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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 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Pion Structure Function from Leading Neutron Electroproduction and SU(2) Flavor Asymmetry

We examine the efficacy of pion exchange models to simultaneously describe leading neutron electroproduction at HERA and the dbar-ubar flavor asymmetry in the proton. A detailed chi^2 analysis of the ZEUS and H1 cross sections, when combined with constraints on the pion flux from Drell-Yan data, allows regions of applicability of one-pion exchange to be delineated. The analysis disfavors several models of the pion flux used in the literature, and yields an improved extraction of the pion structure function and its uncertainties at small parton momentum fractions in the pion. We also provide estimates for leading proton structure functions in upcoming tagged deep-inelastic scattering experiments at Jefferson Lab on the deuteron with forward protons.

Melnitchouk, Wolodymyr↗
DOE OSTI2025

A compendium of human gene functions derived from evolutionary modelling

A comprehensive, computable representation of the functional repertoire of all macromolecules encoded within the human genome is a foundational resource for biology and biomedical research. The Gene Ontology Consortium has been working towards this goal by generating a structured body of information about gene functions, which now includes experimental findings reported in more than 175,000 publications for human genes and genes in experimentally tractable model organisms 1,2 . Here, we describe the results of a large, international effort to integrate all of these findings to create a representation of human gene functions that is as complete and accurate as possible. Specifically, we apply an expert-curated, explicit evolutionary modelling approach to all human protein-coding genes. This approach integrates available experimental information across families of related genes into models that reconstruct the gain and loss of functional characteristics over evolutionary time. The models and the resulting set of 68,667 integrated gene functions cover approximately 82% of human protein-coding genes. The functional repertoire reveals a marked preponderance of molecular regulatory functions, and the models provide insights into the evolutionary origins of human gene functions. We show that our set of descriptions of functions can improve the widely used genomic technique of Gene Ontology enrichment analysis. The experimental evidence for each functional characteristic is recorded, thereby enabling the scientific community to help review and improve the resource, which we have made publicly available.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

A Rate Theory Model of Radiation-Induced Swelling in an Austenitic Stainless Steel

Many rate theory models of cavity (void) swelling have been published over the past 50 years, all having the same, or similar, structures. A rigorous validation of the models has not been possible because of the dearth of information concerning the microstructures that correspond with the swelling data. Whereas the lack of microstructure information is still an issue for historical swelling data, in the past 10–20 years data have been published on the evolution of the microstructure (point defect yields from collision cascades, cavity number densities, and dislocation densities/yield strengths) allowing certain gaps in information to be filled when considering historic swelling data. With reasonable estimates of key microstructure parameters, a standard rate theory model can be applied, and the model parameter space explored, in connection with historical swelling data. By using published data on: (i) yield strength as a function of dose and temperature (to establish an empirical expression for dislocation density evolution); (ii) cavity number densities as a function of temperature; and (iii) freely migrating defect (FMD) production as a function of primary knock-on atom (PKA) spectrum, the necessary parameter and microstructure inputs that were previously unknown can be used in model development. This paper describes a rate-theory model for void swelling of 316 stainless steel irradiated in the EBR-2 reactor as a function of irradiation temperature and neutron dose.

36 MATERIALS SCIENCE↗
DOE OSTI2026

MixPI: Mixed-time slicing path integral software for quantized molecular dynamics simulations

We introduce the MixPI software to implement path integral molecular dynamics (PIMD) simulations for the study of condensed phase systems where nuclear quantum effects (NQEs) are important. In contrast to existing PIMD simulation software, MixPI enables the implementation of mixed quantum–classical path integral simulations where only a subset of system degrees of freedom (dofs) are treated quantum mechanically in an extended phase space while the remaining dofs are described classically. We expect this software to be particularly useful for simulations of electron and proton transfer in condensed phase systems, as well as for the study of biological and material systems where only a handful of dofs contribute significantly to the observed NQEs. We demonstrate the use of MixPI in two different systems. The first is a simple water model where we implement a set of mixed quantum–classical simulations to compute average energy and radial distribution functions. We use these simulations to benchmark the effectiveness of MixPI and to demonstrate how it enables systematic investigation into the origin of observed NQEs. We then compute radial distribution functions for a system where MixPI is essential: a solvated metal (M 2+ ) cation described using an explicit quantized electron localized on an M 3+ ion in water.

