3,838 research outputs found
Modeling field evaporation degradation of metallic surfaces by first principles calculations: A case study for Al, Au, Ag, and Pd
Indexación: Scopus.Under the effects of an extreme electric field, the atoms on a metallic surface evaporate by breaking their bonds with the surface. In this work, we present the effects of a high electric field, by the use of computational simulations, for different metallic surface chemistries: Al, Au, Ag, and Pd. To model this bond breaking procedrure (i.e. field evaporation), we use density functional theory through the Quantum-Espresso (QE) simulation package, which incorporates the electric fields by adding a saw-like funcion into the Hamiltonian. This approach, known as dipole correction, was applied to all simulations as is implemented in the QE package. In this work, we calculate the evaporation field (Fe ) for all metallic species, which corresponds to the mean field at which atoms can break their bonds from the surface and evaporate. This result is compared with experimantal data from Atom Probe Tomography (APT) and computational data from prior simulations. © Published under licence by IOP Publishing Ltd.This work was supported by the Proyecto FONDECYT Iniciación 11130501. JP Also acknowledges partial support from Proyecto FONDECYT Regular 1140514 and Proyecto UAB-775. CL acknowledges support from Proyecto FONDECYT Iniciación 11150279, Proyecto PAI-79140025, and Proyecto DI-1350-16/R.https://iopscience.iop.org/article/10.1088/1742-6596/1043/1/01203
Impact of extreme electrical fields on charge density distributions in Al3Sc alloy
Indexación: Web of Science.In this study, the authors investigated how extreme electrical fields affect charge distribution of metallic surfaces and bond character at the moment of evaporation. The surface structure and neighborhood chemistry were also studied as a function of various field evaporation pathways. Density functional theory (DFT) was used to model the surface bonding and charge distribution and then correlate the DFT results with experimental results by comparing the calculated evaporation fields with atom probe tomography measurements. The evaporation fields of different surface neighborhood chemistries in L1(2)-Al3Sc were calculated, with the Sc atoms occupying the corners of a cubic unit cell and the Al atoms occupying the face centers. Al-Al surface atoms are found via DFT to be more likely to evaporate as dimers because of the Al-Al shared charge density. In contrast, Al-Sc evaporates as single ions due to the increased density localized around the Sc atom. This difference in evaporation behavior correlates with the resistance to degradation under extreme fields. This work allows better interpretation of the atom probe data by clarifying the relationship between different evaporation events and the role of surface and subsurface chemistry. (C) 2016 Author(s).http://avs.scitation.org/doi/10.1116/1.496483
Theory and design of InGaAsBi mid-infrared semiconductor lasers: type-I quantum wells for emission beyond 3 m on InP substrates
We present a theoretical analysis and optimisation of the properties and
performance of mid-infrared semiconductor lasers based on the dilute bismide
alloy InGaAsBi, grown on conventional (001) InP
substrates. The ability to independently vary the epitaxial strain and emission
wavelength in this quaternary alloy provides significant scope for band
structure engineering. Our calculations demonstrate that structures based on
compressively strained InGaAsBi quantum wells (QWs)
can readily achieve emission wavelengths in the 3 -- 5 m range, and that
these QWs have large type-I band offsets. As such, these structures have the
potential to overcome a number of limitations commonly associated with this
application-rich but technologically challenging wavelength range. By
considering structures having (i) fixed QW thickness and variable strain, and
(ii) fixed strain and variable QW thickness, we quantify key trends in the
properties and performance as functions of the alloy composition, structural
properties, and emission wavelength, and on this basis identify routes towards
the realisation of optimised devices for practical applications. Our analysis
suggests that simple laser structures -- incorporating
InGaAsBi QWs and unstrained ternary
InGaAs barriers -- which are compatible with established
epitaxial growth, provide a route to realising InP-based mid-infrared diode
lasers.Comment: Submitted versio
Grand challenges in marine conservation and sustainable use
This document is protected by copyright and was first published by Frontiers. All rights reserved. It is reproduced with permission.Open access journa
DIVERSITY AND VIRULENCE OF SOYBEAN CYST NEMATODE (\u3ci\u3eHeterodera glycines\u3c/i\u3e Ichinohe) IN NEBRASKA
Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is one of the most economically important soybean pathogens in the United States. Best management practices are the use of resistant cultivars and crop rotation. Though there are several genetic sources of SCN resistance, most of the SCN-resistant cultivars are derived from a single resistance source (PI 88788). Other states have reported an increase in virulence to PI 88788 due to prolonged use of this resistance. In this thesis, two studies were conducted to characterize the diversity and virulent phenotypes of SCN populations in Nebraska.
The first study assessed the virulent phenotypes of SCN field populations and their diversity in Nebraska by conducting HG type tests on 118 populations from 36 soybean-producing counties. 46.6%, 29.7%, and 88.1% of populations were virulent on PI 88788, Peking, and PI 548316 resistance respectively. No populations were virulent on PI 437654 (Hartwig). Virulence to PI 88788, PI 209332, and PI 548316 was common and found in nearly every county. Many counties also had populations virulent on Peking, PI 90763, and PI 89772.
The second study investigated the mitochondrial diversity of SCN in Nebraska as well as the diversity within a field. Previous work examining the haplotype diversity of SCN using CO1 mitochondrial markers found low diversity and two primary haplotypes – one common and found throughout the U.S. while the second, the MNNE haplotype, was only found in Minnesota and northeast Nebraska. Markers were developed to determine if there is association of the MNNE haplotype with HG type and the incidence of the MNNE haplotype in Nebraska. No association was found between the MNNE haplotype and HG type. Populations from the original Nebraska field did not contain the MNNE haplotype, however it was confirmed to be in the original isolates suggesting the MNNE haplotype is found at very low frequencies in the field. Information on virulence and diversity of SCN in Nebraska will provide insight for development and selection of SCN resistant cultivars.
Advisor: Loren J. Giesle
Setting standards for statistical sampling in auditing
https://egrove.olemiss.edu/dl_proceedings/1069/thumbnail.jp
An extreme rotation measure in the high-redshift radio galaxy PKS B0529-549
We present the results of a radio polarimetric study of the high-redshift
radio galaxy PKS B0529-549 (z=2.575), based on high-resolution 12 mm and 3 cm
images obtained with the Australia Telescope Compact Array (ATCA). The source
is found to have a rest-frame Faraday rotation measure of -9600 rad m^{-2}, the
largest seen thus far in the environment of a z > 2 radio galaxy. In addition,
the rest-frame Faraday dispersion in the screen responsible for the rotation is
calculated to be 5800 rad m^{-2}, implying rotation measures as large as -15400
rad m^{-2}. Using supporting near-IR imaging from the Very Large Telescope
(VLT), we suggest that the rotation measure originates in the Ly-alpha halo
surrounding the host galaxy, and estimate the magnetic field strength to be ~10
microGauss. We also present a new optical spectrum of PKS B0529-549 obtained
with the New Technology Telescope (NTT), and propose that the emission-line
ratios are best described by a photoionization model. Furthermore, the host
galaxy is found to exhibit both hot dust emission at 8.0 microns and
significant internal visual extinction (~1.6 mag), as inferred from Spitzer
Space Telescope near/mid-IR imaging.Comment: 12 pages, 6 figures, accepted for publication in MNRA
- …