1,388 research outputs found
A study of the elements copper through uranium in Sirius A: Contributions from STIS and ground-based spectra
We determine abundances or upper limits for all of the 55 stable elements
from copper to uranium for the A1 Vm star Sirius. The purpose of the study is
to assemble the most complete picture of elemental abundances with the hope of
revealing the chemical history of the brightest star in the sky, apart from the
Sun. We also explore the relationship of this hot metallic-line (Am) star to
its cooler congeners, as well as the hotter, weakly- or non-magnetic
mercury-manganese (HgMn) stars. Our primary observational material consists of
{\em Hubble Space Telescope} () spectra taken with the Space Telescope
Imaging Spectrograph (STIS) in the ASTRAL project. We have also used archival
material from the %\citep/{ayr10}. satellite, and from the
Goddard High-Resolution Spectrograph (GHRS), as well as ground-based spectra
from Furenlid, Westin, Kurucz, Wahlgren, and their coworkers, ESO spectra from
the UVESPOP project, and NARVAL spectra retrieved from PolarBase. Our analysis
has been primarily by spectral synthesis, and in this work we have had the
great advantage of extensive atomic data unavailable to earlier workers. We
find most abundances as well as upper limits range from 10 to 100 times above
solar values. We see no indication of the huge abundance excesses of 1000 or
more that occur among many chemically peculiar (CP) stars of the upper main
sequence. The picture of Sirius as a hot Am star is reinforced.Comment: With 6 Figures and 4 Tables; accepted for publication in Ap
Polarizations and differential calculus in affine spaces
Within the framework of mappings between affine spaces, the notion of -th
polarization of a function will lead to an intrinsic characterization of
polynomial functions. We prove that the characteristic features of derivations,
such as linearity, iterability, Leibniz and chain rules, are shared -- at the
finite level -- by the polarization operators. We give these results by means
of explicit general formulae, which are valid at any order , and are based
on combinatorial identities. The infinitesimal limits of the -th
polarizations of a function will yield its -th derivatives (without
resorting to the usual recursive definition), and the above mentioned
properties will be recovered directly in the limit. Polynomial functions will
allow us to produce a coordinate free version of Taylor's formula
A large stellar evolution database for population synthesis studies. II. Stellar models and isochrones for an alpha-enhanced metal distribution
[Abridged] We present a large, new set of stellar evolution models and
isochrones for an alpha-enhanced metal distribution typical of Galactic halo
and bulge stars; it represents a homogeneous extension of our stellar model
library for a distribution already presented in Pietrinferni et al.(2004). The
effect of the alpha-element enhancement has been properly taken into account in
the nuclear network, opacity, equation of state and, for the first time, the
bolometric corrections, and color transformations. This allows us to avoid the
inconsistent use - common to all alpha-enhanced model libraries currently
available - of scaled-solar bolometric corrections and color transformations
for alpha-enhanced models and isochrones. We show how bolometric corrections to
magnitudes obtained for the U,B portion of stellar spectra for T_{eff}<=6500K,
are significantly affected by the metal mixture, especially at the higher
metallicities. We also provide complete sets of evolutionary models for
low-mass, He-burning stellar structures covering the whole metallicity range,
to enable synthetic horizontal branch simulations. We compare our database with
several widely used stellar model libraries from different authors, as well as
with various observed color magnitude and color-color diagrams (Johnson-Cousins
BVI and near infrared magnitudes, Stromgren colors) of Galactic field stars and
globular clusters. We also test our isochrones comparing integrated optical
colors and Surface Brightness Fluctuation magnitudes with selected globular
cluster data. We find a general satisfactory agreement with the empirical
constraints.Comment: 46 pages, 20 figures, ApJ in press, the whole database presented in
this paper can be foud at http://www.te.astro.it/BASTI/index.ph
Systematic screening as a strategy to increase services integration and revenues in Honduras
