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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Laser-pulse compression in a collisional plasma under weak-relativistic ponderomotive nonlinearity

We present theory and numerical analysis which demonstrate laser-pulse compression in a collisional plasma under the weak-relativistic ponderomotive nonlinearity. Plasma equilibrium density is modified due to the ohmic heating of electrons, the collisions, and the weak relativistic-ponderomotive force during the interaction of a laser pulse with plasmas. First, within one-dimensional analysis, the longitudinal self-compression mechanism is discussed. Three-dimensional analysis (spatiotemporal) of laser pulse propagation is also investigated by coupling the self-compression with the self-focusing. In the regime in which the laser becomes self-focused due to the weak relativistic-ponderomotive nonlinearity, we provide results for enhanced pulse compression. The results show that the matched interplay between self-focusing and self-compression can improve significantly the temporal profile of the compressed pulse. Enhanced pulse compression can be achieved by optimizing and selecting the parameters such as collision frequency, ion-temperature, and laser intensity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Planck 2018 results - VIII. Gravitational lensing

We present measurements of the cosmic microwave background (CMB) lensing potential using the final Planck 2018 temperature and polarization data. Using polarization maps filtered to account for the noise anisotropy, we increase the significance of the detection of lensing in the polarization maps from 5σ to 9σ. Combined with temperature, lensing is detected at 40σ. We present an extensive set of tests of the robustness of the lensing-potential power spectrum, and construct a minimum-variance estimator likelihood over lensing multipoles 8 ≤ L ≤ 400 (extending the range to lower L compared to 2015), which we use to constrain cosmological parameters. We find good consistency between lensing constraints and the results from the Planck CMB power spectra within the ΛCDM model. Combined with baryon density and other weak priors, the lensing analysis alone constrains σ 8 Ωm 0.25 = 0.589 ± 0.020 (1σ errors). Also combining with baryon acoustic oscillation data, we find tight individual parameter constraints, σ8 = 0.811 ± 0.019, H0 = 67.9-1.3+1.2 km s -1 Mpc -1 , and Ω m = 0.303 -0.018 +0.016 . Combining with Planck CMB power spectrum data, we measure σ 8 to better than 1% precision, finding σ 8 = 0.811 ± 0.006. CMB lensing reconstruction data are complementary to galaxy lensing data at lower redshift, having a different degeneracy direction in σ 8 - Ω m space; we find consistency with the lensing results from the Dark Energy Survey, and give combined lensing-only parameter constraints that are tighter than joint results using galaxy clustering. Using the Planck cosmic infrared background (CIB) maps as an additional tracer of high-redshift matter, we make a combined Planck-only estimate of the lensing potential over 60% of the sky with considerably more small-scale signal. We additionally demonstrate delensing of the Planck power spectra using the joint and individual lensing potential estimates, detecting a maximum removal of 40% of the lensing-induced power in all spectra. The improvement in the sharpening of the acoustic peaks by including both CIB and the quadratic lensing reconstruction is detected at high significance.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

South Asian monsoon precipitation in CMIP5: a link between inter-model spread and the representations of tropical convection

CMIP5 models exhibit a mean dry bias and a large inter-model spread in simulating Indian monsoon precipitation but the origins of the bias and spread have not been well understood. Using moisture and energy budget analysis that exploits the weak temperature gradients in the tropics, we show that they are linked to the convection simulated over the equatorial Indian Ocean. About half of the 21 models analyzed operate at the steep gradient of the non-linear relationship between the normalized precipitable water and normalized precipitation, where small differences in the former are amplified as large differences in precipitation. These models preferentially produce higher precipitation over the equatorial Indian Ocean, and contribute disproportionately to the inter-model spread and multi-model mean dry bias in monsoon precipitation. Conversely, models on the flat side of the relationship are in better agreement with each other and with observations. Under the RCP8.5 forcing scenario, models on the steep part of the relationship project stronger response to warming and dominate the inter-model spread in the projection. This study identified the normalized precipitable water as a key metric for understanding the behavior of model simulated equatorial and Indian monsoon precipitation.

