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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

Structure and Parameter Uncertainty in Centennial Projections of Forest Community Structure and Carbon Cycling

Secondary forest regrowth shapes community succession and biogeochemistry for decades, including in the Upper Great Lakes region. Vegetation models encapsulate our understanding of forest function, and whether models can reproduce multi‐decadal succession patterns is an indication of our ability to predict forest responses to future change. We test the ability of a vegetation model to simulate C cycling and community composition during 100 years of forest regrowth following stand‐replacing disturbance, asking (a) Which processes and parameters are most important to accurately model Upper Midwest forest succession? (b) What is the relative importance of model structure versus parameter values to these predictions? We ran ensembles of the Ecosystem Demography model v2.2 with different representations of processes important to competition for light. We compared the magnitude of structural and parameter uncertainty and assessed which sub‐model–parameter combinations best reproduced observed C fluxes and community composition. On average, our simulations underestimated observed net primary productivity (NPP) and leaf area index (LAI) after 100 years and predicted complete dominance by a single plant functional type (PFT). Out of 4,000 simulations, only nine fell within the observed range of both NPP and LAI, but these predicted unrealistically complete dominance by either early hardwood or pine PFTs. A different set of seven simulations were ecologically plausible but under‐predicted observed NPP and LAI. Parameter uncertainty was large; NPP and LAI ranged from ~0% to >200% of their mean value, and any PFT could become dominant. The two parameters that contributed most to uncertainty in predicted NPP were plant–soil water conductance and growth respiration, both unobservable empirical coefficients. We conclude that (a) parameter uncertainty is more important than structural uncertainty, at least for ED‐2.2 in Upper Midwest forests and (b) simulating both productivity and plant community composition accurately without physically unrealistic parameters remains challenging for demographic vegetation models.

canopy radiative transfer↗
DOE OSTI2017

Catalyst support structure, catalyst including the structure, reactor including a catalyst, and methods of forming same

Structures, catalysts, and reactors suitable for use for a variety of applications, including gas-to-liquid and coal-to-liquid processes and methods of forming the structures, catalysts, and reactors are disclosed. The catalyst material can be deposited onto an inner wall of a microtubular reactor and/or onto porous tungsten support structures using atomic layer deposition techniques.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Rate-sensitive and self-releasing battery cells and battery-cell structures as structural and/or energy-absorbing vehicle components

A battery system includes a load bearing structure having battery cells, or structures formed by battery cells, and at least one mechanical switch, and an electrical connection coupled with the battery cells of the load bearing structure. A battery has a rate-sensitive component that is configured to deform into a first state to provide a first reaction force under a mechanical loading of a first magnitude. The rate-sensitive component is configured to deform into a second state to provide a second reaction force under a mechanical loading of a second magnitude.

25 ENERGY STORAGE↗
DOE OSTI2015

Crystal structure, electronic structure, and photoluminescent properties of SrMoO{sub 4}:Tb{sup 3+} phosphors

Highlights: • SrMoO{sub 4}:Tb{sup 3+} phosphor samples were synthesized at different temperatures. • The crystal and electronic structures, and luminescence properties were studied. • The excitation peak shifts to red with increasing the sintering temperature. • The luminescence mechanism of SrMoO{sub 4}:Tb{sup 3+} was suggested. - Abstract: The experimental and theoretical studies of the optical properties of SrMoO{sub 4}:Tb{sup 3+} phosphors were carried out. The structural, optical, and electronical properties of the phosphors were systematically studied. The phosphor samples were crystallized at different temperatures via a sol–gel method. Excitation spectra of SrMoO{sub 4}:Tb{sup 3+} powder samples exhibited gradual red shift and luminescent intensity changed with increasing the sintering temperature. Such spectral changes depend strongly on the crystallographic properties such as lattice parameters and crystallinity. The shift of the excitation spectra is mainly ascribed to the covalent bond interaction between Mo−O bonds. An energy band model was demonstrated to describe the luminescence mechanism in the material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Quaternary Chalcogenide Semiconductors with 2D Structures: Rb 2 ZnBi 2 Se 5 and Cs 6 Cd 2 Bi 8 Te 17

