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At least 595 records · Page 33

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NASA NTRS1977

Performance characteristics of a three-axis superconducting rock magnetometer

A series of measurements are carried out with the purpose of quantitatively determining the characteristics of a commercial 6.8 cm access superconducting rock magnetometer located in the magnetic properties laboratory at the Goddard Space Flight Center. The measurements show that although a considerable improvement in measurement speed and signal to noise ratios can be obtained using such an instrument, a number of precautions are necessary to obtain accuracies comparable with more conventional magnetometers. These include careful calibration of the sensor outputs, optimum positioning of the sample within the detection region and quantitatively establishing the degree of cross-coupling between the detector coils. In order to examine the uniformity of response for each detector, the responses are mapped as a function of position, using a small dipole.

Lienert, B. R.↗

NASA NTRS1977

Solar wind and micrometeorite effects in the lunar regolith

Using available data from the literature, an outline is formulated for the major physical and chemical effects expected during solar-wind bombardment of the lunar regolith. In agreement with results of Auger and other analyses of the composition of lunar grain surfaces, this outline predicts that solar-wind sputtering will tend to clean exposed grain surfaces by ejecting material at velocities exceeding lunar escape velocity. Results are also discussed which show that Fe is partially reduced in the outer few 10 nm of grain surfaces and that this reduced Fe forms 10-nm-diameter metal spheres throughout the glass during agglutinate formation by micrometeorite impacts. These metal spheres give the agglutinates their distinctive optical and magnetic properties and are partially responsible for the decreasing albedo of the lunar surface with exposure age.

Housley, R. M.↗

NASA NTRS1976

Effect of magnetic field on reduction of nickel oxide

Results of observations recorded during constant temperature reduction of NiO, a paramagnetic substance, to Ni, a ferromagnetic element, are presented. The application of a large magnetic field (4,200 oersted) does not result in an acceleration of the reduction rate. To explain earlier observations that 500- and 1,400-oersted magnetic fields increase the reduction rate of iron ore which contains hematite (Fe2O3), Peters (1973) had suggested that thermodynamics theory could predict the acceleration in reaction rate when product and reactant species differ widely in their magnetic properties.

Rowe, M. W.↗

NASA NTRS1978

Bonding core mating surfaces improves transformer

Modifications to assembly procedures for C-core transformers virtually eliminates changes in core end gaps due to temperature cycling during impregnation and potting stages, thus stabilizing magnetization properties of core.

Mclyman, W. T.↗

NASA NTRS1975

Lunar Science Conference, 6th, Houston, Tex., March 17-21, 1975, Proceedings. Volume 3 - Physical studies

Recent investigations of the moon are reported. Topics discussed include the Apollo 17 site, selenography, craters, remote sensing, selenophysics, lunar surface fields and particles, magnetic properties of lunar samples, physical property measurements, surface-correlated properties, micrometeoroids, solar-system regoliths, and cosmic rays. Lunar orbital data maps are presented, and the evolution of lunar features is examined.

Merrill, R. B.↗

NASA NTRS1979

Application of the minimum correlation technique to the correction of the magnetic field measured by magnetometers on spacecraft

Some aspects of the problem of obtaining precise, absolute determination of the vector of low magnetic fields existing in the interplanetary medium are addressed. In the case of a real S/C, there is always the possibility of a spurious field which includes the spacecraft residual field and/or possible field from the sensors, due to both electronic drifts or changes of the magnetic properties of the sensor core. These latter effects may occur during storage of the sensors prior to launching and/or in-flight. The reliability is demonstrated for a method which postulates that there should be no correlation between changes in measured field magnitude and changes in the measured inclination of the field with respect to any one of three fixed Cartesian component directions. Application of this minimum correlation technique to data from IMP-8 and Helios 1-2 shows it is appropriate for determination of the zero offset corrections of triaxial magnetometers. In general, a number of the order of 1000 consecutive data points is sufficient for a good determination.

Mariani, F.↗

NASA NTRS1979

Shock induced magnetic effects in fine particle iron dispersions

Magnetic effects associated with shock induced transformation of fcc antiferromagnetic iron precipitates in polycrystalline copper disks at levels up to 5 GPa in weak magnetic fields (H not greater than 0.5 Oe) were investigated. The demagnetization and anisotropy associated with second order transition, the effects of plastic deformation in imparting magnetic anisotropy and magnetic hardening, and the influence of post shock thermal transients on magnetization associated with recovery, recrystallization and grain growth were studied. It was found that on the microsecond time scale of the shock induced first order transformation, the field sense is recorded in the transformed iron particles. For a given particle size the degree of transformation of fcc iron depends on the level of the shock. For a given shock level the resultant magnetic properties depend on the particle size distribution, with maximum effects noted in specimens with 400 to 600 A particles.

