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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 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Information Content of Aerosol Retrievals in the Sunglint Region

We exploit quantitative metrics to investigate the information content in retrievals of atmospheric aerosol parameters (with a focus on single-scattering albedo), contained in multi-angle and multi-spectral measurements with sufficient dynamical range in the sunglint region. The simulations are performed for two classes of maritime aerosols with optical and microphysical properties compiled from measurements of the Aerosol Robotic Network. The information content is assessed using the inverse formalism and is compared to that deriving from observations not affected by sunglint. We find that there indeed is additional information in measurements containing sunglint, not just for single-scattering albedo, but also for aerosol optical thickness and the complex refractive index of the fine aerosol size mode, although the amount of additional information varies with aerosol type.

aerosols↗
NASA NTRSDate not supplied

Prediction of Broadband Blade-Wake Back-Scatter Noise from a Hovering Ideally Twisted Rotor using OVERFLOW2-ANOPP2

This work illustrates the use of a hybrid RANS/LES framework for the prediction of broadband noise via integral formulations from an ideally twisted hovering rotor. Four simulations were conducted, which investigated the effect of different turbulence modeling and spatiotemporal resolutions. The aerodynamic performance and aeroacoustics predicted by these four computational cases were compared against data acquired in the Small Hover Anechoic Chamber at the NASA Langley Research Center and against previous simulations conducted using the lattice-Boltzmann solver, PowerFLOW. The simulation case with the finest spatial resolution had the most favorable aerodynamic performance and broadband noise comparison with measured data; however, the simulation case utilizing the SST-DDES turbulence model predicted the most accurate tonal noise signature. Aerodynamic flowfield visualizations identified near-wake trailing edge vortex shedding, perpendicular blade-vortex interactions, and tip vortex formation, which are known to cause broadband noise. The fluid dynamics associated with a new broadband noise source, blade-wake back-scatter, were also identified. Lastly, a broadband noise source visualization technique was utilized to confirm the presence of blade-wake back-scatter as a dominant broadband noise source.

blade-wake back-scatter↗
DOE OSTI2020

Spectroscopic signatures of next-nearest-neighbor hopping in the charge and spin dynamics of doped one-dimensional antiferromagnets

In this work, we study the impact of next-nearest-neighbor (nnn) hopping on the low-energy collective excitations of strongly correlated doped antiferromagnetic cuprate spin chains. Specifically, we use exact diagonalization and the density matrix renormalization group method to study the single-particle spectral function, the dynamical spin and charge structure factors, and the Cu L-edge resonant inelastic x-ray scattering (RIXS) intensity of the doped t-t'-J model for a set of t' values. We find evidence for the breakdown of spin-charge separation as |t'| increases and identify its fingerprints in the dynamical response functions. The inclusion of nnn hopping couples the spinon and holon excitations, resulting in the formation of a spin-polaron, where a ferromagnetic spin polarization cloud dresses the doped carrier. The spin-polaron manifests itself as additional spectral weight in the dynamical correlation functions, which appear simultaneously in the spin- and charge-sensitive channels. We also demonstrate that RIXS can provide a unique view of the spin-polaron, due to its sensitivity to both the spin and charge degrees of freedom.

1D spin chains↗
DOE OSTI2016

Role of Confinement on Adsorption and Dynamics of Ethane and an Ethane–CO 2 Mixture in Mesoporous CPG Silica

It was found that ethane is confined to mineral and organic pores in certain shale formations. Effects of confinement on structural and dynamic properties of ethane in mesoporous controlled pore glass (CPG) were studied by gravimetric adsorption and quasi-elastic neutron scattering (QENS) measurements. The obtained isotherms and scattering data complement each other by quantifying the relative strength of the solid–fluid interactions and the transport properties of the fluid under confinement, respectively. We used a magnetic suspension balance to measure the adsorption isotherms at two temperatures and over a range of pressures corresponding to a bulk density range of 0.01–0.35 g/cm 3 . Key confinement effects were highlighted through differences between isotherms for the two pore sizes. A comparison was made with previously published isotherms for CO 2 on the same CPG materials. Behavior of ethane in the smaller pore size was probed further using quasi-elastic neutron scattering. By extracting the self-diffusivity and residence time, we were able to study the effect of pressure and transition from gaseous to supercritical densities on the dynamics of confined ethane. Moreover, a temperature variation QENS study was also completed with pure ethane and a CO 2 –ethane mixture. Activation energies extracted from the Arrhenius plots show the effects of CO 2 addition on ethane mobility.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Scanning Tunneling Microscopy Observation of Phonon Condensate

Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance. The observed coherence of these quasi-bound states most likely arises from phase- and frequency-synchronized dynamics of all phonon modes, and indicates the formation of many-body condensate of optical phonons around resonant defects. We found that increasing the strength of the scattering resonance causes the increase of the condensate droplet radius without affecting the condensate fraction inside it. The condensate can be observed at room temperature.

36 MATERIALS SCIENCE↗
NASA NTRS1998

A New Optical Aerosol Spectrometer

An optical particle spectrometer capable of measuring aerosol particle size distributions from 0.02 to 100 micrometers has been developed. This instrument combines several optical methods in one, in-situ configuration; it can provide continuous data collection to encompass the wide dynamic size ranges and concentrations found in studies of modeled planetary atmospheres as well as terrestrial air quality research. Currently, the system is incorporated into an eight liter capacity spherical pressure vessel that is appropriate both for flowthrough and for in-situ particle generation. The optical sizing methods include polarization ratio, The scattering, and forward scattering detectors, with illumination from a fiber-coupled, Argon-ion laser. As particle sizes increase above 0.1 micrometer, a customized electronics and software system automatically shifts from polarization to diffraction-based measurements as the angular scattering detectors attain acceptable signal-to-noise ratios. The number concentration detection limits are estimated to be in the part-per-trillion (ppT by volume) range, or roughly 1000 submicron particles per cubic centimeter. Results from static experiments using HFC134A (approved light scattering gas standard), flow-through experiments using sodium chloride (NaCl) and carbon particles, and dynamic 'Tholin' (photochemical produced particles from ultraviolet (UV)-irradiated acetylene and nitrogen) experiments have been obtained. The optical spectrometer data obtained with particles have compared well with particle sizes determined by electron microscopy. The 'Tholin' tests provided real-time size and concentration data as the particles grew from about 30 nanometers to about 0.8 micrometers, with concentrations ranging from ppT to ppB, by volume. Tests are still underway, to better define sizing accuracy and concentration limits, these results will be reported.

Fonda, Mark↗
DOE OSTI2023

The critical role of ultra-low-energy vibrations in the relaxation dynamics of molecular qubits

Improving the performance of molecular qubits is a fundamental milestone towards unleashing the power of molecular magnetism in the second quantum revolution. Taming spin relaxation and decoherence due to vibrations is crucial to reach this milestone, but this is hindered by our lack of understanding on the nature of vibrations and their coupling to spins. Here we propose a synergistic approach to study a prototypical molecular qubit. It combines inelastic X-ray scattering to measure phonon dispersions along the main symmetry directions of the crystal and spin dynamics simulations based on DFT. We show that the canonical Debye picture of lattice dynamics breaks down and that intra-molecular vibrations with very-low energies of 1-2 meV are largely responsible for spin relaxation up to ambient temperature. We identify the origin of these modes, thus providing a rationale for improving spin coherence. The power and flexibility of our approach open new avenues for the investigation of magnetic molecules with the potential of removing roadblocks toward their use in quantum devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Nucleon Viewed as a Borromean Bound-State

We explain how the emergent phenomenon of dynamical chiral symmetry breaking ensures that Poincare covariant analyses of the three valence-quark scattering problem in continuum quantum field theory yield a picture of the nucleon as a Borromean bound-state, in which binding arises primarily through the sum of two separate contributions. One involves aspects of the non-Abelian character of Quantum Chromodynamics that are expressed in the strong running coupling and generate tight, dynamical color-antitriplet quark-quark correlations in the scalar-isoscalar and pseudovector-isotriplet channels. This attraction is magnified by quark exchange associated with diquark breakup and reformation, which is required in order to ensure that each valence-quark participates in all diquark correlations to the complete extent allowed by its quantum numbers. Combining these effects, we arrive at a properly antisymmetrised Faddeev wave function for the nucleon and calculate, e.g. the flavor-separated versions of the Dirac and Pauli form factors and the proton's leading-twist parton distribution amplitude. We conclude that available data and planned experiments are capable of validating the proposed picture.

