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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Coupling-dependent antiferromagnetic-ferromagnetic ordering in a pinwheel artificial spin ice

Nanopatterned magnetic thin films offer a platform for exploration of tailored magnetic properties such as emergent long-range order. A prominent example is artificial spin ice (ASI), where an arrangement of nanoscale magnetic elements, acting as macrospins, interact via their dipolar fields. In this study, we discuss the transition from antiferromagnetic (AFM) to ferromagnetic (FM) long-range order in a square lattice ASI as the magnetic elements are gradually rotated through 45⁢° to a “pinwheel” configuration. The AFM-FM transition is observed experimentally using synchrotron radiation x-ray spectromicroscopy and occurs for a certain rotation angle of the nanomagnets, dependent on the dipolar coupling strength determined by the separation of the magnets in the lattice. Large-scale magnetic dipole simulations show that the point-dipole approximation fails to capture the correct AFM-FM transition angle. However, excellent agreement with experimental data is obtained using a dumbbell-dipole model, which better reflects the actual dipolar fields of the magnets. This model also explains the coupling dependence of the transition angle, another feature not captured by the point-dipole model. Our findings resolve a discrepancy between measurement and theory in previous work on “pinwheel” ASIs and establish the coupling dependence of the AFM-FM transition. The revised dipole model, with a more accurate representation of the stray field, offers more precise control of magnetic order in artificial spin systems.

Artificial spin ice↗
DOE OSTI2016

Relativistic Anandan quantum phase and the Aharonov–Casher effect under Lorentz symmetry breaking effects in the cosmic string spacetime

From the modified Maxwell theory coupled to gravity, we establish a possible scenario of the violation of the Lorentz symmetry and write an effective metric for the cosmic string spacetime. Then, we investigate the arising of an analogue of the Anandan quantum phase for a relativistic Dirac neutral particle with a permanent magnetic dipole moment in the cosmic string spacetime under Lorentz symmetry breaking effects. Besides, we analyse the influence of the effects of the Lorentz symmetry violation and the topology of the defect on the Aharonov–Casher geometric quantum phase in the nonrelativistic limit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Signature of a spin-up magnetar from multi-band afterglow rebrightening of GRB 100814A

In recent years, more and more gamma-ray bursts (GRBs) with late rebrightenings in their multi-band afterglows have revealed the late-time activity of their central engines. GRB 100814A is a special case among the well-sampled events, with complex temporal and spectral evolution. The single power-law shallow decay index of the optical light curve observed by GROND between 640 s and 10 ks is α{sub opt}=0.57±0.02, which apparently conflicts with expectations from the simple external shock model. In particular, there is remarkable rebrightening in the optical to near-infrared bands at late times, challenging the external shock model with synchrotron emission coming from the interaction of the blast wave with the surrounding interstellar medium. In this paper, we invoke a magnetar with spin evolution to explain the complex multi-band afterglow emission of GRB 100814A. The initial shallow decay phase in the optical bands and the plateau in the X-ray can be explained as being due to energy injection from a spin-down magnetar. At late times, with materials from the fall-back disk falling onto the central object of the burster, the angular momentum of the accreted materials is transferred to the magnetar, which leads to a spin up process. As a result, the magnetic dipole radiation luminosity will increase, resulting in significant rebrightening of the optical afterglow. We show that the model can well reproduce the observed multi-band afterglow emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Comprehensive tracking study for the H-dipoles and common magnets in the splitter sections of the Cornell/Brookhaven Energy-Recovery-Linac Test Accelerator

The Cornell-Brookhaven Energy-Recovery-Linac Test Accelerator will have two splitter sections responsible for and guiding beams of 42, 78, 114, and 150 MeV energies between the Fixed-Field Alternating Gradient return loop and the Main Linac Cryomodule [6], correcting optics, and providing path length adjustments. Modeling of all 36 H-dipole magnets under contract with Elytt Energy has been completed. Four common dipoles, two of which are needed for next year’s Fractional Arc Test, will be added to the order with Elytt. The design of these magnets is underway. This report describes the findings of the tracking studies of the 36 H-dipoles and gives the status of the common dipoles.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Synthesis, Characterization and Comparative Luminescence Studies of Rare-Earth-Doped Gd{sub 2}O{sub 3} Nanoparticles

