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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 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Tetragonal and collapsed-tetragonal phases of CaFe 2 As 2 : A view from angle-resolved photoemission and dynamical mean-field theory

We present a study of the tetragonal to collapsed-tetragonal transition of CaFe 2 As 2 using angle-resolved photoemission spectroscopy and dynamical mean field theory-based electronic structure calculations.We observe that the collapsed-tetragonal phase exhibits reduced correlations and a higher coherence temperature due to the stronger Fe-As hybridization. Furthermore, a comparison of measured photoemission spectra and theoretical spectral functions shows that momentum-dependent corrections to the density functional band structure are essential for the description of low-energy quasiparticle dispersions. We introduce those using the recently proposed combined screened exchange + dynamical mean field theory scheme.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Easy-plane anisotropic-exchange magnets on a honeycomb lattice: Quantum effects and dealing with them

We provide analytical and numerical insights into the phase diagram and other properties of the extended Kitaev-Heisenberg model on the honeycomb lattice in the easy-plane limit, in which interactions are only between spin components that belong to the plane of magnetic ions. This parameter subspace allows for a much-needed systematic quantitative investigation of spin excitations in the ordered phases and of their generic features. Specifically, we demonstrate that in this limit one can consistently take into account magnon interactions in both zero-field zigzag and field-polarized phases. For the nominally polarized phase, we propose a regularization of the unphysical divergences that occur at the critical field and are plaguing the 1/S approximation in this class of models. For the explored parameter subspace, all symmetry-allowed terms of the standard parametrization of the extended Kitaev-Heisenberg model, such as K, J, and Γ, are significant, making the offered consideration relevant to a much wider parameter space. Furthermore, the dynamical structure factor near the paramagnetic critical point illustrates this relevance by showing features that are reminiscent of the ones observed in α–RuCl 3 , underscoring that they are not unique and should be common to a wide range of parameters of the model and, by extension, to other materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Electron Scattering by High-frequency Whistler Waves at Earth’s Bow Shock

Electrons are accelerated to non-thermal energies at shocks in space and astrophysical environments. While different mechanisms of electron acceleration have been proposed, it remains unclear how non-thermal electrons are produced out of the thermal plasma pool. Here, we report in situ evidence of pitch-angle scattering of non-thermal electrons by whistler waves at Earth’s bow shock. On 2015 November 4, the Magnetospheric Multiscale (MMS) mission crossed the bow shock with an Alfvén Mach number ∼11 and a shock angle ∼84°. In the ramp and overshoot regions, MMS revealed bursty enhancements of non-thermal (0.5–2 keV) electron flux, correlated with high-frequency (0.2–0.4 Ω{sub ce}, where Ω{sub ce} is the cyclotron frequency) parallel-propagating whistler waves. The electron velocity distribution (measured at 30 ms cadence) showed an enhanced gradient of phase-space density at and around the region where the electron velocity component parallel to the magnetic field matched the resonant energy inferred from the wave frequency range. The flux of 0.5 keV electrons (measured at 1 ms cadence) showed fluctuations with the same frequency. These features indicate that non-thermal electrons were pitch-angle scattered by cyclotron resonance with the high-frequency whistler waves. However, the precise role of the pitch-angle scattering by the higher-frequency whistler waves and possible nonlinear effects in the electron acceleration process remains unclear.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Scaling Analysis of Two–Phase Flow in Fractal Permeability Fields

Fluid mixing in permeable media is essential in many practical applications. The mixing process is a consequence of velocity fluctuations owing to geological heterogeneities and mobility contrast of fluids. Heterogeneities in natural rocks are often spatially correlated, and their properties, such as permeability, may be described using fractal distributions. This work models the fractal characteristics of such permeability fields in which the covariance function is expressed as a power-law function. A generalized scaling relation is derived relating various fractal permeability fields using the magnitude of their fluctuations. Here, this relation reveals the self-similar behavior of two-phase flow in such permeable media. To that end, a recently developed, high-resolution numerical simulator is employed to validate the analytically derived scaling relations. Two flow problems are considered in which flow is governed by 1) a linear, and 2) a nonlinear transport equation. Due to the probabilistic representation of the fractal permeability fields, a sensitivity study is conducted for each flow scenario to determine the number of realizations required for statistical convergence. Scaling analysis is performed using ensemble averages of simulated saturation profiles and their mixing lengths. Results support the validity of the developed scaling relation across the range of investigated flow conditions at intermediate times. The dynamics of linear flow in the asymptotic regime is affected by the correlation structure of heterogeneity. In nonlinear flow, scaling behavior appears to be dominated by the degree of nonlinearity.

