3,180 research outputs found
The inner circumstellar disk of the UX Ori star V1026 Sco
The UX Ori type variables (named after the prototype of their class) are
intermediate-mass pre-main sequence objects. One of the most likely causes of
their variability is the obscuration of the central star by orbiting dust
clouds. We investigate the structure of the circumstellar environment of the
UX~Ori star V1026 Sco (HD 142666) and test whether the disk inclination is
large enough to explain the UX Ori variability. We observed the object in the
low-resolution mode of the near-infrared interferometric VLTI/AMBER instrument
and derived H- and K-band visibilities and closure phases. We modeled our AMBER
observations, published Keck Interferometer observations, archival MIDI/VLTI
visibilities, and the spectral energy distribution using geometric and
temperature-gradient models. Employing a geometric inclined-ring disk model, we
find a ring radius of 0.15 +- 0.06 AU in the H band and 0.18 +- 0.06 AU in the
K band. The best-fit temperature-gradient model consists of a star and two
concentric, ring-shaped disks. The inner disk has a temperature of
1257^{+133}_{-53} K at the inner rim and extends from 0.19 +- 0.01 AU to 0.23
+- 0.02 AU. The outer disk begins at 1.35^{+0.19}_{-0.20} AU and has an inner
temperature of 334^{+35}_{-17} K. The derived inclination of
48.6^{+2.9}_{-3.6}deg approximately agrees with the inclination derived with
the geometric model (49 +- 5deg in the K band and 50 +- 11deg in the H band).
The position angle of the fitted geometric and temperature-gradient models are
163 +- 9deg (K band; 179 +- 17deg in the H band) and 169.3^{+4.2}_{-6.7}deg,
respectively. The narrow width of the inner ring-shaped model disk and the disk
gap might be an indication for a puffed-up inner rim shadowing outer parts of
the disk. The intermediate inclination of ~50deg is consistent with models of
UX Ori objects where dust clouds in the inclined disk obscure the central star
Prostaglandin E2-like activity of 20:3n-9 platelet lipoxygenase end-product
Abstract5,8,11-Icosatrienoic acid (20:3n-9), a fatty acid associated with platelet hyperactivity, was oxygenated by platelet lipoxygenase. The end-product of this pathway was purified by high-performance liquid chromatography (HPLC) and characterized as 12-hydroxy-5,8,10-icosatrienoic acid [12-OH-20:3(5,8,10)] by capillary gas-liquid mass spectrometry. When tested upon platelet aggregation, 12-OH-20:3(5,8,10) exhibited a biphasic effect. At low concentrations (below 5 × 10−7 M) it potentiated aggregation but inhibited it at higher levels, a pattern similar to that obtained with prostaglandin E2. However, since the amounts of 12-OH-20:3(5,8,10) generated under thrombin stimulation are in the range of concentrations with potentiating effects, it seems that the 12-OH derivative is responsible for the hyperaggrebility of 20: 3n-9-rich platelets
PLoS One
Estimating and selecting risk factors with extremely low prevalences of exposure for a binary outcome is a challenge because classical standard techniques, markedly logistic regression, often fail to provide meaningful results in such settings. While penalized regression methods are widely used in high-dimensional settings, we were able to show their usefulness in low-dimensional settings as well. Specifically, we demonstrate that Firth correction, ridge, the lasso and boosting all improve the estimation for low-prevalence risk factors. While the methods themselves are well-established, comparison studies are needed to assess their potential benefits in this context. This is done here using the dataset of a large unmatched case-control study from France (2005-2008) about the relationship between prescription medicines and road traffic accidents and an accompanying simulation study. Results show that the estimation of risk factors with prevalences below 0.1% can be drastically improved by using Firth correction and boosting in particular, especially for ultra-low prevalences. When a moderate number of low prevalence exposures is available, we recommend the use of penalized techniques
Abolishing user fees for children and pregnant women trebled uptake of malaria-related interventions in Kangaba, Mali.
Malaria is the most common cause of morbidity and mortality in children under 5 in Mali. Health centres provide primary care, including malaria treatment, under a system of cost recovery. In 2005, Médecins sans Frontieres (MSF) started supporting health centres in Kangaba with the provision of rapid malaria diagnostic tests and artemisinin-based combination therapy. Initially MSF subsidized malaria tests and drugs to reduce the overall cost for patients. In a second phase, MSF abolished fees for all children under 5 irrespective of their illness and for pregnant women with fever. This second phase was associated with a trebling of both primary health care utilization and malaria treatment coverage for these groups. MSF's experience in Mali suggests that removing user fees for vulnerable groups significantly improves utilization and coverage of essential health services, including for malaria interventions. This effect is far more marked than simply subsidizing or providing malaria drugs and diagnostic tests free of charge. Following the free care strategy, utilization of services increased significantly and under-5 mortality was reduced. Fee removal also allowed for more efficient use of existing resources, reducing average cost per patient treated. These results are particularly relevant for the context of Mali and other countries with ambitious malaria treatment coverage objectives, in accordance with the United Nations Millennium Development Goals. This article questions the effectiveness of the current national policy, and the effectiveness of reducing the cost of drugs only (i.e. partial subsidies) or providing malaria tests and drugs free for under-5s, without abolishing other related fees. National and international budgets, in particular those that target health systems strengthening, could be used to complement existing subsidies and be directed towards effective abolition of user fees. This would contribute to increasing the impact of interventions on population health and, in turn, the effectiveness of aid
Dark-bright mixing of interband transitions in symmetric semiconductor quantum dots
In photoluminescence spectra of symmetric [111] grown GaAs/AlGaAs quantum
dots in longitudinal magnetic fields applied along the growth axis we observe
in addition to the expected bright states also nominally dark transitions for
both charged and neutral excitons. We uncover a strongly non-monotonous, sign
changing field dependence of the bright neutral exciton splitting resulting
from the interplay between exchange and Zeeman effects. Our theory shows
quantitatively that these surprising experimental results are due to
magnetic-field-induced \pm 3/2 heavy-hole mixing, an inherent property of
systems with C_3v point-group symmetry.Comment: 5 pages, 3 figure
Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields
A precise characterisation of the red giants in the seismology fields of the
CoRoT satellite is a prerequisite for further in-depth seismic modelling.
