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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

A Machine Learning Assisted Development of a Model for the Populations of Convective and Stratiform Clouds

Abstract Traditional parameterizations of the interaction between convection and the environment have relied on an assumption that the slowly varying large‐scale environment is in statistical equilibrium with a large number of small and short‐lived convective clouds. They fail to capture nonequilibrium transitions such as the diurnal cycle and the formation of mesoscale convective systems as well as observed precipitation statistics and extremes. Informed by analysis of radar observations, cloud‐permitting model simulation, theory, and machine learning, this work presents a new stochastic cloud population dynamics model for characterizing the interactions between convective and stratiform clouds, with the goal of informing the representation of these interactions in global climate models. Fifteen wet seasons of precipitating cloud observations by a C‐band radar at Darwin, Australia are fed into a machine learning algorithm to obtain transition functions that close a set of coupled equations relating large‐scale forcing, mass flux, the convective cell size distribution, and the stratiform area. Under realistic large‐scale forcing, the derived transition functions show that, on the one hand, interactions with stratiform clouds act to dampen the variability in the size and number of convective cells and therefore in the convective mass flux. On the other, for a given convective area fraction, a larger number of smaller cells is more favorable for the growth of stratiform area than a smaller number of larger cells. The combination of these two factors gives rise to solutions with a few convective cells embedded in a large stratiform area, reminiscent of mesoscale convective systems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

An algorithm for nonrelativistic quantum-mechanical finite-nuclear-mass variational calculations of nitrogen atom in L = 0, M = 0 states using all-electrons explicitly correlated Gaussian basis functions

An algorithm for quantum-mechanical nonrelativistic variational calculations of L = 0 and M = 0 states of atoms with an arbitrary number of s electrons and with three p electrons have been implemented and tested in the calculations of the ground {sup 4}S state of the nitrogen atom. The spatial part of the wave function is expanded in terms of all-electrons explicitly correlated Gaussian functions with the appropriate pre-exponential Cartesian angular factors for states with the L = 0 and M = 0 symmetry. The algorithm includes formulas for calculating the Hamiltonian and overlap matrix elements, as well as formulas for calculating the analytic energy gradient determined with respect to the Gaussian exponential parameters. The gradient is used in the variational optimization of these parameters. The Hamiltonian used in the approach is obtained by rigorously separating the center-of-mass motion from the laboratory-frame all-particle Hamiltonian, and thus it explicitly depends on the finite mass of the nucleus. With that, the mass effect on the total ground-state energy is determined.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Biomarker Mapping on Skin Tape Strips Using MALDI Mass Spectrometry Imaging

Keratinocyte organization and biochemistry are important in forming the skin’s protective barrier. Intrinsic and extrinsic factors can affect skin barrier function at the cellular and molecular levels. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometric imaging, a technique which combines both molecular aspects and histological details, has proven to be a valuable method in various disciplines including pharmacology, dermatology and cosmetology. It typically requires ex vivo samples, prepared following frozen tissue sectioning. This paper demonstrates the feasibility of performing MALDI analysis on tape strips collected non-invasively on skin. The aim is to obtain molecular imaging of corneocytes on tapes towards novel biological insights. Tapes were collected from two skin sites (volar forearm and cheek) of human volunteers. Ten molecules relating to skin barrier function were detected with a single mode of acquisition at high spatial resolution with a 7 T MALDI-Fourier transform ion cyclotron resonance (FTICR) instrument. The method sensitivity was adequate to create molecular maps which could be overlaid on transmission microscopy images of the same area of the tape. Analysis of the molecular distributions from tapes at the two skin sites was consistent with the known skin properties of the two sites, confirming the validity of the observations. Hierarchical clustering analysis was used to differentiate corneocyte populations based on their molecular profiles. Furthermore, morphological analysis provided a new way of considering statistical populations of corneocytes on the same tape, rather than measuring a single averaged value, providing additional useful information relating to their structure-function relationship. .

