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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 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Thermoelectric properties of doped BaHfO{sub 3}

We have studied the structural stability, electronic structure, optical properties and thermoelectric properties of doped BaHfO{sub 3} by full potential linearized augmented plane wave (FP-LAPW) method. The electronic structure of BaHfO{sub 3} doped with Sr shows enhances the indirect band gaps of 3.53 eV, 3.58 eV. The charge density plots show strong ionic bonding in Ba-Hf, and ionic and covalent bonding between Hf and O. Calculations of the optical spectra, viz., the dielectric function, refractive index and extinction coefficient are performed for the energy range are calculated and analyzed. Thermoelectric properties of semi conducting are also reported first time. The doped BaHfO{sub 3} is approximately wide band gap semiconductor with the large p-type Seebeck coefficient. The power factor of BaHfO{sub 3} is increased with Sr doping, decreases because of low electrical resistivity and thermal conductivity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Electronic properties of Laves phase ZrFe{sub 2} using Compton spectroscopy

First-ever experimental Compton profile of Laves phase ZrFe{sub 2}, using indigenous 20 Ci {sup 137}Cs Compton spectrometer, is presented. To analyze the experimental electron momentum density, we have deduced the theoretical Compton profiles using density functional theory (DFT) and hybridization of DFT and Hartree-Fock scheme within linear combination of atomic orbitals (LCAO) method. The energy bands and density of states are also calculated using LCAO prescription. The theoretical profile based on local density approximation gives a better agreement with the experimental profile than other reported schemes. The present investigations validate the inclusion of correlation potential of Perdew-Zunger in predicting the electronic properties of ZrFe{sub 2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Studies of ferroelectric and dielectric properties of pure and doped barium titanate prepared by sol-gel method

In this work, Barium Titanate (BaTiO{sub 3}) powders were synthesized via Sol-Gel auto combustion method using citric acid as a chelating agent. We study the behavior of ferroelectric and dielectric properties of pure and doped BaTiO{sub 3} on different concentration. To understand the phase and structure of the powder calcined at 900°C were characterized by X-ray Diffraction shows that tetragonal phase is dominant for pure and doped BTO and data fitted by Rietveld Refinement. Electric and Dielectric properties were characterized by P-E Hysteresis and Dielectric measurement. In P-E measurement ferroelectric loop tracer applied for different voltage. The temperature dependant dielectric constant behavior was observed as a function of frequency recorded on hp-Hewlett Packard 4192A, LF impedance, 5Hz-13Hz analyzer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Resonance coupling in plasmonic nanomatryoshka homo- and heterodimers

Here, we examine the electromagnetic (EM) energy coupling and hybridization of plasmon resonances between closely spaced concentric nanoshells known as “nanomatryoshka” (NM) units in symmetric and antisymmetric compositions using the Finite Difference Time Domain (FDTD) analysis. Utilizing plasmon hybridization model, we calculated the energy level diagrams and verified that, in the symmetric dimer (in-phase mode in a homodimer), plasmonic bonding modes are dominant and tunable within the considered bandwidth. In contrast, in the antisymmetric dimer (out-of-phase mode in a heterodimer), due to the lack of the geometrical symmetry, new antibonding modes appear in the extinction profile, and this condition gives rise to repeal of dipolar field coupling. We also studied the extinction spectra and positions of the antibonding and bonding modes excited due to the energy coupling between silver and gold NM units in a heterodimer structure. Our analysis suggest abnormal shifts in the higher energy modes. We propose a method to analyze the behavior of multilayer concentric nanoshell particles in an antisymmetric orientation employing full dielectric function calculations and the Drude model based on interband transitions in metallic components. This study provides a method to predict the behavior of the higher energy plasmon resonant modes in entirely antisymmetric structures such as compositional heterodimers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

