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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Evolution of Intrinsic and Magnetic Field-Induced Magnetic Anisotropies in Strongly Phase-Separated Manganite Thin Films

Single crystalline thin film (∼ 100 nm) of La{sub 0.18}Pr{sub 0.40}Ca{sub 0.42}MnO{sub 3} is grown on (001) oriented LaAlO{sub 3} substrates and the evolution of anisotropy associated with the supercooling behaviour of the magnetic liquid is studied as a function of temperature and magnetic field. The angle-dependent magnetization measurements ascertain that the easy magnetic axis lies in the plane of the film while the hard axis is along the plane normal. The ratio of the easy and hard axes magnetizations (M{sub ||} and M{sub ⊥}) measured at 10 K, viz., M{sub ||}/M{sub ⊥} (10 K) = 2.6, confirms the strongly anisotropic nature of the film. The easy axis ferromagnetic (FM) transition temperature (T{sub C}) is smaller than that along the hard axis. The giant hysteresis in FCC–FCW M–T, which manifests the magnetic liquid behaviour of the strongly phase-separated manganites is appreciably narrowed along the hard axis. The strain glass state is also less dominant along the easy axis. The analysis of the M–H data brings out that the easy axis remanence (M{sub r||}) shows a nonlinear temperature dependence, while the one corresponding to the hard axis (M{sub r⊥}) shows a nearly linear behaviour. The coercivity (H{sub C}) follows a law of the type H{sub C}(T)=H{sub C}(0)(1−AT{sup b}). The value of exponent b ∼ 0.5 for single-domain particles, but in the present case, the best fit to the experimental data yields the exponent b ≈ 0.25 for both H{sub C||} and H{sub C⊥}. The smaller value of the exponent is attributed to the non-canonical nature of the ferromagnetic state and the associated strongly phase-separated nature of the LPCMO thin film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Spontaneous Supercrystal Formation During a Strain‐Engineered Metal–Insulator Transition

Abstract Mott metal–insulator transitions possess electronic, magnetic, and structural degrees of freedom promising next‐generation energy‐efficient electronics. A previously unknown, hierarchically ordered, and anisotropic supercrystal state is reported and its intrinsic formation characterized in‐situ during a Mott transition in a Ca 2 RuO 4 thin film. Machine learning‐assisted X‐ray nanodiffraction together with cryogenic electron microscopy reveal multi‐scale periodic domain formation at and below the film transition temperature ( T Film ≈ 200–250 K) and a separate anisotropic spatial structure at and above T Film . Local resistivity measurements imply an intrinsic coupling of the supercrystal orientation to the material's anisotropic conductivity. These findings add a new degree of complexity to the physical understanding of Mott transitions, opening opportunities for designing materials with tunable electronic properties.

Gorobtsov, Oleg Yu.↗
DOE OSTI2022

RASER MRI: Magnetic resonance images formed spontaneously exploiting cooperative nonlinear interaction

The spatial resolution of magnetic resonance imaging (MRI) is limited by the width of Lorentzian point spread functions associated with the transverse relaxation rate 1/T 2 * . Here, we show a different contrast mechanism in MRI by establishing RASER (radio-frequency amplification by stimulated emission of radiation) in imaged media. RASER imaging bursts emerge out of noise and without applying radio-frequency pulses when placing spins with sufficient population inversion in a weak magnetic field gradient. Small local differences in initial population inversion density can create stronger image contrast than conventional MRI. This different contrast mechanism is based on the cooperative nonlinear interaction between all slices. On the other hand, the cooperative nonlinear interaction gives rise to imaging artifacts, such as amplitude distortions and side lobes outside of the imaging domain. Contrast mechanism and artifacts are explored experimentally and predicted by simulations on the basis of a proposed RASER MRI theory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Topological surface superconductivity in FeSe 0.45 Te 0.55

