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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Optimization of algorithmic errors in analog quantum simulations

Due to rapidly improving quantum computing hardware, Hamiltonian simulations of relativistic lattice field theories have seen a resurgence of attention. Furthermore, this computational tool requires turning the formally infinite-dimensional Hilbert space of the full theory into a finite-dimensional one. For gauge theories, a widely used basis for the Hilbert space relies on the representations induced by the underlying gauge group, with a truncation that keeps only a set of the lowest dimensional representations. This works well at large bare gauge coupling, but becomes less efficient at small coupling, which is required for the continuum limit of the lattice theory. In this work, we develop a new basis suitable for the simulation of an SU(2) lattice gauge theory in the maximal tree gauge. In particular, we show how to perform a Hamiltonian truncation so that the eigenvalues of both the magnetic and electric gauge-fixed Hamiltonian are mostly preserved, which allows for this basis to be used at all values of the coupling. Little prior knowledge is assumed, so this may also be used as an introduction to the subject of Hamiltonian formulations of lattice gauge theories.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Structural, electronic and elastic properties of REIr{sub 2} (RE=La and Ce) Laves phase compounds

REIr{sub 2} (RE = La and Ce) Laves phase intermetallic compounds were investigated with respect to their structural, electronic and elastic properties using full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation (GGA) as implemented in WIEN2k code. The ground state properties such as lattice constants (a{sub 0}), bulk modulus (B), pressure derivative of bulk modulus (B′) and density of state at Fermi level N(E{sub F}) have been obtained by optimization method. The electronic structure (BS, TDOS and PDOS) reveals that these Laves phase compounds are metallic in nature. The calculated elastic constants indicate that these compounds are mechanically stable at ambient pressure and found to be ductile in nature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Current understanding of Oxidative Coupling of Methane (OCM) reaction over supported Mn-Na 2 WO 4 catalysts

This perspective reviews the current understanding of the Oxidative Coupling of Methane (OCM) reaction over the supported Mn-Na 2 WO 4 /SiO 2 catalyst, with a focus on recent insights gained from state-of-the-art in-situ and operando spectroscopic characterization and chemical probe experiments under controlled environments. The supported Mn-Na 2 WO 4 /SiO 2 catalyst exhibits dynamic structural changes during the OCM reaction, involving multiple reactive lattice and adsorbed oxygen species, each associated with different oxide phases. These oxygen species play distinct roles in various steps of the OCM mechanism. The catalytic active sites for activation of CH 4 are associated with isolated surface Na-WO x sites on the SiO 2 support and the role of surface MnO x sites on SiO 2 is to oxidatively dehydrogenate C 2 H 6 to C 2 H 4 . Furthermore, this paper provides a detailed discussion of these roles and also introduces new experimental data from Temporal Analysis of Products (TAP) studies to clarify the ongoing debate in the literature regarding the contributions of lattice versus adsorbed oxygen species in OCM reaction product formation. Additionally, recommendations are offered for optimizing the performance of supported Mn-Na 2 WO 4 /SiO 2 catalysts to enhance CH 4 activation and C 2 product selectivity.

03 - NATURAL GAS↗
DOE OSTI2024

Reducing beta functions in the NSLS-II long straight section for NEXT-III beamlines

The NSLS-II Experimental Tools III (NEXT-III) Project with the goal of building 8-12 new beamlines is ongoing. We were requested to explore the possibility of modifying the long straight section in Cell 26 to accommodate two new undulators for Advanced Nanoscale Imaging (ANI) Beamline and Tender X-ray Nanoprobe (TXN) Beamline. The scope of work includes: linear lattice matching; confirmation of the minimum ID gaps consistent with beam stay-clear limitations; calculation of the X-ray brightness; optimization of the dynamic aperture and momentum acceptance; multi-particle tracking to confirm the injection efficiency does not deteriorate significantly. The beam simulations have to be done using the most recent NSLS-II lattice model with all present insertion devices and realistic magnet errors, misalignments, and apertures. Originally two lattice options were considered for the assessment:1) with single -minimum beta functions and 2) NSLS-II with double-minimum beta functions. However, since the beamlines are not interested in the reduction of the horizontal beta function, just the vertical one, we decided to stop considering the single-minimum option because the current vertical beta is already low (3.3m) and further reducing it at the straight section center can increase it too much at the edge of a long ID, and limit the beam stay-clear. So, this report is focused on the double mini-beta scheme only.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Microstructure and Mechanical Properties of Spray-Formed 7075 Alloy During Retrogression

