52 research outputs found
First-principles study of the effect of charge on the stability of a diamond nanocluster surface
Effects of net charge on the stability of the diamond nanocluster are investigated using the first-principles pseudopotential method with the local density approximation. We find that the charged nanocluster favors the diamond phase over the reconstruction into a fullerene-like structure. Occupying the dangling bond orbitals in the outermost surface, the excess charge can stabilize the bare diamond surface and destabilize the C-H bond on the hydrogenated surface. In combination with recent experimental results, our calculations suggest that negative charging could promote the nucleation and further growth of low-pressure diamond.open8
The barriers and facilitators influencing the sustainability of hospital-based interventions: a systematic review
Acknowledgements University of Stirling for providing financial support for open access costs Funding This review was funded by the Chief Scientist Office, grant number GCA/17/26. JC, PC and EAD are employed by the Nursing, Midwifery and Allied Health Professions Research Unit, which is funded by the Chief Scientist Office in Scotland.Peer reviewedPublisher PD
Evidence for perinatal and child health care guidelines in crisis settings: can Cochrane help?
<p>Abstract</p> <p>Background</p> <p>It is important that healthcare provided in crisis settings is based on the best available research evidence. We reviewed guidelines for child and perinatal health care in crisis situations to determine whether they were based on research evidence, whether Cochrane systematic reviews were available in the clinical areas addressed by these guidelines and whether summaries of these reviews were provided in Evidence Aid.</p> <p>Methods</p> <p>Broad internet searches were undertaken to identify relevant guidelines. Guidelines were appraised using AGREE and the clinical areas that were relevant to perinatal or child health were extracted. We searched The Cochrane Database of Systematic Reviews to identify potentially relevant reviews. For each review we determined how many trials were included, and how many were conducted in resource-limited settings.</p> <p>Results</p> <p>Six guidelines met selection criteria. None of the included guidelines were clearly based on research evidence. 198 Cochrane reviews were potentially relevant to the guidelines. These reviews predominantly addressed nutrient supplementation, breastfeeding, malaria, maternal hypertension, premature labour and prevention of HIV transmission. Most reviews included studies from developing settings. However for large portions of the guidelines, particularly health services delivery, there were no relevant reviews. Only 18 (9.1%) reviews have summaries in Evidence Aid.</p> <p>Conclusions</p> <p>We did not identify any evidence-based guidelines for perinatal and child health care in disaster settings. We found many Cochrane reviews that could contribute to the evidence-base supporting future guidelines. However there are important issues to be addressed in terms of the relevance of the available reviews and increasing the number of reviews addressing health care delivery.</p
Multi-messenger observations of a binary neutron star merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transientâs position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta
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C/2014 UN<inf>271</inf>(Bernardinelli-Bernstein): The Nearly Spherical Cow of Comets
C/2014 UN271 (Bernardinelli-Bernstein) is a comet incoming from the Oort
cloud which is remarkable in having the brightest (and presumably largest)
nucleus of any well-measured comet, and having been discovered at heliocentric
distance au farther than any Oort-cloud member. We describe the
properties that can be inferred from images recorded until the first reports of
activity in June 2021. The orbit has with perihelion of 10.97 au
to be reached in 2031, and previous aphelion at au. Backwards
integration of the orbit under a standard Galactic tidal model and known
stellar encounters suggests this is a pristine new comet, with a perihelion of
au on its previous perihelion passage 3.5 Myr ago. The photometric
data show an unresolved nucleus with absolute magnitude colors that
are typical of comet nuclei or Damocloids, and no secular trend as it traversed
the range 34--23 au. For -band geometric albedo this implies a
diameter of km. There is strong evidence of brightness
fluctuations at mag level, but no rotation period can be discerned. A
coma consistent with a ``stationary' surface-brightness distribution
grew in scattering cross-section at an exponential rate from
m to m as the comet approached from 28 to 20 au. The activity is
consistent with a simple model of sublimation of a surface species in radiative
equilibrium with the Sun. The inferred enthalpy of sublimation matches those of
and . More-volatile species -- and -- must be
far less abundant on the sublimating surfaces
A Search of the Full Six Years of the Dark Energy Survey for Outer Solar System Objects
We present the results of a search for outer Solar System objects in the full
six years of data (Y6) from the Dark Energy Survey (DES). The DES covered a
contiguous deg of the southern sky with deg
exposures in the optical/IR filters between 2013 and 2019. This search
yielded 815 trans-Neptunian objects (TNOs), one Centaur and one Oort cloud
comet, with 461 objects reported for the first time in this paper. We present
methodology that builds upon our previous search carried out on the first four
years of data. Here, all DES images were reprocessed with an improved detection
pipeline that leads to an average completeness gain of 0.47 mag per exposure,
as well as an improved transient catalog production and optimized algorithms
for linkage of detections into orbits. All objects were verified by visual
inspection and by computing the sub-threshold significance, the total
signal-to-noise ratio in the stack of images in which the object's presence is
indicated by the orbit fit, but no detection was reported. This yields a highly
pure catalog of TNOs complete to mag and distances
au. The Y6 TNOs have minimum (median) of 7 (12) distinct nights' detections and
arcs of 1.1 (4.2) years, and will have magnitudes available in a
further publication. We present software for simulating our observational
biases that enable comparisons of population models to our detections. Initial
inferences demonstrating the statistical power of the DES catalog are: the data
are inconsistent with the CFEPS-L7 model for the classical Kuiper Belt; the 16
``extreme'' TNOs ( au, au) are consistent with the null
hypothesis of azimuthal isotropy; and non-resonant TNOs with au,
au show a highly significant tendency to be sunward of the major mean motion
resonances, whereas this tendency is not present for au
Multi-messenger Observations of a Binary Neutron Star Merger
On 2017 August 17 a binary neutron star coalescence candidate (later
designated GW170817) with merger time 12:41:04 UTC was observed through
gravitational waves by the Advanced LIGO and Advanced Virgo detectors.
The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray
burst (GRB 170817A) with a time delay of ⌠1.7 {{s}} with respect to
the merger time. From the gravitational-wave signal, the source was
initially localized to a sky region of 31 deg2 at a
luminosity distance of {40}-8+8 Mpc and with
component masses consistent with neutron stars. The component masses
were later measured to be in the range 0.86 to 2.26 {M}ÈŻ
. An extensive observing campaign was launched across the
electromagnetic spectrum leading to the discovery of a bright optical
transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC
4993 (at ⌠40 {{Mpc}}) less than 11 hours after the merger by the
One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The
optical transient was independently detected by multiple teams within an
hour. Subsequent observations targeted the object and its environment.
Early ultraviolet observations revealed a blue transient that faded
within 48 hours. Optical and infrared observations showed a redward
evolution over âŒ10 days. Following early non-detections, X-ray and
radio emission were discovered at the transientâs position ⌠9
and ⌠16 days, respectively, after the merger. Both the X-ray and
radio emission likely arise from a physical process that is distinct
from the one that generates the UV/optical/near-infrared emission. No
ultra-high-energy gamma-rays and no neutrino candidates consistent with
the source were found in follow-up searches. These observations support
the hypothesis that GW170817 was produced by the merger of two neutron
stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and
a kilonova/macronova powered by the radioactive decay of r-process
nuclei synthesized in the ejecta.</p
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