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At least 667 records · Page 37

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NASA NTRS1984

Reconnection at the earth's magnetopause - Magnetic field observations and flux transfer events

Theoretical models of plasma acceleration by magnetic-field-line reconnection at the earth magnetopause and the high-resolution three-dimensional plasma measurements obtained with the ISEE satellites are compared and illustrated with diagrams, graphs, drawings, and histograms. The history of reconnection theory and the results of early satellite observations are summarized; the thickness of the magnetopause current layer is discussed; problems in analyzing the polarization of current-layer rotation are considered; and the flux-transfer events responsible for periods of patchy reconnection are characterized in detail. The need for further observations and refinements of the theory to explain the initiation of reconnection and identify the mechanism determining whether it is patchy or steady-state is indicated.

Russell, C. T.↗

NASA NTRS1987

Planetary science - 1983-1986

Results obtained in the U.S. planetary science programs during 1983-1986 are discussed in a brief review. Topics examined include Halley observations and probes, the flyby of comet Giacobini-Zinner by ISEE-3 (ICE), the Voyager 2 encounter with Uranus, analysis of Voyager 1 and 2 data from the Jupiter and Saturn systems, Pioneer Venus Orbiter observations, theoretical models of lunar evolution, and antarctic meteorites of lunar and perhaps Martian origin.

Clifford, Stephen M.↗

DOE OSTI2018

Forced Synchronization of Electroconvective Roll Oscillations in Nematic Liquid Crystals

The forced phase locking in a system of the oscillating electroconvective rolls that form in a nematic liquid crystal layer in a dc electric field is studied. As a result of the action of an additive ac electric field with a small amplitude, the system of oscillators is found to be divided into clusters, where oscillations are fully phase locked. The electroconvective rolls in neighboring clusters oscillate in antiphase and the clusters are separated by Ising walls. The phase locking is shown to be maximal at the forcing frequency that is close to the double frequency of the natural oscillations of rolls. A model is proposed to describe spatially distributed phase oscillators, and it takes into account the symmetries of a system of electroconvective rolls and external forcing. The results of numerical simulations agree well with the experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1981

Non-E x B ordered ion beams upstream of the earth's bow shock

The unexpected appearance of spin modulations in the fixed voltage electrostatic analyzer detectors on ISEE 1 and 2 has made it possible to study the plasma properties of the upstream ions in high time resolution. Using an isotropic flowing Maxwellian distribution to model the count rate modulations, estimates have been obtained of the local plasma temperature and three-dimensional flow velocity of the observed upstream ion population. It is found that in almost all of the observations of upstream particles there exist beam-like ions with temperatures in the range 5-80 eV. Their flow velocities cannot be ordered by E x B. This last point separates these observations from the previously reported reflected and diffuse populations of upstream ions. Mechanisms that can gyrophase bunch the ions reflected at the bow shock are discussed as a method of explaining the data.

Gurgiolo, C.↗

NASA NTRS2017

Radiation Hardening by Software Techniques on FPGAs: Flight Experiment Evaluation and Results

We present our work on implementing Radiation Hardening by Software (RHBSW) techniques on the Xilinx Virtex5 FPGAs PowerPC 440 processors on the SpaceCube 2.0 platform. The techniques have been matured and tested through simulation modeling, fault emulation, laser fault injection and now in a flight experiment, as part of the Space Test Program- Houston 4-ISS SpaceCube Experiment 2.0 (STP-H4-ISE 2.0). This work leverages concepts such as heartbeat monitoring, control flow assertions, and checkpointing, commonly used in the High Performance Computing industry, and adapts them for use in remote sensing embedded systems. These techniques are extremely low overhead (typically <1.3%), enabling a 3.3x gain in processing performance as compared to the equivalent traditionally radiation hardened processor. The recently concluded STP-H4 flight experiment was an opportunity to upgrade the RHBSW techniques for the Virtex5 FPGA and demonstrate them on-board the ISS to achieve TRL 7. This work details the implementation of the RHBSW techniques, that were previously developed for the Virtex4-based SpaceCube 1.0 platform, on the Virtex5-based SpaceCube 2.0 flight platform. The evaluation spans the development and integration with flight software, remotely uploading the new experiment to the ISS SpaceCube 2.0 platform, and conducting the experiment continuously for 16 days before the platform was decommissioned. The experiment was conducted on two PowerPCs embedded within the Virtex5 FPGA devices and the experiment collected 19,400 checkpoints, processed 253,482 status messages, and incurred 0 faults. These results are highly encouraging and future work is looking into longer duration testing as part of the STP-H5 flight experiment.

