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An ASKAP Search for a Radio Counterpart to the First High-significance Neutron Star-Black Hole Merger LIGO/Virgo S190814bv
We present results from a search for a radio transient associated with the LIGO/Virgo source S190814bv, a likely neutron star-black hole (NSBH) merger, with the Australian Square Kilometre Array Pathfinder. We imaged a 30 deg2 field at ΔT = 2, 9, and 33 days post-merger at a frequency of 944 MHz, comparing them to reference images from the Rapid ASKAP Continuum Survey observed 110 days prior to the event. Each epoch of our observations covers 89% of the LIGO/Virgo localization region. We conducted an untargeted search for radio transients in this field, resulting in 21 candidates. For one of these, AT2019osy, we performed multiwavelength follow-up and ultimately ruled out the association with S190814bv. All other candidates are likely unrelated variables, but we cannot conclusively rule them out. We discuss our results in the context of model predictions for radio emission from NSBH mergers and place constrains on the circum-merger density and inclination angle of the merger. This survey is simultaneously the first large-scale radio follow-up of an NSBH merger, and the most sensitive widefield radio transients search to-date
The completeness and reliability of threshold and false-discovery-rate source extraction algorithms for compact continuum sources
The process of determining the number and characteristics of sources in
astronomical images is so fundamental to a large range of astronomical problems
that it is perhaps surprising that no standard procedure has ever been defined
that has well understood properties with a high degree of statistical rigour on
completeness and reliability. There are now a large number of commonly used
software tools for accomplishing this task, typically with different tools
being used for images acquired using different technologies. Despite this,
there have been relatively few quantitative analyses of the robustness or
reliability of individual tools, or the details of the techniques they
implement. We have an opportunity to redress this omission in the context of
surveys planned with the Australian Square Kilometre Array Pathfinder (ASKAP).
The Evolutionary Map of the Universe (EMU) survey with ASKAP, a continuum
survey of the Southern Hemisphere up to declination +30 deg, aims to utilise an
automated source identification and measurement approach that is demonstrably
optimal, to maximise the reliability, utility and robustness of the resulting
radio source catalogues. A key stage in source extraction methods is the
background estimation (background level and noise level) and the choice of a
threshold high enough to reject false sources yet not so high that the
catalogues are significantly incomplete. In this analysis we present results
from testing such algorithms as implemented in the SExtractor, Selavy
(Duchamp), and sfind tools on simulated data. In particular the effects of
background estimation, threshold and false-discovery rate settings are
explored. For parameters that give similar completeness, the false-discovery
rate method employed by sfind results in a more reliable catalogue compared to
the peak threshold methods of SExtractor and Selavy.Comment: 17 pages, 13 figures, accepted by PAS
Spectroscopy of globular clusters in the low-luminosity spiral galaxy NGC 45
CONTEXT: Extragalactic globular clusters have been studied in elliptical
galaxies and in a few luminous spiral galaxies, but little is known about
globular clusters in low-luminosity spirals.
AIMS: Past observations with the ACS have shown that NGC 45 hosts a large
population of globular clusters (19), as well as several young star clusters.
In this work we aim to confirm the bona fide globular cluster status for 8 of
19 globular cluster candidates and to derive metallicities, ages, and
velocities.
METHODS: VLT/FORS2 multislit spectroscopy in combination with the Lick/IDS
system was used to derive velocities and to constrain metallicities and
[alpha/Fe] element ratio of the globular clusters.
RESULTS: We confirm the 8 globular clusters as bona fide globular clusters.