First-principles study of water adsorption on α-SiO{sub 2} [110] surface

We have investigated the structural and electronic properties of water molecule adsorbed silicon dioxide (α-SiO{sub 2}) [110] surface and analyzed the influence of water molecule on its energetics, structure and electronic properties using density functional theory based first principles calculations. The inhomogeneous topology of the α-SiO{sub 2} clean surface promotes a total charge density displacement on the adsorbed water molecule and giving rise to electron-rich as well as hole-rich region. The electronic charge transfer from a α-SiO{sub 2} to the water molecule occurs upon the formation of a partially occupied level laying above conduction band level.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Comparison of Rotor Wake Identification and Characterization Methods for the Analysis of Wake Dynamics and Evolution

Optimal wind power plant design requires understanding of wind turbine wake physics and validation of engineering wake models under wake-controlled operating conditions. In this work, we have developed and investigated several different wake identification and characterization methods for analyzing wake evolution and dynamics. The accuracy and robustness of these methods, based on Gaussian function fitting and adaptive contour identification, have been assessed by application to a large-eddy simulation data set. A new contour-based method based on downstream momentum deficit has been considered. Uncertainties arising from wake-identification errors result in characterizations of the wake expansion, recovery, and meandering motion that differ by 19% of the rotor area, 4% of the freestream, and 15% rotor diameter, respectively.

17 WIND ENERGY↗
DOE OSTI2018

Model for scattering with proliferating resonances: Many coupled square wells

We present a multichannel model for elastic interactions, composed of an arbitrary number of coupled finite square-well potentials, and derive semianalytic solutions for its scattering behavior. Despite the model's simplicity, it is flexible enough to include many coupled short-ranged resonances in the vicinity of the collision threshold, as is necessary to describe ongoing experiments in ultracold molecules and lanthanide atoms. Here, we also introduce a simple but physically realistic statistical ensemble for parameters in this model. We compute the resulting probability distributions of nearest-neighbor resonance spacings and analyze them by fitting to the Brody distribution. We quantify the ability of alternative distribution functions, for resonance spacing and resonance number variance, to describe the crossover regime. The analysis demonstrates that the multichannel square-well model with the chosen ensemble of parameters naturally captures the crossover from integrable to chaotic scattering as a function of closed-channel coupling strength.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Theoretical Analysis of Resonant Tunneling Enhanced Field Emission

In this paper, we develop an exact analytical quantum theory for field emission from surfaces with a nearby quantum well, by solving the one-dimensional time-independent Schrödinger equation. The quantum well, which may be introduced by ions, atoms, nanoparticles, etc., is simplified as a square potential well with depth H, width d, and distance to the surface L. The theory is used to analyze the effects of the quantum well (d, H, and L), the cathode properties (work function W and Fermi energy E F ), and dc field F. It is found that the quantum well can lead to resonant tunneling enhanced field emission up to several orders of magnitude larger than that from bare cathode surfaces. In the meantime, the electron-emission-energy spectrum is significantly narrowed. The strong enhancement region is bounded by the conditions eFL + H ≥ W + C and eFL ≤ W, with e being the elementary charge (positive) and C a constant dependent on dc field F. It is also found that the linear shift of resonance peaks in the electron-emission-energy spectrum with dc field F follows ε p =ε p⁢0 –e⁢FL, with ε p⁢0 being approximately the eigenenergies for electrons confined in a square potential well without a dc field. Finally, the theory provides insights for the design of high-efficiency field emitters, which can produce a high current and highly collimated electron beams.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Possible role of grain-boundary and dislocation structure for the magnetic-flux trapping behavior of niobium: A first-principles study

In this work, first-principles methods were used to understand magnetic flux trapping at vacancies, dislocations, and grain boundaries in high-purity superconducting niobium. Full-potential linear augmented plane-wave methods were applied in progressively greater complexity, starting at simple vacancies and extending to screw dislocations and tilt grain boundaries to analyze the effects of magnetic field on the superconducting state surrounding these defects. Density-functional theory calculations identified changes in electronic structure at the dislocation core and different types of symmetric tilt grain boundaries relative to bulk niobium. Electron redistribution enhanced nonparamagnetic effects and thus perturb superconductivity, resulting in local conditions suitable for premature flux penetration and subsequently flux pinning. Since the coherence length of superconducting niobium at 0 K is significantly larger than the lattice parameter, the effects of line and planar defects in niobium are predicted to be stronger for defect clusters than single defects in isolation, which is consistent with recent experimental observations. Controlling accumulation or depletion of charge at the defects, e.g., by segregation of an impurity atom, can mitigate these tendencies thus increasing the quality of superconducting niobium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Relaxation dynamics of vortex lines in disordered type-II superconductors following magnetic field and temperature quenches

