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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Solar flares and avalanches in driven dissipative systems

The contention of Lu and Hamilton (1991) that the energy release process in solar flares can be understood as avalanches of many small reconnection events is further developed. The dynamics of the complex magnetized plasma of solar active regions is modeled with a simple driven dissipative system, consisting of a vector field with local instabilities that cause rapid diffusion of the field. It is argued that the avalanches in this model are analogous to solar flares. The distributions of avalanches in this model are compared with the solar flare frequency distributions obtained from ISEE 3/ICE satellite observations. Quantitative agreement is found with the energy, peak luminosity, and duration distributions over four orders of magnitude in flare energy, from the largest flares down to the completeness limit of the observations. It is predicted that the power-law solar flare frequency distributions will be found to continue downward with the same logarithmic slopes to an energy of about 3 x 10 exp 25 ergs and duration of about 0.3 s, with deviations from power-law behavior below these values.

Lu, Edward T.↗
DOE OSTI2023

Three-state Potts nematic order in stacked frustrated spin models with SO(3) symmetry

Here, we propose stacked two-dimensional lattice designs of frustrated and SO(3) symmetric spin models consisting of antiferromagnetic (AF) triangular and ferromagnetic (FM) sixfold symmetric sublattices that realize emergent $\mathbb{Z}_{3}$ Potts nematic order. Considering bilinear-biquadratic spin interactions, our models describe an SO(3)-symmetric triangular lattice AF subject to a fluctuating magnetization arising from the FM coupled sublattice. We focus on the classical AFM-FM windmill model and map out the zero- and finite-temperature phase diagram using Monte Carlo simulations and analytical calculations. We discover a state with composite Potts nematic order above the ferrimagnetic three-sublattice up-up-down ground state and relate it to Potts phases in SO(3)-broken Heisenberg and Ising AFMs in external magnetic fields. Finally, we show that the biquadratic exchange in our model is automatically induced by thermal and quantum fluctuations in the purely bilinear Heisenberg model, easing the requirements for realizing these lattice designs experimentally.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1979

Implementation of ISEE-3 trajectory control

Control of the trajectory and attitude for the International Sun-Earth Explorer-3 (ISEE-3) spacecraft is performed using an onboard hydrazine propulsion system. This paper describes the spacecraft hardware and operational limitations that were considered in the planning, execution, and evaluation of all ISEE-3 maneuvers performed to date. Propulsion system performance and spacecraft dynamics models as implemented in the maneuver support computer software are described. Examples are presented that show how maneuver goals are achieved while satisfying mission orbit and attitude constraints. Procedures used in the development of maneuver plans are detailed for the second midcourse correction maneuver which typifies maneuver operations in general.

Erickson, J. A.↗
NASA NTRS1981

A comparison of helium and heavy ion spectra in He/3/ rich solar flares with a model calculation

He isotopes, O and Fe in He(3) rich solar flares are studied during the 1977 to 1979 period with the MPI/UoMd particle experiment on ISEE-1 and ISEE-3. The study revealed that the He(3) spectrum is generally harder than that of He(4), and the O spectrum is harder than that of Fe. The spectra are compared with a stationary model based on stochastic Fermi acceleration in Alfven turbulence including a rigidity dependent particle loss. Model calculations fit the He(3) and He(4) spectra between 0.4 and 4.0 MeV/nucleon, with discrepancies at lower and higher energies, and the O and Fe spectra cannot be fitted simultaneously.

Mobius, E.↗
DOE OSTI2024

Complex orders and chirality in the classical Kitaev-Γ model

It is well recognized that the low-energy physics of many Kitaev materials is governed by two dominant energy scales, the Ising-type Kitaev coupling 𝐾 and the symmetric off-diagonal Γ coupling. An understanding of the interplay between these two scales is therefore the natural starting point toward a quantitative description that includes subdominant perturbations that are inevitably present in real materials. This study focuses on the classical 𝐾−Γ model on the honeycomb lattice, with a specific emphasis on the region 𝐾< 0 and Γ > 0 , which is the most relevant for the available materials and which remains enigmatic in both quantum and classical limits, despite much effort. We employ large-scale Monte Carlo simulations on specially designed finite-size clusters and unravel the presence of a complex multisublattice magnetic order in a wide region of the phase diagram, whose structure is characterized in detail. We show that this order can be quantified in terms of a coarse-grained scalar-chirality order, featuring a counterrotating modulation on the two spin sublattices. Here, we also provide a comparison to previous studies and discuss the impact of quantum fluctuations on the phase diagram.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Cost of emulating a small quantum annealing problem in the circuit model

Demonstrations of quantum advantage for certain sampling problems have generated considerable excitement for quantum computing and have further spurred the development of circuit-model quantum computers, which represent quantum programs as a sequence of quantum gates acting on a finite number of qubits. Amongst this excitement, analog quantum computation has become less prominent, with the expectation that circuit-model quantum computers will eventually be sufficient for emulating analog quantum computation and thus rendering analog quantum computation obsolete. In this work we explore the basic requirements for emulating a specific analog quantum computation in the circuit model: the preparation of a biased superposition of degenerate ground states of an Ising Hamiltonian using an adiabatic evolution. We show that the overhead of emulation is substantial even for this simple problem. This supports using analog quantum computation for solving time-dependent Hamiltonian dynamics in the short term and midterm, assuming analog errors can be made low enough and coherence times long enough to solve problems of practical interest.