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Dielectron Azimuthal Anisotropy at mid-rapidity in Au+Au collisions at root s=200GeV

We report on the first measurement of the azimuthal anisotropy (v₂) of dielectrons (e⁺e⁻ pairs) at mid-rapidity from √( s NN)=200 GeV Au + Au collisions with the STAR detector at the Relativistic Heavy Ion Collider (RHIC), presented as a function of transverse momentum (p T ) for different invariant-mass regions. In the mass region Mee<1.1 GeV/c² the dielectron v₂ measurements are found to be consistent with expectations from π⁰,η,ω, and Φ decay contributions. In the mass region 1.1 ee <2.9GeV/c², the measured dielectron v₂ is consistent, within experimental uncertainties, with that from the cc¯ contributions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Peculiar velocities in redshift space: formalism, N-body simulations and perturbation theory

Direct measurements of peculiar velocities of galaxies and clusters of galaxies can in principle provide explicit information on the three dimensional mass distribution, but this information is modulated by the fact that velocity field is sampled at galaxy positions, and is thus probing galaxy momentum. We derive expressions for the cross power spectrum between the density and momentum field and the auto spectrum of the momentum field in redshift space, by extending the distribution function method to these statistics. The resulting momentum cross and auto power spectra in redshift space are expressed as infinite sums over velocity moment correlators in real space, as is the case for the density power spectrum in redshift space. We compute each correlator using Eulerian perturbation theory (PT) and halo biasing model and compare the resulting redshift-space velocity statistics to those measured from N-body simulations for both dark matter and halos. We find that in redshift space linear theory predictions for the density-momentum cross power spectrum as well as for the momentum auto spectrum fail to predict the N-body results at very large scales. On the other hand, our nonlinear PT prediction for these velocity statistics, together with real-space power spectrum for dark matter from simulations, improves the accuracy for both dark matter and halos. We also present the same analysis in configuration space, computing the redshift-space pairwise mean infall velocities and velocity correlation function and compare to nonlinear PT.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A NEW MODEL FOR DARK MATTER HALOS HOSTING QUASARS

A new model for quasar-hosting dark matter halos, meeting two physical conditions, is put forth. First, significant interactions are taken into consideration to trigger quasar activities. Second, satellites in very massive halos at low redshift are removed from consideration due to their deficiency in cold gas. We analyze the Millennium Simulation to find halos that meet these two conditions and simultaneously match two-point auto-correlation functions of quasars and cross-correlation functions between quasars and galaxies at z = 0.5-3.2. The masses of the quasar hosts found decrease with decreasing redshift, with the mass thresholds being [(2-5) × 10{sup 12}, (2-5) × 10{sup 11}, (1-3) × 10{sup 11}] M {sub ☉} for median luminosities of ∼[10{sup 46}, 10{sup 46}, 10{sup 45}] erg s{sup –1} at z = (3.2, 1.4, 0.53), respectively, an order of magnitude lower than those inferred based on halo occupation distribution modeling. In this model, quasar hosts are primarily massive central halos at z ≥ 2-3 but increasingly dominated by lower mass satellite halos experiencing major interactions toward lower redshift. However, below z = 1, satellite halos in groups more massive than ∼2 × 10{sup 13} M {sub ☉} do not host quasars. Whether for central or satellite halos, imposing the condition of significant interactions substantially boosts the clustering strength compared to the total population with the same mass cut. The inferred lifetimes of quasars at z = 0.5-3.2 of 3-30 Myr are in agreement with observations. Quasars at z ∼ 2 would be hosted by halos of mass ∼5 × 10{sup 11} M {sub ☉} in this model, compared to ∼3 × 10{sup 12} M {sub ☉} previously thought, which would help reconcile with the observed, otherwise puzzling high covering fractions for Lyman limit systems around quasars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Correcting systematic bias and instrument measurement drift with mzRefinery

Systematic bias in mass measurement adversely affects data quality and negates the advantages of high precision instruments. We introduce the mzRefinery tool into the ProteoWizard package for calibration of mass spectrometry data files. Using confident peptide spectrum matches, three different calibration methods are explored and the optimal transform function is chosen. After calibration, systematic bias is removed and the mass measurement errors are centered at zero ppm. Because it is part of the ProteoWizard package, mzRefinery can read and write a wide variety of file formats. In conclusion, we report on availability; the mzRefinery tool is part of msConvert, available with the ProteoWizard open source package at http://proteowizard.sourceforge.net/

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

Strain and electric field induced electronic properties of two-dimensional hybrid bilayers of transition-metal dichalcogenides

