1,945 research outputs found
Structure and dynamics of the interface between a binary hard-sphere crystal of NaCl type and its coexisting binary fluid
Molecular dynamics simulations are performed to study the [100] and [111]
orientations of the crystal-melt interface between an ordered two-component
hard sphere with a NaCl structure and its coexisting binary hard-sphere fluid.
The diameter ratio of the two types of hard spheres making up the mixture is
taken to be 0.414. This work complements our earlier interface simulations [J.
Chem. Phys.116, 3410] for the same diameter ratio at lower pressures where the
smaller component is immiscible in the solid and the fluid mixture coexists
with a pure FCC crystal of large particles. Density profiles and diffusion
coefficient profiles are presented for the AB interfacial system. We find that
for this system, the transition from crystal-like to fluid-like behavior of
both the density and diffusion constant profiles occurs over a narrower region
than that seen in our previous studies [J. Chem. Phys. 116, 3410] of the
FCC/binary fluid system. But similar to what was found in the FCC/binary fluid
interface the transition region for the large particle diffusion constant is
shifted about the size of the large particles toward the fluid phase relative
to that for the small particles.Comment: 8 page
The type IIb SN 2008ax: the nature of the progenitor
A source coincident with the position of the type IIb supernova (SN) 2008ax
is identified in pre-explosion Hubble Space Telescope (HST) Wide Field
Planetary Camera 2 observations in three optical filters. We identify and
constrain two possible progenitor systems: (i) a single massive star that lost
most of its hydrogen envelope through radiatively driven mass loss processes,
prior to exploding as a helium-rich Wolf-Rayet star with a residual hydrogen
envelope, and (ii) an interacting binary in a low mass cluster producing a
stripped progenitor. Late time, high resolution observations along with
detailed modelling of the SN will be required to reveal the true nature of this
progenitor star.Comment: 5 pages, 2 figures, resolution of figure 1 reduced, figure 2 revised,
some revision following referee's comments, accepted for publication in MNRAS
letter
Experience of and access to maternity care in the UK by immigrant women: a narrative synthesis systematic review
© 2019 Author(s). One in four births in the UK is to foreign-born women. In 2016, the figure was 28.2%, the highest figure on record, with maternal and perinatal mortality also disproportionately higher for some immigrant women. Our objective was to examine issues of access and experience of maternity care by immigrant women based on a systematic review and narrative synthesis of empirical research. Review methods: A research librarian designed the search strategies (retrieving literature published from 1990 to end June 2017). We retrieved 45 954 citations and used a screening tool to identify relevance. We searched for grey literature reported in databases/websites. We contacted stakeholders with expertise to identify additional research. Results: We identified 40 studies for inclusion: 22 qualitative, 8 quantitative and 10 mixed methods. Immigrant women, particularly asylum-seekers, often booked and accessed antenatal care later than the recommended first 10 weeks. Primary factors included limited English language proficiency, lack of awareness of availability of the services, lack of understanding of the purpose of antenatal appointments, immigration status and income barriers. Maternity care experiences were both positive and negative. Women with positive perceptions described healthcare professionals as caring, confidential and openly communicative in meeting their medical, emotional, psychological and social needs. Those with negative views perceived health professionals as rude, discriminatory and insensitive to their cultural and social needs. These women therefore avoided continuously utilising maternity care. We found few interventions focused on improving maternity care, and the effectiveness of existing interventions have not been scientifically evaluated. Conclusions: The experiences of immigrant women in accessing and using maternity care services were both positive and negative. Further education and training of health professionals in meeting the challenges of a super-diverse population may enhance quality of care, and the perceptions and experiences of maternity care by immigrant women
An Upper Mass Limit on a Red Supergiant Progenitor for the Type II-Plateau Supernova SN 2006my
We analyze two pre-supernova (SN) and three post-SN high-resolution images of
the site of the Type II-Plateau supernova SN 2006my in an effort to either
detect the progenitor star or to constrain its properties. Following image
registration, we find that an isolated stellar object is not detected at the
location of SN 2006my in either of the two pre-SN images. In the first, an
I-band image obtained with the Wide-Field and Planetary Camera 2 on board the
Hubble Space Telescope, the offset between the SN 2006my location and a
detected source ("Source 1") is too large: > 0.08", which corresponds to a
confidence level of non-association of 96% from our most liberal estimates of
the transformation and measurement uncertainties. In the second, a similarly
obtained V-band image, a source is detected ("Source 2") that has overlap with