The engineering of Majorana zero modes in topological superconductors, a paradigm for the realization of topological quantum computing and topology-based devices, has been hampered by the absence of materials with sufficiently large superconducting gaps. Recent experiments, however, have provided enthralling evidence for the existence of topological surface superconductivity in the iron-based superconductor FeSe 0.45 Te 0.55 possessing a full s> ± -wave gap of a few meV. Here, we propose a mechanism for the emergence of topological superconductivity on the surface of FeSe 0.45 Te 0.55 by demonstrating that the interplay between the s ± -wave symmetry of the superconducting gap, surface magnetism, and a Rashba spin–orbit interaction gives rise to robust topological superconducting phases. Moreover, the proposed mechanism explains a series of experimentally observed hallmarks of topological superconductivity, such as the emergence of Majorana zero modes in the center of vortex cores and at the end of line defects, as well as of chiral Majorana edge modes along domain walls. We also propose that the spatial distribution of supercurrents near a domain wall is a characteristic signature measurable via a scanning superconducting quantum interference device that can distinguish between chiral Majorana edge modes and trivial in-gap states.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Magnetization Reversal of Three-Dimensional Nickel Anti-Sphere Arrays

Three-dimensional antisphere arrays (3DAAs) of Ni have been fabricated here using electrochemical deposition into self-assembled polystyrene sphere templates, which offers the advantage of straightforward scalability. Using the first-order reversal curve (FORC) method, the magnetic reversal mechanism is identified from the characteristic features in the FORC distribution. A left-bending boomerang-like feature is observed in the thinnest sample, which transforms to a ridge oriented along the local coercivity H c axis with increasing sample thickness. This transformation identifies a change in the reversal process from an exchange dominated domain-growth reversal to a localized weakly interacting particle-like reversal. Micromagnetic simulations confirm the decrease in domain growth and increase of pinning behaviors as the thickness of the Ni 3DAAs structure increases, providing strong support to the FORC analysis and interpretation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Bistable and Multi-Domain States of α-Fe/(PrDy)(FeCo)B Ferromagnetic Microwires

In this paper, we obtained α-Fe(50 at %)(PrDy)(FeCo)B(48 at %) microwires by extraction of a hanging drop of the (PrDy)(FeCo)B melt in the electron beam. A single microwire with a diameter of 50 μm and a length of 0.8–6 mm and with an amorphous (PrDy)(FeCo)B content of ~48% and a polycrystalline α‑Fe phase of ~52% is shown to have a rectangular narrow magnetic hysteresis loop and, accordingly, a bistable state with a switching field of ~100 Oe. Shortening the wire to ~0.6 mm leads to a sharp deviation from the loop rectangularity and a decrease in the slope of the dependence of magnetization on the field and coercive force to 20 Oe. In the near-surface layers consisting of an amorphous phase (PrDy)(FeCo)B, oriented regions of reverse magnetization are observed. The role of the magnetic dipole interaction in the formation of the magnetic hysteresis loop of chaotic ensembles of microwires with various compositions is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Comparative analysis of KRAS4a and KRAS4b splice variants reveals distinctive structural and functional properties

KRAS, the most frequently mutated oncogene in human cancer, produces two isoforms, KRAS4a and KRAS4b, through alternative splicing. These isoforms differ in exon 4, which encodes the final 15 residues of the G-domain and hypervariable regions (HVRs), vital for trafficking and membrane localization. While KRAS4b has been extensively studied, KRAS4a has been largely overlooked. Our multidisciplinary study compared the structural and functional characteristics of KRAS4a and KRAS4b, revealing distinct structural properties and thermal stability. Position 151 influences KRAS4a’s thermal stability, while position 153 affects binding to RAF1 CRD protein. Nuclear magnetic resonance analysis identified localized structural differences near sequence variations and provided a solution-state conformational ensemble. Notably,KRAS4aexhibits substantial transcript abundance in bile ducts, liver, and stomach, with transcript levels approachingKRAS4bin the colon and rectum. Functional disparities were observed in full-length KRAS variants, highlighting the impact of HVR variations on interaction with trafficking proteins and downstream effectors like RAF and PI3K within cells.

