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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 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Anomalous behavior of nonequilibrium excitations in U O 2

Ultrafast optical pump-probe studies of uranium dioxide (UO 2 ) under pressure were performed in order to better understand the material's response to ionizing radiation. Photoexcitation generates oscillations in the time-resolved reflectivity at two distinct GHz-scale frequencies. The higher-frequency mode is attributed to a coherent longitudinal acoustic mode. The lower-frequency mode does not correspond to any known excitation under equilibrium conditions. The frequency and lifetime of the low-frequency mode are studied as a function of pressure. Abrupt changes in the pressure-dependent slopes of these attributes are observed at ~10 GPa, which correlates with an electronic transition in UO 2 . Variation of probe wavelength reveals that the low- k dispersion of the low-frequency mode does not fit into either an optical or acoustic framework. Rather, we propose that this mode is related to the dynamical magnetic structure of UO 2 . As a result, the implications of these results help account for the anomalously small volume of damage known to be caused by ionizing radiation in UO 2 ; we propose that the existence of the low-frequency mode enhances the material's transient thermal conductivity, while its long lifetime lengthens the timescale over which energy is dissipated. Both mechanisms enhance damage recovery.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1982

Capella revisited

The highlights of two studies of Capella, a spectroscopic binary, undertaken during the third and fourth years of the IUE are given. The first program consists of high dispersion spectroscopy at critical phases of the Capella orbit. The second program is a two month monitoring effort to search for ultraviolet modulations induced by the rotation of magnetic active regions onto and off of the visible hemisphere of the Capella secondary.

Ayres, T. R.↗
NASA NTRS1982

Modulation of energetic particle fluxes by a mixed mode of transverse and compressional waves

Modulation characteristics of particle fluxes in the presence of a mixed mode of compressional and transverse magnetic waves at hydromagnetic frequencies are investigated through kinetic perturbation of the distribution function. The magnetospheric medium where the particles are modulated contains both the magnetic and pressure gradients. The modulation features are found to be strongly dependent on the energy and pitch angle of the particles. Drifting particles can resonate with waves whose phase velocities are close to their drift velocities. When this occurs, the modulation amplitudes become significantly large and large phase shifts will occur. It is pointed out that resonance is important for particles with mid pitch angles (40-70 deg). The phase shift between the particle modulations and the magnetic field oscillations are strongly controlled by the combined effects of transverse and compressional wave components and/or the occurrence of drift resonance. Numerical calculations are performed using the dispersion relation of drift mirror Alfven waves as an example of waves with both compressional and transverse components.

Lin, C. S.↗
NASA NTRS1993

Mineralogy of three slightly palagonitized basaltic tephra samples from the summit of Mauna Kea, Hawaii

The paper characterizes the mineralogy and spectral properties of three slightly palagonitized basaltic tephra samples collected near the summit of Mauna Kea in order to contribute to the basis for inferring mineralogy and processes for Martian surface materials. The mineralogy of size fractions of these samples is examined by diffuse reflectance and FIR spectroscopy, optical microscopy, X-ray diffraction, Moessbauer spectroscopy, magnetic analysis, EMPA, TEM, and SEM. For the 20-1000 micron size fraction, sample HWMK11 (red) is essentially completely oxidized and has a hematite (Ti-hematite) pigment dispersed throughout the silicate matrix. Sample HWMK12 (black) has the lowest proportion of ferric-bearing phases and is thus least weathered. For HWMK11, the amount of hematite is essentially constant, and mica is present only in the coarse clay-sized fraction; smectites are low in structural Fe.

Golden, D. C.↗
DOE OSTI2022

The Complexity and Challenges of Irradiation-Induced Phase Instability Phenomenon in Nuclear Power Plant Components

High energy irradiation by neutrons or ions of metastable austenitic 300-series steels appears to initiate formation of bcc-phases with different morphology and elemental composition compared to that of retained ferrite. Extensive formation of specific Fe-rich ferrite was observed on the grain boundaries of annealed Russian steel 12Cr18Ni10Ti, an analog of AISI 321, after irradiation in the center-core region of sodium-cooled BN-350 fast reactor (SFR) doses up to 57 dpa at ~1×10-6dpa/sec. The ferrite fraction determined from scanning electron microscopy (SEM) closely matched the magnetic fraction determined using a ferritscope confirmed by X-ray diffraction analysis and selected area diffraction patterns. Chemical composition of the secondary phases was determined by energy dispersive X-ray analysis using transmission electron microscope, showing Fe-rich ferrite domains. Fe-ion irradiation (2.3 MeV) was used to study the accumulation of ferrite and martensite phases at higher dpa rates. The very high etchability of these ferrite particles in alcohol-based solutions may signal a very high etching in hot water, leading to accelerated intergranular cracking, especially upon long-term exposure during extended plant lifetimes.

