695 research outputs found
AOtools - a Python package for adaptive optics modelling and analysis
AOtools is a Python package that is open-source and aimed at providing tools for adaptive optics users and researchers. We present version 1.0, which contains tools for adaptive optics processing, including analysing data in the pupil plane, images and point spread functions in the focal plane, wavefront sensors, modelling of atmospheric turbulence, physical optical propagation of wavefronts, and conversion between frequently used adaptive optics and astronomical units. The main drivers behind AOtools is that it should be easy to install and use. To achieve this the project features extensive documentation, automated unit testing and is registered on the Python Package Index. AOtools is under continuous active development to expand the features available, and we encourage everyone involved in adaptive optics to become involved and contribute to the project
Optimization of Sample Preparation and Phloroglucinol Analysis of Marselan Grape Skin Proanthocyanidins using HPLC-DADESI- MS/MS
Proanthocyanidins are a group of oligomeric or polymeric flavan-3-ols that are highly significantcontributors to astringency in grapes and wines. An orthogonal L9(3)4 test was adopted to determine theoptimal extraction conditions and acid-catalysis cleavage of proanthocyanidins in the presence of excessphloroglucinol. The qualitative and quantitative analyses were done using HPLC-DAD-ESI-MS/MS. Theresults showed that the maximum extraction was obtained using 0.3 mol/L of HCl and 0.005 g of ascorbicacid with incubation at 70°C for 20 min. The precision and accuracy of this method were acceptable. Thecomposition of free flavan-3-ols and proanthocyanidins in the skins of ‘Marselan’ grapes (Vitis vinifera L.cv.) was investigated. (-)-Epigallocatechin was found to be the most abundant free flavan-3-ol monomerand terminal subunits, whereas the extension subunits were mainly (-)-epicatechin-3-O-gallate in the earlydevelopmental stages, and primarily (-)-epigallocatechin and (-)-epicatechin in the middle and late stages
Clusters in the inner spiral arms of M51: the cluster IMF and the formation history
We study the cluster population in a region of 3.2x3.2 kpc^2 in the inner
spiral arms of the intergacting galaxy M51, at a distance of about 1 to 3 kpc
from the nucleus, based on HST--WFPC2 images taken through five broadband and
two narrowband filters. We found 877 cluster candidates and we derived their
ages, initial masses and extinctions by comparing their energy distribution
with the Starburst99 cluster models. We describe the 3 and 2-dimensional
least-square energy fitting method that was used (3DEF, 2DEF). The lack of
[OIII] emission in even the youngest clusters with strong H-alpha emission,
indicates the absence of the most massive stars and suggests a mass upper limit
of about 25 to 30 solar masses. The mass versus age distribution of the
clusters shows a drastic decrease in the number of clusters with age, which
indicates that cluster disruption is occurring on a timescale of about 10 Myr
for low mass clusters. The cluster initial mass function for clusters younger
than 10 Myr has an exponent of alpha = 2.0 (+- 0.05) We derived the cluster
formation history from clusters with an initial mass larger than 10^4 solar
masses. There is no evidence for a peak in the cluster formation rate within a
factor two at about 200 to 400 Myr ago, i.e. at the time of the interaction
with the companion galaxy NGC 5194.Comment: 15 pages, 15 figures. Accepted for publication by Astronomy and
Astrophysic
Comparison of multiple and logistic regression analyses of relativistic electron flux enhancement at geosynchronous orbit following storms.
Many factors influence relativistic outer radiation belt electron fluxes, such as waves in the ultra low frequency (ULF) Pc5, very low frequency (VLF), and electromagnetic ion cyclotron (EMIC) frequency bands, seed electron flux, Dst disturbance levels, substorm occurrence, and solar wind inputs. In this work we compared relativistic electron flux post storm vs. pre‐storm using three methods of analysis: 1) multiple regression to predict flux values following storms, 2) multiple regression to predict the size and direction of the change in electron flux, and 3) multiple logistic regression to predict only the probability of the flux rising or falling. We determined which is the most predictive model, and which factors are most influential. We found that a linear regression predicting the difference in pre‐storm and post storm flux (Model 2) results in the highest validation correlations. The logistic regression used in Model 3 had slightly weaker predictive abilities than the other two models, but had most value in providing a prediction of the probability of the electron flux increasing after a storm. Of the variables used (ULF Pc5 and VLF waves, seed electrons, substorm activity, and EMIC waves), the most influential in the final model were ULF Pc5 waves and the seed electrons. IMF Bz, Dst, and solar wind number density, velocity, and pressure did not improve any of the models, and were deemed unnecessary for effective predictions
Polarimetric Properties of Flux-Ropes and Sheared Arcades in Coronal Prominence Cavities
The coronal magnetic field is the primary driver of solar dynamic events.
Linear and circular polarization signals of certain infrared coronal emission
lines contain information about the magnetic field, and to access this
information, either a forward or an inversion method must be used. We study
three coronal magnetic configurations that are applicable to polar-crown
filament cavities by doing forward calculations to produce synthetic
polarization data. We analyze these forward data to determine the
distinguishing characteristics of each model. We conclude that it is possible
to distinguish between cylindrical flux ropes, spheromak flux ropes, and
sheared arcades using coronal polarization measurements. If one of these models
is found to be consistent with observational measurements, it will mean
positive identification of the magnetic morphology that surrounds certain
quiescent filaments, which will lead to a greater understanding of how they
form and why they erupt.Comment: 22 pages, 8 figures, Solar Physics topical issue: Coronal Magnetis
The Carboniferous carbon isotope record from sedimentary organic matter: can we disentangle the carbon cycle?
