377 research outputs found
Abundance analysis of prime B-type targets for asteroseismology II. B6--B9.5 stars in the field of view of the CoRoT
The CoRoT satellite is collecting precise time-resolved photometry for tens
of asteroseismology targets. To ensure a correct interpretation of the CoRoT
data, the atmospheric parameters, chemical compositions, and rotational
velocities of the stars must be determined. The main goal of the ground-based
seismology support program for the CoRoT mission was to obtain photometric and
spectroscopic data for stars in the fields monitored by the satellite. These
ground-based observations were collected in the GAUDI archive. High-resolution
spectra of more than 200 B-type stars are available in this database, and about
45% of them is analysed here. To derive the effective temperature of the stars,
we used photometric indices. Surface gravities were obtained by comparing
observed and theoretical Balmer line profiles. To determine the chemical
abundances and rotational velocities, we used a spectrum synthesis method,
which consisted of comparing the observed spectrum with theoretical ones based
on the assumption of LTE. Atmospheric parameters, chemical abundances, and
rotational velocities were determined for 89 late-B stars. The dominant species
in their spectra are iron-peak elements. The average Fe abundance is
7.24+/-0.45 dex. The average rotational velocity is 126 km/sec, but there are
13 and 20 stars with low and moderate Vsin i values, respectively. The analysis
of this sample of 89 late B-type stars reveals many chemically peculiar (CP)
stars. Some of them were previously known, but at least 9 new CP candidates,
among which at least two HgMn stars, are identified in our study. These CP
stars as a group exhibit Vsin i values lower than the stars with normal surface
chemical composition.Comment: 21 pages, 13 figures, accepted to Astronomy and Astrophysic
Magnetism, chemical spots, and stratification in the HgMn star phi Phoenicis
Mercury-manganese (HgMn) stars have been considered as non-magnetic and
non-variable chemically peculiar (CP) stars for a long time. However, recent
discoveries of the variability in spectral line profiles have suggested an
inhomogeneous surface distribution of chemical elements in some HgMn stars.
From the studies of other CP stars it is known that magnetic field plays a key
role in the formation of surface spots. All attempts to find magnetic fields in
HgMn stars have yielded negative results. In this study, we investigate the
possible presence of a magnetic field in phi Phe (HD 11753) and reconstruct
surface distribution of chemical elements that show variability in spectral
lines.We also test a hypothesis that a magnetic field is concentrated in
chemical spots and look into the possibility that some chemical elements are
stratified with depth in the stellar atmosphere. Our analysis is based on
high-quality spectropolarimetric time-series observations, covering a full
rotational period of the star. Spectra were obtained with the HARPSpol at the
ESO 3.6-m telescope. Combining information from all suitable spectral lines, we
set an upper limit of 4 G on the mean longitudinal magnetic field. For chemical
spots, an upper limit on the longitudinal field varies between 8 and 15 G. We
confirmed the variability of Y, Sr, and Ti and detected variability in Cr
lines. Stratification analysis showed that Y and Ti are not concentrated in the
uppermost atmospheric layers. Our spectropolarimetric observations rule out the
presence of a strong, globally-organised magnetic field in phi Phe. This
implies an alternative mechanism of spot formation, which could be related to a
non-equilibrium atomic diffusion. However, the typical time scales of the
variation in stratification predicted by the recent time-dependent diffusion
models exceed significantly the spot evolution time-scale reported for phi Phe.Comment: Accepted for publication in Astronomy & Astrophysics, 15 pages, 15
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Possible Race and Gender Divergence in Association of Genetic Variations with Plasma von Willebrand Factor: A Study of ARIC and 1000 Genome Cohorts
The synthesis, secretion and clearance of von Willebrand factor (VWF) are regulated by genetic variations in coding and promoter regions of the VWF gene. We have previously identified 19 single nucleotide polymorphisms (SNPs), primarily in introns that are associated with VWF antigen levels in subjects of European descent. In this study, we conducted race by gender analyses to compare the association of VWF SNPs with VWF antigen among 10,434 healthy Americans of European (EA) or African (AA) descent from the Atherosclerosis Risk in Communities (ARIC) study. Among 75 SNPs analyzed, 13 and 10 SNPs were associated with VWF antigen levels in EA male and EA female subjects, respectively. However, only one SNP (RS1063857) was significantly associated with VWF antigen in AA females and none was in AA males. Haplotype analysis of the ARIC samples and studying racial diversities in the VWF gene from the 1000 genomes database suggest a greater degree of variations in the VWF gene in AA subjects as compared to EA subjects. Together, these data suggest potential race and gender divergence in regulating VWF expression by genetic variations
Canalization effect in the coagulation cascade and the interindividual variability of oral anticoagulant response. a simulation Study
