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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

The target asymmetry P_z in {gamma}p-->p{pi}^+{pi}^- with the CLAS spectrometer at Jefferson Laboratory

The study of baryon resonances provides a deeper understanding of the strong interaction because the dynamics and relevant degrees of freedom hidden within them are reflected by the properties of the excited states of baryons. Higher-lying excited states at and above 1.9 GeV/c{sup 2} are generally predicted to have strong couplings to the {pi}{pi}N final states via {pi}{Delta} or {rho}N intermediate states. Double-pion photoproduction is therefore important to find and investigate properties of highmass resonances. The CLAS g9a (FROST) experiment, as part of the N* spectroscopy program at Jefferson Laboratory (JLab), has accumulated photoproduction data using linearly- and circularly-polarized photons incident on a longitudinally-polarized butanol target in the photon energy range 0.3 to 2.4 GeV. In this contribution, the extraction of the target asymmetry for the reaction {gamma}p {yields} p{pi}{sup +}{pi}{sup -} will be described and preliminary results will be presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Synergy between Fe and Ni in the optimal performance of (Ni,Fe)OOH catalysts for the oxygen evolution reaction

The oxygen evolution reaction (OER) is critical to solar production of fuels, but the reaction mechanism underlying the performance for a best OER catalyst, Fe-doped NiOOH [(Ni,Fe)OOH], remains highly controversial. We used grand canonical quantum mechanics to predict the OER mechanisms including kinetics and thus overpotentials as a function of Fe content in (Ni,Fe)OOH catalysts. We find that density functional theory (DFT) without exact exchange predicts that addition of Fe does not reduce the overpotential much. However, DFT with exact exchange predicts dramatic improvement in performance for (Ni,Fe)OOH, leading to an overpotential of 0.42 V and a Tafel slope of 23 mV/decade (dec), in good agreement with experiments, 0.3–0.4 V and 30 mV/dec. We reveal that the high spin d 4 Fe(IV) leads to efficient formation of an active O radical intermediate, while the closed shell d 6 Ni(IV) catalyzes the subsequent O–O coupling, and thus it is the synergy between Fe and Ni that delivers the optimal performance for OER.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Proton-coupled electron transfer of macrocyclic ring hydrogenation: The chlorinphlorin

Significance The chemical reduction of unsaturated bonds occurs by hydrogenation with H 2 as the reductant. Conversely, in biology, the unavailability of H 2 engenders the typical reduction of unsaturated bonds with electrons and protons from different cofactors, requiring olefin hydrogenation to occur by proton-coupled electron transfer (PCET). Moreover, the redox noninnocence of tetrapyrrole macrocycles furnishes unusual PCET intermediates, including the phlorin, which is an intermediate in tetrapyrrole ring reductions. Whereas the phlorin of a porphyrin is well established, the phlorin of a chlorin is enigmatic. By controlling the PCET reactivity of a chlorin, including the use of a hangman functionality to manage the proton transfer, the formation of a chlorinphlorin by PCET is realized, and the mechanism for its formation is defined.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Effective field theory and keV lines from dark matter

We survey operators that can lead to a keV photon line from dark matter decay or annihilation. We are motivated in part by recent claims of an unexplained 3.5 keV line in galaxy clusters and in Andromeda, but our results could apply to any hypothetical line observed in this energy range. We find that given the amount of flux that is observable, explanations in terms of decay are more plausible than annihilation, at least if the annihilation is directly to Standard Model states rather than intermediate particles. The decay case can be explained by a scalar or pseudoscalar field coupling to photons suppressed by a scale not far below the reduced Planck mass, which can be taken as a tantalizing hint of high-scale physics. The scalar case is particularly interesting from the effective field theory viewpoint, and we discuss it at some length. Because of a quartically divergent mass correction, naturalness strongly suggests the theory should be cut off at or below the 1000 TeV scale. The most plausible such natural UV completion would involve supersymmetry. These bottom-up arguments reproduce expectations from top-down considerations of the physics of moduli. A keV line could also arise from the decay of a sterile neutrino, in which case a renormalizable UV completion exists and no direct inference about high-scale physics is possible.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Characterizing and quantifying uncertainty in projections of climate change impacts on air quality

Climate change can aggravate air pollution, with important public health and environmental consequences. While major sources of uncertainty in climate change projections - greenhouse gas (GHG) emissions scenario, model response, and internal variability - have been investigated extensively, their propagation to estimates of air quality impacts has not been systematically assessed. Here, we compare these uncertainties using a coupled modeling framework that includes a human activity model, an Earth system model of intermediate complexity, and a global atmospheric chemistry model. Uncertainties in projections of U.S. air quality under 21st century climate change are quantified based on a climate-chemistry ensemble that includes multiple initializations, representations of climate sensitivity, and climate policy scenarios, under constant air pollution emissions. We find that climate-related uncertainties are comparable at mid-century, making it difficult to distinguish the impact of variations in GHG emissions on ozone and particulate matter pollution. While GHG emissions scenario eventually becomes the dominant uncertainty based on the scenarios considered, all sources of uncertainty are significant through the end of the century. The results provide insights into intrinsically different uncertainties in projections of air pollution impacts and the potential for large ensembles to better capture them.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2011

