Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “conducting structure”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

The time development of a blast wave with shock heated electrons

Accurate approximations are presented for the time development of both edge conditions and internal structures of a blast wave with shock heated electrons, and equal ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform ambient density case) and have negligible external pressure. Account is taken of possible saturation of the thermal conduction flux. The structures evolve smoothly to the adiabatic structures.

Edgar, R. J.↗
NASA NTRS1984

The time development of a blast wave with shock-heated electrons

Accurate approximations are presented for the time development of both edge conditions and internal structures of a blast wave with shock heated electrons, and equal ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform ambient density case) and have negligible external pressure. Account is taken of possible saturation of the thermal conduction flux. The structures evolve smoothly to the adiabatic structures.

Edgar, R. J.↗
DOE OSTI2015

Mechanical properties of niobium radio-frequency cavities

Radio-frequency cavities made of bulk niobium are one of the components used in modern particle accelerators. The mechanical stability is an important aspect of cavity design, which typically relies on finite-element analysis simulations using material properties from tensile tests on sample. This contribution presents the results of strain and resonant frequency measurements as a function of a uniform pressure up to 722 kPa, applied to single-cell niobium cavities with different crystallographic structure, purity and treatments. In addition, burst tests of high-purity multi-cell cavities with different crystallographic structure have been conducted up to the tensile strength of the material. Finite-element analysis of the single-cell cavity geometry is in good agreement with the observed behavior in the elastic regime assuming a Young's modulus value of 88.5 GPa and a Poisson's ratio of 0.4, regardless of crystallographic structure, purity or treatment. However, the measured yield strength and tensile strength depend on crystallographic structure, material purity and treatment. In particular, the results from this study show that the mechanical properties of niobium cavities with large crystals are comparable to those of cavities made of fine-grain niobium.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characteristics of the Li{sup +}-Ion Conductivity of Li{sub 3}R{sub 2}(PO{sub 4}){sub 3} Crystals (R = Fe, Sc) in the Superionic State

The characteristics of Li+-ion conductivity σdc of structural γ modifications of Li{sub 3}R{sub 2}(PO{sub 4}){sub 3} compounds (R = Fe, Sc) existing in the superionic state have been investigated by impedance spectroscopy. The type of structural framework [R{sub 2}P{sub 3}O{sub 12}]{sub ∞}{sup 3-} affects the σdc value and the σdc activation enthalpy in these compounds. The ion transport activation enthalpy in γ-Li{sub 3}R{sub 2}(PO{sub 4}){sub 3} (ΔH{sub σ} = 0.31 ± 0.03 eV) is lower than in γ-Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} (ΔH{sub σ} = 0.36 ± 0.03 eV). The conductivity of γ-Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} (σ{sub dc} = 0.02 S/cm at 573 K) is twice as high as that of γ-Li{sub 3}R{sub 2}(PO{sub 4}){sub 3}. A decrease in temperature causes a structural transformation of Li{sub 3}R{sub 2}(PO{sub 4}){sub 3} from the superionic γ modification (space group Pcan) through the intermediate metastable β modification (space group P2{sub 1}/n) into the “dielectric” α modification (space group P2{sub 1}/n). Upon cooling, σdc for both phosphates decreases by a factor of about 100 at the superionic TSIC transition. In Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} σdc gradually decreases in the temperature range T{sub SIC} = 430–540 K, whereas in Li{sub 3}R{sub 2}(PO{sub 4}){sub 3} σdc undergoes a jump at T{sub SIC} = 540 ± 25 K. Possible crystallochemical factors responsible for the difference in the σdc and ΔH{sub σ} values and the thermodynamics and kinetics of the superionic transition for Li{sub 3}R{sub 2}(PO{sub 4}){sub 3} are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic structure of the quadrupolar ordered heavy-fermion compound YbRu 2 Ge 2 measured by angle-resolved photoemission

We studied the electronic structure of the heavy-fermion compound Yb(Ru 1–x Rh x ) 2 Ge 2 with x = 0 and nominally x = 0.125 using ARPES and LDA calculations. We find a valence band structure of Yb corresponding to a noninteger valence close to 3+. The three observed crystal electric field levels with a splitting of 32 and 75 meV confirm the suggested configuration with a quasiquartet ground state. The experimentally determined band structure of the conduction electrons with predominantly Ru 4d character is well reproduced by our calculations. YbRu 2 Ge 2 undergoes a nonmagnetic phase transition into a ferroquadrupolar ordered state below 10.2 K and then to an antiferromagnetically ordered state below 6.5 K. A small hole Fermi surface shows nesting features in our calculated band structure and its size determined by ARPES is close to the magnetic ordering wave vector found in neutron scattering. The transitions are suppressed when YbRu 2 Ge 2 is doped with 12.5% Rh. In conclusion, the electron doping leads to a shift of the band structure and successive Lifshitz transitions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of pressure on the interlayer transport and the electronic structure in the organic quasi-two-dimensional bilayer metal θ-(BETS){sub 4}HgBr{sub 4}(C{sub 6}H{sub 5}Cl)