D a, Merezhko↗
DOE OSTI2016

Crystal structures and magnetic properties of magnetite (Fe{sub 3}O{sub 4})/Polyvinyl alcohol (PVA) ribbon

Ribbon of magnetite (Fe{sub 3}O{sub 4})/Polyvinyl Alcohol (PVA) nanoparticles have been successfully fabricated with various concentration of PVA synthesized by co-precipitation method. Particle size of nanoparticles Fe{sub 3}O{sub 4} sample and ribbon Fe{sub 3}O{sub 4}/PVA 25% sample is about 9.34 nm and 11.29 nm, respectively. The result of Vibrating Sample Magnetometer (VSM) showed that saturation magnetization value decreased from 76.99 emu/g to 15.01 emu/g and coercivity increased from 49.30 Oe to 158.35 Oe as increasing concentration of PVA. Atomic Force Microscopy (AFM) analysis showed that encapsulated PVA given decreasing agglomeration, controlled shape of nanoparticles Fe{sub 3}O{sub 4} more spherical and dispersed. Surface roughness decreased with increasing concentration of PVA.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2017

MMS Observation of Inverse Energy Dispersion in Shock Drift Accelerated Ions

The four Magnetospheric Multiscale (MMS) spacecraft observed a ∼1 min burst of energetic ions (50–1000 keV) in the region upstream from the subsolar quasi-perpendicular bow shock on 6 December 2015. The composition, flux levels, and spectral indices of these energetic protons, helium, and oxygen ions greatly resemble those seen in the outer magnetosphere earlier while MMS crossed the magnetopause and differ significantly from those simultaneously observed far upstream by Advanced Composition Explorer (ACE). However, the event cannot be explained solely in terms of leakage from the magnetosphere. The strongly southward orientation of the interplanetary magnetic field (IMF) lines at the time of the event precludes any connection to the magnetosphere. This point is confirmed by the presence of energetic electrons, known to occur on magnetic field lines that graze the bow shock rather than connect to the magnetosphere. We suggest that the ions gradient drifted out of the nearby quasi-parallel foreshock and into the quasi-perpendicular bow shock. Each of the ion species exhibited an inverse energy dispersion. As predicted by models for shock drift acceleration, the energies of the ions increased as 𝜃(sub Bn), the angle between the IMF and the shock normal, increased. Finally, we note that a similar event was observed a few minutes later in the subsolar magnetosheath, indicating that such events can be swept downstream of the bow shock.

Lee, S. H.↗
DOE OSTI2026

Data for Magnetic Anisotropy due to Localized Structural Defects in Strained Yttrium Iron Garnet Thin Films

This dataset contains electron microscopy, magnetic, and X-ray diffraction characterization data for YIG/YSGG thin films associated with the manuscript "Magnetic anisotropy due to localized structural defects in strained yttrium iron garnet thin films". Characterizations include: scanning electron nano diffraction (SEND, or 4D-STEM), dark field transmission electron microscopy (DF-TEM), energy dispersive X-ray spectroscopy (EDS), ferrimagnetic resonance (FMR), superconducting quantum interference device (SQUID), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD).

Electron microscopy↗
DOE OSTI2021

Elucidating the mechanisms of enhanced lignin bioconversion by an alkali sterilization strategy

Biological lignin valorization represents an emerging green approach to upgrade lignin for sustainable and economic biorefineries. However, lignin generally exhibits poor water solubility and inhomogeneous distribution in an aqueous medium, significantly limiting its bioconversion efficiency. Herein, we develop a novel alkali sterilization strategy to effectively enhance the dispersion and fermentation performance of lignin substrates. The colloidal particle size and molecular structure variations of lignin during the sterilization were thoroughly investigated to reveal the mechanisms of enhanced fermentation performance. Results showed that alkali sterilization achieved a completely aseptic effect when mixing lignin medium at an initial pH of 12.7 for 24 h. Dynamic light scattering (DLS) analysis demonstrated that the hydrodynamic volume of colloidal lignin particles decreased by 96.3% by alkali sterilization compared with the conventional thermal sterilization. Moreover, lignin characterizations by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) suggested that alkali sterilization modified the lignin molecular structure by generating 50% more hydrophilic carboxyl groups, reducing the weight-average molecular weight (M w ) by 23.0%, and narrowing the molar-mass dispersity (D M ) by 23.8%. The generation of lignin substrates with more uniform distribution and lower molecular weight improved Rhodococcus opacus PD630 cell growth and metabolism. Microbial cell amount, lignin degradation, and lipid production in alkali sterilized medium increased by 309%, 30.3%, and 48.3%, respectively, compared to those in thermally sterilized medium. These results clearly demonstrated that alkali sterilization dramatically improved the lignin bioconversion performance. Furthermore, this work presents a facile and effective sterilization strategy to overcome inhomogeneous lignin distribution in aqueous fermentation media, showing great potentials as a platform technique for promoting biological lignin valorization.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

