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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Atacama Cosmology Telescope: Constraints on prerecombination early dark energy

The early dark energy (EDE) scenario aims to increase the value of the Hubble constant (H0) inferred from cosmic microwave background (CMB) data over that found in the standard cosmological model (Λ CDM ), via the introduction of a new form of energy density in the early Universe. The EDE component briefly accelerates cosmic expansion just prior to recombination, which reduces the physical size of the sound horizon imprinted in the CMB. Previous work has found that nonzero EDE is not preferred by Planck CMB power spectrum data alone, which yield a 95% confidence level (C.L.) upper limit f EDE < 0.087 on the maximal fractional contribution of the EDE field to the cosmic energy budget. In this paper, we fit the EDE model to CMB data from the Atacama Cosmology Telescope (ACT) data release 4. We find that a combination of ACT, large-scale Planck TT (similar to WMAP), Planck CMB lensing, and BAO data prefers the existence of EDE at >99.7 % C .L . : f EDE = 0.091$^{+0.020}_{-0.036}$, with H 0 = 70.9$^{+1.0}_{-2.0}$ km/s/Mpc (both 68% C.L.). From a model-selection standpoint, we find that EDE is favored over Λ CDM by these data at roughly 3 σ significance. In contrast, a joint analysis of the full Planck and ACT data yields no evidence for EDE, as previously found for Planck alone. We show that the preference for EDE in ACT alone is driven by its TE and EE power spectrum data. The tight constraint on EDE from Planck alone is driven by its high-ℓ TT power spectrum data. Understanding whether these differing constraints are physical in nature, due to systematics, or simply a rare statistical fluctuation is of high priority. Here, the best-fit EDE models to ACT and Planck exhibit coherent differences across a wide range of multipoles in TE and EE, indicating that a powerful test of this scenario is anticipated with near-future data from ACT and other ground-based experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Confronting interacting dark radiation scenarios with cosmological data

Dark radiation (DR) is generally predicted in new physics scenarios that address fundamental puzzles of the Standard Model or tensions in the cosmological data. Cosmological data have the sensitivity to constrain not only the energy density of DR but also whether it is interacting. In this paper, we present a systematic study of five types of interacting DR (free-streaming, fluid, decoupling, instantaneous decoupling, and recoupling DR) and their impact on cosmological observables. We modify the Boltzmann hierarchy to describe all these types of interacting DR under the relaxation time approximation. We, for the first time, robustly calculate the collision terms for recoupling scalar DR and provide a better estimation of the recoupling transition redshift. We demonstrate the distinct features of each type of DR on the cosmic microwave background and matter power spectra. We perform Markov-chain Monte Carlo scans using the Planck 2018 data and baryon acoustic oscillation data. Assuming no new physics in the standard model neutrino sector, we find no statistically significant constraints on the couplings of DR, although there is a slight preference for the fluidlike limit of all the cases. In the case of instantaneous decoupling DR, this limit corresponds to a late transition redshift around recombination. Furthermore, the ΔN eff constraint varies marginally depending on the type of DR.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Observation of χ c J → 3 ( K + K − )

By analyzing ( 27.12 ± 0.14 ) × 10 8 ψ ( 3686 ) events collected with the BESIII detector operating at the BEPCII collider, the decay processes χ c J → 3 ( K + K − ) ( J = 0 , 1, 2) are observed for the first time with statistical significances of 8.2 σ , 8.1 σ , and 12.4 σ , respectively. The product branching fractions of ψ ( 3686 ) → γ χ c J , χ c J → 3 ( K + K − ) are presented and the branching fractions of χ c J → 3 ( K + K − ) decays are determined to be B χ c 0 → 3 ( K + K − ) = ( 10.7 ± 1.8 ± 1.1 ) × 10 − 6 , B χ c 1 → 3 ( K + K − ) = ( 4.2 ± 0.9 ± 0.5 ) × 10 − 6 , and B χ c 2 → 3 ( K + K − ) = ( 7.2 ± 1.1 ± 0.8 ) × 10 − 6 , where the first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2025

Search for η c ( 2 S ) → ω ω and ω ϕ and measurements of χ c J → ω ω and ω ϕ in ψ ( 2 S ) radiative processes

