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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Simulating Observations of Southern Ocean Clouds and Implications for Climate

Southern Ocean (S. Ocean) clouds are important for climate prediction. Yet previous global climate models failed to accurately represent cloud phase distributions in this observation-sparse region. In this study, data from the Southern Ocean Clouds, Radiation, Aerosol, Transport Experimental Study (SOCRATES) experiment is compared to constrained simulations from a global climate model (the Community Atmosphere Model, CAM). Nudged versions of CAM are found to reproduce many of the features of detailed in situ observations, such as cloud location, cloud phase, and boundary layer structure. The simulation in CAM6 has improved its representation of S. Ocean clouds with adjustments to the ice nucleation and cloud microphysics schemes that permit more supercooled liquid. Comparisons between modeled and observed hydrometeor size distributions suggest that the modeled hydrometeor size distributions represent the dual peaked shape and form of observed distributions, which is remarkable given the scale difference between model and observations. Comparison to satellite observations of cloud physics is difficult due to model assumptions that do not match retrieval assumptions. Some biases in the model's representation of S. Ocean clouds and aerosols remain, but the detailed cloud physical parameterization provides a basis for process level improvement and direct comparisons to observations. This is crucial because cloud feedbacks and climate sensitivity are sensitive to the representation of S. Ocean clouds.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Solving the strong CP problem with massless grand-color quarks

We propose a solution to the strong CP problem that specifically relies on massless quarks and has no light axion. The QCD color group SU(3) c is embedded into a larger, simple gauge group (grand-color) where one of the massless, colored fermions enjoys an anomalous chiral symmetry, rendering the strong CP phase unphysical. The grand-color gauge group G GC is Higgsed down to SU(3) c × ${G}_{c^{\prime }}$, after which ${G}_{c^{\prime }}$ eventually confines at a lower scale, spontaneously breaking the chiral symmetry and generating a real, positive mass to the massless, colored fermion. Since the chiral symmetry has a ${G}_{c^{\prime }}$ anomaly, there is no corresponding light Nambu-Goldstone boson. The anomalous chiral symmetry can be an accidental symmetry that arises from an exact discrete symmetry without introducing a domain wall problem. Potential experimental signals of our mechanism include vector-like quarks near the TeV scale, pseudo Nambu-Goldstone bosons below the 10 GeV scale, light dark matter decay, and primordial gravitational waves from the new strong dynamics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Dynamics of heavy quarks in strongly coupled $\mathcal{N}$ = 4 SYM plasma

We calculate the probability distribution P(k) for a heavy quark with velocity v propagating through strongly coupled N = 4 SYM plasma in the ’t Hooft limit (N c → ∞, λ = g 2 N c → ∞) at a temperature T to acquire a momentum k due to interactions with the plasma. This distribution encodes the well-known drag coefficient η D and the transverse and longitudinal momentum diffusion coefficients κ T and κ L . The jet quenching parameter $\hat{q}$ can be extracted from P(k) for v = 1. Going beyond these known Gaussian characteristics of P(k), our calculation determines all of the higher order and mixed moments to leading order in 1/$\sqrt{λ}$ for the first time. These non-Gaussian features of P(k) include qualitatively novel correlations between longitudinal energy loss and transverse momentum broadening at nonzero v. We show that all higher moments scale characteristically with an effective temperature of the boosted plasma in the heavy quark rest frame, and we demonstrate that these non-Gaussian characteristics can be sizable in magnitude and even dominant in physically relevant situations. We use these results to derive a Kolmogorov equation for the evolution of the probability distribution for the total momentum of a heavy quark that propagates through strongly coupled plasma. This evolution equation accounts for all higher order correlations between transverse momentum broadening and longitudinal energy loss, which we have calculated from first principles. It reduces to a Fokker-Planck equation when truncated to only include the effects of η D , κ T and κ L . Remarkably, while heavy quarks do not reach kinetic equilibrium with the plasma if evolved with this Fokker-Planck equation, by showing that the Boltzmann distribution is a static solution of the all-order Kolmogorov equation that we have derived we demonstrate that heavy quarks do reach kinetic equilibrium if evolved with this equation. Our results thus provide a dynamically complete framework for understanding the thermalization of a heavy quark that may be initially far from equilibrium in the strongly coupled N = 4 SYM plasma — as well as new insight into heavy quark transport and equilibration in quark-gluon plasma.