Their velocities indicate halo or bulge-like kinematics, with little or no
overall rotation. From absorption indices such as H_beta, H_gamma, and H_delta
and the combined [MgFe]' index, we found that the globular clusters are
metal-poor [Z/H]<=-0.33 dex and [alpha/Fe]<=0.0 element ratio. These results
argue in favor of a population of globular clusters formed during the
assembling of the galaxy.Comment: Accepted for publication in Astronomy and Astrophysics. 10 pages, 6
figures. Table 6 and Fig. 6 will only be published in the electronic edition
of the A&A journa
Antlia Dwarf Galaxy: Distance, quantitative morphology and recent formation history via statistical field correction
We apply a statistical field correction technique originally designed to
determine membership of high redshift galaxy clusters to Hubble Space Telescope
imaging of the Antlia Dwarf Galaxy; a galaxy at the very edge of the Local
Group. Using the tip of the red giant branch standard candle method coupled
with a simple Sobel edge detection filter we find a new distance to Antlia of
1.31 +/- 0.03 Mpc. For the first time for a Local Group Member, we compute the
concentration, asymmetry and clumpiness (CAS) quantitative morphology
parameters for Antlia from the distribution of resolved stars in the HST/ACS
field, corrected with a new method for contaminants and complement these
parameters with the Gini coefficient (G) and the second order moment of the
brightest 20 per cent of the flux (M_20). We show that it is a classic dwarf
elliptical (C = 2.0, A = 0.063, S = 0.077, G = 0.39 and M_20 = -1.17 in the
F814W band), but has an appreciable blue stellar population at its core,
confirming on-going star-formation. The values of asymmetry and clumpiness, as
well as Gini and M_20 are consistent with an undisturbed galaxy. Although our
analysis suggests that Antlia may not be tidally influenced by NGC 3109 it does
not necessarily preclude such interaction.Comment: Accepted for publication in MNRA
Salt reduction strategies in Portuguese school meals, from pre-school to secondary education-the Eat Mediterranean program
High sodium (salt) consumption is associated with an increased risk of developing non-communicable diseases. However, in most European countries, Portugal included, sodium intake is still high. This study aimed to assess the sodium content of school meals before and after the Eat Mediterranean (EM) intervention-a community-based program to identify and correct nutritional deviations through the implementation of new school menus and through schools' food handlers training. EM (2015-2017) was developed in 25 schools (pre to secondary education) of two Portuguese Municipalities, reaching students aged 3-21 years old. Samples of the complete meals (soup + main course + bread) from all schools were collected, and nutritional quality and laboratory analysis were performed to determine their nutritional composition, including sodium content. Overall, there was a significant decrease (-23%) in the mean sodium content of the complete school meals, which was mainly achieved by the significant reduction of 34% of sodium content per serving portion of soup. In conclusion, EM had a positive effect on the improvement of the school meals' sodium content, among the participant schools. Furthermore, school setting might be ideal for nutrition literacy interventions among children, for flavors shaping, and for educating towards less salty food acceptance
Accuracy of magnetic resonance studies in the detection of chondral and labral lesions in femoroacetabular impingement : systematic review and meta-analysis
Background: Several types of Magnetic resonance imaging (MRI) are commonly used in imaging of femoroacetabular impingement (FAI), however till now there are no clear protocols and recommendations for each type. The aim of this meta-analysis is to detect the accuracy of conventional magnetic resonance imaging (cMRI), direct magnetic resonance arthrography (dMRA) and indirect magnetic resonance arthrography (iMRA) in the diagnosis of chondral and labral lesions in femoroacetabular impingement (FAI).
Methods: A literature search was finalized on the 17th of May 2016 to collect all studies identifying the accuracy of cMRI, dMRA and iMRA in diagnosing chondral and labral lesions associated with FAI using surgical results (arthroscopic or open) as a reference test. Pooled sensitivity and specificity with 95% confidence intervals using a random-effects meta-analysis for MRI, dMRA and iMRA were calculated also area under receiver operating characteristic (ROC) curve (AUC) was retrieved whenever possible where AUC is equivocal to diagnostic accuracy.
