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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Multi-Wavelength Modeling and Analysis of the Center-to-Limb Effects of Solar Spectroscopy and Helioseismology

An accurate interpretation of observed solar dynamics with different instruments requires modeling solar magnetoconvection indifferent regimes, as well as taking into account center-to-limb effects, magnetic fields, and turbulence. Realistic 3D radiative MHD modeling of the solar magnetoconvection and atmosphere allows us to generate synthetic observables that directly link the physical properties of the solar plasma to spectroscopic and helioseismic observables. In this work, we investigate the influence of the center-to-limb effects for a wide range of wavelengths, which correspond to the operational lines of HMI/SDO, Hinode, DKIST, and other instruments. In particular, we discuss the wavelength-dependency of the center-to-limb helioseismic observations of acoustic travel times that are used for diagnostics of the deep meridional circulation, as well as 'concave' Sun effect. The presented study will support interpretation of helioseismic inversion results by taking into account realistic coupling of subsurface and atmosphere, and geometry-related effects. In particular, it allows us to improve accuracy of solar subsurface measurements from the SoHO and SDO missions, and resolve the long-standing problem of the meridional circulation and evolution with the solar cycle.

SMD↗
NASA NTRS2005

Space Weathering: A Proposed Laboratory Approach to Explaining the Sulfur Depletion on Eros

Space weathering is the cumulative effect of physical and chemical changes that occur to substances exposed on the exterior of body void of an atmosphere [1], in this case the regolith on asteroid Eros. It is only recently that the scientific community has accepted the theory first developed in the mid- 1970s by Hapke and his colleagues of how space weathering occurs. The theory [1] asserts that optical and magnetic effects, first studied on moon rocks and lunar regolith, are caused by submicroscopic metallic iron (SMFe), smaller than the wavelength of light in vapor deposit coatings, on regolith grains, and in agglutinates. This vapor is generated by solar wind and micrometeorite impacts and does not require additional heating, melting, or a reducing environment to produce space weathering. One of the major finds of the first detailed reconnaissance of an asteroid by the NEAR Shoemaker mission was that the surface of Eros was essentially chondritic yet showed major depletions in sulfur [2, 3]. Here we propose space weathering sputtering experiments that may contribute to the explanation of sulfur depletion on asteroid Eros.

Franzen, M. A.↗
NASA NTRS1994

The effects of Kelvin-Helmholtz instability on resonance absorption layers in coronal loops

One of the long-standing uncertainties in the wave-resonance theory of coronal heating is the stability of the resonance layer. The wave motions in the resonance layer produce highly localized shear flows which vary sinusoidally in time with the resonance period. This configuration is potentially susceptible to the Kelvin-Helmholtz instability (KHI), which can enhance small-scale structure and turbulent broadening of shear layers on relatively rapid ideal timescales. We have investigated numerically the response of a characteristic velocity profile, derived from resonance absorption models, to finite fluid perturbations comparable to photospheric fluctuations. We find that the KHI primarily should affect long (approximately greater than 6 x 10(exp 4) km) loops where higher velocity flows (M approximately greater than 0.2) exist in resonance layers of order 100 km wide. There, the Kelvin-Helmholtz growth time is comparable to or less than the resonance quarter-period, and the potentially stabilizing magnetic effects are not felt until the instability is well past the linear growth stage. Not only is the resonance layer broadened by the KHI, but also the convective energy transport out of the resonance layer is increased, thus adding to the efficiency of the wave-resonance heating process. In shorter loops, e.g., those in bright points and compact flares, the stabilization due to the magnetic field and the high resonance frequency inhibit the growth of the Kelvin-Helmholtz instability beyond a minimal level.

Karpen, Judith T.↗
NASA NTRS1990

Earth's external magnetic fields at low orbital altitudes

Under our Jun. 1987 proposal, Magnetic Signatures of Near-Earth Distributed Currents, we proposed to render operational a modeling procedure that had been previously developed to compute the magnetic effects of distributed currents flowing in the magnetosphere-ionosphere system. After adaptation of the software to our computing environment we would apply the model to low altitude satellite orbits and would utilize the MAGSAT data suite to guide the analysis. During the first year, basic computer codes to run model systems of Birkeland and ionospheric currents and several graphical output routines were made operational on a VAX 780 in our research facility. Software performance was evaluated using an input matchstick ionospheric current array, field aligned currents were calculated and magnetic perturbations along hypothetical satellite orbits were calculated. The basic operation of the model was verified. Software routines to analyze and display MAGSAT satellite data in terms of deviations with respect to the earth's internal field were also made operational during the first year effort. The complete set of MAGSAT data to be used for evaluation of the models was received at the end of the first year. A detailed annual report in May 1989 described these first year activities completely. That first annual report is included by reference in this final report. This document summarizes our additional activities during the second year of effort and describes the modeling software, its operation, and includes as an attachment the deliverable computer software specified under the contract.