Holography and Hydrodynamics↗
DOE OSTI2022

Discrimination between individual dust and bioparticles using aerosol time-of-flight mass spectrometry

Ice nucleating particles (INPs) impact cloud properties and precipitation processes through their ability to trigger cloud glaciation. Dust and bioparticles are two important sources of INPs that have markedly different atmospheric loadings and ice nucleating efficiencies. In situ identification of the sources of INPs in clouds has been accomplished using single particle mass spectrometry (SPMS). However, external mixtures of dust and bioparticles present a unique challenge as they have overlapping mass spectral ion signatures, complicating their unambiguous identification. This study presents a detailed discussion of dust and bioparticle SPMS signatures, uniting data from a broad array of studies. As emphasized, the ion signals from both dust and bioparticles are highly sensitive to ionization conditions. To understand the observed variations, we characterize the mass spectral dependence of distinct dust and bioparticle samples using total positive ion intensity (TPII) as an indicator of the laser pulse energy each particle encountered. Through this analysis, a broad range of characteristic biogenic low intensity ion peaks that may be useful to distinguish bioparticles from dust became apparent and are highlighted. Insights informed by this analysis were utilized to identify bioparticles in ambient SPMS data. Ambient particles exhibiting both dust and characteristic biogenic spectral fingerprints were excluded from the bioparticle classification. Although bioparticles only made up 0.2% of all sampled particles, their abundance was moderately correlated with INP concentrations measured at 15 °C.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Response to Comment on “Radiation-Belt Remediation Using Space-Based Antennas and Electron Beams” by G. Ganguli and C. Crabtree

Ganguli and Crabtree have written a comment about a recent article by the authors listed above on radiation-belt remediation. They have objected to our evaluation of the Naval Research Laboratory’s chemical release concept which states that this concept may be impractical due to an apparently low overall efficiency. In their comment, they provide a scientific argument and refer to the published literature to counter our statement. Here, in this response, we provide more details on our numerical calculations and experimental results which led to this evaluation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

TGCM: (T)rait, (G)ene, and (C)rop Growth (M)odel Directed Targeted Gene Characterization in Sorghum (Final Technical Report)

Understanding which genes control important crop traits could help scientists develop better bioenergy and food crops more efficiently. However, plant genomes contain tens of thousands of genes, and testing each one individually is expensive and time-consuming. This project developed computational tools to predict which genes are most likely to matter, allowing researchers to focus their efforts where they will have the greatest impact. This project developed and validated integrated approaches combining machine learning, quantitative genetics, and crop growth modeling to improve the efficiency of functional gene characterization in sorghum (Sorghum bicolor), a critical bioenergy and food security crop. The research addressed a fundamental challenge in plant biology: the majority of genes in plant genomes lack experimentally validated functions, making it difficult to prioritize which genes to study using resource-intensive reverse genetics approaches.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

STRIDES: a 3.9 per cent measurement of the Hubble constant from the strong lens system DES J0408−5354

We present a blind time-delay cosmographic analysis for the lens system DES J0408−5354. This system is extraordinary for the presence of two sets of multiple images at different redshifts, which provide the opportunity to obtain more information at the cost of increased modelling complexity with respect to previously analysed systems. We perform detailed modelling of the mass distribution for this lens system using three band Hubble Space Telescope imaging. We combine the measured time delays, line-of-sight central velocity dispersion of the deflector, and statistically constrained external convergence with our lens models to estimate two cosmological distances. We measure the ‘effective’ time-delay distance corresponding to the redshifts of the deflector and the lensed quasar |$D_{\Delta t}^{\rm eff}=$||$3382_{-115}^{+146}$| Mpc and the angular diameter distance to the deflector D_d = |$1711_{-280}^{+376}$| Mpc, with covariance between the two distances. From these constraints on the cosmological distances, we infer the Hubble constant H_0= |$74.2_{-3.0}^{+2.7}$| km s^−1 Mpc^−^1 assuming a flat ΛCDM cosmology and a uniform prior for Ω_m as |$\Omega _{\rm m} \sim \mathcal {U}(0.05, 0.5)$|⁠. This measurement gives the most precise constraint on H_0 to date from a single lens. Our measurement is consistent with that obtained from the previous sample of six lenses analysed by the H_0 Lenses in COSMOGRAIL’s Wellspring (H0LiCOW) collaboration. It is also consistent with measurements of H_0 based on the local distance ladder, reinforcing the tension with the inference from early Universe probes, for example, with 2.2σ discrepancy from the cosmic microwave background measurement.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Identification of the Elusive Methyl-Loss Channel in the Crossed Molecular Beam Study of Gas-Phase Reaction of Dicarbon Molecules (C 2 ; X 1 Σ g + /a 3 Π u ) with 2-Methyl-1,3-butadiene (C 5 H 8 ; X 1 A')