Segovia, Jorge↗
DOE OSTI2016

Ion-momentum imaging of dissociative attachment of electrons to molecules

Here, we present an overview of experiments and theory relevant to dissociative electron attachment studied by momentum imaging. We describe several key examples of characteristic transient anion dynamics in the form of small polyatomic electron-molecule systems. In each of these examples the so-called axial recoil approximation is found to break down due to correlation of the electronic and nuclear degrees of freedom of the transient anion. Guided by anion fragment momentum measurements and predictions of the electron scattering attachment probability in the molecular frame, we demonstrate that accurate predictions of the dissociation dynamics can be achieved without a detailed investigation of the surface topology of the relevant electronic states or the fragment trajectories on those surfaces.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2016

Magnetization dynamics and frustration in the multiferroic double perovskite Lu 2 MnCoO 6

Here, we investigate the magnetic ordering and the magnetization dynamics (from kHz to THz time scales) of the double perovskite Lu 2 MnCoO 6 using elastic neutron diffraction, muon spin relaxation, and micro-Hall magnetization measurements. This compound is known to be a type II multiferroic with the interesting feature that a ferromagneticlike magnetization hysteresis loop couples to an equally hysteretic electric polarization in the bulk of the material despite a zero-field magnetic ordering of the type ↑↑↓↓ along Co-Mn spin chains. Here we explore the unusual dynamics of this compound and find extremely strong fluctuations, consistent with the axial next-nearest-neighbor Ising (ANNNI) model for frustrated spin chains. We identify three temperature scales in Lu 2 MnCoO 6 corresponding to the onset of highly fluctuating long-range order below T N = 50±3 K identified from neutron scattering, the onset of magnetic and electric hysteresis, with change in kHz magnetic and electric dynamics below a 30 K temperature scale, and partial freezing of ~MHz spin fluctuations in the muon spin relaxation data below 12 ± 3 K. Our results provide a framework for understanding the multiferroic behavior of this compound and its hysteresis and dynamics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Comparative analysis of plasmon modes in layered Lindhard metals and strange metals

The enigmatic strange metal remains one of the central unsolved problems of 21st century science. Understanding this phase of matter requires knowledge of the momentum- and energy-resolved dynamic charge susceptibility 𝜒⁡(𝑞,𝜔), especially at finite momentum. Inelastic electron scattering (EELS), performed in either transmission or reflection geometry, is a powerful probe of 𝜒⁡(𝑞,𝜔). For the prototypical strange metal Bi 2 ⁢Sr 2 ⁢CaCu 2 ⁢O 8+𝑥 , transmission- and reflection EELS, and infrared (IR) spectroscopy agree at 𝑞∼0, all revealing a highly damped plasmon near 1 eV. At larger 𝑞, however, EELS results show unresolved discrepancies. Since IR data are highly reproducible, it is advantageous to use IR data to calculate what the expected EELS response should be at modest 𝑞. Building on prior momentum-resolved reflection geometry M-EELS work [Chen et al., Phys. Rev. B 109, 045108 (2024)], we extend this approach to transmission EELS for finite stacks of metallic layers, comparing a “textbook” Lindhard metal to a strange metal. In the Lindhard case, the low-𝑞 response is dominated by long-lived, standing wave plasmon modes arising from interlayer Coulomb coupling, with in-plane dispersions that resemble the well-known Fetter modes of layered metals. This behavior depends only on the geometry and the long-range nature of the Coulomb interaction and is largely insensitive to layer details. At larger 𝑞, the response reflects the microscopic properties of individual layers. For the strange metal, calculations based on IR data predict a highly damped plasmon with weak dispersion and no distinct surface mode. While our results match IR and M-EELS at low 𝑞, they do not reproduce any published EELS spectra at large 𝑞, highlighting unresolved discrepancies that demand further experimental investigation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

High-Frequency Plasma Waves and Pitch Angle Scattering Induced by Pulsed Electron Beams