Continuous control of light group velocity from subluminal to superluminal propagation with a standing-wave coupling field in a Rb vapor cell

We present the continuous control of the light group velocity from subluminal to superluminal propagation with an on-resonant standing-wave coupling field in the 5S{sub 1/2}-5P{sub 1/2} transition of the {Lambda}-type system of {sup 87}Rb atoms. When a coupling field was changed from a traveling-wave to a standing-wave field by adjusting the power of a counterpropagating coupling field, the probe pulse propagation continuously transformed from subluminal propagation, due to electromagnetically induced transparency with the traveling-wave coupling field, to superluminal propagation, due to narrow enhanced absorption with the standing-wave coupling field. The group velocity of the probe pulse was measured to be approximately 0.004c to -0.002c as a function of the disparity between the powers of the copropagating and the counterpropagating coupling fields.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Quasiparticle Spectroscopy, Transport, and Magnetic Properties of Nb Films Used in Superconducting Qubits

Niobium thin films on silicon substrate used in the fabrication of superconducting qubits have been characterized using scanning and transmission electron microscopy, electrical transport, magnetization, the London penetration depth - based quasiparticle spectroscopy, and real-space real-time magneto-optical imaging. Here we study niobium films to provide an example of a comprehensive analytical set that may benefit superconducting circuits such as those used in quantum computers. The films have a superconducting transition temperature of T c = 9.35 K and a fairly clean superconducting gap. The estimated superfluid density is enhanced at intermediate temperatures. These observations are consistent with the recent theory of anisotropic strong-coupling superconductivity in Nb and indicate outstanding quality. However, the response to the magnetic field is complicated, exhibiting significantly irreversible behavior and insufficient heat dissipation (to a substrate), leading to thermomagnetic instabilities. This may present a challenge for further improvement of transmon quantum coherence. Possible mitigation strategies are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Impact of the nuclear symmetry energy on the pygmy dipole resonance

The correlation between the pygmy dipole strength and the symmetry energy of nuclear matter is reanalyzed. While previous calculations [A. Klimkiewicz et al., Phys. Rev. C 76, 051603(R) (2007); A. Carbone, G. Colo, A. Bracco, L.-G. Cao, P. F. Bortignon, F. Camera, and O. Wieland, Phys. Rev. C 81, 041301 (2010).] have clearly shown a direct correlation between both quantities, it remains unclear to what extent experimental as well as theoretical uncertainties can allow for an accurate determination of the symmetry energy. For this reason, we have recalculated the low-lying strength distributions of the giant dipole resonances for {sup 130}Sn and {sup 132}Sn that have been recently measured, taking into account the above uncertainties. The calculations are performed within two microscopic models, namely, the discrete quasiparticle random phase approximation (DRPA) and the quasiparticle continuum RPA, which is an extension of the DRPA that takes the coupling to the single-particle continuum into account in an exact way.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Determining g A / g V with High-Resolution Spectral Measurements Using a LiInSe 2 Bolometer

Neutrinoless double beta decay (0νββ) processes sample a wide range of intermediate forbidden nuclear transitions, which may be impacted by quenching of the axial vector coupling constant (g A /g V ), the uncertainty of which plays a pivotal role in determining the sensitivity reach of 0νββ experiments. Here we present measurements performed on a high-resolution LiInSe 2 bolometer in a “source = detector” configuration to measure the spectral shape of the fourfold forbidden β decay of 115 In . The value of g A /g V is determined by comparing the spectral shape of theoretical predictions to the experimental β spectrum taking into account various simulated background components as well as a variety of detector effects. We find evidence of quenching of g A /g V at >5 σ with a model-dependent quenching factor of 0.655 ± 0.002 as compared to the free-nucleon value for the interacting shell model. We also measured the 115 In half-life to be [5.18 ± 0.06(stat) $^{+0.005}_{- 0.015}$(sys)] x 10 14 yr within the interacting shell model framework. This Letter demonstrates the power of the bolometeric technique to perform precision nuclear physics single-β decay measurements, which along with improved nuclear modeling can help reduce the uncertainties in the calculation of several decay nuclear matrix elements including those used in 0νββ sensitivity calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Shallow-circuit variational quantum eigensolver based on symmetry-inspired Hilbert space partitioning for quantum chemical calculations