chemical physics↗
DOE OSTI2016

Describing the Diverse Geometries of Gold from Nanoclusters to Bulk—A First-Principles-Based Hybrid Bond-Order Potential

Molecular dynamics simulations using empirical force fields (EFFs) are crucial for gaining fundamental insights into atomic structure and long time scale dynamics of Au nanoclusters with far-reaching applications in energy and devices. This approach is thwarted by the failure of currently available EFFs in describing the size-dependent dimensionality and diverse geometries exhibited by Au clusters (e.g., planar structures, hollow cages, tubes, pyramids, space-filled structures). Here, we mitigate this issue by introducing a new hybrid bond-order potential (HyBOP), which accounts for (a) short-range interactions via Tersoff-type BOP terms that accurately treat bond directionality and (b) long-range dispersion effects by a scaled Lennard–Jones term whose contribution depends on the local atomic density. We optimized the independent parameters for our HyBOP using a global optimization scheme driven by genetic algorithms. Moreover, to ensure good transferability of these parameters across different length scales, we used an extensive training data set that encompasses structural and energetic properties of 1000 13-atom Au clusters, surface energies, as well as bulk polymorphs, obtained from density functional theory (DFT) calculations. Our newly developed HyBOP has been found to accurately describe (a) global minimum energy configurations at different cluster sizes as well as order of stability of various cluster configurations at any size, (b) critical size of transition from planar to globular clusters, (c) evolution of structural motifs with cluster size, and (c) thermodynamics, structure, elastic properties, and energetic ordering of bulk condensed phases as well as surfaces, in excellent agreement with DFT calculations and spectroscopic experiments. This makes our newly developed HyBOP a valuable, computationally robust but inexpensive tool for investigating a wide range of materials phenomena occurring in Au at the atomistic level.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental Investigations to Enhance the Tribological Performance of Engine Oil by Using Nano-Boric Acid and Functionalized Multiwalled Carbon Nanotubes: A Comparative Study to Assess Wear in Bronze Alloy

In various mechanical systems, lubricants are generally used to reduce friction and wear; thus, the total energy loss in the mechanical systems can be minimized by the proper enhancement of lubrication properties. In general, friction modifiers and antiwear additives are used to improve the tribological properties of the lubricant. However, the use of these additives has to be phased out due to their fast chemical degradation in their applications and other environmental issues. In recent years, the use of nanoparticles as a potential lubricant additive has received considerable attention because of its excellent mechanical and tribological characteristics. The present work describes the tribological behavior of nano-boric acid, multiwalled carbon nanotubes (MWCNTs), and functionalized multiwalled carbon nanotubes (FMWCNTs) modified with carboxylic acid. These nanoparticles were used to enhance the tribological properties of engine oil (SAE20W40) used to lubricate bronze alloy samples. The performance of these nano-coolants was assessed on a linear reciprocating ball-on-flat tribometer. Results highlight the friction and wear behavior of the nano-boric acid, MWCNTs, and FMWCNTs under three varying parameters such as the effect of nanoparticles concentration, load-carrying capacity, and sliding speed. The addition of nano-boric acid, MWCNTs, and FMWCNTs has significantly improved the tribological properties of the base lubricant. The addition of 0.5 wt.% of nano-boric acid, MWCNTs, and FMWCNTs to the base lubricant has decreased the coefficient of friction by 19.76, 30.55, and 35.65%, respectively, and a significant reduction in wear volume by 55.17, 71.42, and 88.97% was obtained in comparison with base lubricant.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Properties, Physiological Functions and Involvement of Basidiomycetous Alcohol Oxidase in Wood Degradation