Wasilewski, P. J.↗

NASA NTRS1979

The extended mission of Viking

The extended mission of the Viking project emphasizing the study of weather on Mars is presented. Samples were acquired for the analysis of surface material, and investigations were made of the physical and magnetic properties of the surface, with orbiters and landers producing large quantities of photographs of the surface and of atmospheric phenomena. The operation and chronology of Viking Orbiter 1 and 2 and Viking Lander 1, including the Viking continuation, the survey, and the orbiter completion missions are discussed.

Snyder, C. W.↗

NASA NTRS1980

Immunomicrospheres - Reagents for cell labeling and separation

Immunomicrospheres are specially designed microscopic particles that have antibodies or similar molecules chemically bound to their surfaces. The antibody-coated microspheres react in a highly specific way with target cells, viruses, or other antigenic agents. Immunomicrospheres may be synthesized so that they incorporate compounds that are highly radioactive, intensely fluorescent, magnetic, electron opaque, highly colored, or pharmacologically active. These various types of microspheres may be coated with pure, highly specific monoclonal antibodies obtained by the new hybridoma cell cloning techniques or with conventional antibody preparations. Some of the many present and potential applications for these new reagents are (1) new types of radioimmune or immunofluorescent assays, (2) improved fluorescence microscopy, (3) separation of cells on the basis of the fluorescent, electrophoretic, or magnetic properties of bound immunomicrospheres, (4) markers for use in several types of electron or standard light microscopy, and (5) delivery of lethal compouds to specific undesirable living cells. The combination of the various new types of synthetic microspheres and the newly available homogeneous antibodies offers new opportunities in research, diagnosis, and therapy.

Rembaum, A.↗

NASA NTRS1981

Altered basaltic glass - A terrestrial analog to the soil of Mars

In order to understand the nature of weathering processes and the formation of clay-like substances on Mars, analogous terrestrial processes and materials have been examined including sideromelane and palagonite. It is shown that palagonite is a good analog to the soil of Mars to the level of precision available from Viking and ground-based telescopic spectral measurements. Points of resemblance between the two materials include bulk chemical composition, particle size, reflectance spectra, and magnetic properties. A mechanism for the formation of Martian soil, based on a palagonite model, is proposed.

Allen, C. C.↗

NASA NTRS1982

Gravitationally induced convection during directional solidification of off-eutectic Mn-Bi alloys

The effects of thermal and solute gradient, gravity induced convection during vertical directional solidification, on longitudinal macrosegregation of Bi and Mn rich off-eutectic starting compositions, has been studied as a function of composition, growth velocity and gravity vector orientation. Since the morphology of these alloys is characterized by an aligned, rodlike permanent magnet composite when grown cooperatively, the magnetic properties were used to measure composition segregation and the transition from dendritic to composite growth. Severe macrosegregation was observed in all cases studied and the degree of convection inferred by modeling the observed composition segregation using a stagnant film approach. Morphological stability was found to follow a constitutional supercooling-type law for both Bi and Mn rich compositions.

Pirich, R. G.↗

NASA NTRS1985

Eddy-Current Reference Standard

Magnetic properties of metallic reference standards duplicated and stabilized for eddy-current coil measurements over long times. Concept uses precisely machined notched samples of known annealed materials as reference standards.

Ambrose, H. H., Jr.↗

NASA NTRS1984

Magnetic cristobalite (?) - A possible new magnetic phase produced by the thermal decomposition of nontronite

The effect of heat treatment for 1 h or more at 900-1000 C on the magnetic properties of nontronite, an iron-rich smectite clay thought to be an important component of Martian regolith, is investigated experimentally, extending the findings of Moskowitz and Hargraves (1982). The results are presented in graphs and tables and discussed. A phase with Curie temperature 200-220 C, remanent coercivity greater than 800 mT, and a type-2 room-temperature-coercivity response to thermomagnetic cycling is observed and attributed to an iron-substituted cristobalite which may form by topotactic growth from a smectite precursor.

