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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

THE EPOCH OF DISK SETTLING: z {approx} 1 TO NOW

We present evidence from a sample of 544 galaxies from the DEEP2 Survey for evolution of the internal kinematics of blue galaxies with stellar masses ranging 8.0 < log M {sub *}(M {sub Sun }) < 10.7 over 0.2 < z < 1.2. DEEP2 provides galaxy spectra and Hubble imaging from which we measure emission-line kinematics and galaxy inclinations, respectively. Our large sample allows us to overcome scatter intrinsic to galaxy properties in order to examine trends in kinematics. We find that at a fixed stellar mass, galaxies systematically decrease in disordered motions and increase in rotation velocity and potential well depth with time. Massive galaxies are the most well ordered at all times examined, with higher rotation velocities and less disordered motions than less massive galaxies. We quantify disordered motions with an integrated gas velocity dispersion corrected for beam smearing ({sigma} {sub g}). It is unlike the typical pressure-supported velocity dispersion measured for early type galaxies and galaxy bulges. Because both seeing and the width of our spectral slits comprise a significant fraction of the galaxy sizes, {sigma} {sub g} integrates over velocity gradients on large scales which can correspond to non-ordered gas kinematics. We compile measurements of galaxy kinematics from the literature over 1.2 < z < 3.8 and do not find any trends with redshift, likely for the most part, because these data sets are biased toward the most highly star-forming systems. In summary, over the last {approx}8 billion years since z = 1.2, blue galaxies evolve from disordered to ordered systems as they settle to become the rotation-dominated disk galaxies observed in the universe today, with the most massive galaxies being the most evolved at any time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Structural and chemical disorder enhance point defect diffusion and atomic transport in Ni 3 Al-based γ' phase

The ordered L1 2 γ' Ni 3 Al intermetallic inclusions are routinely used as strengthening constituents in Ni-based superalloys and recent high-entropy alloys. As there are different metallic elements relative to the alloy matrix, the composition of γ' phase inclusions usually suffers some variations. In this work, we studied the elemental partition and its influence on atomic transport properties in a model (NiCo) 3 Al γ' phase with chemical and structural disorder. Combining the Monte Carlo and molecular static techniques, we first determined the elemental distribution in such compositionally-complexed γ' phase. The results suggest that Co tends to segregate, which profoundly influences defect energetics and diffusion properties. By modeling thermally activated diffusion by molecular dynamics, we found that chemical disorder induced by Co can enhance vacancy diffusion while significantly suppress diffusion via interstitial atom migration, as compared to the stoichiometric γ' Ni 3 Al. We further reveal that these observations are closely related to the defect energetics in these systems. Furthermore, our results explain the effects of disorder, long- and short-range orders on the diffusion properties in multicomponent intermetallic alloys, which helps to understand the stability and, thus, γ'-phase-assisted strengthening at different conditions including annealing and irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Chemical short-range order in derivative Cr–Ta–Ti–V–W high entropy alloys from the first-principles thermodynamic study

The development of high-entropy alloys (HEAs) focuses on exploring compositional regions in multi-component systems with all alloy elements in equal or near-equal atomic concentrations. Initially it was based on the main idea that high mixing configurational entropy contributions to the alloy free energy could promote the formation of a single solid solution phase. By using the ab-initio based Cluster Expansion (CE) Hamiltonian model constructed for the quinary bcc Cr–Ta–Ti–V–W system in combination with Monte Carlo (MC) simulations, we show that the phase stability and chemical short-range order (SRO) of the equiatomic quinary and five sub-quaternary systems, as well as their derivative alloys, can dramatically change the order–disorder transition temperatures (ODTT) as a function of alloy compositions. In particular, it has been found, that the equiatomic quaternary Ta–Ti–V–W and Cr–Ta–Ti–W alloys had the lowest order–disorder transition temperature (500 K) among all the analysed equiatomic compositions. In all investigated alloy systems, the strongest chemical ordering has been observed between Cr and V, which led to the conclusion that decreasing the concentration of either Cr or V might be beneficial in terms of decreasing the ODTT. It also predicts that increasing concentration of Ti significantly decreases the ODTT. Our analysis of chemical SRO as a function of alloy composition allows to understand the microstructure evolution of HEAs as a function of temperature in excellent agreement with available experimental observations. Importantly, our free energy of mixing and SRO calculations predict that the origin of precipitates formed by Cr- and V-rich in the sub-quaternary Cr–Ta–V–W system is driven by the thermodynamics. The modelling results are in an excellent agreement with experimental observation of Cr and V segregation in the W 0.38 Ta 0.36 Cr 0.15 V 0.11 alloy which in turns shows an exceptional radiation resistance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Flat band carrier confinement in magic-angle twisted bilayer graphene

