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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Are the Galactic-bulge X-ray sources magnetized?

This paper attempts to demonstrate that a better understanding of Galactic-bulge X-ray sources can be achieved if their magnetic moments are assumed to have the same values as those of young pulsars. It is argued that most of the matter leaving the inner edge of the accretion disk can reach the neutron star's surface in the form of massive clumps in quasi-Keplerian orbits. As a result, most of the accretion flow covers a broad equatorial belt rather than the polar caps, and the star shines as an almost unpulsed source. The liberation of half of the accretion power before the surface is reached can lead to the reported UHE pulses and bright infrared bursts. Spasmodic accretion is discussed as a model for gamma-ray bursts, and the observed low-energy X-ray absorption features are considered as an indication of strong magnetic fields shifted to lower energies during super-Eddington outbursts.

Kundt, W.↗
NASA NTRS2004

Crustal Magnetic Spectra from Correlated Sources on Mars

The spectral method for distinguishing crustal from core-source magnetic fields has been re-examined, modified and applied to both a comprehensive geomagnetic field model and an altitude normalized magnetic map of Mars. These observational spectra are fairly fitted by theoretical forms expected from certain elementary classes of magnetic sources. For Earth we found fields from a core radius 3512 +/- 64 km and a crust represented by a shell of random dipolar sources at radius 6367 +/- 14 km. For Mars we found only a field from a crust represented in the same way, but 46 +/- 10 km below the planetary menu radius. More realistic theoretical spectra, allowing for crustal thickness, oblateness and magnetization by a planet centered dipole, were derived and discussed, as were spectral effects of laterally correlated sources. The main effect of laterally correlated sources is to soften the spectrum at high degrees. We tend to over-estimate source shell depth when this is omitted. To include this effect simply size and magnetization distribution functions for extended sources are recast as a characteristic diameter and mean square magnetization amplitude for an ensemble of vertically magnetized spherical caps on a shell. For small caps, and at moderated degrees, the practical derivatives of the log-theoretical spectrum with respect to amplitude, shell radius, and cap diameter are approximately proportional to l, n, and -n **2, respectively. Separation of diameter from amplitude from layer thickness. Results from applications to observational spectra are discussed, noting that there are now several fine field models for Mars; moreover, the terrestrial magnetic spectrum at high degrees, as revised, updated with high precision Oerstad data, and upgrade with high resolution Champ data, appears softer than before.

Voorhies, Coerte V.↗
NASA NTRS2005

More on Magnetic Spectra from Correlated Crustal Sources on Mars

The spectral method for distinguishing crustal from core-source magnetic fields has been re-examined, modified and applied to both a comprehensive geomagnetic field model and an altitude normalized magnetic map of Mars. These observational spectra are fairly fitted by theoretical forms expected from certain elementary classes of magnetic sources. For Earth we found fields from a core of radius 3512 plus or minus 64 km, in accord with the 3480 km seismologic radius, and a crust represented by a shell of random dipolar sources at radius 6367 plus or minus 14 km, just beneath the 6371.0 km mean radius. For Mars we found only a field from a crust represented in same way, but 46 plus or minus 10 km below the planetary mean radius of 3389.5 km, and with sources about 9.6 plus or minus 3.2 times stronger than Earth's. It is remarkable that the same simple theoretical form should fairly fit crustal magnetic spectra for both worlds and return crustal-source depth estimates of plausible magnitude. Evidently, the idea of an ensemble of compact, quasi-independent, magnetized regions within these planetary crusts has some merit. Yet such estimates, at best a kind of average, depend upon both the observational spectrum fitted and the physical basis of the theoretical spectrum.

Voorhies, C. V.↗
NASA NTRS1993

Magnetic field sources and their threat to magnetic media

Magnetic storage media (tapes, disks, cards, etc.) may be damaged by external magnetic fields. The potential for such damage has been researched, but no objective standard exists for the protection of such media. This paper summarizes a magnetic storage facility standard, Publication 933, that ensures magnetic protection of data storage media.

Jewell, Steve↗
NASA NTRS1979

Lodestone-explanation for magnetic properties and characterization of the source of magnetic hardening

The microstructure of Class I lodestones was investigated by X-ray diffraction and by optical and transmission electron microscopy, and the behavior of lodestone magnetization was studied at temperatures of 4 to 825 K. It was found that intense magnetization is associated with the gamma Fe2O3-Fe3O4 intergrowth. Thermal demagnetization of the lodestone studied was nearly complete at 300 C. The loss of natural remanence was found to be associated with transformation of gamma Fe2O3 to alpha Fe2O3.