Extensive research efforts have been devoted to describing yeast alcohol oxidase (AO) and its promoter region, which is vastly applied in studies of heterologous gene expression. However, little is known about basidiomycetous AO and its physiological role in wood degradation. This review describes several alcohol oxidases from both white and brown rot fungi, highlighting their physicochemical and kinetic properties. Moreover, the review presents a detailed analysis of available AO-encoding gene promoter regions in basidiomycetous fungi with a discussion of the manipulations of culture conditions in relation to the modification of alcohol oxidase gene expression and changes in enzyme production. The analysis of reactions catalyzed by lignin-modifying enzymes (LME) and certain lignin auxiliary enzymes (LDA) elucidated the possible involvement of alcohol oxidase in the degradation of derivatives of this polymer. Combined data on lignin degradation pathways suggest that basidiomycetous AO is important in secondary reactions during lignin decomposition by wood degrading fungi. With numerous alcoholic substrates, the enzyme is probably engaged in a variety of catalytic reactions leading to the detoxification of compounds produced in lignin degradation processes and their utilization as a carbon source by fungal mycelium.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Hybrid particle-in-cell simulations of laser-driven plasma interpenetration, heating, and entrainment

Kinetic-ion, quasineutral, fluid-electron particle-in-cell simulations of interpenetrating carbon–carbon plasma flows in 2D RZ cylindrical geometry are presented. The simulations are initialized with solid density targets that are subsequently irradiated by 10 14 W/cm 2 intensity lasers using a raytracing package. The ablation, interpenetration, heating, slowing, entrainment, and stagnation of the plasma flows evolve self-consistently within the code. The particle density, velocity phase space, and fits to the velocity distribution functions are used, along with analytical collisional stopping rates, to interpret the dynamics of the flow evolution. Comparisons to multifluid simulations are described and used to highlight ion-kinetic effects in the setup. Synthetic Thomson scattering diagnostic signals are generated using detailed knowledge of the plasma distribution functions. The large scale of the system, 1 × 1 mm for 2 ns, and the detailed dynamics extracted demonstrate that such hybrid codes are powerful tools for the design and evaluation of laboratory-scale high-energy-density plasma physics experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

De novo design of buttressed loops for sculpting protein functions

In natural proteins, structured loops have central roles in molecular recognition, signal transduction and enzyme catalysis. However, because of the intrinsic flexibility and irregularity of loop regions, organizing multiple structured loops at protein functional sites has been very difficult to achieve by de novo protein design. Here we describe a solution to this problem that designs tandem repeat proteins with structured loops (9–14 residues) buttressed by extensive hydrogen bonding interactions. Experimental characterization shows that the designs are monodisperse, highly soluble, folded and thermally stable. Crystal structures are in close agreement with the design models, with the loops structured and buttressed as designed. We demonstrate the functionality afforded by loop buttressing by designing and characterizing binders for extended peptides in which the loops form one side of an extended binding pocket. The ability to design multiple structured loops should contribute generally to efforts to design new protein functions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Hardness, elastic modulus, and wear resistance of hafnium oxide-based films grown by atomic layer deposition

The investigation of mechanical properties of atomic layer deposition HfO{sub 2} films is important for implementing these layers in microdevices. The mechanical properties of films change as a function of composition and structure, which accordingly vary with deposition temperature and post-annealing. This work describes elastic modulus, hardness, and wear resistance of as-grown and annealed HfO{sub 2}. From nanoindentation measurements, the elastic modulus and hardness remained relatively stable in the range of 163–165 GPa and 8.3–9.7 GPa as a function of deposition temperature. The annealing of HfO{sub 2} caused significant increase in hardness up to 14.4 GPa due to film crystallization and densification. The structural change also caused increase in the elastic modulus up to 197 GPa. Wear resistance did not change as a function of deposition temperature, but improved upon annealing.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Black hole formation in a contracting universe

We study the evolution of cosmological perturbations in a contracting universe. We aim to determine under which conditions density perturbations grow to form large inhomogeneities and collapse into black holes. Our method consists in solving the cosmological perturbation equations in complete generality for a hydrodynamical fluid. We then describe the evolution of the fluctuations over the different length scales of interest and as a function of the equation of state for the fluid, and we explore two different types of initial conditions: quantum vacuum and thermal fluctuations. We also derive a general requirement for black hole collapse on sub-Hubble scales, and we use the Press-Schechter formalism to describe the black hole formation probability. For a fluid with a small sound speed (e.g., dust), we find that both quantum and thermal initial fluctuations grow in a contracting universe, and the largest inhomogeneities that first collapse into black holes are of Hubble size and the collapse occurs well before reaching the Planck scale. For a radiation-dominated fluid, we find that no black hole can form before reaching the Planck scale. In the context of matter bounce cosmology, it thus appears that only models in which a radiation-dominated era begins early in the cosmological evolution are robust against the formation of black holes. Yet, the formation of black holes might be an interesting feature for other models. We comment on a number of possible alternative early universe scenarios that could take advantage of this feature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Gauge theory for the cuprates near optimal doping