58 GEOSCIENCES↗
DOE OSTI2016

Validation of the Five-Phase Method for Simulating Complex Fenestration Systems with Radiance against Field Measurements

The Five-Phase Method (5-pm) for simulating complex fenestration systems with Radiance is validated against field measurements. The capability of the method to predict workplane illuminances, vertical sensor illuminances, and glare indices derived from captured and rendered high dynamic range (HDR) images is investigated. To be able to accurately represent the direct sun part of the daylight not only in sensor point simulations, but also in renderings of interior scenes, the 5-pm calculation procedure was extended. The validation shows that the 5-pm is superior to the Three-Phase Method for predicting horizontal and vertical illuminance sensor values as well as glare indices derived from rendered images. Even with input data from global and diffuse horizontal irradiance measurements only, daylight glare probability (DGP) values can be predicted within 10% error of measured values for most situations.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Quantum phase-sensitive diffraction and imaging using entangled photons

We propose a quantum diffraction imaging technique whereby one photon of an entangled pair is diffracted off a sample and detected in coincidence with its twin. The image is obtained by scanning the photon that did not interact with matter. We show that when a dynamical quantum system interacts with an external field, the phase information is imprinted in the state of the field in a detectable way. The contribution to the signal from photons that interact with the sample scales as ∝ I p 1 / 2 , where I p is the source intensity, compared with ∝ I p of classical diffraction. This makes imaging with weak fields possible, providing high signal-to-noise ratio, avoiding damage to delicate samples. A Schmidt decomposition of the state of the field can be used for image enhancement by reweighting the Schmidt modes contributions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Modulation-doping a correlated electron insulator

Abstract Correlated electron materials (CEMs) host a rich variety of condensed matter phases. Vanadium dioxide (VO 2 ) is a prototypical CEM with a temperature-dependent metal-to-insulator (MIT) transition with a concomitant crystal symmetry change. External control of MIT in VO 2 —especially without inducing structural changes—has been a long-standing challenge. In this work, we design and synthesize modulation-doped VO 2 -based thin film heterostructures that closely emulate a textbook example of filling control in a correlated electron insulator. Using a combination of charge transport, hard X-ray photoelectron spectroscopy, and structural characterization, we show that the insulating state can be doped to achieve carrier densities greater than 5 × 10 21 cm −3 without inducing any measurable structural changes. We find that the MIT temperature (T MIT ) continuously decreases with increasing carrier concentration. Remarkably, the insulating state is robust even at doping concentrations as high as ~0.2 e − /vanadium. Finally, our work reveals modulation-doping as a viable method for electronic control of phase transitions in correlated electron oxides with the potential for use in future devices based on electric-field controlled phase transitions.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Effects on the geomagnetic tail at 60 earth radii of the geomagnetic storm of April 9, 1971.

A geomagnetic storm beginning with an sc occurred on Apr. 9, 1971. During the storm the charged particle lunar environment experiment at the Apollo 14 site, the solar wind spectrometer experiment at the Apollo 12 site, and the Ames magnetometers on Explorer 35 took data in the magnetosheath, at the magnetopause, in the plasma sheet, and in the high-latitude geomagnetic tail. The MIT Faraday cup and Ames magnetometers on board Explorer 33 monitored the solar wind. The data show that the storm was caused by a corotating tangential discontinuity in the solar wind, the magnetopause position is strongly dependent on the attack angle of the solar wind, and the tail field strength was indirectly measured to increase from 10 to 14 gamma after the sc. During the main phase the field strength in the tail was observed to increase to between 28 and 34 gamma. This increase is consistent with a thermal and magnetic compression of the tail radius from about 26 to about 16 earth radii.

Burke, W. J.↗
NASA NTRS1990

Acceleration of runaway electrons in solar flares

The dc electric field acceleration of electrons out of a thermal plasma and the evolution of the runaway tail are studied numerically, using a relativistic quasi-linear code based on the Ritz-Galerkin method and finite elements. A small field-aligned electric field is turned on at a certain time. The resulting distribution function from the runaway process is used to calculate the synchrotron emission during the evolution of the runaway tail. It is found that, during the runaway tail formation, which lasts a few tens of seconds for typical solar flare conditions, the synchrotron emission level is low, almost ot the same order as the emission from the thermal plasma, at the high-frequency end of the spectrum. However, the emission is enhanced explosively in a few microseconds by several orders of magnitude at the time the runaway tail stops growing along the magnetic field and tends toward isotropy due to the pitch-angle scattering of the fast particles. Results indicate that, in order to account for the observed synchrotron emission spectrum of a typical solar flare, the electric field acceleration phase must be accompanied or preceded by a heating phase which yields an enhanced electron temperature of about 2-15 keV in the flare region if the electric field is 0.1-0.2 times the Dreicer field and cyclotron-to-plasma frequency ratios are of order 1-2.

