6,600 research outputs found
A Search for Intrinsic Polarization in O Stars with Variable Winds
New observations of 9 of the brightest northern O stars have been made with
the Breger polarimeter on the 0.9~m telescope at McDonald Observatory and the
AnyPol polarimeter on the 0.4~m telescope at Limber Observatory, using the
Johnson-Cousins UBVRI broadband filter system. Comparison with earlier
measurements shows no clearly defined long-term polarization variability. For
all 9 stars the wavelength dependence of the degree of polarization in the
optical range can be fit by a normal interstellar polarization law. The
polarization position angles are practically constant with wavelength and are
consistent with those of neighboring stars. Thus the simplest conclusion is
that the polarization of all the program stars is primarily interstellar.
The O stars chosen for this study are generally known from ultraviolet and
optical spectroscopy to have substantial mass loss rates and variable winds, as
well as occasional circumstellar emission. Their lack of intrinsic polarization
in comparison with the similar Be stars may be explained by the dominance of
radiation as a wind driving force due to higher luminosity, which results in
lower density and less rotational flattening in the electron scattering inner
envelopes where the polarization is produced. However, time series of
polarization measurements taken simultaneously with H-alpha and UV spectroscopy
during several coordinated multiwavelength campaigns suggest two cases of
possible small-amplitude, periodic short-term polarization variability, and
therefore intrinsic polarization, which may be correlated with the more widely
recognized spectroscopic variations.Comment: LaTeX2e, 22 pages including 11 tables; 12 separate gif figures; uses
aastex.cls preprint package; accepted by The Astronomical Journa
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Implementation of an interior point source in the ultra weak variational formulation through source extraction
The Ultra Weak Variational Formulation (UWVF) is a powerful numerical method for the approximation of acoustic, elastic and electromagnetic waves in the time-harmonic regime. The use of Trefftz-type basis functions incorporates the known wave-like behaviour of the solution in the discrete space, allowing large reductions in the required number of degrees of freedom for a given accuracy, when compared to standard finite element methods. However, the UWVF is not well disposed to the accurate approximation of singular sources in the interior of the computational domain. We propose an adjustment to the UWVF for seismic imaging applications, which we call the Source Extraction UWVF. Differing fields are solved for in subdomains around the source, and matched on the inter-domain boundaries. Numerical results are presented for a domain of constant wavenumber and for a domain of varying sound speed in a model used for seismic imaging
Studies in the Lake Ontario Basin using ERTS-1 and high altitude data
Studies in the Lake Ontario Basin are designed to provide input for models of river basin discharge and macro-scale features of lake circulation. Lake studies appear to require high altitude imagery to record the dynamic features of Lake Ontario so that ERTS-1 data may be interpreted. Land area studies require input of soil moisture, land use and soil-sediment-geomorphology measurements some of which appear to be available, on a regional scale from ERTS-1 products
A performance evaluation of commercial fibrinogen reference preparations and assays for Clauss and PT-derived fibrinogen
The wide availability of fibrinogen estimations based on the prothrombin time (PT-Fg) has caused concern about the variability and clinical utility of fibrinogen assays. In a multi-centre study, we investigated fibrinogen assays using various reagents and analysers, Clauss assays generally gave good agreement, although one reagent gave 15-30% higher values in DIC and thrombolysis. Two commercial reference preparations had much lower potencies than the manufacturers declared, and plasma turbidity influenced parallelism in some Clauss assays, PT-Fg assays gave higher values than Clauss and showed calibrant dependent effects, the degree of disparity correlating with calibrant and test sample turbidity. Analyser and thromboplastin dependent differences were noted. The relationship between Clauss and PT-Fg assays was sigmoid, and the plateau of maximal PT-Fg differed by about 2 g/l between reagents. ELISA and immunonephelometric assays correlated well, but with a high degree of scatter. Antigen levels were higher than Clauss, but slightly lower than PT-Fg assays, which appeared to be influenced by degraded fibrinogen. Clauss assays are generally reproducible between centres, analysers and reagents, but PT-Fg assays are not reliable in clinical settings
The VLT-FLAMES Tarantula Survey XXII. Multiplicity properties of the B-type stars
We investigate the multiplicity properties of 408 B-type stars observed in
the 30 Doradus region of the Large Magellanic Cloud with multi-epoch
spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a
cross-correlation method to estimate relative radial velocities from the helium
and metal absorption lines for each of our targets. Objects with significant
radial-velocity variations (and with an amplitude larger than 16 km/s) are
classified as spectroscopic binaries. We find an observed spectroscopic binary
fraction (defined by periods of 0.1) for the B-type
stars, f_B(obs) = 0.25 +/- 0.02, which appears constant across the field of
view, except for the two older clusters (Hodge 301 and SL 639). These two
clusters have significantly lower fractions of 0.08 +/- 0.08 and 0.10 +/- 0.09,
respectively. Using synthetic populations and a model of our observed epochs
and their potential biases, we constrain the intrinsic multiplicity properties
of the dwarf and giant (i.e. relatively unevolved) B-type stars in 30 Dor. We
obtain a present-day binary fraction f_B(true) = 0.58 +/- 0.11, with a flat
period distribution. Within the uncertainties, the multiplicity properties of
the B-type stars agree with those for the O stars in 30 Dor from the VFTS.Comment: Accepted by A&
The VLT-FLAMES Tarantula Survey XXIII. Two massive double-lined binaries in 30 Doradus
Aims. We investigate the characteristics of two newly discovered short-period, double-lined, massive binary systems in the Large
Magellanic Cloud, VFTS 450 (O9.7 IIâIb + O7::) and VFTS 652 (B1 Ib + O9: III:).
