793 research outputs found
Evaluation of cosmic ray rejection algorithms on single-shot exposures
To maximise data output from single-shot astronomical images, the rejection
of cosmic rays is important. We present the results of a benchmark trial
comparing various cosmic ray rejection algorithms. The procedures assess
relative performances and characteristics of the processes in cosmic ray
detection, rates of false detections of true objects and the quality of image
cleaning and reconstruction. The cosmic ray rejection algorithms developed by
Rhoads (2000), van Dokkum (2001), Pych (2004) and the IRAF task xzap by
Dickinson are tested using both simulated and real data. It is found that
detection efficiency is independent of the density of cosmic rays in an image,
being more strongly affected by the density of real objects in the field. As
expected, spurious detections and alterations to real data in the cleaning
process are also significantly increased by high object densities. We find the
Rhoads' linear filtering method to produce the best performance in detection of
cosmic ray events, however, the popular van Dokkum algorithm exhibits the
highest overall performance in terms of detection and cleaning.Comment: 12 pages, 4 figures, accepted for publication in PAS
Spring Hydrology of Colorado Bend State Park, Central Texas
Karst development in Ellenburger carbonates near Colorado Bend State Park in central Texas exhibits complex polygenetic origins, with porosity development dominated by an early hypogene phase that has subsequently been overprinted to varying degrees by epigene processes. Quarterly physicochemical and continuous thermal monitoring analyses of eight springs in the study area indicate that modern groundwater flow paths are highly variable. Springs exhibit patterns that range from shallow, distributed recharge into diffuse-flow dominated systems, to focused recharge into well-connected conduit systems, to deep-circulation systems that equilibrate with bedrock. All springs, except Sulphur Spring, exhibit physicochemical characteristics indicative of proximal epigenic groundwater flow through Ellenburger carbonates, while Sulphur Spring shows elevated temperature and dissolved-ion concentrations indicative of longer groundwater flow paths through deeper strata. The polygenetic nature of karst development in the Colorado Bend State Park has created an enhanced porosity structure which forms a complex modern groundwater flow network
Organic-Vapor-Liquid-Solid Deposition with an Impinging Gas Jet
A method for rapid, mass-efficient deposition of highly crystalline organic films under near ambient conditions of pressure and temperature is reported based on delivery of an organic precursor via an impinging gas jet to a substrate coated by a thin liquid solvent layer. Films of the organic semiconductor tetracene were deposited by sublimation into a flow of argon carrier gas directed at an indium-tin-oxide/glass substrate coated by a thin layer of bis(2-ethylhexyl)sebecate, and growth was followed in situ with optical microscopy. A fluid dynamics model is applied to account for the gas phase transport and aggregation, and the results compared to experiment. The combination of gas jet delivery with an organic-vapor-liquid-solid growth mechanism leads to larger crystals and lower nucleation densities than on bare surfaces, with markedly different nucleation and growth kinetics. An explanation based on enhanced solution-phase diffusivity and a larger critical nucleus size in the liquid layer is proposed to account for the differences
Accredited qualifications for capacity development in disaster risk reduction and climate change adaptation
Increasingly practitioners and policy makers working
across the globe are recognising the importance of
bringing together disaster risk reduction and climate
change adaptation. From studies across 15 Pacific island
nations, a key barrier to improving national resilience
to disaster risks and climate change impacts has been
identified as a lack of capacity and expertise resulting
from the absence of sustainable accredited and quality
assured formal training programmes in the disaster risk
reduction and climate change adaptation sectors. In the
2016 UNISDR Science and Technology Conference
on the Implementation of the Sendai Framework for
Disaster Risk Reduction 2015–2030, it was raised that
most of the training material available are not reviewed
either through a peer-to-peer mechanism or by the
scientific community and are, thus, not following quality
assurance standards. In response to these identified
barriers, this paper focuses on a call for accredited formal
qualifications for capacity development identified in the
2015 United Nations landmark agreements in DRR and
CCA and uses the Pacific Islands Region of where this
is now being implemented with the launch of the Pacific
Regional Federation of Resilience Professionals, for
DRR and CCA. A key issue is providing an accreditation
and quality assurance mechanism that is shared across
boundaries. This paper argues that by using the United
Nations landmark agreements of 2015, support for a
regionally accredited capacity development that ensures
all countries can produce, access and effectively use
scientific information for disaster risk reduction and
climate change adaptation. The newly launched Pacific
Regional Federation of Resilience Professionals who
work in disaster risk reduction and climate change
adaptation may offer a model that can be used more
widely
Race and Sex Differences in QRS Interval and Associated Outcome Among Patients with Left Ventricular Systolic Dysfunction
BACKGROUND: Prolonged QRS duration is associated with increased mortality among heart failure patients, but race or sex differences in QRS duration and associated effect on outcomes are unknown.
METHODS AND RESULTS: We investigated QRS duration and morphology among 2463 black and white patients with heart failure and left ventricular ejection fraction ≤35% who underwent coronary angiography and 12-lead electrocardiography at Duke University Hospital from 1995 through 2011. We used multivariable Cox regression models to assess the relationship between QRS duration and all-cause mortality and investigate race-QRS and sex-QRS duration interaction. Median QRS duration was 105 ms (interquartile range [IQR], 92-132) with variation by race and sex (P<0.001). QRS duration was longest in white men (111 ms; IQR, 98-139) followed by white women (108 ms; IQR, 92-140), black men (100 ms; IQR, 91-120), and black women (94 ms; IQR, 86-118). Left bundle branch block was more common in women than men (24% vs 14%) and in white (21%) versus black individuals (12%). In black patients, there was a 16% increase in risk of mortality for every 10 ms increase in QRS duration up to 112 ms (hazard ratio, 1.16; 95% CI, 1.07, 1.25) that was not present among white patients (interaction, P=0.06).
CONCLUSIONS: Black individuals with heart failure had a shorter QRS duration and more often had non-left bundle branch block morphology than white patients. Women had left bundle branch block more commonly than men. Among black patients, modest QRS prolongation was associated with increased mortality
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