Abstract Magic-angle twisted bilayer graphene has emerged as a powerful platform for studying strongly correlated electron physics, owing to its almost dispersionless low-energy bands and the ability to tune the band filling by electrostatic gating. Techniques to control the twist angle between graphene layers have led to rapid experimental progress but improving sample quality is essential for separating the delicate correlated electron physics from disorder effects. Owing to the 2D nature of the system and the relatively low carrier density, the samples are highly susceptible to small doping inhomogeneity which can drastically modify the local potential landscape. This potential disorder is distinct from the twist angle variation which has been studied elsewhere. Here, by using low temperature scanning tunneling spectroscopy and planar tunneling junction measurements, we demonstrate that flat bands in twisted bilayer graphene can amplify small doping inhomogeneity that surprisingly leads to carrier confinement, which in graphene could previously only be realized in the presence of a strong magnetic field.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Experimental and Computational Investigation of High Entropy Alloys for Elevated-Temperature Applications

To create and design novel structural materials with enhanced creep-resistance, fundamental studies have been conducted on high-entropy alloys (HEAs), using (1) thermodynamic calculations, (2) mechanical tests, (3) neutron diffraction, (4) characterization techniques, and (5) crystal-plasticity finite-element modeling (CPFEM), to explore future candidates for next-generation power plants. All the constituent binary and ternary systems of the Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems were thermodynamically modeled within the whole composition range. Comparisons between the calculated phase diagrams and literature data are in good agreement. Seven types of HEAs were fabricated from Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems. The Al x CrCuFeMnNi HEAs have disordered [face-centered cubic (FCC) + body-centered cubic (BCC)] crystal structures, not FCC or BCC single structure. Excessive alloying of the Al element results in the change of both microstructural and mechanical properties in Al x CoCrFeNi HEAs. There are mainly three structural features in Al x CoCrFeNi: (1) the morphology, (2) the volume fractions of the constitute phases, and (3) existing temperatures of all six phases. After homogenization, the Al 0.3 CoCrFeNi material is a pure FCC solid solution. After aging at 700 °C for 500 hours, the optimal microstructure combinations, the FCC matrix, needle-like B2 phase within grains, and granular σ phase along grain boundary, is achieved for Al 0.3 CoCrFeNi. The cold-rolling process is utilized to reduce the grain size of Al 0.1 CoCrFeNi and Al 0.3 CoCrFeNi. The chemical elemental partitioning of FCC, BCC, B2, and σphases at different temperatures, before and after mechanical tests, in Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems are quantitatively characterized by both synchrotron X-ray diffraction, neutron diffraction with levitation, scanning electron microscopy (SEM), advanced atom probe tomography (APT), and transmission electron microscopy (TEM). In-situ neutron diffraction experiments were conducted to study the strengthening effect of B2 phase on tensile properties of Al 0.3 CoCrFeNi HEAs directly. The results shows the creep behavior of Al 0.3 CoCrFeNi is superior to conventional alloys, and the heat treatment introduces secondary B2 phase into the FCC matrix, which increase the yielding strength, decrease the ductility, diminish the serrated flow during compression tests at high temperatures. In summary, the outcomes of the development of the HEAs with creep resistance include: (1) Suitable candidates, for the application to boilers and steam and gas turbines at temperatures above 760 °C and a stress of 35 MPa. (2) Fundamental understanding on the precipitate stability and deformation mechanisms of both single-phase and precipitate-strengthened alloys at room and elevated temperatures, and (3) The demonstration of an integrated approach, coupling modeling [thermodynamic calculations and crystal-plasticity finite-element modeling (CPFEM)] and focused experiments, to identify HEAs that outperform conventional alloys for high-temperature applications, which will be applicable for the discovery and development of other high-temperature materials in the power-generating industry.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Fluorinated cation-disordered rocksalt materials and methods of making thereof

This disclosure provides systems, methods, and apparatus related to lithium metal oxyfluorides. In one aspect, a method for manufacturing a lithium metal oxyfluoride having a general formula Li 1+x (MM′) z O 2-y F y , with 0.6 ≤ z ≤ 0.95, 0 < y ≤ 0.67, and 0.0 5 ≤ x ≤ 0.4, the lithium metal oxyfluoride having a cation-disordered rocksalt structure, includes: providing at least one lithium-based precursor; providing at least one redox-active transition metal-based precursor; providing at least one redox-inactive transition metal-based precursor; providing at least one fluorine-based precursor comprising a fluoropolymer; and mixing the at least one lithium-based precursor, the at least one redox-active transition metal-based precursor, the at least redox-inactive transition metal-based precursor, and the at least one fluorine-based precursor comprising a fluoropolymer to form a mixture.