The mechanical properties, conductivity, microstructure, precipitation behavior and evolution process of elements and phases of spray-formed 7075 alloy during retrogression are studied by the tensile test, electric test, hardness test, transmission electron microscope (TEM), x-ray diffraction (XRD) analysis, electron-dispersive spectroscopy (EDS) and lattice parameter measurements. The results show that the mechanical properties and conductivity of the alloy can be effectively improved when treated at a suitable retrogression temperature and time. According to the TEM observations, XRD analysis, EDS and an accurate measurement of the lattice parameter, the redissolution of elements and precipitated phases can be readily observed. From the optimization selection of the RRA treatment for the 7075 alloy, the regularity of redissolution and precipitation of the elements and phases are evaluated. The ultimate tensile strength, yield strength, hardness, elongation and conductivity of the spray-formed 7075 alloy after preaging at 120 °C for 16 h, retrogression at 200 °C for 8 min and reaging at 120 °C for 24 h are 791, 736 MPa, 181 HBW, 8.5% and 22.6 MS/m, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Bi-Substituted Iron Garnet Films for Thermomagnetic Recording, Photonics, and Plasmonics: Optimization of Synthesis Conditions Using Scanning Probe Microscopy

We present the results of studies on the optimization of the synthesis of Bi-substituted iron garnet (Bi : IG) films by liquid-phase epitaxy and vacuum deposition followed by crystallization. The effect of the parameter of mismatch between the crystal lattices of the film and the substrate on the functional properties of thin single-crystal high-coercive Bi : IG films is demonstrated. The regime of high-temperature annealing of deposited films was optimized in order to form layers with a high bismuth concentration for magnetophotonic and magnetoplasmonic structures. It was established that annealing of the Bi : IG layer under a SiO{sub 2} layer deposited on top will reduce the roughness of interfaces in multilayer structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Heterobilayers of 2D materials as a platform for excitonic superfluidity

Excitonic condensate has been long-sought within bulk indirect-gap semiconductors, quantum wells, and 2D material layers, all tried as carrying media. Here, we propose intrinsically stable 2D semiconductor heterostructures with doubly-indirect overlapping bands as optimal platforms for excitonic condensation. After screening hundreds of 2D materials, we identify candidates where spontaneous excitonic condensation mediated by purely electronic interaction should occur, and hetero-pairs Sb 2 Te 2 Se/BiTeCl, Hf 2 N 2 I 2 /Zr 2 N 2 Cl 2 , and LiAlTe 2 /BiTeI emerge promising. Unlike monolayers, where excitonic condensation is hampered by Peierls instability, or other bilayers, where doping by applied voltage is required, rendering them essentially non-equilibrium systems, the chemically-specific heterostructures predicted here are lattice-matched, show no detrimental electronic instability, and display broken type-III gap, thus offering optimal carrier density without any gate voltages, in true-equilibrium. Predicted materials can be used to access different parts of electron-hole phase diagram, including BEC-BCS crossover, enabling tantalizing applications in superfluid transport, Josephson-like tunneling, and dissipationless charge counterflow.

36 MATERIALS SCIENCE↗
NASA NTRS1994

The use of the Regier number in the structural design with flutter constraints

This preliminary investigation introduces the use of the Regier number as a flutter constraint criterion for aeroelastic structural optimization. Artificial neural network approximations are used to approximate the flutter criterion requirements as a function of the design Mach number and the parametric variables defining the aspect ratio, center of gravity, taper ratio, mass ratio, and pitch inertia of the wing. The presented approximations are simple enough to be used in the preliminary design stage without a well defined structural model. An example problem for a low-speed, high-aspect-ratio, light-aircraft wing is presented. The example problem is analyzed for the flutter Mach number using doublet lattice aerodynamics and the PK solution method. The use of the Regier number constraint criterion to optimize the example problem for minimum structural mass while maintaining a constant flutter Mach number is demonstrated.