Klumpar, D. M.↗
NASA NTRS1965

Plasma.

Plasma physics and engineering applications noting sheath or Debye length, Hall effect, magnetic field technology and reflectivity conductivity

PLASMA PHYSICS↗
NASA NTRS1973

The moon as a high temperature condensate.

The accretion during condensation mechanism, if it occurs during the early over-luminous stage of the sun, can explain the differences in composition of the terrestrial planets and the moon. An important factor is the variation of pressure and temperature with distance from the sun, and in the case of the moon and captured satellites of other planets, with distance from the median plane. Current estimates of the temperature and pressure in the solar nebula suggest that condensation will not be complete in the vicinity of the terrestrial planets, and that depending on location, iron, magnesium silicates and the volatiles will be at least partially held in the gaseous phase and subject to separation from the dust by solar wind and magnetic effects associated with the transfer of angular momentum just before the sun joins the Main Sequence. Many of the properties of the moon, including the 'enrichment' in Ca, Al, Ti, U, Th, Ba, Sr and the REE and the 'depletion' in Fe, Rb, K, Na and other volatiles can be understood if the moon represents a high temperature condensate from the solar nebula.

Anderson, D. L.↗
NASA NTRS1970

Accelerated electromagnetic systems

Summaries on the electrodynamic research are presented. Data cover accelerated systems, electric and magnetic effects, and Sommerfield's riddle.

Source record↗
NASA NTRS1974

Auroral particle precipitation and Birkeland currents

Correlated measurements that provide information on Birkeland (field aligned) currents are reviewed. Because of the obvious importance of field-aligned electric fields with regard to Birkeland currents, the last section of the paper is devoted to a presentation of recent data on the observations of field-aligned auroral electron fluxes and monoenergetic peaks in the spectrum. Experimental data cannot yet define the overall magnetospheric pattern of the Birkeland current system. The largest body of data regarding these currents comes from polar-orbiting satellites. These data indicate that current sheets are associated with auroral displays and that field-aligned electron fluxes on the order of 1-keV energy are significant charge carriers for the conventional current out of the atmosphere. Rocket observations verify that electrons responsible for the production of auroral forms carry a significant fraction of the current necessary to produce local magnetic effects that require Birkeland currents for their explanations.

Arnoldy, R. L.↗
NASA NTRS1974

Protons as the prime contributors to the storm time ring current

Following a large magnetic storm (17 June 1972), Explorer 45 measured the equatorial particle populations and magnetic field. Using data obtained during the symmetic recovery phase, it is shown that through a series of self-consistent calculations, the measured protons with energies from 1 to 872 keV, can account for the observed ring current magnetic effects within experimental uncertainities. This enables an upper limit to be set for the heavy ion contribution to the storm time ring current.

Berko, F. W.↗
NASA NTRS1975

Protons as the prime contributors to storm time ring current

Following a large sudden commencement on June 17, 1972, a large magnetic storm evolved, with a well-developed main phase and recovery phase. Explorer 45 (S3-A), with its apogee near 16 hours local time in June, measured the equatorial particle populations and magnetic field throughout this period. By use of data obtained during the symmetric recovery phase it is shown that through a series of self-consistent calculations, the measured protons, with energies from 1 to 872 keV, can account for almost all of the observed ring current magnetic effects within the limits of experimental uncertainties. This enables us to set an upper limit to the heavy ion contribution to the storm time ring current of a few percent of the proton contribution.

Berko, F. W.↗
NASA NTRS1980

Cable-splice detector

Detector has possible uses in aerial cable-car systems, equipment handling in mines, boreholes, and undersea operations, and other applications where moving steel cable must be measured, monitored, or controlled. Detector consists of Hall-effect magnetic sensor located close to cable. Magnetic markings on cable are converted to electrical signals. Signals are filtered, amplified, and can actuate alarm.

Lee, R. D.↗