We study the effects of rapid temperature and magnetic field changes on the nonequilibrium relaxation dynamics of magnetic vortex lines in disordered type-II superconductors by employing an elastic line model and performing Langevin molecular dynamics simulations. In a previously equilibrated system, either the temperature is suddenly changed or the magnetic field is instantaneously altered which is reflected in adding or removing flux lines to or from the system. Here, the subsequent aging properties are investigated in samples with either randomly distributed pointlike or extended columnar defects, which allows us to distinguish the complex relaxation features that result from either type of pinning centers. One-time observables such as the radius of gyration and the fraction of pinned line elements are employed to characterize steady-state properties, and two-time correlation functions such as the vortex line height autocorrelations and their mean-square displacement are analyzed to study the nonlinear stochastic relaxation dynamics in the aging regime.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Polarizing Oxygen Vacancies in Insulating Metal Oxides under a High Electric Field

We demonstrate a thermodynamic formulation to quantify defect formation energetics in an insulator under high electric field. As a model system, we analyzed neutral oxygen vacancies (color centers) in alkaline-earth-metal binary oxides using density functional theory, Berry phase calculations, and maximally localized Wannier functions. Work of polarization lowers the field dependent electric Gibbs energy of formation of this defect. This is attributed mainly to the ease of polarizing the two electrons trapped in the vacant site, and secondarily to the defect induced reduction in bond stiffness and softening of phonon modes. In conclusion, the formulation and analysis have implications for understanding the behavior of insulating oxides in electronic, magnetic, catalytic, and electrocaloric devices under high electric field.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

BigData Express: Toward Schedulable, Predictable, and High-Performance Data Transfer

Big Data has emerged as a driving force for scientific discoveries. Large scientific instruments (e.g., colliders, and telescopes) generate exponentially increasing volumes of data. To enable scientific discovery, science data must be collected, indexed, archived, shared, and analyzed, typically in a widely distributed, highly collaborative manner. Data transfer is now an essential function for science discoveries, particularly within big data environments. Although significant improvements have been made in the area of bulk data transfer, the currently available data transfer tools and services can not successfully address the high-performance and time-constraint challenges of data transfer required by extreme-scale science applications for the following reasons: disjoint end-to-end data transfer loops, cross-interference between data transfers, and existing data transfer tools and services are oblivious to user requirements (deadline and QoS requirements). Fermilab has been working on the BigData Express project to address these problems. BigData Express seeks to provide a schedulable, predictable, and high-performance data transfer service for big data science. The BigData Express software is being deployed and evaluated at multiple research institutions, which include UMD, StarLight, FNAL, KISTI, KSTAR, SURFnet, Ciena, and other sites. Meanwhile, the BigData Express research team is collaborating with the StarLight International/National Communications Exchange Facility to deploy BigData Express at various research platforms, including Pacific Research Platform, National Research Platform, and Global Research Platform. It is envisioned that we are working toward building a high-performance data transfer federation for big data science.

Lu, Qiming↗
DOE OSTI2023

Local adaptation of switchgrass drives trait relations to yield and differential responses to climate and soil environments