Dunn, H. J.↗
DOE OSTI2020

Phase behavior of continuous-space systems: A supervised machine learning approach

The phase behavior of complex fluids is a challenging problem for molecular simulations. Supervised machine learning (ML) methods have shown potential for identifying the phase boundaries of lattice models. In this work, we extend these ML methods to continuous-space systems. We propose a convolutional neural network model that utilizes grid-interpolated coordinates of molecules as input data of ML and optimizes the search for phase transitions with different filter sizes. We test the method for the phase diagram of two off-lattice models, namely, the Widom–Rowlinson model and a symmetric freely jointed polymer blend, for which results are available from standard molecular simulations techniques. The ML results show good agreement with results of previous simulation studies with the added advantage that there is no critical slowing down. We find that understanding intermediate structures near a phase transition and including them in the training set is important to obtain the phase boundary near the critical point. The method is quite general and easy to implement and could find wide application to study the phase behavior of complex fluids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Density functional investigation of intermolecular effects on {sup 13}C NMR chemical-shielding tensors modeled with molecular clusters

A quantum-chemical method for modeling solid-state nuclear magnetic resonance chemical-shift tensors by calculations on large symmetry-adapted clusters of molecules is demonstrated. Four hundred sixty five principal components of the {sup 13}C chemical-shielding tensors of 24 organic materials are analyzed. The comparison of calculations on isolated molecules with molecules in clusters demonstrates that intermolecular effects can be successfully modeled using a cluster that represents a local portion of the lattice structure, without the need to use periodic-boundary conditions (PBCs). The accuracy of calculations which model the solid state using a cluster rivals the accuracy of calculations which model the solid state using PBCs, provided the cluster preserves the symmetry properties of the crystalline space group. The size and symmetry conditions that the model cluster must satisfy to obtain significant agreement with experimental chemical-shift values are discussed. The symmetry constraints described in the paper provide a systematic approach for incorporating intermolecular effects into chemical-shielding calculations performed at a level of theory that is more advanced than the generalized gradient approximation. Specifically, NMR parameters are calculated using the hybrid exchange-correlation functional B3PW91, which is not available in periodic codes. Calculations on structures of four molecules refined with density plane waves yield chemical-shielding values that are essentially in agreement with calculations on clusters where only the hydrogen sites are optimized and are used to provide insight into the inherent sensitivity of chemical shielding to lattice structure, including the role of rovibrational effects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

X-ray Diffraction Studies of Single-Crystal Materials for Broad Battery Applications

Single-crystal materials have attracted growing interest in battery research due to their well-defined crystallographic orientation, absence of grain boundaries, and enhanced mechanical and electrochemical stability. This Review provides a comprehensive overview of recent advances in the synthesis, structural evolution, and performance optimization of single-crystal electrodes and solid electrolytes. Particular focus is placed on the application of advanced X-ray diffraction (XRD) techniques, including operando synchrotron diffraction, reciprocal space mapping, and Bragg coherent diffraction imaging, which have enabled in-depth investigations of lattice strain, cation disorder, phase transitions, and defect formation. Representative case studies across Ni-rich layered oxides, spinel-type cathodes, and garnet-based electrolytes are examined to highlight the structural features unique to single crystals. Additionally, the synergistic integration of XRD with machine learning, tomography, and spectroscopy is discussed as a powerful direction for real-time analysis and predictive modeling. Furthermore, these insights provide critical guidance for the rational design of high-performance single-crystal materials in lithium, sodium, and solid-state battery systems.

25 ENERGY STORAGE↗
DOE OSTI2022

Study of reference burnup steps optimization in fuel segment data file generation for NEXUS/ANC9 code system

For any two-step core design code system, the cross-section files are the primary factor to determine the accuracy of the system prediction. For a once-through cross-section system to cover all potential applicable conditions, the system may need to perform tens of thousands state points of lattice calculations. These calculations take a significant amount of CPU times and computing power, especially when a fine or ultra-fine energy group library is used. As computer power increases, so does the calculational complexity. Therefore, it is important to make the lattice calculations effective and efficient. Based on the Westinghouse core design code system NEXUS/ANC9, this work focuses on the reference burnup steps used by the lattice code when performing the calculations. Following the fundamental cross-section methodology and analyzing the contribution of each individual terms, this study provides an applicable solution of the optimized reference burnup steps. The test results show that, with the existing cross-section methodology, it is possible to significantly reduce the lattice calculation cases and cross-section file generation time without sacrificing the accuracy of system prediction. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2014

High piezoelectric performance and temperature dependence of ferroelectric and piezoelectric properties of Bi(Mg 0.5 Zr 0.5 )O 3 –PbTiO 3 near morphotropic phase boundary