Using ( 2712 ± 14 ) × 10 6 ψ ( 2 S ) events collected with the BESIII detector at the BEPCII collider, we search for the decays η c ( 2 S ) → ω ω and η c ( 2 S ) → ω ϕ via the process ψ ( 2 S ) → γ η c ( 2 S ) . No statistically significant signals are observed. The upper limits of their product branching fractions at the 90% confidence level are determined to be B ( ψ ( 2 S ) → γ η c ( 2 S ) , η c ( 2 S ) → ω ω ) < 1.04 × 10 − 6 and B ( ψ ( 2 S ) → γ η c ( 2 S ) , η c ( 2 S ) → ω ϕ ) < 1.85 × 10 − 7 , respectively. We also update the branching fractions of χ c J → ω ω and χ c J → ω ϕ via the ψ ( 2 S ) → γ χ c J transition. Their branching fractions are determined to be B ( χ c 0 → ω ω ) = ( 10.66 ± 0.11 ± 0.57 ) × 10 − 4 , B ( χ c 1 → ω ω ) = ( 6.43 ± 0.07 ± 0.31 ) × 10 − 4 , B ( χ c 2 → ω ω ) = ( 8.75 ± 0.08 ± 0.42 ) × 10 − 4 , B ( χ c 0 → ω ϕ ) = ( 1.18 ± 0.03 ± 0.07 ) × 10 − 4 , B ( χ c 1 → ω ϕ ) = ( 2.04 ± 0.15 ± 0.11 ) × 10 − 5 , and B ( χ c 2 → ω ϕ ) = ( 9.58 ± 1.07 ± 0.76 ) × 10 − 6 , where the first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2025

Ablikim, M.↗
DOE OSTI2021

Ionization state and dielectric constant in cold rarefied hydrocarbon plasmas of inertial confinement fusion

A combined approach to study cold rarefied matter is introduced that includes a semianalytical method based on the free-energy minimization and ab initio calculations based on the finite-temperature density-functional theory. The approach is used to calculate the ionization state of hydrocarbon (CH) under the shock-release conditions in inertial confinement fusion. Furthermore, the dielectric constant of CH is calculated using the Kubo-Greenwood formulation and contribution from atomic polarizabilities is found to be as important as the free-electron contribution. Using the ionization state and dielectric constant, the electron density profile in the rarefaction wave of the shock-release plasma is obtained.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Variational Approach to Monte Carlo Renormalization Group

We present a Monte Carlo method for computing the renormalized coupling constants and the critical exponents within renormalization theory. The scheme, which derives from a variational principle, overcomes critical slowing down, by means of a bias potential that renders the coarse grained variables uncorrelated. Here, the two-dimensional Ising model is used to illustrate the method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Measurement of C P Violation in B 0 → K S 0 π 0 Decays at Belle II

We report a measurement of the C P -violating parameters C and S in B 0 → K S 0 π 0 decays at Belle II using a sample of 387 × 10 6 B B ¯ events recorded in e + e − collisions at a center-of-mass energy corresponding to the ϒ ( 4 S ) resonance. These parameters are determined by fitting the proper decay-time distribution of a sample of 415 signal events. We obtain C = − 0.0 4 − 0.15 + 0.14 ± 0.05 and S = 0.7 5 − 0.23 + 0.20 ± 0.04 , where the first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2023

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Observation of an Axial-Vector State in the Study of the Decay ψ ( 3686 ) → ϕ η η ′

Using ( 2712.4 ± 14.3 ) × 10 6 ψ ( 3686 ) events collected with the BESIII detector at BEPCII, a partial wave analysis of the decay ψ ( 3686 ) → ϕ η η ′ is performed with the covariant tensor approach. In addition to the established states h 1 ( 1900 ) and ϕ ( 2170 ) , an axial-vector state with a mass near 2.3 GeV / c 2 is observed for the first time. Its mass and width are measured to be 2316 ± 9 stat ± 3 0 syst MeV / c 2 and 89 ± 1 5 stat ± 2 6 syst MeV , respectively. The product branching fractions of B [ ψ ( 3686 ) → X ( 2300 ) η ′ ] B [ X ( 2300 ) → ϕ η ] and B [ ψ ( 3686 ) → X ( 2300 ) η ] B [ X ( 2300 ) → ϕ η ′ ] are determined to be ( 4.8 ± 1.3 stat ± 0.7 syst ) × 10 − 6 and ( 2.2 ± 0.7 stat ± 0.7 syst ) × 10 − 6 , respectively. The branching fraction B [ ψ ( 3686 ) → ϕ η η ′ ] is measured for the first time to be ( 3.14 ± 0.1 7 stat ± 0.2 4 syst ) × 10 − 5 . The first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2025