A versatile X-ray phase retarder for lock-in XMCD measurements

X-ray magnetic circular dichroism (XMCD) is a technique commonly used to probe magnetic properties of materials with element and orbital selectivity, which requires the use of circularly polarized (CP) X-rays. It is possible to accomplish XMCD experiments with fixed CP and alternating the magnetic field orientation, but most reliable data are obtained when alternating the magnetization orientation and the polarization between right and left helicities. A versatile strategy has been developed to perform XMCD experiments using a hard X-ray quarter-wave plate, at both polychromatic dispersive and conventional monochromatic optics, in combination with synchronous data acquisition. The switching frequency waveform is fed into a lock-in amplifier to detect and amplify the XMCD signal. The results on a reference sample demonstrate an improvement in data quality and acquisition time. The instrumentation successfully generated 98% of CP X-rays switching the beam helicity at 13 Hz, with the possibility of faster helicity switching once it is installed at the new Brazilian fourth-generation source, SIRIUS.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Interplay between magnetism and band topology in the kagome magnets R Mn 6 Sn 6

Kagome-lattice magnets R Mn 6 Sn 6 recently emerged as a new platform to exploit the interplay between magnetism and topological electronic states. Some of the most exciting features of this family are the dramatic dependence of the easy magnetization direction on the rare-earth specie, despite other magnetic and electronic properties being essentially unchanged, and the kagome geometry of the Mn planes that in principle can generate flat bands and Dirac points; gapping of the Dirac points by spin-orbit coupling has been suggested recently to be responsible for the observed anomalous Hall response in the member TbMn 6 Sn 6 . In this paper, we address both issues with ab initio calculations. We have discovered the significant role played by higher-order crystal-field parameters and rare-earth magnetic anisotropy constants in these systems. Further, we demonstrate that the microscopic origin of rare-earth magnetic anisotropy can also be quantified and understood at various levels: ab initio, phenomenological, and analytical. In particular, using a simple and physically transparent analytical model based on perturbation theory, we are able to explain, with full quantitative agreement, the evolution of rare-earth magnetic anisotropy across the series. We analyze in detail the topological properties of Mn-dominated bands and demonstrate how they emerge from the multiorbital planar kagome model. We further show that, despite this fact, most of the topological features at the Brillouin zone corner K are strongly 3D and therefore cannot explain the observed quasi-2D anomalous Hall effect, while the most pronounced quasi-2D dispersion are too far removed from the Fermi level. By employing self-consistent calculations with ab initio many-body approaches, we demonstrate that the exchange-correlation effects beyond the density functional theory for itinerant Mn- d electrons do not significantly alter the obtained electronic and magnetic structure. Therefore, we conclude that, contrary to previous claims, the most pronounced 2D kagome-derived topological band features bear little relevance to transport in RMn 6 Sn 6 , albeit they may possibly be brought to focus by electron or hole doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Determination of the characteristic magnetic pre-sheath length at divertor surfaces using micro-engineered targets on DiMES at DIII-D