The behavior of the interlayer resistance and the magnetoresistance in the organic quasi-twodimensional bilayer metal θ-(BETS){sub 4}HgBr{sub 4}(C{sub 6}H{sub 5}Cl) is studied at normal pressure and a hydrostatic pressure of 10 kbar. The interlayer transport under atmospheric pressure is found to occur in an incoherent mode. The applied pressure does not change the electronic structure of the conducting layers and causes a transition to a weakly coherent mode at low temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Mo Atom Rearrangement Drives Layer-Dependent Reactivity in Two-Dimensional MoS 2

Two-dimensional (2D) materials offer a valuable platform for manipulating and studying chemical reactions at the atomic level, owing to the ease of controlling their microscopic structure at the nanometer scale. While extensive research has been conducted on the structure-dependent chemical activity of 2D materials, the influence of structural transformation during the reaction has remained largely unexplored. In this work, we report the layer-dependent chemical reactivity of MoS 2 during a nitridation atomic substitution reaction and attribute it to the rearrangement of Mo atoms. Our results show that the chemical reactivity of MoS 2 decreases as the number of layers is reduced in the few-layer regime. In particular, monolayer MoS 2 exhibits significantly lower reactivity compared with its few-layer and multilayer counterparts. Atomic-resolution transmission electron microscopy (TEM) reveals that MoN nanonetworks form as reaction products from monolayer and bilayer MoS 2 , with the continuity of the MoN crystals increasing with layer number, consistent with the local conductivity mapping data. The layer-dependent reactivity is attributed to the relative stability of the hypothetically formed MoN phase, which retains the number of Mo atomic layers present in the precursor. Specifically, the low chemical reactivity of monolayer MoS 2 is attributed to the high energy cost associated with Mo atom diffusion and migration necessary to form multilayer Mo lattices in the thermodynamically stable MoN phase. In conclusion, this study underscores the critical role of lattice rearrangement in governing chemical reactivity and highlights the potential of 2D materials as versatile platforms for advancing the understanding of materials chemistry at the atomic scale.

Chemical reactivity↗
NASA NTRS2005

Utilization of the Building-Block Approach in Structural Mechanics Research

In the last 20 years NASA has worked in collaboration with industry to develop enabling technologies needed to make aircraft safer and more affordable, extend their lifetime, improve their reliability, better understand their behavior, and reduce their weight. To support these efforts, research programs starting with ideas and culminating in full-scale structural testing were conducted at the NASA Langley Research Center. Each program contained development efforts that (a) started with selecting the material system and manufacturing approach; (b) moved on to experimentation and analysis of small samples to characterize the system and quantify behavior in the presence of defects like damage and imperfections; (c) progressed on to examining larger structures to examine buckling behavior, combined loadings, and built-up structures; and (d) finally moved to complicated subcomponents and full-scale components. Each step along the way was supported by detailed analysis, including tool development, to prove that the behavior of these structures was well-understood and predictable. This approach for developing technology became known as the "building-block" approach. In the Advanced Composites Technology Program and the High Speed Research Program the building-block approach was used to develop a true understanding of the response of the structures involved through experimentation and analysis. The philosophy that if the structural response couldn't be accurately predicted, it wasn't really understood, was critical to the progression of these programs. To this end, analytical techniques including closed-form and finite elements were employed and experimentation used to verify assumptions at each step along the way. This paper presents a discussion of the utilization of the building-block approach described previously in structural mechanics research and development programs at NASA Langley Research Center. Specific examples that illustrate the use of this approach are included from recent research and development programs for both subsonic and supersonic transports.

Rouse, Marshall↗
DOE OSTI2015

Features of high-frequency measurements of the impedance of metal-insulator-semiconductor structures with an ultrathin oxide

The possibilities of using the data of high-frequency measurements of the impedance of metal-oxide-semiconductor structures with an ultrathin insulating layer for determining the parameters of the semiconductor and the tunneling characteristics of the insulator are considered. If the accuracy of the experiment makes it possible to record both the active and reactive impedance components, the thickness of the surface depletion layer, the resistance of the semiconductor base portion, the differential tunnel conductivity of the insulating layer, and the differential tunneling-stimulated current of the generation of electron-hole pairs are calculated using the values of the capacitance and conduction of the structure measured at two frequencies. In the case, where the values of the active component of the impedance is beyond the accuracy of measurements, analysis of the parameters is possible upon four-frequency organization of the experiment from the values of only the capacitances with an increased accuracy of their measurements. A test for the necessary accuracy of data of such an experiment is formulated. If the test fails, it is possible to determine only the capacitance of the surface depletion layer in the semiconductor and, in this case, it is sufficient to implement only the single-frequency experiment.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Influence of fiber packing structure on permeability

