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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
NASA NTRS1992

Development of 3D electromagnetic modeling tools for airborne vehicles

The main goal of this report is to advance the development of methodologies for scattering by airborne composite vehicles. Although the primary focus continues to be the development of a general purpose computer code for analyzing the entire structure as a single unit, a number of other tasks are also being pursued in parallel with this effort. One of these tasks discussed within is on new finite element formulations and mesh termination schemes. The goal here is to decrease computation time while retaining accuracy and geometric adaptability.The second task focuses on the application of wavelets to electromagnetics. Wavelet transformations are shown to be able to reduce a full matrix to a band matrix, thereby reducing the solutions memory requirements. Included within this document are two separate papers on finite element formulations and wavelets.

Volakis, John L.↗
NASA NTRS1994

JPL Fourier transform ultraviolet spectrometer

The Fourier Transform Ultraviolet Spectrometer (FTUVS) is a new high resolution interferometric spectrometer for multiple-species detection in the UV, visible and near-IR. As an OH sensor, measurements can be carried out by remote sensing (limb emission and column absorption), or in-situ sensing (long-path absorption or laser-induced fluorescence). As a high resolution detector in a high repetition rate (greater than 10 kHz) LIF system, OH fluorescence can be discriminated against non-resonant background emission and laser scatter, permitting (0, 0) excitation.

Cageao, R. P.↗
DOE OSTI2015

An efficient tensor transpose algorithm for multicore CPU, Intel Xeon Phi, and NVidia Tesla GPU

An efficient parallel tensor transpose algorithm is suggested for shared-memory computing units, namely, multicore CPU, Intel Xeon Phi, and NVidia GPU. The algorithm operates on dense tensors (multidimensional arrays) and is based on the optimization of cache utilization on x86 CPU and the use of shared memory on NVidia GPU. From the applied side, the ultimate goal is to minimize the overhead encountered in the transformation of tensor contractions into matrix multiplications in computer implementations of advanced methods of quantum many-body theory (e.g., in electronic structure theory and nuclear physics). A particular accent is made on higher-dimensional tensors that typically appear in the so-called multireference correlated methods of electronic structure theory. Depending on tensor dimensionality, the presented optimized algorithms can achieve an order of magnitude speedup on x86 CPUs and 2-3 times speedup on NVidia Tesla K20X GPU with respect to the na ve scattering algorithm (no memory access optimization). Furthermore, the tensor transpose routines developed in this work have been incorporated into a general-purpose tensor algebra library (TAL-SH).

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1994

A spectral boundary integral equation method for the 2-D Helmholtz equation

In this paper, we present a new numerical formulation of solving the boundary integral equations reformulated from the Helmholtz equation. The boundaries of the problems are assumed to be smooth closed contours. The solution on the boundary is treated as a periodic function, which is in turn approximated by a truncated Fourier series. A Fourier collocation method is followed in which the boundary integral equation is transformed into a system of algebraic equations. It is shown that in order to achieve spectral accuracy for the numerical formulation, the nonsmoothness of the integral kernels, associated with the Helmholtz equation, must be carefully removed. The emphasis of the paper is on investigating the essential elements of removing the nonsmoothness of the integral kernels in the spectral implementation. The present method is robust for a general boundary contour. Aspects of efficient implementation of the method using FFT are also discussed. A numerical example of wave scattering is given in which the exponential accuracy of the present numerical method is demonstrated.

Hu, Fang Q.↗
DOE OSTI2017

Magnetic phase transformations and magnetotransport phenomena in La{sub 0.7}Sr{sub 0.3}Mn{sub 1–} {sub x}Co{sub x}O{sub 3} perovskite compounds