Ablikim, M.↗
DOE OSTI2025

Bayesian model mixing with multireference energy density functional

Reliably predicting nuclear properties across the entire chart of isotopes is important for applications ranging from nuclear astrophysics to superheavy science to nuclear technology. To this day, however, all the theoretical models that can scale at the level of the chart of isotopes remain semiphenomenological. Because they are fitted locally, their predictive power can vary significantly; different versions of the same theory provide different predictions. Bayesian model mixing takes advantage of such imperfect models to build a local mixture of a set of models to make improved predictions. Earlier attempts to use Bayesian model mixing for mass table calculations relied on models treated at single-reference energy density functional level, which fail to capture some of the correlations caused by configuration mixing or the restoration of broken symmetries. In this study we have applied Bayesian model mixing techniques within a multireference energy density functional (MR-EDF) framework. We considered predictions of two-particle separation energies from particle number projection or angular momentum projection with four different energy density functionals—a total of eight different MR-EDF models. We used a hierarchical Bayesian stacking framework with a Dirichlet prior distribution over weights together with an inverse log-ratio transform to enable positive correlations between different models. We found that Bayesian model mixing provides significantly improved predictions compared to the participating models. Published by the American Physical Society 2025

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Analysis of chaotic dynamic regimes using series of interburst intervals

The problem of reconstruction of dynamic systems in the presence of noise using series of interburst intervals is solved. It is shown that the reconstruction procedure can be applied to strongly nonlinear noisy oscillatory processes. The results make it possible to generalize the method for analysis of dynamic systems with respect to recovery time to a wide variety of neuron oscillators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Measurement of the W-boson mass and width with the ATLAS detector using proton–proton collisions at $\sqrt{s}=7$ TeV

Proton-proton collision data recorded by the ATLAS detector in 2011, at a centre-of-mass energy of 7 TeV, have been used for an improved determination of the W-boson mass and a first measurement of the W-boson width at the LHC. Recent fits to the proton parton distribution functions are incorporated in the measurement procedure and an improved statistical method is used to increase the measurement precision. The measurement of the W-boson mass yields a value of m w = 80,366.5 ± 9.8 (stat.) ± 12.5 (syst.) MeV = 80,366.5 ± 15.9 MeV, and the width is measured as Γ w = 2202 ± 32 (stat.) ± 34 (syst.) MeV = 2202 ± 47 MeV. The first uncertainty components are statistical and the second correspond to the experimental and physics-modelling systematic uncertainties. Both results are consistent with the expectation from fits to electroweak precision data. The present measurement of m w is compatible with and supersedes the previous measurement performed using the same data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Comparison of unfolding methods using RooFitUnfold

In this study we describe RooFitUnfold, an extension of the RooFit statistical software package to treat unfolding problems, and which includes most of the unfolding methods that commonly used in particle physics. The package provides a common interface to these algorithms as well as common uniform methods to evaluate their performance in terms of bias, variance and coverage. In this paper we exploit this common interface of RooFitUnfold to compare the performance of unfolding with the Richardson–Lucy, Iterative Dynamically Stabilized, Tikhonov, Gaussian Process, bin-by-bin and inversion methods on several example problems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Optimization of the deep neural network parameters for generating homogenized fuel assembly data for nodal codes