Hagos, Samson (ORCID:0000000175919933)↗
DOE OSTI2026

Seasonal variation of the surface cross-shelf exchange in the northern South China Sea: a Lagrangian perspective

Previous studies on cross-shelf exchange, predominantly adopted an Eulerian perspective, struggled to identify water sources and pathways. Using a high-resolution regional ocean modeling system (ROMS) and Lagrangian particle tracking, this study systematically investigates the seasonal variation and dynamics of surface cross-shelf exchange in the northern South China Sea (NSCS) from a Lagrangian perspective. Based on daily released 30-day drifter trajectories we identify the key pathways, source regions for surface cross-shelf exchange, revealing pronounced seasonal variability. Results show the surface cross-shelf exchange generally following monsoon-driven Ekman transport. However, local dynamics, especially topographic modulation, can outweigh the expected Ekman-driven transport, producing surface exchange patterns opposite to that predicted from the prevailing winds. Topographic effects vary across different scales. In the coastal waters of western Guangdong during winter, despite downwelling-favorable winds, the modulation of alongshore currents by island topography induces an eastward pressure gradient. This gradient, through geostrophic balance, drives offshore flows opposite to wind-driven Ekman onshore transport. Furthermore, the eastern widened shelf exhibits a distinct seasonal variation of cross-shelf exchange, with strong offshore transport (opposite to the direction of Ekman transport) in winter and exceedingly weak exchange in summer. Analysis of the underlying mechanisms reveals that this winter offshore transport is primarily attributed to geostrophic flows driven by surface pressure gradient that is jointly modulated by the Kuroshio intrusion and local widened shelf topography, and enhanced by cumulative submesoscale processes. In summer, a persistent and strong along-isobath jet acts as a dynamic barrier, effectively suppressing the exchange. These findings highlight the important role of topography in regulating surface material transport, and have important implications for predicting the advection and dispersion of plankton or oil spills over the continental shelf influenced by monsoon.

Hao, Dongliang↗
DOE OSTI2025

Modular Assembly of FTO|Chromophore-Catalyst Hierarchical Films Based on Strong Dipole Interactions

Here, we have designed and characterized modular self-assembled hierarchical films containing a molecular catalyst tethered to an anchoring molecule by means of dipole-induced dipole interactions. In order to do so, two new Co III -based molecular catalyst candidates were designed, namely, [Co III L 1 (pyrr) 2 ]ClO 4 (Co1) and [Co III L 2 (pyrr) 2 ]ClO 4 (Co2), where L 1 and L 2 are the respective deprotonated forms of N,N′-[4,5-bis(dodecyloxy)-1,2-phenylene]dipicolinamide and N,N′-[4,5-bis(methoxyethoxy)-1,2-phenylene]dipicolinamide and were characterized by electrochemical, electronic, and film formation properties. Species Co1 and Co2 were deposited onto an anchor molecule such as octylphosphonic acid (OPA) or the chromophoric [Ru II (bpy PO3H ) 2 (bpy C7 )]Cl 2 (Ru) previously attached onto conductive fluorine-doped tin oxide (FTO). Four hierarchical films of the form substrate|anchor-catalyst were obtained, namely, FTO|OPA-Co1, FTO|OPA-Co2, FTO|Ru-Co1, and FTO|Ru-Co2, and the role of dipole-dipole interactions between anchor and catalyst modules was assessed. These newly synthesized hierarchical films were characterized by a host of surface-specific methods that include X-ray photoelectron spectroscopy, ellipsometry, X-ray fluorescence, and water contact angle, thus enabling an unprecedented level of analysis. Compared to the weak C-H van der Waals interactions exhibited by Co1, the presence of alkoxy chains in Co2 ensures stronger dipole-dipole interactions with the alkyl chain of the anchors due to O···H formation. The persistence of their redox properties, which include metal oxidation, and directionality of electron transport were probed suggesting direct relevance to catalytic processes such as water oxidation.

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

Kinetic and Mechanistic Characterization of Low-Overpotential, H2O2-Selective Reduction of O2 Catalyzed by N2O2-Ligated Cobalt Complexes

A soluble, bis-ketiminate-ligated Co complex [Co(N2O2)] was recently shown to catalyze selective reduction of O2 to H2O2 with an overpotential as low as 90 mV. Here we report experimental and computational mechanistic studies of the Co(N2O2)-catalyzed O2 reduction reaction (ORR) with deca-methylferrocene (Fc*) as the reductant in the presence of AcOH in MeOH. Analysis of the Co/O2 binding stoichiometry and kinetic studies support an O2 reduction pathway involving a mononuclear cobalt species. The catalytic rate exhibits a first-order kinetic dependence on [Co(N2O2)] and [AcOH], but no dependence on [Fc*] or [O2]. Differential pulse voltammetry and computational studies support CoIII-hydroperoxide as the catalyst resting state and protonation of this species as the rate-limiting step of the catalytic reaction. These results contrast previous mechanisms proposed for other Co-catalyzed ORR systems, which commonly feature rate-limiting protonation of a CoIII-superoxide adduct earlier in the catalytic cycle. Computational studies show that protonation is strongly favored at the proximal oxygen of the CoIII(OOH) species, accounting for the high selectivity for formation of hydrogen peroxide. Further analysis shows that a weak dependence of the ORR rate on the pKa of the protonated CoIII(OOH) species across a series of Co(N2O2) catalysts provides a rationale for the unusually low overpotential observed for O2 reduction.