Wasilewski, P. J.↗
NASA NTRS1977

Sources of magnetic fields in recurrent interplanetary streams

The sources of magnetic fields in recurrent streams were examined. Most fields and plasmas at 1 AU were related to coronal holes, and the magnetic field lines were open in those holes. Some of the magnetic fields and plasmas were related to open field line regions on the sun which were not associated with known coronal holes, indicating that open field lines are more basic than coronal holes as sources of the solar wind. Magnetic field intensities in five equatorial coronal holes ranged from 2G to 18G. Average measured photospheric magnetic fields along the footprints of the corresponding unipolar fields on circular equatorial arcs at 2.5 solar radii had a similar range and average, but in two cases the intensities were approximately three times higher than the projected intensities. The coronal footprints of the sector boundaries on the source surface at 2.5 solar radii, meandered between -45 deg and +45 deg latitude, and their inclination ranged from near zero to near ninety degrees.

Burlaga, L. F.↗
NASA NTRS1978

Sources of magnetic fields in recurrent interplanetary streams

The paper examines sources of magnetic fields in recurrent streams observed by the Imp 8 and Heos spacecraft at 1 AU and by Mariner 10 en route to Mercury between October 31, 1973 and February 9, 1974, during Carrington rotations 1607-1610. Although most fields and plasmas at 1 AU were related to coronal holes and the magnetic field lines were open in those holes, some of the magnetic fields and plasmas at 1 AU were related to open field line regions on the sun which were not associated with known coronal holes, indicating that open field lines may be more basic than coronal holes as sources of the solar wind. Magnetic field intensities in five equatorial coronal holes, certain photospheric magnetic fields, and the coronal footprints of the sector boundaries on the source surface are characterized.

Burlaga, L. F.↗
NASA NTRS1985

Separation of core and crustal magnetic field sources

Fluid motions in the electrically conducting core and magnetized crustal rocks are the two major sources of the magnetic field observed on or slightly above the Earth's surface. The exact separation of these two contributions is not possible without imposing a priori assumptions about the internal source distribution. Nonetheless models like these were developed for hundreds of years Gauss' method, least squares analysis with a truncated spherical harmonic expansion was the method of choice for more than 100 years although he did not address separation of core and crustal sources, but rather internal versus external ones. Using some arbitrary criterion for appropriate truncation level, we now extrapolate downward core field models through the (approximately) insulating mantle. Unfortunately our view can change dramatically depending on the degree of truncation for describing core sources.

Shure, L.↗
NASA NTRS2005

A Global Map of Mars' Crustal Magnetic Field Based on Electron Reflectometry

One of the great surprises of the Mars Global Surveyor mission was the discovery of intensely magnetized crust. Magnetic sources on Mars are at least ten times stronger than their terrestrial counterparts, probably requiring large volumes of coherently magnetized material, very strong remanence, or both. Although much of the attention so far has been placed on the strong crustal fields in the southern highlands, magnetic sources do exist in the younger low-lying plains. The strength and morphology of these sources could yield clues to the thermal and magnetic history of the northern plains. Low altitude (approx. 100 km) Magnetometer (MAG) data obtained during aerobraking have the greatest spatial resolution and sensitivity for identifying crustal magnetic sources from orbit, but those data are sparse and therefore limit the ability to discern morphology. Fully sampled MAG data obtained in the 400-km altitude mapping orbit have been differenced with respect to latitude (Br/Lat) to minimize the influence of induced fields from the solar wind interaction and thus enhance the sensitivity to weak crustal sources. Here we describe independent results from the Electron Reflectometer (ER), which remotely measures the magnetic field intensity at approx. 170 km altitude, and is roughly seven times more sensitive to crustal magnetic sources than measurements of Br from the mapping orbit.

Mitchell, D. L.↗
DOE OSTI2020

Functionalizing magnet additive manufacturing with in-situ magnetic field source

Additive manufacturing via 3-D printing technologies have become a frontier in materials research, including its application in the development and recycling of permanent magnets. This work addresses the opportunity to integrate magnetic field sources into 3-D printing process in order to enable printing, alignment of anisotropic permanent magnets or magnetizing of magnetic filler materials, without requiring further processing. Specifically, a nonaxisymmetric electromagnet-type field source architecture was designed, modelled, constructed, installed to a fused filament commercial 3-D printer, and tested. The testing was performed by applying magnetic field while printing composite anisotropic Nd-Fe-B + Sm-Fe-N powders bonded in Nylon12 (65 vol.%) and recycled Sm-Co powder bonded in PLA (15 vol.%). Magnetic characterization indicated that the degree-of-alignment of the magnet powders increased both with alignment field strength (controlled by the electric current applied to the magnetizing system) and the printing temperature. Both coercivity and remanence were found to be strongly dependent on the degree-of-alignment, except for printing performed below but near the Curie temperature of Nd-Fe-B (310 ° C). At applied field of 0.15 kOe, Sm-Co and hybrid Nd-Fe-B/Sm-Fe-N printed samples showed degrees-of-alignment of 83 % and 65 %, respectively. The variations in coercivity were consistent with previous observations in bonded magnet materials. This work verifies that integration of magnetic field sources into 3-D printing processes will result in magnetic alignment of particles while ensuring that other advantages of 3-D printing are retained.

3-D printing↗