Hybrid Flight Architectures↗

DOE OSTI2015

Non-monotonic resonance in a spatially forced Lengyel-Epstein model

We study resonant spatially periodic solutions of the Lengyel-Epstein model modified to describe the chlorine dioxide-iodine-malonic acid reaction under spatially periodic illumination. Using multiple-scale analysis and numerical simulations, we obtain the stability ranges of 2:1 resonant solutions, i.e., solutions with wavenumbers that are exactly half of the forcing wavenumber. We show that the width of resonant wavenumber response is a non-monotonic function of the forcing strength, and diminishes to zero at sufficiently strong forcing. We further show that strong forcing may result in a π/2 phase shift of the resonant solutions, and argue that the nonequilibrium Ising-Bloch front bifurcation can be reversed. We attribute these behaviors to an inherent property of forcing by periodic illumination, namely, the increase of the mean spatial illumination as the forcing amplitude is increased.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2025

Nature of quantum criticality in the Ising ferromagnet TbV 6 Sn 6

TbV 6 Sn 6 is a topological metal where ferromagnetic Tb ions with strong uniaxial magnetic anisotropy interact with V kagome layers. Inelastic neutron scattering (INS) measurements show that the Tb ions adopt an Ising doublet ground state. Here, we consider whether a transverse magnetic field can drive TbV 6 Sn 6 toward a quantum critical point, providing a rare example of transverse-field Ising criticality in a metallic compound. High-field magnetization measurements reveal a first-order-like spin-reorientation transition at 25.6 T. Our INS-based magnetic model finds that this is caused by an avoided crossing of an excited-state singlet with the ground-state doublet. Surprisingly, our model predicts that quantum critical and tricritical points are accessible within the range of experimentally determined model parameters and may be reached by varying the direction of an applied magnetic field.

36 MATERIALS SCIENCE↗

DOE OSTI2019

U 2 Ni 2 Sn and the origin of magnetic anisotropy in uranium compounds

Here, U 2 Ni 2 Sn is a member of a large family of intermetallic compounds with the tetragonal Mo 2 FeB 2 crystal structure. It orders antiferromagnetically at 25 K with propagation vector $q = (0, 0, \frac{1}{2})$. Magnetization, magnetoacoustic, and neutron-diffraction experiments on a single crystal provide evidence that the uranium moments align parallel to the $c$ axis with the anisotropy energy of ≈170 K, indicating that U 2 Ni 2 Sn can be classified as an Ising system. The results are at variance with previous studies on polycrystals, which indicated different magnetic structure, and which were incompatible with the $5f - 5f$ two-ion anisotropy model dominant in most U band systems. High-field magnetization studies exhibit a weak linear response for fields along the basal plane up to the highest field applied (60 T), while the $c$-axis magnetization curve exhibits three metamagnetic transitions at approximately 30, 39, and 50 T. The U magnetic moments of $0.87 μ_B$, the low magnetic entropy, and the enhanced Sommerfeld coefficient $γ$ = 187 mJ/mol f.u.K 2 suggest that U 2 Ni 2 Sn can be classified as an itinerant antiferromagnet with strong electron-electron correlations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1986

A theoretical and empirical study of the response of the high latitude thermosphere to the sense of the 'Y' component of the interplanetary magnetic field

Patterns of magnetospheric energetic plasma precipitation as a function of the Y component of the Interplanetary Magnetic Field (IMF) are studied. The development of a three-dimensional, time-dependent global thermospheric model using a polar conversion electric field with a dependence on the Y component of the IMF to evaluate thermospheric wind circulation is examined. Thermospheric wind data from the ISEE-3 satellite, Dynamics Explorer-2 satellite, and a ground-based Fabry-Perot interferometer in Kiruna, Sweden, collected on December 1, 2, 6, 25, 1981 and February 12, 13, 1982 are described. The observed data and simulations of polar thermospheric winds are compared. In the Northern Hemisphere a strong antisunward ion flow on the dawn side of the geomagnetic polar cap is observed when the BY is positive, and the flow is detected on the dusk side when the BY is negative. It is concluded that the strength and direction of the IMF directly control the transfer of solar wind momentum and energy to the high latitude thermosphere.