Wang, Yu-Heng↗
DOE OSTI2016

Insight into magnetic, ferroelectric and elastic properties of strained BiFeO{sub 3} thin films through Mössbauer spectroscopy

We have studied the magnetic order of highly strained (001)-oriented BiFeO{sub 3} (BFO) thin films using {sup 57}Fe Conversion Electron Mössbauer Spectrometry. From 90 K to 620 K the films exhibit a collinear antiferromagnetic structure, in contrast with the cycloidal structure observed in bulk BFO. Moreover, we find that both the planar magnetic anisotropy for compressive strain and out-of-plane anisotropy for tensile strain persist from 90 K up to the Néel temperature (T{sub N}), which itself shows only a weak strain dependence. An analysis of the line asymmetry of the paramagnetic doublet for temperatures above T{sub N} is used to reveal the strain-dependent rotation of the polarization direction, consistent with previous observations. Our results show that the lattice dynamics in BFO films are strongly strain-dependent, offering avenues toward acoustic phonon devices. Finally, we use the versatility of Mössbauer spectroscopy technique to reveal various multi-property features including magnetic states, polarization direction and elastic strain.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Probing the neutrino mass through the cross correlation between the Rees-Sciama effect and weak lensing

Cosmology plays a fundamental role to determine the neutrino mass, therefore also to determine its mass hierarchy, since the massive neutrino contributes to the total matter density in the Universe at the background and perturbation levels, once it becomes non-relativistic. After the non-relativistic transition the fluctuations are smashed out at the scales k >> k {sub fs} . Therefore, the missing fluctuation in the total matter is imprinted on the large scale structure, say the suppression of the matter power spectrum Δ P / P ≈ -8 f {sub ν} at the scales k >> k {sub fs} . In this paper, instead of considering the linear perturbation theory, which is well understood in the presence of neutrino, we propose to use the cross correlation between the Rees-Sciama effect and weak lensing to probe the neutrino mass. At the small scales, the density contrast grows faster than the background scale factor δ ∼ a , that makes a sign flipping on Φ' ∝ Hδ d ln (δ/ a )/ d ln a , which happens only in the non-linear regime. We show that the flipping scale in the cross power spectrum between the Rees-Sciama effect and weak lensing depends on the neutrino mass by assuming the shallow and deep weak lensing surveys. Our analysis shows that the Deep survey has larger signal-to-noise ratio S / N ∼ 160. Finally, we use the Fisher information matrix to forecast constraint on the neutrino mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Thermal conductivity of amorphous and nanocrystalline silicon films prepared by hot-wire chemical-vapor deposition

We report 3..omega.. thermal conductivity measurements of amorphous and nanocrystalline silicon thin films from 85 to 300 K prepared by hot-wire chemical-vapor deposition, where the crystallinity of the films is controlled by the hydrogen dilution during growth. The thermal conductivity of the amorphous silicon film is in agreement with several previous reports of amorphous silicon prepared by a variety of deposition techniques. The thermal conductivity of the as-grown nanocrystalline silicon film is 70% higher and increases 35% more after an anneal at 600 degrees C. They all have similarly weak temperature dependence. Structural analysis shows that the as-grown nanocrystalline silicon is approximately 60% crystalline, nanograins and grain boundaries included. The nanograins, averaging 9.1 nm in diameter in the as-grown film, are embedded in an amorphous matrix. The grain size increases to 9.7 nm upon annealing, accompanied by the disappearance of the amorphous phase. We extend the models of grain boundary scattering of phonons with two different non-Debye dispersion relations to explain our result of nanocrystalline silicon, confirming the strong grain size dependence of heat transport for nanocrystalline materials. However, the similarity in thermal conductivity between amorphous and nanocrystalline silicon suggests the heat transport mechanisms in both structures may not be as dissimilar as we currently understand.

