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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Behavior of solitary waves of coupled nonlinear Schrödinger equations subjected to complex external periodic potentials with odd-$\mathcal{PT}$ symmetry

In this work, we discuss the response of both moving and trapped solitary wave solutions of a two-component nonlinear Schrödinger system in 1 + 1 dimensions to an odd-$\mathcal{PT}$ external periodic complex potential. The dynamical behavior of perturbed solitary waves is explored by conducting numerical simulations of the nonlinear system and using a collective coordinate variational approximation. We present case examples corresponding to choices of parameter values and initial conditions involved therein. The results of the collective coordinate approximation are compared against numerical simulations where we observe qualitatively good agreement between the two. Unlike the case for a single-component solitary wave in a complex periodic $\mathcal{PT}$-symmetric potential, the collective coordinate equations do not have a small oscillation regime, and initially the height of the two components changes in opposite directions often causing instability. We find that the dynamic stability criteria we have used in the one-component case are a good indicator for the onset of dynamic instabilities in the present setup.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Orbital-spin locking and its optical signatures in altermagnets

Altermagnets, magnetic materials with zero magnetization and spin-split band structure, have gained tremendous attention recently for their rich physics and potential applications. Here, we report on a microscopic tight-binding model that unveils a unique coupling between orbitals and spins in d-wave altermagnets, which gives rise to momentum-dependent and spin-selective optical absorption. This coupling promotes the controlled optical excitation of up or down spins depending on the polarization direction of linearly polarized light. Such an effect originates from the coupling of orbitals to the sublattice degree of freedom through the crystal field, which is then coupled to spins through the antiferromagnetic interaction. Our crystal field analysis, which is general to any type of altermagnet, helps understand the onset of altermagnetism from a microscopic point of view, and we use our results to propose clear magneto-optical signatures of our predictions. Our findings shine light on the interplay between orbitals and spins in altermagnets, thus paving the way towards novel orbitronic and optospintronic devices.

Vila, Marc↗
DOE OSTI2022

Preshot Report for Carbonara: Dynamics of a Boron Carbide Sandwich

The main purpose of the Carbonara experiment is to provide much-needed data to inform physics modeling of boron carbide (B 4 C) subjected to a sweeping high explosive (HE) detonation. The proposed experiment will include three separate shots, each employing a rectangular slab of HE (4” × 3” × 1”) sandwiched between two wedges of B 4 C, see Fig.1. In each case the top B 4 C wedge tapers from a height of 2.5 cm to 0.5 cm, while the bottom wedge tapers from 1.5 cm to 0.5 cm. The wedges are 4” in the direction of the proton beam, and 3” in the direction transverse to the beam. Three shots are currently planned, each one using a different HE: PBX 9501, PBX 9502, and PBX 9701. The HE will be initiated using a line wave generator (LWG) to preserve planar symmetry, in conjunction with a Comp. B booster to smooth out the profile for the initial condition on the main charge and to aid in initiation of the PBX 9502 shot. In each case the booster spans the entire length and height of the main HE slab and extends 0.5” in toward the LWG.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ultralow-temperature cryogenic transmission electron microscopy using a new helium flow cryostat stage

Advances in cryogenic electron microscopy have opened new avenues for probing quantum phenomena in correlated materials. This study reports the installation and performance of a new side-entry condenZero cryogenic cooling system for JEOL (Scanning) Transmission Electron Microscopes (S/TEM), utilizing compressed liquid helium (LHe) and designed for imaging and spectroscopy at ultra-low temperatures. The system includes an external dewar mounted on a vibration-damping stage and a pressurized, low-noise helium transfer line with a remotely controllable needle valve, ensuring stable and efficient LHe flow with minimal thermal and mechanical noise. Performance evaluation demonstrates a stable base temperature of 4.37 K measured using a Cernox bare chip sensor on the holder with temperature fluctuations within ±0.004 K. Complementary in-situ electron energy-loss spectroscopy (EELS) via aluminum bulk plasmon analysis was used to measure the local specimen temperature and validate cryogenic operation during experiments. The integration of cryogenic cooling with other microscopy techniques, including electron diffraction and Lorentz TEM, was demonstrated by resolving charge density wave (CDW) transitions in NbSe2 using electron diffraction, and imaging nanometric magnetic skyrmions in MnSi via Lorentz TEM. In conclusion, this platform provides reliable cryogenic operation below 7 K, establishing a low-drift route for direct visualization of electronic and magnetic phase transformations in quantum materials.