Homogenized fuel assembly (FA) data is a typical input data for nodal codes. Generating that data, however, could be time-consuming. One of promising ways to mitigate the computational burden of generating macroscopic cross-sections is to use trained artificial neural network (ANN) models for predicting nuclear data. However, there is a challenge to make the model support variable FA geometry. In this work, two most common types of FA were combined in one ANN model. Since there could be multiple ways of converting 2-dimensional FA data into 1-dimensional input vector for ANN, three different approaches of data flattening were evaluated. The input parameters included each fuel pin enrichment, fuel temperature, moderator temperature and boron concentration. The output parameters were 2-group macroscopic cross-sections (XS) and pin power distribution (HFF). A fully connected deep neural network (DNN) model was trained and tested using pre-generated data obtained with lattice physics code STREAM. The results of this study showed no statistically significant difference in the accuracy of XS and HFF generation for all 3 tested input vector orders. This means that fully connected DNN for XS generation demonstrated input sequence invariance. Results of comparing predicted XS data with reference solutions were found sufficiently close considering the reduction of computation time offered by ANN. Mean relative difference (MRD) for all output XS parameters was found below 0.7%, while HFF MRD was found higher compared to XS values, in some cases slightly exceeding 1%, mostly near guide tube locations. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2020

The effect of geographic sampling on evaluation of extreme precipitation in high-resolution climate models

Traditional approaches for comparing global climate models and observational data products typically fail to account for the geographic location of the underlying weather station data. For modern global high-resolution models with a horizontal resolution of tens of kilometers, this is an oversight since there are likely grid cells where the physical output of a climate model is compared with a statistically interpolated quantity instead of actual measurements of the climate system. In this paper, we quantify the impact of geographic sampling on the relative performance of high-resolution climate model representations of precipitation extremes in boreal winter (December–January–February) over the contiguous United States (CONUS), comparing model output from five early submissions to the HighResMIP subproject of the CMIP6 experiment. We find that properly accounting for the geographic sampling of weather stations can significantly change the assessment of model performance. Across the models considered, failing to account for sampling impacts the different metrics (extreme bias, spatial pattern correlation, and spatial variability) in different ways (both increasing and decreasing). We argue that the geographic sampling of weather stations should be accounted for in order to yield a more straightforward and appropriate comparison between models and observational data sets, particularly for high-resolution models with a horizontal resolution of tens of kilometers. While we focus on the CONUS in this paper, our results have important implications for other global land regions where the sampling problem is more severe.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1976

Response of linear dynamic systems with random coefficients

Numerous models of physical systems contain parameters whose values are not known exactly. The physical and mathematical complexities arising in the prediction of the statistical behavior of such systems are discussed. Although the discussions are far from providing a satisfactory solution to such problems, they perhaps, by utilization of simple examples, will create a greater awareness of the statistical effect of random parameters.

Dickerson, J.↗
NASA NTRS1982

Model atmospheres, predicted spectra, and colors

Theoretical models of stellar atmospheres and the process of forming a spectrum are reviewed with particular reference to the spectra of B stars. In the case of classical models the stellar atmosphere is though to consist of plane parallel layers of gas in which radiative and hydrostatic equilibrium exists. No radiative energy is lost or gained in the model atmosphere, but the detailed shape of the spectrum is changed as a result of the interactions with the ionized gas. Predicted line spectra using statistical equilibrium local thermodynamic equilibrium (LTE), and non-LTE physics are compared and the determination of abundances is discussed. The limitations of classical modeling are examined. Models developed to demonstrate what motions in the upper atmosphere will do to the spectrum and to explore the effects of using geometries different from plane parallel layer are reviewed. In particular the problem of radiative transfer is addressed.

Source record↗
NASA NTRS1988

Galactic interstellar abundance surveys with IUE. III - Silicon, manganese, iron, sulfur, and zinc

This paper continues a survey of intestellar densities, abundances, and cloud structure in the Galaxy using the IUE satellite. A statistical data set of 223 O3-B2.5 stars is constructed, including 53 stars in the Galactic halo. It is found that S II lines in B stars, of luminosity classes IV and V, have possible contamination from stellar S II, particular for stars with v sin i less than 200 km/s. The mean logarithmic depletions are -1.00, -1.19. -0.63, and -0.23 (Si, Mn,Fe,S, Zn). Depletions of Si, Mn, and Fe correlate with the mean hydrogen density n-bar along the line of sight, with a turnover for n-bar greater than 1/cm. Sulfur depletions correlate with n-bar along the line of sight. The slight Zn depletion correlation also appears to be statistically insignificant. No correlation of depletion is found with the physical density derived from H2 rotational states in 21 lines of sight. Depletion variations in the disk are consistent with a Galactic abundance gradient or with enhanced mean depletions in the anticenter region.

Van Steenberg, Michael E.↗