14 SOLAR ENERGY↗
DOE OSTI2017

Rashba torque beyond the Boltzmann regime

We study spin torques induced by Rashba spin-orbit coupling in two-dimensional ferromagnets under the good-metal condition ε F τ / ℏ >> 1 ( ε F the Fermi energy, τ the electron lifetime) by employing the Kubo formula. We find that in the presence of spin-dependent disorder the Rashba torque changes greatly as the system evolves out of the weak-disorder limit where ℏ / τ is much smaller than any intrinsic energy scale characterizing the multiband structure. The antidamping-like component of Rashba torque can be comparable to and larger than the field-like one out of the weak-disorder limit. The semiclassical Boltzmann theory produces the same results as microscopic linear response calculations only in the weak-disorder limit. Our analysis indicates that rich behaviors of various nonequilibrium phenomena beyond the Boltzmann theory may also be present even when ε F τ / ℏ >> 1 in multiband systems where ε F is not the unique intrinsic energy scale.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

First Results on Dark Matter Substructure from Astrometric Weak Lensing

Low-mass structures of dark matter (DM) are expected to be entirely devoid of light-emitting regions and baryons. Precisely because of this lack of baryonic feedback, small-scale substructures of the Milky Way are a relatively pristine testing ground for discovering aspects of DM microphysics and primordial fluctuations on subgalactic scales. In this work, we report results from the first search for Galactic DM subhalos with time-domain astrometric weak gravitational lensing. The analysis is based on a matched-filter template of local lensing corrections to the proper motion of stars in the Magellanic Clouds. We describe a data analysis pipeline detailing sample selection, background subtraction, and handling outliers and other systematics. For tentative candidate lenses, we identify a signature based on an anomalous parallax template that can unequivocally confirm the presence of a DM lens, opening up prospects for robust discovery potential with full time-series data. We present our constraints on substructure fraction f l ≲5 at 90% CL (and f l ≲2 at 50% CL) for compact lenses with radii r l <1pc, with best sensitivity reached for lens masses M l around 10 7 -10 8 M ⊙ . Parametric improvements are expected with future astrometric data sets; by end of mission, Gaia could reach f l ≲10 -3 for these massive point-like objects, and be sensitive to lighter and/or more extended subhalos for O(1) substructure fractions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Solving Graph Laplacian Systems Through Recursive Bisections and Two-Grid Preconditioning

We present a parallelizable direct method for computing the solution to graph Laplacian-based linear systems derived from graphs that can be hierarchically bipartitioned with small edge cuts. For a graph of size n with constant-size edge cuts, our method decomposes a graph Laplacian in time O(n log n), and then uses that decomposition to perform a linear solve in time O(n log n). We then use the developed technique to design a preconditioner for graph Laplacians that do not have this property. Finally, we augment this preconditioner with a two-grid method that accounts for much of the preconditioner's weaknesses. We present an analysis of this method, as well as a general theorem for the condition number of a general class of two-grid support graph-based preconditioners. Numerical experiments illustrate the performance of the studied methods.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Argonne Reactor Code Software Verification and Validation Plan for the Versatile Test Reactor

This Argonne Reactor Code (ARC) software has taken a pivotal role in the design work of the Versatile Test Reactor. The ARC software itself consists of several independent or semiindependent pieces of software that are used in concert to carry out specific analysis and design objectives. In this report, we discuss the validation that is needed for the ARC software overall and discuss available, usable experimental data and how it relates to the VTR project. We also discuss the verification that is required for the ARC software with respect to its usage in the VTR project and give some concrete examples as to what it must accomplish. A list of goals for the verification and validation work are presented as the general procedure that will be implemented for every individual piece of software in ARC. The ARC software has been continuously developed for over 50 years and many of the features used for the VTR project have thus been rigorously tested for accuracy during that timeframe. The ARC software is presently under source code control and undergoes nightly regression testing of not only the individual pieces, but the interconnected aspects that are common to most analysis projects. Its greatest weakness, from a software verification and validation perspective, is both a lack of documentation and outdated documentation. As an example, much of the previous validation work will require contemporary effort to re-evaluate given the updated base data libraries and modifications to the software that have occurred since. This requires new documentation to be produced to support the usage of the software in the VTR project. The bulk of the ARC software is focused on steady state neutronics and TH behavior of a reactor system. In this regard, we have identified the ZPPR, FFTF, and EBR-II programs as the best candidates for sources of validation data for the VTR project. The ZPPR-15 series in the ZPPR program was chosen as it is the best representation of the VTR fuel form and reactor core layout of all of the ZPPR measurements. Additional support for it comes from the fact that most of the data has already been processed into usable ARC models for VTR validation. The FFTF and EBR-II reactors were both functional reactors that provide reactor scale measurements. FFTF is clearly a closer match to VTR and its startup measurements would be a very valuable validation basis. EBR-II has invaluable burnup related measurements that will play a key role in the ARC software validation work. Each piece of ARC software will require a report detailing the software verification. The validation work will be logically split into the results of modeling each identified experimental resource (ZPPR, EBR-II, FFTF). The intended timeline for the VTR project is to have the ARC software verified and validated by the end of fiscal year 2020. This is incumbent on sufficient funding allocated to V&V activities and no change in programmatic priorities.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2023

