearby ISM is approx.60%-70% subsolar if S is undepleted. Both H(0) and H(+) need to be included when evaluating abundances of ions found in warm diffuse clouds. Models 2 and 8 yield an H filtration factor of approx.0.46. Gas-to-dust mass ratios for the ISM toward epsilon CMa are R(sub gd) = 178-183 for solar abundances of Holweger or R(sub gd) = 611-657 for an interstellar abundance standard 70% solar. Direct observations of dust grains in the solar system by Ulysses and Galileo yield R(sub gd) appr0x. 115 for models 2 and 8, supporting earlier results (Frisch and coworkers). If the local ISM abundances are subsolar, then gas and dust are decoupled over small spatial scales. The inferred variation in R(sub gd) over parsec length scales is consistent with the fact that the ISM near the Sun is part of a dynamically active cluster of cloudlets flowing away from the Sco-Cen association. Observations toward stars within approx.500 pc show that R(sub gd) correlates with the percentage of the dust mass that is carried by iron, suggesting that an Fe-rich grain core (by mass) remains after grain destruction. Evidently large dust grains (>10(exp -13) g) and small dust grains (<10(exp -13) g) are not well mixed over parsec length spatial scales in the ISM. It also appears that very small C-dominated dust grains have been destroyed in the ISM within several parsecs of the Sun, since C appears to be essentially undepleted. However, if gas-dust coupling breaks down over the cloud lifetime, the missing mass arguments applied here to determine R(sub gd) and dust grain mineralogy are not appropriate.

Frisch, Priscilla C.↗
NASA NTRS1985

Shock acceleration of diffuse ions at the earth's bow shock Acceleration efficiency and A/Z enhancement

Observations of particle spectra, intensity, and enhancement of alpha particles over protons at diffuse ion events at the quasi-parallel earth bow shock are compared to a Monte Carlo simulation of diffusive shock acceleration. The simulation includes the back reaction of accelerated particles on the shock structure, particle escape at an upstream free escape boundary, and a low energy per nucleon threshold for thermal leakage of downstream, shock-heated particles into the upstream region. The simulation assumes that the same scattering operator that gives rise to shock acceleration can also describe a viscous shock governed by hydrodynamic turbulence. This implies that accelerated ions can be drawn directly from the thermal solar wind with no separate superthermal seed population. Good agreement between the simulation and observations made during nearly radial magnetic field configurations lends support to thermal leakage of downstream, shock-heated ions as the mode of injection for diffusion ion events.

Ellison, D. C.↗
NASA NTRS1979

Laser Techniques in Photovoltaic Research

High-power laser pulses were used to replace the conventional high temperature furnace processing for the p-n junction formation step in high speed, low cost solar cell fabrication. Three different approaches to junction formation were tested: (1) laser annealing of ion-implanted Si in which laser radiation is used to remove the radiation damage and to recover the electrical activity in the implanted layer; (2) a process in which a thin film of dopant is first deposited on the substrate and then incorporated into the near-surface region by laser-induced diffusion; and (3) a process in which a heavily doped amorphous silicon layer is deposited on the Si substrate and epitaxially regrown from the melted substrate layer by laser radiation. All three methods were found to provide suitable candidates for high efficiency Si solar cells.

Young, R. T.↗
NASA NTRS1985

New high-efficiency silicon solar cells

A design for silicon solar cells was investigated as an approach to increasing the cell open-circuit voltage and efficiency for flat-plate terrestrial photovoltaic applications. This deviates from past designs, where either the entire front surface of the cell is covered by a planar junction or the surface is textured before junction formation, which results in an even greater (up to 70%) junction area. The heavily doped front region and the junction space charge region are potential areas of high recombination for generated and injected minority carriers. The design presented reduces junction area by spreading equidiameter dot junctions across the surface of the cell, spaced about a diffusion length or less from each other. Various dot diameters and spacings allowed variations in total junction area. A simplified analysis was done to obtain a first-order design optimization. Efficiencies of up to 19% can be obtained. Cell fabrication involved extra masking steps for selective junction diffusion, and made surface passivation a key element in obtaining good collection. It also involved photolithography, with line widths down to microns. A method is demonstrated for achieving potentially high open-circuit voltages and solar-cell efficiencies.

