2,775 research outputs found
Abell 1201: a Minor merger at second core passage
We present an analysis of the structures and dynamics of the merging cluster
Abell~1201, which has two sloshing cold fronts around a cooling core, and an
offset gas core approximately 500kpc northwest of the center. New Chandra and
XMM-Newton data reveal a region of enhanced brightness east of the offset core,
with breaks in surface brightness along its boundary to the north and east.
This is interpreted as a tail of gas stripped from the offset core. Gas in the
offset core and the tail is distinguished from other gas at the same distance
from the cluster center chiefly by having higher density, hence lower entropy.
In addition, the offset core shows marginally lower temperature and metallicity
than the surrounding area. The metallicity in the cool core is high and there
is an abrupt drop in metallicity across the southern cold front. We interpret
the observed properties of the system, including the placement of the cold
fronts, the offset core and its tail in terms of a simple merger scenario. The
offset core is the remnant of a merging subcluster, which first passed
pericenter southeast of the center of the primary cluster and is now close to
its second pericenter passage, moving at ~1000 km/s. Sloshing excited by the
merger gave rise to the two cold fronts and the disposition of the cold fronts
reveals that we view the merger from close to the plane of the orbit of the
offset core.Comment: accepted by Ap
Field Scanner Design for MUSTANG of the Green Bank Telescope
MUSTANG is a bolometer camera for the Green Bank Telescope (GBT) working at a
frequency of 90 GHz. The detector has a field of view of 40 arcseconds. To
cancel out random emission change from atmosphere and other sources, requires a
fast scanning reflecting system with a few arcminute ranges. In this paper, the
aberrations of an off-axis system are reviewed. The condition for an optimized
system is provided. In an optimized system, as additional image transfer
mirrors are introduced, new aberrations of the off-axis system may be
reintroduced, resulting in a limited field of view. In this paper, different
scanning mirror arrangements for the GBT system are analyzed through the ray
tracing analysis. These include using the subreflector as the scanning mirror,
chopping a flat mirror and transferring image with an ellipse mirror, and
chopping a flat mirror and transferring image with a pair of face-to-face
paraboloid mirrors. The system analysis shows that chopping a flat mirror and
using a well aligned pair of paraboloids can generate the required field of
view for the MUSTUNG detector system, while other systems all suffer from
larger off-axis aberrations added by the system modification. The spot diagrams
of the well aligned pair of paraboloids produced is only about one Airy disk
size within a scanning angle of about 3 arcmin.Comment: 7 pages, 9 figure
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Environment and phenology shape local adaptation in thermal performance
Populations within species often exhibit variation in traits that reflect local adaptation and further shape existing adaptive potential for species to respond to climate change. However, our mechanistic understanding of how the environment shapes trait variation remains poor. Here, we used common garden experiments to quantify thermal performance in eight populations of the marine snail Urosalpinx cinerea across thermal gradients on the Atlantic and the Pacific coasts of North America. We then evaluated the relationship between thermal performance and environmental metrics derived from time-series data. Our results reveal a novel pattern of ‘mixed’ trait performance adaptation, where thermal optima were positively correlated with spawning temperature (cogradient variation), while maximum trait performance was negatively correlated with season length (countergradient variation). This counterintuitive pattern probably arises because of phenological shifts in the spawning season, whereby ‘cold’ populations delay spawning until later in the year when temperatures are warmer compared to ‘warm’ populations that spawn earlier in the year when temperatures are cooler. Our results show that variation in thermal performance can be shaped by multiple facets of the environment and are linked to organismal phenology and natural history. Understanding the impacts of climate change on organisms, therefore, requires the knowledge of how climate change will alter different aspects of the thermal environment
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Diminished warming tolerance and plasticity in low-latitude populations of a marine gastropod
Models of species response to climate change often assume that physiological traits are invariant across populations. Neglecting potential intraspecific variation may overlook the possibility that some populations are more resilient or susceptible than others, creating inaccurate predictions of climate impacts. In addition, phenotypic plasticity can contribute to trait variation and may mediate sensitivity to climate. Quantifying such forms of intraspecific variation can improve our understanding of how climate can affect ecologically important species, such as invasive predators. Here, we quantified thermal performance (tolerance, acclimation capacity, developmental traits) across seven populations of the predatory marine snail (Urosalpinx cinerea) from native Atlantic and non-native Pacific coast populations in the USA. Using common garden experiments, we assessed the effects of source population and developmental acclimation on thermal tolerance and developmental traits of F1 snails. We then estimated climate sensitivity by calculating warming tolerance (thermal tolerance − habitat temperature), using field environmental data. We report that low-latitude populations had greater thermal tolerance than their high latitude counterparts. However, these same low-latitude populations exhibited decreased thermal tolerance when exposed to environmentally realistic higher acclimation temperatures. Low-latitude native populations had the greatest climate sensitivity (habitat temperatures near thermal limits). In contrast, invasive Pacific snails had the lowest climate sensitivity, suggesting that these populations are likely to persist and drive negative impacts on native biodiversity. Developmental rate significantly increased in embryos sourced from populations with greater habitat temperature but had variable effects on clutch size and hatching success. Thus, warming can produce widely divergent responses within the same species, resulting in enhanced impacts in the non-native range and extirpation in the native range. Broadly, our results highlight how intraspecific variation can alter management decisions, as this may clarify whether management efforts should be focused on many or only a few populations