Moghaddam-Taaheri, E.↗
DOE OSTI2017

Tricritical wings and modulated magnetic phases in LaCrGe 3 under pressure

Experimental and theoretical investigations on itinerant ferromagnetic systems under pressure have shown that ferromagnetic quantum criticality is avoided either by a change of the transition order, becoming of the first order at a tricritical point, or by the appearance of modulated magnetic phases. In the first case, the application of a magnetic field reveals a wing-structure phase diagram as seen in itinerant ferromagnets such as ZrZn 2 and UGe 2 . Secondly, no tricritical wings have been observed so far. Here, we report on the discovery of wing-structure as well as the appearance of modulated magnetic phases in the temperature-pressure-magnetic field phase diagram of LaCrGe 3 . Our investigation of LaCrGe 3 reveals a double-wing structure indicating strong similarities with ZrZn 2 and UGe 2 . Unlike these simpler systems, LaCrGe 3 also shows modulated magnetic phases similar to CeRuPO. Our finding provides an example of an additional possibility for the phase diagram of metallic quantum ferromagnets.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Phase collapse and revival of a 1-mode Bose–Einstein condensate induced by an off-resonant optical probe field and superselection rules

Phase collapse and revival for Bose–Einstein condensates are nonlinear phenomena appearing due to atomic collisions. While it has been observed in a general setting involving many modes, for one-mode condensates its occurrence is forbidden by the particle number superselection rule (SSR), which arises because there is no phase reference available. We consider a single mode atomic Bose–Einstein condensate interacting with an off-resonant optical probe field. We show that the condensate phase revival time is dependent on the atom–light interaction, allowing optical control on the atomic collapse and revival dynamics. Incoherent effects over the condensate phase are included by considering a continuous photo-detection over the probe field. We consider conditioned and unconditioned photo-counting events and verify that no extra control upon the condensate is achieved by the probe photo-detection, while further inference of the atomic system statistics is allowed leading to a useful test of the SSR on particle number and its imposition on the kind of physical condensate state.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2012

Method for utilizing properties of the sinc(x) function for phase retrieval on nyquist-under-sampled data

Disclosed herein are systems, methods, and non-transitory computer-readable storage media for simulating propagation of an electromagnetic field, performing phase retrieval, or sampling a band-limited function. A system practicing the method generates transformed data using a discrete Fourier transform which samples a band-limited function f(x) without interpolating or modifying received data associated with the function f(x), wherein an interval between repeated copies in a periodic extension of the function f(x) obtained from the discrete Fourier transform is associated with a sampling ratio Q, defined as a ratio of a sampling frequency to a band-limited frequency, and wherein Q is assigned a value between 1 and 2 such that substantially no aliasing occurs in the transformed data, and retrieves a phase in the received data based on the transformed data, wherein the phase is used as feedback to an optical system.

Dean, Bruce H.↗
DOE OSTI2018

Strain-Driven Nanoscale Phase Competition near the Antipolar–Nonpolar Phase Boundary in Bi 0.7 La 0.3 FeO 3 Thin Films

Complex-oxide materials tuned to be near phase boundaries via chemistry/composition, temperature, pressure, etc. are known to exhibit large susceptibilities. Here, we observe a strain-driven nanoscale phase competition in epitaxially constrained Bi 0.7 La 0.3 FeO 3 thin films near the antipolar-nonpolar phase boundary and explore the evolution of the structural, dielectric, (anti)ferroelectric, and magnetic properties with strain. We find that compressive and tensile strains can stabilize an antipolar PbZrO 3 -like Pbam phase and a nonpolar Pnma orthorhombic phase, respectively. Heterostructures grown with little to no strain exhibit a self-assembled nanoscale mixture of the two orthorhombic phases, wherein the relative fraction of each phase can be modified with film thickness. Subsequent investigation of the dielectric and (anti)ferroelectric properties reveals an electric-field-driven phase transformation from the nonpolar phase to the antipolar phase. X-ray linear dichroism reveals that the antiferromagnetic-spin axes can be effectively modified by the strain-induced phase transition. This evolution of antiferromagnetic-spin axes can be leveraged in exchange coupling between the antiferromagnetic Bi 0.7 La 0.3 FeO 3 and a ferromagnetic Co0.9Fe0.1 layer to tune the ferromagnetic easy axis of the Co 0.9 Fe 0.1 . These results demonstrate that besides chemical alloying, epitaxial strain is an alternative and effective way to modify subtle phase relations and tune physical properties in rare earth-alloyed BiFeO 3 . Furthermore, the observation of antiferroelectric-antiferromagnetic properties in the Pbam Bi 0.7 La 0.3 FeO 3 phase could be of significant scientific interest and great potential in magnetoelectric devices because of its dual antiferroic nature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Field-induced quantum spin liquid in the Kitaev-Heisenberg model and its relation to α – RuCl 3