The crossed molecular beams technique was utilized to explore the reaction of dicarbon C 2 (X 1 Σ g + /a 3 Π u ) with 2-methyl-1,3-butadiene (isoprene, CH 2 C(CH 3 )CHCH 2 ; X 1 A') at a collision energy of 28 ± 1 kJ mol⁻¹ using a supersonic dicarbon beam generated via photolysis (248 nm) of helium-seeded tetrachloroethylene (C 2 Cl 4 ). Here, experimental data combined with previous ab initio calculations provide evidence of the detection of the hitherto elusive methyl elimination channels leading to acyclic resonantly stabilized hexatetraenyl radicals: 1,2,4,5-hexatetraen-3-yl (CH 2 CC•CHCCH 2 ) and/or 1,3,4,5-hexatetraen-3-yl (CH 2 CHC•CCCH 2 ). These pathways are exclusive to the singlet potential energy surface, with the reaction initiated by the barrierless addition of dicarbon to one of the carbon-carbon double bonds in the diene. In combustion systems, both hexatetraenyl radicals can isomerize to the phenyl radical (C 6 H 5 ) through a hydrogen atom assisted isomerization – the crucial reaction intermediate and molecular mass growth species step toward the formation of polycyclic aromatic hydrocarbons (PAHs) and soot.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Microwave Multiplexing on the Keck Array

In this paper, we describe an on-sky demonstration of a microwave-multiplexing readout system in one of the receivers of the Keck Array, a polarimetry experiment observing the cosmic microwave background at the South Pole. During the austral summer of 2018–2019, we replaced the time-division multiplexing readout system with microwave-multiplexing components including superconducting microwave resonators coupled to radio frequency superconducting quantum interference devices at the sub-Kelvin focal plane, coaxial-cable plumbing and amplification between room temperature and the cold stages, and a SLAC Microresonator Radio Frequency system for the warm electronics. In the range 5–6 GHz, a single coaxial cable reads out 528 channels. The readout system is coupled to transition-edge sensors, which are in turn coupled to 150-GHz slot-dipole phased-array antennas. Observations began in April 2019, and we report here on an initial characterization of the system performance.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Absence of Low-Energy Shape Coexistence in 80 Ge: The Nonobservation of a Proposed Excited 0 2 + Level at 639 keV

The 80 Ge structure was investigated in a high-statistics β-decay experiment of 80 Ga using the GRIFFIN spectrometer at TRIUMF-ISAC through γ, β-e, e-γ and γ-γ spectroscopy. No evidence was found for the recently reported 0 2 + 639-keV level suggested as evidence for low-energy shape coexistence in 80Ge. Large-scale shell model calculations performed in 78,80,82 Ge place the 0 2 + level in 80 Ge at 2 MeV. The new experimental evidence combined with shell model predictions indicate that low-energy shape coexistence is not present in 80 Ge.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Formation of Vertically Oriented Channels during Calcination of Surfactant-Templated Titania-Doped Mesoporous Silica Thin Films

Here, the mesoporous structure development during calcination of titania-doped mesoporous silica thin films is characterized by in situ grazing-incidence small angle x-ray scattering (GISAXS). Varying amounts of titania (≤ 6 mol%) are incorporated in cetyltrimethylammonium bromide (CTAB) templated film by two methods in this study: dispersion of titania in the silica matrix, and fixing titania at the pore surface by complexation of the titania precursor with a sugar-based co-surfactant, dodecyl maltoside (C 12 G 2 ). Before calcination, films templated with only CTAB display a mesoporous structure with a mixture of in-plane 2D hexagonal and randomly oriented porous structure, while C 12 G 2 -complexed film possessed randomly oriented mesostructure only. Both methods yield a final structure of hexagonal close-packed pores orthogonally oriented to the substrate after calcination at 500 °C. This is attributed to weak Si-O-Ti bonds which allow sintering to occur at 500 °C, combined with unidirectional thermal contraction of the film in the vertical direction. Anisotropic stress and annealing of the films allows the randomly oriented pores to merge vertically and form channels with pore diameter of 2.3 ± 0.3 nm. Titania doping greater than 1% is required for this transformation in films with no C 12 G 2 surfactant used while the transformation was observed for films with C 12 G 2 complexation even at low (0.005%) titania doping, perhaps accentuated by orientational disorder introduced by the sugar surfactant.