Charge density wave↗
DOE OSTI2026

Electronic coherence evolution at the nearly commensurate-incommensurate CDW boundary of 1⁢T−TaS 2

Transition-metal dichalcogenides host a variety of charge-density-wave phases that couple lattice, charge, and correlation effects. In 1⁢𝑇−TaS 2 , the commensurate and nearly commensurate states are well characterized, yet the transition near 350 K into the incommensurate phase has lacked direct momentum-resolved insight. In this work, we use temperature-dependent angle-resolved photoemission spectroscopy to track the electronic structure across this transition. We observe a suppression of quasiparticle spectral weight at the Brillouin-zone center, coincident with the transport anomaly, but without clear evidence of a full band-gap opening. The transition appears to involve momentum-dependent redistribution of spectral weight, consistent with a loss of coherence that reshapes the Fermi surface while leaving conduction dispersions largely intact. These results suggest that the nearly commensurate–incommensurate transition may not align with a conventional metal-insulator transition picture, but rather as an electronic reconstruction driven by loss of coherence. Our work provides new microscopic insight into the resistivity anomaly near room temperature and may guide design principles for collective electronic switching in transition-metal dichalcogenides.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Pitch-Angle Diffusion in the Earth’s Magnetosphere Organized by the Mozer-Transformed Coordinate System

In the Earth’s dipole magnetosphere finite-gyroradius effects produce a shift of the atmospheric loss cone away from the direction of the magnetic field. This loss-cone shift is theoretically described by the “Mozer transform”, which is based upon the curvature drift of particles crossing the equatorial plane. For positive ions the northern and southern loss cones both shift westward and for electrons the northern and southern loss cones both shift eastward. This loss-cone shift is part of a coordinate-system transform, with the transformed coordinates better organizing the behavior of particle orbits in the dipole magnetic field (e.g. first adiabatic invariants, mirror heights, and bounce times). In this report it is demonstrated that the transformed coordinate system also properly organizes pitch-angle diffusion. This improved organization of the diffusion is true whether the angular scattering is produced by plasma-wave scattering or by field-line-curvature (FLC) scattering. It is shown that FLC scattering and the loss cone shift are linked, so that if FLC scattering is occurring, there is a loss cone shifted away from the magnetic-field direction and the Mozer-transformed coordinates are needed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Numerical simulation of falling film sensible heat transfer over round horizontal tubes

Numerical simulations are performed to explore the heat transfer characteristics of falling films over horizontal round tubes with uniform heat flux imposed for a range of Reynolds numbers spanning the droplet, jet, and sheet regimes. Simulations results agree well with available experimental measurements. The study analyzes the local as well as average heat transfer behavior under the different flow modes. The numerical results show that the local Nusselt number (Nu) distribution depends on the flow features in each mode and varies substantially in all directions for the respective mode. In the droplet mode, the Nu value varies significantly as the droplet impinges and the remnant liquid-bridge retracts (peak instantaneous Nu near 6), followed by wave propagation over the tube surface with peak Nu around 0.25. For the jet modes, the local maximum in the heat transfer occurs off-center to the impingement location with magnitudes of peak Nu = 3.1 for the inline jet mode and Nu = 2.7 for the staggered jet mode, while on the rest of the tube surface, it has an inverse relation with the liquid film thickness. Substantial variations in the heat transfer value are also recorded in the middle of the two impinging jets with Nu = 0.95 in the inline jet mode where the neighboring jets do not interact, and Nu = 0.60 in the crest region of the staggered jet mode where the neighboring jets interact with each other. In the sheet mode, the Nu was seen to depend on the thickness of the liquid waves traversing over the tube surface. Lower Nu values were recorded beneath the crest location of the liquid waves, which increases (1.4–11.6% depending on circumferential location) abruptly in magnitude at the advancing fronts of the waves. The temperature distribution in the liquid film in each of the modes was examined to evaluate the mechanism of heat transfer process. This study also compares the local heat transfer coefficient distribution with the analytical heat transfer models derived to predict heat transfer performance over horizontal tube surfaces.

