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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Spin orbit torque in ferromagnet/topological-quantum-material heterostructures

The main objective of this proposal was to investigate the spin-orbital driven phenomena in topological insulator (TI)/ferromagnet (FM) or transition metal (TM) heterostructures. In particularly, we tried to utilize the spin-momentum locking properties on the surface of TIs to achieve ideal spin-orbit torques (SOTs). In practice, we found that the surface properties have been greatly modified, resulting in much more complicated magneto-transport behaviors than what is expected in SOT-driven magnetotransport. Through systematic and extended investigations, we start to unravel that the nonlinear magnetotransport properties, which was, in the past, mainly attributed to SOT-driven phenomena, can be used to infer the modification of the electronic band structures of TIs and spin textures in FMs which are closely related with charge-spin interconversion phenomena. Regarding the band structures In TIs, we find under electrostatic perturbations imposed by deposition of nonmagnetic TMs, the quantum well states formed on the surface of TIs develop substantial Rashba spin-splitting, which is detected as a bilinear magnetoresistance (BMR). Under magnetic perturbations, the nonlinear planar Hall effect (NPHE) in the topological surface states is greatly enhanced, possibly reflecting the modified surface band structure due to time-reversal symmetry breaking. In a double HM/FM heterostructure where the magnetic anisotropy can be robustly tuned, we observed second-harmonic Hall voltage responses corresponding to domain wall structures with fixed chirality, stabilized by interfacial Dzyaloshinskii–Moriya interaction (DMI). In addition, in the linear transport regime, we utilized inverse-SHE-induced anomalous Hall effect in Pt to probe the exchange bias on the surface of a doped magnetic insulator Tm 3 Fe 5 O 12 .

36 MATERIALS SCIENCE↗
NASA NTRS2017

Redetection of the Ionospheric H3(+) Signature of Saturn's "Ring Rain"

Abstract In April 2011 Saturn's midlatitude ionospheric H3(+) emissions were detected, exhibiting anomalous (nonsolar) H3(+) latitudinal variations consistent with the transport of water from specific locations in Saturn's rings, known as ''ring rain'' . These products, transported to the planet along the magnetic field, may help to explain the unusual pattern of peaks and troughs in electron densities discovered in Saturn's ionosphere by spacecraft flybys. In the present study, we analyzed H3(+) emissions recorded on 23 April 2013, showing for the first time since the original detection that Saturn's midlatitude H3(+) emissions are indeed heavily modified. Although the 2013 emissions are dimmer by almost a factor of 3.7, the latitudinal contrast is greater and uncertainties are lower. Increased H3(+) intensities were found near planetocentric latitudes of 43 deg, 51 deg, and 63 deg, previously identified with sources at the inner edge of the B ring, A ring, and the orbit of Enceladus and associated E ring.

Ionospheric↗
NASA NTRS1985

Theoretical study of anomalously high F region peak altitudes in the polar ionosphere

It is pointed out that during the last solar maximum period several observations of anomalously high F region peak altitudes (hmF2) have been made by high latitude incoherent scatter radars. In the present investigation, a high latitude time-dependent F region model (HLTD) was used to study a range of differing plasma transport processes in order to identify possible source mechanisms for the anomalously high hmF2's. A description of model parameters is presented, and region density profiles are discussed. Attention is given to the solar maximum, the solar minimum, and the asymmetric wind. The results of the HLTD model study of transport effects for a wide range of solar cycle, season, magnetic activity, and neutral wind conditions show that high hmF2 values in the polar cap can be generated without the need for auroral particle precipitation.

Sojka, J. J.↗
DOE OSTI2026

Investigation of Drift Effects in UEDGE Simulations of NSTX-U Edge Plasma With Lithium Divertors

Lithium is a low-Z material, and lithium-based plasma-facing components (PFCs) are planned for the National Spherical Torus Experiment Upgrade (NSTX-U) to explore potential benefits for divertor power exhaust and core plasma management. NSTX-U is a medium-sized spherical tokamak with up to 12 MW of auxiliary heating, capable of generating reactor-relevant plasma conditions. This work presents boundary plasma simulations for NSTX-U with lithium PFCs using the UEDGE code, incorporating full magnetic and 𝐄 ×𝐁 drift physics. The simulations show that drifts strongly influence heat and particle transport: they enhance convective transport, broaden the scrape-off layer heat-flux width 𝜆 𝑞 , and reduce the anomalous heat diffusivity 𝜒 required to reproduce predicted SOL heat-flux width. 𝐄 ×𝐁 drifts provide poloidal transport, while ∇𝐵 (which includes both gradB and curvature) drifts provide radial heat and particle transport. Lithium transport is also affected by drifts, with lithium ions migrating from the outer divertor to the inner divertor through the private flux region (PFR) following the 𝐄 ×𝐁 drifts flow, lowering upstream impurity lithium densities. UEDGE is self-consistently coupled with the Wall-Li model to study plasma lithium PFC interactions depending on the local lithium sourcing based on local plasma conditions and lithium surface temperature. In these simulations, lithium evaporation shows a vapor-shielding effect that reduces divertor heat flux and increases radiative losses once surface temperatures exceed 450°C. This research work provides a first step toward self-consistent modeling of lithium PFCs in NSTX-U, demonstrating the impact of drift-driven plasma transport in SOL and divertor regions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