High-resolution FEROS and HARPS spectra were obtained as part of the
ground-based follow-up campaigns for 19 targets holding great asteroseismic
potential. These data are used to accurately estimate their fundamental
parameters and the abundances of 16 chemical species in a self-consistent
manner. Some powerful probes of mixing are investigated (the Li and CNO
abundances, as well as the carbon isotopic ratio in a few cases). The
information provided by the spectroscopic and seismic data is combined to
provide more accurate physical parameters and abundances. The stars in our
sample follow the general abundance trends as a function of the metallicity
observed in stars of the Galactic disk. After an allowance is made for the
chemical evolution of the interstellar medium, the observational signature of
internal mixing phenomena is revealed through the detection at the stellar
surface of the products of the CN cycle. A contamination by NeNa-cycled
material in the most massive stars is also discussed. With the asteroseismic
constraints, these data will pave the way for a detailed theoretical
investigation of the physical processes responsible for the transport of
chemical elements in evolved, low- and intermediate-mass stars.Comment: Accepted for publication in A&A, 25 pages, 13 colour figures (revised
version after language editing
AMBER/VLTI high spectral resolution observations of the Br emitting region in HD 98922. A compact disc wind launched from the inner disc region
We analyse the main physical parameters and the circumstellar environment of
the young Herbig Be star HD 98922. We present AMBER/VLTI high spectral
resolution (R =12000) interferometric observations across the Br line,
accompanied by UVES high-resolution spectroscopy and SINFONI-AO assisted
near-infrared integral field spectroscopic data. To interpret our observations,
we develop a magneto-centrifugally driven disc-wind model. Our analysis of the
UVES spectrum shows that HD 98922 is a young (~5x10^5 yr) Herbig Be star
(SpT=B9V), located at a distance of 440(+60-50) pc, with a mass accretion rate
of ~9+/-3x10^(-7) M_sun yr^(-1). SINFONI K-band AO-assisted imaging shows a
spatially resolved circumstellar disc-like region (~140 AU in diameter) with
asymmetric brightness distribution. Our AMBER/VLTI UT observations indicate
that the Br emitting region (radius ~0.31+/-0.04 AU) is smaller than
the continuum emitting region (inner dust radius ~0.7+/-0.2 AU), showing
significant non-zero V-shaped differential phases (i.e. non S-shaped, as
expected for a rotating disc). The value of the continuum-corrected pure
Br line visibility at the longest baseline (89 m) is ~0.8+/-0.1, i.e.
the Br emitting region is partially resolved. Our modelling suggests
that the observed Br line-emitting region mainly originates from a disc
wind with a half opening angle of 30deg, and with a mass-loss rate of ~2x10(-7)
M_sun yr^(-1). The observed V-shaped differential phases are reliably
reproduced by combining a simple asymmetric continuum disc model with our
Br disc-wind model. The Br emission of HD 98922 can be modelled
with a disc wind that is able to approximately reproduce all interferometric
observations if we assume that the intensity distribution of the dust continuum
disc is asymmetric.Comment: Accepted for publication on Astronomy \& Astrophysics. High
resolution figures published on the main journal (see Astronomy &
Astrophysics: Forthcoming) or at
www.researchgate.net/profile/Alessio_Caratti_o_Garatti/publication
Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints
Context. The availability of asteroseismic constraints for a large sample of
red giant stars from the CoRoT and Kepler missions paves the way for various
statistical studies of the seismic properties of stellar populations.
Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant
stars (Morel et al 2014) to compare theoretical stellar evolution models to
observations of the open cluster NGC 6633 and field stars.
Methods. In order to explore the effects of rotation-induced mixing and
thermohaline instability, we compare surface abundances of carbon isotopic
ratio and lithium with stellar evolution predictions. These chemicals are
sensitive to extra-mixing on the red-giant branch.
Results. We estimate mass, radius, and distance for each star using the
seismic constraints. We note that the Hipparcos and seismic distances are
different. However, the uncertainties are such that this may not be
significant. Although the seismic distances for the cluster members are self
consistent they are somewhat larger than the Hipparcos distance. This is an
issue that should be considered elsewhere. Models including thermohaline
instability and rotation-induced mixing, together with the seismically
determined masses can explain the chemical properties of red-giants targets.
However, with this sample of stars we cannot perform stringent tests of the
current stellar models. Tighter constraints on the physics of the models would
require the measurement of the core and surface rotation rates, and of the
period spacing of gravity-dominated mixed modes. A larger number of stars with
longer times series, as provided by Kepler or expected with Plato, would help
for ensemble asteroseismology.Comment: Accepted 03/05/201
Evaluation of the Choice of GP Practice Pilot, 2012-13
The choice of general practice pilot began in April 2012 for 12 months and allowed patients to choose to seek care from any volunteer general practice in four volunteer Primary Care Trust (PCT) areas of the country (Westminster, Salford, Manchester and Nottingham City) without being restricted by practice boundaries. Patients could either register with a pilot practice as an out of area (OoA) patient, or be seen as a ‘day patient’, while remaining registered with their original practice. The aim of the evaluation was to describe the uptake of the pilot scheme, and give an early indication of its potential costs and benefits for participating practices and patients over a 12-month period, recognising that it would not be possible to quantify costs and benefits definitively over such a short time
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