Development of resource-friendly quantum algorithms remains highly desirable for noisy intermediate-scale quantum computing. Based on the variational quantum eigensolver (VQE) with unitary coupled-cluster Ansatz, we demonstrate that partitioning of the Hilbert space made possible by the point-group symmetry of the molecular systems greatly reduces the number of variational operators by confining the variational search within a subspace. In addition, we found that instead of including all subterms for each excitation operator, a single-term representation suffices to reach required accuracy for various molecules tested, resulting in an additional shortening of the quantum circuit by a factor of 4–8. With these strategies, VQE calculations on a noise-free quantum simulator achieve energies within a few meVs of those obtained with the full unitary coupled-cluster Ansatz with single and double excitations for the H 4 -square, H 4 -chain, and H 6 -hexagon molecules, while the number of cnot gates, a measure of the quantum-circuit depth, is reduced by a factor of as large as 35. Furthermore, we introduced an efficient “score” parameter to rank the excitation operators, so that the operators causing larger energy reduction can be applied first. Using the H 4 square and H 4 chain as examples, We demonstrated on noisy quantum simulators that the first few variational operators can bring the energy within the chemical accuracy, while additional operators do not improve the energy since the accumulative noise outweighs the gain from the expansion of the variational Ansatz.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

MLIR loop optimizations for High-Level Synthesis: a case study

High-Level Synthesis (HLS) tools simplify the design of hardware accelerators by automatically generating Verilog/VHDL code starting from a general purpose software programming language. They include a wide range of optimization techniques in the process, most of them performed on a low-level intermediate representation (IR) of the code. Introducing optimizations on a higher level of abstraction could significantly contribute to the automated design process results; for example, polyhedral techniques for the manipulation of loops could have a significant impact on the generated accelerators when applied on a specialized IR. We use loop pipelining as a case study to explore the introduction of compiler-based transformations on top of an existing HLS process. We leverage the Multi-Level Intermediate Representation (MLIR) framework and an external scheduler to implement the required transformations, and couple them with existing HLS tools to evaluate the improvements that loop pipelining brings to the performance of generated accelerators. The proposed approach can be integrated with other high-level transformations on the MLIR representation, combining different techniques to obtain pre-optimized inputs for HLS that do not have to rely on a specific backend tool.

Curzel, Serena↗
DOE OSTI2015

TORUS: Theory of Reactions for Unstable iSotopes.Topical Collaboration for Nuclear Theory Project. Period: June 1, 2010 - May 31, 2015

The work of this collaboration during its existence is summarized. The mission of the TORUS Topical Collaboration was to develop new methods that advance nuclear reaction theory for unstable isotopes by using three-body techniques to improve direct reaction calculations. This multi-institution collaborative effort was and remains directly relevant to three areas of interest: the properties of nuclei far from stability, microscopic studies of nuclear input parameters for astrophysics, and microscopic nuclear reaction theory. The TORUS project focused on understanding the details of (d,p) reactions for neutron transfer to heavier nuclei. The bulk of the work fell into three areas: coupled channel theory, modeling (d,p) reactions with a Faddeev-AGS approach, and capture reactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Catalytic Upgrading of Key Biorefining Building Blocks to Renewable Chemicals, Polymeric Materials, and Liquid Fuels

The central objective of this project is to develop efficient, selective, and cost-effective catalytic systems for upgrading of key biorefining building blocks derived from catalytic conversion of plant biomass into value-added chemicals, polymeric materials, and liquid fuels. More specifically, the proposed work for the current grant period seeks to accomplish the following three specific objectives: (a) developing cost-effective and recyclable catalysts for selective upgrading (direct coupling) of the C 6 biorefining building block 5-hydroxymethylfurfural (HMF) into C 12 intermediates and for integrating biomass conversion and upgrading processes; (b) transforming the upgraded C 12 intermediates into polyols, polyurethanes, polyesters, and diesel fuels; and (c) reforming the upgraded intermediates into premium C 12 centered liquid hydrocarbon transportation fuels via selective hydrodeoxygenation catalysis.

