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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 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Evidence for charge delocalization crossover in the quantum critical superconductor CeRhIn5

Abstract The nature of charge degrees-of-freedom distinguishes scenarios for interpreting the character of a second order magnetic transition at zero temperature, that is, a magnetic quantum critical point (QCP). Heavy-fermion systems are prototypes of this paradigm, and in those, the relevant question is where, relative to a magnetic QCP, does the Kondo effect delocalize their f -electron degrees-of-freedom. Herein, we use pressure-dependent Hall measurements to identify a finite-temperature scale E loc that signals a crossover from f -localized to f -delocalized character. As a function of pressure, E loc ( P ) extrapolates smoothly to zero temperature at the antiferromagnetic QCP of CeRhIn 5 where its Fermi surface reconstructs, hallmarks of Kondo-breakdown criticality that generates critical magnetic and charge fluctuations. In 4.4% Sn-doped CeRhIn 5 , however, E loc ( P ) extrapolates into its magnetically ordered phase and is decoupled from the pressure-induced magnetic QCP, which implies a spin-density-wave (SDW) type of criticality that produces only critical fluctuations of the SDW order parameter. Our results demonstrate the importance of experimentally determining E loc to characterize quantum criticality and the associated consequences for understanding the pairing mechanism of superconductivity that reaches a maximum T c in both materials at their respective magnetic QCP.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Key Factors in Semi-Generic Coarse-Grained Modeling of Solid Polymer Electrolytes

Given the long length and time scales of interest and strong interactions present in solid polymer electrolytes, coarse-grained molecular models can be useful in understanding the molecular basis of their structure and transport properties. Rather than representing atoms individually, coarse-grained models use beads representing groups of atoms, making the system simpler and more efficient. Generic coarse-grained models, that are not built based on matching a particular atomistic system, can provide insight into the important physical considerations that apply across different chemical systems, though it can be unclear how to best match to experimental systems and capture relevant experimental behaviors with as simple of a model as possible. Here, we build on generic bead-spring models, but use stiff angle potentials, set different bead properties for different polymer types, and include additional ion parameters, creating a semi-generic coarse-grained model that can map more specifically to polymers and copolymers with different chain architectures, component glass transition temperatures, and ion solvation behaviors. We set most parameters with basic homopolymer data such as glass transition temperatures, Kuhn length, density, and dielectric constant, with further adjustment based on data from the polymer electrolyte system. We specifically model polystyrene-block-poly(oligo-oxyethylene methyl ether methacrylate) (PS-b-POEM) with lithium triflate salt, considering the POEM to be made of a poly(methylmethacrylate) backbone with poly(ethylene oxide) side chains. Solvation of ions is accounted for by additional polymer-ion interactions of the form -S/r4, plus additional lithium-polymer Lennard-Jones interactions. We find these potentials have different effects and discuss strategies for setting these parameters.

Zhang, Yuanhao↗
DOE OSTI2021

Two-dimensional multifunctional materials from endohedral fullerenes

A multifunctional two-dimensional (2D) material is theoretically predicted based on systematic ab initio calculations and model simulations for the honeycomb lattice of endohedral fullerene W@C 28 molecules. It has structural bistability, ferroelectricity, multiple magnetic phases, and excellent valley characters and can be easily functionalized by the proximity effect with magnetic isolators such as MnTiO 3 . Furthermore, we may also manipulate the valley Hall and spin transport properties by selectively switching a few W@C 28 molecules to the metastable phase. These conclusions contribute to integrating different functions in a single 2D material for technological innovations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Maximum strength and dislocation patterning in multi–principal element alloys

Multi–principal element alloys (MPEAs) containing three or more components in high concentrations render a tunable chemical short-range order (SRO). Leveraging large-scale atomistic simulations, we probe the limit of Hall-Petch strengthening and deformation mechanisms in a model CrCoNi alloy and unravel chemical ordering effects. The presence of SRO appreciably increases the maximum strength and lowers the propensity for faulting and structure transformation, accompanied by intensification of planar slip and strain localization. Deformation grains exhibit notably different microstructures and dislocation patterns that prominently depend on their crystallographic orientation and the number of active slip planes. Grain of single-planar slip attains the highest volume fraction of deformation-induced structure transformation, and grain with double-slip planes develops the densest dislocation network. These results advancing the fundamental understanding of deformation mechanisms and dislocation patterning in MPEAs suggest a mechanistic strategy for tuning mechanical behavior through simultaneously tailoring grain texture and local chemical order.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Mobility in single crystal Bi2Se3.