High-temperature anomalous Hall effect driven by frustrated spin fluctuations in the antiferromagnetic delafossite metal PdCrO 2

Metallic delafossite oxides are of exceptional interest due to their ultraclean metallic transport. In the case of PdCrO 2 , this arises in a triangular-lattice antiferromagnet, creating a unique opportunity to study frustrated magnetism in a very clean metal. Here, we combine a chemical vapor transport crystal growth approach with magnetic, thermodynamic, magnetotransport, and neutron scattering measurements to elucidate the striking anomalous Hall effect (AHE) in antiferromagnetic PdCrO 2 . The unconventional AHE (with anomalous Hall conductivity ~10 5 Ω −1 cm −1 ) and a large positive magnetoresistance effect (>1,000%) are shown to exhibit complex temperature dependencies, persisting to almost seven times the Néel temperature (~250 K). These effects are directly compared to elastic neutron scattering, inelastic neutron scattering, and neutron magnetic pair distribution function data, establishing unambiguous links between anomalous magnetotransport properties and directly probed short-range spin fluctuations. The latter occur over a notably broad temperature range due to geometrical magnetic frustration. Connecting to recent experimental and theoretical developments, these findings are discussed in terms of a temperature-dependent interplay between chiral spin order and chiral spin fluctuations, significantly elucidating the high-temperature anomalous magnetotransport in such compounds.

anomalous Hall effect↗
DOE OSTI2022

Recent Trends in Transport of Surface Carbonaceous Aerosols to the Upper-Troposphere-Lower-Stratosphere Linked to Expansion of the Asian Summer Monsoon Anticyclone

Using Modern-Era Retrospective analysis for Research and Applications Version-2 (MERRA-2) re-analyses, we have examined recent trends (2000–2019) in transport of surface carbonaceous aerosols (CAs), that is, organic carbon and black carbon, to the upper troposphere and lower stratosphere (UTLS) during the Asian summer monsoon (ASM). We find a significant increased concentration of UTLS CA, linked to a linear trend in an expansion of the Asian Summer Monsoon Anticyclone (ASMA). Over core monsoon latitudes (25°–35°N), the trends in UTLS CA are enabled by increased upward transport from surface sources via an intensified monsoon meridional circulation, with increased latent heating over the southern Tibetan Plateau and foothill regions, enhanced by feedback processes associated with radiative heating by UTLS CA. In the extra-tropics, increased UTLS CA stems primarily from an extended source of increased wildfire emissions over eastern Siberia and northern Asia, coincident with a large-scale anomalous anticyclone with enhanced surface warming and drying near (80°–120°E, 55°–70°N). Here, CAs are transported upward from the surface to the ULS, likely by increased pyro-convection associated with enhanced wildfires, and enter the tropical UTLS via increased equatorward transport on the eastern flanks of anomalous upper-level anticyclones, coupled to the expanded ASMA. Overall, the increasing UTLS CA trends associated with expansion of the ASMA are consistent with a hydrostatic expansion of a warming troposphere, reflected in a rise in the tropical tropopause and consequential dynamical adjustments of the ASM subtropical jetstream, modulating the climate of the greater ASM region.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2021

Extreme High Greenland Blocking Index Leads to the Reversal of Davis and Nares Strait Net Transport Towards the Arctic Ocean

Baffin Bay exports Arctic Water to the North Atlantic while receiving northward flowing Atlantic Water. Warm Atlantic Water has impacted the retreat of tidewater glaciers draining the Greenland Ice Sheet. Periods of enhanced Atlantic Water transport into Baffin Bay have been observed, but the oceanic processes are still not fully explained. At the end of 2010 the net transport at Davis Strait, the southern gateway to Baffin Bay, reversed from southward to northward for a month, leading to significant northward oceanic heat transport into Baffin Bay. This was associated with an extreme high in the Greenland Blocking Index and a stormtrack path that shifted away from Baffin Bay. Thus fewer cyclones in the Irminger Sea resulted in less frequent northerly winds along the western coast of Greenland, allowing anomalous northward penetration of warm waters, reversing the volume and heat transport at Davis Strait.

