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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Novel Theoretical Prediction of Structural Properties, Ferromagnetic Ordering, and Electronic Structure of Fe{sub 2}PbC MAX Phase

In this study, we have investigated the magnetic stability; ferromagnetic ordering; and structural, elastic, and electronic properties of Fe{sub 2}PbC compound. The calculations are performed by the use of full-potential linearized augmented plane wave method implemented in WIEN2k code. We have found that the ferromagnetic state of Fe{sub 2}PbC is more stable than non-magnetic state configuration at their equilibrium lattice parameters. The structural and elastic properties suggest that Fe{sub 2}PbC is an anisotropic material, which is stable in the hexagonal MAX phase. The electronic structures show that Fe{sub 2}PbC has metallic-covalent-ionic character. The ferromagnetic performance of Fe{sub 2}PbC is confirmed by the total magnetic moment of 4.15 μ{sub B}, where its main contribution is originated from Fe atoms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1979

Nonlinear stability of solar type III radio bursts. II - Application to observations near 1 AU

A set of rate equations including strong turbulence effects and anomalous resistivity are solved using parameters which model several solar type III bursts. Analysis of these bursts has led to quantitative comparisons between several of the observed phenomena and the theory. Through use of an analytic model for the time evolution of the energetic electron exciter, it is found that the exciter distributions observed at 1 AU are unstable to the excitation of the linear bump-in-tail instability, amplifying Langmuir waves above the threshold for the oscillating two-stream instability (OTSI). The OTSI and the attendant anomalous resistivity produce a rapid spectral transfer of Langmuir waves to short wavelengths, out of resonance with the electron exciter. In addition, the various parameters needed to model the bursts are extrapolated inside 1 AU with similar results. Finally, reabsorption of the Langmuir waves by the beam is shown to be unimportant in all cases, even at 0.1 AU.

Goldstein, M. L.↗
DOE OSTI2019

Microwave Spectroscopy of a Weakly Pinned Charge Density Wave in a Superinductor

A chain of small Josephson junctions (a.k.a. superinductor) emerged recently as a high-inductance, low-loss element of superconducting quantum devices. We notice that the intrinsic parameters of a typical superinductor in fact place it into the Bose glass universality class for which the propagation of waves in a sufficiently long chain is hindered by pinning. Its weakness provides for a broad crossover from the spectrum of well-resolved plasmon standing waves at high frequencies to the low-frequency excitation spectrum of a pinned charge density wave. We relate the scattering amplitude of microwave photons reflected off a superinductor to the dynamics of a Bose glass. The dynamics at long and short scales compared to the Larkin pinning length determines the low- and high-frequency asymptotes of the reflection amplitude.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Specificities of Spin Wave Focusing in EuO and EuS Crystals

Specificities of spin wave focusing in EuO and EuS crystals are studied. It is shown that spin wave focusing is absent in the long-wave approximation: it is observed only for wave vectors in the second half of the Brillouin zone (aq≳ π, where a is the lattice constant and q is the magnitude of the wave vector). It was found that, for EuO and EuS crystals, the directions of spin wave focusing differ due to the different signs of the exchange integrals responsible for the exchange interaction of the magnetic moment with the second neighbors. The directions along which a magnon caustic is formed are determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

EXAFS Spectroscopy of Fractional Mixed-Valence Charge Density Wave Systems

We present extended X-ray absorption fine structure (EXAFS) spectra and modeling of a series of structurally tunable quasi-one-dimensional mixed-valence platinum–halide linear chain materials, [Pt(en 2 )][Pt(en 2 )X 2 ](ClO 4 ) 4 with X = Cl, Br, I. The materials exhibit a commensurate charge density wave with fractional charge states on alternating platinum ions in the chain, as well as a Peierls distortion with alternating platinum–halide bond lengths. The amplitude of the charge density wave and, correspondingly, the extent of the Peierls distortion are controlled by the identity of the bridging halide ion. We have carried out ab initio multiple scattering calculations using the FEFF9 code to relate the oriented Pt L III EXAFS spectra to the tunable electronic and structural properties. The spectral modeling reveals distinct photoelectron threshold energy values for the two inequivalent platinum ions in each of the mixed-valence chains, with values that vary systematically with fractional valence state. The difference in the photoelectron threshold energies of the two inequivalent platinum ions within each material correlates directly with the amplitude of the charge density wave, reflecting the decrease in charge density wave strength through the halide series X = Cl, Br, and I. We use dynamical matrix modeling to relate the experimentally determined mean-square relative displacement parameters for the metal–halide bond distances to the chain–axis vibrational modes that modulate the charge density wave structure. In addition, we discuss the EXAFS fitting results for the Pt–I bond lengths in the [Pt(en 2 )][Pt(en 2 )I 2 ](ClO 4 ) 4 complex in comparison to previous, mutually inconsistent structural determinations for this material.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Wave optics simulations for new soft x-ray beamlines at NSLS-II