Ahn, Juhyeon↗
DOE OSTI2024

Exploring the impact of the local environment on charge transfer states at molecular donor-acceptor heterojunctions

This program explored a broad range of charge transfer (CT) states in organic solar cells with the goal of understanding how molecular energetics, structure, and morphology influence CT state energy and dynamics, and how this in turn influences solar cell performance. We identified new types of delocalized CT states at ordered molecular heterojunctions, determined the factors that dictate CT state energetic disorder in bulk heterojunctions, determined that hot CT state dissociation is negligible for most systems, that the occupation of CT states is generally non-thermal in disordered heterojunctions, and that quasi-equilibrium generally does not hold in organic solar cells. These findings allowed us to demonstrate the lowest loss in potential of any organic solar cell to date and provide valuable guidance for designing higher efficiency organic solar cells in the future.

14 SOLAR ENERGY↗
DOE OSTI2021

Metal–insulator transition and low-density phases in a strongly-interacting two-dimensional electron system

Highlights: • Quantum phase transition observed in ultrahigh mobility SiGe/Si/SiGe quantum wells. • Metallic state observed in a strongly interacting spinless two-valley electron system. • Indication of band flattening at the Fermi level reported. • Transport evidence for a sliding two-dimensional quantum electron solid reported. We review recent experimental results on the metal–insulator transition and low-density phases in strongly-interacting, low-disordered silicon-based two-dimensional electron systems. Special attention is given to the metallic state in ultra-clean SiGe quantum wells and to the evidence for a flat band at the Fermi level and a quantum electron solid.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Thermal radiation in systems of many dipoles

Systems of many nanoparticles or volume-discretized bodies exhibit collective radiative properties that could be used for enhanced, guided, or tunable thermal radiation. These are commonly treated as assemblies of point dipoles with interactions described by Maxwell's equations and thermal fluctuations correlated by the fluctuation-dissipation theorem. Here, we demonstrate the equivalence of different theories for these systems and provide a complete derivation of many-dipole thermal radiation, showing that the correct use of the fluctuation-dissipation theorem depends on the definitions of fluctuating and induced dipole moments. We formulate a method to calculate the diffusive radiative thermal conductivity of arbitrary collections of nanoparticles; this allows the comparison of thermal radiation to other heat-transfer modes and across different material systems. We calculate the radiative thermal conductivity of ordered and disordered arrays of SiC and SiO 2 nanoparticles and show that thermal radiation can significantly contribute to thermal transport in these systems, because packed nanoparticles have low phonon thermal conductivity. Finally, we demonstrate that the radiative heat transfer strongly depends on the materials and geometrical arrangement of the nanoparticle array, and we verify our calculations by comparison to the exact solution for a one-dimensional particle chain.

42 ENGINEERING↗
DOE OSTI2015

Formation and Restacking of Disordered Smectite Osmotic Hydrates

Clay swelling, an important phenomenon in natural systems, can dramatically affect the properties of soils and sediments. Something of particular interest in low-salinity, saturated systems are osmotic hydrates, forms of smectite in which the layer separation greatly exceeds the thickness of a single smectite layer due to the intercalation of water. In situ X-ray diffraction (XRD) studies have shown a strong link between ionic strength and average interlayer spacing in osmotic hydrates but also indicate the presence of structural disorder that has not been fully described. In the present study the structural state of expanded smectite in sodium chloride solutions was investigated by combining very low electron dose, high-resolution cryogenic-transmission electron microscopy observations with XRD experiments. Wyoming smectite (SWy-2) was embedded in vitreous ice to evaluate clay structure in aqua. Lattice-fringe images showed that smectite equilibrated in aqueous, low-ionic-strength solutions, exists as individual smectite layers, osmotic hydrates composed of parallel layers, as well as disordered layer conformations. There was no evidence found here for edge-to-sheet attractions, but significant variability in interlayer spacing was observed. Whether this variation could be explained by a dependence of the magnitude of long-range cohesive (van der Waals) forces on the number of layers in a smectite particle was investigated here. Calculations of the Hamaker constant for layer-layer interactions showed that van der Waals forces may span at least five layers plus the intervening water and confirmed that forces vary with layer number. The drying of the disordered osmotic hydrates induced re-aggregation of the smectite to form particles that exhibited coherent scattering domains. Clay disaggregation and restacking may be considered as an example of oriented attachment, with the unusual distinction that it may be cycled repeatedly by changing solution conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Absence of many-body localization in a single Landau level