Recently considerable excitement has arisen due to the experimental observation of a field-induced spin liquid phase in the compound α– RuCl 3 . Yet, the nature of this putative spin liquid phase and the relevant microscopic model Hamiltonian remain still unclear. In this work, we address these questions by performing large-scale numerical simulations of a generalized Kitaev-Heisenberg model proposed to describe the physics of α– RuCl 3 . Although an intermediate phase does not appear for in-plane magnetic fields, our results strongly suggest that a stable intermediate spin liquid phase, sandwiched between a magnetically ordered phase at low fields and a high-field polarized phase, can be induced by out-of-plane magnetic fields. Moreover, we show that this field-induced spin liquid phase can be smoothly connected to a spin liquid possessing a spinon Fermi surface as proposed recently for the Kitaev model. The relevance of our findings to α– RuCl 3 is also discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Phase I Investigations at the Former CCC/USDA Grain Storage Facility in Montgomery City, Missouri, in 2010-2011

This report presents the technical findings of Phase I of Argonne’s studies. The Phase I field investigation was initiated on October 18, 2010. The work was conducted in accord with (1) the final site-specific Phase I Work Plan for Montgomery City (Argonne 2010; approved by the MDNR [2010]); (2) applicable Missouri regulations; and (3) the standard operating procedures, quality assurance/quality control (QA/QC) measures, and general health and safety policies outlined in the Master Work Plan (Argonne 2002) for operations in Kansas, which was reviewed by the MDNR and accepted for current use. A draft master plan specific to work in Missouri and a set of draft standard operating procedures are in review with the MDNR. The site-specific Work Plan for Montgomery City (Argonne 2010) (1) summarizes the pre-existing knowledge base for the Montgomery City investigation site compiled by Argonne and (2) describes the site-specific technical objectives and the intended scope of work developed for the first phase of the investigation. Three primary technical objectives were identified for the Phase I studies, as follows: 1. Update the presently identified inventory and status of private and public drinking water wells in the immediate vicinity of the former CCC/USDA grain storage facility, and sample the identified wells for volatile organic compounds (VOCs) and geochemical analyses. In conjunction with this effort, determine the present sources(s) of drinking water for all residents in an approximate 0.5-mi radius of the former CCC/USDA facility. 2. Investigate for possible evidence of a soil source of carbon tetrachloride contamination in the unconsolidated sediments beneath the former CCC/USDA facility that might affect the underlying bedrock aquifer units. 3. Obtain preliminary information on the site-specific lithologic and hydrologic characteristics of the unconsolidated sediments overlying bedrock at the former CCC/USDA grain storage location. Section 2 of this report describes the investigative methods used in the 2010-2011 studies and provides a chronological summary of the field events conducted. Section 3 presents a summary of the resulting field and laboratory data. These data, together with information presented in the site-specific Work Plan (Argonne 2010), are interpreted and integrated in Section 4 to (1) develop a preliminary conceptual model of the hydrogeologic framework affecting groundwater and potential contaminant migration in the vicinity of the former CCC/USDA facility and (2) serve as a basis for the initial consideration of contaminant levels and potential exposure pathways that might be of concern in the evaluation of risks to human health, public welfare, and the environment. The working conclusions drawn from the 2010-2011 studies are presented, along with recommendations, in Section 5.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Using the carrier-envelope phase to control strong-field dissociation of $\mathrm{HeH^+}$ at midinfrared wavelengths

We study the response of HeH + to an intense, few-cycle laser pulse. Specifically, we present the carrier-envelope phase (CEP) dependence of the kinetic-energy-release spectrum, the spatial asymmetry, and the total dissociation probability in two-cycle pulses with an intensity of 10 14 W/cm 2 and wavelengths of 3200 and 4000 nm. Strong spatial asymmetries are found in spite of the fact that the electron always becomes localized as He+H + , demonstrating that control of such asymmetries can be obtained via control of the nuclear degrees of freedom—as opposed to its usual interpretation as control over the electronic degrees of freedom. Finally, we explain these CEP effects in terms of our photon-phase representation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Uncharacteristic second order martensitic transformation in metals via epitaxial stress fields

While most phase transformations, e.g., ferroelectric or ferromagnetic, can be first or second order depending on external applied fields, martensitic transformations in metallic alloys are nearly universally first order. We demonstrate that epitaxial stress originating from the incorporation of a tailored second phase can modify the free energy landscape that governs the phase transition and change its order from first to second. High-fidelity molecular dynamics simulations show a remarkable change in the character of the martensitic transformation in Ni–Al alloys near the critical point. We observe the continuous evolution of the transformation order parameter and scaling with power-law exponents comparable to those in other ferroic transitions exhibiting critical behavior. Our theoretical work provides a foundation for recent experimental and computational results on martensites near critical points.

36 MATERIALS SCIENCE↗