Galvanomagnetic effects are measured in p-type Bi2Se3 in magnetic fields to 8 tesla. Both Hall and conductivity mobilities are determined between 4.2 and 300 K. Carrier compensation, as well as nearly equal electron and hole mobilities are found in samples with approximately 10 to the 25th power per cu m 3 total carrier concentration.

Woollam, j. A.↗
NASA NTRS1979

Full-scale aircraft simulation with cryogenic tunnels and status of the National Transonic Facility

The effect of thermal and caloric imperfections in cryogenic nitrogen on boundary layers was determined to indicate that in order to simulate nonadiabatic laminar or turbulent boundary layers in a cryogenic nitrogen wind tunnel, the flight enthalpy ratio, rather than the temperature ratio, should be reproduced. The absence of significant real gas effects on both viscous and inviscid flows makes it unlikely that there will be large real gas effects on the cryogenic tunnel simulation of shock boundary layer interactions or other complex flow conditions encountered in flight. Condensation effects were studied to determine the minimum usable temperature and indicated that under most circumstances free stream Mach number rather than maximum local Mach number determines the onset of condensation effects.

Kilgore, R. A.↗
NASA NTRS1964

On the Mechanics of Transition Produced by Particles Passing Through an Initially Laminar Boundary Layer and the Estimated Effect on the LFC Performance of the X-21 Aircraft

Numerous flight tests of the X-21 aircraft have shown total loss of LFC while flying within, or in the proximity of, visible clouds. In addition, erratic LFC performance has been observed in conditions of light haze when the humidity of the air is relatively high. An investigation of the phenomena which might account for loss of LFC in or near clouds and for the erratic performance in light haze has been conducted. The phenomena considered in the investigation are classified as either thermodynamic effects or mechanical effects. The results derived from the study of thermodynamic and mechanical effects are presented with recommendations for follow-up work.

Hall, G. R.↗
NASA NTRS1997

Parametric Analysis of Cyclic Phase Change and Energy Storage in Solar Heat Receivers

A parametric study on cyclic melting and freezing of an encapsulated phase change material (PCM), integrated into a solar heat receiver, has been performed. The cyclic nature of the present melt/freeze problem is relevant to latent heat thermal energy storage (LHTES) systems used to power solar Brayton engines in microgravity environments. Specifically, a physical and numerical model of the solar heat receiver component of NASA Lewis Research Center's Ground Test Demonstration (GTD) project was developed. Multi-conjugate effects such as the convective fluid flow of a low-Prandtl-number fluid, coupled with thermal conduction in the phase change material, containment tube and working fluid conduit were accounted for in the model. A single-band thermal radiation model was also included to quantify reradiative energy exchange inside the receiver and losses through the aperture. The eutectic LiF-CaF2 was used as the phase change material (PCM) and a mixture of He/Xe was used as the working fluid coolant. A modified version of the computer code HOTTube was used to generate results in the two-phase regime. Results indicate that parametric changes in receiver gas inlet temperature and receiver heat input effects higher sensitivity to changes in receiver gas exit temperatures.

Hall, Carsie A., III↗
NASA NTRS1965

Response of a WB-47E Airplane to Runway Roughness at Eielson AFB, Alaska, September 1964

An investigation has been conducted to measure the response of a WB-47E airplane to the roughness of the runway at Eielson AFB, Alaska. The acceleration level in the pilot's compartment and the pitching oscillation of the airplane were found to be sufficiently high to possibly cause pilot discomfort and have an adverse effect on the precision of take-off.