The compositions La{sub 0.7}Sr{sub 0.3}Mn{sub 1–} {sub x}Co{sub x}O{sub 3} (0.13 ≤ x ≤ 1) are studied by neutron diffraction, magnetometry, and measuring the magnetotransport properties. The substitution of cobalt ions for manganese ions is shown to decrease the magnetization and the Curie temperature from 270 K (x = 0.13) to 140 K (x = 0.33). As the cobalt ion content increases to x = 0.5, the Curie temperature increases to 190 K, the magnetization decreases, and the electrical resistivity increases. At x > 0.5, the temperature of transition into a paramagnetic state decreases to 68 K (x = 0.8) and then again increases to 225 K for the La{sub 0.7}Sr{sub 0.3}CoO{sub 3} composition. The magnetoresistive effect in the range 0.3 ≤ x ≤ 0.4 reaches 97% and decreases gradually with increasing temperature without anomalies near the Curie point. At x ≤ 0.2, the magnetoresistive effect increases near the Curie temperature. The composition at x = 0.6 is stoichiometric, and no coherent magnetic contribution to neutron scattering is detected. The magnetic properties near x ∼ 0.5 are assumed to be caused by partial ordering of Co{sup 3+} and Mn{sup 4+} ions, and the Co{sup 3+} ions can be in both low- and high-spin states. The magnetic interaction between Co{sup 3+} ions in a high-spin state and Mn{sup 4+} is predominantly ferromagnetic, and the ferromagnetic part of the exchange interactions is close to the ferromagnetic part. These data are used to plot a magnetic La{sub 0.7}Sr{sub 0.3}Mn{sub 1–} {sub x}Co{sub x}O{sub 3} phase diagram.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Magnetic excitations, nonclassicality, and quantum wake spin dynamics in the Hubbard chain

Recent work has demonstrated that quantum Fisher information (QFI), a witness of multipartite entanglement, and magnetic Van Hove correlations G(r,t), a probe of local real-space real-time spin dynamics, can be successfully extracted from inelastic neutron scattering on spin systems through accurate measurements of the dynamical spin structure factor S(k,ω). In this work, we apply theoretically these ideas to the half-filled Hubbard chain with nearest-neighbor hopping, away from the strong-coupling limit. This model has nontrivial redistribution of spectral weight in S(k,ω) going from the noninteracting limit (U = 0) to strong coupling (U→∞), where it reduces to the Heisenberg quantum spin chain. We use the density matrix renormalization group to find S(k,ω), from which QFI is then calculated. We find that QFI grows with U. With realistic energy resolution it becomes capable of witnessing bipartite entanglement above U=2.5 (in units of the hopping), where it also changes slope. This point is also proximate to slope changes of the bandwidth W(U) and the half-chain von Neumann entanglement entropy. We compute G(r,t) by Fourier transforming S(k,ω). The results indicate a crossover in the short-time short-distance dynamics at low U characterized by ferromagnetic light-cone wavefronts, to a Heisenberg-type behavior at large U featuring antiferromagnetic light cones and spatially period-doubled antiferromagnetism. We find this crossover has largely been completed by U=3. Our results thus provide evidence that, in several aspects, the strong-coupling limit of the Hubbard chain is reached qualitatively already at a relatively modest interaction strength. We discuss experimental candidates for observing the G(r,t) dynamics found at low U.

1-dimensional systems↗
DOE OSTI2024

Light-Induced Transformation of Virus-Like Particles on TiO 2

Titanium dioxide (TiO 2 ) shows significant potential as a self-cleaning material to inactivate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and prevent virus transmission. This study provides insights into the impact of UV-A light on the photocatalytic inactivation of adsorbed SARS-CoV-2 virus-like particles (VLPs) on a TiO 2 surface at the molecular and atomic levels. X-ray photoelectron spectroscopy, combined with density functional theory calculations, reveals that spike proteins can adsorb on TiO 2 predominantly via their amine and amide functional groups in their amino acids blocks. We employ atomic force microscopy and grazing-incidence small-angle X-ray scattering (GISAXS) to investigate the molecular-scale morphological changes during the inactivation of VLPs on TiO 2 under light irradiation. Notably, in situ measurements reveal photoinduced morphological changes of VLPs, resulting in increased particle diameters. These results suggest that the denaturation of structural proteins induced by UV irradiation and oxidation of the virus structure through photocatalytic reactions can take place on the TiO 2 surface. The in situ GISAXS measurements under an N 2 atmosphere reveal that the virus morphology remains intact under UV light. This provides evidence that the presence of both oxygen and UV light is necessary to initiate photocatalytic reactions on the surface and subsequently inactivate the adsorbed viruses. The chemical insights into the virus inactivation process obtained in this study contribute significantly to the development of solid materials for the inactivation of enveloped viruses.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Influence of Domain Walls in the Incommensurate Charge Density Wave State of Cu Intercalated 1 T –TiSe 2

