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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Evaluating the networking characteristics of the Cray XC-40 Intel Knights Landing-based Cori supercomputer at NERSC

There are many potential issues associated with deploying the Intel Xeon Phi™ (code named Knights Landing [KNL]) manycore processor in a large-scale supercomputer. One in particular is the ability to fully utilize the high-speed communications network, given that the serial performance of a Xeon Phi TM core is a fraction of a Xeon®core. In this paper, we take a look at the trade-offs associated with allocating enough cores to fully utilize the Aries high-speed network versus cores dedicated to computation, e.g., the trade-off between MPI and OpenMP. In addition, we evaluate new features of Cray MPI in support of KNL, such as internode optimizations. We also evaluate one-sided programming models such as Unified Parallel C. We quantify the impact of the above trade-offs and features using a suite of National Energy Research Scientific Computing Center applications.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Physics-preserving enriched Galerkin method for a fully-coupled thermo-poroelasticity model

This paper proposes a new numerical method for a fully-coupled, quasi-static thermo-poroelasticity model in a unified enriched Galerkin (EG) method framework. In our method, the mechanics sub-problem is solved using a locking-free EG method, and the flow and heat sub-problems are solved using a locally-conservative EG method. The proposed method offers mass and energy conservation properties with much lower costs than other methods with the same properties, including discontinuous Galerkin methods and mixed finite element methods. The well-posedness and optimal a priori error estimates are carefully derived. Here, several numerical tests confirm the theoretical optimal convergence rates and the mass and energy conservation properties of the new method.

15 GEOTHERMAL ENERGY↗
DOE OSTI2026

Self-supervised and multi-fidelity learning for extended predictive soil spectroscopy

Infrared spectroscopy is a cost-effective, non-destructive, and environmentally benign technology that is increasingly recognized as an important solution for meeting the global demand for soil data. While both near-infrared (NIR) and mid-infrared (MIR) diffuse reflectance spectroscopy enable rapid estimation of soil properties, they present a significant trade-off: NIR offers superior scalability and lower operational costs, whereas MIR provides higher analytical fidelity by capturing fundamental molecular vibrations. In this study, we propose a self-supervised, multi-fidelity learning framework designed to bridge this gap. Our approach leverages large-scale MIR spectral libraries to learn a compact, transferable latent representation, into which NIR spectra are subsequently aligned for downstream prediction. The workflow consists of pretraining a latent model on a large MIR library, adapting the representation using a smaller paired NIR–MIR dataset, and evaluating generalization on an independent external test set. Across a range of chemical and physical soil properties, we found that MIR-derived embeddings improved prediction accuracy relative to baseline models that used raw MIR inputs. Predictions derived from the spectrum conversion (NIR to MIR) task did not match the performance of the original MIR spectra but were similar or superior to predictive performance of NIR-only models, suggesting the unified spectral latent space can effectively leverage the larger and more diverse MIR dataset for prediction of soil properties not well represented in current NIR libraries.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Extension of Hopfield’s Electron Transfer Model To Accommodate Site–Site Correlation

Extension of the Förster analogue for the ET rate constant (based on virtual intermediate electron detachment or attachment states) with inclusion of site–site correlation due to coulomb terms associated with solvent reorganization energy and the driving force, has been developed and illustrated for a simple three-state, two-mode model. Furthermore, the model is applicable to charge separation (CS), recombination (CR), and shift (CSh) ET processes, with or without an intervening bridge. The model provides a unified perspective on the role of virtual intermediate states in accounting for the thermal Franck–Condon weighted density of states (FCWD), the gaps controlling superexchange coupling, and mean absolute redox potentials, with full accommodation of site–site coulomb interactions. We analyzed two types of correlation: aside from the site–site correlation due to coulomb interactions, we have emphasized the intrinsic “nonorthogonality” which generally pertains to reaction coordinates (RCs) for different ET processes involving multiple electronic states, as may be expressed by suitably defined direction cosines (cos(θ)). A pair of RCs may be nonorthogonal even when the site–site coulomb correlations are absent. While different RCs are linearly independent in the mathematical sense for all θ ≠ 0°, they are independent in the sense of being “uncorrelated” only in the limit of orthogonality (θ = 90°). There is application to more than two coordinates is straightforward and may include both discrete and continuum contributions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Designing Anion-Exchange Ionomers with Oriented Nanoscale Phase Separation at a Silver Interface