09 BIOMASS FUELS↗
DOE OSTI2018

Understanding the Deformation Mechanisms of FeNiMnAlCr High Entropy Alloys

The aim of this project was to understand the microstructure and mechanical properties of Fe-Ni-Mn-Al-Cr high entropy alloys. High entropy alloys are defined as materials containing five or more elements with each element constituting 5-35 atomic percent of the alloy. We performed several different tasks in this project. 1) We showed that reducing the crystal or grain size in single-phase Fe40Ni11Mn35Al8Cr6 containing either 1.1 atomic percent carbon added or with no carbon added produced a substantial increase in strength with a small reduction in ductility. The finer grain size material was produced by cold rolling followed by heating to recrystallize the microstructure. The changes in strength and ductility were related to observed changes in deformation structure as determined by transmission electron microscopy. We also examined how the deformation behavior changed with temperature from -200°C to 200°C. 2) We showed that heating Fe36Ni18Mn33Al13 with and without 1.26 at.% carbon led to ordered body-centered cubic precipitates forming in the materials, which were both initially two-phase. The heat treatment again led to substantial increases in strength with some reduction in ductility. 3) We examined whether titanium additions (2 atomic percent) to Fe42Ni18Mn33Al13 could improve the mechanical properties. We examined both as-cast material and material that had been recrystallized to produce a fine grain size. In both cases ordered body-centered cubic precipitates were present. Again, the recrystallization and resulting reduction in grain size increased the yield strength and reduced the ductility. We also showed, using high-resolution electron microscopy, that contrary to some predictions, having an alloy containing a range of atoms with different atomic diameters produced no lattice distortions. 4) We used scanning electron microscopy and transmission electron microscopy coupled with energy dispersive x-ray spectroscopy to show that carbides formed during intermediate temperature (≤800oC) heating of carbon-doped Fe40Ni11Mn35Al8Cr6. In addition to forming within the grains, the carbides coated the grain boundaries. This produced an increase in strength but a drastic reduction in ductility. However, we showed by hot rolling we could get both high strength and high ductility for this material. The work led to nine publications in referred journals and contributed to the education of two Ph.D. students. In addition, ten presentations (six of which were invited) at conferences, at a university and at a national laboratory in Germany.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Improved RF Isolation Amplifier

Circuit has high reverse isolation and wide bandwidth. Wideband isolation amplifier has low intermodulation distortion and high reverse isolation. Circuit does not require selected or matched components or directional coupling device. Circuit used in applications requiring high reverse isolation such as receiver intermediate-frequency (IF) strips and frequency distribution systems. Also applicable in RF and video signaling.

Stevens, G. L.↗
DOE OSTI2022

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Niobium thin films on silicon substrate used in the fabrication of superconducting qubits have been characterized using scanning and transmission electron microscopy, electrical transport, magnetization, quasiparticle spectroscopy, and real-space real-time magneto-optical imaging. We study niobium films to provide an example of a comprehensive analytical set that may benefit superconducting circuits such as those used in quantum computers. The films show outstanding superconducting transition temperature of $T_{c}=9.35$ K and a fairly clean superconducting gap, along with superfluid density enhanced at intermediate temperatures. These observations are consistent with the recent theory of anisotropic strong-coupling superconductivity in Nb. However, the response to the magnetic field is complicated, exhibiting significantly irreversible behavior and insufficient heat conductance leading to thermo-magnetic instabilities. These may present an issue for further improvement of transmon quantum coherence. Possible mitigation strategies are discussed.

Joshi, Kamal R.↗
DOE OSTI2023

Tunable electron–flexural phonon interaction in graphene heterostructures

Peculiar electron-phonon interaction characteristics underpin the ultrahigh mobility, electron hydrodynamics, superconductivity, and superfluidity observed in graphene heterostructures. Here, the Lorenz ratio (L) between the electronic thermal conductivity and the product of the electrical conductivity and temperature provides unique insight into electron-phonon interactions that is inaccessible to past graphene measurements. Here we show an unusual L peak in degenerate graphene near 60 Kelvin and decreased peak magnitude with increased mobility. When combined with ab initio calculations of the many-body electron-phonon self-energy and analytical models, this experimental observation reveals that broken reflection symmetry in graphene heterostructures can relax a restrictive selection rule to allow quasielastic electron coupling with an odd number of flexural phonons, contributing to the increase of L toward the Sommerfeld limit at an intermediate temperature sandwiched between the low-temperature hydrodynamic regime and the inelastic electron-phonon scattering regime above 120 Kelvin. In contrast to past practices of neglecting flexural phonon contributions to transport in two-dimensional materials, this work suggests that tunable electron-flexural phonon coupling can provide a handle to control quantum matter at the atomic scale, such as magic angle twisted bilayer graphene where low-energy excitations may mediate Cooper pairing of flat-band electrons.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Kähler moduli double inflation

We show that double inflation is naturally realized in Kähler moduli inflation, which is caused by moduli associated with string compactification. We find that there is a small coupling between the two inflatons which leads to amplification of perturbations through parametric resonance in the intermediate stage of double inflation. This results in the appearance of a peak in the power spectrum of the primordial curvature perturbation. We numerically calculate the power spectrum and show that the power spectrum can have a peak on observationally interesing scales. We also compute the TT-spectrum of CMB based on the power spectrum with a peak and see that it better fits WMAP 7-years data.

79 ASTRONOMY AND ASTROPHYSICS↗