Abstract Switchgrass, a potential biofuel crop, is a genetically diverse species with phenotypic plasticity enabling it to grow in a range of environments. Two primary divergent ecotypes, uplands and lowlands, exhibit trait combinations representative of acquisitive and conservative growth allocation strategies, respectively. Whether these ecotypes respond differently to various types of environmental drivers remains unclear but is crucial to understanding how switchgrass varieties will respond to climate change. We grew two upland, two lowland, and two intermediate/hybrid cultivars of switchgrass at three sites along a latitudinal gradient in the central United States. Over a 4‐year period, we measured plant functional traits and biomass yields and evaluated genotype‐by‐environment (G × E) interaction effects by analyzing switchgrass responses to soil and climate variables. We found substantial evidence of G × E interactions on biomass yield, primarily due to deviations in the response of the southern lowland cultivar Alamo, which produced more biomass in hotter and drier environments relative to other cultivars. While lowland cultivars had the highest potential for yield, their yields were more variable year‐to‐year compared to other cultivars, suggesting greater sensitivity to environmental perturbations. Models comparing soil and climate principal components as explanatory variables revealed soil properties, especially nutrients, to be most effective at predicting switchgrass biomass yield. Also, positive correlations between biomass yield and conservative plant traits, such as high stem mass and tiller height, became stronger at lower latitudes where the climate is hotter and drier, regardless of ecotype. Lowland cultivars, however, showed a greater predisposition to exhibit these conservative traits. These results suggest switchgrass trait allocation trade‐offs that prioritize aboveground biomass production are more tightly associated in hot, dry environments and that lowland cultivars may exhibit a more specialized strategy relative to other cultivars. Altogether, this research provides essential knowledge for improving the viability of switchgrass as a biofuel crop.

09 BIOMASS FUELS↗
DOE OSTI2016

SU-G-TeP4-08: Automating the Verification of Patient Treatment Parameters

Purpose: To automate the daily verification of each patient’s treatment by utilizing the trajectory log files (TLs) written by the Varian TrueBeam linear accelerator while reducing the number of false positives including jaw and gantry positioning errors, that are displayed in the Treatment History tab of Varian’s Chart QA module. Methods: Small deviations in treatment parameters are difficult to detect in weekly chart checks, but may be significant in reducing delivery errors, and would be critical if detected daily. Software was developed in house to read TLs. Multiple functions were implemented within the software that allow it to operate via a GUI to analyze TLs, or as a script to run on a regular basis. In order to determine tolerance levels for the scripted analysis, 15,241 TLs from seven TrueBeams were analyzed. The maximum error of each axis for each TL was written to a CSV file and statistically analyzed to determine the tolerance for each axis accessible in the TLs to flag for manual review. The software/scripts developed were tested by varying the tolerance values to ensure veracity. After tolerances were determined, multiple weeks of manual chart checks were performed simultaneously with the automated analysis to ensure validity. Results: The tolerance values for the major axis were determined to be, 0.025 degrees for the collimator, 1.0 degree for the gantry, 0.002cm for the y-jaws, 0.01cm for the x-jaws, and 0.5MU for the MU. The automated verification of treatment parameters has been in clinical use for 4 months. During that time, no errors in machine delivery of the patient treatments were found. Conclusion: The process detailed here is a viable and effective alternative to manually checking treatment parameters during weekly chart checks.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Investigating the Relative Contribution from Tropical Indo-Pacific SST to Asian Monsoon Precipitation Variability Using LIM

Abstract A critical issue is determining the factors that control the year-to-year variability in precipitation over southern Asia. In this study, we employ a cyclostationary linear inverse model (CS-LIM) to quantify the relative contribution of tropical Pacific and Indian Ocean sea surface temperature anomalies (SSTAs) to the interannual variability of the Asian monsoon, especially Indian summer monsoon rainfall (ISMR). Through a series of CS-LIM experiments, we isolate the impacts of the direct forcing from Pacific SSTAs, Indian Ocean SSTAs, and their interaction on Asian monsoon rainfall variability. Our results reveal distinct patterns of influence with the direct forcing from the Pacific (Indian) Ocean tending to enhance (reduce) the magnitude of precipitation variability, while the Indo-Pacific interaction acts to strongly damp the variability of Asian monsoon precipitation, especially over India. We further investigate these specific impacts on ISMR by analyzing the relationship between tropical Indo-Pacific SSTAs and the leading three empirical orthogonal functions (EOFs) of ISMR. The results from our CS-LIM experiments indicate that the direct forcing from El Niño–Southern Oscillation (ENSO) enhances the variability of the first and third EOFs, while the Indian Ocean SSTA opposes ENSO’s effects, which is consistent with previous studies. Our new results show that the tropical Indo-Pacific interaction strongly damps ISMR variability, which is due to the ENSO-induced Indian Ocean dipole (IOD) opposing the direct impacts from ENSO on ISMR. Additionally, reduced ENSO amplitude and duration associated with the Indo-Pacific interaction may also contribute to the damping effect on ISMR, but this requires further study to understand the relevant mechanisms.