<p>Abstract</p> <p>Background</p> <p>Increasing the predictability and reducing the rate of side effects of oral anticoagulant treatment (OAT) requires further clarification of the cause of about 50% of the interindividual variability of OAT response that is currently unaccounted for. We explore numerically the hypothesis that the effect of the interindividual expression variability of coagulation proteins, which does not usually result in a variability of the coagulation times in untreated subjects, is unmasked by OAT.</p> <p>Results</p> <p>We developed a stochastic variant of the Hockin-Mann model of the tissue factor coagulation pathway, using literature data for the variability of coagulation protein levels in the blood of normal subjects. We simulated <it>in vitro </it>coagulation and estimated the Prothrombin Time and the INR across a model population. In a model of untreated subjects a "canalization effect" can be observed in that a coefficient of variation of up to 33% of each protein level results in a simulated INR of 1 with a clinically irrelevant dispersion of 0.12. When the mean and the standard deviation of vitamin-K dependent protein levels were reduced by 80%, corresponding to the usual Warfarin treatment intensity, the simulated INR was 2.98 ± 0.48, a clinically relevant dispersion, corresponding to a reduction of the canalization effect.</p> <p>Then we combined the Hockin-Mann stochastic model with our previously published model of population response to Warfarin, that takes into account the genetical and the phenotypical variability of Warfarin pharmacokinetics and pharmacodynamics. We used the combined model to evaluate the coagulation protein variability effect on the variability of the Warfarin dose required to reach an INR target of 2.5. The dose variance when removing the coagulation protein variability was 30% lower. The dose was mostly related to the pretreatment levels of factors VII, X, and the tissue factor pathway inhibitor (TFPI).</p> <p>Conclusions</p> <p>It may be worth exploring in experimental studies whether the pretreatment levels of coagulation proteins, in particular VII, X and TFPI, are predictors of the individual warfarin dose, even though, maybe due to a canalization-type effect, their effect on the INR variance in untreated subjects appears low.</p
No magnetic field in the spotted HgMn star mu Leporis
Chemically peculiar stars of the mercury-manganese (HgMn) type represent a
new class of spotted late-B stars, in which evolving surface chemical
inhomogeneities are apparently unrelated to the presence of strong magnetic
fields but are produced by some hitherto unknown astrophysical mechanism. The
goal of this study is to perform a detailed line profile variability analysis
and carry out a sensitive magnetic field search for one of the brightest HgMn
stars - mu Lep. We acquired a set of very high-quality intensity and
polarization spectra of mu Lep with the HARPSpol polarimeter. These data were
analyzed with the multiline technique of least-squares deconvolution in order
to extract information on the magnetic field and line profile variability. Our
spectra show very weak but definite variability in the lines of Sc, all Fe-peak
elements represented in the spectrum of mu Lep, as well as Y, Sr, and Hg.
Variability might also be present in the lines of Si and Mg. Anomalous profile
shapes of Ti II and Y II lines suggest a dominant axisymmetric distribution of
these elements. At the same time, we found no evidence of the magnetic field in
mu Lep, with the 3 sigma upper limit of only 3 G for the mean longitudinal
magnetic field. This is the most stringent upper limit on the possible magnetic
field derived for a spotted HgMn star. The very weak variability detected for
many elements in the spectrum mu Lep suggests that low-contrast chemical
inhomogeneities may be common in HgMn stars and that they have not been
recognized until now due to the limited precision of previous spectroscopic
observations and a lack of time-series data. The null result of the magnetic
field search reinforces the conclusion that formation of chemical spots in HgMn
stars is not magnetically driven.Comment: Accepted for publication in Astronomy & Astrophysic
Estimating the Impact of Adding C-Reactive Protein as a Criterion for Lipid Lowering Treatment in the United States
BACKGROUND: There is growing interest in using C-reactive protein (CRP) levels to help select patients for lipid lowering therapy—although this practice is not yet supported by evidence of benefit in a randomized trial. OBJECTIVE: To estimate the number of Americans potentially affected if a CRP criteria were adopted as an additional indication for lipid lowering therapy. To provide context, we also determined how well current lipid lowering guidelines are being implemented. METHODS: We analyzed nationally representative data to determine how many Americans age 35 and older meet current National Cholesterol Education Program (NCEP) treatment criteria (a combination of risk factors and their Framingham risk score). We then determined how many of the remaining individuals would meet criteria for treatment using 2 different CRP-based strategies: (1) narrow: treat individuals at intermediate risk (i.e., 2 or more risk factors and an estimated 10–20% risk of coronary artery disease over the next 10 years) with CRP > 3 mg/L and (2) broad: treat all individuals with CRP > 3 mg/L. DATA SOURCE: Analyses are based on the 2,778 individuals participating in the 1999–2002 National Health and Nutrition Examination Survey with complete data on cardiac risk factors, fasting lipid levels, CRP, and use of lipid lowering agents. MAIN MEASURES: The estimated number and proportion of American adults meeting NCEP criteria who take lipid-lowering drugs, and the additional number who would be eligible based on CRP testing. RESULTS: About 53 of the 153 million Americans aged 35 and older meet current NCEP criteria (that do not involve CRP) for lipid-lowering treatment. Sixty-five percent, however, are not currently being treated, even among those at highest risk (i.e., patients with established heart disease or its risk equivalent)—62% are untreated. Adopting the narrow and broad CRP strategies would make an additional 2.1 and 25.3 million Americans eligible for treatment, respectively. The latter strategy would make over half the adults age 35 and older eligible for lipid-lowering therapy, with most of the additionally eligible (57%) coming from the lowest NCEP heart risk category (i.e., 0–1 risk factors). CONCLUSION: There is substantial underuse of lipid lowering therapy for American adults at high risk for coronary disease. Rather than adopting CRP-based strategies, which would make millions more lower risk patients eligible for treatment (and for whom treatment benefit has not yet been demonstrated in a randomized trial), we should ensure the treatment of currently defined high-risk patients for whom the benefit of therapy is established