The localization properties of the highly excited states of a system projected into a single Landau level are analyzed. An analysis of level spacing ratios for finite size systems shows a clear crossover from extended (GUE) to localized (Poisson) statistics, indicating a many-body localization transition. However, the location of this transition depends very strongly on system size, and appears to scale to infinite disorder in the thermodynamic limit. This result does not depend on the properties of the ground state (such as whether the ground state exhibits topological order), as expected for a transition of highly excited eigenstates. We therefore conclude that many-body localization does not exist in these systems. Our results demonstrate that a subthermodynamic number of single particle effectively extended states is sufficient to cause all many-body states to become extended.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Disordered surface vibrations in jammed sphere packings

We study the vibrational properties near a free surface of disordered spring networks derived from jammed sphere packings. In bulk systems, without surfaces, it is well understood that such systems ω* frequency is controlled by ΔZ = $\langle$Z$\rangle$ - 2d, the difference between the average coordination of the spheres and twice the spatial dimension, d, of the system, which vanishes at the jamming transition. In the presence of a free surface we find that there is a density of disordered vibrational modes associated with the surface that extends far below ω . The total number of these low-frequency surface modes is controlled by ΔZ, and the profile of their decay into the bulk has two characteristic length scales, which diverge as ΔZ -1/2 and ΔZ -1 as the jamming transition is approached.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Floquet engineering with spatially nonuniform driving fields

In Floquet engineering, we apply a time-periodic modulation to change the effective behavior of a wave system. In this work, we generalize Floquet engineering to more fully exploit spatial degrees of freedom, expanding the scope of effective behaviors we can access. We develop a perturbative procedure to engineer space-time dependent driving forces that effectively transform broad classes of tight-binding systems into one another. We demonstrate several applications, including removing disorder, undoing Anderson localization, and enhancing localization to an extreme in spatially modulated waveguides. This procedure straightforwardly extends to other types of physical systems and different Floquet driving field implementations.

42 ENGINEERING↗
DOE OSTI2018

The Absence of the Selfaveraging Property of the Entanglement Entropy of Disordered Free Fermions in One Dimension

We consider the macroscopic system of free lattice fermions in one dimension assuming that the one-body Hamiltonian of the system is the one dimensional discrete Schrödinger operator with independent identically distributed random potential. We show analytically and numerically that the variance of the entanglement entropy of the segment [−M,M] of the system is bounded away from zero as M→∞. This manifests the absence of the selfaveraging property of the entanglement entropy in our model, meaning that in the one-dimensional case the complete description of the entanglement entropy is provided by its whole probability distribution. This also may be contrasted the case of dimension two or more, where the variance of the entanglement entropy per unit surface area vanishes as M→∞ [8], thereby guaranteeing the representativity of its mean for large M in the multidimensional case.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Developmental neurotoxic effects of two pesticides: Behavior and biomolecular studies on chlorpyrifos and carbaryl

In recent times, an increased occurrence of neurodevelopmental disorders, such as neurodevelopmental delays and cognitive abnormalities has been recognized. Exposure to pesticides has been suspected to be a possible cause of these disorders, as these compounds target the nervous system of pests. Due to the similarities of brain development and composition, these pesticides may also be neurotoxic to humans. We studied two different pesticides, chlorpyrifos and carbaryl, which specifically inhibit acetylcholinesterase (AChE) in the nervous system. The aim of the study was to investigate if the pesticides can induce neurotoxic effects, when exposure occurs during a period of rapid brain growth and maturation. The results from the present study show that both compounds can affect protein levels in the developing brain and induce persistent adult behavior and cognitive impairments, in mice neonatally exposed to a single oral dose of chlorpyrifos (0.1, 1.0 or 5 mg/kg body weight) or carbaryl (0.5, 5.0 or 20.0 mg/kg body weight) on postnatal day 10. The results also indicate that the developmental neurotoxic effects induced are not related to the classical mechanism of acute cholinergic hyperstimulation, as the AChE inhibition level (8–12%) remained below the threshold for causing systemic toxicity. The neurotoxic effects are more likely caused by a disturbed neurodevelopment, as similar behavioral neurotoxic effects have been reported in studies with pesticides such as organochlorines, organophosphates, pyrethroids and POPs, when exposed during a critical window of neonatal brain development. - Highlights: • A single neonatal exposure to chlorpyrifos or carbaryl induced developmental neurotoxic effects. • The neurotoxic effects were not caused by acute AChE inhibition. • The neurotoxic effects manifested as altered levels of neuroproteins in the developing brain. • The neurotoxic effects manifested as adult persistent aberrant behavior and cognitive function. • The neurotoxic effects are suggested to be caused by disrupted brain development.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Inhibition of microRNA-182-5p contributes to attenuation of lupus nephritis via Foxo1 signaling

