619 research outputs found
Oxygen impurities in NiAl: Relaxation effects
We have used a full-potential linear muffin-tin orbital method to calculate
the effects of oxygen impurities on the electronic structure of NiAl. Using the
supercell method with a 16-atom supercell we have investigated the cases where
an oxygen atom is substitutionally placed at either a nickel or an aluminum
site. Full relaxation of the atoms within the supercell was allowed. We found
that oxygen prefers to occupy a nickel site over an aluminum site with a site
selection energy of 138 mRy (21,370 K). An oxygen atom placed at an aluminum
site is found to cause a substantial relaxation of its nickel neighbors away
from it. In contrast, this steric repulsion is hardly present when the oxygen
atom occupies the nickel site and is surrounded by aluminum neighbors. We
comment on the possible relation of this effect to the pesting degradation
phenomenon (essentially spontaneous disintegration in air) in nickel
aluminides.Comment: To appear in Phys. Rev. B (Aug. 15, 2001
Random Dirac operators with time-reversal symmetry
Quasi-one-dimensional stochastic Dirac operators with an odd number of
channels, time reversal symmetry but otherwise efficiently coupled randomness
are shown to have one conducting channel and absolutely continuous spectrum of
multiplicity two. This follows by adapting the criteria of Guivarch-Raugi and
Goldsheid-Margulis to the analysis of random products of matrices in the group
SO, and then a version of Kotani theory for these operators. Absence of
singular spectrum can be shown by adapting an argument of Jaksic-Last if the
potential contains random Dirac peaks with absolutely continuous distribution.Comment: parts of introduction made more precise, corrections as follow-up on
referee report
Electric current circuits in astrophysics
Cosmic magnetic structures have in common that they are anchored
in a dynamo, that an external driver converts kinetic energy into internal
magnetic energy, that this magnetic energy is transported as Poynting fl ux across the magnetically dominated structure, and that the magnetic energy
is released in the form of particle acceleration, heating, bulk motion,
MHD waves, and radiation. The investigation of the electric current system is
particularly illuminating as to the course of events and the physics involved.
We demonstrate this for the radio pulsar wind, the solar flare, and terrestrial
magnetic storms
Effect of controlled disorder on quasiparticle thermal transport in BiSrCaCuO
Low temperature thermal conductivity, , of optimally-doped Bi2212 was
studied before and after the introduction of point defects by electron
irradiation. The amplitude of the linear component of remains
unchanged, confirming the universal nature of heat transport by zero-energy
quasiparticles. The induced decrease in the absolute value of at
finite temperatures allows us to resolve a nonuniversal term in due to
conduction by finite-energy quasiparticles. The magnitude of this term provides
an estimate of the quasiparticle lifetime at subkelvin temperatures.Comment: 5 pages including 2 .eps figuer
Small-polaron hopping conductivity in bilayer manganite LaSrMnO
We report anisotropic resistivity measurements on a
LaSrMnO single crystal over a temperature range
from 2 to 400 K and in magnetic fields up to 14 T. For K, the
temperature dependence of the zero-field in-plane resistivity
obeys the adiabatic small polaron hopping mechanism, while the out-of-plane
resistivity can be ascribed by an Arrhenius law with the same
activation energy. Considering the magnetic character of the polarons and the
close correlation between the resistivity and magnetization, we developed a
model which allows the determination of . The excellent
agreement of the calculations with the measurements indicates that small
polarons play an essential role in the electrical transport properties in the
paramagnetic phase of bilayer manganites.Comment: 4 pages, 3 figures, to appear in Physical Review
Vibration reduction of composite plates by piezoelectric patches using a modified artificial bee colony algorithm
Prediagnostic smoking is associated with binary and quantitative measures of ER protein and ESR1 mRNA expression in breast tumors