The study on the permeability of an aligned fiber bundle is the key building block in modeling the permeability of advanced woven and braided preforms. Available results on the permeability of fiber bundles in the literature show that a substantial difference exists between numerical and analytical calculations on idealized fiber packing structures, such as square and hexagonal packing, and experimental measurements on practical fiber bundles. The present study focuses on the variation of the permeability of a fiber bundle under practical process conditions. Fiber bundles are considered as containing openings and fiber clusters within the bundle. Numerical simulations on the influence of various openings on the permeability were conducted. Idealized packing structures are used, but with introduced openings distributed in different patterns. Both longitudinal and transverse flow are considered. The results show that openings within the fiber bundle have substantial effect on the permeability. In the longitudinal flow case, the openings become the dominant flow path. In the transverse flow case, the fiber clusters reduce the gap sizes among fibers. Therefore the permeability is greatly influenced by these openings and clusters, respectively. In addition to the porosity or fiber volume fraction, which is commonly used in the permeability expression, another fiber bundle status parameter, the ultimate fiber volume fraction, is introduced to capture the disturbance within a fiber bundle.

Cai, Zhong↗
DOE OSTI2013

Purification and SAXS Analysis of the Integrin Linked Kinase, PINCH, Parvin (IPP) Heterotrimeric Complex

The heterotrimeric protein complex containing the integrin linked kinase (ILK), parvin, and PINCH proteins, termed the IPP complex, is an essential component of focal adhesions, where it interacts with many proteins to mediate signaling from integrin adhesion receptors. Here we conduct a biochemical and structural analysis of the minimal IPP complex, comprising full-length human ILK, the LIM1 domain of PINCH1, and the CH2 domain of α-parvin. We provide a detailed purification protocol for IPP and show that the purified IPP complex is stable and monodisperse in solution. Using small-angle X-ray scattering (SAXS), we also conduct the first structural characterization of IPP, which reveals an elongated shape with dimensions 120×60×40 Å. Flexibility analysis using the ensemble optimization method (EOM) is consistent with an IPP complex structure with limited flexibility, raising the possibility that inter-domain interactions exist. However, our studies suggest that the inter-domain linker in ILK is accessible and we detect no inter-domain contacts by gel filtration analysis. This study provides a structural foundation to understand the conformational restraints that govern the IPP complex.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Characterization of LiFePO{sub 4} cathode by addition of graphene for lithium ion batteries

The improvement of LiFePO{sub 4} (LFP) cathode performance has been performed by addition of Graphene (LFP+Graphene). The cathode was prepared from the active material with 5 wt % graphene and 10 wt % polyvinylidene fluoride in an n-methyl pyrrolidone solvent. Another cathode material used only 5% artificial graphite for comparison (LFP+Graphite). The crystal structure, microstructure, electronic conductivity, electrochemical impedance spectroscopy (EIS) of the cathodes were characterized by X-ray diffraction, SEM, and Impedance spectroscopy, respectively. Two half cell coin batteries were assembled using a lithium metal as an anode and LiPf{sub 6} as an electrolyte, and two cathodes (LFP+Graphene) and (LFP+Graphite). Charge discharge performance of battery was characterized by Battery analyser (BTS 8). The electronic conductivity of cathode with grapheme increased of about one order magnitude compared with the only cathode with graphite, namely from 1.97E-7S/cm (LFP+Graphite) to 1.92E-6S/cm (LFP+Graphene). The charge-discharge capacity after 10{sup th} cycles of LiFePO{sub 4} with graphene decreased of about 0.68% from 114.3 mAh/g to113.1 mAh/g, while LFP with graphite decreased of about 2.84% from 110.2 mAh/g to 107.1 mAh, at 0.1C-rates. It could be concluded that the addition of graphene has increased the ionic conductivity, and improved performance of the LFP lithium ion battery, such as higher capacity and better efficiency.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Structural coherence model for predicting molten salt thermal conductivity informed by the pair distribution function

To enable thermal behavior prediction and design optimization of molten salt reactors, thermal conductivity of molten salts must be characterized in terms of salt composition and temperature. Current theoretical models fail to provide consistent approximations for all halide mixtures, particularly actinide-bearing melts. This study aims to link the short-range order structure of molten salts to the mean free path of energy carriers through a simple structural coherence model informed by the partial pair distribution function. The proposed method is used to predict the thermal conductivity of 33 alkali and alkaline earth halide salts. Predictions approximate experimental measurements with a mean absolute error of 15.7% for dissociating, complexing, and actinide salts, including unary LiCl, NaCl, and MgCl 2 as well as mixtures LiF–NaF–KF (FLiNaK), LiF–BeF 2 (FLiBe), and NaCl–UCl 3 . The work provides evidence for the validity of energy carrier descriptions of molecular-level heat transfer in molten salts, with implications for improved theories of liquid energy transport in general.