We report performance of polymer electrolyte-based energy systems is significantly impacted by transport within the electrode catalyst layer, where ionomer thin films coat catalyst particles. Proton exchange ionomer thin films have been thoroughly characterized, but few studies have critically examined anion-exchange ionomer (AEI) thin films. Further, none have reported nanoscale phase separation for hydrocarbon AEIs, which is critical to mitigate transport resistances. In this work, a set of hydrocarbon-based AEIs with nanoscale phase separation are developed from tunable block copolymer systems composed of polyisoprene (PIp) and polychloromethylstyrene (PCMS). The effect of the PIp/PCMS ratio, architecture, and thickness on the thin-film morphology of the neutral block copolymer precursors on silicon and silver substrates is investigated using grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM). AEIs are prepared by quaternizing with trimethylamine or methylpiperidine and their cation-dependent morphology is characterized at 60 °C and 95% RH. A perpendicularly aligned morphology is observed on silver, while no phase separation is observed on silicon, indicating that silver-polymer interfacial interactions drive phase separation. After quaternization, dipole-dipole interactions induce some disorder, but nanoscale phase separation is still maintained. GISAXS patterns are modeled using a Unified Fit approach to understand water uptake and swelling, and recommendations for AEI design are presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Mechanism for fluctuating pair density wave

Abstract In weakly coupled BCS superconductors, only electrons within a tiny energy window around the Fermi energy, E F , form Cooper pairs. This may not be the case in strong coupling superconductors such as cuprates, FeSe, SrTiO 3 or cold atom condensates where the pairing scale, E B , becomes comparable or even larger than E F . In cuprates, for example, a plausible candidate for the pseudogap state at low doping is a fluctuating pair density wave, but no microscopic model has yet been found which supports such a state. In this work, we write an analytically solvable model to examine pairing phases in the strongly coupled regime and in the presence of anisotropic interactions. Already for moderate coupling we find an unusual finite temperature phase, below an instability temperature T i , where local pair correlations have non-zero center-of-mass momentum but lack long-range order. At low temperature, this fluctuating pair density wave can condense either to a uniform d -wave superconductor or the widely postulated pair-density wave phase depending on the interaction strength. Our minimal model offers a unified framework to understand the emergence of both fluctuating and long range pair density waves in realistic systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

FAIR principles for AI models with a practical application for accelerated high energy diffraction microscopy

Abstract A concise and measurable set of FAIR (Findable, Accessible, Interoperable and Reusable) principles for scientific data is transforming the state-of-practice for data management and stewardship, supporting and enabling discovery and innovation. Learning from this initiative, and acknowledging the impact of artificial intelligence (AI) in the practice of science and engineering, we introduce a set of practical, concise, and measurable FAIR principles for AI models. We showcase how to create and share FAIR data and AI models within a unified computational framework combining the following elements: the Advanced Photon Source at Argonne National Laboratory, the Materials Data Facility, the Data and Learning Hub for Science, and funcX, and the Argonne Leadership Computing Facility (ALCF), in particular the ThetaGPU supercomputer and the SambaNova DataScale ® system at the ALCF AI Testbed. We describe how this domain-agnostic computational framework may be harnessed to enable autonomous AI-driven discovery.

47 OTHER INSTRUMENTATION↗
DOE OSTI2012

Metal Oxidation Kinetics and the Transition from Thin to Thick Films

We report an investigation of growth kinetics and transition from thin to thick films during metal oxidation. In the thin film limit (< 20 nm), Cabrera and Mott’s theory is usually adopted by explicitly considering ionic drift through the oxide in response to electric fields, where the growth kinetics follow an inverse logarithmic law . It is generally accepted that Wagner’s theory, involving self-diffusion, is valid only in the limit of thick film regime (>1μm) and leads to parabolic growth kinetics , where l is the oxide film thickness. Theory presented here unifies the two models and provides a complete description of oxidation including the transition from thin to thick film. The range of validity of Cabrera and Mott’s theory and Wagner’s theory can be well defined in terms of the Debye-Hückel screening length. The transition from drift-dominated ionic transport for thin film to diffusion-dominated transport for thick film is found to strictly follow the direct logarithmic law that is frequently observed in many experiments.

