402 research outputs found
Ionization state, excited populations and emission of impurities in dynamic finite density plasmas: I. The generalized collisional-radiative model for light elements
The paper presents an integrated view of the population structure and its role in establishing the ionization state of light elements in dynamic, finite density, laboratory and astrophysical plasmas. There are four main issues, the generalized collisional-radiative picture for metastables in dynamic plasmas with Maxwellian free electrons and its particularizing to light elements, the methods of bundling and projection for manipulating the population equations, the systematic production/use of state selective fundamental collision data in the metastable resolved picture to all levels for collisonal-radiative modelling and the delivery of appropriate derived coefficients for experiment analysis. The ions of carbon, oxygen and neon are used in illustration. The practical implementation of the methods described here is part of the ADAS Project
GAIA: Composition, Formation and Evolution of the Galaxy
The GAIA astrometric mission has recently been approved as one of the next
two `cornerstones' of ESA's science programme, with a launch date target of not
later than mid-2012. GAIA will provide positional and radial velocity
measurements with the accuracies needed to produce a stereoscopic and kinematic
census of about one billion stars throughout our Galaxy (and into the Local
Group), amounting to about 1 per cent of the Galactic stellar population.
GAIA's main scientific goal is to clarify the origin and history of our Galaxy,
from a quantitative census of the stellar populations. It will advance
questions such as when the stars in our Galaxy formed, when and how it was
assembled, and its distribution of dark matter. The survey aims for
completeness to V=20 mag, with accuracies of about 10 microarcsec at 15 mag.
Combined with astrophysical information for each star, provided by on-board
multi-colour photometry and (limited) spectroscopy, these data will have the
precision necessary to quantify the early formation, and subsequent dynamical,
chemical and star formation evolution of our Galaxy. Additional products
include detection and orbital classification of tens of thousands of
extra-Solar planetary systems, and a comprehensive survey of some 10^5-10^6
minor bodies in our Solar System, through galaxies in the nearby Universe, to
some 500,000 distant quasars. It will provide a number of stringent new tests
of general relativity and cosmology. The complete satellite system was
evaluated as part of a detailed technology study, including a detailed payload
design, corresponding accuracy assesments, and results from a prototype data
reduction development.Comment: Accepted by A&A: 25 pages, 8 figure
First SOLPS‐ITER simulations of ASDEX Upgrade partially detached H‐mode with boron impurity : the missing radiation at the outer strike‐point region
Partially detached H‐modes are the baseline regime for the future ITER operation. The ASDEX Upgrade partially detached H‐mode is modeled using the SOLPS‐ITER code with drifts enabled and compared with experimental data. For the first time, boron (B) impurity is simulated in the Scrape‐off layer (SOL) and divertor. A comparison between divertor diagnostics and discrepancies between Langmuir probe and Divertor Thomson scattering/Stark broadening diagnostic are discussed. In the modeling, experimental target profiles are reproduced if the experimental level of radiation in the SOL and divertor is achieved using nitrogen (N) impurity seeding. Bolometry measurements detect substantial radiation from the partially detached outer strike point. With B radiation, this maximum in bolometry data is reproduced in the modeling, which is not possible with N alone
Dielectronic recombination data for dynamic finite-density plasmas I. Goals and methodology
A programme is outlined for the assembly of a comprehensive dielectronic
recombination database within the generalized collisional--radiative (GCR)
framework. It is valid for modelling ions of elements in dynamic finite-density
plasmas such as occur in transient astrophysical plasmas such as solar flares
and in the divertors and high transport regions of magnetic fusion devices. The
resolution and precision of the data are tuned to spectral analysis and so are
sufficient for prediction of the dielectronic recombination contributions to
individual spectral line emissivities. The fundamental data are structured
according to the format prescriptions of the Atomic Data and Analysis Structure
(ADAS) and the production of relevant GCR derived data for application is
described and implemented following ADAS. The requirements on the dielectronic
recombination database are reviewed and the new data are placed in context and
evaluated with respect to older and more approximate treatments. Illustrative
results validate the new high-resolution zero-density dielectronic
recombination data in comparison with measurements made in heavy-ion storage
rings utilizing an electron cooler. We also exemplify the role of the
dielectronic data on GCR coefficient behaviour for some representative light
and medium weight elements.Comment: 14 Pages, 9 Figures. Submitted to Astronomy & Astrophysics April 12,
200
Alimentary fluoride intake in preschool children
<p>Abstract</p> <p>Background</p> <p>The knowledge of background alimentary fluoride intake in preschool children is of utmost importance for introducing optimal and safe caries preventive measures for both individuals and communities. The aim of this study was to assess the daily fluoride intake analyzing duplicate samples of food and beverages. An attempt was made to calculate the daily intake of fluoride from food and swallowed toothpaste.</p> <p>Methods</p> <p>Daily alimentary fluoride intake was measured in a group of 36 children with an average age of 4.75 years and an average weight of 20.69 kg at baseline, by means of a double plate method. This was repeated after six months. Parents recorded their child's diet over 24 hours and collected duplicated portions of food and beverages received by children during this period. Pooled samples of food and beverages were weighed and solid food samples were homogenized. Fluoride was quantitatively extracted from solid food samples by a microdiffusion method using hexadecyldisiloxane and perchloric acid. The content of fluoride extracted from solid food samples, as well as fluoride in beverages, was measured potentiometrically by means of a fluoride ion selective electrode.</p> <p>Results</p> <p>Average daily fluoride intake at baseline was 0.389 (SD 0.054) mg per day. Six months later it was 0.378 (SD 0.084) mg per day which represents 0.020 (SD 0.010) and 0.018 (SD 0.008) mg of fluoride respectively calculated per kg bw/day.</p> <p>When adding the values of unwanted fluoride intake from the toothpaste shown in the literature (0.17-1.21 mg per day) the estimate of the total daily intake of fluoride amounted to 0.554-1.594 mg/day and recalculated to the child's body weight to 0.027-0.077 mg/kg bw/day.</p> <p>Conclusions</p> <p>In the children studied, observed daily fluoride intake reached the threshold for safe fluoride intake. When adding the potential fluoride intake from swallowed toothpaste, alimentary intake reached the optimum range for daily fluoride intake. These results showed that in preschool children, when trying to maximize the benefit of fluoride in caries prevention and to minimize its risk, caution should be exercised when giving advice on the fluoride containing components of child's diet or prescribing fluoride supplements.</p