42 ENGINEERING↗
DOE OSTI2022

Surface plasmons induce topological transition in graphene/α-MoO3 heterostructures

Abstract Polaritons in hyperbolic van der Waals materials—where principal axes have permittivities of opposite signs—are light-matter modes with unique properties and promising applications. Isofrequency contours of hyperbolic polaritons may undergo topological transitions from open hyperbolas to closed ellipse-like curves, prompting an abrupt change in physical properties. Electronically-tunable topological transitions are especially desirable for future integrated technologies but have yet to be demonstrated. In this work, we present a doping-induced topological transition effected by plasmon-phonon hybridization in graphene/α-MoO 3 heterostructures. Scanning near-field optical microscopy was used to image hybrid polaritons in graphene/α-MoO 3 . We demonstrate the topological transition and characterize hybrid modes, which can be tuned from surface waves to bulk waveguide modes, traversing an exceptional point arising from the anisotropic plasmon-phonon coupling. Graphene/α-MoO 3 heterostructures offer the possibility to explore dynamical topological transitions and directional coupling that could inspire new nanophotonic and quantum devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Geometry and dynamics of passive scalar structures in compressible turbulent mixing

We present a structure-based numerical analysis of passive scalar mixing in decaying homogeneous isotropic turbulence (DHIT) and shock-turbulence interaction canonical configurations. The analysis focuses on the temporal evolution of ensembles of passive scalar structures, initialized as spheres of different sizes relative to the Taylor microscale. An algorithm is introduced to track the evolution of each individual structure and the interactions with other structures in the ensemble, relating changes in the surface geometry and the underlying physical processes (turbulent transport, scalar dissipation, and shock compression). The tracking algorithm is applied to datasets from shock-capturing direct numerical simulations of DHIT, with Taylor microscale Reynolds number Re λ =40 and turbulence Mach number M t =0.2 ⁠, and STI cases in which the turbulence is processed by a shock wave at Mach numbers M = 1.5 and 3.0. Temporal surface convolution increases for initially larger structures, resulting in a higher probability of locally hyperbolic geometries where breakup into smaller structures occurs. Shock-induced deformation of the structures amplifies breakup processes, enhancing mixing, particularly for larger structures. Mixing enhancement by the shock is manifested as an amplification of the surface-averaged scalar gradient, which increases for initially larger structures. The alignment between the scalar gradient and the most extensional strain-rate eigendirection on the scalar isosurfaces also increases across the shock. Larger magnitudes of the scalar gradient and its alignment with the most compressive strain-rate eigendirection correlate with flatter surface regions. Shock-induced structure compression increases the area coverage of flat regions, where the amplification of scalar gradient is localized.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Ultrafast charge dynamics and photoluminescence in bilayer MoS 2

Our examination of the interplay of ultrafast charge dynamics and electron–phonon interaction in the AA' stacked bilayer MoS 2 provides a microscopic basis for understanding the features (two peaks) in the emission spectrum. We demonstrate that while the initial accumulation of excited charge occurs at and near the Q point of the two-dimensional Brillioun zone, emission takes place predominantly through two pathways: direct charge recombination at the K point and indirect phonon-assisted recombination of electrons at the K valley and holes at the Γ hill of the Brillouin zone. Analysis of the wave vector dependencies of the electron–phonon interaction traces the higher energy peak to phonon-assisted relaxation of the excited electrons from the Q to the K valley in the conduction band. Our results thus reveal the importance of ultrafast charge dynamics in understanding photoemissive properties of a few-layer transition-metal dichalcogenide. These calculations are based on time dependent density functional theory in the density matrix formulation.

Materials Science↗
DOE OSTI2025

Sensitivity of the dynamic-shell target to laser drive nonuniformities

The dynamic-shell concept for inertial confinement fusion (ICF) uses an initially homogeneous target and a carefully shaped laser pulse to form a shell and implode it. The laser pulse consists of a series of pickets that drive shocks into the target. The first few shocks converge inwards and rebound from the center of the target, creating an expanding, low-density plasma. Subsequent shocks are launched into the expanding plasma and eventually coalesce to form a shell, which is then imploded with a traditional ICF laser pulse. This study describes radiation-hydrodynamic simulations that investigate the sensitivity of dynamic-shell targets to imperfections in the laser drive. A one-dimensional (1D) study looks at mistiming and power variations in the pickets and a two-dimensional (2D) study examines irradiation perturbations imposed by the laser-beam geometry. Simulations show that less than ~2% power imbalance or 200 ps timing variation in the pickets is sufficient to keep the yield above 90% of the maximum. Additionally, the 2D simulations show that 72 or more beams are required to keep irradiation nonuniformities low enough to obtain fusion yields close to that of 1D simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Torque and Angular-Momentum Transfer in Merging Rotating Bose-Einstein Condensates