Cherenkov radiation from a pulse of charge propagating along the magnetic field in a magnetized plasma is analyzed using theory and fluid–kinetic simulations. Besides radiation into whistler modes, the subject of many previous investigations in laboratory and space, radiation can occur through extraordinary (X) modes. Theory and simulations demonstrate that X mode radiation efficiencies can be orders of magnitude higher than those into whistler modes. Test particle simulations of the dynamics of energetic electrons in the beam–generated wavefield show that X modes can also induce pitch angle scattering much more efficiently than whistlers. While coherence effects associated with spreading of realistic beam pulses may limit the size of the X mode source region, a simple model of beam dynamics suggests that the size of this region could be substantial (hundreds of meters for ionospheric conditions). Furthermore, these results have potentially important implications for many problems, including understanding losses in the near–Earth environment and radiation belt remediation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

BEAM DYNAMICS CHALLENGES IN THE DESIGN OF THE ELECTRON-ION COLLIDER

The Electron-Ion Collider (EIC), presently under construction at Brookhaven National Laboratory, will collide polarized high-energy electron beams with hadron beams, achieving luminosities up to 1 × 1034 cm¿2 s¿1 in the center-of-mass energy range of 20-140 GeV. To achieve such high luminosity, we adopt high bunch intensities for both beams, small and flat transverse beam sizes at the interaction point (IP), a large crossing angle of 25 mrad, and a novel strong hadron cooling in the Hadron Storage Ring (HSR) to counteract intra-beam scattering (IBS) at the collision energy. In this talk, we will review the beam dynamics challenges in the design of the EIC, particularly the single-particle dynamic aperture, polarization maintenance, beam-beam interaction, impedance budget and instabilities. We will also briefly mention some technical challenges associated with beam dynamics, such as strong hadron cooling, multipoles and noises of crab cavities, power supply current ripples, and the vacuum upgrade to existing beam pipes of the Hadron Storage Ring of the EIC.

Luo, Y.↗
DOE OSTI2018

Anharmonic stabilization and lattice heat transport in rocksalt β -GeTe

Peierls-Boltzmann transport equation, coupled with third-order anharmonic lattice dynamics calculations, has been widely used to model lattice thermal conductivity (κ l ) in bulk crystals. However, its application to materials with structural phase transition at relatively high temperature is fundamentally challenged by the presence of lattice instabilities (imaginary phonon modes). Additionally, its accuracy suffers from the absence of higher-than-third-order phonon scattering processes, which are important near/above the Debye temperature. In this letter, we present an effective scheme that combines temperature-induced anharmonic phonon renormalization and four-phonon scattering to resolve these two theoretical challenges. Here, we apply this scheme to investigate the lattice dynamics and thermal transport properties of GeTe, which undergoes a second-order ferroelectric phase transition from rhombohedral α-GeTe to rocksalt β-GeTe at about 700 K. Our results on the high-temperature phase β-GeTe at 800 K confirm the stabilization of β-GeTe by temperature effects. We find that considering only three-phonon scattering leads to significantly overestimated κ l of 3.8 W/mK at 800 K, whereas including four-phonon scattering reduces κ l to 1.7 W/mK, a value comparable with experiments. To explore the possibility to further suppress κ l , we show that alloying β-GeTe with heavy cations such as Pb and Bi can effectively reduce κ l to about 1.0 W/mK, whereas particle size needs to be around 10 nm through nanostructuring to achieve a comparable reduction in κ l .

36 MATERIALS SCIENCE↗
NASA NTRS1994

Lidar measurements of ozone and aerosol distributions during the 1992 airborne Arctic stratospheric expedition

The NASA Langley airborne differential absorption lidar system was operated from the NASA Ames DC-8 aircraft during the 1992 Airborne Arctic Stratospheric Expedition to investigate the distribution of stratospheric aerosols and ozone (O3) across the Arctic vortex from January to March 1992. Aerosols from the Mt. Pinatubo eruption were found outside and inside the Arctic vortex with distinctly different scattering characteristics and spatial distributions in the two regions. The aerosol and O3 distributions clearly identified the edge of the vortex and provided additional information on vortex dynamics and transport processes. Few polar stratospheric clouds were observed during the AASE-2; however, those that were found had enhanced scattering and depolarization over the background Pinatubo aerosols. The distribution of aerosols inside the vortex exhibited relatively minor changes during the AASE-2. Ozone depletion inside the vortex as limited to less than or equal to 20 percent in the altitude region from 15-20 km.

