2,255 research outputs found
A systematic numerical study of the tidal instability in a rotating triaxial ellipsoid
The full non-linear evolution of the tidal instability is studied numerically
in an ellipsoidal fluid domain relevant for planetary cores applications. Our
numerical model, based on a finite element method, is first validated by
reproducing some known analytical results. This model is then used to address
open questions that were up to now inaccessible using theoretical and
experimental approaches. Growth rates and mode selection of the instability are
systematically studied as a function of the aspect ratio of the ellipsoid and
as a function of the inclination of the rotation axis compared to the
deformation plane. We also quantify the saturation amplitude of the flow driven
by the instability and calculate the viscous dissipation that it causes. This
tidal dissipation can be of major importance for some geophysical situations
and we thus derive general scaling laws which are applied to typical planetary
cores
A new interferometric study of four exoplanet host stars : {\theta} Cygni, 14 Andromedae, {\upsilon} Andromedae and 42 Draconis
Studying exoplanet host stars is of the utmost importance to establish the
link between the presence of exoplanets around various types of stars and to
understand the respective evolution of stars and exoplanets.
Using the limb-darkened diameter (LDD) obtained from interferometric data, we
determine the fundamental parameters of four exoplanet host stars. We are
particularly interested in the F4 main-sequence star, {\theta} Cyg, for which
Kepler has recently revealed solar-like oscillations that are unexpected for
this type of star. Furthermore, recent photometric and spectroscopic
measurements with SOPHIE and ELODIE (OHP) show evidence of a quasi-periodic
radial velocity of \sim150 days. Models of this periodic change in radial
velocity predict either a complex planetary system orbiting the star, or a new
and unidentified stellar pulsation mode.
We performed interferometric observations of {\theta} Cyg, 14 Andromedae,
{\upsilon} Andromedae and 42 Draconis for two years with VEGA/CHARA (Mount
Wilson, California) in several three-telescope configurations. We measured
accurate limb darkened diameters and derived their radius, mass and temperature
using empirical laws.
We obtain new accurate fundamental parameters for stars 14 And, {\upsilon}
And and 42 Dra. We also obtained limb darkened diameters with a minimum
precision of \sim 1.3%, leading to minimum planet masses of Msini=5.33\pm 0.57,
0.62 \pm 0.09 and 3.79\pm0.29 MJup for 14 And b, {\upsilon} And b and 42 Dra b,
respectively. The interferometric measurements of {\theta} Cyg show a
significant diameter variability that remains unexplained up to now. We propose
that the presence of these discrepancies in the interferometric data is caused
by either an intrinsic variation of the star or an unknown close companion
orbiting around it.Comment: 10 pages + 2 pages appendix, 16 figures, accepted for publication in
A&
Searching for faint companions with VLTI/PIONIER. I. Method and first results
Context. A new four-telescope interferometric instrument called PIONIER has
recently been installed at VLTI. It provides improved imaging capabilities
together with high precision. Aims. We search for low-mass companions around a
few bright stars using different strategies, and determine the dynamic range
currently reachable with PIONIER. Methods. Our method is based on the closure
phase, which is the most robust interferometric quantity when searching for
faint companions. We computed the chi^2 goodness of fit for a series of binary
star models at different positions and with various flux ratios. The resulting
chi^2 cube was used to identify the best-fit binary model and evaluate its
significance, or to determine upper limits on the companion flux in case of non
detections. Results. No companion is found around Fomalhaut, tau Cet and
Regulus. The median upper limits at 3 sigma on the companion flux ratio are
respectively of 2.3e-3 (in 4 h), 3.5e-3 (in 3 h) and 5.4e-3 (in 1.5 h) on the
search region extending from 5 to 100 mas. Our observations confirm that the
previously detected near-infrared excess emissions around Fomalhaut and tau Cet
are not related to a low-mass companion, and instead come from an extended
source such as an exozodiacal disk. In the case of del Aqr, in 30 min of
observation, we obtain the first direct detection of a previously known
companion, at an angular distance of about 40 mas and with a flux ratio of
2.05e-2 \pm 0.16e-2. Due to the limited u,v plane coverage, its position can,
however, not be unambiguously determined. Conclusions. After only a few months
of operation, PIONIER has already achieved one of the best dynamic ranges
world-wide for multi-aperture interferometers. A dynamic range up to about
1:500 is demonstrated, but significant improvements are still required to reach
the ultimate goal of directly detecting hot giant extrasolar planets.Comment: 11 pages, 6 figures, accepted for publication in A&
Search for low-mass PMS companions around X-ray selected late B stars
We have observed 49 X-ray detected bright late B-type dwarfs to search for
close low-mass pre-main sequence (PMS) companions using the European Southern
Observatory's ADONIS (Adaptive Optics Near Infrared System) instrument. We
announce the discovery of 21 new companions in 9 binaries, 5 triple, 4
quadruple system and 1 system consisting of five stars. The detected new
companions have K magnitudes between 6.5 mag and 17.3 mag. and angular
separations ranging from 0.2 and 14.1 arcsec (18-2358 AU).Comment: Accepted for publication in Astronomy and Astrophysic
Enhanced Halpha activity at periastron in the young and massive spectroscopic binary HD200775
Young close binaries clear central cavities in their surrounding circumbinary
