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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

On Geomagnetism and Paleomagnetism

A statistical description of Earth's broad scale, core-source magnetic field has been developed and tested. The description features an expected, or mean, spatial magnetic power spectrum that is neither "flat" nor "while" at any depth, but is akin to spectra advanced by Stevenson and McLeod. This multipole spectrum describes the magnetic energy range; it is not steep enough for Gubbins' magnetic dissipation range. Natural variations of core multipole powers about their mean values are to be expected over geologic time and are described via trial probability distribution functions that neither require nor prohibit magnetic isotropy. The description is thus applicable to core-source dipole and low degree non-dipole fields despite axial dipole anisotropy. The description is combined with main field models of modem satellite and surface geomagnetic measurements to make testable predictions of: (1) the radius of Earth's core, (2) mean paleomagnetic field intensity, and (3) the mean rates and durations of both dipole power excursions and durable axial dipole reversals. The predicted core radius is 0.7% above the 3480 km seismologic value. The predicted root mean square paleointensity (35.6 mu T) and mean Virtual Axial Dipole Moment (about 6.2 lx 1022 Am(exp 2)) are within the range of various mean paleointensity estimates. The predicted mean rate of dipole power excursions, as defined by an absolute dipole moment <20% of the 1980 value, is 9.04/Myr and 14% less than obtained by analysis of a 4 Myr paleointensity record. The predicted mean rate of durable axial dipole reversals (2.26/Myr) is 2.3% more than established by the polarity time-scale for the past 84 Myr. The predicted mean duration of axial dipole reversals (5533 yr) is indistinguishable from an observational value. The accuracy of these predictions demonstrates the power and utility of the description, which is thought to merit further development and testing. It is suggested that strong stable stratification of Earth's uppermost outer core leads to a geologically long interval of no dipole reversals and a very nearly axisymmetric field outside the core. Statistical descriptions of other planetary magnetic fields are outlined.

Voorhies, Coerte V.↗
NASA NTRS2003

Pulsed Magnetic Field Driven Gas Core Reactors for Space Power & Propulsion Applications

The present results indicated that: 1. A pulsed magnetic driven fission power concept, PMD-GCR is developed for closed (NER) and semi-open (NTR) operations. 2. In power mode, power is generated at alpha less than 1 for power levels of hundreds of KW or higher 3. IN semi open NTR mode, PMD-GCR generates thrust at I(sub sp) approx. 5,000 s and jet power approx. 5KW/Kg. 4. PMD-GCR is highly subcritical and is actively driven to critically. 5. Parallel path with fusion R&D needs in many areas including magnet and plasma.

Anghaie, Samim↗
DOE OSTI2021

Formation and evolution of protostellar accretion discs – I. Angular-momentum budget, gravitational self-regulation, and numerical convergence

Here, we investigate the formation and early evolution of a protostellar disc from a magnetized prestellar core using non-ideal magnetohydrodynamic (MHD) simulations including ambipolar diffusion and Ohmic dissipation. The dynamical contraction of the prestellar core ultimately leads to the formation of a first hydrostatic core, after ambipolar diffusion decouples the magnetic field from the predominantly neutral gas. The hydrostatic core accumulates angular momentum from the infalling material, evolving into a rotationally supported torus; this ‘first hydrostatic torus’ then forms an accreting protostar and a rotationally supported disc. The disc spreads out by gravitational instability, reaching ~30 au in diameter at ~3 kyr after protostar formation. The total mass and angular momentum of the protostar–disc system are determined mainly by accretion of gas from an infalling pseudo-disc, which has low specific angular momentum because of magnetic braking; their removal from the protostar–disc system by outflow and disc magnetic braking are negligible, in part because the magnetic field is poorly coupled there. The redistribution of angular momentum within the protostar–disc system is facilitated mainly by gravitational instability; this allows formation of relatively large discs even when the specific angular momentum of infalling material is low. We argue that such discs should remain marginally unstable as they grow (with Toomre Q ~ 1–2), an idea that is broadly consistent with recent observational estimates for Class 0/I discs. We discuss the numerical convergence of our results, and show that properly treating the inner boundary condition is crucial for achieving convergence at an acceptable computational cost.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Metal Amorphous Nanocomposite (MANC) Alloy Cores with Spatially Tuned Permeability for Advanced Power Magnetics Applications