Davis Strait↗
DOE OSTI2023

Widely Tunable Berry Curvature in the Magnetic Semimetal Cr 1+ δ Te 2

Abstract Magnetic semimetals have increasingly emerged as lucrative platforms hosting spin‐based topological phenomena in real and momentum spaces. Cr 1+ δ Te 2 is a self‐intercalated magnetic transition metal dichalcogenide (TMD), which exhibits topological magnetism and tunable electron filling. While recent studies have explored real‐space Berry curvature effects, similar considerations of momentum‐space Berry curvature are lacking. Here, the electronic structure and transport properties of epitaxial Cr 1+ δ Te 2 thin films are systematically investigated over a range of doping, δ (0.33 – 0.71). Spectroscopic experiments reveal the presence of a characteristic semi‐metallic band region, which shows a rigid like energy shift with δ. Transport experiments show that the intrinsic component of the anomalous Hall effect (AHE) is sizable and undergoes a sign flip across δ. Finally, density functional theory calculations establish a link between the doping evolution of the band structure and AHE: the AHE sign flip is shown to emerge from the sign change of the Berry curvature, as the semi‐metallic band region crosses the Fermi energy. These findings underscore the increasing relevance of momentum‐space Berry curvature in magnetic TMDs and provide a unique platform for intertwining topological physics in real and momentum spaces.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Endless Dirac nodal lines in kagome-metal Ni3In2S2

Abstract Topological semimetals are a frontier of quantum materials. In multiband electronic systems, topological band crossings can form closed curves, known as nodal lines. In the presence of spin–orbit coupling and/or symmetry-breaking operations, topological nodal lines can break into Dirac/Weyl nodes and give rise to interesting transport properties, such as the chiral anomaly and giant anomalous Hall effect. Recently, the time-reversal symmetry-breaking induced Weyl fermions are observed in a kagome-metal Co 3 Sn 2 S 2 , triggering interests in nodal-line excitations in multiband kagome systems. Here, using first-principles calculations and symmetry-based indicator theories, we find six endless nodal lines along the stacking direction of kagome layers and two nodal rings in the kagome plane in nonmagnetic Ni 3 In 2 S 2 . The linear dipsersive electronic structure, confirmed by angle-resolved photoemission spectroscopy, induces large magnetoresistance up to 2000% at 9 T. Our results establish a diverse topological landscape of multiband kagome metals.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Analysis of Tempered Fractional Operators

Tempered fractional operators are useful in models for subsurface transport and diffusion due to their ability to capture anomalous diffusion: a behavior which the classical partial differential equation models cannot describe. We analyze tempered fractional operators within the nonlocal vector calculus framework in order to assimilate them to the rigorous mathematical structure developed for nonlocal models. First, we show they are special instances of generalized nonlocal operators in correspondence of a proper choice of nonlocal kernels. Then, we work towards showing tempered fractional operators are equivalent to truncated fractional operators. These truncated operators are useful because they are less computationally intensive than the tempered operators.

97 MATHEMATICS AND COMPUTING↗
NASA NTRSDate not supplied

TPSAS-NF1676L-22727-DND

Satellite based top-of-atmosphere (TOA) and surface radiation budget observations are combined with mass corrected vertically integrated atmospheric energy divergence and tendency from reanalysis to infer the regional distribution of the TOA, atmospheric and surface energy budget terms over the globe. Hemispheric contrasts in the energy budget terms are used to determine the radiative and combined sensible and latent heat contributions to the cross-equatorial heat transports in the atmosphere (AHTEQ) and ocean (OHTEQ). The contrast in net atmospheric radiation implies an AHTEQ from the northern hemisphere (NH) to the southern hemisphere (SH) (0.75 PW), while the hemispheric difference in sensible and latent heat implies an AHTEQ in the opposite direction (0.51 PW), resulting in a net NH to SH AHTEQ (0.24 PW). At the surface, the hemispheric contrast in the radiative component (0.95 PW) dominates, implying a 0.44 PW SH to NH OHTEQ. Coupled Model Intercomparison Project Phase 5 (CMIP5) models with excessive net downward surface radiation and surface-to-atmosphere sensible and latent heat transport in the SH relative to the NH exhibit anomalous northward AHTEQ and overestimate SH tropical precipitation. The hemispheric bias in net surface radiative flux is due to too much longwave surface radiative cooling in the NH tropics in both clear and all-sky conditions and excessive shortwave surface radiation in the SH subtropics and extratropics due to an underestimation in reflection by clouds.