The magnetic pre-sheath (MPS) width, L MPS , is a critical parameter to define the sheath potential, which controls the ion trajectory of low-Z species (D, T, He, and C), as well as the prompt re-deposition of high-Z species. In this work, to determine L MPS , we fabricated micro-trenches (30×30×4 µm) via focused ion beam (FIB) milling on a silicon surface and exposed them to L-mode deuterium plasmas in DIII-D via the Divertor Material Evaluation System (DiMES) removable sample exposure probe. The areal distribution of impurity depositions, mainly consisting of carbon, was measured by energy-dispersive X-ray spectroscopy (EDS) to reveal the deuterium ion shadowing effect on the trench floors. The carbon deposition profiles showed that the erosion was maximized for the azimuthal direction of φ = -40° (referenced to the toroidal magnetic field direction) as well as the polar angle of θ = 80°. A Monte Carlo equation-of-motion model, based on a collisionless MPS, was used to calculate the azimuthal and polar deuterium ion angle distributions (IADs) for a range of L MPS = k × ρ i , where ρ i is the ion gyro radius and k = 0.5-4. Then, gross erosion profiles were calculated by a Monte Carlo micro-patterning and roughness (MPR) code for ion sputtering using as input the calculated azimuthal and polar IADs for each value of k . Good agreement with the experimental C deposition profiles was obtained for the case k = 2.5-3.5. This result is consistent with a previous kinetic modeling prediction of k ~ 3, as well as previous analytical investigations that predicted the L MPS to be several ion gyro radii. A validation of theoretical sheath models supports its applicability to ITER and pilot plant divertors to successfully predict plasma-materials interactions.

Erosion↗
NASA NTRS2021

Extragalactic Magnetism with SOFIA (Legacy Program). I. The Magnetic Field in the Multiphase Interstellar Medium of M51*

The recent availability of high-resolution far-infrared (FIR) polarization observations of galaxies using HAWC+/SOFIA has facilitated studies of extragalactic magnetic fields in the cold and dense molecular disks. We investigate whether any significant structural differences are detectable in the kiloparsec-scale magnetic field of the grand design face-on spiral galaxy M51 when traced within the diffuse (radio) and the dense and cold (FIR) interstellar medium (ISM). Our analysis reveals a complex scenario where radio and FIR polarization observations do not necessarily trace the same magnetic field structure. We find that the magnetic field in the arms is wrapped tighter at 154 μm than at 3 and 6 cm; statistically significant lower values for the magnetic pitch angle are measured at FIR in the outskirts (R ≥ 7 kpc) of the galaxy. This difference is not detected in the interarm region. We find strong correlations of the polarization fraction and total intensity at FIR and radio with the gas column density and 12CO(1–0) velocity dispersion. We conclude that the arms show a relative increase of small-scale turbulent B-fields at regions with increasing column density and dispersion velocities of the molecular gas. No correlations are found with H i neutral gas. The star formation rate shows a clear correlation with the radio polarized intensity, which is not found in FIR, pointing to a small-scale dynamo-driven B-field amplification scenario. This work shows that multiwavelength polarization observations are key to disentangling the interlocked relation between star formation, magnetic fields, and gas kinematics in the multiphase ISM.

Spiral galaxies↗
DOE OSTI2015

Structural and magnetic effects of Cd{sub 1-x}In{sub x}Cr{sub 2}Se{sub 4}

Polycrystalline CdCr{sub 2}Se{sub 4} spinels with non-magnetic indium substitution were investigated with an aim to study the influence of non-magnetic substitution at the Cd site on its structural and magnetic properties. We carried out powder XRD and magnetic measurements on three compositions: Cd{sub 1-x}In{sub x}Cr{sub 2}Se{sub 4} (x=0, 0.05, 0.1). The XRD patterns were analyzed by carrying out Rietveld analysis and structural parameters were estimated. Phase purity of the compounds using reitveld refinement technique where confirming the indium distribution at tetrahedral site of the cubic close-packed sublattice formed by the selenium ions. The chemical compositions of these compounds were determined by energy dispersive x-ray analysis. Compared to parent compound, CdCr{sub 2}Se{sub 4}, the ferromagnetic Curie temperature T{sub C} was found to decrease from 130K to 123K and 114K as x varied from 0 to 0.05 and 0.1 respectively, whereas the saturation magnetization increases in Cd{sub 0.95}In{sub 0.05}Cr{sub 2}Se{sub 4} and again decreases in Cd{sub 0.9}In{sub 0.1}Cr{sub 2}Se{sub 4}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Asymmetric magnon excitation by spontaneous toroidal ordering