Metal amorphous nanocomposite (MANC) alloys are an emerging class of soft magnetic materials showing promise for a range of inductive components targeted for higher power density and higher efficiency power conversion applications including inductors, transformers, and rotating electrical machinery. Magnetization reversal mechanisms within these alloys are typically determined by composition optimization as well as controlled annealing treatments to generate a nanocomposite structure composed of nanocrystals embedded in an amorphous precursor. Here in this paper we demonstrate the concept of spatially varying the permeability within a given component for optimization of performance by using the strain annealing process. The concept is realized experimentally through the smoothing of the flux profile from the inner to outer core radius achieved by a monotonic variation in tension during the strain annealing process. Great potential exists for an extension of this concept to a wide range of other power magnetic components and more complex spatially varying permeability profiles through advances in strain annealing techniques and controls.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electrodeposited Co{sub 93.2}P{sub 6.8} nanowire arrays with core-shell microstructure and perpendicular magnetic anisotropy

We demonstrate the formation of an unusual core-shell microstructure in Co{sub 93.2}P{sub 6.8} nanowires electrodeposited by alternating current (ac) in an alumina template. By means of transmission electron microscopy, it is shown that the coaxial-like nanowires contain amorphous and crystalline phases. Analysis of the magnetization data for Co-P alloy nanowires indicates that a ferromagnetic core is surrounded by a weakly ferromagnetic or non-magnetic phase, depending on the phosphor content. The nanowire arrays exhibit an easy axis of magnetization parallel to the wire axis. For this peculiar composition and structure, the coercivity values are 2380 ± 50 and 1260 ± 35 Oe, parallel and perpendicular to the plane directions of magnetization, respectively. This effect is attributed to the core-shell structure making the properties and applications of these nanowires similar to pure cobalt nanowires with an improved perpendicular anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1978

Depositional and surface exposure history of the Shorty Crater core 74001/2 - FMR and magnetic studies

Surface exposure (maturity) indices and concentrations of FeO and metallic iron were determined at 0.5-cm intervals of the Apollo 17 core section, which sampled a pyroclastic deposit on the rim of Shorty Crater. The determinations showed that all of the soil in the core is extremely immature. An exposure history of the core is proposed: accumulation (about 3.6 billion years ago), shallow burial (during the first 20 million years), deep burial (till about 10-15 million years ago), followed by excavation (10-15 million years ago), and in situ reworking (till the present).

Morris, R. V.↗
DOE OSTI2019

The Magnetic Properties of the Spin-1 Ising Fullerene Cage with a Core-Shell Structure

Magnetic properties of Ising-type endohedral fullerene (IEF), which are formed by an atom encapsulated inside a diluted magnetic spherical cage, have been investigated theoretically as a function of its system parameters, and magnetism calculations by using effective field theory (EFT) were performed. Theoretical studies have been carried out to understand the effect on magnetic behaviors by the diluted magnetic surface, crystal field, and exchange couplings. The results display the first second-order phase transitions and tricritical point. The reentrant phenomena have been observed within a certain parameter range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2004

Insulator coated magnetic nanoparticulate composites with reduced core loss and method of manufacture thereof

A series of bulk-size magnetic/insulating nanostructured composite soft magnetic materials with significantly reduced core loss and its manufacturing technology. This insulator coated magnetic nanostructured composite is comprises a magnetic constituent, which contains one or more magnetic components, and an insulating constituent. The magnetic constituent is nanometer scale particles (1-100 nm) coated by a thin-layered insulating phase (continuous phase). While the intergrain interaction between the immediate neighboring magnetic nanoparticles separated by the insulating phase (or coupled nanoparticles) provide the desired soft magnetic properties, the insulating material provides the much demanded high resistivity which significantly reduces the eddy current loss. The resulting material is a high performance magnetic nanostructured composite with reduced core loss.