A facile direct precipitation method was used for the synthesis of luminescence nanomaterial. Gd{sub 2}O{sub 3} doped with rare earth element Eu{sup 3+} is synthesized by polyol route. The synthesized nanoparticles show their characteristic red emission. The nanoparticles are characterized by x-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and photoluminescence (PL) study. The synthesized nanoparticles are spherical particles with ~ 30 nm size. The photoluminescence studies show the characteristic Eu{sup 3+} red emission. The PL study shows the intensity of the magnetic dipole transition ({sup 5}D{sub 0}→ {sup 7}F{sub 1}) at 592 nm compared to that of the electronic dipole transition ({sup 5}D{sub 0}→ {sup 7}F{sub 2}) at 615 nm. The nanomaterials can show significant application in various display devices and biomedical applications for tracking.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Diffractive Hyperbola of a Skin Layer

Based on an analysis of physics of the phase transition from the quasistatic state field to the running wave field of elementary electric and magnetic dipoles located in absorbing media, it is concluded that the skin layer is formed at the boundary of this phase transition. The possibility is considered of obtaining the diffractive hyperbola of the skin layer and its subsequent application for sensing of objects in strongly absorbing media.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

First Detection of Sign-reversed Linear Polarization from the Forbidden [O I] 630.03 nm Line

We report on the detection of linear polarization of the forbidden [O i] 630.03 nm spectral line. The observations were carried out in the broader context of the determination of the solar oxygen abundance, an important problem in astrophysics that still remains unresolved. We obtained spectro-polarimetric data of the forbidden [O i] line at 630.03 nm as well as other neighboring permitted lines with the Solar Optical Telescope of the Hinode satellite. A novel averaging technique was used, yielding very high signal-to-noise ratios in excess of 10{sup 5}. We confirm that the linear polarization is sign-reversed compared to permitted lines as a result of the line being dominated by a magnetic dipole transition. Our observations open a new window for solar oxygen abundance studies, offering an alternative method to disentangle the Ni i blend from the [O i] line at 630.03 nm that has the advantage of simple LTE formation physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

FINGERPRINTS OF GALACTIC LOOP I ON THE COSMIC MICROWAVE BACKGROUND

We investigate possible imprints of galactic foreground structures such as the ''radio loops'' in the derived maps of the cosmic microwave background. Surprisingly, there is evidence for these not only at radio frequencies through their synchrotron radiation, but also at microwave frequencies where emission by dust dominates. This suggests the mechanism is magnetic dipole radiation from dust grains enriched by metallic iron or ferrimagnetic molecules. This new foreground we have identified is present at high galactic latitudes, and potentially dominates over the expected B-mode polarization signal due to primordial gravitational waves from inflation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Spin polarization through axially chiral linkers: Length dependence and correlation with the dissymmetry factor

Abstract The chiral‐induced spin selectivity (CISS) effect relates to the spin‐selective electron transport through chiral molecules; therefore, the chiral molecules act as spin filters. In past studies, correlation was found between the magnitude of the spin filtering and the intensity of the circular dichroism (CD) spectrum (the first Compton peak) of the molecules. Since the intensity of the CD peak relates to both the magnitude of the electric and magnetic dipole transitions, it was not clear which of these properties correlate with the CISS effect. This work aims at addressing this question. By studying the spin‐dependent conduction and the CD spectra of the thiol‐functionalized enantiopure binaphthalene (BINAP) and ternaphthalene (TERNAP), we found that both BINAP and TERNAP exhibit a similar spin polarization of 50%, despite the first Compton peak in TERNAP being almost twice as intense as the peak in BINAP. These results can be explained by the similar values of their anisotropy (or dissymmetry) factor, g abs , which is proportional to the magnetic transition dipole moment. Hence, we concluded that the CISS effect is proportional to the transition dipole moment in chiral molecules, namely, to the dissymmetry factor.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Bending of electromagnetic waves in all-dielectric particle array waveguides