the SN 2006my location but is definitively an extended object. Through
artificial star tests carried out on the precise location of SN 2006my in the
images, we derive a 3-sigma upper bound on the luminosity of a red supergiant
that could have remained undetected in our pre-SN images of log L/L_Sun = 5.10,
which translates to an upper bound on such a star's initial mass of 15 M_Sun
from the STARS stellar evolutionary models. Although considered unlikely, we
can not rule out the possibility that part of the light comprising Source 1,
which exhibits a slight extension relative to other point sources in the image,
or part of the light contributing to the extended Source 2, may be due to the
progenitor of SN 2006my. Only additional, high-resolution observations of the
site taken after SN 2006my has faded beyond detection can confirm or reject
these possibilities.Comment: Minor text changes from Version 1. Appendix added detailing the
determination of confidence level of non-association of point sources in two
registered astronomical image
Comprehensive multi-wavelength modelling of the afterglow of GRB050525A
The Swift era has posed a challenge to the standard blast-wave model of Gamma
Ray Burst (GRB) afterglows. The key observational features expected within the
model are rarely observed, such as the achromatic steepening (`jet-break') of
the light curves. The observed afterglow light curves showcase additional
complex features requiring modifications within the standard model. Here we
present optical/NIR observations, millimeter upper limits and comprehensive
broadband modelling of the afterglow of the bright GRB 0505025A, detected by
Swift. This afterglow cannot be explained by the simplistic form of the
standard blast-wave model. We attempt modelling the multi-wavelength light
curves using (i) a forward-reverse shock model, (ii) a two-component outflow
model and (iii) blast-wave model with a wind termination shock. The
forward-reverse shock model cannot explain the evolution of the afterglow. The
two component model is able to explain the average behaviour of the afterglow
very well but cannot reproduce the fluctuations in the early X-ray light curve.
The wind termination shock model reproduces the early light curves well but
deviates from the global behaviour of the late-time afterglow.Comment: 20 pages, 6 figures, accepted for publication in MNRA
Strangers in the night: nightlife studies and new urban tourism
This paper draws together recent scholarship from the study of urban tourism and nightlife. Though studies of urban tourism do not always specifically address nightlife, and likewise studies of the night and nightlife do not always examine tourism, both bodies of research overlap in important ways. Concerns about commercialisation, gentrification, displacement, and urban change are to be found in both bodies of research. However, while the study of urban tourism typically recognises the erasure of the host / guest binary and seeks to destabilise the notion of who is a tourist or stranger, studies of nightlife often rest on a much clearer distinction between who belongs and who does not. An argument proposed here is that while the host / guest, tourist / non-tourist binary is perhaps reconfiguring, the night and nightlife spaces reinstate these binaries in various ways. This paper thinks through debates about tourists and residents in the night, focusing in particular on questions of belonging, place identification and gentrification through night-time uses
Three-phase point in a binary hard-core lattice model?
Using Monte Carlo simulation, Van Duijneveldt and Lekkerkerker [Phys. Rev.
Lett. 71, 4264 (1993)] found gas-liquid-solid behaviour in a simple
two-dimensional lattice model with two types of hard particles. The same model
is studied here by means of numerical transfer matrix calculations, focusing on
the finite size scaling of the gaps between the largest few eigenvalues. No
evidence for a gas-liquid transition is found. We discuss the relation of the
model with a solvable RSOS model of which the states obey the same exclusion
rules. Finally, a detailed analysis of the relation with the dilute three-state
Potts model strongly supports the tricritical point rather than a three-phase
point.Comment: 17 pages, LaTeX2e, 13 EPS figure
Dealing with mobility: Understanding access anytime, anywhere
The rapid and accelerating move towards the adoption and use of mobile technologies has increasingly provided people and organisations with the ability to work away from the office and on the move. The new ways of working afforded by these technologies are often characterised in terms of access to information and people âanytime, anywhereâ. This paper presents a study of mobile workers that highlights different facets of access to remote people and information, and different facets of anytime, anywhere. Four key factors in mobile work are identified from the study: the role of planning, working in âdead timeâ, accessing remote technological and informational resources, and monitoring the activities of remote colleagues. By reflecting on these issues, we can better understand the role of technology and artefact use in mobile work and identify the opportunities for the development of appropriate technological solutions to support mobile workers
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