Highlights: • MiR-182–5p is up-regulated in LN patients. • Foxo1 is down-regulated in LN patients. • MiR-185–5p promotes development of LN by inhibiting Foxo1. • Inhibition of miR-182–5p attenuates LN symptoms. MiR-182–5p suppresses expression of Foxo1 that is a protective factor in renal disorders and is up-regulated in systemic lupus erythematosus patients. Thus, we hypothesized that dys-function of miR-182–5p/Foxo1 axis contributed to development of lupus nephritis (LN). Firstly, we investigated the expressions of miR-182–5p and Foxo1 in LN patients and during growth of LN MRL/lpr mice. Then we subjected MRL/lpr mice to the injection of miR-182–5p antagomirs and assessed the effect of miR-182–5p inhibition on renal structure and function. In vitro, we administrated renal cell lines with TGF-β1 to explore the relation between renal fibrosis and miR-182–5p. The level of miR-182–5p was up-regulated in high Chronicity Index patients while the level of Foxo1 was suppressed. The progression of LN in mice was associated with the increased level of miR-182–5p and the decreased level of Foxo1. The inhibition of miR-182–5p ameliorated renal structure and function impairments associated with LN, along with the increased expression of Foxo1. The administration of TGF-β1 in vitro increased the expression of miR-182–5p in renal cells in an overall dose-dependent manner. The current study demonstrated that the expression of miR-182–5p was increased in LN patients, contributing to the suppression of Foxo1 and development of LN.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

31P MAS-NMR study of flux-grown rare-earth element orthophosphate (monazite/xenotime) solid solutions: Evidence of random cation distribution from paramagnetically shifted NMR resonances

We present 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra of flux-grown solid solutions of La1-xCexPO4 ( x between 0.027 and 0.32) having the monoclinic monazite structure, and of Y1-xMxPO4 (M = Vn+, Ce3+, Nd3+, x between 0.001 and 0.014) having the tetragonal zircon structure. Paramagnetically shifted NMR resonances are observed in all samples due to the presence of paramagnetic Vn+, Ce3+, and Nd3+ in the diamagnetic LaPO4 or YPO4. As a first-order observation, the number and relative intensity of these peaks is related to the symmetry and structure of the diamagnetic host phase. The presence of paramagnetic shifts allows for increased resolution between NMR resonances for distinct atomic species which leads to the observation of low intensity peaks related to PO4 species having more than one paramagnetic neighbor two or four atomic bonds away. Through careful analysis of peak areas and comparison with predictions for simple models, it was determined that solid solutions in the systems examined here are characterized by complete disorder (random distribution) of diamagnetic La3+ or Y3+ with the paramagnetic substitutional species Ce3+ and Nd3+. The increased resolution given by the paramagnetic interactions also leads to the observation of splitting of specific resonances in the 31P NMR spectra that may be caused by local, small-scale distortions from the substitution of ions having dissimilar ionic radii.

Palke, A. C.↗
DOE OSTI2014

Photometric study of single-shot energy-dispersive x-ray diffraction at a laser plasma facility

The low repetition rates and possible shot-to-shot variations in laser-plasma studies place a high value on single-shot diagnostics. For example, white-beam scattering methods based on broadband backlighter x-ray sources are used to determine changes in the structure of laser-shocked crystalline materials by the evolution of coincidences of reciprocal lattice vectors and kinematically allowed momentum transfers. Here, we demonstrate that white-beam techniques can be extended to strongly disordered dense plasma and warm dense matter systems where reciprocal space is only weakly structured and spectroscopic detection is consequently needed to determine the static structure factor and thus, the ion-ion radial distribution function. Specifically, we report a photometric study of energy-dispersive x-ray diffraction (ED-XRD) for structural measurement of high energy density systems at large-scale laser facilities such as OMEGA and the National Ignition Facility. We find that structural information can be obtained in single-shot ED-XRD experiments using established backlighter and spectrometer technologies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