We propose and demonstrate experimentally an alternative approach for realizing subwavelength photonic structures, exploiting the waveguiding properties of chains of high-index dielectric disks with both electric and magnetic dipole resonances. We reveal that the electromagnetic energy can be efficiently guided through sharp corners by means of the mode polarization conversion at waveguide bends. We confirm experimentally the guidance through a 90° bend in the microwave frequency range.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Upper limits to the magnetic field in central stars of planetary nebulae

More than about 20 central stars of planetary nebulae (CSPNs) have been observed spectropolarimetrically, yet no clear, unambiguous signal of the presence of a magnetic field in these objects has been found. We perform a statistical (Bayesian) analysis of all the available spectropolarimetric observations of CSPN to constrain the magnetic fields in these objects. Assuming that the stellar field is dipolar and that the dipole axis of the objects is oriented randomly (isotropically), we find that the dipole magnetic field strength is smaller than 400 G with 95% probability using all available observations. The analysis introduced allows integration of future observations to further constrain the parameters of the distribution, and it is general, so that it can be easily applied to other classes of magnetic objects. We propose several ways to improve the upper limits found here.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Achromat Design for Multi-Pulse Test Line

This note describes the design of a 90° achromatic bend on DARHT Axis 2 to support multi-pulse target studies. The achromatic bend consists of two 45° dipole magnets with a focusing quadrupole centered between the dipoles. The optical design of the achromat is described followed by a discussion of the sensitivity to space charge and variations in the beam energy. The preliminary design of the magnets is then described with a description of the electro-mechanical parameters.

42 ENGINEERING↗
DOE OSTI2016

Collider study on the loop-induced dark matter mediation

Collider experiments are one of the most promising ways to constrain Dark Matter (DM) interactions. For DM couplings involving light mediators, especially for the loop-mediated interactions, a meaningful interpretation of the results requires to go beyond effective field theory. In this note we discuss the study of the magnetic dipole interacting DM, focusing on a model with anarchic dark flavor structure. By including the momentum-dependent form factors that mediate the coupling – given by the Dark Penguin – in collider processes, we study bounds from monophoton, diphoton, and non-pointing photon searches at the LHC. We also compare our results to constraints from the direct detection experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

BINARY NEUTRON STAR MERGERS: A JET ENGINE FOR SHORT GAMMA-RAY BURSTS

We perform magnetohydrodynamic simulations in full general relativity (GRMHD) of quasi-circular, equal-mass, binary neutron stars that undergo merger. The initial stars are irrotational, n = 1 polytropes and are magnetized. We explore two types of magnetic-field geometries: one where each star is endowed with a dipole magnetic field extending from the interior into the exterior, as in a pulsar, and the other where the dipole field is initially confined to the interior. In both cases the adopted magnetic fields are initially dynamically unimportant. The merger outcome is a hypermassive neutron star that undergoes delayed collapse to a black hole (spin parameter a / M {sub BH} ∼ 0.74) immersed in a magnetized accretion disk. About 4000 M ∼ 60( M {sub NS}/1.625 M {sub ⊙}) ms following merger, the region above the black hole poles becomes strongly magnetized, and a collimated, mildly relativistic outflow—an incipient jet—is launched. The lifetime of the accretion disk, which likely equals the lifetime of the jet, is Δ t ∼ 0.1 ( M {sub NS}/1.625 M {sub ⊙}) s. In contrast to black hole–neutron star mergers, we find that incipient jets are launched even when the initial magnetic field is confined to the interior of the stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

On a relation of the angular frequency to the Aharonov–Casher geometric phase in a quantum dot

