6,965 research outputs found
Piloting a manualised weight management programme (Shape Up-LD) for overweight and obese persons with mild-moderate learning disabilities: study protocol for a pilot randomised controlled trial
National obesity rates have dramatically risen over the last decade. Being obese significantly reduces life expectancy, increases the risk of a range of diseases, and compromises quality of life. Costs to both the National Health Service and society are high. An increased prevalence of obesity in people with learning disabilities has been demonstrated. The consequences of obesity are particularly relevant to people with learning disabilities who are already confronted by health and social inequalities. In order to provide healthcare for all, and ensure equality of treatment for people with learning disabilities, services must be developed specifically with this population in mind. The aim of this project is to pilot the evaluation of a manualised weight management programme for overweight and obese persons with mild-moderate learning disabilities (Shape Up-LD)
High Resolution Linear Polarimetric Imaging for the Event Horizon Telescope
Images of the linear polarization of synchrotron radiation around Active
Galactic Nuclei (AGN) identify their projected magnetic field lines and provide
key data for understanding the physics of accretion and outflow from
supermassive black holes. The highest resolution polarimetric images of AGN are
produced with Very Long Baseline Interferometry (VLBI). Because VLBI
incompletely samples the Fourier transform of the source image, any image
reconstruction that fills in unmeasured spatial frequencies will not be unique
and reconstruction algorithms are required. In this paper, we explore
extensions of the Maximum Entropy Method (MEM) to linear polarimetric VLBI
imaging. In contrast to previous work, our polarimetric MEM algorithm combines
a Stokes I imager that uses only bispectrum measurements that are immune to
atmospheric phase corruption with a joint Stokes Q and U imager that operates
on robust polarimetric ratios. We demonstrate the effectiveness of our
technique on 7- and 3-mm wavelength quasar observations from the VLBA and
simulated 1.3-mm Event Horizon Telescope observations of Sgr A* and M87.
Consistent with past studies, we find that polarimetric MEM can produce
superior resolution compared to the standard CLEAN algorithm when imaging
smooth and compact source distributions. As an imaging framework, MEM is highly
adaptable, allowing a range of constraints on polarization structure.
Polarimetric MEM is thus an attractive choice for image reconstruction with the
EHT.Comment: 19 pages, 9 figures. Accepted for publication in ApJ. Imaging code
available at https://github.com/achael/eht-imaging
Relative Astrometry of Compact Flaring Structures in Sgr A* with Polarimetric VLBI
We demonstrate that polarimetric interferometry can be used to extract
precise spatial information about compact polarized flares of Sgr A*. We show
that, for a faint dynamical component, a single interferometric baseline
suffices to determine both its polarization and projected displacement from the
quiescent intensity centroid. A second baseline enables two-dimensional
reconstruction of the displacement, and additional baselines can self-calibrate
using the flare, enhancing synthesis imaging of the quiescent emission. We
apply this technique to simulated 1.3-mm wavelength observations of a "hot
spot" embedded in a radiatively inefficient accretion disk around Sgr A*. Our
results indicate that, even with current sensitivities, polarimetric
interferometry with the Event Horizon Telescope can achieve ~5 microarcsecond
relative astrometry of compact flaring structures near Sgr A* on timescales of
minutes.Comment: 9 Pages, 4 Figures, accepted for publication in Ap
Magnetic fields in protoplanetary disks
Magnetic fields likely play a key role in the dynamics and evolution of
protoplanetary discs. They have the potential to efficiently transport angular
momentum by MHD turbulence or via the magnetocentrifugal acceleration of
outflows from the disk surface, and magnetically-driven mixing has implications
for disk chemistry and evolution of the grain population. However, the weak
ionisation of protoplanetary discs means that magnetic fields may not be able
to effectively couple to the matter. I present calculations of the ionisation
equilibrium and magnetic diffusivity as a function of height from the disk
midplane at radii of 1 and 5 AU. Dust grains tend to suppress magnetic coupling
by soaking up electrons and ions from the gas phase and reducing the
conductivity of the gas by many orders of magnitude. However, once grains have
grown to a few microns in size their effect starts to wane and magnetic fields
can begin to couple to the gas even at the disk midplane. Because ions are
generally decoupled from the magnetic field by neutral collisions while
electrons are not, the Hall effect tends to dominate the diffusion of the
magnetic field when it is able to partially couple to the gas.