Tunability of the electronic properties of two-dimensional bilayer hetero structures of transition-metal dichalcogenides (i.e., MX{sub 2}-M′X′{sub 2} with (M, M′ = Mo, W; X, X′ = S, Se) is investigated. Application of both strain and electric field is found to modify the band gap and carrier effective mass in the hybrid bilayers considered. The calculated results based on density functional theory suggest that the tensile strain considerably changes the band gap of semiconducting bilayers; it makes the band gap to be indirect, and later initiates the semiconductor-to-metal transition. Application of the external electric fields, on the other hand, shows asymmetric variation in the band gap leading to the closure of the gap at about 0.5–1.0 V/Å. Tuning of the band gap and carrier effective mass in such a controlled manner makes the hybrid bilayers of transition metal dichalcogenides to be promising candidates for application in electronic devices at nanoscale.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

THE FORMATION OF THE PRIMITIVE STAR SDSS J102915+172927: EFFECT OF THE DUST MASS AND THE GRAIN-SIZE DISTRIBUTION

Understanding the formation of the extremely metal-poor star SDSS J102915+172927 is of fundamental importance to improve our knowledge on the transition between the first and second generation of stars in the universe. In this paper, we perform three-dimensional cosmological hydrodynamical simulations of dust-enriched halos during the early stages of the collapse process including a detailed treatment of the dust physics. We employ the astrochemistry package krome coupled with the hydrodynamical code enzo assuming grain-size distributions produced by the explosion of core-collapse supernovae (SNe) of 20 and 35 M {sub ⊙} primordial stars, which are suitable to reproduce the chemical pattern of the SDSS J102915+172927 star. We find that the dust mass yield produced from Population III SNe explosions is the most important factor that drives the thermal evolution and the dynamical properties of the halos. Hence, for the specific distributions relevant in this context, the composition, the dust optical properties, and the size range have only minor effects on the results due to similar cooling functions. We also show that the critical dust mass to enable fragmentation provided by semi-analytical models should be revised, as we obtain values one order of magnitude larger. This determines the transition from disk fragmentation to a more filamentary fragmentation mode, and suggests that likely more than one single SN event or efficient dust growth should be invoked to get such high dust content.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

No X-rays from the very nearby type Ia SN 2014J: Constraints on its environment

Deep X-ray observations of the post-explosion environment around the very nearby Type Ia SN 2014J (d{sub L} = 3.5 Mpc) reveal no X-ray emission down to a luminosity L{sub x} < 7 × 10{sup 36} erg s{sup –1} (0.3-10 keV) at δt ∼ 20 days after the explosion. We interpret this limit in the context of inverse Compton emission from upscattered optical photons by the supernova shock and constrain the pre-explosion mass-loss rate of the stellar progenitor system to be M-dot <10{sup −9} M{sub ⊙} yr{sup −1} (for wind velocity v{sub w} = 100 km s{sup –1}). Alternatively, the SN shock might be expanding into a uniform medium with density n{sub CSM} < 3 cm{sup –3}. These results rule out single-degenerate (SD) systems with steady mass loss until the terminal explosion and constrain the fraction of transferred material lost at the outer Lagrangian point to be ≤1%. The allowed progenitors are (1) white dwarf-white dwarf progenitors, (2) SD systems with unstable hydrogen burning experiencing recurrent nova eruptions with recurrence time t < 300 yr, and (3) stars where the mass loss ceases before the explosion.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Chemical Cartography. I. A Carbonicity Map of the Galactic Halo

We present the first map of carbonicity, [C/Fe], for the halo system of the Milky Way, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. This map, which explores distances up to 15 kpc from the Sun, reveals clear evidence for the dual nature of the Galactic halo, based on the spatial distribution of stellar carbonicity. The metallicity distribution functions of stars in the inner- and outer-halo regions of the carbonicity map reproduce those previously argued to arise from contributions of the inner- and outer-halo populations, with peaks at [Fe/H] = −1.5 and −2.2, respectively. From consideration of the absolute carbon abundances for our sample, A (C), we also confirm that the carbon-enhanced metal-poor (CEMP) stars in the outer-halo region exhibit a higher frequency of CEMP-no stars (those with no overabundances of heavy neutron-capture elements) than of CEMP- s stars (those with strong overabundances of elements associated with the s -process), whereas the stars in the inner-halo region exhibit a higher frequency of CEMP- s stars. We argue that the contrast in the behavior of the CEMP-no and CEMP- s fractions in these regions arises from differences in the mass distributions of the mini-halos from which the stars of the inner- and outer-halo populations formed, which gives rise in turn to the observed dichotomy of the Galactic halo.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Soil Organic Matter Dynamics in the Critical Zone