disk from which the stars can still accrete material. This process takes place
within the very first astronomical units, and is still not well constrained as
the observational evidence has been gathered, until now, only by means of
spectroscopy. The young object HD200775 (MWC361) is a massive spectroscopic
binary (separation of ~15.9mas, ~5.0~AU), with uncertain classification
(early/late Be), that shows a strong and variable Halpha emission. We aim to
study the mechanisms that produce the Halpha line at the AU-scale. Combining
the radial velocity measurements and astrometric data available in the
literature, we determined new orbital parameters. With the VEGA instrument on
the CHARA array, we spatially and spectrally resolved the Halpha emission of
HD200775, at low and medium spectral resolutions (R~1600 and 5000) over a full
orbital period (~3.6 years). We observe that the Halpha equivalent width varies
with the orbital phase, and increases close to periastron, as expected from
theoretical models that predict an increase of the mass transfer from the
circumbinary disk to the primary disk. In addition, using spectral visibilities
and differential phases, we find marginal variations of the typical extent of
the Halpha emission (at 1 to 2-sigma level) and location (at 1 to 5-sigma
level). The spatial extent of the Halpha emission, as probed by a Gaussian
FWHM, is minimum at the ascending node (0.67+/-0.20 mas, i.e., 0.22+/-0.06 AU),
and more than doubles at periastron. In addition, the Gaussian photocenter is
slightly displaced in the direction opposite to the secondary, ruling out the
scenario in which all or most of the Halpha emission is due to accretion onto
the secondary. These findings, together with the wide Halpha line profile, may
be due to a non-spherical wind enhanced at periastron.Comment: Accepted by Astronomy & Astrophysic
Mid-infrared guided optics: a perspective for astronomical instruments
Research activities during the last decade have shown the strong potential of
photonic devices to greatly simplify ground based and space borne astronomical
instruments and to improve their performance. We focus specifically on the
mid-infrared wavelength regime (about 5-20 microns), a spectral range offering
access to warm objects (about 300 K) and to spectral features that can be
interpreted as signatures for biological activity (e.g. water, ozone, carbon
dioxide). We review the relevant research activities aiming at the development
of single-mode guided optics and the corresponding manufacturing technologies.
We evaluate the experimentally achieved performance and compare it with the
performance requirements for applications in various fields of astronomy. Our
goal is to show a perspective for future astronomical instruments based on
mid-infrared photonic devices.Comment: 16 pages, published in OSA Optics Express (see
http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-3-1947
Risk communication films: Process, product and potential for improving preparedness and behaviour change
The medium of film is well established for education and communication about hazardous phenomena as it provides engaging ways to directly view hazards and their impacts. Empirical analysis can help to understand films' effectiveness in informing populations at risk and catalysing action to reduce risk. Using volcanic eruptions as a focus, an evidence-based methodology was devised to create, use, and track the outcomes of digital film tools designed to raise hazard and risk awareness, and develop preparedness efforts. Experiences from two contrasting eruptions were documented, with the secondary purpose of fostering social and cultural memories of eruptions, developed in response to demand from at-risk communities during field-based research. The films were created as a partnership with local volcano monitoring scientists and at-risk populations who, consequently, became the leading focus of the films, thus offering a substantial contrast to other types of hazard communication. The films were analysed by sharing them with at-risk communities and evaluating the immediate influence on learning and affect. Results indicated that the use of local content and actors to share experiences and teach valuable lessons were inspirational. Recognizable faces and spaces helped to convey disaster risk reduction messages. They also motivated audiences to consider ownership of risk and potential actions to reduce risk and strengthen resilience. This study demonstrated the effectiveness of co-production in the design and execution of intervention strategies for volcanic risk reduction. Co-production of films with local agencies resulted in products that were contextually appropriate, meaningful for audiences, and useful risk communication tools
Randomized trial evaluating the framing of cardiovascular risk and its impact on blood pressure control [ISRCTN87597585]
BACKGROUND: The format or frame in which the results of randomized trials are presented has been shown to influence health professional's self-reported practice. We sought to investigate the effect of framing cardiovascular risk as two different formats in a randomized trial. METHODS: We recruited 457 patients aged between 60 and 79 years with high blood pressure from 20 family practices in Avon, UK. Patients were randomized to cardiovascular risk presented either as 1) an absolute risk level (AR) or as 2) the number needed to treat to prevent an adverse event (NNT). The main outcome measures were: 1) percentage of patients in each group with a five-year cardiovascular risk ≥ 10%, 2) systolic and diastolic blood pressure, 3) intensity of prescribing of cardiovascular medication. RESULTS: Presenting cardiovascular risk as either an AR or NNT had no impact reducing cardiovascular risk at 12 month follow up, adjusted odds ratio 1.53 (95%CI 0.76 to 3.08). There was no difference between the two groups in systolic (adjusted difference 0.97 mmHg, 95%CI -2.34 mmHg to 4.29 mmHg) or diastolic (adjusted difference 0.70 mmHg, 95%CI -1.05 mmHg to 2.45 mmHg) blood pressure. Intensity of prescribing of blood pressure lowering drugs was not significantly different between the two groups at six months follow up. CONCLUSIONS: Presenting cardiovascular risk in clinical practice guidelines as either an AR or NNT had a similar influence on patient outcome and prescribing intensity. There is no difference in patient outcomes when these alternative formats of risk are used in clinical practice guidelines