We report a low-temperature scanning tunneling microscopy study of the charge density wave (CDW) order in 1T–TiSe 2 and Cu 0.08 TiSe 2 . In pristine 1T–TiSe 2 we observe a long-range coherent commensurate CDW (CCDW) order. In contrast, Cu 0.08 TiSe 2 displays an incommensurate CDW (ICDW) phase with localized CCDW domains separated by domain walls. Furthermore, density of states measurements indicate that the domain walls host an extra population of fermions near the Fermi level which may play a role in the emergence of superconductivity in this system. Fourier transform scanning tunneling spectroscopy studies suggest that the dominant mechanism for CDW formation in the ICDW phase may be electron-phonon coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Ab Initio Structure Factors for Spin-Dependent Dark Matter Direct Detection

We present converged ab initio calculations of structure factors for elastic spin-dependent WIMP scattering off all nuclei used in dark matter direct-detection searches: 19 F, 23 Na, 27 Al, 29 Si, 73 Ge, 12 7I, and 129,131 Xe. From a set of established two- and three-nucleon interactions derived within chiral effective field theory, we construct consistent WIMP-nucleon currents at the one-body level, including effects from axial-vector two-body currents. We then apply the in-medium similarity renormalization group to construct effective valence-space Hamiltonians and consistently transformed operators of nuclear responses. Combining the recent advances of natural orbitals with three-nucleon forces expressed in large spaces, we obtain basis-space converged structure factors even in heavy nuclei. Generally results are consistent with previous calculations but large uncertainties in 127 I highlight the need for further study.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Detection, monitoring, and determination of location of changes in metallic structures using multimode acoustic signals

Acoustic transducers generate and receive acoustic signals at multiple locations along a surface of rigid structure, wherein longitudinal spacing between transducer locations define measurement zones. Acoustic signals with chosen amplitude-time-frequency characteristics excite multiple vibration modes in the structure within each zone. Small mechanical changes in inspection zones lead to scattering and attenuation of broadband acoustic signals, which are detectable as changes in received signal characteristics as part of a through-transmission technique. Additional use of short, narrowband pulse acoustic signals as part of a pulse-echo technique allows determination of the relative location of the mechanical change within each zone based on the differential delay profiles. For accurate acoustic modeling and simulation, the mesh size, time step, time delay, and time-window size are optimized. Frequency normalization of the Short-Time Fourier Transform of acoustic response output improves experiment-simulation cross-validation. Applications of the method to structures with arbitrarily complex geometries are also demonstrated.

Findikoglu, Alp Tugrul↗
DOE OSTI2025

Polyhalohydrins: Investigating Vicinal Functionalities by Ring-Opening of Epoxides on Polyolefins

Halohydrins are functional groups that are underexplored in polymer science. This study synthesized and examined structure–property relationships of halohydrin-functionalized polymers derived from polycyclooctene (PCOE), which was obtained via ring-opening metathesis polymerization (ROMP). The polyhalohydrins, including polychlorohydrin, polybromohydrin, and polyiodohydrin, were produced through a two-step process involving epoxidation of PCOE followed by epoxide ring-opening using hydrochloric, hydrobromic, or hydroiodic acid. These stereoirregular and regioirregular polymers are amorphous as measured by differential scanning calorimetry and X-ray scattering. Lap joint shear testing revealed an enhanced adhesive performance in polychlorohydrin and polybromohydrin, with the former demonstrating nearly three times the ultimate shear stress compared to a model polyethylene, hydrogenated PCOE. Additionally, contact angle measurements and surface free energy analysis showed an increase in hydrophilicity and polarity from iodine- to bromine- to chlorine-functionalized polyhalohydrins, aligning with trends in adhesion strength. Furthermore, these results underscore the potential of halohydrin functionalization as a versatile approach for tuning surface properties, offering new opportunities for polymer-to-polymer transformations.