When rotating classical fluid drops merge together, angular momentum can be advected from one to another due to the viscous shear flow at the drop interface. It remains elusive what the corresponding mechanism is in inviscid quantum fluids such as Bose-Einstein condensates (BECs). In this work, we report our theoretical study of an initially static BEC merging with a rotating BECin three-dimensional space along the rotational axis. We show that a solitonlike sheet, resembling a corkscrew, spontaneously emerges at the interface. Furthermore, rapid angular momentum transfer at a constant rate universally proportional to the initial angular-momentum density is observed. Strikingly, this transfer does not necessarily involve fluid advection or drifting of the quantized vortices. We reveal that the corkscrew structure can exert a torque that directly creates angular momentum in the static BEC and annihilates angular momentum in the rotating BEC. Uncovering this intriguing angular momentum transport mechanism may benefit our understanding of various coherent matter-wave systems, spanning from atomtronics on chips to dark matter BECs at cosmic scales.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Field-dependent nonelectronic contributions to thermal conductivity in a metallic ferromagnet with low Gilbert damping

Heat conduction in metals is typically dominated by electron transport since electrons carry both charge and heat. In magnetic metals magnons, or spin waves, excitations of the magnetic order can be used to transport information. Heat conduction via magnons has been previously shown mostly for insulating magnets with low Gilbert damping and resulting long spin-wave lifetimes where conduction electrons cannot contribute. Here we show that thin films of properly optimized metallic ferromagnetic (FM) alloys show significant nonelectronic contributions to heat conduction, which furthermore depend on the direction of an applied magnetic field. These measurements are enabled by micromachined thermal isolation platforms optimized for thermal conductivity measurements of thin-film systems. Electrical conductivity measurements on exactly the same samples allow application of the Wiedemann-Franz relation, which shows large nonelectronic contributions to thermal conductivity for the cobalt-iron alloy with 25% Co. This composition has been shown to have exceptionally low damping for a metallic FM. The thermal conductivity of a 75-nm-thick film of the 25% Co alloy changes by more than 20% at some temperatures, while a reference sample with 50% cobalt that has much higher damping shows no field-direction dependence. Our measurements indicate that applied magnetic fields alter the magnon lifetimes in these films and that these magnons contribute to thermal conductivity in this metallic magnetic alloy with low Gilbert damping.

36 MATERIALS SCIENCE↗
DOE OSTI2026

OC6 Phase III: Validation of Wind Turbine Aerodynamic Loading During Surge/Pitch Motion

The objective of Phase III of the Offshore Code Comparison Collaboration, Continued, with Correlation and unCertainty (OC6) project was to validate the accuracy of aerodynamic load predictions by offshore wind modeling tools for a floating offshore wind turbine as it experiences large surge-translational and pitch-rotational motion, as would occur during normal operation. The test data considered were generated at Politecnico di Milano – a wind tunnel with a robotic excitation system to emulate wave loading on the wind turbine. Testing was performed using a scaled version of the DTU 10-MW reference model, and motion was prescribed as harmonic oscillations in the surge and pitch directions, independently. A variety of models were examined in the project, performing a three-way validation between engineering-level tools, higher-fidelity tools, and measurement data from two wind tunnel experimental campaigns. The Load Cases (LC) considered in this testing are as follows: LC 1.X - Steady Wind LC 2.X - Unsteady Wind - Surge Motion LC 3.X - Unsteady Wind - Pitch Motion Details on the results of the OC6 Phase III campaign can be found in the following reference: Bergua R., et al. OC6 project Phase III: validation of the aerodynamic loading on a wind turbine rotor undergoing large motion caused by a floating support structure, Wind Energ. Sci., 8, 465–485, https://doi.org/10.5194/wes-8-465-2023, 2023.

