SEARCH · Search NASA
Results for “Structural Effects”
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.
Physically Based Modeling of PEMFC Cathode Catalyst Layers: Effective Microstructure and Ionomer Structure–Property Relationship Impacts
Abstract This work presents a pseudo-two-dimensional proton exchange membrane fuel cell (PEMFC) model incorporating Nafion ionomer structure–property relationships in the cathode catalyst layer (CL) to capture and explain losses at low Pt loading. Structural data from neutron reflectometry and thin film Nafion conductivity measurements predict variations in the oxygen diffusion coefficient and ionic conductivity with changing CL ionomer thickness and Pt loading. By including these structure–property relationships, predicted polarization curves agree closely with previously published experimental data from cells with Pt loadings between 0.025 and 0.2 mg/cm2. Results demonstrate that structure–property relationships based on physically measurable ionomer and CL properties provide a feasible interpretation of PEMFC CL phenomena for a range of Pt loadings and help explain previously unaccounted-for losses at low Pt. Results also show that simulations must account for surface species coverage variations in order to properly capture the kinetic losses. Finally, results suggest that an increase in ionomer thickness surrounding the C/Pt surfaces may lead to improved cell performance due to improved ionic conductivity.
Purcell Effect in Tamm Plasmon Structures with QD Emitter
We study Tamm plasmon structure based on GaAs/Al{sub 0.95}GaAs distributed Bragg reflector covered by thin silver layer, with active area formed by InAs quantum dots. We have measured the spectral and angular characteristics of photoluminescence and performed theoretical calculation of the spontaneous emission rate (modal Purcell factor) in the structure by using S-quantization formalism. We show that for Tamm plasmon mode the spontaneous emission can be enhanced by more than an order of magnitude, despite absorption in metallic layer.
Effect of Epitaxial-Structure Design and Growth Parameters on the Characteristics of Metamorphic Lasers of the 1.46-μm Optical Range Based on Quantum Dots Grown on GaAs Substrates
The characteristics of lasers of the 1.44–1.46-μm optical range grown on GaAs substrates using a metamorphic buffer are studied. The active region of the laser contains 10 rows of InAs/In{sub 0.4}Ga{sub 0.6}As/In{sub 0.2}Ga{sub 0.8}As quantum dots. It is shown that the use of special selective high-temperature annealing along with the application of short-period In{sub 0.2}Ga{sub 0.8}As/In{sub 0.2}Al{sub 0.3}Ga{sub 0.5}As short-period superlattices makes it possible to substantially decrease the density of threading dislocations in the active region. A threshold current density of 1300 A cm{sup –2}, external differential quantum efficiency of 38%, and maximal pulsed-mode output power of 13 W are attained for a laser with a broad area 3 mm in length.
Effect of the Crystal Structure on the Electrical Properties of Thin-Film PZT Structures
A new method of two-stage crystallization of lead zirconate–titanate (PZT) films using a seed sublayer with a low excess lead content has been proposed and realized. A seed layer with a strong texture of perovskite Pe(111) grains is formed from a solution with a lead excess of 0–5 wt %; the fast growth of the grains is provided by the deposition of the main film from a solution with high lead content. As a result, a strong Pe(111) texture with complete suppression of the Pe(100) orientation forms. An analysis of current–voltage dependences of the transient currents and the distributions of the local conductivity measured by the contact AFM method reveals two various mechanisms of current percolation that are determined by traps in the bulk and at the perovskite grain interfaces.
Influence of Size Effects on the Electronic Structure of Hexagonal Gallium Telluride
Using methods of the density functional theory, the electronic band structure of a hexagonal modification of the layered GaTe semiconductor has been calculated. The structural parameters of a bulk crystal with the β-polytype symmetry have been determined taking into account van der Waals interactions and agree with experimental data for polycrystalline films within 2%. Estimates for the position of extrema of the upper valence band and the lower conduction band have been obtained with respect to the vacuum level for bulk β-GaTe and for ultrathin plates with the number of elementary layers ranging from 1 to 10, which corresponds to a thickness range of 0.5–8 nm. The calculations demonstrate that hexagonal GaTe is an indirect band gap semiconductor with a forbidden band width varying from 0.8 eV in the bulk material to 2.3 eV in the monolayer.