Browell, Edward V.↗
NASA NTRS2014

The Architecture of the LkCa 15 Transitional Disk Revealed by High-contrast Imaging

We present four new epochs of Ks-band images of the young pre-transitional disk around LkCa 15, and perform extensive forward modeling to derive the physical parameters of the disk. We find indications of strongly anisotropic scattering (Henyey-Greenstein g = 0.67+0.18 −0.11) and a significantly tapered gap edge ('round wall'), but see no evidence that the inner disk, whose existence is predicted by the spectral energy distribution, shadows the outer regions of the disk visible in our images. We marginally confirm the existence of an offset between the disk center and the star along the line of nodes; however, the magnitude of this offset (x = 27+19 −20 mas) is notably lower than that found in our earlier H-band images (Thalmann et al. 2010). Intriguingly, we also find, at high significance, an offset of y = 69+49 −25 mas perpendicular to the line of nodes. If confirmed by future observations, this would imply a highly elliptical- or otherwise asymmetric-disk gap with an effective eccentricity of e ≈ 0.3. Such asymmetry would most likely be the result of dynamical sculpting by one or more unseen planets in the system. Finally, we find that the bright arc of scattered light we see in direct imaging observations originates from the near side of the disk, and appears brighter than the far side because of strong forward scattering.

anisotropic scattering↗
DOE OSTI2017

Quantitative Measurements of the Temperature-Dependent Microscopic and Macroscopic Dynamics of a Molecular Dopant in a Conjugated Polymer

Understanding the nature of dopant dynamics in the solid state is critical for improving the longevity and stability of organic electronic devices and for optimizing the doping-induced solubility control (DISC) patterning method. Here in this work, we use quasi-elastic neutron scattering (QENS) and fluorescence quenching techniques to develop a comprehensive picture of both the microscopic and macroscopic dynamics of the soluble p-type molecular dopant tetrafluoromethyloxycarbonyltricyanoquinodimethane (F4MCTCNQ) in the conductive polymer poly(3-hexylthiophene-2,5-diyl) (P3HT). Specifically, fast dynamics (ps–ns) of the dopant, such as the methyl and the methoxycarbonyl group rotations, are observed in QENS experiments. From confocal fluorescence microscope experiments, longer-range/slower dopant diffusion (ms–days) is captured. However, in order to fit these data, it is necessary to incorporate a Langmuir isotherm equilibrium between the neutral and ionized dopant molecules. Ionized F4MCTCNQ is strongly favored by the equilibrium, but it diffuses 3 orders of magnitude slower than neutral species. Moreover, the macroscopic diffusion is found to depend mostly on the minority concentration of neutral dopant molecules in the film. In conclusion, the global diffusion coefficient of the monoester-substituted dopant F4MCTCNQ is shown to be more than an order of magnitude smaller than that of the widely used dopant F4TCNQ.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Estimating ionization states and continuum lowering from ab initio path integral Monte Carlo simulations for warm dense hydrogen

Warm dense matter (WDM) is an active field of research, with applications ranging from astrophysics to inertial confinement fusion. Ionization degree and continuum lowering are important quantities to understand how materials behave under these conditions, but can be difficult to diagnose since experimental campaigns are limited and often require model-dependent analysis. This is especially true for hydrogen, which has a comparably low scattering cross section, making high-quality data particularly difficult to obtain. Consequently, building equation of state tables often relies on simulations in combination with untested approximations to extract properties from experiments. Here, we investigate an approach for extracting the ionization potential depression and ionization degree—quantities which are otherwise not directly accessible from the physical model—from first-principles path integral Monte Carlo (PIMC) simulations utilizing a chemical model. In contrast to experimental measurements, where noise and nonequilibrium effects add to the uncertainty of the inferred parameters, PIMC simulations provide a clean signal with well-defined thermodynamic conditions. Comparisons against commonly used models show a qualitative agreement, but we find deviations primarily for the high-density and high-temperature cases. We also demonstrate the decreasing sensitivity of the dynamic structure factor with respect to both ionization and continuum lowering for increasing scattering angles in x-ray Thomson scattering experiments. Our work has important implications for the design of future experiments, but also offers qualitative understanding of structure factors and the imaginary-time correlation function obtained from first-principles quantum Monte Carlo simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