Science & Technology - Other Topics↗
DOE OSTI2019

Mechanism by which Tungsten Oxide Promotes the Activity of Supported V 2 O 5 /TiO 2 Catalysts for NO X Abatement: Structural Effects Revealed by 51 V MAS NMR Spectroscopy

Growing concern for environmental pollutants coupled with an expansion of energy demand has promoted significant interest in technologies to abate contaminating species. Nitrogen oxides are particularly alarming due to their numerous detrimental impacts to the environment and public health, where selective catalytic reduction to inert N 2 is an industrially-relevant mitigation technology. Herein, we provide unique, molecular-level insight on the structure and reactivity of V 2 O 5 (-WO 3 )/TiO 2 catalysts employed at stationary facilities for NO x removal. Detailed catalytic testing, spectroscopy (nuclear magnetic resonance, Raman, and electron paramagnetic resonance), and electronic structure-based predictions of 51 V chemical shifts help clarify the promotional role of tungsten oxide and identify an active site requirement for SCR of NO x . We show that progressive addition of vanadia to the catalyst surface increases the catalytic SCR performance and promotes the formation of larger vanadium domains, demonstrating the proportional relationship of SCR reaction rate to [VO x loading]2 for supported V 2 O 5 /TiO 2 catalysts with increasing surface vanadia coverage. Tungsten oxide incorporation enhances catalyst reactivity which is shown to stem not from electronic effects, but from changes to the vanadium structure as observed spectroscopically. The progressive addition of tungsten oxide to the catalyst surface also increases the catalytic performance and promotes the formation of larger vanadium domains, which are beneficial for catalytic turnover in a two-site model. Further, unique monomeric species are confidently ascribed to distorted tetrahedral and square pyramidal structures, resolving a long-standing uncertainty in literature assignments for the signals. These findings provide strong support for both the dual-site requirement for the SCR reaction and the important structural promotional effect that tungsten offers for mitigation of these harmful pollutants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

High-fidelity, hyper-accurate, and evolved mutants rewire atomic-level communication in CRISPR-Cas9

The high-fidelity (HF1), hyper-accurate (Hypa), and evolved (Evo) variants of the CRISPR-associated protein 9 (Cas9) endonuclease are critical tools to mitigate off-target effects in the application of CRISPR-Cas9 technology. The mechanisms by which mutations in recognition subdomain 3 (Rec3) mediate specificity in these variants are poorly understood. Here, solution nuclear magnetic resonance and molecular dynamics simulations establish the structural and dynamic effects of high-specificity mutations in Rec3, and how they propagate the allosteric signal of Cas9. We reveal conserved structural changes and dynamic differences at regions of Rec3 that interface with the RNA:DNA hybrid, transducing chemical signals from Rec3 to the catalytic His-Asn-His (HNH) domain. The variants remodel the communication sourcing from the Rec3 α helix 37, previously shown to sense target DNA complementarity, either directly or allosterically. This mechanism increases communication between the DNA mismatch recognition helix and the HNH active site, shedding light on the structure and dynamics underlying Cas9 specificity and providing insight for future engineering principles.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Spectral narrowing and spin echo for localized carriers with heavy-tailed L evy distribution of hopping times

We study analytically the free induction decay and the spin echo decay originating from the localized carriers moving between the sites which host random magnetic fields. Due to disorder in the site positions and energies, the on-site residence times, , are widely spread according to the L evy distribution. The power-law tail ∝ τ -1-∝ in the distribution of does not affect the conventional spectral narrowing for α > 2, but leads to a dramatic acceleration of the free induction decay in the domain 2 > α > 1. The next abrupt acceleration of the decay takes place as becomes smaller than 1. In the latter domain the decay does not follow a simple-exponent law. To capture the behavior of the average spin in this domain, we solve the evolution equation for the average spin using the approach different from the conventional approach based on the Laplace transform. Unlike the free induction decay, the tail in the distribution of the residence times leads to the slow decay of the spin echo. The echo is dominated by realizations of the carrier motion for which the number of sites, visited by the carrier, is minimal.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Low-field magnetic anomalies in single crystals of the A-type square-lattice antiferromagnet EuGa 4