This operations research study, undertaken by the Honduras Family Planning Association (Asociación Hondureña de Planificación de Familia—ASHONPLAFA), tested the effectiveness of systematic screening to increase the number of services and revenue per visit in a reproductive health program. Despite monitoring plans, provider compliance with the intervention was low; the overall proportion of clients screened was less than 11 percent, and the frequency of screening varied greatly by clinic contact point. Although the study did not show an increase in the mean number of services per client, the negative results could reasonably be attributed to lack of implementation of the intervention. After consultation with the ASHONPLAFA marketing department, the executive director ordered that the strategy be implemented in all clinics, along with a system to monitor the utilization of a simplified screening form, designed to be less time consuming and less intrusive than the form tested during the experiment. The new form is limited to services most likely to be needed by clients, as indicated by the study’s analysis of unmet need and potential demand
Recommended from our members
Forest and wildlife habitat analysis using remote sensing and geographic information systems
Forest and wildlife habitat analyses were conducted
at the H.J. Andrews Experimental Forest in the Central
Cascade Mountains of Oregon using remotely sensed data and
a geographic information system (GIS). Landsat Thematic
Mapper(TM) data were used to determine forest successional
stages, and to analyze the structure of both old and young
conifer forests. Two successional stage maps were
developed. One was developed from six TM spectral bands
alone, and the second was developed from six TM spectral
bands and a relative sun incidence band. Including the
sun incidence band in the classification improved the
mapping accuracy in the two youngest successional stages,
but did not improve overall accuracy or accuracy of the
two oldest successional stages. Mean spectral values for
old-growth and mature stands were compared in seven TM
bands and seven band transformations. Differences between
mature and old-growth successional stages were greatest
for the band ratio of TM 4/5 (P = 0.00005) and the
multiband transformation of wetness (P = 0.00003). The
age of young conifer stands had the highest correlation to
TM 4/5 values (r = 0.9559) of any of the TM band or band
transformations used. TM 4/5 ratio values of poorly
regenerated conifer stands were significantly different
from well regenerated conifer stands after age 15
(P = 0.0000). TM 4/5 was named a "Successional Stage
Index" (SSI) because of its ability to distinguish forest
successional stages.
The forest successional stage map was used as input
into a vertebrate richness model using GIS. The three
variables of 1) successional stage, 2) elevation, and 3)
site moisture were used in the GIS to predict the spatial
occurrence of small mammal, amphibian, and reptile species
based on primary and secondary habitat requirements.
These occurrence or habitat maps were overlayed to tally
the predicted number of vertebrate at any given point in
the study area. Overall, sixty-three and sixty-seven
percent of the model predictions for vertebrate occurrence
matched the vertebrates that were trapped in the field in
eight forested stands. Of the three model variables, site
moisture appeared to have the greatest influence on the
pattern of high vertebrate richness in all vertebrate
classes
Oxidative stress in stable cystic fibrosis patients: Do we need higher antioxidant plasma levels?
Recommended from our members
Phosphoinositide 3-kinase δ inhibition promotes antitumor responses but antagonizes checkpoint inhibitors.
Multiple modes of immunosuppression restrain immune function within tumors. We previously reported that phosphoinositide 3-kinase δ (PI3Kδ) inactivation in mice confers resistance to a range of tumor models by disrupting immunosuppression mediated by regulatory T cells (Tregs). The PI3Kδ inhibitor idelalisib has proven highly effective in the clinical treatment of chronic lymphocytic leukemia and the potential to extend the use of PI3Kδ inhibitors to nonhematological cancers is being evaluated. In this work, we demonstrate that the antitumor effect of PI3Kδ inactivation is primarily mediated through the disruption of Treg function, and correlates with tumor dependence on Treg immunosuppression. Compared with Treg-specific PI3Kδ deletion, systemic PI3Kδ inactivation is less effective at conferring resistance to tumors. We show that PI3Kδ deficiency impairs the maturation and reduces the capacity of CD8+ cytotoxic T lymphocytes (CTLs) to kill tumor cells in vitro, and to respond to tumor antigen-specific immunization in vivo. PI3Kδ inactivation antagonized the antitumor effects of tumor vaccines and checkpoint blockade therapies intended to boost the CD8+ T cell response. These findings provide insights into mechanisms by which PI3Kδ inhibition promotes antitumor immunity and demonstrate that the mechanism is distinct from that mediated by immune checkpoint blockade.ELL was supported by the Yousef Jameel Scholarship (Cambridge Trust). DG was
funded by a grant from Karus Therapeutics Ltd. RR and KO received institute support from
Biotechnology and Biological Sciences Research Council (BBSRC) BBS/E/B/000C0407, -
C0409, -C0427 and -C0428 and project grant BB/N007794/1. RR was supported by Wellcome
Trust grant 105663/Z/14/Z. KO was also supported by Wellcome Trust grant 095198/Z/10/Z
- …