Daud, T.↗
NASA NTRS1977

"Solar ponds"

Array uses low-cost materials and heavy construction methods to make collection and storage of solar energy economical on large scale required for commercial operation. Series of long trenches are dug side by side over an area large in comparison to heat diffusivity of soil.

Miller, C. G.↗
NASA NTRS1977

Bright X-ray arcs and the emergence of solar magnetic flux

The Skylab S-056 and S-082A experiments and ground-based magnetograms have been used to study the role of bright X-ray arcs and the emergence of solar magnetic flux in the McMath region 12476. The S-056 X-ray images show a system of one or sometimes two bright arcs within a diffuse emitting region. The arcs seem to directly connect regions of opposite magnetic polarity in the photosphere. Magnetograms suggest the possible emergence of a magnetic flux. The width of the main arc is approximately 6 arcsec when most clearly defined, and the length is approximately 30-50 arcsec. Although the arc system is observed to vary in brightness over a period exceeding 24 hours, it remains fixed in orientation. The temperature of the main arc is approximately 3 x 10 to the 6th K. It is suggested that merging magnetic fields may provide the primary energy source, perhaps accompanied by resistive heating from a force-free current.

Chapman, G. A.↗
NASA NTRS1979

X-ray studies of quasars with the Einstein Observatory

Results of an investigation of the X-ray properties of quasars conducted using the Einstein Observatory (HEAO 2) are reported. The positions, fluxes and luminosities of 35 known quasars were observed by the Einstein high-resolution imaging detector and the imaging proportional counter. Assuming optical redshifts as valid distance indicators, 0.5-4.5 keV X-ray luminosities ranging from 10 to the 43rd to 10 to the 47 ergs/sec are obtained, with evidence of very little cold gas absorption. Flux variability on a time scale of less than 10,000 sec is observed for the quasar OX 169, which implies a mass between 8 x 10 to the 5th and 2 x 10 to the 8th solar masses for the black hole assumed to be responsible for the emission. Preliminary results of the quasar survey also indicate that quasars contribute significantly to the diffuse X-ray background.

Tananbaum, H.↗
NASA NTRS1983

The cool DC white dwarf Stein 2051B

Visual scans from the Kitt-Peak 2.1-m telescope and UV spectra from the IUE satellite are combined in a spectroscopic study of the bright DC white dwarf, Stein 2051B. With a cooling age near 2 billion years, and a resulting atmospheric mass of hydrogen of the order of 6 x 10 to the 17th g, the accretion rate over the star's lifetime is less than 2 x 10 to the -25th solar masses/year. This is far below the predictions of standard accretion theories, and requires unreasonably strong suppression of hydrogen accretion in this star if the accretion-diffusion theory is to account for the carbon abundance found. It is suggested that the carbon may have been brought to the surface by convective mixing.

Wegner, G.↗
NASA NTRS1984

IRAS observations of cometary dust

It is pointed out that solid material present in the coma and tail of a comet is revealed by the scattering of sunlight and thermal emission of absorbed solar radiation. The large beam size and low background of the cold Infrared Astronomy Satellite (IRAS) telescope make it extremely well suited to the measurement of faint diffuse thermal emission from solid grains associated with comets. The IRAS project was conducted jointly by the Netherlands, the United Kingdom, and the U.S. Its basic objective involved a survey of the sky in four wavelength regions centered on 12, 25, 60, and 100 microns. The present paper is mainly concerned with IRAS observations of the coma-nucleus regions as defined by the maximum in the intensity distribution. Attention is given to circumstances of comet observations, dust production rates, and a discussion of the results.

Walker, R. G.↗
NASA NTRS1987

Energy diffusion of pickup ions upstream of comets

A steady state model of pickup ion energization upstream of a cometary bow wave is presented in order to investigate the effects of quasi-linear energy diffusion in the turbulence there. The model assumes that the ions are immediately isotropized at pickup, and it includes the effects of adiabatic acceleration in the slowing solar wind and of continual pickup of ions as the comet is approached. By taking all physical quantities to fall off as power laws with distance from the comet, an analytical expression is obtained for the distribution function of pickup ions in the reference frame moving with the solar wind. To illustrate the application of this model, the model results are compared to the observations of pickup ions at comet Giacobini-Zinner. At present, this is the only cometary encounter for which sufficient quantitative information is available. The model does not compare well with these observations, but it is not clear whether the differences are due to artificial problems in the model or the data analysis or to the action of other energization processes at this comet. Preliminary results from the Halley encounters appear to agree more closely with this model.