Oxidation, Cabrera and Mott, Wagner, transition, l↗
DOE OSTI2015

Origin of the broad three-terminal Hanle signals in Fe/SiO{sub 2}/Si tunnel junctions

Lorentzian-shaped broader three-terminal Hanle (B-3TH) signals are observed in Fe/SiO{sub 2}/Si tunnel junction devices at 6–300 K. We propose a spin conducting model, which explains all the characteristics of our experimental results, such as field angle dependence and bias dependence of the B-3TH signals, as well as experimental results reported by other groups. It was found that the shape of the B-3TH signals is determined by the spin depolarization at the Fe/SiO{sub 2} interface caused by local magnetic fields, unlike the conventional understanding. The shape of the B-3TH signals, including narrower and inverted Hanle signals, reflects the magnetic order of an ultrathin paramagnetic layer formed at the Fe/SiO{sub 2} interface. Our model provides a unified explanation of the B-3TH signals observed in three-terminal Hanle measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Effect of doping on the electron transport in polyfluorene

In this paper, electron transport of pure and DMC doped polyfluorne (PF) films have been studied at various doping concentrations. Pure films show space charge limited conduction with field and temperature dependent mobility. The J–V characteristics of doped PF were ohmic at low voltages due to thermally released carriers from dopant states. At higher voltages the current density increases nonlinearly due to field dependent mobility and carrier concentration thereby filling of tail states of HOMO of the host. The conductivity of doped films were analyzed using the Unified Gaussian Disorder Model (UGDM). The carrier concentration obtained from the fitting show a non-linear dependence on doping concentration which may be due to a combined effect of thermally activated carrier generation and increased carrier mobility.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

A typological framework of non-floodplain wetlands for global collaborative research and sustainable use

Non-floodplain wetlands (NFWs) are important but vulnerable inland freshwater systems that are receiving increased attention and protection worldwide. However, a lack of consistent terminology, incohesive research objectives, and inherent heterogeneity in existing knowledge hinder cross-regional information sharing and global collaboration. To address this challenge and facilitate future management decisions, we synthesized recent work to understand the state of NFW science and explore new opportunities for research and sustainable NFW use globally. Results from our synthesis show that although NFWs have been widely studied across all continents, regional biases exist in the literature. We hypothesize these biases in the literature stem from terminology rather than real geographical bias around existence and functionality. To confirm this observation, we explored a set of geographically representative NFW regions around the world and characteristics of research focal areas. We conclude that there is more that unites NFW research and management efforts than we might otherwise appreciate. Furthermore, opportunities for cross-regional information sharing and global collaboration exist, but a unified terminology will be needed, as will a focus on wetland functionality. Based on these findings, we discuss four pathways that aid in better collaboration, including improved cohesion in classification and terminology, and unified approaches to modeling and simulation. In turn, legislative objectives must be informed by science to drive conservation and management priorities. Finally, an educational pathway serves to integrate the measures and to promote new technologies that aid in our collective understanding of NFWs. Our resulting framework from NFW synthesis serves to encourage interdisciplinary collaboration and sustainable use and conservation of wetland systems globally.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Anomalous Hall effect at the Lifshitz transition in ZrTe 5

Zirconium pentatelluride ZrTe 5 is a topological semimetal. The presence of a temperature-induced Lifshitz transition, in which the Fermi level goes from the conduction band to the valence band with increasing temperature, provides unique opportunities to study the interplay between Fermi-surface topology, dynamics of Dirac fermions, and Berry curvature in one system. Here we present a combined experimental and theoretical study and show that a low-energy model can be used to understand the complicated Hall response and large anomalous Hall effect observed in ZrTe 5 over a wide range of temperature and magnetic field. We found that the anomalous Hall contribution dominates the Hall response in a narrow temperature window around the Lifshitz transition, away from which the orbital contribution dominates. Moreover, our results indicate that a topological phase transition coexists with the Lifshitz transition. To conclude, our model provides a unifying framework to understand the Hall effect in semimetals with large Zeeman splitting and nontrivial topology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Model for QCD ground state with magnetic disorder

We explore an ansatz for the QCD vacuum in the Coulomb gauge that describes gauge field fluctuations in the presence of a weakly interacting gas of Abelian monopoles. Such magnetic disorder leads to long-range correlations which are manifested through the area law for the Wilson loop. In particular we focus on the role of the residual monopole-monopole interactions in providing the mechanism for suppression of the gluon propagator at low momenta which also leads to low-momentum enhancement in the ghost propagator.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Naturalness and stability of the generalized Chaplygin gas in the seesaw cosmon scenario