The body-centered-tetragonal antiferromagnet EuGa 4 was recently identified as a Weyl nodal-line semimetal that exhibits the topological Hall effect below its reported antiferromagnetic (AFM) ordering temperature T N = 15 – 16.5 K which we find to be T N = 16.4 ( 2 ) K. The Eu +2 ions are located at the corners and body centers of the unit cells. EuGa 4 exhibits A-type antiferromagnetic order below T N , where the Eu 2+ spin-7/2 moments are ferromagnetically aligned in the ab plane with the Eu moments in adjacent Eu planes along the c axis aligned antiferromagnetically. Low-field magnetization versus field M(H ab ) data at T = 2 K with the field aligned in the ab plane are reported that exhibit anomalous positive curvature up to a critical field H c1 at which a second-order transition occurs with H c1 ≈ 0.85 kOe for H∥ [1,1,0] and ≈ 4.8 kOe for H∥[1,0,0]. For larger fields, the linear behavior M ab = χ(T N ) H a b is followed until the critical field H c is reached at which all moments become aligned with the applied field. A theory is formulated for T = 0 K that fits the observed M(H ab ) behavior at T = 2 K well, where domains of A -type AFM order with fourfold rotational symmetry occur in the AFM state in zero field. The moments in the four domains reorient to become almost perpendicular to H ab at H c1 , followed by increasing canting of all moments toward the field with increasing field up to H c which is reported to be 71 kOe. A first-order transition in M(H ab ) at H ab = H c1 is predicted by the theory for T = 0 K when H ab is at a small angle from the [1,0,0] direction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Ferromagnetic glass-coated microwires with good heating properties for magnetic hyperthermia

The heating properties of Fe 71.7 Si 11 B 13.4 Nb 3 Ni 0.9 amorphous glass-coated microwires are explored for prospective applications in magnetic hyperthermia. We show that a single 5 mm long wire is able to produce a sufficient amount of heat, with the specific loss power (SLP) reaching a value as high as 521 W/g for an AC field of 700 Oe and a frequency of 310 kHz. The large SLP is attributed to the rectangular hysteresis loop resulting from a peculiar domain structure of the microwire. For an array of parallel microwires, we have observed an SLP improvement by one order of magnitude; 950 W/g for an AC field of 700 Oe. The magnetostatic interaction strength essential in the array of wires can be manipulated by varying the distance between the wires, showing a decreasing trend in SLP with increasing wire separation. The largest SLP is obtained when the wires are aligned along the direction of the AC field. The origin of the large SLP and relevant heating mechanisms are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Connected and leading disconnected hadronic light-by-light contribution to the muon anomalous magnetic moment with a physical pion mass

We report a lattice QCD calculation of the hadronic light-by-light contribution to the muon anomalous magnetic moment at a physical pion mass. The calculation includes the connected diagrams and the leading, quark-line-disconnected diagrams. We incorporate algorithmic improvements developed in our previous work. The calculation was performed on the 48 3 × 96 ensemble generated with a physical pion mass and a 5.5 fm spatial extent by the RBC and UKQCD Collaborations using the chiral, domain wall fermion formulation. We find a HLbL μ = 5.35(1.35) × 10 –10 , where the error is statistical only. The finite-volume and finite lattice-spacing errors could be quite large and are the subject of ongoing research. Finally, the omitted disconnected graphs, while expected to give a correction of order 10%, also need to be computed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

