2,129 research outputs found
First-principles calculation of the elastic dipole tensor of a point defect: Application to hydrogen in α-zirconium
The elastic dipole tensor is a fundamental quantity relating the elastic field and atomic structure of a point defect. We review three methods in the literature to calculate the dipole tensor and apply them to hydrogen in α -zirconium using density functional theory (DFT). The results are compared with the dipole tensor deduced from earlier experimental measurements of the λ tensor for hydrogen in α -zirconium. There are significant errors with all three methods. We show that calculation of the λ tensor, in combination with experimentally measured elastic constants and lattice parameters, yields dipole tensor components that differ from experimental values by only 10%â20%. There is evidence to suggest that current state-of-the-art DFT calculations underestimate bonding between hydrogen and α -zirconium
Near-infrared optical properties and proposed phase-change usefulness of transition metal disulfides
The development of photonic integrated circuits would benefit from a wider
selection of materials that can strongly-control near-infrared (NIR) light.
Transition metal dichalcogenides (TMDs) have been explored extensively for
visible spectrum opto-electronics, but the NIR properties of these layered
materials have been less-studied. The measurement of optical constants is the
foremost step to qualify TMDs for use in NIR photonics. Here we measure the
complex optical constants for select sulfide TMDs (bulk crystals of MoS2, TiS2
and ZrS2) via spectroscopic ellipsometry in the visible-to-NIR range. Through
Mueller matrix measurements and generalized ellipsometry, we explicitly measure
the direction of the ordinary optical axis. We support our measurements with
density functional theory (DFT) calculations, which agree with our measurements
and predict giant birefringence. We further propose that TMDs could find use as
photonic phase-change materials, by designing alloys that are thermodynamically
adjacent to phase boundaries between competing crystal structures, to realize
martensitic (i.e. displacive, order-order) switching.Comment: supplementary at end of document. 6 main figure
Scattering solutions of the spinless Salpeter equation
A method to compute the scattering solutions of a spinless Salpeter equation
(or a Schrodinger equation) with a central interaction is presented. This
method relies on the 3-dimensional Fourier grid Hamiltonian method used to
compute bound states. It requires only the evaluation of the potential at
equally spaced grid points and yields the radial part of the scattering
solution at the same grid points. It can be easily extended to the case of
coupled channel equations and to the case of non-local interactions.Comment: 7 page
Optimization tools for distance-preserving flag fault-tolerant error correction
Lookup table decoding is fast and distance preserving, making it attractive
for near-term quantum computer architectures with small-distance quantum error
correcting codes. In this work, we develop several optimization tools which can
potentially reduce the space and time overhead required for flag fault-tolerant
error correction (FTEC) with lookup table decoding on Calderbank-Shor-Steane
(CSS) codes. Our techniques include the compact lookup table construction, the
Meet-in-the-Middle technique, the adaptive time decoding for flag FTEC, the
classical processing technique for flag information, and the separated and
counting technique. We evaluate the performance of our tools using
numerical simulation of hexagonal color codes of distances 3, 5, 7, and 9 under
circuit-level noise. Combining all tools can result in more than an order of
magnitude increase in pseudothreshold for the hexagonal color code of distance
9, from to .Comment: 28 pages, 16 figure
Delayed presentation of an arteriovenous malformation after cerebellar hemangioblastoma resectionâCase report
AbstractIntroductionHaemangioblastoma has been uncommonly reported to occur in coexistence either temporally or spatially with the development of an arteriovenous malformations (AVM). We present a case of a delayed AVM following haemangioblastoma resection.Presentation of case44 year old female initially presented with a several week history of headaches, vertigo and nausea and emesis and was found to have a cystic lesion with a solid enhancing component on Magnetic Resonance Imaging (MRI) in the superior aspect of the vermis. She underwent gross total resection and final pathology was consistent with WHO grade I haemangioblastoma. One year later, patient re-presented with headaches, dizziness and left trochlear nerve palsy with rotary nystagmus. Imaging revealed a left posterior tentorial paramedian cerebellar vascular nidus with venous drainage into the left transverses sinus suspicious for arteriovenous malformation. She underwent gross total resection of the lesion. Final pathology confirmed the diagnosis of an arteriovenous malformation.DiscussionRecent research supports both haemangioblastoma and AVM are of embryologic origin but require later genetic alterations to develop into symptomatic lesions. It is unclear in our case if the AVM was present at the time of the initial haemangioblastoma resection or developed de novo after tumor resection. However, given the short time between tumor resection and presentation of AVM, de novo AVM although possible, appears less likely.ConclusionAVM and haemangioblastoma rarely presents together either temporally or spatially. We present a case of a delayed AVM following haemangioblastoma resection. More research is needed to elucidate the rare intermixture of these lesions
Deconstructing Fahr's disease/syndrome of brain calcification in the era of new genes
Introduction
There are now a number genes, known to be associated with familial primary brain calcification (PFBC), causing the so called âFahr'sâ disease or syndrome. These are SCL20A2, PDGFB, PDGFRB and XPR1. In this systematic review, we analyse the clinical and radiological features reported in genetically confirmed cases with PFBC. We have additionally reviewed pseudohypoparathyroidism which is a close differential diagnosis of PFBC in clinical presentation and is also genetically determined.
Methods
We performed a Medline search, from 1st Jan 2012 through to 7th November 2016, for publications with confirmed mutations of SCL20A2, PDGFB, PDGFRB, and XPR1 and found twenty papers with 137 eligible cases. A second search was done for publications of cases with Pseudohypoparathyroidism or pseudopseudohypoparathyroidism, and found 18 publications with 20 eligible cases.
Results
SLC20A2 was the most common gene involved with 75 out of 137 cases included with PFBC (55%) followed by PDGFB (31%) and PDGFRB (11%). Statistically significant correlation was found between the presence of parkinsonism with SLC20A2 mutations, headache in PDGFB and generalised tonic-clonic seizures in patients with pseudohypoparathyroidism.
Conclusion
We combine statistical analysis and clinical inference to suggest a diagnostic algorithm based on the observations in this study to help with investigation of a patient with neurological features and brain calcification
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