Confidence Calibration Metrics

This technical report serves to summarize a literature search conducted that covered confidence calibration. This report is meant to serve as a solid starting reference for individuals interested in learning more about the confidence calibration domain as well as for individuals more familiar with this work – as a summarizing document for calibration metrics is notably lacking in the literature. This report is not meant to serve as a comprehensive review of everything that has been done in this field – in fact, the reader is encouraged to look further into this domain. We describe confidence and calibration and discuss properties of good calibration metrics. We detail various calibration and calibration-tangential metrics, presenting equations, algorithms, parameters, and an analysis of strengths and weaknesses. We apply a subset of these metrics to eight proxy confidence assessment datasets. We examine the various metrics in the context of model confidence. Finally, we discuss promising future directions and outstanding questions.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2023

Guanajuato Policy Options for Land Transportation Greenhouse Gas Reduction [Slides]

NREL consulted the Mexican state of Guanajuato to help them identify and prioritize policies that are specifically applicable to their land transportation system and help them meet their greenhouse gas (GHG) reduction goals. Three focus groups were held across Guanajuato to get the input from a wide variety of users of the transportation system. These focus groups performed a SWOT (strengths, weaknesses, opportunities and threats) analysis of Guanajuato's transportation system and logged the policy goals of participants. NREL then developed a menu of policy options that have been used successfully in relevant countries and prioritized these policies based on the weighted input from stakeholder groups. The most applicable policies were a paid parking strategy, regional transit master plan, and expanded bike and pedestrian infrastructure. Case studies of these three policies, plus a few more, were then presented to inform Guanajuato of how these policies could successfully be implemented. Finally, the GHG reductions for five of the most applicable policies were estimated to reduce emissions from Guanajuato's land transportation system nearly 40% below business-as-usual emissions by 2050.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2024

NEXUS-DC: Nuclear Energy eXpedition for US Data Centers [Slides]

This presentation covers the growing interest in utilizing nuclear power to satisfy the increasing energy demands of data centers in the United States, emphasizing the factors that accelerate reactor deployment. It addresses clean and reliable energy needs, highlights the importance of power supply redundancy for reliability, and discusses challenges and solutions related to cooling, waste heat reuse, and techno-economics. Additionally, it includes a strength, weakness, opportunities and threat analysis and emphasizes community engagement and collaboration for accelerating regulatory approvals and reactor deployment.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1981

Adaptation of the TH Epsilon Mu formalism for the analysis of the equivalence principle in the presence of the weak and electroweak interaction

The TH epsilon mu formalism, used in analyzing equivalence principle experiments of metric and nonmetric gravity theories, is adapted to the description of the electroweak interaction using the Weinberg-Salam unified SU(2) x U(1) model. The use of the TH epsilon mu formalism is thereby extended to the weak interactions, showing how the gravitational field affects W sub mu (+ or -1) and Z sub mu (0) boson propagation and the rates of interactions mediated by them. The possibility of a similar extension to the strong interactions via SU(5) grand unified theories is briefly discussed. Also, using the effects of the potentials on the baryon and lepton wave functions, the effects of gravity on transition mediated in high-A atoms which are electromagnetically forbidden. Three possible experiments to test the equivalence principle in the presence of the weak interactions, which are technologically feasible, are then briefly outline: (1) K-capture by the FE nucleus (counting the emitted X-ray); (2) forbidden absorption transitions in high-A atoms' vapor; and (3) counting the relative Beta-decay rates in a suitable alpha-beta decay chain, assuming the strong interactions obey the equivalence principle.

Fennelly, A. J.↗
NASA NTRS1983

An evaluation of soundings, analyses and model forecasts derived from TIROS-N and NOAA-6 satellite data

TIROS-N and NOAA-6 temperature soundings over North America during three days in January 1980, and synoptic analyses and numerical-model forecasts derived from them, are compared with conventional data and analyses from NMC's limited-area fine-mesh model (LFM). The collocated sounding comparison revealed significant errors, especially near the surface and the tropopause. Satellite-derived thermal gradients were found to be weak, and thickness-analysis difference fields to propagate eastward, suggesting that sounding errors are correlated with synoptic patterns. The same pattern of anomalies is seen in the model forecasts. More detailed determinations of the correlation detected here could be used to optimize the assimilation of satellite soundings to conventional data.

Koehler, T. L.↗