Norman G Loeb↗
NASA NTRS2022

Recent Trends in Transport of Surface Carbonaceous Aerosols to the Upper-Troposphere-Lower-Stratosphere Linked to Expansion of the Asian Summer Monsoon Anticyclone

Using MERRA-2 re-analyses, we have examined recent trends (2000-2019) in transport of surface carbonaceous aerosols (CA), i.e., organic carbon (OC) and black carbon (BC), to the upper troposphere (UT) and lower stratosphere (LS) during the Asian summer monsoon (ASM). We find a significant increased concentration of UTLS CA, linked to a linear trend in an expansion of the Asian Summer Monsoon Anticyclone (ASMA). Over core monsoon latitudes (25°-35°N), the trends in UTLS CA are enabled by increased upward transport from surface sources via an intensified monsoon meridional circulation, with increased latent heating over the southern Tibetan Plateau and foothill regions, enhanced by feedback processes associated with radiative heating by UTLS CA. In the extra-tropics, increased UTLS CA stems primarily from an extended source of increased wildfire emissions over eastern Siberia and northern Asia, coincident with a large-scale anomalous anticyclone with enhanced surface warming and drying near (80°-120°E, 55°-70°N). Here, carbonaceous aerosols are transported upward from the surface to the LS, likely by increased pyro-convection associated with enhanced wildfires, and enter the tropical UTLS via increased equator ward transport on the eastern flanks of anomalous upper-level anticyclones, coupled to the expanded ASMA. Overall, the increasing UTLS CA trends associated with expansion of the ASMA are consistent with a hydrostatic expansion of a warming troposphere, reflected in a rise in the tropical tropopause and consequential dynamical adjustments of the [ASM subtropical jetstream, modulating the climate of the greater ASM region.

interdecadal trends↗
DOE OSTI2022

Proximity-magnetized quantum spin Hall insulator: monolayer 1 T’ WTe2/Cr2Ge2Te6

Abstract Van der Waals heterostructures offer great versatility to tailor unique interactions at the atomically flat interfaces between dissimilar layered materials and induce novel physical phenomena. By bringing monolayer 1 T’ WTe 2 , a two-dimensional quantum spin Hall insulator, and few-layer Cr 2 Ge 2 Te 6 , an insulating ferromagnet, into close proximity in an heterostructure, we introduce a ferromagnetic order in the former via the interfacial exchange interaction. The ferromagnetism in WTe 2 manifests in the anomalous Nernst effect, anomalous Hall effect as well as anisotropic magnetoresistance effect. Using local electrodes, we identify separate transport contributions from the metallic edge and insulating bulk. When driven by an AC current, the second harmonic voltage responses closely resemble the anomalous Nernst responses to AC temperature gradient generated by nonlocal heater, which appear as nonreciprocal signals with respect to the induced magnetization orientation. Our results from different electrodes reveal spin-polarized edge states in the magnetized quantum spin Hall insulator.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Anomalous Hall effect in the weak-itinerant ferrimagnet FeCr 2 Te 4

In this study, we carried out a comprehensive study of electronic transport, thermal, and thermodynamic properties in Fe Cr 2 Te 4 single crystals. It exhibits bad-metallic behavior and anomalous Hall effect (AHE) below a weak-itinerant paramagnetic-to-ferrimagnetic transition T c ~ 123 K. The linear scaling between the anomalous Hall resistivity ρ x y and the longitudinal resistivity ρ x x implies that the AHE in Fe Cr 2 Te 4 is most likely dominated by an extrinsic skew-scattering mechanism rather than an intrinsic KL or an extrinsic side-jump mechanism, which is supported by our Berry phase calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2016

Tropospheric Column Ozone Response to ENSO in GEOS-5 Assimilation of OMI and MLS Ozone Data