Isenberg, Philip A.↗
NASA NTRS1988

Downstream energetic proton and alpha particles during quasi-parallel interplanetary shock events

This paper considers the energetic particle populations in the downstream region of three quasi-parallel interplanetary shock events, which was explored using the ISEE 3 Ultra Low Energy Charge Analyzer sensor, which unambiguously identifies protons and alpha particles using the electrostatic deflection versus residual energy technique. The downstream particles were found to exhibit anisotropies due largely to convection in the solar wind. The spectral indices of the proton and the alpha-particle distribution functions were found to be remarkably constant during the downstream period, being generally insensitive to changes in particle flux levels, magnetic field direction, and solar wind densities. In two of the three events, the proton and the alpha spectra were the same throughout the entire downstream period, supporting the prediction of diffusive shock acceleration theory.

Tan, L. C.↗
NASA NTRS1981

Correlation of the cosmic-ray intensity with solar-terrestrial parameters

Results are presented of numerical simulations of cosmic ray drift due to perturbations in the interplanetary medium affecting solar-terrestrial parameters. Computations were performed for a model spherical heliosphere of radius 25 AU, with an interplanetary magnetic field in the shape of an Archimedean spiral with magnitude of 5 gamma at 1 AU, corresponding to a wind velocity of 400 km/sec, and diffusion coefficients corresponding to the assumption that the parallel mean free path is somewhat larger han the cyclotron radius at earth orbit, and its spatial dependence is proportional to the gyroradius. It is found that perturbations in the heliospheric equatorial regions affect galactic cosmic rays more effectively when the Northern Hemisphere heliospheric magnetic field is directed inward rather than outward, with perturbations in the parallel drift coefficient more effective than perturbations in solar wind velocity or perpendicular drift velocity. Results are consistent with the observed variation of the correlation between the geomagnetic aa index and the neutron monitor counting rate on Mt. Washington with the solar cycle.

Jokipii, J. R.↗
NASA NTRSDate not supplied

The Hourly GHI, DHI and DNI: Intercomparison of the CERES-Based Data and the NSRDB Data through Comparison with the Ground-Based BSRN Data

The NASA Clouds and the Earth’s Radiant Energy System (CERES) SYN1deg(Ed4.1) provides hourly global horizontal irradiance (GHI), diffuse horizontal irradiance (DHI) and direct horizontal irradiance (DirHI) at 1-degree latitude by 1-degree longitude resolution, and the time span is from March 2000 to near present. While the GHI agrees well with the ground-based Baseline Surface Radiation Network (BSRN) data, the DHI and DirHI are, respectively, positively and negatively biased against the BSRN data, and so is the direct normal irradiance (DNI) derived simply by dividing the DirHI by the cosine of the hourly solar zenith angle (SZA). We found that the biases tend to be well-defined functions of cos(SZA) and the cloud fraction (CLFR). We thus performed a bias-correction on the hourly DHI and DNI in the latitude-cos(SZA)-CLFR phase space, and therefrom, we derived the hourly global tilted irradiance (GTI) at a number of tilt angles using the isotropic diffuse irradiance model, and the results agree well with the GTI derived from the original BSRN near-instantaneous records. Meanwhile, the National Renewable Energy Laboratory (NREL) has produced the National Solar Radiation Database (NSRDB) with finer spatiotemporal resolution using its Physical Solar Model (PSM) and surface-based measured data, model results and satellite-based data as inputs. Now the NSRDB data covers not only the United States and its neighboring regions, but Europe, Africa, Asia and Oceania. The available temporal resolutions are 5, 10, 15, 30 and 60 minutes and the spatial resolutions are 2, 4 and 10 km, depending on the selected region. In this presentation, we compare both the CERES-based and NSRDB GHI, DHI and DNI with their BSRN counterparts and show how finer spatial resolution may give us an advantage in data accuracy and usability.