A comprehensive analysis of the 13C composition of sedimentary organic matter from Euramerican
Carboniferous successions indicates there are significant shifts in 13C through this key time interval.
Our studies have revealed that, at an individual location, the source and delivery mechanism of the
sediment contribute to the type of organic matter preserved and, in turn this influences the
measured 13C values from bulk sedimentary organic matter of organic matter
Recommended from our members
HOx observations over West Africa during AMMA: impact of isoprene and NOx
Aircraft OH and HO2 measurements made over West Africa during the AMMA field campaign in summer 2006 have been investigated using a box model constrained to observations of long-lived species and physical parameters. "Good" agreement was found for HO2 (modelled to observed gradient of 1.23 ± 0.11). However, the model significantly overpredicts OH concentrations. The reasons for this are not clear, but may reflect instrumental instabilities affecting the OH measurements. Within the model, HOx concentrations in West Africa are controlled by relatively simple photochemistry, with production dominated by ozone photolysis and reaction of O(1D) with water vapour, and loss processes dominated by HO2 + HO2 and HO2 + RO2. Isoprene chemistry was found to influence forested regions. In contrast to several recent field studies in very low NOx and high isoprene environments, we do not observe any dependence of model success for HO2 on isoprene and attribute this to efficient recycling of HOx through RO2 + NO reactions under the moderate NOx concentrations (5–300 ppt NO in the boundary layer, median 76 ppt) encountered during AMMA. This suggests that some of the problems with understanding the impact of isoprene on atmospheric composition may be limited to the extreme low range of NOx concentrations
A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source
We present a quantitative model of the magnetic energy stored and then
released through magnetic reconnection for a flare on 26 Feb 2004. This flare,
well observed by RHESSI and TRACE, shows evidence of non-thermal electrons only
for a brief, early phase. Throughout the main period of energy release there is
a super-hot (T>30 MK) plasma emitting thermal bremsstrahlung atop the flare
loops. Our model describes the heating and compression of such a source by
localized, transient magnetic reconnection. It is a three-dimensional
generalization of the Petschek model whereby Alfven-speed retraction following
reconnection drives supersonic inflows parallel to the field lines, which form
shocks heating, compressing, and confining a loop-top plasma plug. The
confining inflows provide longer life than a freely-expanding or
conductively-cooling plasma of similar size and temperature. Superposition of
successive transient episodes of localized reconnection across a current sheet
produces an apparently persistent, localized source of high-temperature
emission. The temperature of the source decreases smoothly on a time scale
consistent with observations, far longer than the cooling time of a single
plug. Built from a disordered collection of small plugs, the source need not
have the coherent jet-like structure predicted by steady-state reconnection
models. This new model predicts temperatures and emission measure consistent
with the observations of 26 Feb 2004. Furthermore, the total energy released by
the flare is found to be roughly consistent with that predicted by the model.
Only a small fraction of the energy released appears in the super-hot source at
any one time, but roughly a quarter of the flare energy is thermalized by the
reconnection shocks over the course of the flare. All energy is presumed to
ultimately appear in the lower-temperature T<20 MK, post-flare loops
Telemedicine quality and outcomes in stroke: A scientific statement for healthcare professionals from the American Heart Association/American Stroke Association
Purpose - Telestroke is one of the most frequently used and rapidly expanding applications of telemedicine, delivering much-needed stroke expertise to hospitals and patients. This document reviews the current status of telestroke and suggests measures for ongoing quality and outcome monitoring to improve performance and to enhance delivery of care. Methods - A literature search was undertaken to examine the current status of telestroke and relevant quality indicators. The members of the writing committee contributed to the review of specific quality and outcome measures with specific suggestions for metrics in telestroke networks. The drafts were circulated and revised by all committee members, and suggestions were discussed for consensus. Results - Models of telestroke and the role of telestroke in stroke systems of care are reviewed. A brief description of the science of quality monitoring and prior experience in quality measures for stroke is provided. Process measures, outcomes, tissue-type plasminogen activator use, patient and provider satisfaction, and telestroke technology are reviewed, and suggestions are provided for quality metrics. Additional topics include licensing, credentialing, training, and documentation
Relativistic Hydrodynamic Evolutions with Black Hole Excision
We present a numerical code designed to study astrophysical phenomena
involving dynamical spacetimes containing black holes in the presence of
relativistic hydrodynamic matter. We present evolutions of the collapse of a
fluid star from the onset of collapse to the settling of the resulting black
hole to a final stationary state. In order to evolve stably after the black
hole forms, we excise a region inside the hole before a singularity is
encountered. This excision region is introduced after the appearance of an
apparent horizon, but while a significant amount of matter remains outside the
hole. We test our code by evolving accurately a vacuum Schwarzschild black
hole, a relativistic Bondi accretion flow onto a black hole, Oppenheimer-Snyder
dust collapse, and the collapse of nonrotating and rotating stars. These
systems are tracked reliably for hundreds of M following excision, where M is
the mass of the black hole. We perform these tests both in axisymmetry and in
full 3+1 dimensions. We then apply our code to study the effect of the stellar
spin parameter J/M^2 on the final outcome of gravitational collapse of rapidly
rotating n = 1 polytropes. We find that a black hole forms only if J/M^2<1, in
agreement with previous simulations. When J/M^2>1, the collapsing star forms a
torus which fragments into nonaxisymmetric clumps, capable of generating
appreciable ``splash'' gravitational radiation.Comment: 17 pages, 14 figures, submitted to PR
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