Background: Smoking is a possible risk factor for breast cancer and has been linked to increased risk of estrogen receptor-positive (ER+) disease in some epidemiologic studies. It is unknown whether smoking has quantitative effects on ER expression. Methods: We examined relationships between smoking and ER expression from tumors of 1,888 women diagnosed with invasive breast cancer from a population-based study in North Carolina. ER expression was characterized using binary (±) and continuous measures for ER protein, ESR1 mRNA, and a multigene luminal score (LS) that serves as a measure of estrogen signaling in breast tumors. We used logistic and linear regression models to estimate temporal and dose-dependent associations between smoking and ER measures. Results: The odds of ER+, ESR1+, and LS+ tumors among current smokers (at the time of diagnosis), those who smoked 20 or more years, and those who smoked within 5 years of diagnosis were nearly double those of nonsmokers. Quantitative levels of ESR1 were highestamong current smokers compared with never smokers overall [mean (log2) = 9.2 vs. 8.7, P > 0.05] and among ER+ cases; however, we did not observe associations betweensmokingmeasures and continuous ER protein expression. Conclusions: In relationship to breast cancer diagnosis, recent smoking was associated with higher odds of the ER+, ESR1+, and LS+ subtype. Current smoking was associated with elevated ESR1 mRNA levels and an elevated LS, but not with altered ER protein. Impact: A multigene LS and single-gene ESR1 mRNA may capture tumor changes associated with smoking
Evolving unipolar memristor spiking neural networks
© 2015 Taylor & Francis. Neuromorphic computing – brain-like computing in hardware – typically requires myriad complimentary metal oxide semiconductor spiking neurons interconnected by a dense mesh of nanoscale plastic synapses. Memristors are frequently cited as strong synapse candidates due to their statefulness and potential for low-power implementations. To date, plentiful research has focused on the bipolar memristor synapse, which is capable of incremental weight alterations and can provide adaptive self-organisation under a Hebbian learning scheme. In this paper, we consider the unipolar memristor synapse – a device capable of non-Hebbian switching between only two states (conductive and resistive) through application of a suitable input voltage – and discuss its suitability for neuromorphic systems. A self-adaptive evolutionary process is used to autonomously find highly fit network configurations. Experimentation on two robotics tasks shows that unipolar memristor networks evolve task-solving controllers faster than both bipolar memristor networks and networks containing constant non-plastic connections whilst performing at least comparably
High temperature decomposition of Cu 2 BaSnS 4 with Sn loss reveals newly identified compound Cu2Ba3Sn2S8
The earth abundant quaternary compound Cu2BaSnS4 is being currently studied as a candidate for photovoltaics and as a photocathode for water splitting. However, the chemical stability of this phase during synthesis is unclear. The synthesis of other quaternary tin sulphur based absorbers e.g., Cu2ZnSnS4 involves an annealing step at high temperature under sulphur gas atmosphere, which can lead to decomposition into secondary phases involving Sn loss from the sample. As the presence of secondary phases can be detrimental for device performance, it is crucial to identify secondary phase chemical, structural and optoelectronic properties. Here we used a combination of in situ EDXRD XRF and TEM to identify a decomposition pathway for Cu2BaSnS4. Our study reveals that, while Cu2BaSnS4 remains stable at high sulphur partial pressure, the material decomposes at high temperatures into Cu4BaS3 and the hitherto unknown compound Cu2Ba3Sn2S8 if the synthesis is performed under low partial pressure of sulphur. The presence of Cu4BaS3 in devices could be harmful due to its high conductivity and relatively lower band gap compared to Cu2BaSnS4. The analysis of powder diffraction data reveals that the newly identified compound Cu2Ba3Sn2S8 crystallizes in the cubic system space group I 43d with a lattice parameter of a 14.53 1 . A yellow powder of Cu2Ba3Sn2S8 has been synthesized, exhibiting an absorption onset at 2.19 e
The yield of head CT in syncope: a pilot study
Although head CT is often routinely performed in emergency department (ED) patients with syncope, few studies have assessed its value
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