1,226 research outputs found
Long-term prognosis for individuals with hypertension undergoing coronary artery calcium scoring
To examine the performance of coronary artery calcification (CAC) for stratifying long-term risk of death in asymptomatic hypertensive patients
No peaks without valleys: The stable mass transfer channel for gravitational-wave sources in light of the neutron star-black hole mass gap
Gravitational-wave (GW) detections are starting to reveal features in the
mass distribution of double compact objects. The lower end of the black hole
(BH) mass distribution is especially interesting as few formation channels
contribute here and because it is more robust against variations in the cosmic
star formation than the high mass end. In this work we explore the stable mass
transfer channel for the formation of GW sources with a focus on the low-mass
end of the mass distribution. We conduct an extensive exploration of the
uncertain physical processes that impact this channel. We note that, for
fiducial assumptions, this channel reproduces the peak at in the GW-observed binary BH mass distribution remarkably
well, and predicts a cutoff mass that coincides with the upper edge of the
purported neutron star BH mass gap. The peak and cutoff mass are a consequence
of unique properties of this channel, namely (1) the requirement of stability
during the mass transfer phases, and (2) the complex way in which the final
compact object masses scale with the initial mass. We provide an analytical
expression for the cutoff in the primary component mass and show that this
adequately matches our numerical results. Our results imply that selection
effects resulting from the formation channel alone can provide an explanation
for the purported neutron star--BH mass gap in GW detections. This provides an
alternative to the commonly adopted view that the gap emerges during BH
formation.Comment: Accepted for publication in ApJ associated code is available at
https://github.com/LiekeVanSon/LowMBH_and_StableChanne
'Surely the most natural scenario in the worldâ: Representations of âFamilyâ in BBC Pre-school Television
Historically, the majority of work on British childrenâs television has adopted either an institutional or an audience focus, with the texts themselves often overlooked. This neglect has meant that questions of representation in British childrenâs television â including issues such as family, gender, class or ethnicity - have been infrequently analysed in the UK context. In this article, we adopt a primarily qualitative methodology and analyse the various textual manifestations of âfamilyâ, group, or community as represented in a selected number of BBC pre-school programmes. In doing so, we question the (limited amount of) international work that has examined representations of the family in childrenâs television, and argue that nuclear family structures do not predominate in this sphere
Optimal Packings of Superballs
Dense hard-particle packings are intimately related to the structure of
low-temperature phases of matter and are useful models of heterogeneous
materials and granular media. Most studies of the densest packings in three
dimensions have considered spherical shapes, and it is only more recently that
nonspherical shapes (e.g., ellipsoids) have been investigated. Superballs
(whose shapes are defined by |x1|^2p + |x2|^2p + |x3|^2p <= 1) provide a
versatile family of convex particles (p >= 0.5) with both cubic- and
octahedral-like shapes as well as concave particles (0 < p < 0.5) with
octahedral-like shapes. In this paper, we provide analytical constructions for
the densest known superball packings for all convex and concave cases. The
candidate maximally dense packings are certain families of Bravais lattice
packings. The maximal packing density as a function of p is nonanalytic at the
sphere-point (p = 1) and increases dramatically as p moves away from unity. The
packing characteristics determined by the broken rotational symmetry of
superballs are similar to but richer than their two-dimensional "superdisk"
counterparts, and are distinctly different from that of ellipsoid packings. Our
candidate optimal superball packings provide a starting point to quantify the
equilibrium phase behavior of superball systems, which should deepen our
understanding of the statistical thermodynamics of nonspherical-particle
systems.Comment: 28 pages, 16 figure
Proteome Analyses of Strains Cyanothece ATCC 51142 and PCC 7822 of the Diazotrophic Cyanobacterium Cyanothece sp. Under Culture Conditions Resulting in Enhanced H2 Production.