Crisis Visits and Psychiatric Hospitalizations Among Patients Attending a Community Clinic in Rural Southern California
Ethnic minorities from disadvantaged socioeconomic backgrounds report increased utilization of mental health emergency services; however findings have been inconsistent across ethnic/racial groups. In this study we describe patients who present to a rural crisis unit in Southern California, examine rates of psychiatric hospitalizations across ethnic/racial groups, and investigate factors that are associated with increased psychiatric hospitalizations in this sample. This is a retrospective study of 451 racially and ethnically diverse patients attending a crisis unit in Imperial County, California. Chart review and data abstraction methods were used to characterize the sample and identify factors associated with psychiatric crises and subsequent hospitalizations. The sample was predominantly Latino/Hispanic (58.5%). Based on chart review, common psychosocial stressors which prompted a crisis center visit were: (a) financial problems; (b) homelessness; (c) partner or family conflict; (d) physical and health problems; (e) problems at school/work; (f) medication compliance; (g) aggressive behavior; (h) delusional behavior; (i) addiction and (j) anxiety/depression. Bivariate analyses revealed that Hispanics had a disproportionately lower rate of psychiatric hospitalizations while African Americans had a higher rate. Multivariate analyses which included demographic, clinical and psychosocial stressor variables revealed that being African American, having a psychotic disorder, and presenting as gravely disabled were associated with a higher likelihood of hospitalization while partner/family conflict was associated with a lesser likelihood in this rural community. These data elucidate the need for longitudinal studies to understand the interactions between psychosocial stressors, ethnicity and social support as determinants of psychiatric hospitalizations
Systematically missing confounders in individual participant data meta-analysis of observational cohort studies.
One difficulty in performing meta-analyses of observational cohort studies is that the availability of confounders may vary between cohorts, so that some cohorts provide fully adjusted analyses while others only provide partially adjusted analyses. Commonly, analyses of the association between an exposure and disease either are restricted to cohorts with full confounder information, or use all cohorts but do not fully adjust for confounding. We propose using a bivariate random-effects meta-analysis model to use information from all available cohorts while still adjusting for all the potential confounders. Our method uses both the fully adjusted and the partially adjusted estimated effects in the cohorts with full confounder information, together with an estimate of their within-cohort correlation. The method is applied to estimate the association between fibrinogen level and coronary heart disease incidence using data from 154,012 participants in 31 cohort
Arsenic in drinking water and cerebrovascular disease, diabetes mellitus, and kidney disease in Michigan: a standardized mortality ratio analysis
BACKGROUND: Exposure to arsenic concentrations in drinking water in excess of 300 μg/L is associated with diseases of the circulatory and respiratory system, several types of cancer, and diabetes; however, little is known about the health consequences of exposure to low-to-moderate levels of arsenic (10–100 μg/L). METHODS: A standardized mortality ratio (SMR) analysis was conducted in a contiguous six county study area of southeastern Michigan to investigate the relationship between moderate arsenic levels and twenty-three selected disease outcomes. Disease outcomes included several types of cancer, diseases of the circulatory and respiratory system, diabetes mellitus, and kidney and liver diseases. Arsenic data were compiled from 9251 well water samples tested by the Michigan Department of Environmental Quality from 1983 through 2002. Michigan Resident Death Files data were amassed for 1979 through 1997 and sex-specific SMR analyses were conducted with indirect adjustment for age and race; 99% confidence intervals (CI) were reported. RESULTS: The six county study area had a population-weighted mean arsenic concentration of 11.00 μg/L and a population-weighted median of 7.58 μg/L. SMR analyses were conducted for the entire six county study area, for only Genesee County (the most populous and urban county), and for the five counties besides Genesee. Concordance of results across analyses is used to interpret the findings. Elevated mortality rates were observed for both males (M) and females (F) for all diseases of the circulatory system (M SMR, 1.11; CI, 1.09–1.13; F SMR, 1.15; CI, 1.13,-1.17), cerebrovascular diseases (M SMR, 1.19; CI, 1.14–1.25; F SMR, 1.19; CI, 1.15–1.23), diabetes mellitus (M SMR, 1.28; CI, 1.18–1.37; F SMR, 1.27; CI, 1.19–1.35), and kidney diseases (M SMR, 1.28; CI, 1.15–1.42; F SMR, 1.38; CI, 1.25–1.52). CONCLUSION: This is some of the first evidence to suggest that exposure to low-to-moderate levels of arsenic in drinking water may be associated with several of the leading causes of mortality, although further epidemiologic studies are required to confirm the results suggested by this ecologic SMR analysis
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