543 research outputs found
Nearly defect-free dynamical models of disordered solids: The case of amorphous silicon
It is widely accepted in the materials modeling community that defect-free
realistic networks of amorphous silicon cannot be prepared by quenching from a
molten state of silicon using classical or ab initio molecular-dynamics (MD)
simulations. In this work, we address this long-standing problem by producing
nearly defect-free ultra-large models of amorphous silicon, consisting of up to
half-a-million atoms, using classical molecular-dynamics simulations. The
structural, topological, electronic, and vibrational properties of the models
are presented and compared with experimental data. A comparison of the models
with those obtained from using the modified Wooten-Winer-Weaire bond-switching
algorithm shows that the models are on par with the latter, which were
generated via event-based total-energy relaxations of atomistic networks in the
configuration space. The MD models produced in this work represent the highest
quality of amorphous-silicon networks so far reported in the literature using
molecular-dynamics simulations.Comment: 8 pages, 8 figure
One possible explanation for the α* relation in non-crystalline materials
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43032/1/10855_2004_Article_BF00719868.pd
Atom probe characterisation of segregation driven Cu and Mn-Ni-Si co-precipitation in neutron irradiated T91 tempered-martensitic steel
The T91 grade and similar 9Cr tempered-martensitic steels (also known as
ferritic-martensitic) are leading candidate structural alloys for fast fission
nuclear and fusion power reactors. At low temperatures (300 to 400 C)
neutron irradiation hardens and embrittles these steels, therefore it is
important to investigate the origin of this mode of life limiting property
degradation. T91 steel specimens were separately neutron irradiated to 2.14 dpa
at 327 C and 8.82 dpa at 377 C in the Idaho National Laboratory
Advanced Test Reactor. Atom probe tomography was used to investigate the
segregation driven formation of Mn-Ni-Si-rich (MNSPs) and Cu-rich (CRP)
co-precipitates. The precipitates increase in size and, slightly, in volume
fraction at the higher irradiation temperature and dose, while their
corresponding compositions were very similar, falling near the Si(Mn,Ni) phase
field in the Mn-Ni-Si projection of the Fe-based quaternary phase diagram.
While the structure of the precipitates has not been characterized, this
composition range is distinctly different than that of the typically cited
G-phase. The precipitates are composed of CRP with MNSP appendages. Such
features are often observed in neutron irradiated reactor pressure vessel (RPV)
steels. However, the Si, Ni, Mn, P and Cu solutes concentrations are lower in
the T91 than in typical RPV steels. Thus, in T91 precipitation primarily takes
place in solute segregated regions of line and loop dislocations. These results
are consistent with the model for radiation induced segregation driven
precipitation of MNSPs proposed by Ke et al. Cr-rich alpha prime (')
phase formation was not observed.Comment: Pre-print (not peer reviewed
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Morphological Evolution and Dealloying During Corrosion of Ni20Cr (wt.%) in Molten FLiNaK Salts
The dealloying corrosion behavior of the FCC Ni20Cr (wt%) in molten LiF-NaF-KF (FLiNaK) salts at 600 °C under varying applied potentials was investigated. Using in-operando electrochemical techniques and a multi-modal suite of characterization methods, we connect electrochemical potential, thermodynamic stability, and electro-dissolution kinetics to the corrosion morphologies. Notably, under certain potential regimes, a micron-scale bicontinuous structure, characterized by a network of interconnected pores and ligaments riched with the composition of the more noble (MN) element, becomes prominent. At other potentials both MN and less noble (LN) elements dealloy but at different rates. The dealloying process consists of lattice and grain boundary diffusion of Cr to the metal/salt interface, interphase Cr oxidation, accompanied by surface diffusion of Ni to form interconnected ligaments. At higher potentials, the bicontinuous porous structure undergoes further surface coarsening. Concurrently, Cr(II), Cr(III), and Ni(II) begin to dissolve, with the dissolution of Ni occurring at a significantly slower rate. When solid-state transport of Cr is exceeded by the interfacial rates, dealloying depths are limited
Posterior translacrimal approach to the maxillary sinus
Background:
This study aimed to compare the view into the maxillary sinus using the posterior translacrimal approach compared with grade 3 antrostomy.
Methods:
Grade 3 antrostomy followed by a posterior translacrimal approach was performed on four cadavers. The maximum intramaxillary view was documented endoscopically guided by electromagnetic navigation. Representative screenshots were evaluated in a blinded manner by three independent sinus surgeons. In addition, a prospective investigation of specific complications in the post-operative course of consecutive patients was performed.
Results:
In the cadaver study, the posterior translacrimal approach provided a significantly better view into the maxillary sinus compared with grade 3 antrostomy. In the clinical study, only 1 out of 20 patients reported on a minor problem with lacrimal drainage at 6 months.
Conclusion:
The posterior translacrimal approach to visualising the maxillary sinus should be considered a strong alternative to more radical techniques
Design and Bolometer Characterization of the SPT-3G First-year Focal Plane
During the austral summer of 2016-17, the third-generation camera, SPT-3G,
was installed on the South Pole Telescope, increasing the detector count in the
focal plane by an order of magnitude relative to the previous generation.
Designed to map the polarization of the cosmic microwave background, SPT-3G
contains ten 6-in-hexagonal modules of detectors, each with 269 trichroic and
dual-polarization pixels, read out using 68x frequency-domain multiplexing.
Here we discuss design, assembly, and layout of the modules, as well as early
performance characterization of the first-year array, including yield and
detector properties.Comment: Conference proceeding for Low Temperature Detectors 2017. Accepted
for publication: 27 August 201
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