Zhang, Yide↗
DOE OSTI2018

Phase-control synthesis and catalytic property of magnetic Ni@NixPy core-shell microstructures

Highlights: • Ni@Ni{sub x}P{sub y} core-shell microstructures are synthesized by a low-temperature phosphidation route. • The initial Ni/NaH{sub 2}PO{sub 2} molar ratio can strongly affect the phase of the final product. • Ni@Ni{sub x}P{sub y} microstructures present good catalytic activity for the reduction of 4-nitrophenol. • The catalytic property of Ni@Ni{sub x}P{sub y} microstructures presents markedly phase-dependent features. - Abstract: Magnetic Ni@Ni{sub x}P{sub y} core-shell microstructures were successfully synthesized by a simple low-temperature phosphidation route, employing Ni nanospheres as the initial nickel source, NaH{sub 2}PO{sub 2}·H{sub 2}O as the phosphorus ion source. The phosphidation reaction was carried out in N{sub 2} atmosphere at 300 °C for 2 h. Experiments showed that the initial Ni/NaH{sub 2}PO{sub 2} molar ratio could strongly affect the phase of the final product. When the Ni/NaH{sub 2}PO{sub 2} molar ratio of 1:2.77 was used, hexagonal Ni{sub 2}P phase was obtained; while the Ni/NaH{sub 2}PO{sub 2} molar ratio was 1:5.54, hexagonal Ni{sub 5}P{sub 4} phase was produced. It was found that the magnetic properties of the products gradually decreased with the conversion from Ni nanospheres, to Ni@Ni{sub 2}P and to Ni@Ni{sub 5}P{sub 4}. Moreover, initial Ni nanospheres, Ni@Ni{sub 2}P and Ni@Ni{sub 5}P{sub 4} core-shell microstructures presented outstanding catalytic activities for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in excess NaBH{sub 4} solution. Ni@Ni{sub 5}P{sub 4} core-shell microstructures owned the best catalytic activity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1983

Performance measurements of a pilot superconducting solenoid model core for a wind tunnel magnetic suspension and balance system

The results of experimental demonstrations of a superconducting solenoid model core in the Southampton University Magnetic Suspension and Balance System are detailed. Technology and techniques relevant to large-scale wind tunnel MSBSs comprise the long term goals. The magnetic moment of solenoids, difficulties peculiar to superconducting solenoid cores, lift force and pitching moment, dynamic lift calibration, and helium boil-off measurements are discussed.

Goodyer, M. J.↗
DOE OSTI2021

Magnetostrictive loss reduction through stress relief annealing in an FeNi-based metal amorphous nanocomposite

FeNi-based metal amorphous nanocomposite alloys are emerging soft magnetic materials with promise for high-speed motor applications. Here we demonstrate a technique to optimize magnetic properties in toroidal cores wound from strain annealed (Fe 70 Ni 30 ) 80 Nb 4 Si 2 B 14 amorphous metal ribbon (AMR). In-line strain annealing (SA) of the AMR yields a strip permeability that monotonically decreases with increasing SA tensions. After winding into toroidal cores, dramatic changes in magnetic properties are observed and determined to be of magnetostrictive origin. A procedure to re-anneal wound toroidal cores to reduce hysteresis and reverse magnetostrictive effects is developed inclusive of casting curvature effects. Here, we investigate re-annealing temperatures between 300 – 470 °C for cores produced from each SA condition. Magnetic core loss, W L , coercivity, H c , squareness ratio, K r , and permeability, µ r , are measured as a function of (stress relief) re-annealing temperature to optimally achieve W 1T,400Hz = 0.51 W/kg, H c = 2.42 A/m, K r = 0.22, and µ r = 35,300.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Particle Size on the Spin Pinning Effect in the fcc-FePt Nanoparticles

In this work, the Fe{sub 60}Pt{sub 40} nanoparticles were synthesized through the chemical reduction method by using the Fe(CO){sub 5} and the Pt(acac){sub 2} as the metallic precursor. The particle size of the synthesized FePt nanoparticles was controlled by adjusting the reaction conditions involving of the Fe(CO){sub 5}-injecting temperature and the soak time of reaction. The structure, morphology, and magnetic properties of the synthesized FePt nanoparticles were characterized by XRD, TEM, and vibrating sample magnetometer (VSM), respectively. The synthesized nanoparticles exhibit uniform size and good dispersity. The magnetization behaviors indicate that the nanoparticles present the core-shell magnetic structure including the ferromagnetic core part and the spin-disorder shell part. There exists a spin pinning effect of the shell part on the core part. The increase of particle size weakens the spin pinning effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2000