Functional groups↗
NASA NTRS1977

A comparison between the current models of mid-latitude spread F and data from the Arecibo Observatory

The current models of mid-latitude F sub s are studied. The assumptions and derivations of the Reid model, the Scannapieco model, and the Perkins model are presented in detail. Incoherent-scatter data of the density profiles and velocity profiles were obtained in order that the models could be evaluated on the basis of experimental data. Initial studies indicated that the Perkins model was most representative of the data from Arecibo, so a detailed comparison of the predictions of the Perkins model and the data was made. Two of four nights studied are nights with F sub s. The Perkins model is derived in a frame of reference moving with the velocity of the neutral wind; the model is transformed to the rest frame to facilitate comparison with data. Several data handling techniques are introduced. In particular, an integration interval that remains constant in length, but follows the vertical motion of the peak of the F layer is used to obtain the field integrated quantities of the Perkins model.

Imel, G.↗
DOE OSTI2016

Charge transport properties of graphene: Effects of Cu-based gate electrode

Using the first-principles nonequilibrium Green's function method, we study effects of Cu and Ni@Cu used as the Cu-based gate electrode on the charge transport of graphene in the field effect transistors (FET). We find that the transmission of graphene decreases with both Cu and Ni@Cu absorbed in the scatter region. Especially, noticeable transmission gaps are present around the Femi level. The transmission gaps are still effective, and considerable cut-off regions are found under the non-equilibrium environment. The Ni@Cu depresses the transmission of graphene more seriously than the Cu and enlarges the transmission gap in armchair direction. The effects on the charge transport are attributed to the redistribution of electronic states of graphene. Both Cu and Ni@Cu induce the localization of states, so as to block the electronic transport. The Ni@Cu transforms the interaction between graphene and gate electrode from the physisorption to the chemisorption, and then induces more localized states, so that the transmission decreases further. Our results suggest that besides being used to impose gate voltage, the Cu-based gate electrode itself will have a considerable effect on the charge transport of graphene and induces noticeable transmission gap in the FET.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

CHESS: The future direct geometry spectrometer at the second target station

CHESS, chopper spectrometer examining small samples, is a planned direct geometry neutron chopper spectrometer designed to detect and analyze weak signals intrinsic to small cross sections (e.g., small mass, small magnetic moments, or neutron absorbing materials) in powders, liquids, and crystals. CHESS is optimized to enable transformative investigations of quantum materials, spin liquids, thermoelectrics, battery materials, and liquids. The broad dynamic range of the instrument is also well suited to study relaxation processes and excitations in soft and biological matter. The 15 Hz repetition rate of the Second Target Station at the Spallation Neutron Source enables the use of multiple incident energies within a single source pulse, greatly expanding the information gained in a single measurement. Furthermore, the high flux grants an enhanced capability for polarization analysis. This enables the separation of nuclear from magnetic scattering or coherent from incoherent scattering in hydrogenous materials over a large range of energy and momentum transfer. This paper presents optimizations and technical solutions to address the key requirements envisioned in the science case and the anticipated uses of this instrument.

47 OTHER INSTRUMENTATION↗
NASA NTRS1994

Comparison of column abundances from three infrared spectrometers during AASE 2

Three Fourier transform infrared (FTIR) spectromenters were based on board the NASA DC-8 during the second Airborne Arctic Stratospheric Expedition (AASE II) in 1992. Two FTIRs used solar absorption and one used thermal emission. We compare over 2000 measurements from these 3 FTIRs, on 12 DC-8 flights, for closely coincident air masses and times, both inside and outside the polar vortex. In the majority of cases the offset biases are quite small, in the range 1-4%, and comparable to the absolute precisions expected. In most cases the rms scatter is in the range 4-11%; this scatter is unlikely to be geophysical, but rather is probably instrumental or analytical in origin.