In this work, two new layered compounds Rb 2 ZnBi 2 Se 5 and Cs 6 Cd 2 Bi 8 Te 17 are described. Rb 2 ZnBi 2 Se 5 crystallizes in the orthorhombic space group Pnma, with lattice parameters of a = 15.6509(17) Å, b = 4.218(8) Å, and c = 18.653(3) Å. Cs 6 Cd 2 Bi 8 Te 17 crystallizes in the monoclinic C2/m space group, with a = 28.646(6) Å, b = 4.4634(9) Å, c = 21.164(4) Å, and β = 107.65(3)°. The two structures are different and composed of anionic layers which are formed by inter connecting of BiQ 6 octahedra (Q = Se or Te) and MQ 4 (M = Zn or Cd) tetrahedra. The space between the layers hosts alkali metal as counter cations. The rubidium atoms of Rb 2 ZnBi 2 Se 5 structure can be exchanged with other cations (Cd 2+ , Pb 2+ and Zn 2+ ) in aqueous solutions forming new phases. Rb 2 ZnBi 2 Se 5 is an n-type semiconductor and exhibits an indirect band gap energy of 1.0 eV. Rb 2 ZnBi 2 Se 5 is a congruently melting compound (mp ~644 °C). The thermal conductivity of this semiconductor is very low with 0.38 W· m -1 ·K -1 at 873 K. Density functional theory (DFT) calculations suggest that the low lattice thermal conductivity of Rb 2 ZnBi 2 Se 5 is attributed to heavy Bi atom induced slow phonon velocities and large Gruneisen parameters especially in the a and c directions. The thermoelectric properties of Rb 2 ZnBi 2 Se 5 were characterized with the highest ZT value of ~0.25 at 839 K.

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

Accurate Thermochemistry of Complex Lignin Structures via Density Functional Theory, Group Additivity, and Machine Learning

A molecular-level understanding of lignin structures and bond dissociation energies could facilitate depolymerization technologies. Still, this information is currently limited due to the lack of databases and the simplification of surrogate models. Here, substitution effects on seven common linkages in lignin polymers are systematically investigated. An automated reaction network generator is employed to create a database of structures. A new group additivity (GA) model based on principal component analysis (PCA) descriptors is introduced and trained on gas-phase density functional theory data of 4100 species at the M06-2X/6-311++G(d,p) level. Hydrogen bonds, local steric, and nonaromatic ring contributions are also incorporated. Lastly, we improve the accuracy of the group additivity model to reach the G4 theory by computing a data set of 770 species at this level and using a data fusion approach.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Recent Developments in the General Atomic and Molecular Electronic Structure System

A discussion of many of the recently implemented features of GAMESS (General Atomic and Molecular Electronic Structure System) and LibCChem (the C++ CPU/GPU library associated with GAMESS) is presented. These features include fragmentation methods like the fragment molecular orbital, effective fragment potential and effective fragment molecular orbital methods, hybrid MPI/OpenMP approaches to Hartree-Fock and resolution of the identity second order perturbation theory. Many new coupled cluster theory methods have been implemented in GAMESS, as have multiple levels of density functional/tight binding theory. The role of accelerators, especially graphical processing units, is discussed in the context of the new features of LibCChem, as is the associated problem of power consumption as the power of computers increases dramatically. The process by which a complex program suite like GAMESS is maintained and developed is considered. Future developments are briefly summarized.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Bayesian Structural Time Series for Behind-the-Meter Photovoltaic Disaggregation: Preprint

Distributed photovoltaic (PV) generation often occurs ``behind the meter": a grid operator can only observe the net load, which is the sum of the gross load and distributed PV generation. This lack of observability poses a challenge to system operation at both bulk level and distribution level. The lack of real-time or near-future disaggregated estimates of gross load and PV generation will lead to over scheduling of energy production and regulation reserves, reliability constraints violations, wear and tear of controller devices, and potentially cascading failures of a system. In this paper we propose the use of a Bayesian Structural Time Series (BSTS) model with local solar irradiance measurements to disaggregate the summed PV generation and gross load signals at a downstream measurement site. BSTSs are a highly expressive model class that blends classic time series models with the powerful Bayesian state space estimation framework. Disaggregation is done probabilistically, which automatically quantifies the uncertainties of the estimated PV generation and gross load consumption. Depending on the data availability in real-time, it can be used to disaggragate PV and gross load at customer site, or can be used at the feeder level. In this paper, we focus on solving the problem at feeder level. We compare the performance of a BSTS model as well as a handful of state-of-the-art methods on a Pecan Street AMI dataset, using the National Solar Radiation Database (NSRDB) to estimate local irradiance.