Moskowitz, B. M.↗

NASA NTRS1984

SPAR X Technical Report for Experiment 76-22 Directional Solidification of Magnetic Composites

The effects of gravity on Bridgman-Stockbarger directional solidification of off-eutectic Bi/MnBi were studied in reduced gravity aboard the SPAR X flight and compared to normal-gravity investigations and previous eutectic Bi/MnBi SPAR flight experiments. The directional solidification of off-eutectic Bi/MnBi results in either a dendritic structure connected with local cooperative growth or a coupled low volume fraction faceted/non faceted aligned rod eutectic whose Mn macrosegregation, MnBi rod size, interrod spacing, and thermal and magnetic properties are sensitive functions of the solidification processing conditions. Two hypoeutectic and two hypereutectic samples were solidified during 605 sec of furnace travel, with an initial 265 sec low-gravity interval. Comparison Earth-gravity samples were solidified in the same furance assembly under identical processing conditions. Macrosegregation in the low-g samples was consistent with a metastable increase in Mn solubility in the Bi matrix, in partial agreement with previous Bi/MnBi SPAR findings of MnBi volume reduction.

Bethin, J.↗

NASA NTRS1985

Advanced detectors and signal processing for bubble memories

The feasibility of combining silicon and magnetic bubble technologies is demonstrated. Results of bubble film annealing indicate that a low temperature silicon on garnet technology is the most likely one to succeed commercially. Annealing ambients are also shown to have a major effect on the magnetic properties of bubble films. Functional MOSFETs were fabricated on bubble films coated with thick (approximately 1 micron) SiO2 layers. The two main problems with these silicon on garnet MOSFETs are low electron mobilities and large gate leakage currents. Results indicate that the laser recrystallized silicon and gate oxide (SiO2) layers are contaminated. The data suggest that part of the contaminating ions originate in the sputtered oxide spacer layer and part originates in the bubble film itself. A diffusion barrier, such as silicon nitride, placed between the bubble film and the silicon layer should eliminate the contamination induced problem.

Kryder, M. H.↗

NASA NTRS1985

Variation of the temperature coefficient of collapse field in bismuth-based bubble garnets

An approximation to the collapse-field formula is used to show its dependence on magnetization and wall energy and the effect of additions of Gd, Sm, and Eu on 1-micron Bi:YIG bubble materials. The collapse field, magnetization, and wall energy are fitted to quadratic functions of temperature from -50 to 150 C. It is shown that the addition of the various classes of rare earths reduces the temperature derivative of the collapse field in Bi:YIG. Gd influences the collapse field through the magnetization, Sm affects it through the domain wall energy, and Eu does both. The singular magnetic properties of Eu result in the most nearly constant temperature dependence of the collapse field and the best match to a barium-ferrite bias magnite.

Fratello, V. J.↗

NASA NTRS1985

The feasibility of silicon on garnet technology

The feasibility of combining silicon and magnetic bubble technologies is demonstrated. Functional MOSFETs have been fabricated on top of bubble films coated with 1-micron thick SiO2 layers. The large grain silicon necessary for these devices is obtained by laser recrystallization of polycrystalline silicon (polysilicon). The laser-recrystallization process causes changes in the magnetic properties of the bubble film; however, these changes can be reversed by subsequent thermal anneals. The required temperature treatments after laser annealing are compatible with the MOSFET fabrication process.

Rasky, P. H. L.↗

NASA NTRS1986

Iron oxide and hydroxide precipitation from ferrous solutions and its relevance to Martian surface mineralogy

Experiments were performed to examine if the ubiquitousness of a weak magnetic component in all Martian surface fines tested with the Viking Landers can be attributed to ferric iron precipitation in aqueous solution under oxidizing conditions at neutral pH. Ferrous solutions were mixed in deionized water and various minerals were added to separate liquid samples. The iron-bearing additives included hematite, goethite, magnetite, maghemite, lepidocrocite and potassium bromide blank at varying concentrations. IR spectroscopic scans were made to identify any precipitates resulting from bubbling oxygen throughout the solutions; the magnetic properties of the precipitates were also examined. The data indicated that the lepidocrocite may have been preferentially precipitated, then aged to maghemite. The process would account for the presumed thin residue of maghemite on the present Martian surface, long after abundant liquid water on the Martian surface vanished.

Posey-Dowty, J.↗