By analysing the behaviour of a neutral particle with permanent magnetic dipole moment confined to a quantum dot in the presence of a radial electric field, Coulomb-type and linear confining potentials, then, an Aharonov–Bohm-type effect for bound states and a dependence of the angular frequency of the system on the Aharonov–Casher geometric phase and the quantum numbers associated with the radial modes, the angular momentum and the spin are obtained. In particular, the possible values of the angular frequency and the persistent spin currents associated with the ground state are investigated in two different cases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

THE INCLINATION ANGLE AND EVOLUTION OF THE BRAKING INDEX OF PULSARS WITH PLASMA-FILLED MAGNETOSPHERE: APPLICATION TO THE HIGH BRAKING INDEX OF PSR J1640–4631

The recently discovered rotationally powered pulsar PSR J1640–4631 is the first to have a braking index measured, with high enough precision, that is greater than 3. An inclined magnetic rotator in vacuum or plasma would be subject not only to spin-down but also to an alignment torque. The vacuum model can address the braking index only for an almost orthogonal rotator, which is incompatible with the single-peaked pulse profile. The magnetic dipole model with the corotating plasma predicts braking indices between 3 and 3.25. We find that the braking index of 3.15 is consistent with two different inclination angles, 18.°5 ± 3° and 56° ± 4°. The smaller angle is preferred given that the pulse profile has a single peak and the radio output of the source is weak. We infer the change in the inclination angle to be at the rate −0.°23 per century, three times smaller in absolute value than the rate recently observed for the Crab pulsar.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Slow Orbital Evolution of the Accreting Millisecond Pulsar IGR J0029+5934

The accreting millisecond pulsars IGR J00291+5934 and SAX J1808.4–3658 are two compact binaries with very similar orbital parameters. The latter has been observed to evolve on a very short timescale of ∼70 Myr, which is more than an order of magnitude shorter than expected. There is an ongoing debate on the possibility that the pulsar spin-down power ablates the companion, generating large amounts of mass-loss in the system. Therefore it is interesting to study whether IGR J00291+5934 does show a similar behavior as its twin system SAX J1808.4–3658. In this work we present the first constraints on the orbital period derivative of IGR J00291+5934. By using XMM-Newton data recorded during the 2015 outburst and adding the previous results of the 2004 and 2008 outbursts, we are able to measure a 90% confidence level allowed range of −5×10{sup −13}< P-dot {sub b}<6×10{sup −13}. This implies that the binary is evolving on a timescale longer than 0.5 Gyr, which is compatible with the expected timescale of mass transfer driven by angular momentum loss via gravitational radiation. We discuss the scenario in which the power loss from magnetic dipole radiation of the neutron star is hitting the companion star. If this model is applied to SAX J1808.4–3658, then the difference in orbital behavior can be ascribed to a different efficiency for the conversion of the spin-down power into energetic relativistic pulsar wind and X-ray/gamma-ray radiation for the two pulsars, with IGR J00291+5934 requiring an extraordinarily low efficiency of less than ∼5% to explain the observations. We thus conclude that the pulsar wind ablation model is unlikely to be an accurate description of the mechanism driving the orbital evolution of the two systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Protection layers on a superconducting microwave resonator toward a hybrid quantum system

We propose a protection scheme of a superconducting microwave resonator to realize a hybrid quantum system, where cold neutral atoms are coupled with a single microwave photon through magnetic dipole interaction at an interface inductor. The evanescent field atom trap, such as a waveguide/nanofiber atom trap, brings both surface-scattered photons and absorption-induced broadband blackbody radiation which result in quasiparticles and a low quality factor at the resonator. A proposed multiband protection layer consists of pairs of two dielectric layers and a thin nanogrid conductive dielectric layer above the interface inductor. We show numerical simulations of quality factors and reflection/absorption spectra, indicating that the proposed multilayer structure can protect a lumped-element microwave resonator from optical photons and blackbody radiation while maintaining a reasonably high quality factor.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