The effects of spontaneous toroidal ordering on magnetic excitation are theoretically investigated for a localized spin model that includes a staggered Dzyaloshinsky–Moriya interaction and anisotropic exchange interactions, which arise from the antisymmetric spin–orbit coupling and the multiorbital correlation effect. We show that the model exhibits a Néel-type antiferromagnetic order, which simultaneously accompanies a ferroic toroidal order. We find that the occurrence of toroidal order modulates the magnon dispersion in an asymmetric way with respect to the wave number: a toroidal dipole order on the zigzag chain leads to a band-bottom shift, while a toroidal octupole order on the honeycomb lattice gives rise to a valley splitting. These asymmetric magnon excitations could be a source of unusual magnetic responses, such as nonreciprocal magnon transport. A variety of modulations are discussed while changing the lattice and magnetic symmetries. Furthermore, the implications regarding candidate materials for asymmetric magnon excitations are presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Simultaneous observations of giant pulses from pulsar PSR B0950+08 at 42 and 74 MHz

We report the detection of giant pulse (GP) emission from PSR B0950+08 in 12 hr of observations made simultaneously at 42 and 74 MHz, using the first station of the Long Wavelength Array. We detected 275 GPs (in 0.16% of the pulse periods) and 465 GPs (0.27%) at 42 and 74 MHz, respectively. The pulsar is weaker and produces less frequent GPs than at 100 MHz. Here, GPs are taken as having ⩾ 10 times the flux density of an average pulse (AP); their cumulative distribution of pulse strength follows a power law, with an index of −4.1 at 42 MHz and −5.1 at 74 MHz, which is much less steep than would be expected if we were observing the tail of a Gaussian distribution of normal pulses. We detected no other transient pulses in a wide dispersion measure range from 1 to 5000 pc cm{sup −3}. There were 128 GPs detected within the same periods from both 42 and 74 MHz, which means more than half of them are not generated in a wide band. The CLEAN-based algorithm was used to deconvolve the the effect of scattering broadening and we have concluded that the scattering effect from the interstellar medium at 42 and 74 MHz is weak and cannot be distinguished from the pulse profiles. We calculated the altitude r of the emission region using the dipolar magnetic field model. We found r(42 MHz) = 29.27 km (0.242% of R{sub LC}) and r(74 MHz) = 29.01 km (0.240% of R{sub LC}) for the AP, while for GPs, r(42 MHz) = 29.10 km (0.241% of R{sub LC}) and r(74 MHz) = 28.95 km (0.240% of R{sub LC}). GPs, which have a double-peak structure, have a smaller mean peak-to-peak separation compared to the AP.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Microstructures, magnetic and electric properties of diluted magnetic semiconductors InTe{sub 1−x} Fe{sub x} (Co{sub x})

Highlights: ► The prepared InTe{sub 0.9}Fe{sub 0.1} was found to be ferromagnetic at room temperature and can be characterized as diluted magnetic semiconductors. ► The presence of staking faults, various types of defects, strained lattice, grain boundaries and the impurity of minor non-magnetic phase were suggested to participate in high temperature ferromagnetism. - Abstract: InTe compound doped by 10% of Fe or Co respectively was synthesized. X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), vibrating sample magnetometer (VSM) and Kiethley electrometer were used for characterizing the prepared samples. XRD show the presence of InTe{sub 0.9}Fe{sub 0.1} or InTe{sub 0.9}Co{sub 0.1} together with minor In{sub 4}Te{sub 3} phase. InTe{sub 0.9}Fe{sub 0.1} is ferromagnetic with high Curie and high blocking temperature, while InTe{sub 0.9}Co{sub 0.1} is antiferromagnetic with two high Neels temperatures. σRT of InTe{sub 0.9}Fe{sub 0.1} and InTe{sub 0.9}Co{sub 0.1} are greater than those of InTe. The higher conductivity is due to the higher carrier's density obtained from the interaction of the sp-d orbitals, of the electric and magnetic system. The presence of In{sub 4}Te{sub 3} minor phase and different kinds of defects are taking major roles in the formation of high Tc ferromagnetism and antiferromagnetism.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tuning the band topology of GdSb by epitaxial strain

Rare-earth monopnictide (RE-V) semimetal crystals subjected to hydrostatic pressure have shown interesting trends in magnetoresistance, magnetic ordering, and superconductivity, with theory predicting pressure-induced band inversion. Yet, thus far, there have been no direct experimental reports of interchanged band order in RE-Vs due to strain. This work studies the evolution of band topology in biaxially strained GdSb(001) epitaxial films using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT). As biaxial strain is tuned from tensile to compressive strain, the gap between the hole and the electron bands dispersed along [001] decreases. The conduction and valence band shifts seen in DFT and ARPES measurements are explained by a tight-binding model that accounts for the orbital symmetry of each band. Finally, we discuss the effect of biaxial strain on carrier compensation and magnetic ordering temperature.

36 MATERIALS SCIENCE↗