Meteorology & Atmospheric Sciences↗
DOE OSTI2025

Hydropower Biological Evaluation Toolset (HBET) Version 3.0: User Guide

The Hydropower Biological Evaluation Tools (HBET) software package, developed by Pacific Northwest National Laboratory (PNNL), is designed to assemble, organize, and process data collected by Sensor Fish and live fish. HBET enable users to characterize the hydraulic conditions of hydropower structures and estimate fish injury and mortality rates from various stressors. Future updates of the software may support other technologies, such as bead tracking in physical models and computational fluid dynamics. The HBET program can be customized to analyze different hydraulic applications, including turbines, spillways, weirs, pumped storage, and other user-defined functions, and therefore, help researchers, turbine designers, hydropower operators, and regulators better evaluate hydropower structures regarding their environmental sustainability and cost-effectiveness. Added content to the user guide about the new feature for predicting absolute injury rates.

13 HYDRO ENERGY↗
DOE OSTI2022

A Strong-QCD Regime Measurement of the Proton’s Spin Structure

The theory of the strong force, Quantum Chromodynamics (QCD) remains one of the most important ways to understand the fundamental properties of ordinary matter. However, at low momentum transfer Q 2 , in the regime where the strong force becomes extremely strong, our understanding of QCD for ordinary nucleons becomes hazy. Several cutting edge theories such as Chiral Perturbation Theory (χPT) and Lattice QCD have provided valuable predictions in this regime, but Lattice QCD has not yet extended predictions of many important quantities to this kinematic region, and Chiral Perturbation Theory has faced several important disagreements with experimental data for the neutron over the last several decades. It is therefore of extreme importance to have a benchmark of experimental data in the low energy regime for the proton’s behavior, as a test of leading theories for the behavior of QCD in this regime. The E08-027 (g2p) experiment ran at Jefferson Lab in 2012 with the goal of collecting this valuable data, and though I was still completing my undergraduate studies at the time, I became involved in the analysis in 2015 and built on the previous work to complete it and analyze the exciting results. This experiment achieved a high precision measurement of the spin structure functions g1 and g2 for the proton, quantities which describe the internal spin structure of the proton. These measurements were taken in the valuable low Q 2 region described above, and used to extract several moments of these spin structure functions which can be directly compared to the cutting-edge predictions of Chiral Perturbation Theory. Though the experiment’s timeline was such that I didn’t have a chance to work directly on the experimental setup, I had the opportunity to acquire hands-on experience working on a polarized target at UNH which is very similar to the crucial polarized target used in the g2p experiment. Full details of the g2p experiment and my experimental work at the University of New Hampshire are presented in this thesis, as well as a detailed description of the analysis process and the exciting benchmark results, which serve as a direct test of all current and future theories of QCD in the low-Q 2 regime.

Ruth, David↗
DOE OSTI2015

Use of nonlocal helium microplasma for gas impurities detection by the collisional electron spectroscopy method

The collisional electron spectroscopy (CES) method, which lays the ground for a new field for analytical detection of gas impurities at high pressures, has been verified. The CES method enables the identification of gas impurities in the collisional mode of electron movement, where the advantages of nonlocal formation of the electron energy distribution function (EEDF) are fulfilled. Important features of dc negative glow microplasma and probe method for plasma diagnostics are applied. A new microplasma gas analyzer design is proposed. Admixtures of 0.2% Ar, 0.6% Kr, 0.1% N{sub 2}, and 0.05% CO{sub 2} are used as examples of atomic and molecular impurities to prove the possibility for detecting and identifying their presence in high pressure He plasma (50–250 Torr). The identification of the particles under analysis is made from the measurements of the high energy part of the EEDF, where maxima appear, resulting from the characteristic electrons released in Penning reactions of He metastable atoms with impurity particles. Considerable progress in the development of a novel miniature gas analyzer for chemical sensing in gas phase environments has been made.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