Morris, Garland J.↗
NASA NTRS2007

Plasma Propulsion Testing Capabilities at Arnold Engineering Development Center

This paper describes the results of a series of experiments aimed at quantifying the plasma propulsion testing capabilities of a 12-ft diameter vacuum facility (12V) at USAF-Arnold Engineering Development Center (AEDC). Vacuum is maintained in the 12V facility by cryogenic panels lining the interior of the chamber. The pumping capability of these panels was shown to be great enough to support plasma thrusters operating at input electrical power >20 kW. In addition, a series of plasma diagnostics inside the chamber allowed for measurement of plasma parameters at different spatial locations, providing information regarding the chamber's effect on the global plasma thruster flowfield. The plasma source used in this experiment was Hall thruster manufactured by Busek Co. The thruster was operated at up to 20 kW steady-state power in both a lower current and higher current mode. The vacuum level in the chamber never rose above 9 x 10(exp -6) torr during the course of testing. Langmuir probes, ion flux probes, and Faraday cups were used to quantify the plasma parameters in the chamber. We present the results of these measurements and estimates of pumping speed based on the background pressure level and thruster propellant mass flow rate.

Polzin, Kurt A.↗
NASA NTRS2019

Variation in Ion Acceleration Characteristics of the HERMeS Hall Thruster During Magnetic Optimization

To reduce design risks for future magnetically shielded Hall thrusters, a test was performed on the HERMeS to obtain data for optimizing the effect of magnetic shielding. As a part of this test, laser-induced fluorescence velocimetry was used to characterize the variations in the ion acceleration with different magnetic configurations. Four magnetic configurations representing varying amounts of magnetic shielding between the high-energy discharge plasma and the discharge channel walls were tested. The ion velocity data points to the possibility that different plasma-wall interaction physics applies to a magnetically shielded thruster than a non-shielded thruster. The transition point is very prominent and can potentially be used to test whether a thruster is fully magnetically shielded.

HERMeS↗
DOE OSTI2025

Numerical Simulation of Electron Magnetohydrodynamics with Landau-quantized Electrons in Magnetar Crusts

Abstract In magnetar crusts, magnetic fields are sufficiently strong to confine electrons into a small to moderate number of quantized Landau levels. This can have a dramatic effect on the crust's thermodynamic properties, generating field-dependent de Haas–van Alphen oscillations. We previously argued that the large-amplitude oscillations of the magnetic susceptibility could enhance the ohmic dissipation of the magnetic field by continuously generating small-scale, rapidly dissipating field features. This could be important to magnetar field evolution and contribute to their observed higher temperatures. To study this, we performed quasi-3D numerical simulations of electron MHD in a representative volume of neutron star crust matter, for the first time including the magnetization and magnetic susceptibility resulting from Landau quantization. We find that the potential enhancement in the ohmic dissipation rate due to this effect can be a factor ∼3 for temperatures of the order of 10 8 K, and ∼4.5 for temperatures of the order of 5 × 10 7 K, depending on the magnetic field configuration. The nonlinear Hall term is crucial to this amplification: without it, the magnetic field decay is only enhanced by a factor ≲2 even at 5 × 10 7 K. These effects generate a high wavenumber plateau in the magnetic energy spectrum associated with the small-scale de Haas–van Alphen oscillations. Our results suggest that this mechanism could help explain the magnetar heating problem, though due to the effect's temperature-dependence, full magneto-thermal evolution simulations in a realistic stellar model are needed to judge whether it is viable explanation.

Rau, Peter B. (ORCID:0000000152209277)↗
NASA NTRS1995

A spectroscopic and photometric study of 12 BM Camelopardalis

Radial velocities from 1916.95 to 1991.95 and photometry from l979.25, both published and new in this paper, are presented and analyzed. A new solution of the radial velocity curve reveals a new period of 80.90 days and an eccentricity of e = 0.05 +/- 0.02, both very different from the 80.17 days and 0.35 found by Abt et al. (1969). An alternative solution with e = 0 is given because we cannot decide firmly whether or not the small eccentricity is real. We find V sin i = 11.3 +/- 0.3 km/s from Maidanak and 10 unequal depth. 0.048 mins and 0.026 mins. The orbital ephemeris for conjunction (K gisnt behind) is JD(hel.) 2,448,111.1 (+/- 0.4 days ) + 80.898 days (+/- 0.004 days ) E, consistent with both the radial velocities and the photometry. With the ellipticity effect removed, the light curve shows residual variability which we fit with a two-spot model. During the 13 years covered by photometry there were nine different starspots, the largest one producing a light loss of 0.19 mins. Rotation periods for the nine spots ranged from 78.6 +/- 0.5 days to 83.7 +/- 0.4 days from which we concluded that the K giant does rotate synchronously but with a differential rotation coefficient of k = 0.06 +/- 0.01. Lifetimes for the nine spots ranged from 1.1 to greater than 4.2 yr and were consistent with the empirical spot lifetime laws of Hall & Henry (1994). Use of the mass function, the orbital period, the V sin i, the two different ellipticity effect amplitudes, and various logical constraints led to ranges of possible masses, radii and inclinations. The most believable solution was around i = 90 deg, R(sub 1) = 24 solar radii, M(sub 1) = 1.1 solar mass, and M(sub 2) = 0.6 solar mass. THe Rossby number for the K giant is 0.48, small enough compared to the critical value of 0.65 to explain why, though rotating 'slowly', it does have large spots.