The seesaw mechanism is conceived on the basis that a mass scale, {xi}, and a dimensionless scale, s, can be fine-tuned in order to control the dynamics of active and sterile neutrinos through cosmon-type equations of motion: the seesaw cosmon equations. This allows for sterile neutrinos to be a dark matter candidate. In this scenario, the dynamical masses and energy densities of active and sterile neutrinos can be consistently embedded into the generalized Chaplygin gas (GCG), the unified dark sector model. In addition, dark matter adiabatically coupled to dark energy allows for a natural decoupling of the (active) mass varying neutrino component from the dark sector. Thus mass varying neutrinos turn into a secondary effect. Through the scale parameters, {xi} and s, the proposed scenario allows for a convergence among three distinct frameworks: the cosmon scenario, the seesaw mechanism for mass generation, and the GCG model. It is found that the equation of state of the perturbations is the very one of the GCG background cosmology so that all the results from this approach are maintained, being smoothly modified by active neutrinos. Constrained by the seesaw relations, it is shown that the mass varying mechanism is responsible for the stability against linear perturbations and is indirectly related to the late time cosmological acceleration.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Multilepton signatures of a hidden sector in rare B decays

We explore the sensitivity of flavor-changing b{yields}s transitions to a (sub-) GeV hidden sector with generic couplings to the standard model through the Higgs, vector, and axion portals. The underlying two-body decays of B mesons, B{yields}X{sub s}S, and B{sup 0}{yields}SS, where S denotes a generic new GeV-scale particle, may significantly enhance the yield of monochromatic lepton pairs in the final state via prompt S{yields}ll decays. Existing measurements of the charged lepton spectrum in neutral-current semileptonic B decays provide bounds on the parameters of the light sector that are significantly more stringent than the requirements of naturalness. New search modes, such as B{yields}X{sub s}+n(ll) and B{sup 0}{yields}n(ll) with n{>=}2, can provide additional sensitivity to scenarios in which both the Higgs and vector portals are active, and are accessible to (super-) B factories and hadron colliders.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Constraints on the light pseudoscalar meson distribution amplitudes from their meson-photon transition form factors

The meson-photon transition form factors {gamma}{gamma}*{yields}P (P stands for {pi}, {eta} and {eta}') provide strong constraints on the distribution amplitudes of the pseudoscalar mesons. In this paper, these transition form factors are calculated under the light-cone perturbative QCD approach, in which both the valence and nonvalence quarks' contributions have been taken into consideration. To be consistent, a unified wave function model is adopted to analyze these form factors. It is shown that with the proper charm component f{sub {eta}}'{sup c}{approx}-30 MeV and a moderate DA with B{approx}0.30, the experimental data on Q{sup 2}F{sub {eta}{gamma}}(Q{sup 2}) and Q{sup 2}F{sub {eta}'{gamma}}(Q{sup 2}) in the whole Q{sup 2} region can be explained simultaneously. Furthermore, a detailed discussion on the form factors' uncertainties caused by the constituent quark masses m{sub q} and m{sub s}, the parameter B, the mixing angle {phi}, and f{sub {eta}'}{sup c} are presented. It is found that, by adjusting these parameters within their reasonable regions, one can improve the form factor to a certain degree but cannot solve the puzzle for Q{sup 2}F{sub {pi}{gamma}}(Q{sup 2}), especially to explain the behavior of the {pi}-{gamma} form factor within the whole Q{sup 2} region consistently. We hope further experimental data on these form factors in the large Q{sup 2} region can clarify the present situation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Observations on the radiative corrections to pion {beta} decay

We find that, in the local V-A theory, the radiative corrections to pion {beta}-decay involving the weak vector current, when evaluated in the current algebra (CA) formulation in which quarks are the fundamental underlying fields, show a small difference with the more elementary calculations based directly on the pion fields. We show that this difference arises from a specific short-distance effect that depends on the algebra satisfied by the weak and electromagnetic currents. On the other hand, we present a simple theoretical argument that concludes that this difference does not occur when the CA formulation is compared with the chiral perturbation theory ({chi}PT) approach. Comparisons with previous studies, and with a more recent calculation based on {chi}PT, are included. We also briefly review the important differences between the results in the local V-A theory and the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

QCD Running Coupling in the Nonperturbative and Near-Perturbative Regimes

We use analytic continuation to extend the gauge-gravity duality nonperturbative description of the strong force coupling into the transition, near-perturbative, regime where perturbative effects become important. By excluding the unphysical region in coupling space from the flow of singularities in the complex plane, we derive a specific relation between the scales relevant at large and short distances; this relation is uniquely fixed by requiring maximal analyticity. The unified effective coupling model gives an accurate description of the data in the nonperturbative and the near-perturbative regions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