Alternative Splicing Regulates Targeting of Malate Dehydrogenase in Yarrowia lipolytica
Alternative pre-mRNA splicing is a major mechanism contributing to the proteome complexity of most eukaryotes, especially mammals. In less complex organisms, such as yeasts, the numbers of genes that contain introns are low and cases of alternative splicing (AS) with functional implications are rare. We report the first case of AS with functional consequences in the yeast Yarrowia lipolytica. The splicing pattern was found to govern the cellular localization of malate dehydrogenase, an enzyme of the central carbon metabolism. This ubiquitous enzyme is involved in the tricarboxylic acid cycle in mitochondria and in the glyoxylate cycle, which takes place in peroxisomes and the cytosol. In Saccharomyces cerevisiae, three genes encode three compartment-specific enzymes. In contrast, only two genes exist in Y. lipolytica. One gene (YlMDH1, YALI0D16753g) encodes a predicted mitochondrial protein, whereas the second gene (YlMDH2, YALI0E14190g) generates the cytosolic and peroxisomal forms through the alternative use of two 3′-splice sites in the second intron. Both splicing variants were detected in cDNA libraries obtained from cells grown under different conditions. Mutants expressing the individual YlMdh2p isoforms tagged with fluorescent proteins confirmed that they localized to either the cytosolic or the peroxisomal compartment
The organisation and delivery of health improvement in general practice and primary care: a scoping study
Background
This project examines the organisation and delivery of health improvement activities by and within general practice and the primary health-care team. The project was designed to examine who delivers these interventions, where they are located, what approaches are developed in practices, how individual practices and the primary health-care team organise such public health activities, and how these contribute to health improvement. Our focus was on health promotion and ill-health prevention activities.
Aims
The aim of this scoping exercise was to identify the current extent of knowledge about the health improvement activities in general practice and the wider primary health-care team. The key objectives were to provide an overview of the range and type of health improvement activities, identify gaps in knowledge and areas for further empirical research. Our specific research objectives were to map the range and type of health improvement activity undertaken by general practice staff and the primary health-care team based within general practice; to scope the literature on health improvement in general practice or undertaken by health-care staff based in general practice and identify gaps in the evidence base; to synthesise the literature and identify effective approaches to the delivery and organisation of health improvement interventions in a general practice setting; and to identify the priority areas for research as defined by those working in general practice.
Methods
We undertook a comprehensive search of the literature. We followed a staged selection process involving reviews of titles and abstracts. This resulted in the identification of 1140 papers for data extraction, with 658 of these papers selected for inclusion in the review, of which 347 were included in the evidence synthesis. We also undertook 45 individual and two group interviews with primary health-care staff.
Findings
Many of the research studies reviewed had some details about the type, process or location, or who provided the intervention. Generally, however, little attention is paid in the literature to examining the impact of the organisational context on the way services are delivered or how this affects the effectiveness of health improvement interventions in general practice. We found that the focus of attention is mainly on individual prevention approaches, with practices engaging in both primary and secondary prevention. The range of activities suggests that general practitioners do not take a population approach but focus on individual patients. However, it is clear that many general practitioners see health promotion as an integral part of practice, whether as individual approaches to primary or secondary health improvement or as a practice-based approach to improving the health of their patients. Our key conclusion is that there is currently insufficient good evidence to support many of the health improvement interventions undertaken in general practice and primary care more widely.
Future Research
Future research on health improvement in general practice and by the primary health-care team needs to move beyond clinical research to include delivery systems and be conducted in a primary care setting. More research needs to examine areas where there are chronic disease burdens – cancer, dementia and other disabilities of old age. Reviews should be commissioned that examine the whole prevention pathway for health problems that are managed within primary care drawing together research from general practice, pharmacy, community engagement, etc
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