Soil is the thin, vital layer of Earth’s surface that forms the foundation of the Critical Zone and sustains life. This chapter explores the intricate dynamics of soil organic matter within the critical zone, focusing on three key thematic areas: deep soil organic matter, wildfire organic matter interactions, and organic matter erosion. Soil organic matter, although a small fraction of soil mass, plays a crucial role in soil function and ecosystem stability. The complexity of soil organic matter arises from its diverse chemical composition and interactions with minerals, which influence its persistence in the environment. This chapter begins by examining deep soil organic matter, which constitutes a significant portion of global carbon storage. We discuss how deep soil organic matter, typically isolated from surface processes, may become vulnerable to decomposition and carbon release due to disturbances. Next, we explore the impacts of fire on soil organic matter, particularly the formation and stability of pyrolyzed organic matter. The decomposition of pyrolyzer organic matter is influenced by its chemical composition and the surrounding environmental conditions, with implications for carbon cycling and soil fertility in post-fire ecosystems. Finally, the chapter addresses the role of erosion in soil organic matter dynamics. Erosion, accelerated by human activities, redistributes soil organic matter across landscapes, affecting its turnover and the broader biogeochemical cycles. We consider how micro-topographic features and erosion processes interact to influence soil OM stability and carbon sequestration. By synthesizing recent advances in these areas, this chapter provides a comprehensive overview of the complex and dynamic nature of soil organic matter in the critical zone, highlighting its importance in understanding the critical zone in the face of environmental change.

Moreland, Kimber↗
DOE OSTI2025

Search for vector-like leptons coupling to first- and second-generation Standard Model leptons in pp collisions at s = 13 TeV with the ATLAS detector

A search for pair production of vector-like leptons coupling to first- and second-generation Standard Model leptons is presented. The search is based on a dataset of proton-proton collisions at s$$ \sqrt{s} $$ = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1. Events are categorised depending on the flavour and multiplicity of leptons (electrons or muons), as well as on the scores of a deep neural network targeting particular signal topologies according to the decay modes of the vector-like leptons. In each of the signal regions, the scalar sum of the transverse momentum of the leptons and the missing transverse momentum is analysed. The main background processes are estimated using dedicated control regions in a simultaneous fit with the signal regions to data. No significant excess above the Standard Model background expectation is observed and limits are set at 95% confidence level on the production cross-sections of vector-like electrons and muons as a function of the vector-like lepton mass, separately for SU(2) doublet and singlet scenarios. The resulting mass lower limits are 1220 GeV (1270 GeV) and 320 GeV (400 GeV) for vector-like electrons (muons) in the doublet and singlet scenarios, respectively.

Aad, G↗
DOE OSTI2023

Growth of cosmic structure

We review one of the most fruitful areas in cosmology today that bridge theory and data - the temporal growth of large-scale structure. We go over the growth's physical foundations, and derive its behavior in simple cosmological models. While doing so, we explain how measurements of growth can be used to understand theory. We then review how some of the most mature cosmological probes-galaxy clustering, gravitational lensing, the abundance of clusters of galaxies, cosmic velocities, and cosmic microwave background-can be used to probe the growth of structure. We report the current constraints on growth, which are summarized as measurements of the parameter combination fσ 8 as a function of redshift, or else as the mass fluctuation amplitude parameter S 8 . Here, we finally illustrate several statistical approaches, ranging from the "growth index" parameterization to more general comparisons of growth and geometry, that can sharply test the standard cosmological model and indicate the presence of modifications to general relativity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Observational constraints on the tilted flat-XCDM and the untilted nonflat XCDM dynamical dark energy inflation parameterizations

