1,676 research outputs found
Oxygen vacancy segregation and space-charge effects in grain boundaries of dry and hydrated BaZrO3
A space-charge model is applied to describe the equilibrium effects of
segregation of double-donor oxygen vacancies to grain boundaries in dry and wet
acceptor-doped samples of the perovskite oxide BaZrO3. The grain boundary core
vacancy concentrations and electrostatic potential barriers resulting from
different vacancy segregation energies are evaluated. Density-functional
calculations on vacancy segregation to the mirror-symmetric \Sigma 3 (112)
[-110] tilt grain boundary are also presented. Our results indicate that oxygen
vacancy segregation can be responsible for the low grain boundary proton
conductivity in BaZrO3 reported in the literature
Observational manifestations of solar magneto-convection -- center-to-limb variation
We present the first center-to-limb G-band images synthesized from high
resolution simulations of solar magneto-convection. Towards the limb the
simulations show "hilly" granulation with dark bands on the far side, bright
granulation walls and striated faculae, similar to observations. At disk center
G-band bright points are flanked by dark lanes. The increased brightness in
magnetic elements is due to their lower density compared with the surrounding
intergranular medium. One thus sees deeper layers where the temperature is
higher. At a given geometric height, the magnetic elements are cooler than the
surrounding medium. In the G-band, the contrast is further increased by the
destruction of CH in the low density magnetic elements. The optical depth unity
surface is very corrugated. Bright granules have their continuum optical depth
unity 80 km above the mean surface, the magnetic elements 200-300 km below. The
horizontal temperature gradient is especially large next to flux
concentrations. When viewed at an angle, the deep magnetic elements optical
surface is hidden by the granules and the bright points are no longer visible,
except where the "magnetic valleys" are aligned with the line of sight. Towards
the limb, the low density in the strong magnetic elements causes unit
line-of-sight optical depth to occur deeper in the granule walls behind than
for rays not going through magnetic elements and variations in the field
strength produce a striated appearance in the bright granule walls.Comment: To appear in ApJL. 6 pages 4 figure
TFAM forces mtDNA to make a U-turn
The mammalian mitochondrial transcription factor A (TFAM) is encoded in the nucleus and imported into mitochondria, where it functions as an activator of mtDNA transcription and packages mtDNA into DNA-protein aggregates called mitochondrial nucleoids. Two X-ray crystallography studies in this issue reveal that TFAM shapes mtDNA into a sharp U-turn, thereby providing a molecular mechanism for its dual roles in the expression and maintenance of mtDNA.VetenskapsrĂĄdetPublishe
Barriers Broken. Production Relations and Agrarian Change in South India
This book studies agrarian change and the factors which have the potential to control and direct the course of such change. Hence it deals with a fundamental issue which has a direct bearing on poverty. Based on a survey of 367 agrarian households in South India, this book systematically compares two major ecotypes in Indian agriculture: rainfed cultivation and irrigated agriculture. The authors link this ecological analysis to class relations, technology, and patterns of agriarian change, especially after the Green Revolution. They then go on to compare land and labour relations, class structures, credit and usurious relations, and agricultural productivity in these two ecotypes
Scattering Wave Functions at Bound State Poles
The normalisation relation between the bound and scattering S-state wave
functions, extrapolated to the bound state pole, is derived from the
Schroedinger equation. It is shown that, unlike previous work, the result does
not depend on the details of the potential through the corresponding Jost
function but is given uniquely in terms of the binding energy. The
generalisations to higher partial waves and one-dimensional scattering are
given.Comment: 15 pages Latex. No graph
Comparing Auditory Noise Treatment with Stimulant Medication on Cognitive Task Performance in Children with Attention Deficit Hyperactivity Disorder: Results from a Pilot Study
Background: Recent research has shown that acoustic white noise (80 dB) can improve task performance in people with attention deficits and/or Attention Deficit Hyperactivity Disorder (ADHD). This is attributed to the phenomenon of stochastic resonance in which a certain amount of noise can improve performance in a brain that is not working at its optimum. We compare here the effect of noise exposure with the effect of stimulant medication on cognitive task performance in ADHD. The aim of the present study was to compare the effects of auditory noise exposure with stimulant medication for ADHD children on a cognitive test battery. A group of typically developed children (TDC) took the same tests as a comparison. Methods: Twenty children with ADHD of combined or inattentive subtypes and twenty TDC matched for age and gender performed three different tests (word recall, spanboard and n-back task) during exposure to white noise (80 dB) and in a silent condition. The ADHD children were tested with and without central stimulant medication. Results: In the spanboard- and the word recall tasks, but not in the 2-back task, white noise exposure led to significant improvements for both non-medicated and medicated ADHD children. No significant effects of medication were found on any of the three tasks. Conclusion: This pilot study shows that exposure to white noise resulted in a task improvement that was larger than the one with stimulant medication thus opening up the possibility of using auditory noise as an alternative, non-pharmacological treatment of cognitive ADHD symptoms
Three-dimensional modeling of the Ca II H&K lines in the solar atmosphere
CHROMIS, a new imaging spectrometer at the Swedish 1-m Solar Telescope (SST),
can observe the chromosphere in the H and K lines of Ca II at high spatial and
spectral resolution. Accurate modeling as well as an understanding of the
formation of these lines are needed to interpret the SST/CHROMIS observations.
Such modeling is computationally challenging because these lines are influenced
by strong departures from local thermodynamic equilibrium, three-dimensional
radiative transfer, and partially coherent resonance scattering of photons. We
aim to model the CaII H&K lines in 3D model atmospheres to understand their
formation and to investigate their diagnostic potential for probing the
chromosphere. We model the synthetic spectrum of Ca II using the radiative
transfer code Multi3D in three different radiation-magnetohydrodynamic model
atmospheres computed with the Bifrost code. We classify synthetic intensity
profiles according to their shapes and study how their features are related to
the physical properties in the model atmospheres. We investigate whether the
synthetic data reproduce the observed spatially-averaged line shapes,
center-to-limb variation and compare with SST/CHROMIS images. The
spatially-averaged synthetic line profiles show too low central emission peaks,
and too small separation between the peaks. The trends of the observed
center-to-limb variation of the profiles properties are reproduced by the
models. The Ca II H&K line profiles provide a temperature diagnostic of the
temperature minimum and the temperature at the formation height of the emission
peaks. The Doppler shift of the central depression is an excellent probe of the
velocity in the upper chromosphere.Comment: 19 pages, 20 figures, accepted for publication by A&
Identification of Agrarian Classes: A Methodological Essay with Empirival Material from South India
SSTRED: A data-processing and metadata-generating pipeline for CHROMIS and CRISP
We present a data pipeline for the newly installed SST/CHROMIS imaging
spectrometer, as well as for the older SST/CRISP spectropolarimeter. The aim is
to provide observers with a user-friendly data pipeline, that delivers
science-ready data with the metadata needed for archival. We generalized the
CRISPRED data pipeline for multiple instruments and added metadata according to
recommendations worked out as part of the SOLARNET project. We made
improvements to several steps in the pipeline, including the MOMFBD image
restoration. A part of that is a new fork of the MOMFBD program called REDUX,
with several new features that are needed in the new pipeline. The CRISPEX data
viewer has been updated to accommodate data cubes stored in this format. The
pipeline code, as well as REDUX and CRISPEX are all freely available through
git repositories or web download. We derive expressions for combining
statistics of individual frames into statistics for a set of frames. We define
a new extension to the World Coordinate System, that allow us to specify cavity
errors as distortions to the spectral coordinate.Comment: Draf
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