3,468 research outputs found
How the First Stars Regulated Star Formation. II. Enrichment by Nearby Supernovae
Metals from Population III (Pop III) supernovae led to the formation of less
massive Pop II stars in the early universe, altering the course of evolution of
primeval galaxies and cosmological reionization. There are a variety of
scenarios in which heavy elements from the first supernovae were taken up into
second-generation stars, but cosmological simulations only model them on the
largest scales. We present small-scale, high-resolution simulations of the
chemical enrichment of a primordial halo by a nearby supernova after partial
evaporation by the progenitor star. We find that ejecta from the explosion
crash into and mix violently with ablative flows driven off the halo by the
star, creating dense, enriched clumps capable of collapsing into Pop II stars.
Metals may mix less efficiently with the partially exposed core of the halo, so
it might form either Pop III or Pop II stars. Both Pop II and III stars may
thus form after the collision if the ejecta do not strip all the gas from the
halo. The partial evaporation of the halo prior to the explosion is crucial to
its later enrichment by the supernova.Comment: Accepted to Ap
Socioeconomic inequalities in attitudes towards cancer: an international cancer benchmarking partnership study.
Socioeconomic status (SES) differences in attitudes towards cancer have been implicated in the differential screening uptake and the timeliness of symptomatic presentation. However, the predominant emphasis of this work has been on cancer fatalism, and many studies focus on specific community subgroups. This study aimed to assess SES differences in positive and negative attitudes towards cancer in UK adults. A population-based sample of UK adults (n=6965, age≥50 years) completed the Awareness and Beliefs about Cancer scale, including six belief items: three positively framed (e.g. 'Cancer can often be cured') and three negatively framed (e.g. 'A cancer diagnosis is a death sentence'). SES was indexed by education. Analyses controlled for sex, ethnicity, marital status, age, self-rated health, and cancer experience. There were few education-level differences for the positive statements, and overall agreement was high (all>90%). In contrast, there were strong differences for negative statements (all Ps<0.001). Among respondents with lower education levels, 57% agreed that 'treatment is worse than cancer', 27% that cancer is 'a death sentence' and 16% 'would not want to know if I have cancer'. Among those with university education, the respective proportions were 34, 17 and 6%. Differences were not explained by cancer experience or health status. In conclusion, positive statements about cancer outcomes attract near-universal agreement. However, this optimistic perspective coexists alongside widespread fears about survival and treatment, especially among less-educated groups. Health education campaigns targeting socioeconomically disadvantaged groups might benefit from a focus on reducing negative attitudes, which is not necessarily achieved by promoting positive attitudes
Automated Vessel Segmentation Using Infinite Perimeter Active Contour Model with Hybrid Region Information with Application to Retinal Images
Automated detection of blood vessel structures is becoming of crucial interest for better management of vascular disease. In this paper, we propose a new infinite active contour model that uses hybrid region information of the image to approach this problem. More specifically, an infinite perimeter regularizer, provided by using L 2 Lebesgue measure of the γ-neighborhood of boundaries, allows for better detection of small oscillatory (branching) structures than the traditional models based on the length of a feature's boundaries (i.e., H 1 Hausdorff measure). Moreover, for better general segmentation performance, the proposed model takes the advantage of using different types of region information, such as the combination of intensity information and local phase based enhancement map. The local phase based enhancement map is used for its superiority in preserving vessel edges while the given image intensity information will guarantee a correct feature's segmentation. We evaluate the performance of the proposed model by applying it to three public retinal image datasets (two datasets of color fundus photography and one fluorescein angiography dataset). The proposed model outperforms its competitors when compared with other widely used unsupervised and supervised methods. For example, the sensitivity (0.742), specificity (0.982) and accuracy (0.954) achieved on the DRIVE dataset are very close to those of the second observer's annotations