Chemical and Charge Imbalance Induced by Radionuclide Decay: Effects on Waste Form Structure
This is a technical report summarizing the experimental and theoretical results for model waste form of aluminosilicate pollucite, obtained from January to September, 2012.
Final Technical Report for DE-SC0012297
This is the final report on the work performed in award DE-SC0012297, Cosmic Frontier work in support of the LSST Dark Energy Science Collaboration's work to develop algorithms, simulations, and statistical tests to ensure optimal extraction of the dark energy properties from galaxy clusters observed with LSST. This work focused on effects that could produce a systematic error on the measurement of cluster masses (that will be used to probe the effects of dark energy on the growth of structure). These effects stem from the deviations from pure ellipticity of the gravitational lensing signal and from the blending of light of neighboring galaxies. Both these effects are expected to be more significant for LSST than for the stage III experiments such as the Dark Energy Survey. We calculate the magnitude of the mass error (or bias) for the first time and demonstrate that it can be treated as a multiplicative correction and calibrated out, allowing mass measurements of clusters from gravitational lensing to meet the requirements of LSST's dark energy investigation.
Effect of Micro-Structural Dispersity of SiMo Ductile Iron on High Temperature Performance during Static Oxidation
High silicon and molybdenum (SiMo) ductile iron is commonly used for car exhaust systems, and its micro-structural dispersity depends on intrinsic parameters, which include alloy composition and inoculation efficiency, as well as extrinsic factors, such as casting wall thickness and molding material, which define cooling rate during solidification. Micro-structural dispersity is referred to as the degree of heterogeneity of sizes of structural constituencies within the microstructure. A variation in the micro-structural dispersity could impact the high temperature performance of SiMo ductile iron during static oxidation and transient thermo-mechanical loading conditions. In this study, static high temperature tests were performed on SiMo ductile iron solidified in a casting with varying wall thicknesses from 5 mm to 100 mm. The faster solidified specimens (taken from near chilled casting surfaces) had extremely high micro-structural dispersity as compared to the thicker section samples. After thermal exposure, each of the samples were characterized using 2D sections and 3D µCT images, and the results indicated an order of magnitude difference in graphite phase dispersity. The surface degradation was quantified after static oxidation experiments were implemented at temperature intervals between 650 °C and 800 °C. Non-destructive µCT 3D analysis and SEM/EDS were performed on cross sections and used to quantify the scale topology and structure. Carbon analysis was used to decouple the scale formation and decarburization phenomena that occurred within the samples. These methods enabled the quantification of the oxidation of the SiMo cast iron with different micro-structural dispersity levels after being exposed to high temperature static oxidation. Additionally, the complex material behavior during oxidation-assisted transient thermo-mechanical loading will be presented in a separate article.
Effects of unique band structure of h -BN probed by photocurrent excitation spectroscopy
Here, by employing a photocurrent excitation spectroscopy measurement, a direct bandgap of ~6.46 eV has been resolved for the first time in thick B-10 enriched h-BN films. Together with previous band calculations, an unconventional energy diagram has been constructed to capture the unique features of h-BN: h-BN has a minimum direct bandgap of ~6.5 eV and a bandgap of ~6.1 eV which is indirect with the conduction band minimum (CBM) at M-point and valence band maximum (VBM) at K-point in the Brillouin zone, and the energy levels of the donor and acceptor impurities are measured relative to CBM and VBM, respectively.
Crystal-Field Splitting and Correlation Effect on the Electronic Structure of A2IrO3
N/A
Ionic Aggregate Structure in Ionomer Melts: Effect of Molecular Architecture on Aggregates and the Ionomer Peak.
Abstract not provided.
Ionic Aggregate Structure in Ionomer Melts: Effect of Molecular Architecture on Aggregates and the Ionomer Peak: Supplemental Information section.
Abstract not provided.
Effect of Pore-Structure on Production of Furans and Value Added Chemicals from Biomass
Explore the source record for details and available documents.
Size and synthesis effects on the crystalline structure of barium titanate.
Abstract not provided.
Neutron Irradiation Effects on the Graphitic Structure of a Fine-Grain Graphite
Explore the source record for details and available documents.
Effect of beam time structure on the neutronics of an accelerator driven subcritical reactor
N/A