Actinide mixtures↗
DOE OSTI2023

Influence of electronic transport on electrochemical performance of (Cu,Mn) 3 O 4 solid oxide fuel cell cathodes

Alkaline Earth free spinel oxides provide a potential benefit over Sr-doped perovskite-based materials commonly used as electrodes in high-temperature electrochemical energy conversion devices, e.g., solid oxide fuel cells (SOFCs). Sr-segregation is a known issue leading to performance degradation. In this study, Cu x Mn 3-x O 4 (x = 1, 1.2, and 1.5) porous electrodes were examined as SOFC cathodes using electrochemical impedance spectroscopy to investigate the oxygen reduction reaction (ORR) kinetics in relation to the material's intrinsic conductivity, the extrinsic electrode structure, and the cell test design. Similar to the electronic conducting (La,Sr)MnO 3 SOFC cathodes, the ORR kinetics of Cu x Mn 3-x O 4 spinel electrodes was governed by the oxygen adsorption and diffusion at the particle surface as well as the charge transfer at the triple phase boundaries. The overall electrode polarization resistance was highly dependent on contact density with the metallic current collector, active material particle connectivity, electrode thickness, and the intrinsic electronic materials conductivity. Here, we describe the importance of effective electronic charge transport parallel to the electrode surface in maximizing the electrochemically active electrode volume and enhancing electrode performance. We discuss an approach to optimize cell and electrode design with respect to active materials properties. This aspect is critical to ensure reliable evaluation of new materials, since laboratory-scale button-cells typically exhibit a high degree of electrode microstructure (e.g. porosity, thickness) and electrical contact density variation from sample to sample.

(Cu,Mn)3O4↗
DOE OSTI2014

Pressure-induced magnetic, structural, and electronic phase transitions in LaFeO{sub 3}: A density functional theory (generalized gradient approximation) + U study

We have investigated the behavior of orthoferrite LaFeO{sub 3} at ambient conditions and under pressure using DFT (generalized gradient approximation (GGA)) + U approach. Ground state electronic (band gap) and magnetic properties are considerably improved due to the Hubbard correction. Moreover, the experimentally observed pressure-driven phase transition, namely, the simultaneous occurrence of spin crossover, isostructural volume collapse, and drastic reduction in electrical resistance (electronic phase transition) is nicely described by GGA + U calculations. In particular, despite a sharp drop in resistance, a small band gap still remains in the low spin state indicating an insulator to semiconductor phase transition, in good agreement with the experiments but in contrast to GGA, which predicts metallic behavior in low spin state. We discuss the origin of variation in electronic structure of LaFeO{sub 3} in low spin state as obtained from GGA to GGA + U methods. These results emphasize the importance of correlation effects in describing the pressure-driven phase transition in LaFeO{sub 3} and other rare-earth orthoferrites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Water, Ion, and Proton Dynamics and Interactions in Nanoconfined Systems

The research was directed at understanding the role that nanoconfinement has on the dynamics and structure of liquids confined in nanometer size structures. Experiments were conducted using ultrafast infrared methods. The methods were two dimensional infrared (2D IR) spectroscopy and polarization pump-probe (PSPP) experiments. In addition FT-IR spectroscopy was used. To augment the experimental work, high level molecular dynamics simulations of the systems were conducted. The system used for confinement were nanoporous silica with essentially monodispersed pores. Pores of different diameters were studies, i.e., 2.5 nm to 8 nm. Water and organic liquids were investigated. The experiments were performed on a vibrational probe molecule, i.e., the CN stretch of the anion SeCN-. The 2D IR experiments measured spectral diffusion, which directly reported on the structural dynamics of the confined liquids. 2D IR was also used to perform chemical exchange measurements, which observed the formation and dissociation of molecular complexes with surface silanols. The PSPP experiments measured orientational relaxation of the probe molecule as well as it vibrational lifetime. All of the observables depended on the diameter of the pores and the type of liquid. The simulations of the observables provided detailed structural information on the structure of the confined liquids and there interactions with the surfaces. In addition to the study of the confinement in nanopores, water in hydrogels was also studied. The same experimental methods were used along with MD simulations. It was found the influence of hydrogels on water did not come from confinement of the water in the hydrogel polymer network, but rather from the interactions of the water with the individual monomers that compose the polymer. In addition, the temperature dependence of a polymer/water system was tracked from below to above the lower critical solution temperature to observe the nature of the phase separated polymer and how water responded to the phase separation.

36 MATERIALS SCIENCE↗