We describe the phase diagram of a 2+1-dimensional SU(2) gauge theory of fluctuating incommensurate spin density waves for the hole-doped cuprates. Our primary assumption is that all low-energy fermionic excitations are gauge neutral and electron-like, while the spin density wave order is fractionalized into Higgs fields transforming as adjoints of the gauge SU(2). The confining phase of the gauge theory is a conventional Fermi liquid with a large Fermi surface (and its associated d-wave superconductor). There is a quantum phase transition to a Higgs phase describing the “pseudogap” at lower doping. Depending on the quartic terms in the Higgs potential, the Higgs phase exhibits one or more of charge density wave, Ising-nematic, time-reversal odd scalar spin chirality, and Z 2 topological orders. It is notable that the emergent broken symmetries in our theory of fluctuating spin density waves coincide with those observed in diverse experiments. For the electron-doped cuprates, the spin density wave fluctuations are at wave vector (π,π), and then the corresponding SU(2) gauge theory only has a crossover between the confining and Higgs regimes, with an exponentially large confinement scale deep in the Higgs regime. Here, on the Higgs side, for both the electron- and hole-doped cases, and at scales shorter than the confinement scale (which can be infinite when Z 2 topological order is present), the electron spectral function has a “fractionalized Fermi liquid” form with small Fermi surfaces. We also describe the deconfined quantum criticality of the Higgs transition in the limit of a large number of Higgs flavors, and perturbatively discuss its coupling to fermionic excitations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Wormhole calculus, replicas, and entropies

We investigate contributions of spacetime wormholes, describing baby universe emission and absorption, to calculations of entropies and correlation functions, for example those based on the replica method. We find that the rules of the “wormhole calculus”, developed in the 1980s, together with standard quantum mechanical prescriptions for computing entropies and correlators, imply definite rules for limited patterns of connection between replica factors in simple calculations. These results stand in contrast with assumptions that all topologies connecting replicas should be summed over, and call into question the explanation for the latter. In a “free” approximation baby universes introduce probability distributions for coupling constants, and we review and extend arguments that successive experiments in a “parent” universe increasingly precisely fix such couplings, resulting in ultimately pure evolution. Once this has happened, the nontrivial question remains of how topology-changing effects can modify the standard description of black hole information loss.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Study of Critical Current and n-Values of 2G HTS Tapes: Their Magnetic Field-Angular Dependence

Since many applications of YBCO tapes operate in external magnetic fields, it is necessary to investigate the magneto-angular dependence of critical current and n-values in coated conductors. In this paper, five commercial YBCO tapes with different microstructures produced by three different manufacturers are chosen. The selected samples have a width of 2.0, 4.0, 4.8, 6.0 or 12 mm, with copper, brass or stainless steel laminations. The critical current density dependence J{sub c}(B, θ) and n-values characteristics n(B, θ) of the tapes are comprehensively measured under various magnetic fields and orientations. Afterwards, the obtained experimental data sets are successfully fitted using a novel multi-objective model which considers the material anisotropy. By using this approach, a fitting function I{sub c}(B, θ) can always be obtained to accurately describe the experimental data, regardless of the fabrication and width differences of the superconducting tapes. Moreover, our experiment shows that when subject to different external magnetic fields, the angular dependence of n-values characteristics is directly correlated with the corresponding critical current profiles. Our results are helpful to predict the critical current of electromagnetically interacting 2G HTS wires, thereby improving the design and performance of the devices made from YBCO tapes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Hot Deformation and Processing Maps of B{sub 4}C/6061Al Nanocomposites Fabricated by Spark Plasma Sintering