In this work, we performed fully- and partially-coherent synchrotron emission and propagation simulations with the "Synchrotron Radiation Workshop" computer code to analyze the performance of two soft X-ray beamlines under development at the National Synchrotron Light Source II: Soft X-ray Nanoprobe (SXN), and Angle-Resolved Photoemission Spectroscopy (ARPES) and Resonant Inelastic X-ray Scattering (RIXS) Imaging (ARI). The SXN beamline intends to provide high flux and high spatial resolution coherent soft X-ray imaging capabilities using both zone plate and lensless coherent imaging techniques. The ARI beamline aims to perform high flux ARPES and RIXS experiments with a focal spot size at the sample approaching 100 nm using highly-demagnifying mirrors in Kirkpatrick-Baez geometry. To accurately calculate the resolution and the degree of X-ray coherence provided by the two state-of-the-art beamlines, partial coherence effects are required to be taken into account in wave optics simulations for these two beamlines. In this talk, beamline performance parameters such as spot size, degree of coherence, flux, and energy resolution at the sample are presented. The effects of mirror surface slope errors on beamline performance were studied and some suggestions for further optimization are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Updated determination of N * resonance parameters using a unitary, multichannel formalism

Results are presented for an updated multichannel energy-dependent partial-wave analysis of πN scattering. Our earlier research incorporated single-energy amplitudes for πN→πN, γN→πN, πN→ππN, πN→ηN, and πN→KΛ. The present work incorporates new single-energy solutions for γp→ηp up to a center-of-mass (c.m.) energy of 1990 MeV, γp→K+Λ up to a c.m. energy of 2230 MeV, and γn→ηn up to a c.m. energy of 1885 MeV, as well as updated single-energy solutions for πN→ηN, πN→KΛ, and γN→πN. Here, we introduce and discuss the resonance parameters obtained from a combined fit of all these single-energy amplitudes. Our determined energy-dependent amplitudes support an excellent description of the corresponding measured observables.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1992

Homogeneous quantum electrodynamic turbulence

The electromagnetic field equations and Dirac equations for oppositely charged wave functions are numerically time-integrated using a spatial Fourier method. The numerical approach used, a spectral transform technique, is based on a continuum representation of physical space. The coupled classical field equations contain a dimensionless parameter which sets the strength of the nonlinear interaction (as the parameter increases, interaction volume decreases). For a parameter value of unity, highly nonlinear behavior in the time-evolution of an individual wave function, analogous to ideal fluid turbulence, is observed. In the truncated Fourier representation which is numerically implemented here, the quantum turbulence is homogeneous but anisotropic and manifests itself in the nonlinear evolution of equilibrium modal spatial spectra for the probability density of each particle and also for the electromagnetic energy density. The results show that nonlinearly interacting fermionic wave functions quickly approach a multi-mode, dynamic equilibrium state, and that this state can be determined by numerical means.