On Geomagnetism and Paleomagnetism I

A partial description of Earth's broad scale, core-source magnetic field has been developed and tested three ways. The description features an expected, or mean, spatial magnetic power spectrum that is approximately inversely proportional to horizontal wavenumber atop Earth's core. This multipole spectrum describes a magnetic energy range; it is not steep enough for Gubbins' magnetic dissipation range. Temporal variations of core multipole powers about mean values are to be expected and are described statistically, via trial probability distribution functions, instead of deterministically, via trial solution of closed transport equations. The distributions considered here are closed and neither require nor prohibit magnetic isotropy. The description is therefore applicable to, and tested against, both dipole and low degree non-dipole fields. In Part 1, a physical basis for an expectation spectrum is developed and checked. The description is then combined with main field models of twentieth century satellite and surface geomagnetic field measurements to make testable predictions of the radius of Earth's core. The predicted core radius is 0.7% above the 3480 km seismological value. Partial descriptions of other planetary dipole fields are noted.

Voorhies, Coerte V.↗
DOE OSTI2019

Magnetic Behavior of Ni/NiO Core–Shell Nanoparticles under Electromagnetic Waves for Oil–Water Interfacial Tension Reduction

The increasing demand for oil and gas has led to a hope of developing more efficient recovery methods. It is well known that nanoparticles adsorbed at the oil–water interface, but there is no consensus that has been reached on whether magnetic nanoparticles under electromagnetic waves affect the interfacial tension. In this paper, nickel/nickel oxide nanoparticles have been synthesized using sol–gel auto combustion method. The product was characterized using x-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, Fourier transforms infrared spectroscopy and vibrating sample magnetometer. The results show the Ni/NiO phases and the ferromagnetic nature of the sample. The Ni/NiO nanofluids were prepared to investigate the effect on oil–water interfacial tension in enhanced oil recovery under electromagnetic waves using an inverted pendant drop method. The results show a significant decrease in interfacial tension under electromagnetic waves of frequency 2.2 kHz at low wt.% of Ni/NiO and at room temperature. The decrease in the interfacial tension has been observed by increasing the temperature to 90 °C using temperature controller. The decrease in the interfacial tension could be due to the interaction of oscillating B-field of waves and magnetic domains of adsorbing nanoparticles at the oil–water interface which disturbed the oil–water interface.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Nanoscale magnetization inhomogeneity within single phase nanopillars

We report observation of a radial dependence in the magnetic anisotropy of epitaxially strained CoFe 2 O 4 nanopillars in a BaTiO 3 matrix. This archetypal example of a multiferroic heterostructure with a self-assembling three-dimensional architecture possesses significant out-of-plane uniaxial magnetic anisotropy. Here, the anisotropy originates from the large magnetostriction of CoFe 2 O 4 and the state of stress within the nanocomposite. Magnetometry suggests the existence of two magnetic phases with different anisotropies. Micromagnetic simulations of a core-shell magnetic anisotropy qualitatively reproduce features of the magnetic hysteresis and elucidate the magnetization reversal mechanism: The magnetization initially reorients within the pillar core, followed by that of the shell. This is consistent with polarized small-angle neutron scattering which can be described by a CoFe 2 O 4 magnetization that is nonuniform on nanometer length scales. As the length scale of inhomogeneity of the magnetic anisotropy is similar to estimates of the relaxation of the displacement field from the CoFe 2 O 4 –BaTiO 3 interface, stress and its influence on structure provide an important route to new functionality of vertically aligned nanopillars for applications in low-power memory, computing, and sensing.

36 MATERIALS SCIENCE↗
NASA NTRS1986

Magnetic field in molecular cloud cores: Limits on field strengths and linewidths

Preliminary observations by others indicate that the magnetic field strength in dense molecular cloud cores is on the order of 30 micro G, much closer to the background field strength than to the flux-freezing prediction for this density. This result implies that some process must exist to decrease the magnetic field strength in these regions to much less than its flux-frozen value, e.g., ambipolar diffusion. At these moderate field strengths, magnetohydrodynamic waves in the cores provide a good explanation of observed supra-thermal molecular linewidths.

Goodman, A. A.↗