Bayesian structural time series↗
DOE OSTI2019

Nuclear Structure Effects in the Hyperfine Structure of Muonic Lithium, Beryllium, and Boron

Nuclear structure corrections to hyperfine splitting of energy levels in muonic lithium, beryllium, and boron ions are calculated. Account is taken of the contributions from the two-photon exchange amplitudes, including the vacuum polarization effect, and from the one-photon amplitude, which provide corrections to the nuclear structure and recoil of order α{sup 5} and α{sup 6}. Numerical results for different parametrizations of electromagnetic form factors are compared.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Structural transitions in Pb(In 1/2 Nb 1/2 )O 3 under pressure

Here, Raman scattering, x-ray diffraction, and first-principles calculations were employed to investigate the behavior of disordered Pb(In 1/2 Nb 1/2 )O 3 (PIN) under pressure up to 50 GPa. The experiments were performed at room temperature while ab-initio calculations were carried out at 0 K. Raman spectra for disordered PIN show broad bands but a peak near the 380 cm -1 increases its intensity with pressure. The linewidth of the band at 550 cm -1 also increases with pressure, while two of the Raman peaks merge above 6 GPa. Above 16 GPa, we observe additional splitting of the band at 50 cm -1 . The pressure evolution of the diffraction patterns for PIN shows obvious splitting for Bragg peaks above 16 GPa; the results indicate a possible lowering symmetry transition. We identified that the transition at 0.5 GPa is from pseudo-cubic to orthorhombic (Pbam), the transitions at 16 GPa are isostructure transitions due to changes in linear compressibility and octahedral titling, and the transition at 30 GPa is from orthorhombic to monoclinic. First-principles calculations results indicated that ground state is Pbam with antiferrodisdortion consistent with experiment.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Comprehensive Analysis of the Interphasial and Structural Evolution over Long–Term Cycling of Ultrahigh–Nickel Cathodes in Lithium–Ion Batteries

Ultrahigh-Ni layered oxides hold great promise as high-energy-density cathodes at an affordable cost for lithium-ion batteries, yet their practical application is greatly hampered by the poor cyclability. Herein, by employing LiNi 0.94 Co 0.06 O 2 as a model cathode in a full-cell configuration, the interphasial and structural evolution processes of ultrahigh-Ni layered oxides are systematically investigated over the course of their service life (1500 cycles). By applying advanced analytic techniques (e.g., Li-isotope labeling, region-of-interest method), the dynamic chemical evolution on the cathode surface is revealed with spatial resolution, and the correlation between lattice distortion and cathode surface reactivity is established. Benefiting from in situ X-ray diffraction (XRD) analysis, the ultrahigh-Ni layered oxide is demonstrated to undergo dual-phase reaction mechanisms with huge lattice variation, which leads to a decrease in crystallinity and secondary particle pulverization. Furthermore, the critical impact of cathode surface reaction on the graphite anode–electrolyte interphase (AEI) is revealed at nanometer scale, and a universal chemical/physical evolution process of the AEI is illustrated, for the first time. Finally, the practical viability of ultrahigh-Ni layered oxides is demonstrated through Al-doping strategy. Finally, this work presents a comprehensive understanding of the structural and interphasial degradation of ultrahigh-Ni layered oxide cathodes for developing high-energy-density lithium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2015

Surface and Structural Investigation of a MnO x Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions

Abstract Catalytically active MnO x species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnO x catalysts form without supports in situ under photocatalytic conditions. Our most active 4 MnO x catalyst (∼0.84 mmol O 2 mol Mn −1 s −1 ) forms from a Mn 4 O 4 bearing a metal–organic framework. 4 MnO x is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m 2 g −1 ) and small regions of crystallinity and layer flexibility. In contrast, the S MnO x formed from Mn 2+ salt gives an amorphous species of lower surface area (80 m 2 g −1 ) and lower activity (∼0.15 mmol O 2 mol Mn −1 s −1 ). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p 3/2 core levels detects enriched Mn 3+ and Mn 2+ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.

Deibert, Benjamin J.↗
DOE OSTI2018

Distinguishing enantiomeric amino acids with chiral cyclodextrin adducts and structures for lossless ion manipulations

Enantiomeric molecular evaluations remain an enormous challenge for current analytical techniques. To date, derivatizations strategies and long separation times are generally required in these studies, and the development and implementation of new approaches is greatly desired to increase speed and distinguish currently unresolvable compounds. Herein, we describe a method using chiral cyclodextrin adducts and structures for lossless ion manipulations (SLIM) ion mobility to achieve rapid, high resolution separations of D and L enantiomeric amino acids. In the analyses, chiral cyclodextrin adducts are added to each sample. Two cyclodextrins were found to sandwich each amino acid and form host-guest noncovalent complexes that were distinct for each D and L amino acid pair studied and thus separable with ion mobility (IM) in SLIM devices. The SLIM was also used to accumulate much larger ion populations than previously feasible for evaluation and therefore allow enantiomeric measurements of higher sensitivity and resolution than previously reported by any other IM-based approach.