Methods. We perform model-atmosphere analyses to characterise the photospheric properties of both members of each binary (denoting the âprimaryâ as the spectroscopically more conspicuous component). Radial velocities and optical photometry are used to estimate the binary-system parameters.
Results. We estimate Teff = 27 kK, log g = 2.9 (cgs) for the VFTS 450 primary spectrum (34 kK, 3.6: for the secondary spectrum); and Teff = 22 kK, log g = 2.8 for the VFTS 652 primary spectrum (35 kK, 3.7: for the secondary spectrum). Both primaries show surface nitrogen enrichments (of more than 1 dex for VFTS 652), and probable moderate oxygen depletions relative to reference LMC abundances. We determine orbital periods of 6.89 d and 8.59 d for VFTS 450 and VFTS 652, respectively, and argue that the primaries must be close to filling their Roche lobes. Supposing this to be the case, we estimate component masses in the range âŒ20â50 Mâ.
Conclusions. The secondary spectra are associated with the more massive components, suggesting that both systems are high-mass analogues of classical Algol systems, undergoing case-A mass transfer. Difficulties in reconciling the spectroscopic analyses with the light-curves and with evolutionary considerations suggest that the secondary spectra are contaminated by (or arise in) accretion disks
Advancing methodology for scoping reviews: recommendations arising from a scoping literature review (SLR) to inform transformation of Children and Adolescent Mental Health Services
Background
There is consensus that health services commissioning and clinical practice should be driven by scientific evidence. However, workload pressures, accessibility of peer reviewed publications and skills to find, appraise, and synthesise relevant evidence are often cited as barriers to uptake of research evidence by practitioners and commissioners alike. In recent years a growing requirement for rapid evidence synthesis to inform commissioning decisions about healthcare service delivery and provision of care contributed to an increasing popularity of scoping literature reviews (SLRs). Yet, comprehensive guidelines for conducting and reporting SLRs are still relatively scarce.
Methods
The exemplar review used as a worked example aimed to provide a readily available, comprehensive, and user-friendly repository of research evidence for local commissioners to help them make evidence-informed decisions about redesigning East of England Children and Adolescent Mental Health Services. In conducting the review, we were broadly guided by Arksey and OâMalleyâs framework, however some modifications were made at different stages to better reflect the largely pragmatic objective of this review. This paper compares the methodology used with existing methodological frameworks for scoping studies, to add to the existing knowledge base.
Results
We proposed the following advancements to the existing SLR frameworks: (i) Assemble a research team with complementary skills and expertise; (ii); Draw on expertise of external partners, particularly practitioners, decision-makers and commissioners who will be translating findings into practice; (iii) Pre-register the review protocol. Keep a detailed record of all steps and decisions and consider how they would impact on generalisability and utility of review findings; (iv) Use systematic procedures for literature searchers, selection of studies, data extraction and analysis; (v) If feasible, appraise the quality of included evidence; (vi) Be transparent about limitations of findings.
Conclusions
Despite some methodological limitations, scoping literature reviews are a useful method of rapidly synthesising a large body of evidence to inform commissioning and transformation of CAMHS. SLRs allow researchers to start with a broader questions, to explore the issue from different perspectives and perhaps find more comprehensive solutions that are not only effective, but also accounted for their feasibility and acceptability to key stakeholders
LSC-2019-Post-transcriptional dysregulation as a novel mechanism underlying non-responsive severe asthma
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