Cultures of the cyanobacterial genus Cyanothece have been shown to produce high levels of biohydrogen. These strains are diazotrophic and undergo pronounced diurnal cycles when grown under N2-fixing conditions in light-dark cycles. We seek to better understand the way in which proteins respond to these diurnal changes, and we performed quantitative proteome analysis of Cyanothecesp. strains ATCC 51142 and PCC 7822 grown under 8 different nutritional conditions. Nitrogenase expression was limited to N2-fixing conditions, and in the absence of glycerol, nitrogenase gene expression was linked to the dark period. However, glycerol induced expression of nitrogenase during part of the light period, together with cytochrome c oxidase (Cox), glycogen phosphorylase (Glp), and glycolytic and pentose phosphate pathway (PPP) enzymes. This indicated that nitrogenase expression in the light was facilitated via higher levels of respiration and glycogen breakdown. Key enzymes of the Calvin cycle were inhibited in Cyanothece ATCC 51142 in the presence of glycerol under H2-producing conditions, suggesting a competition between these sources of carbon. However, in Cyanothece PCC 7822, the Calvin cycle still played a role in cofactor recycling during H2 production. Our data comprise the first comprehensive profiling of proteome changes in Cyanothece PCC 7822 and allow an in-depth comparative analysis of major physiological and biochemical processes that influence H2 production in both strains. Our results revealed many previously uncharacterized proteins that may play a role in nitrogenase activity and in other metabolic pathways and may provide suitable targets for genetic manipulation that would lead to improvement of large-scale H2 production
A First Search for Prompt Radio Emission from a Gravitational-Wave Event
Multimessenger observations of the binary neutron star merger GW170817 have
enabled the discovery of a diverse array of electromagnetic counterparts to
compact binary mergers, including an unambiguous kilonova, a short gamma-ray
burst, and a late-time radio jet. Beyond these counterparts, compact binary
mergers are additionally predicted to be accompanied by prompt low-frequency
radio emission. The successful observation of a prompt radio counterpart would
be immensely valuable, but is made difficult by the short delay between the
gravitational-wave and prompt electromagnetic signals as well as the poor
localization of gravitational-wave sources. Here, we present the first search
for prompt radio emission accompanying a gravitational-wave event, targeting
the binary black hole merger GW170104 detected by the Advanced LIGO and Virgo
gravitational-wave observatories during their second (O2) observing run. Using
the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), we search
a region for transient radio emission within
approximately one hour of GW170104, obtaining an upper limit of
on its equivalent isotropic
luminosity between 27-84 MHz. We additionally discuss plans to target binary
neutron star mergers in Advanced LIGO and Virgo's upcoming O3 observing run.Comment: 13 pages + appendices, 7 figures, submitted to Ap
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"Engaging with birth stories in pregnancy: a hermeneutic phenomenological study of women's experiences across two generations"
BACKGROUND: The birth story has been widely understood as a crucial source of knowledge about childbirth. What has not been reported is the effect that birth stories may have on primigravid women's understandings of birth. Findings are presented from a qualitative study exploring how two generations of women came to understand birth in the milieu of other's stories. The prior assumption was that birth stories must surely have a positive or negative influence on listeners, steering them towards either medical or midwifery-led models of care.
METHODS: A Heideggerian hermeneutic phenomenological approach was used. Twenty UK participants were purposively selected and interviewed. Findings from the initial sample of 10 women who were pregnant in 2012 indicated that virtual media was a primary source of birth stories. This led to recruitment of a second sample of 10 women who gave birth in the 1970s-1980s, to determine whether they were more able to translate information into knowledge via stories told through personal contact and not through virtual technologies
RESULTS: Findings revealed the experience of 'being-in-the-world' of birth and of stories in that world. From a Heideggerian perspective, the birth story was constructed through 'idle talk' (the taken for granted assumptions of things, which come into being through language). Both oral stories and those told through technology were described as the 'modern birth story'. The first theme 'Stories are difficult like that', examines the birth story as problematic and considers how stories shape meaning. The second 'It's a generational thing', considers how women from two generations came to understand what their experience might be. The third 'Birth in the twilight of certainty,' examines women's experience of Being in a system of birth as constructed, portrayed and sustained in the stories being shared.
CONCLUSIONS: The women pregnant in 2012 framed their expectations in the language of choice, whilst the women who birthed in the 1970s-1980s framed their experience in the language of safety. For both, however, the world of birth was the same; saturated with, and only legitimised by the birth of a healthy baby. Rather than creating meaningful understanding, the 'idle talk' of birth made both cohorts fearful of leaving the relative comfort of the 'system', and of claiming an alternative birth
"Studs": a squat-type defect in rails
In the mid-2000s a rail defect that was classified as a "squat" became increasingly common on London Underground's track. By 2006 there were about 600 of these and they had become the Underground's single most common rail defect. This defect occurred almost exclusively on lines carrying relatively new rolling stock. The work reported here was undertaken initially to characterize this defect, advise as to whether it was indeed a squat and propose a hypothesis that explained its mechanism of formation. The paper includes observations and measurements from track and initial results of metallurgical analysis. The hypothesis for formation of the defects is presented, and both similarities and differences are discussed between these defects and the classical "squat". The defect on London Underground appears to be the same as that described by Marich and his colleagues in Australia and by Li and his colleagues in the Netherlands. It is evidently not a rolling contact fatigue defect. In order to avoid confusion arising from simple misuse of an established term, it is proposed that these defects be given a different name, for which âstudâ is proposed. Evidence to date is that the "stud" is a significantly more benign defect than a "squat"
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