Palliative care initiation in pediatric oncology patients: A systematic review
Palliative care (PC) aims to improve quality of life for patients and their families. The World Health Organization and American Academy of Pediatrics recommend that PC starts at diagnosis for children with cancer. This systematic review describes studies that reported PC timing in the pediatric oncology population. The following databases were searched: PubMed, Web of Science, CINAHL, and PsycInfo databases. Studies that reported time of PC initiation were independently screened and reviewed by 2 researchers. Studies describing pilot initiatives, published prior to 1998, not written in English, or providing no empirical time information on PC were excluded. Extracted data included sample characteristics and timing of PC discussion and initiation. Of 1120 identified citations, 16 articles met the inclusion criteria and comprised the study cohort. Overall, 54.5% of pediatric oncology patients received any palliative service prior to death. Data revealed PC discussion does not occur until late in the illness trajectory, and PC does not begin until close to time of death. Despite efforts to spur earlier initiation, many pediatric oncology patients do not receive any palliative care service, and those who do, predominantly receive it near the time of death. Delays occur both at first PC discussion and at PC initiation. Efforts for early PC integration must recognize the complex determinants of PC utilization across the illness timeline
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A Single Visualization Technique for Displaying Multiple Metabolite-Phenotype Associations.
To assist with management and interpretation of human metabolomics data, which are rapidly increasing in quantity and complexity, we need better visualization tools. Using a dataset of several hundred metabolite measures profiled in a cohort of ~1500 individuals sampled from a population-based community study, we performed association analyses with eight demographic and clinical traits and outcomes. We compared frequently used existing graphical approaches with a novel 'rain plot' approach to display the results of these analyses. The 'rain plot' combines features of a raindrop plot and a conventional heatmap to convey results of multiple association analyses. A rain plot can simultaneously indicate effect size, directionality, and statistical significance of associations between metabolites and several traits. This approach enables visual comparison features of all metabolites examined with a given trait. The rain plot extends prior approaches and offers complementary information for data interpretation. Additional work is needed in data visualizations for metabolomics to assist investigators in the process of understanding and convey large-scale analysis results effectively, feasibly, and practically
The Positive and Negative Impacts of the COVID-19 Pandemic Towards Youths’ Mental Health
Due to quarantine measures, the impact of COVID-19 on youths\u27 mental health may be more significant than on their physical health. This study aims to map out the positive and negative implications that COVID-19 brings concerning mental health. The main dependent variable of our study will be the evaluated mental health of Singaporean youths. Based on previous research and articles, we have chosen the difference in education level as our key independent variable and social isolation, lack of physical activity, family conflicts, and family emotional support as the control variables. Our study will be conducted through a survey on Singapore\u27s primary and secondary school students by multi-stage cluster sampling and stratified sampling. The cross-sectional data collected will be sorted and analyzed through t-test, chi-square test, and regression analysis. The findings of this study can help schools and governments in their development and implementation of policies to improve our youths’ mental health which has become an important issue in recent times. The survey data will aid us in better understanding the pandemic\u27s effects on Singaporean youths\u27 mental health, especially since the pandemic has been continuing longer than most expected
CEO pay, shareholder returns, and accounting profits
We assess the impact on CEO pay (including salary, cash bonus, and benefits in kind) of changes in both accounting and shareholder returns in 99 British companies in the years 1972-89. After correcting for heterogeneity biases inherent in the standard specifications of the problem, we find a strong positive relationship between CEO pay and within-company changes in shareholder returns, and no statistically significant relationship between CEO pay and within-company changes in accounting returns. Differences between firms in long-term average profitability do appear to have a substantial effect on CEO pay, while differences between firms in shareholder returns add nothing to the within-firm pay dynamics.These findings call into question the rationale for explicitly share-based incentive schemes
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