Quantum algorithms & computation↗
NASA NTRS1984

Anomalously high potentials observed on ISEE

Data from the two electric field experiments and from the plasma composition experiment on ISEE-1 show that the spacecraft charged to close to -70 V in sunlight at about 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of some -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. Potential barriers can be formed because of differential charging on the spacecraft or because of the presence of space charge. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely, if these precautions were effective. Modeling of this event is required to determine if the barrier was produced by the presence of space charge.

Whipple, E. C.↗
NASA NTRS1987

Quadrennial review of the magnetotail

The findings of research conducted on the magnetotail in the years 1983-1986 are presented. The topics discussed include observations of the distant (between 60 and 220 earth radii) and the near-earth (earthward of 35 earth radii) magnetotail regions by the ISEE l, 2, and 3 and IMP 8 spacecraft, and magnetotail theory and modeling. These studies established the association between substorms and plasmoids in the deep tail and the linkage between the magnetosphere and the ionosphere via field-aligned currents and electric fields.

Huang, C. Y.↗
NASA NTRS1989

Modeling of an interplanetary disturbance event tracked by the interplanetary scintillation method

The interplanetary disturbance event of August 25-29, 1978 was modeled in an attempt to reproduce the corresponding interplanetary scintillation observations and simultaneous ISEE-3 satellite data. A shock wave generated from the region of a disappearing filament on August 23 is shown to account for the observed shock wave structure, but not the broad high-speed stream behind the shock wave. A shock wave generated by the sudden activation of the coronal hole on the same day is able to account for the high-speed stream.

Akasofu, S.-I.↗
DOE OSTI2021

Ice, glass, and solid phases in artificial spin systems with quenched disorder

We present a numerical study on a disordered artificial spin-ice system, which interpolates between the long-range ordered square ice and the fully degenerate shakti ice. Starting from the square-ice geometry, disorder is implemented by adding vertical/horizontal magnetic islands to the center of some randomly chosen square plaquettes of the array at different densities. When no island is added, we have ordered square ice. When all square plaquettes have been modified, we obtain shakti ice, which is disordered yet in a topological phase corresponding to the Rys F-model. In between, geometrical frustration due to these additional center spins disrupts the long-range Ising order of square ice, giving rise to a spin-glass regime at low temperatures. The artificial spin system proposed in our work provides an experimental platform to study the interplay between quenched disorder and geometrical frustration.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1984

Ionic charge state measurements during He(+)-rich solar particle events

Ionic charge state measurements of carbon, oxygen, and iron in He(+)-rich energetic particle events are presented. The data have been obtained with the Max-Planck-Institut/University of Maryland sensor system on the ISEE 3 spacecraft. The ionic charge states cannot be explained in terms of a model in which the coronal temperature determines a charge equilibrium which is subsequently frozen-in nor in terms of charge exchange during transition through coronal matter after acceleration. It is concluded that the acceleration and probably also the injection process is biased against particles with high mass-to-charge ratios. The plasma injected into the acceleration process must consist of material of cold (not greater than 8.5 x 10 to the 4th K) as well as hot (2.5 x 10 to the 6th K) origin. The cold material must be more abundant than the hot material.

Hovestadt, D.↗
NASA NTRS1987

High spacecraft potentials on ISEE-1 in sunlight

Data from two electric field experiments and from the plasma composition experiment on ISEE-1 show that the spacecraft charged to close to -70 V in sunlight at about 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of some -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. Potential barriers can be formed by differential charging on the spacecraft or by the presence of space charge. The stringent electrostatic cleanliness specifications imposed on ISEE made the presence of differential charging seem unlikely, if these precautions were effective. Modeling of the event to determine if the barrier was produced by the presence of space charge suggested that this could not explain the observed barrier. The angular shape of the distribution could be successfully modeled as a product of differential charging on the solar arrays. This implies that the conductive coating was not completely effective in preventing differential charging, and that differential charging did occur.

Whipple, E. C., Jr.↗
NASA NTRS1985

A simple model for the formation of 'reflected', 'intermediate', and 'diffuse' ion distributions upstream of earth's bow shock

Detailed energetic ion and low-frequency wave experiments on ISEE 1, 2, and 3, have established correlations between the types of ion populations and waves observed to exist in the earth's foreshock region. The present calculation has the objective to quantitatively test the picture obtained for the earth's foreshock region. An analysis is conducted of the coupled spatial and temporal evolution of upstream protons and hydromagnetic waves by means of a simple model in which the protons are represented by counterstreaming beams which resonate with hydromagnetic waves, exciting the outward propagating modes and damping the inward propagating modes at a single wave number.