Shebalin, John V.↗
DOE OSTI2022

Observation of breakdown wave mechanism in avalanche ionization produced atmospheric plasma generated by a picosecond CO 2 laser

Understanding the formation and long-timescale evolution of atmospheric plasmas produced by ultrashort, long-wavelength infrared (LWIR) pulses is an important but partially understood problem. Of particular interest are plasmas produced in air with a peak laser intensity ~10 12 W/cm 2 , the so-called clamping intensity observed in LWIR atmospheric guiding experiments where tunneling and multi-photon ionization operative at near-IR or shorter wavelengths are inoperative. We find that avalanche breakdown on the surface of aerosol (dust) particles can act to seed the breakdown of air observed above the 200 GW/cm 2 threshold when a train of 3 ps 10.6 μm laser pulses separated by 18 ps is used. The breakdown first appears at the best focus but propagates backward toward the focusing optic as the plasma density approaches critical density and makes forward propagation impossible. The velocity of the backward propagating breakdown can be as high as 10 9 cm/s, an order of magnitude greater than measured with ns pulse-produced breakdown, and can be explained rather well by the so-called breakdown wave mechanism. Transverse plasma expansion with a similar velocity is assisted by UV photoionization and is observed as a secondary longitudinal breakdown mechanism in roughly 10% of the shots. When a cm-size, TW power beam is propagated, interception of aerosol particles is guaranteed and several (40 cm -3 ) breakdown sites appear, each initially producing a near-critical density plasma. On a 10 ns–1 μs timescale, shockwaves from each site expand radially and coalesce to produce a large hot gas channel. The radial velocity of the expansion agrees well with the prediction of the blast wave theory developed for ultrafast atmospheric detonations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Space–time structure of weak magnetohydrodynamic turbulence

The two-time energy spectrum of weak magnetohydrodynamic turbulence is found by applying a wave-turbulence closure to the cumulant hierarchy constructed from the dynamical equations. Solutions are facilitated via asymptotic expansions in terms of the small parameter $\varepsilon$ , describing the ratio of time scales corresponding to Alfvénic propagation and nonlinear interactions between counter-propagating Alfvén waves. The strength of nonlinearity at a given spatial scale is further quantified by an integration over all possible delta-correlated modes compliant in a given set of three-wave interactions that are associated with energy flux through the said scale. The wave-turbulence closure for the two-time spectrum uncovers a secularity occurring on a time scale of order $\varepsilon ^{-2}$ , and the asymptotic expansion for the spectrum is reordered in a manner comparable to the one-time case. It is shown that for the regime of stationary turbulence, the two-time energy spectrum exponentially decays on a lagged time scale $(\varepsilon ^2 \gamma _k^s)^{-1}$ in proportion to the strength of the associated three-wave interactions, characterized by nonlinear decorrelation frequency $\gamma _k^s$ . The scaling of the form $k_{\perp } v_0 \chi _0$ exhibited by this frequency is reminiscent of random sweeping by the outer scale with characteristic fluctuation velocity $v_0$ that is modified due to competition with Alfvénic propagation (characterized by $\chi _0$ ) at the said scale. A brief calculation of frequency broadening of the power spectrum due to nonlinear interactions is also presented.

Physics↗
DOE OSTI2026

Uncovering the linear boron environment in Na 3 BP 2 through solid-state 11 B NMR spectroscopy

Boron-based compounds exhibit a wide range of structural diversity, with potential applications spanning organic and inorganic chemistry. Herein, we focus on the characterization of the linear boron-phosphorus unit P═B═P in Na 3 BP 2 using solid-state nuclear magnetic resonance (ssNMR) spectroscopy and density functional theory (DFT) calculations. High-resolution 11 B ssNMR spectra were recorded at two fields, and key parameters such as chemical shift anisotropy (CSA), quadrupolar coupling constants (C Q ), and electric field gradient (EFG) tensors were extracted. The 11 B NMR results revealed a distinct chemical environment for the two-coordinate boron atom, with a CSA span (Ω) of 280 ppm and a C Q of 3.0 MHz. These values were further validated through periodic plane-wave DFT calculations, which showed good agreement with experimental results. The obtained spectral parameters are compared to other linear boron units, such as the BO 2 motif, providing a broader context for understanding boron coordination in inorganic compounds. This work expands the body of NMR knowledge on boron-containing materials, particularly for linear boron motifs. The findings contribute to the growing field of boron chemistry and its potential applications in advanced materials.

