3,792 research outputs found
A combined XAS and XRD Study of the High-Pressure Behaviour of GaAsO4 Berlinite
Combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD)
experiments have been carried out on GaAsO4 (berlinite structure) at high
pressure and room temperature. XAS measurements indicate four-fold to six-fold
coordination changes for both cations. The two local coordination
transformations occur at different rates but appear to be coupled. A reversible
transition to a high pressure crystalline form occurs around 8 GPa. At a
pressure of about 12 GPa, the system mainly consists of octahedral gallium
atoms and a mixture of arsenic in four-fold and six-fold coordinations. A
second transition to a highly disordered material with both cations in six-fold
coordination occurs at higher pressures and is irreversible.Comment: 8 pages, 5 figures, LaTeX2
Dipole-quadrupole interactions and the nature of phase III of compressed hydrogen
A new class of strongly infrared active structures is identified for phase
III of compressed molecular H2 by constant-pressure ab initio molecular
dynamics and density-functional perturbation calculations. These are planar
quadrupolar structures obtained as a distortion of low-pressure quadrupolar
phases, after they become unstable at about 150 GPa due to a zone-boundary soft
phonon. The nature of the II-III transition and the origin of the IR activity
are rationalized by means of simple electrostatics, as the onset of a
stabilizing dipole-quadrupole interaction.Comment: 4 pages, 3 figures. To appear in Phys. Rev. Let
#Globalhealth Twitter Conversations on #Malaria, #HIV, #TB, #NCDS, and #NTDS: a Cross-Sectional Analysis
Perturbation theory of the dynamic inverse spin Hall effect with charge conservation
We present gauge-invariant theory of the dynamic inverse spin Hall effect
driven by the spin--orbit interaction in metallic systems. Charge conservation
is imposed diagrammatically by including vertex corrections. We show the charge
current is induced by an effective electric field that is proportional to the
spin current pumped by the magnetization dynamics. The result is consistent
with recent experiments.Comment: 16pages, 5figure
Pedagogical demonstration of twitter data analysis: A case study of world AIDS day, 2014
As a pedagogical demonstration of Twitter data analysis, a case study of HIV/AIDS-related tweets around World AIDS Day, 2014, was presented. This study examined if Twitter users from countries with various income levels responded differently to World AIDS Day. The performance of support vector machine (SVM) models as classifiers of relevant tweets was evaluated. A manual coding of 1,826 randomly sampled HIV/AIDS-related original tweets from November 30 through December 2, 2014 was completed. Logistic regression was applied to analyze the association between the World Bank-designated income level of users’ self-reported countries and Twitter contents. To identify the optimal SVM model, 1278 (70%) of the 1826 sampled tweets were randomly selected as the training set, and 548 (30%) served as the test set. Another 180 tweets were separately sampled and coded as the held-out dataset. Compared with tweets from low-income countries, tweets from the Organization for Economic Cooperation and Development countries had 60% lower odds to mention epidemiology (adjusted odds ratio, aOR = 0.404; 95% CI: 0.166, 0.981) and three times the odds to mention compassion/support (aOR = 3.080; 95% CI: 1.179, 8.047). Tweets from lower-middle-income countries had 79% lower odds than tweets from low-income countries to mention HIV-affected sub-populations (aOR = 0.213; 95% CI: 0.068, 0.664). The optimal SVM model was able to identify relevant tweets from the held-out dataset of 180 tweets with an accuracy (F1 score) of 0.72. This study demonstrated how students can be taught to analyze Twitter data using manual coding, regression models, and SVM models
GARIMAS 1 - GAlapagos RIft MAssive Sulphides : Cruise 32 of MS SONNE, 09.05.-09.07.1984 ; cruise report
First Principles Calculation of Elastic Properties of Solid Argon at High Pressures
The density and the elastic stiffness coefficients of fcc solid argon at high
pressures from 1 GPa up to 80 GPa are computed by first-principles
pseudopotential method with plane-wave basis set and the generalized gradient
approximation (GGA). The result is in good agreement with the experimental
result recently obtained with the Brillouin spectroscopy by Shimizu et al.
[Phys. Rev. Lett. 86, 4568 (2001)]. The Cauchy condition was found to be
strongly violated as in the experimental result, indicating large contribution
from non-central many-body force. The present result has made it clear that the
standard density functional method with periodic boundary conditions can be
successfully applied for calculating elastic properties of rare gas solids at
high pressures in contrast to those at low pressures where dispersion forces
are important.Comment: 4 pages, 5 figures, submitted to PR
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