Gaia Data Release 1: Open cluster astrometry: Performance, limitations, and future prospects
Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric
Solution (TGAS). This is a subset of about 2 million stars for which, besides
the position and photometry, the proper motion and parallax are calculated
using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We
investigate the scientific potential and limitations of the TGAS component by
means of the astrometric data for open clusters. Methods. Mean cluster parallax
and proper motion values are derived taking into account the error correlations
within the astrometric solutions for individual stars, an estimate of the
internal velocity dispersion in the cluster, and, where relevant, the effects
of the depth of the cluster along the line of sight. Internal consistency of
the TGAS data is assessed. Results. Values given for standard uncertainties are
still inaccurate and may lead to unrealistic unit-weight standard deviations of
least squares solutions for cluster parameters. Reconstructed mean cluster
parallax and proper motion values are generally in very good agreement with
earlier Hipparcos-based determination, although the Gaia mean parallax for the
Pleiades is a significant exception. We have no current explanation for that
discrepancy. Most clusters are observed to extend to nearly 15 pc from the
cluster centre, and it will be up to future Gaia releases to establish whether
those potential cluster-member stars are still dynamically bound to the
clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters
far beyond their more easily visible cores, and can provide membership
assessments based on proper motions and parallaxes. A combined HR diagram shows
the same features as observed before using the Hipparcos data, with clearly
increased luminosities for older A and F dwarfs
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Gaia Data Release 1: Summary of the astrometric, photometric, and survey properties
At about 1000 days after the launch of Gaia we present the first Gaia data
release, Gaia DR1, consisting of astrometry and photometry for over 1 billion
sources brighter than magnitude 20.7. We summarize Gaia DR1 and provide
illustrations of the scientific quality of the data, followed by a discussion
of the limitations due to the preliminary nature of this release. Gaia DR1
consists of: a primary astrometric data set which contains the positions,
parallaxes, and mean proper motions for about 2 million of the brightest stars
in common with the Hipparcos and Tycho-2 catalogues and a secondary astrometric
data set containing the positions for an additional 1.1 billion sources. The
second component is the photometric data set,consisting of mean G-band
magnitudes for all sources. The G-band light curves and the characteristics of
~3000 Cepheid and RR Lyrae stars, observed at high cadence around the south
ecliptic pole, form the third component. For the primary astrometric data set
the typical uncertainty is about 0.3 mas for the positions and parallaxes, and
about 1 mas/yr for the proper motions. A systematic component of ~0.3 mas
should be added to the parallax uncertainties. For the subset of ~94000
Hipparcos stars in the primary data set, the proper motions are much more
precise at about 0.06 mas/yr. For the secondary astrometric data set, the
typical uncertainty of the positions is ~10 mas. The median uncertainties on
the mean G-band magnitudes range from the mmag level to ~0.03 mag over the
magnitude range 5 to 20.7. Gaia DR1 represents a major advance in the mapping
of the heavens and the availability of basic stellar data that underpin
observational astrophysics. Nevertheless, the very preliminary nature of this
first Gaia data release does lead to a number of important limitations to the
data quality which should be carefully considered before drawing conclusions
from the data
From Data to Software to Science with the Rubin Observatory LSST
The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) dataset
will dramatically alter our understanding of the Universe, from the origins of
the Solar System to the nature of dark matter and dark energy. Much of this
research will depend on the existence of robust, tested, and scalable
algorithms, software, and services. Identifying and developing such tools ahead
of time has the potential to significantly accelerate the delivery of early
science from LSST. Developing these collaboratively, and making them broadly
available, can enable more inclusive and equitable collaboration on LSST
science.
To facilitate such opportunities, a community workshop entitled "From Data to
Software to Science with the Rubin Observatory LSST" was organized by the LSST
Interdisciplinary Network for Collaboration and Computing (LINCC) and partners,
and held at the Flatiron Institute in New York, March 28-30th 2022. The
workshop included over 50 in-person attendees invited from over 300
applications. It identified seven key software areas of need: (i) scalable
cross-matching and distributed joining of catalogs, (ii) robust photometric
redshift determination, (iii) software for determination of selection
functions, (iv) frameworks for scalable time-series analyses, (v) services for
image access and reprocessing at scale, (vi) object image access (cutouts) and
analysis at scale, and (vii) scalable job execution systems.
This white paper summarizes the discussions of this workshop. It considers
the motivating science use cases, identified cross-cutting algorithms,
software, and services, their high-level technical specifications, and the
principles of inclusive collaborations needed to develop them. We provide it as
a useful roadmap of needs, as well as to spur action and collaboration between
groups and individuals looking to develop reusable software for early LSST
science.Comment: White paper from "From Data to Software to Science with the Rubin
Observatory LSST" worksho
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