chiral separations, cyclodextrins, enantiomers, io↗
DOE OSTI2015

Fluid–Structure Interaction Analysis of Papillary Muscle Forces Using a Comprehensive Mitral Valve Model with 3D Chordal Structure

Numerical models of native heart valves are being used to study valve biomechanics to aid design and development of repair procedures and replacement devices. These models have evolved from simple two-dimensional approximations to complex three-dimensional, fully coupled fluid-structure interaction (FSI) systems. Such simulations are useful for predicting the mechanical and hemodynamic loading on implanted valve devices. A current challenge for improving the accuracy of these predictions is choosing and implementing modeling boundary conditions. In order to address this challenge, we are utilizing an advanced in-vitro system to validate FSI conditions for the mitral valve system. Explanted ovine mitral valves were mounted in an in vitro setup, and structural data for the mitral valve was acquired with *CT. Experimental data from the in-vitro ovine mitral valve system were used to validate the computational model. As the valve closes, the hemodynamic data, high speed lea et dynamics, and force vectors from the in-vitro system were compared to the results of the FSI simulation computational model. The total force of 2.6 N per papillary muscle is matched by the computational model. In vitro and in vivo force measurements are important in validating and adjusting material parameters in computational models. The simulations can then be used to answer questions that are otherwise not possible to investigate experimentally. This work is important to maximize the validity of computational models of not just the mitral valve, but any biomechanical aspect using computational simulation in designing medical devices.

Comprehensive Computational Model↗
DOE OSTI2019

Effects of ball milling on the structure of cotton cellulose

Cellulose is typically characterized as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding and definitive analysis remain elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 min. X-ray diffraction results were analyzed with the Rietveld method; DNP (dynamic nuclear polarization) natural abundance 2D NMR studies in the next paper in this issue assisted with the interpretation of the 1D analyses in the present work. A conventional NMR model’s paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum frequency generation (SFG) spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and field emission-scanning electron microscopy results showed the changes in particle size; molecular weight and carbonyl group analyses by gel permeation chromatography confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier transform infrared (FTIR) and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability. Although understanding of structural changes as cellulose is amorphized by ball milling is increased by this work, continued effort is needed to improve agreement between the synchrotron and laboratory X-ray methods used herein and to provide physical interpretation of the SFG results.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Modulation of Superconducting Transition Temperature in LaAlO{sub 3}/SrTiO{sub 3} by SrTiO{sub 3} Structural Domains

The tetragonal domain structure in SrTiO{sub 3} (STO) is known to modulate the normal-state carrier density in LaAlO{sub 3}/SrTiO{sub 3} (LAO/STO) heterostructures, among other electronic properties, but the effect of STO domains on the superconductivity in LAO/STO has not been fully explored. Using a scanning SQUID susceptometer microscope to map the superconducting response as a function of temperature in LAO/STO, we find that the superconducting transition temperature is spatially inhomogeneous and modulated in a pattern that is characteristic of structural domains in the STO.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Structural, Electronic, and Magnetic Properties of Binary Heusler Alloys ZCl{sub 3} (Z = Li, Na, K, Rb) with DO{sub 3}-Type Structure from First Principle Calculations

The structural, electronic, and magnetic properties of binary Heusler alloys ZCl{sub 3} (Z = Li, Na, K, Rb) with DO{sub 3}-type structure have been studied by means of the first principle calculations. The calculated results reveal that all four alloys are half-metallic (HM) materials at the stable ferromagnetic ground state. The total magnetic moments (M{sub t}) of LiCl{sub 3}, NaCl{sub 3}, KCl{sub 3,} and RbCl{sub 3} alloys are all 2.000 μ{sub B}/f.u., following the Slater-Pauling rule M{sub t} = 24 − Z{sub t} for the former two alloys, while satisfying the Slater-Pauling rule M{sub t} = 30 − Z{sub t} for the latter two alloys. The spin-up band gaps of the binary Heusler alloys ZCl{sub 3} (Z = Li, Na, K, Rb) are 5.598, 5.687, 6.744, and 6.745 eV at equilibrium lattice constants 7.076, 7.237, 7.588, and 7.819 Å, respectively. The positive cohesion energy and negative formation energy indicate that they are thermodynamically stable. Moreover, wide HM regions for binary Heusler alloys ZCl{sub 3} (Z = Li, Na, K, Rb) show their HM characters are robust when the lattices are expanded or compressed under uniform and tetragonal strains. Finally, the total charge density, magnetic charge density, and charge density difference of the (110) plane for LiCl{sub 3} alloy are analyzed in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