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

Laser-produced plasmas as drivers of laboratory collisionless quasi-parallel shocks

The creation of a repeatable collisionless quasi-parallel shock in the laboratory would provide a valuable platform for experimental studies of space and astrophysical shocks. However, conducting such an experiment presents substantial challenges. Scaling the results of hybrid simulations of quasi-parallel shock formation to the laboratory highlights the experimentally demanding combination of dense, fast, and magnetized background and driver plasmas required. One possible driver for such experiments is high-energy laser-produced plasmas (LPPs). Preliminary experiments at the University of California, Los Angeles, have explored LPPs as drivers of quasi-parallel shocks by combining the Phoenix Laser Laboratory [Niemann et al., J. Instrum. 7, P03010 (2012)] with a large plasma device [Gekelman et al., Rev. Sci. Instrum. 87, 025105 (2016)]. Beam instabilities and waves characteristic of the early stages of shock formation are observed, but spatial dispersion of the laser-produced plasma prematurely terminates the process. This result is illustrated by experimental measurements and Monte Carlo calculations of LPP density dispersion. The experimentally validated Monte Carlo model is then applied to evaluate several possible approaches to mitigating LPP dispersion in future experiments.

Heuer, P. V. (ORCID:0000000150506606)↗
DOE OSTI2020

Measurements of ion velocity distributions in a large scale laser-produced plasma

Laser-produced plasma velocity distributions are an important, but difficult quantity to measure. In this work, we present a noninvasive technique for measuring individual charge state velocity distributions of laser-produced plasmas using a high temporal and spectral resolution monochromator. The novel application of this technique is its ability to detect particles up to seven meters from their inception (significantly larger than most laboratory plasma astrophysics experiments, which take place at or below the millimeter scale). The design and assembly of this diagnostic is discussed in terms of maximizing the signal to noise ratio, maximizing the spatial and temporal resolution, and other potential use cases. The analysis and results of this diagnostic are demonstrated by directly measuring the time-of-flight velocity of all ion charge states in a laser produced carbon plasma.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Freedom of the mixer rotation axis improves performance in the quantum approximate optimization algorithm

Variational quantum algorithms such as the quantum approximate optimization algorithm (QAOA) are particularly attractive candidates for implementation on near-term quantum processors. As hardware realities such as error and qubit connectivity will constrain achievable circuit depth in the near future, new ways to achieve high performance at low depth are of great interest. In this work, we present a modification to QAOA that adds additional variational parameters in the form of freedom of the rotation axis in the XY plane of the mixer Hamiltonian. Here, via numerical simulation, we show that this leads to a drastic performance improvement over standard QAOA at finding solutions to the MaxCut problem on graphs of up to seven qubits. Furthermore, we explore the Z-phase error mitigation properties of our modified Ansatz, its performance under a realistic error model for a neutral atom quantum processor, and the class of problems it can solve in a single round.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

The Atacama Cosmology Telescope: Detection of the pairwise kinematic Sunyaev-Zel’dovich effect with SDSS DR15 galaxies

We present a 5.4$\sigma$ detection of the pairwise kinematic Sunyaev-Zel'dovich (kSZ) effect using Atacama Cosmology Telescope (ACT) and $\it{Planck}$ CMB observations in combination with Luminous Red Galaxy samples from the Sloan Digital Sky Survey (SDSS) DR15 catalog. Results are obtained using three ACT CMB maps: co-added 150 GHz and 98 GHz maps, combining observations from 2008-2018 (ACT DR5), which overlap with SDSS DR15 over 3,700 sq. deg., and a component-separated map using night-time only observations from 2014-2015 (ACT DR4), overlapping with SDSS DR15 over 2,089 sq. deg. Comparisons of the results from these three maps provide consistency checks in relation to potential frequency-dependent foreground contamination. A total of 343,647 galaxies are used as tracers to identify and locate galaxy groups and clusters from which the kSZ signal is extracted using aperture photometry. We consider the impact of various aperture photometry assumptions and covariance estimation methods on the signal extraction. Theoretical predictions of the pairwise velocities are used to obtain best-fit, mass-averaged, optical depth estimates for each of five luminosity-selected tracer samples. A comparison of the kSZ-derived optical depth measurements obtained here to those derived from the thermal SZ effect for the same sample is presented in a companion paper.

79 ASTRONOMY AND ASTROPHYSICS↗