A New Method of Blind Deconvolution for Colour Fundus Retinal Images
Fundus retinal imaging is widely used in the diagnosis and management of eye disease. Blur commonly occurs in the acquisition and when it is severe the resulting loss of resolution hampers accurate clinical assessment. In this paper, we present a new technique to address this challenging problem. We make use of implicitly constrained image deblurring, which is known to provide improved results over unconstrained and explicitly constrained methods, and build this into a multi-channel variational framework for parametric deblurring. We propose a new method for automatically selecting the regularisation parameter in the absence of the true (sharp) image using vessel segmentation. We then modify the model to include a regularisation coefficient function which is dependent on an available image mask in order to avoid potential inaccuracies caused by the addition of artificial masks. We present experimental results to demonstrate the effectiveness of our new method
High-mass Starless Clumps in the inner Galactic Plane: the Sample and Dust Properties
We report a sample of 463 high-mass starless clump (HMSC) candidates within
and . This sample has been singled out from
10861 ATLASGAL clumps. All of these sources are not associated with any known
star-forming activities collected in SIMBAD and young stellar objects
identified using color-based criteria. We also make sure that the HMSC
candidates have neither point sources at 24 and 70 \micron~nor strong extended
emission at 24 m. Most of the identified HMSCs are infrared (
m) dark and some are even dark at 70 m. Their distribution shows
crowding in Galactic spiral arms and toward the Galactic center and some
well-known star-forming complexes. Many HMSCs are associated with large-scale
filaments. Some basic parameters were attained from column density and dust
temperature maps constructed via fitting far-infrared and submillimeter
continuum data to modified blackbodies. The HMSC candidates have sizes, masses,
and densities similar to clumps associated with Class II methanol masers and
HII regions, suggesting they will evolve into star-forming clumps. More than
90% of the HMSC candidates have densities above some proposed thresholds for
forming high-mass stars. With dust temperatures and luminosity-to-mass ratios
significantly lower than that for star-forming sources, the HMSC candidates are
externally heated and genuinely at very early stages of high-mass star
formation. Twenty sources with equivalent radius pc and
mass surface density g cm could be possible high-mass
starless cores. Further investigations toward these HMSCs would undoubtedly
shed light on comprehensively understanding the birth of high-mass stars.Comment: 16 pages, 15 figures, and 5 tables. Accepted for publication in ApJS.
FITS images for the far-IR to sub-mm data, H2 column density and dust
temperature maps of all the HMSC candidates are available at https:
//yuanjinghua.github.io/hmscs.html. Codes used for this work are publicly
available from https://github.com/yuanjinghua/HMSCs_ca
IRDC G030.88+00.13: A Tale of Two Massive Clumps
Massive stars (M \gsim 10 \msun) form from collapse of parsec-scale
molecular clumps. How molecular clumps fragment to give rise to massive stars
in a cluster with a distribution of masses is unclear. We search for cold cores
that may lead to future formation of massive stars in a massive (
\msun), low luminosity ( \lsun) infrared dark cloud (IRDC)
G030.88+00.13. The \nh3 data from VLA and GBT reveal that the extinction
feature seen in the infrared consists of two distinctive clumps along the same
line of sight: The C1 clump at 97 \kms-1 coincides with the extinction in the
Spitzer 8 and 24 m. Therefore, it is responsible for the majority of the
IRDC. The C2 clump at 107 \kms-1 is more compact and has a peak temperature of
45 K. Compact dust cores and \h2O masers revealed in the SMA and VLA
observations are mostly associated with C2, and none is within the IRDC in C1.
The luminosity indicates that neither the C1 nor C2 clump has yet to form
massive protostars. But C1 might be at a precluster forming stage. The
simulated observations rule out 0.1pc cold cores with masses above 8 \msun\
within the IRDC. The core masses in C1 and C2, and those in high-mass
protostellar objects suggest an evolutionary trend that the mass of cold cores
increases over time. Based on our findings, we propose an empirical picture of
massive star formation that protostellar cores and the embedded protostars
undergo simultaneous mass growth during the protostellar evolution.Comment: 29 pages, 7 figures. Accepted to Astrophysical Journa
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