We developed 3 vol.% B{sub 4}C/6061Al nanocomposites by spark plasma sintering. We then characterized their flow and hot deformation behaviors using isothermal compression tests at deformation temperatures of 673-823 K and strain rates of 0.001-1 s{sup −1}. Results indicated that their steady flow characteristic can be described by the Zener–Hollomon parameter (Z) as a hyperbolic-sine function of flow stress. Based on pinning effect from B{sub 4}C nanoparticles, the estimated activation energy was calculated to be 274.80 kJ/mol. At the unstable deformation condition (723 K/1 s{sup −1}) with high Z, flow localization appeared; the main softening mechanisms involved are dynamic recovery and dynamic recrystallization (DRX). At the stable deformation condition (823 K/0.001 s{sup −1}) with low Z, adequate DRX occurred. Based on the processing map and microstructure evolution, the optimum hot working conditions for B{sub 4}C/6061Al nanocomposites were determined to be a deformation temperature of 773-823 K and a strain rate of 0.001-0.003 s{sup −1}. These working conditions were verified by a hot extrusion test.

36 MATERIALS SCIENCE↗
DOE OSTI2022

ARPIST: Provably accurate and stable numerical integration over spherical triangles

Numerical integration on spherical triangles, including the computation of their areas, is a core computation in geomathematics. The commonly used techniques sometimes suffer from instabilities and significant loss of accuracy. We describe a new algorithm, called ARPIST, for accurate and stable integration of functions on spherical triangles. ARPIST is based on an easy-to-implement transformation to the spherical triangle from its corresponding linear triangle via radial projection to achieve high accuracy and efficiency. More importantly, ARPIST overcomes potential instabilities in computing the Jacobian of the transformation, even for poorly shaped triangles that may occur at poles in regular longitude-latitude meshes, by avoiding potential catastrophic rounding errors. We compare our proposed technique with L’Huilier’s Theorem for computing the area of spherical triangles, and also compare it with the recently developed LSQST method (Beckmann et al., 2014) and a radial-basis-function-based technique (Reeger and Fornberg, 2016) for integration of smooth functions on spherical triangulations. In conclusion, our results show that ARPIST enables better or comparable accuracy over previous methods while being easier to implement, significantly faster, and more tolerant of poor element shapes.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Estimating the mechanical properties of hydrating blended cementitious materials: An investigation based on micromechanics

The hydration model of Parrot & Killoh (1984) has been extended to blended cements and coupled to a micromechanical scheme similar to that of Pichler & Hellmich (2011) to estimate the Young modulus and the compressive strength of cementitious materials as a function of time. A finite aspect ratio of 7 is introduced to describe the shape of the hydrates and improve the estimate of the early age strength by the micromechanical scheme. Furthermore, accounting for the stress fluctuations in the cement paste partly explains the fact that the compressive strength of a concrete can be lower than that of its cement paste. Finally, the estimated physical properties are compared to numerous experimental measurements from the literature and new experimental measurements on blended cement pastes featuring significant weight fractions of limestone filler, fly ash or silica fume. It is shown that the present model slightly overestimates the dilution effect.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A near-stationary subspace for ridge approximation

Response surfaces are common surrogates for expensive computer simulations in engineering analysis. However, the cost of fitting an accurate response surface increases exponentially as the number of model inputs increases, which leaves response surface construction intractable for high-dimensional, nonlinear models. Here we describe ridge approximation for fitting response surfaces in several variables. A ridge function is constant along several directions in its domain, so fitting occurs on the coordinates of a low-dimensional subspace of the input space. We review essential theory for ridge approximation – e.g., the best mean-squared approximation and an optimal low-dimensional subspace – and we prove that the gradient-based active subspace is near-stationary for the least-squares problem that defines an optimal subspace. Motivated by the theory, we propose a computational heuristic that uses an estimated active subspace as an initial guess for a ridge approximation fitting problem. We show a simple example where the heuristic fails, which reveals a type of function for which the proposed approach is inappropriate. We then propose a simple alternating heuristic for fitting a ridge function, and we demonstrate the effectiveness of the active subspace initial guess applied to an airfoil model of drag as a function of its 18 shape parameters.

42 ENGINEERING↗