According to consideration on the average radius of B-site cation of BiMeO 3 , we reported that the Bi(Mg 0.5 Zr 0.5 )O 3 –xPbTiO 3 compound at the morphotropic phase boundary (MPB) of x=0.58 possesses a piezoelectric coefficient d33 as high as 306 pC/N. The optimal piezoelectric and ferroelectric properties near the MPB might be attributed to its lower lattice distortion, as described by change of FWHM value for {1 1 1}PC peaks. Furthermore, Bi(Mg 0.5 Zr 0.5 )O 3 –xPbTiO 3 displayed stable ferroelectric and piezoelectric properties over a temperature range from ambient temperature to above 160 °C, as exhibited by temperature dependence polarization and strain versus electric field curves and thermal depoling process.

36 MATERIALS SCIENCE↗
DOE OSTI2020

In Situ Strain Evolution on Pt Nanoparticles during Hydrogen Peroxide Decomposition

Fundamental understanding of structural changes during catalytic reactions is crucial to understanding the underlying mechanisms and optimizing efficiencies. Surface energy and related catalytic mechanisms are widely studied. However, the catalyst lattice deformation induced by catalytic processes is not well understood. Here, we study the strain in an individual platinum (Pt) nanoparticle (NP) using Bragg coherent diffraction imaging under in situ oxidation and reduction reactions. When Pt NPs are exposed to H 2 O 2 , a typical oxidizer and an intermediate during the oxygen reduction reaction process, alternating overall strain distribution near the surface and inside the NP is observed at the (111) Bragg reflection. In contrast, relatively insignificant changes appear in the (200) reflection. Density functional theory calculations are employed to rationalize the anisotropic lattice strain in terms of induced stress by H 2 O 2 adsorption and decomposition on the Pt NP surface. Our study provides deeper insight into the activity-structure relationship in this system.

3D imaging↗
DOE OSTI2016

Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells

Here, we demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300-865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO 2 . Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm 2 is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 10 3 cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%.

14 SOLAR ENERGY↗
DOE OSTI2014

Electronic structure and thermoelectric properties of orthorhombic SrLiAs

The electronic structure and the transport properties of orthorhombic SrLiAs were investigated using first-principles calculations and the semiclassical Boltzmann theory. It is found that the electrical conductivity along the y-direction is higher than those along other two directions, which is most likely originated from the covalent ladder-like structure formed by the Li and As atoms. Moreover, the transport properties of n-type SrLiAs are better than those of p-type one, due to the large band dispersion along the y-direction near the Fermi level. Further, the value of power factor with respect to relaxation time achieves 9.2 × 10{sup 11} W K{sup −2} m{sup −1} s{sup −1} for n-type SrLiAs along the y-direction at 1000 K with an optimal carrier concentration of 6.5 × 10{sup 20 }cm{sup −3}. The obtained minimum lattice thermal conductivity is comparable to those of other Zintl phase compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Generalized representative structures for atomistic systems

A new method is presented to generate atomic structures that reproduce the essential characteristics of arbitrary material systems, phases, or ensembles. Previous methods allow one to reproduce the essential characteristics (e.g. the chemical disorder) of a large random alloy within a small crystal structure. The ability to generate small representations of random alloys, along with the restriction to crystal systems, results from using the fixed-lattice cluster correlations to describe structural characteristics. A more general description of the structural characteristics of atomic systems is obtained using complete sets of atomic environment descriptors. These are used within for generating representative atomic structures without restriction to fixed lattices. A general data-driven approach is provided here utilizing the atomic cluster expansion (ACE) basis. The N-body ACE descriptors are a complete set of atomic environment descriptors that span both chemical and spatial degrees of freedom and are used within for describing atomic structures. The generalized representative structure (GRS) method presented within generates small atomic structures that reproduce ACE descriptor distributions corresponding to arbitrary structural and chemical complexity. It is shown that systematically improvable representations of crystalline systems on fixed parent lattices, amorphous materials, liquids, and ensembles of atomic structures may be produced efficiently through optimization algorithms. With the GRS method, we highlight reduced representations of atomistic machine-learning training datasets that contain similar amounts of information and small 40–72 atom representations of liquid phases. The ability to use GRS methodology as a driver for informed novel structure generation is also demonstrated. The advantages over other data-driven methods and state-of-the-art methods restricted to high-symmetry systems are highlighted.

atomic cluster expansion↗