We use GEOS-5 analyses of Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) ozone observations to investigate the magnitude and spatial distribution of the El Nino Southern Oscillation (ENSO) influence on tropospheric column ozone (TCO) into the middle latitudes. This study provides the first explicit spatially resolved characterization of the ENSO influence and demonstrates coherent patterns and teleconnections impacting the TCO in the extratropics. The response is evaluated and characterized by both the variance explained and sensitivity of TCO to the Nino 3.4 index. The tropospheric response in the tropics agrees well with previous studies and verifies the analyses. A two-lobed response symmetric about the Equator in the western Pacific/Indonesian region seen in some prior studies and not in others is confirmed here. This two-lobed response is consistent with the large-scale vertical transport. We also find that the large-scale transport in the tropics dominates the response compared to the small-scale convective transport. The ozone response is weaker in the middle latitudes, but a significant explained variance of the TCO is found over several small regions, including the central United States. However, the sensitivity of TCO to the Nino 3.4 index is statistically significant over a large area of the middle latitudes. The sensitivity maxima and minima coincide with anomalous anti-cyclonic and cyclonic circulations where the associated vertical transport is consistent with the sign of the sensitivity. Also, ENSO related changes to the mean tropopause height can contribute significantly to the midlatitude response. Comparisons to a 22-year chemical transport model simulation demonstrate that these results from the 9- year assimilation are representative of the longer term. This investigation brings insight to several seemingly disparate prior studies of the El Nino influence on tropospheric ozone in the middle latitudes.

ML↗
DOE OSTI2021

Fractional Laplacian spectral approach to turbulence in a dusty plasma monolayer

This work presents an analytical investigation of anomalous diffusion and turbulence in a dusty plasma monolayer, where energy transport across scales leads to the spontaneous formation of spatially disordered patterns. Many-body simulations of 10,000-particle dusty plasma monolayers are used to demonstrate how the global dynamics depend on the statistical properties of the dust assembly for realistic laboratory conditions. We find that disorder due to variations in the dust size distribution and charge-driven nonlocal interactions resulting in anomalous dust diffusion are key factors for the onset of instabilities. The resulting dynamics exhibit features of inertial turbulence over slightly more than half a decade of scales proportional or smaller than the Debye shielding length. These processes are examined analytically using a recently developed Fractional Laplacian Spectral (FLS) technique, which identifies the active energy channels as a function of scale, disorder concentration, and features of the nonlocal-interactions. The predictions from the theoretical (spectral) analysis demonstrate agreement with the results from the many-body (kinetic) simulations, thus providing a powerful tool for the study of active turbulence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2016

Evaluating Summer-Time Ozone Enhancement Events in the Southeast United States

This study evaluates source attribution of ozone (O3) in the southeast US within O3 lamina observed by the University of Alabama in Huntsville (UAH) Tropospheric Ozone Lidar Network (TOLNet) system during June 2013. This research applies surface-level and airborne in situ data and chemical transport model, GEOS-Chem, simulations in order to quantify the impact of North American anthropogenic emissions, wildfires, lightning NOx, and background stratospheric transport on the observed O3 lamina. During the summer of 2013, two anomalous O3 layers were observed and evaluated: 1) a nocturnal near-surface enhancement and 2) a late evening elevated (3-6 km above ground level) O3 plume. A "brute force" zeroing method was applied in GEOS-Chem to quantify the impact of individual emission sources and transport pathways on the vertical distribution of O3 during the two observed lamina. These model simulations suggest that the nocturnal O3 enhancement on June 12, 2013 below 3 km was primarily due to wildfire emissions and the fact that daily maximum anthropogenic emission contributions occurred during these night-time hours. During the second case study it was predicted that above average contributions from background stratospheric transport was largely contributing to the O3 lamina observed on June 29, 2013 between 3-6 km. Further evaluation suggested that a stratospheric intrusion was likely the main source contributing to this O3 enhancement between 3-6 km. Supporting information from other models, remote-sensing observations, and ground-based airborne in situ data agree with the source attribution predicted by GEOS-Chem simulations for both case studies. Overall, this study demonstrates the dynamic atmospheric chemistry occurring in the southeast US and displays the various emission sources and transport processes impacting O3 enhancements at different vertical levels of the troposphere.

Laminates↗
DOE OSTI2020

Field-induced magnetic phase transitions and the resultant giant anomalous Hall effect in the antiferromagnetic half-Heusler compound DyPtBi

We report field-induced magnetic phase transitions and transport properties of antiferromagnetic DyPtBi. We show that DyPtBi hosts a delicate balance between two different magnetic ground states, which can be controlled by a moderate magnetic field. Furthermore, it exhibits giant anomalous Hall effect (σ A = 1540 Ω –1 cm –1 , θ AHE = 24%) in a field-induced type-I spin structure, presumably attributed to the enhanced Berry curvature associated with avoided band crossings near the Fermi energy and/or nonzero spin chirality. As a result, the latter mechanism points DyPtBi towards a rare potential realization of anomalous Hall effect in an antiferromagnet with face-centered-cubic lattice that was proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