Rees, D.↗

NASA NTRS1995

Unusual locations of Earth's bow shock on September 24 - 25, 1987: Mach number effects

International Sun Earth Explorer 1 (ISEE 1) and Interplanetary Monitoring Platform 8 (IMP 8) data are used to identify 19 crossings of Earth's bow shock during a 30-hour period following 0000 UT on September 24, 1987. Apparent standoff distances for the shock are calculated for each crossing using two methods and the spacecraft location; one method assumes the average shock shape, while the other assumes a ram pressure-dependent shock shape. The shock's apparent standoff distance, normally approximately 14 R(sub E), is shown to increase from near 10 R(sub E) initially to near 19 R(sub E) during an 8-hour period, followed by an excursion to near 35 R(sub E) (where two IMP 8 shock crossings occur) and an eventual return to values smaller than 19 R(sub E). The Alfven M(sub A) and fast magnetosonic M(sub ms). Mach numbers remain above 2 and the number density above 4/cu cm for almost the entire period. Ram pressure effects produce the initial near-Earth shock location, whereas expansions and contractions of the bow shock due to low Mach number effects account, qualitatively and semiquantitatively, for the timing and existence of almost all the remaining ISEE crossings and both IMP 8 crossings. Significant quantitative differences exist between the apparent standoff distances for the shock crossings and those predicted using the observed plasma parameters and the standard model based on Spreiter et al.'s (1966) gasdynamic equation. These differences can be explained in terms of either a different dependence of the standoff distance on Mach number at low M(sub A) and M(sub ms), or variations in shock shape with M(sub A) and M(sub ms) (becoming increasingly "puffed up" with decreasing M(sub A) and M(sub ms), as expected theoretically), or by a combination of both effects.

Cairns, Iver H.↗

DOE OSTI2025

Simulating spin dynamics of supersolid states in a quantum Ising magnet

Motivated by a recent experimental study on the quantum Ising magnet K 2 Co(SeO 3 ) 2 that presented spectroscopic evidence of zero-field supersolidity (Chen et al., arXiv:2402.15869), we simulate the excitation spectrum of the corresponding microscopic XXZ model for the compound, using the recently developed excitation ansatz for infinite projected entangled-pair states. Here, we map out the ground state phase diagram and compute the dynamical spin structure factors across a range of magnetic field strengths, focusing especially on the two supersolid phases found near zero and saturation fields. Our simulated excitation spectra for the zero-field supersolid “Y” phase are in excellent agreement with the experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Stabilizing Fluctuating Spin-Triplet Superconductivity in Graphene via Induced Spin-Orbit Coupling

A recent experiment showed that a proximity-induced Ising spin-orbit coupling enhances the spin-triplet superconductivity in Bernal bilayer graphene. Here, in this work, we show that, due to the nearly perfect spin rotation symmetry of graphene, the fluctuations of the spin orientation of the triplet order parameter suppress the superconducting transition to nearly zero temperature. Our analysis shows that both an Ising spin-orbit coupling and an in-plane magnetic field can eliminate these low-lying fluctuations and can greatly enhance the transition temperature, consistent with the recent experiment. Our model also suggests the possible existence of a phase at small anisotropy and magnetic field which exhibits quasilong-range ordered spin-singlet charge 4⁢e superconductivity, even while the triplet 2⁢e superconducting order only exhibits short-ranged correlations. Finally, we discuss relevant experimental signatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Deviation from the dipole-ice model in the spinel spin-ice candidate MgEr 2 Se 4

In spin-ice research, small variations in structure or interactions drive a multitude of different behaviors, yet the collection of known materials relies heavily on the “227” pyrochlore structure. Here, we present thermodynamic, structural, and inelastic-neutron-scattering data on a spin-ice material, MgEr 2 Se 4 , which contributes to the relatively underexplored family of rare-earth spinel chalcogenides. X-ray and neutron diffraction confirm a normal spinel structure and place Er 3+ moments on an ideal pyrochlore sublattice. Measurement of crystal electric field excitations with inelastic neutron scattering confirms that the moments have perfect Ising character, and further identifies the ground-state Kramers doublet as having dipolar-octupolar form with a significant multipolar character. Heat capacity and magnetic neutron diffuse scattering have icelike features, but are inconsistent with Monte Carlo simulations of the nearest-neighbor and next-nearest-neighbor dipolar spin-ice (DSI) models. A significant remnant entropy is observed as T → 0 K, but again falls short of the full Pauling expectation for DSI, unless significant disorder is added. We show that these observations are fully in line with what has been recently reported for CdEr 2 Se 4 , and point to the importance of quantum fluctuations in these materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Deconfined classical criticality in the anisotropic quantum spin- 1 2 XY model on the square lattice

The anisotropic quantum spin- 1 2 XY model on a linear chain was solved by Lieb, Schultz, and Mattis [] and shown to display a continuous quantum phase transition at the O(2) symmetric point separating two gapped phases with competing Ising long-range order. For the square lattice, the following is known. The two competing Ising ordered phases extend to finite temperatures, up to a boundary where a transition to the paramagnetic phase occurs, and meet at the O(2) symmetric critical line along the temperature axis that ends at a tricritical point at the Berezinskii-Kosterlitz-Thouless transition temperature where the two competing phases meet the paramagnetic phase. We show that the first-order zero-temperature (quantum) phase transition that separates the competing phases as a function of the anisotropy parameter is smoothed by thermal fluctuations into deconfined classical criticality. Published by the American Physical Society 2025