Taiping Zhang↗
NASA NTRS1972

Solar radiation calibration facility.

A recently completed calibration facility for the NASA Mississippi Test Site is described. It combines the spectrum of water cooled long arc xenon radiation sources with the integration sphere concept covered by a special barium sulfate diffusely reflecting paint. The sphere is six feet in diameter and completely encompasses the four xenon sources (2.5 kW each) and the five pyranometers under calibration. The sources are contained within the base of the central pedestal and allow the radiation to be emitted into the lower hemisphere. Only through diffuse reflection and multiple scattering is the radiation finally incident upon the test zone, which is in the equatorial plane of the sphere on the top of the pedestal. The sphere is temperature controlled.

Hershey, T. L.↗
NASA NTRS1973

Observations of spatial structure in the soft X-ray diffuse flux.

Repeated observations of a diffuse source in the region of about 200 deg and +10 deg galactic longitude and latitude, respectively, illustrate the complexity of the low-energy X-ray background. The source is not well correlated with known objects or features, and cannot be explained by geometrically simple models of diffuse emission. The measurements indicate that this emission feature, and by implication a large fraction of the 1/4-keV flux observed in the galactic plane, probably originates outside the solar system.

Bunner, A. N.↗
NASA NTRS1973

Magnetic field reconnection and particle acceleration

After a brief review of steady state reconnection models, the processes are discussed which place an upper limit on the reconnection rate. In many applications the requirement that the width of the diffusion region exceed the ion gyroradius leads to a severe restriction on this limit. Unless the conductivity is much less than the value given by Spitzer's formula, solar flare times may result which are too long by a factor of 1000 or more. Turbulent and gyro effects which may lead to a reduced conductivity are shown to be operative, but only for sufficiently small ratios of plasma to magnetic pressure in the inflow. Particle energization processes associated with magnetic field reconnection and particle reflection by fast shocks are considered. These processes are effective as a first stage in the acceleration of charged particles, but additional multistep processes are needed to reach proton energies above a few MeV.

Sonnerup, B. U. O.↗
NASA NTRS1976

Depletion of solar wind plasma near a planetary boundary

A mathematical model is presented that describes the squeezing of solar wind plasma out along interplanetary magnetic field lines in the region between the bow shock and the effective planetary boundary (in the case of the earth, the magnetopause). In the absence of local magnetic merging the squeezing process should create a 'depletion layer', a region of very low plasma density just outside the magnetopause. Numerical solutions are obtained for the dimensionless magnetohydrodynamic equations describing this depletion process for the case where the solar wind magnetic field is perpendicular to the solar wind flow direction. For the case of the earth, the theory predicts that the density should be reduced by a factor exceeding 2 in a layer about 700-1300 km thick if the Alfven Mach number in the solar wind, is equal to 8. Scaling of the model calculations to Venus and Mars suggests layer thicknesses about 1/10 and 1/15 those of the earth, respectively, neglecting diffusion and ionospheric effects.

Zwan, B. J.↗
NASA NTRS1977

On the fragmentation of cosmic gas clouds. I - The formation of galaxies and the first generation of stars

The formation of galaxies is studied in the context of the fragmentation of massive diffuse ionized gas clouds. A semiquantitative discussion of the role of cooling indicates that there is a characteristic mass of a galaxy (of the order of 500 billion solar masses) which can fragment out of an ionized medium of density not exceeding 10 to the -25th power g/cu cm, whereas more massive galaxies attain a characteristic radius of the order of 60 kpc. The relationship between binding energy and mass is investigated for spheroidal galaxies. The role of H2 and Ly-alpha cooling in the fragmentation of primordial gas clouds is evaluated, and relatively qualitative arguments indicate that the first stars have masses of at least 0.3 solar mass with a characteristic mass of approximately 20 solar masses. When the average heavy-element abundance by mass exceeds about 0.00001, heavy-element cooling prevails over Ly-alpha cooling, and subsequent fragmentation forms second-generation stars of low characteristic mass.

Silk, J.↗