Porter, Andrew P. [Ames Laboratory (AMES), Ames, I↗
NASA NTRS2009

Facilitating Heliophysics Research by the Virtual Wave Observatory (VWO) Context Data Search Capability

Wave phenomena, ranging from freely propagating electromagnetic radiation (e.g., solar radio bursts, AKR) to plasma wave modes trapped in various plasma regimes (e.g., whistlers, Langmuir and ULF waves) and atmospheric gravity waves, are ubiquitous in the heliosphere. Because waves can propagate, wave data obtained at a given observing location may pertain to wave oscillations generated locally or from afar. While wave data analysis requires knowledge of wave characteristics specific to different wave modes, the search for appropriate data for heliophysics wave studies also requires knowledge of wave phenomena. In addition to deciding whether the interested wave activity is electrostatic (i.e., locally trapped) or electromagnetic (with propagation over distances), considerations must be given to the dependence of the wave activity on observer's location or viewing geometry, propagating frequency range and whether the wave data were acquired by passive or active observations. Occurances of natural wave emissions i the magnetosphere (e.g, auroral kilometric radiation) are often dependent also on the state (e.e., context) of the magnetosphere that varies with the changing solar wind, IMF and geomagnetic conditions. Fung and Shao [2008] showed recently that magnetospheric state can be specified by a set of suitably time-shifted solar wind, IMF and the multi-scale geomagnetic response parameters. These parameters form a magnetospheric state vector that provides the basis for searching magnetospheric wave data by their context conditions. Using the IMAGE Radio Plasma Imager (RPI) data and the NASA Magnetospheric State Query System (MSOS) [Fung, 2004], this presentation demonstrates the VWO context data search capability under development and solicits feedback from the Heliophysics research community for improvements.

Fung, Shing F.↗
NASA NTRS1993

LRAT: Lightning Radiative Transfer

In this report, we extend to cloud physics the work done for single and multiple scattering of electromagnetic waves. We consider the scattering of light, visible or infrared, by a spherical cloud represented by a statistically homogeneous ensemble of configurations of N identical spherical water droplets whose centers are uniformly distributed in its volume V. The ensemble is specified by the average number rho of scatterers in unit volume and by rho f(R) with f(R) as the distribution function for separations R of pairs. The incident light, vector-phi(sub 0) a plane electromagnetic wave with harmonic time dependence, is from outside the cloud. The propagation parameter kappa(sub 0) and the index of refraction eta(sub 0) determine physically the medium outside the distribution of scatterers. We solve the interior problem separately to obtain the bulk parameters for the scatterer equivalent to the ensemble of spherical droplets. With the interior solution or the equivalent medium approach, the multiple scattering problem is reduced to that of an equivalent single scatterer excited from outside illumination. A dispersion relation which determines the bulk propagation parameter K and the bulk index of refraction eta of the cloud is given in terms of the vector equivalent scattering amplitude vector-G and the dyadic scattering amplitude tilde-g of the single object in isolation. Based on this transfer model we will have the ability to consider clouds composed of inhomogeneous distribution of water and/or ice particles and we will be able to take into account particle size distributions within the cloud. We will also be able to study the effects of cloud composition (i.e., particle shape, size, composition, orientation, location) on the polarization of the single or the multiple scattered waves. Finally, this study will provide a new starting point for studying the problem of lightning radiative transfer.

Phanord, Dieudonne D.↗
NASA NTRS1999

Investigations of Remote Plasma Irregularites by Radio Sounding: Applications of the Radio Plasma Imager on IMAGE

The Radio Plasma Imager (RPI) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission operates like a radar by transmitting and receiving coherent electromagnetic pulses. Long-range echoes of electromagnetic sounder waves are reflected at remote plasma cutoffs. Thus, analyses of RPI observations will yield the plasma parameters and distances to the remote reflection points. These analyses assume that the reflecting plasma surfaces are cold and are sufficiently smooth that they effectively behave as plane mirrors to the incoming sounder waves, i.e., that geometric optics can be used. The RPI will employ pulse compression and spectral integration techniques, perfected in ground-based ionospheric digital sounders, in order to enhance the signal-to-noise ratio in long-range magnetospheric sounding. When plasma irregularities exist in the remote magnetospheric plasmas that are being probed by the sounder waves, echo signatures may become complicated. Ionospheric sounding experience indicates that while topside sounding echo strengths can actually be enhanced by the presence of irregularities, ground-based sounding indicates that coherent detection techniques can still be employed. In this paper we investigate the plasma conditions that will allow coherent signals to be detected by the RPI and the signatures to be expected, such as scattering and plasma resonances, in the presence of multi-scale irregularities, may possibly have on RPI signals. Sounding of irregular plasma structures in the plasmasphere, plasmapause and magnetopause are also discussed.