Traub, W. A.↗
DOE OSTI2026

Revealing key structures for reversible sulfur redox in amorphous polymeric sulfur

Amorphous polymeric sulfur cathodes, such as sulfurized polyacrylonitrile (SPAN), enable high-energy lithium-sulfur batteries without cobalt or nickel, leveraging abundant sulfur. However, the limited in situ understanding of their synthesis and electrochemistry has impeded targeted optimization. Here, in this study, we integrate operando high-energy total scattering with sulfur K-edge X-ray absorption spectroscopy to monitor SPAN's formation and cycling in real time. Our results show that S-C bond formation halts further fusion of cyclized polyacrylonitrile, fostering π-π stacking and a transition from long-chain to short-chain sulfur-critical for reversible sulfur redox. These features synergistically minimize polysulfide dissolution and charge-transfer resistance, enabling optimized SPAN to achieve high capacity retention over 1,000 cycles. Operando X-ray absorption spectroscopy reveals that residual protons drive thiol-thione tautomerism, with lithium replacement during the first discharge causing ~20% irreversible capacity loss. To enhance performance, minimizing -NH groups and expanding pyridine networks are key. These findings transform SPAN optimization from empirical tuning to mechanism‑guided engineering and point the way towards sulfur loadings and energy densities competitive with state‑of‑the‑art Li‑ion cathodes.

25 ENERGY STORAGE↗
DOE OSTI2022

Enhancing the Reversibility of Lattice Oxygen Redox Through Modulated Transition Metal–Oxygen Covalency for Layered Battery Electrodes

Utilizing reversible lattice oxygen redox (OR) in battery electrodes is an essential strategy to overcome the capacity limitation set by conventional transition metal redox. However, lattice OR reactions are often accompanied with irreversible oxygen oxidation, leading to local structural transformations and voltage/capacity fading. Herein, it is proposed that the reversibility of lattice OR can be remarkably improved through modulating transition metal-oxygen covalency for layered electrode of Na-ion batteries. By developing a novel layered P2-Na 0.6 Mg 0.15 Mn 0.7 Cu 0.15 O 2 electrode, it is demonstrated that the highly electronegative Cu dopants can improve the lattice OR reversibility to 95% compared to 73% for Cu-free counterpart, as directly quantified through high-efficiency mapping of resonant inelastic X-ray scattering. Crucially, the large energetic overlap between Cu 3d and O 2p states dictates the rigidity of oxygen framework, which effectively mitigates the structural distortion of local oxygen environment upon (de)sodiation and leads to the enhanced lattice OR reversibility. The electrode also exhibits a completely solid-solution reaction with an ultralow volume change of only 0.45% and a reversible metal migration upon cycling, which together ensure the improved electrochemical performance. Finally, these results emphasize the critical role of transition metal-oxygen covalency for enhancing the reversibility of lattice OR toward high-capacity electrodes employing OR chemistry.

25 ENERGY STORAGE↗
DOE OSTI2019

Measurement of the (e,e') cross section for12C, 48Ti, 27Al and 40Ar

Many experiments have found that neutrinos have three different flavors, and they can transform from each other. Each flavor is a mixture of three nonzero mass states. In neutrino oscillation experiments, the uncertainty of the extracted oscillation parameters is dependent on the neutrino-nucleus cross section. In recent years various experiments provided precise neutrino and anti-neutrino cross section measurements and they have shown the inability of current Monte Carlo simulations to reproduce the data. A more accurate nuclear structure model of the target employed in neutrino detector is urgently needed to improve the precision of long baseline neutrino experiments. Electron scattering has been one of the most powerful methods of obtaining information about cross sections in the past. In the upcoming deep underground neutrino experiment (DUNE), Liquid Argon Time Projection Chambers (LArTPCs) will be used as the detector technology and argon will be used as the nuclear target. There are very few data available on argon and there is not an accurate nuclear model that describes them accurately, at ~5% level. We have performed an electron-argon scattering experiment at Jefferson Lab (E12-14-012) to provide accurate data that will help build a reliable nuclear model for describing neutrino-argon scattering. The JLab E12-14-012 experiment has successfully taken data in Hall A at the Thomas Jefferson National Accelerator Facility between February and March of 2017. We collected data for the inclusive (e,e') and exclusive (e,e'p) processes for a variety of targets (argon, titanium, aluminum, carbon) at a wide range of kinematic settings. This thesis will present the results of the inclusive double differential cross sections for carbon, titanium, aluminum and argon at beam energy E = 2:222 GeV and scattering angle theta = 15:541 deg with total uncertainties smaller than 5%. The kinematic settings covered a broad range of energy transfers, including deep inelastic scattering (DIS), delta production, and quasielastic scattering.

Dai, Hongxia↗