DQ Admittance Extraction for Inverter-Based Resources: Preprint

The power grid industry is pushing for electro-magnetic transient (EMT)-based studies for generation interconnection and planning process due to high penetrations of inverter-based resource (IBRs). Vendor-specific and site-specific black-box IBR models are preferred in those simulation studies. For small-signal analysis, measurement-based admittance models are necessary. In this paper, we demonstrate the extraction of frequency-domain dq frame IBR models. These linear models are specific to operating conditions. We demonstrate two extraction methods: frequency scan and a step response-based method. The latter relies on converting time-domain responses to Laplace-domain expressions via eigensystem realization analysis (ERA). Both can lead to dq admittance representation and the latter is time saving.

admittance model↗
DOE OSTI2025

Magnetic mesh generation and field line reconstruction for scrape-off layer and divertor modeling in stellarators

The design of divertor targets and baffles for optimal heat and particle exhaust from magnetically confined fusion plasmas requires a combination of fast, low-fidelity models (such as EMC3-Lite (Feng 2022 Plasma Phys. Control. Fusion 64 125012)) for scoping studies and high-fidelity ones (such as EMC3-EIRENE (Feng et al 2014 Contrib. Plasma Phys. 54 426–31)) for verification. Both of those approaches benefit from a magnetic flux tube mesh for fast interpolation and mapping of field line segments (Feng et al 2005 Phys. Plasmas 12 052505). A new automated mesh generator for unstructured quadrilateral flux tubes with adaptive refinement is presented and integrated into FLARE (Frerichs 2024 Nucl. Fusion 64 106034). For HSX with an extended first wall, it is found that several layers of flux tubes can span the entire half field period before splitting is required. This is an advantage over the traditional setup of the EMC3-EIRENE mesh where careful construction of several sub- domains is required already for the much tighter present first wall. In particular, there is no longer the need to manually construct a suitable outer boundary for the mesh. The divide and conquer paradigm with unstructured mesh layout offers a powerful alternative for fast head load approximation that is suitable for integration into optimization workflows. Further examples for W7-X and CTH demonstrate the versatile application range.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

RAM-SCB Runs on Request at CCMC

The Ring current–Atmosphere interactions Model (RAM) with Self-Consistent magnetic (B) field (SCB) combines a large-scale kinetic model of ring current plasma with a three-dimensional (3-D) force-balanced model of the terrestrial magnetic field. RAM-SCB simulates the evolution of major ion species (H + , O + , and He + by default) and electrons as a function of azimuth, radial distance, energy, and pitch angle. Simulation outputs include the Dst index, and pressure and differential flux of the modeled species, thus providing benefit as a science code and to inform surface charging hazard within the model domain. Version 2.2 of this open-source simulation code has now—as of 8 August 2023—been made available for Runs-On-Request via the Community Coordinated Modeling Center.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Study of plasma equilibrium in toroidal fusion devices using mesh-free numerical calculation method

Plasma confinement using external magnetic field is one of the successful ways leading to the controlled nuclear fusion. Development and validation of the solution process for plasma equilibrium in the experimental toroidal fusion devices is the main subject of this work. Solution of the nonlinear 2D stationary problem as posed by the Grad-Shafranov equation gives quantitative information about plasma equilibrium inside the vacuum chamber of hot fusion devices. This study suggests solving plasma equilibrium equation which is essential in toroidal nuclear fusion devices, using a mesh-free method in a condition that the plasma boundary is unknown. The Grad-Shafranov equation has been solved numerically by the point interpolation collocation mesh-free method. Important features of this approach include truly mesh free, simple mathematical relationships between points and acceptable precision in comparison with the parametric results. The calculation process has been done by using the regular and irregular nodal distribution and support domains with different points. The relative error between numerical and analytical solution is discussed for several test examples such as small size Damavand tokamak, ITER-like equilibrium, NSTX-like equilibrium, and typical Spheromak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