Mudry, Christopher (ORCID:0000000340746758)↗

NASA NTRS2018

CAIDA CUI Confirmation for OMRS & LCC SOCRRATES Emulator and iSEE Upgrade, Operations, & Analysis

This internship has focused on providing solutions for the Customer Avionics Interface Development and Analysis (CAIDA) subsystem. The main emulator that has been used during this internship is the Software-Only CEV (Crew Exploration Vehicle) Risk Reduction Analysis and Test Engineering Simulator (SOCRRATES). This emulator uses advanced math and physics methods to simulate specific points in a mission, such as ascent, entry, and orbit. Exploration Ground Systems (EGS) must ensure that all KSC based ground systems can be properly integrated with the flight vehicle software, therefore, the Modeling and Simulation Branch (NE-XM) of the KSC (Kennedy Space Center) Engineering Directorate supports a virtual environment that simulates the interface between ground systems and the flight vehicle. A primary component in assuring that is knowing whether the emulators have incorporated the correct CUIs (Compact Unique Identifiers) into their system, as well as understanding both the static and dynamic responses of the individual CUIs. Also, an effort for verification of Operational Maintenance Requirements Specifications (OMRS) and Launch Commit Criteria (LCC) that are supported by SOCRRATES for the Orion Crew Module were part of the project tasks this semester. This internship also focused on comparing two different simulation Commercial-off-the-shelf (COTS) products and to determine whether or not a COTS package was a viable replacement for the current software that the iSEE (Immersive Simulations and Engineering Environment) lab uses. Upon research and testing, I found that this software was not feasible for the lab. It could not easily load CAD (Computer-Aided Design) or CREO models, give live feedback while the user is in the environment, and was not compatible with a virtual reality headset, all of which are necessary for the lab.

Bundy, Caleb↗

NASA NTRS1982

Use of the thin sheath approximation for obtaining ion temperatures from the ISEE 1 limited aperture RPA

A procedure for analyzing low-energy (less than approximately 100 eV) ion data from the plasma composition experiment on ISEE 1 is set forth. The method is based on a derived analytic expression for particle flux to a limited aperture retarding potential analyzer (RPA) in the thin sheath approximation, which makes allowance for some effects of a charged spacecraft on plasma particle trajectories. Calculations using simulated data are employed in testing the efficacy and accuracy of the technique. On the basis of an analysis of these calculation results and the mathematical model, the method is seen as being able to provide accurate ion temperatures from all good plasmaspheric RPA data. It is noted that corresponding densities and spacecraft potentials should be accurate when spacecraft potentials are negative but that they are subject to error for positive spacecraft potentials, particularly when ion Mach numbers are much less than 1. An analysis of data from a representative ISEE 1 pass produces a plasmasphere temperature profile that is consistent in overall structure with previous observations.

Comfort, R. H.↗

NASA NTRS1979

Satellite observations of the spatial extent and structure of Pc 3, 4, 5 pulsations near the magnetospheric equator

Simultaneous observations of Pc 3, 4, 5 pulsations by five satellites in the pre-noon local time sector at and near synchronous orbit are examined. The periods of these simultaneous pulsations are not the same at the different observation points. This difference is attributed to site dependent resonant conditions. The spatial properties of the temporal phenomenon are demonstrated with observations by ISEE-1 and -2 as they pass through oscillations in a spatially limited region. Fundamental and second harmonic standing Alfven waves are observed simultaneously on the same field line. The periods are consistent with model predictions when the measured plasma composition, which by mass consists mainly of singly ionized oxygen, is taken into account.

Singer, H. J.↗

NASA NTRS1982

The observation of a coronal transient directed at earth

The paper reports the observation of a large coronal transient that can only be interpreted as a three-dimensional structure. Its form is one which has not been observed before: a gradually expanding, sun-centered disk of excess brightness, whose projected radius increased from 4 to 8 solar radii during 0832-0958 UT on November 27, 1979. This earth-directed transient was the source of an interplanetary shock wave that reached ISEE 3 at 0649 UT, November 30, and earth at 0738 UT, November 30. Fitting the shock speed at ISEE 3 and the average transit speed from the sun to ISEE 3 to a power law of the form V = (V sub 0)(r exp -n), it is found that V sub 0 = 1980 km/s and n = 0.294, in good agreement with shock wave models. The shock speed predicted by the power law at 10 solar radii is 1000 km/s, in good agreement with the estimated frontal speed of the transient.

Howard, R. A.↗