Hall, Douglas S.↗
DOE OSTI2021

Measurement of the EMC effect in light and heavy nuclei

In this work, inclusive electron scattering from nuclear targets has been measured to extract the nuclear dependence of the inelastic cross section in Hall C at the Thomas Jefferson National Accelerator facility. Results are presented for 2 H, 3 He, 4 He, 9 B, 12 C, 63 Cu and 197 Au at an incident electron beam energy of 5.77 GeV for a range of momentum transfer from Q 2 = 2 to 7 (GeV/c) 2 . These data improve the precision of the existing measurements of the EMC effect in the nuclear targets at large x, and allow for more detailed examinations of the A dependence of the EMC effect.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Direct TPE measurement via $e^+p/e^-p$ scattering at low $\varepsilon$ in Hall A

The proton elastic form factor ratio can be measured either via Rosenbluth separation in an experiment with unpolarized beam and target, or via the use of polarization degrees of freedom. However, data produced by these two approaches show a discrepancy, increasing with $Q^2$. The proposed explanation of this discrepancy - two-photon exchange - has been tested recently by three experiments. The results support the existence of a small two-photon exchange effect but cannot establish that theoretical treatments at the measured momentum transfers are valid. At larger momentum transfers, theory remains untested, and without further data, it is impossible to resolve the discrepancy. Additionally, a positron beam at Jefferson Lab allows us to directly measure two-photon exchange over an extended $Q^2$ and $\epsilon$ range with high precision. With this, we can validate whether the effect reconciles the form factor ratio measurements, and test several theoretical approaches, valid in different parts of the tested $Q^2$ range. In this proposal, we describe a measurement program in Hall A that combines the Super BigBite, BigBite, and High Resolution Spectrometers to directly measure the two-photon effect. Though the limited beam current of the positron beam will restrict the kinematic reach, this measurement will have very small systematic uncertainties, making it a clean probe of two photon exchange.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Hamiltonian kinetic-Hall magnetohydrodynamics with fluid and kinetic ions in the current and pressure coupling schemes

We present two generalized hybrid kinetic-Hall magnetohydrodynamics (MHD) models describing the interaction of a two-fluid bulk plasma, which consists of thermal ions and electrons, with energetic, suprathermal ion populations described by Vlasov dynamics. The dynamics of the thermal components are governed by standard fluid equations in the Hall MHD limit with the electron momentum equation providing an Ohm's law with Hall and electron pressure terms involving a gyrotropic electron pressure tensor. The coupling of the bulk, low-energy plasma with the energetic particle dynamics is accomplished through the current density (current coupling scheme; CCS) and the ion pressure tensor appearing in the momentum equation (pressure coupling scheme; PCS) in the first and the second model, respectively. The CCS is a generalization of two well-known models, because in the limit of vanishing energetic and thermal ion densities, we recover the standard Hall MHD and the hybrid kinetic-ions/fluid-electron model, respectively. This provides us with the capability to study in a continuous manner, the global impact of the energetic particles in a regime extending from vanishing to dominant energetic particle densities. The noncanonical Hamiltonian structures of the CCS and PCS, which can be exploited to study equilibrium and stability properties through the energy-Casimir variational principle, are identified. As a first application here, we derive a generalized Hall MHD Grad–Shafranov–Bernoulli system for translationally symmetric equilibria with anisotropic electron pressure and kinetic effects owing to the presence of energetic particles using the PCS.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