Results: The search yielded 192 publications which were reviewed according inclusion and exclusion criteria then 21 studies fulfilled the eligibility criteria for the qualitative analysis with a total number of 828 cases, lastly 12 studies were included in the quantitative meta-analysis. Meta-analysis showed that as regard labral lesions the pooled sensitivity, specificity and AUC for cMRI were 0.864, 0.833 and 0.88 and for dMRA were 0.91, 0.58 and 0.92. While in chondral lesions the pooled sensitivity, specificity and AUC for cMRI were 0.76, 0.72 and 0.75 and for dMRA were 0.75, 0.79 and 0.83, while for iMRA were sensitivity of 0.722 and specificity of 0.917.
Conclusions: The present meta-analysis showed that the diagnostic test accuracy was superior for dMRA when compared with cMRI for detection of labral and chondral lesions. The diagnostic test accuracy was superior for labral lesions when compared with chondral lesions in both cMRI and dMRA. Promising results are obtained concerning iMRA but further studies still needed to fully assess its diagnostic accuracy
A new galaxy near the Local Group in Draco
We present HST WFPC2 and ground-based images of the low surface brightness
dwarf Irr/Sph galaxy KKR~25 in Draco. Its colour-magnitude diagram shows red
giant branch stars with the tip at I = 22.32 mag, and the presence of some blue
stars. The derived true distance modulus, 26.35 \+- 0.14 mag, corresponds to
linear distances of KKR25 from the Milky Way and from the Local Group centroid
of 1.86 and 1.79 Mpc, respectively. The absolute magnitude of the galaxy, M_V =
-10.48, its linear diameter (0.54 Kpc) and central surface brightness (24.0 +-
0.2 mag\arcsec^2) are typical of other dIrr/dSphs in the Local Group. Being
situated just beyond the radius of the zero-velocity surface of the Local
Group, KKR25 moves away from the LG centroid at a velocity of V_{LG} = + 72
km/s.Comment: 9 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
How does study quality affect the results of a diagnostic meta-analysis?
Background: The use of systematic literature review to inform evidence based practice in diagnostics is rapidly expanding. Although the primary diagnostic literature is extensive, studies are often of low methodological quality or poorly reported. There has been no rigorously evaluated, evidence based tool to assess the methodological quality of diagnostic studies. The primary objective of this study was to determine the extent to which variations in the quality of primary studies impact the results of a diagnostic meta-analysis and whether this differs with diagnostic test type. A secondary objective was to contribute to the evaluation of QUADAS, an evidence-based tool for the assessment of quality in diagnostic accuracy studies. Methods: This study was conducted as part of large systematic review of tests used in the diagnosis and further investigation of urinary tract infection (UTI) in children. All studies included in this review were assessed using QUADAS, an evidence-based tool for the assessment of quality in systematic reviews of diagnostic accuracy studies. The impact of individual components of QUADAS on a summary measure of diagnostic accuracy was investigated using regression analysis. The review divided the diagnosis and further investigation of UTI into the following three clinical stages: diagnosis of UTI, localisation of infection, and further investigation of the UTI. Each stage used different types of diagnostic test, which were considered to involve different quality concerns. Results: Many of the studies included in our review were poorly reported. The proportion of QUADAS items fulfilled was similar for studies in different sections of the review. However, as might be expected, the individual items fulfilled differed between the three clinical stages. Regression analysis found that different items showed a strong association with test performance for the different tests evaluated. These differences were observed both within and between the three clinical stages assessed by the review. The results of regression analyses were also affected by whether or not a weighting (by sample size) was applied. Our analysis was severely limited by the completeness of reporting and the differences between the index tests evaluated and the reference standards used to confirm diagnoses in the primary studies. Few tests were evaluated by sufficient studies to allow meaningful use of meta-analytic pooling and investigation of heterogeneity. This meant that further analysis to investigate heterogeneity could only be undertaken using a subset of studies, and that the findings are open to various interpretations. Conclusion: Further work is needed to investigate the influence of methodological quality on the results of diagnostic meta-analyses. Large data sets of well-reported primary studies are needed to address this question. Without significant improvements in the completeness of reporting of primary studies, progress in this area will be limited
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