Lee, M. A.↗
NASA NTRS1992

ISEE 3 plasmoid and TCR observations during an extended interval of substorm activity

On April 9-11, 1983, the ISEE 3 spacecraft was continuously located within the earth's magnetotail for more than 36 hours at downstream distances of X = -76 to -80 R(e). During this span of time, 12 major intervals of substorm activity were observed in the AL index with good ISEE 3 telemetry coverage for 11 of them. In addition, there were two small substorms outside of these intervals, both with complete observations in the distant tail. This unusual ISEE 3 data set provides a unique opportunity to test the predictions of the near-earth neutral line model. In particular, the hypothesis that energy stored in the tail lobes during the growth phase is later dissipated, in part, through the release of one or more plasmoids following expansion phase onset is examined. Clear growth phase enhancements in the lobe magnetic field intensity preceded the onsets of nine of the substorms. Plasmoids, or their lobe signatures, traveling compression regions (TCRs), were observed at ISEE 3 in association with all 11 of the major substorm intervals for which there were ISEE observations, as well as for the two small substorms. No plasmoids or TCRs were observed in the absence of substorm activity. If these ISEE 3 observations are representative, then the release of plasmoids down the tail may be a feature common to all substorms.

Slavin, J. A.↗
NASA NTRS1994

A test of source-surface model predictions of heliospheric current sheet inclination

The orientation of the heliospheric current sheet predicted from a source surface model is compared with the orientation determined from minimum-variance analysis of International Sun-Earth Explorer (ISEE) 3 magnetic field data at 1 AU near solar maximum. Of the 37 cases analyzed, 28 have minimum variance normals that lie orthogonal to the predicted Parker spiral direction. For these cases, the correlation coefficient between the predicted and measured inclinations is 0.6. However, for the subset of 14 cases for which transient signatures (either interplanetary shocks or bidirectional electrons) are absent, the agreement in inclinations improves dramatically, with a correlation coefficient of 0.96. These results validate not only the use of the source surface model as a predictor but also the previously questioned usefulness of minimum variance analysis across complex sector boundaries. In addition, the results imply that interplanetary dynamics have little effect on current sheet inclination at 1 AU. The dependence of the correlation on transient occurrence suggests that the leading edge of a coronal mass ejection (CME), where transient signatures are detected, disrupts the heliospheric current sheet but that the sheet re-forms between the trailing legs of the CME. In this way the global structure of the heliosphere, reflected both in the source surface maps and in the interplanetary sector structure, can be maintained even when the CME occurrence rate is high.

Burton, M. E.↗
DOE OSTI2021

Single-ion anisotropy is necessary and appropriate to study the magnetic behavior of ${\mathrm{Tb}}^{3+}$ moments with ${J}_{\text{eff}}=\frac{1}{2}$ on the honeycomb lattice in ${\mathrm{Tb}}_{2}{\mathrm{Ir}}_{3}{\mathrm{Ga}}_{9}$

By developing models of increasing complexity, we show that a model without single-ion anisotropy (SIA) cannot explain the magnetic properties of J eff = 1 / 2 Tb 3+ moments in the orthorhombically distorted, honeycomb material Tb 2 Ir 3 Ga 9 . In four different models for the magnetization of a single honeycomb layer, the only sources of anisotropy are symmetric exchange interactions J nαβ = J nβα along three different bonds n , an anisotropic $\underline{g}$ tensor, and a Dzyalloshinskii-Moriya interaction (asymmetric exchange) that produces the observed canted moment along b . With 21 parameters, the best such model yields χ 2 = 0.065 , which is substantially smaller than χ 2 = 0.112 obtained using a Heisenberg model containing six parameters including easy-axis anisotropy. However, models without SIA fail to reproduce the linear dependence of the magnetization with a field perpendicular to the Ising axis while predicting a saturation magnetization that is far too low. Due to the complex crystal-field environments, we argue that SIA is necessary to study low-symmetry, three-dimensional J eff = 1 / 2 materials containing Tb 3+ ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1983

A study of the temporal and spectral characteristics of gamma ray bursts

Gamma-ray burst data obtained from the ISEE-3 Gamma Ray Burst Spectrometer and the Solar Maximum Mission's Hard X-ray Burst Spectrometer (HXRBS) were analyzed to yield information on burst temporal and spectral characteristics. A Monte Carlo approach was used to simulate the HXRBS response to candidate spectral models. At energies above about 100 keV, the spectra are well fit by exponential forms. At lower energies, 30 keV to 60 keV, depressions below the model continua are apparent in some bursts. The depressions are not instrumental or data-reduction artifacts. The event selection criterion of the ISEE-3 experiment is based on the time to accumulate a present number of photons rather than the photon count per unit time and is consequently independent of event duration for a given burst intensity, unlike most conventional systems. As a result, a significantly greater percentage of fast, narrow events have been detected. The ratio of count rates from two ISEE-3 detectors indicates that bursts with durations or approx. one second have much softer spectra than longer bursts.

Norris, J.↗