Fung, Shing F.↗
DOE OSTI2019

Scale Analysis of Moist Thermodynamics in a Simple Model and the Relationship between Moisture Modes and Gravity Waves

Abstract Observations and theory of convectively coupled equatorial waves suggest that they can be categorized into two distinct groups. Moisture modes are waves whose thermodynamics are governed by moisture fluctuations. The thermodynamics of the gravity wave group, on the other hand, are rooted in buoyancy (temperature) fluctuations. On the basis of scale analysis, it is found that a simple nondimensional parameter—akin to the Rossby number—can explain the processes that lead to the existence of these two groups. This parameter, defined as Nmode, indicates that moisture modes arise when anomalous convection lasts sufficiently long so that dry gravity waves eliminate the temperature anomalies in the convective region, satisfying weak temperature gradient (WTG) balance. This process causes moisture anomalies to dominate the distribution of moist enthalpy (or moist static energy), and hence the evolution of the wave. Conversely, convectively coupled gravity waves arise when anomalous convection eliminates the moisture anomalies more rapidly than dry gravity waves can adjust the troposphere toward WTG balance, causing temperature to govern the moist enthalpy distribution and evolution. Spectral analysis of reanalysis data indicates that slowly propagating waves (cp ~ 3 m s−1) are likely to be moisture modes while fast waves (cp ~ 30 m s−1) exhibit gravity wave behavior, with “mixed moisture–gravity” waves existing in between. While these findings are obtained from a highly idealized framework, it is hypothesized that they can be extended to understand simulations of convectively coupled waves in GCMs and the thermodynamics of more complex phenomena.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2019

Scale Analysis of Moist Thermodynamics in a Simple Model and the Relationship Between Moisture Modes and Gravity Waves

Observations and theory of convectively-coupled equatorial waves suggest that they can be categorized into two distinct groups. Moisture modes are waves whose thermodynamics are governed by moisture fluctuations. The thermodynamics of the gravity wave group, on the other hand, are rooted in buoyancy (temperature) fluctuations. On the basis of scale analysis it is found that a simple nondimensional parameter –akin to the Rossby number– can explain the processes that lead to the existence of these two groups. This parameter, defined as Nmode, indicates that moisture modes arise when anomalous convection lasts sufficiently long so that dry gravity waves eliminate the temperature anomalies in the convective region, satisfying weak temperature gradient (WTG) balance. This process causes moisture anomalies to dominate the distribution of moist enthalpy (or moist static energy), and hence the evolution of the wave. Conversely, convectively-coupled gravity waves arise when anomalous convection eliminates the moisture anomalies more rapidly than dry gravity waves can adjust the troposphere towards WTG balance, causing temperature to govern the moist enthalpy distribution and evolution. Spectral analysis of reanalysis data indicates that slowly-propagating waves (cp ~ 3 m s-1) are likely to be moisture modes while fast waves (cp ~ 30 m s-1) exhibit gravity wave behavior, with "mixed moisture-gravity" waves existing in between. While these findings are obtained from a highly idealized framework, it is hypothesized that they can be extended to understand simulations of convectively-coupled waves in GCMs and the thermodynamics of more complex phenomena.

Angel F Adames↗
NASA NTRS1991

Numerical studies of electron dynamics in oblique quasi-perpendicular collisionless shock waves

Linear and nonlinear electron damping of the whistler precursor wave train to low Mach number quasi-perpendicular oblique shocks is studied using a one-dimensional electromagnetic plasma simulation code with particle electrons and ions. In some parameter regimes, electrons are observed to trap along the magnetic field lines in the potential of the whistler precursor wave train. This trapping can lead to significant electron heating in front of the shock for low beta(e). Use of a 64-processor hypercube concurrent computer has enabled long runs using realistic mass ratios in the full particle in-cell code and thus simulate shock parameter regimes and phenomena not previously studied numerically.

Liewer, P. C.↗