In this work, we constrain tilted spatially-flat and untilted nonflat XCDM dynamical dark energy inflation parameterizations using Planck 2015 cosmic microwave background (CMB) anisotropy data and recent baryonic acoustic oscillations distance measurements, Type Ia supernovae data, Hubble parameter observations, and growth rate measurements. Inclusion of the four non-CMB data sets results in a significant strengthening of the evidence for nonflatness in the nonflat XCDM model from 1.1σ for the CMB data alone to 3.4σ for the full data combination. In this untilted nonflat XCDM case the data favor a spatially-closed model in which spatial curvature contributes a little less than a percent of the current cosmological energy budget; they also mildly favor dynamical dark energy over a cosmological constant at 1.2σ. These data are also better fit by the flat-XCDM parameterization than by the standard ΛCDM model, but only at 0.3σ significance. Current data is unable to rule out dark energy dynamics. The nonflat XCDM parameterization is compatible with the Dark Energy Survey limits on the present value of the rms mass fluctuations amplitude (σ 8 ) as a function of the present value of the nonrelativistic matter density parameter (Ω m ). Furthermore, it does not provide as good a fit to the higher multipole CMB temperature anisotropy data as does the standard tilted flat-ΛCDM model. A number of measured cosmological parameter values differ significantly when determined using the tilted flat-XCDM and the nonflat XCDM parameterizations, including the baryonic matter density parameter and the reionization optical depth.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Integrated data-driven and experimental approaches to accelerate lead optimization targeting SARS-CoV- 2 main protease

Identification of potential therapeutic candidates can be expedited by integrating computational modeling with domain aware machine learning (ML) approaches followed by experimental validation. Generative deep learning models have been recently developed that can generate thousands of new candidates, but their physiochemical properties are typically not optimized. Using our deep learning models and a scaffold as a starting point, we generated tens of thousands of compounds for SARS-CoV-2 M pro that preserve the core scaffold. Here we utilized and implemented several computational tools such as structural alert and toxicity analysis, high throughput virtual screening, ML-based 3D quantitative structure–activity relationships, multi-parameter optimization, and graph neural networks on libraries of generated candidates to predict biological activity and binding affinity a priori. From these collective computational results, eight promising candidates were identified and tested experimentally using Native Mass Spectrometry (MS) and FRET-based functional assays. Two compounds, with quinazoline-2-thiol and acetylpiperidine core moiety showed IC 50 values in the low micromolar range: 2.95±0.0017 µM and 3.41±0.0015 µM, respectively. The molecular dynamics simulations further highlight that binding of these compounds results in allosteric modulations in the chain B and the interface domains of the M pro . The key fragments from these top hits can be used as input for closed loop lead optimization in the integrated pipeline.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

The Effects of Silicon and Niobium Concentration on the Solidification Behavior and Microstructure of Cast Monel Alloys

Cast Monel alloys are used in applications requiring a combination of good mechanical properties and excellent resistance to corrosion. Despite prevalent industrial use, relatively few studies have been conducted to investigate the relationships between composition, solidification behavior, and microstructure. Given that these alloys are used in the cast and welded conditions, these factors have a significant influence over the material properties. Here, in this work, microstructural characterization, electron probe microanalysis, X-ray diffraction, and differential scanning calorimetry were used to study how changes in Si and Nb concentrations affected the solidification path and microstructure of Monel alloys. It was found that increasing Nb concentration stabilized higher amounts of MC carbides and suppressed graphite formation during solidification. It was also found that the high nominal concentration and segregation of Si to the liquid led to the formation of Ni 31 Si 12 and other silicides via terminal eutectic reactions at the end of solidification. A pseudo-binary solidification diagram was constructed using experimental data and was applied to predict the mass fraction of solidified eutectic as a function of composition. The modeled microstructures were found to be in good agreement with experimentally measured phase fractions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Modeling the dynamic response of rock masses with multiple compliant fluid saturated joint sets - Part II: Continuum modeling

Part I of this two-part paper describes enhancements of a mesoscale model to include: many non-persistent fluid saturated joints with finite area, normal compliance with hysteresis and the weakening effects of angular deviation in the joint sets and of fluid pressure in the joints. The objective of this Part II is to use the results of the mesoscale model as simulated data to inspire functional forms in a continuum model for rock masses with multiple compliant fluid saturated joint sets which include these enhancements. Also, an algorithm is proposed for reducing the number of joint sets being modeled. Examples are presented here which show that the continuum model can predict similar anisotropic response to that observed in mesoscale simulations. In contrast with the mesoscale model, the continuum model can be used for large scale simulations of real applications, smoothly transitioning from coupled inelastic thermomechanical response near an explosive source to orthotropic elastic response far from the source.

58 GEOSCIENCES↗