17 WIND ENERGY↗
DOE OSTI2024

Evolving Outer Heliosphere: Tracking Solar Wind Transients from 1 au to the VLISM with IBEX and Voyager 1

Abstract Interstellar Boundary Explorer (IBEX) observations of energetic neutral atom (ENA) fluxes from the heliosphere have greatly enriched our understanding of the interaction of the solar wind (SW) with the local interstellar medium (LISM). However, there has been recent controversy surrounding the inability of most ENA models to produce as high an intensity of ∼0.5–6 keV ENAs as IBEX observes at 1 au, especially as a function of time. In our previous study (E. J. Zirnstein et al.), we introduced a new model that utilizes a data-driven magnetohydrodynamic simulation of the SW–LISM interaction to propagate pickup ions through the heliosheath (HS) after they are nonadiabatically heated at the heliospheric termination shock. E. J. Zirnstein et al. only simulated and analyzed IBEX observations from the direction of Voyager 2. In this study, we expand our model to include fluxes from the direction of Voyager 1, as well as in the low-latitude part (middle) of the ribbon (10° below the ecliptic plane). We show that the model results at Voyager 1 are consistent with E. J. Zirnstein et al.’s results at Voyager 2 in terms of a secondary ENA source contribution of ≲20% from both directions. Our results in the middle of the ribbon also reproduce the data, when including a time-dependent secondary ENA source. Finally, we demonstrate with our simulation that three large pressure waves likely merged in the VLISM and were observed by Voyager 1 as “pf2,” while at least one of the wave’s effects in the HS was observed by IBEX as a brief enhancement in ENA flux in early 2016.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Outward Migration of Super-Jupiters

We report recent simulations show that giant planets of about 1 M J migrate inward at a rate that differs from the type II prediction. Here we show that at higher masses, planets migrate outward. Our result differs from previous ones because of our longer simulation times, lower viscosity, and boundary conditions that allow the disk to reach a viscous steady state. We show that, for planets on circular orbits, the transition from inward to outward migration coincides with the known transition from circular to eccentric disks that occurs for planets more massive than a few Jupiters. In an eccentric disk, the torque on the outer disk weakens due to two effects: the planet launches weaker waves, and those waves travel further before damping. As a result, the torque on the inner disk dominates, and the planet pushes itself outward. Our results suggest that the many super-Jupiters observed by direct imaging at large distances from the star may have gotten there by outward migration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

High-Frequency Gravitational Wave Search with ABRACADABRA-10 cm

ABRACADABRA-10 cm has had great success as a pathfinder lumped-element axion dark matter experiment, setting limits on axion dark matter at the GUT scale. Now, using the interaction of gravitational waves with electrodynamics and a change in readout strategy, we use the ABRA-10 cm detector for the first search for high-frequency gravitational waves using a modified axion detector. Potential sources at these high frequencies (10 kHz to 5 MHz) include merging primordial black hole binaries or superradiance, among other beyond the standard model phenomena. This paper presents the design, results, and challenges from the ABRA-10 cm high-frequency gravitational wave search, showing it is possible to simultaneously look for axions and high-frequency gravitational waves with both searches matching theoretical expectations for sensitivity. Additionally, we conducted the first time series transient search with data from an axion experiment, achieving sensitivity to $10^{-4}$ in strain. Scaled directly to the next generation axion experiment, DMRadio-GUT, this sensitivity would imply a reach to 0.01 $M_{\odot}$ primordial black hole mergers at distances around 3 pc, with prospects to go significantly further with modifications to the readout.

Pappas, Kaliroë M.W. [MIT, LNS] (ORCID:00000003425↗
DOE OSTI2020

X-ray atomic mapping of quantum dots

We report a model-independent atomic-mapping technique for quantum dots (QDs) by combining Bragg reflection x-ray standing wave (XSW) and grazing incidence diffraction (GID) measurements. In this study, we choose GaAs capped InGaAs QDs/GaAs(001) as a model system to show the locations and arrangements of indium atoms within the QDs along various [hkl] directions. This technique directly reveals the actual amount of positional anisotropy and ordering fraction of indium atoms within the QDs by probing the (1¯11), (111), (311), (1¯31), (113), and (1¯13) crystallographic planes. We find that indium atoms are outwardly shifted along the [001] direction by small fractions of the lattice constant, 0.04a GaAs and 0.06a GaAs from Ga sites for 50- and 150-Å GaAs capped InGaAs QDs, respectively. We observe that an improved coherency factor of the indium atoms within the QDs by 45–60% along the [001] and [011] directions reduces the photoluminescence linewidth by 22%, thus making the QDs efficient for QD-laser and optoelectronic device applications. Here, we also find that the position and ordering of In atoms along the (113) and (1¯13) planes are most sensitive to the thickness of the GaAs cap layer. Our XSW-based results are supported by numerical calculations using a QD-macroscopic structural model based on our GID study. We thus show that this atomic-mapping technique will be useful for studying various quantum structures and tuning their properties.

36 MATERIALS SCIENCE↗