For a standard population of 0.1 micron grains the active surface layers have
a combined column of about 2 g/cm^2 at 1 AU; by the time grains have aggregated
to 3 microns the active surface density is 80 g/cm^2. In the absence of grains,
x-rays maintain magnetic coupling to 10% of the disk material at 1 AU (150
g/cm^2). At 5 AU the entire disk thickness becomes active once grains have
aggregated to 1 micron in size.Comment: 11 pages, 11 figs, aastex.cls. Accepted for publication in
Astrophysics & Space Science. v3 corrects bibliograph
Flaring Activity of Sgr A* at 43 and 22 GHz: Evidence for Expanding Hot Plasma
We have carried out Very Large Array (VLA) continuum observations to study
the variability of Sgr A* at 43 GHz (=7mm) and 22 GHz
(=13mm). A low level of flare activity has been detected with a
duration of 2 hours at these frequencies, showing the peak flare
emission at 43 GHz leading the 22 GHz peak flare by to 40 minutes. The
overall characteristics of the flare emission are interpreted in terms of the
plasmon model of Van der Laan (1966) by considering the ejection and
adiabatically expansion of a uniform, spherical plasma blob due to flare
activity. The observed peak of the flare emission with a spectral index
of =1.6 is consistent with the prediction that the peak
emission shifts toward lower frequencies in an adiabatically-expanding
self-absorbed source. We present the expected synchrotron light curves for an
expanding blob as well as the peak frequency emission as a function of the
energy spectral index constrained by the available flaring measurements in
near-IR, sub-millimeter, millimeter and radio wavelengths. We note that the
blob model is consistent with the available measurements, however, we can not
rule out the jet of Sgr A*. If expanding material leaves the gravitational
potential of Sgr A*, the total mass-loss rate of nonthermal and thermal
particles is estimated to be M yr. We
discuss the implication of the mass-loss rate since this value matches closely
with the estimated accretion rate based on polarization measurements.Comment: Revised with new Figures 1 and 2, 17 pages, 4 figures, ApJ (in press
A Multi-Wavelength Study of Sgr A*: The Role of Near-IR Flares in Production of X-ray, Soft -ray and Sub-millimeter Emission
(abridged) We describe highlights of the results of two observing campaigns
in 2004 to investigate the correlation of flare activity in Sgr A* in different
wavelength regimes, using a total of nine ground and space-based telescopes. We
report the detection of several new near-IR flares during the campaign based on
{\it HST} observations. The level of near-IR flare activity can be as low as
mJy at 1.6 m and continuous up to about 40% of the total
observing time. Using the NICMOS instrument on the {\it HST}, the {\it
XMM-Newton} and CSO observatories, we also detect simultaneous bright X-ray and
near-IR flare in which we observe for the first time correlated substructures
as well as simultaneous submillimeter and near-IR flaring. X-ray emission is
arising from the population of near-IR-synchrotron-emitting relativistic
particles which scatter submillimeter seed photons within the inner 10
Schwarzschild radii of Sgr A* up to X-ray energies. In addition, using the
inverse Compton scattering picture, we explain the high energy 20-120 keV
emission from the direction toward Sgr A*, and the lack of one-to-one X-ray
counterparts to near-IR flares, by the variation of the magnetic field and the
spectral index distributions of this population of nonthermal particles. In
this picture, the evidence for the variability of submillimeter emission during
a near-IR flare is produced by the low-energy component of the population of
particles emitting synchrotron near-IR emission. Based on the measurements of
the duration of flares in near-IR and submillimeter wavelengths, we argue that
the cooling could be due to adiabatic expansion with the implication that flare
activity may drive an outflow.Comment: 48 pages, 12 figures, ApJ (in press
Exact calculation of the radiatively-induced Lorentz and CPT violation in QED
Radiative corrections arising from the axial coupling of charged fermions to
a constant vector b_\mu can induce a Lorentz- and CPT-violating Chern-Simons
term in the QED action. We calculate the exact one-loop correction to this term
keeping the full b_\mu dependence, and show that in the physically interesting
cases it coincides with the lowest-order result. The effect of regularization
and renormalization and the implications of the result are briefly discussed.Comment: LaTex, 8 pages; minor correction
Gambling in Great Britain:a response to Rogers
A recent issue of Practice: Social Work in Action featured a paper by Rogers that examined whether the issue of problem gambling was a suitable case for social work. Rogers’ overview was (in various places) out of date, highly selective, contradictory, presented unsupported claims and somewhat misleading. Rogers’ paper is to be commended for putting the issue of problem gambling on the social work agenda. However, social workers need up-to-date information and contextually situated information if they are to make informed decisions in helping problem gamblers
Soil methane sink capacity response to a long-term wildfire chronosequence in Northern Sweden
Boreal forests occupy nearly one fifth of the terrestrial land surface and are recognised as globally important regulators of carbon (C) cycling and greenhouse gas emissions. Carbon sequestration processes in these forests include assimilation of CO2 into biomass and subsequently into soil organic matter, and soil microbial oxidation of methane (CH4). In this study we explored how ecosystem retrogression, which drives vegetation change, regulates the important process of soil CH4 oxidation in boreal forests. We measured soil CH4 oxidation processes on a group of 30 forested islands in northern Sweden differing greatly in fire history, and collectively representing a retrogressive chronosequence, spanning 5000 years. Across these islands the build-up of soil organic matter was observed to increase with time since fire disturbance, with a significant correlation between greater humus depth and increased net soil CH4 oxidation rates. We suggest that this increase in net CH4 oxidation rates, in the absence of disturbance, results as deeper humus stores accumulate and provide niches for methanotrophs to thrive. By using this gradient we have discovered important regulatory controls on the stability of soil CH4 oxidation processes that could not have not been explored through shorter-term experiments. Our findings indicate that in the absence of human interventions such as fire suppression, and with increased wildfire frequency, the globally important boreal CH4 sink could be diminished
On Pair Content and Variability of Sub-Parsec Jets in Quasars
X-ray observations of blazars associated with the OVV (Optically Violently
Variable) quasars put strong constraints on the electron - positron pair
content of radio-loud quasar jets. From those observations, we infer that jets
in quasars contain many more electron - positron pairs than protons, but
dynamically are still dominated by protons. In particular, we show that pure
electron - positron jet models can be excluded, as they overpredict soft X-ray
radiation; likewise, pure proton - electron jets can be excluded, as they
predict too weak nonthermal X-ray radiation. An intermediate case is viable. We
demonstrate that jets which are initially proton-electron ("proto-jets") can be
pair-loaded via interaction with 100 - 300 keV photons produced in hot
accretion disc coronae, likely to exist in active galactic nuclei in general.
If the coronal radiation is powered by magnetic flares, the pair loading is
expected to be non-uniform and non-axisymmetric. Together with radiation drag,
this leads to velocity and density perturbations in a jet and formation of
shocks, where the pairs are accelerated. Such a scenario can explain rapid
(time scale of about a day) variability observed in OVV quasars.Comment: Accepted for publication in the Astrophysical Journa
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