385 research outputs found
Bayesian analysis of the low-resolution polarized 3-year WMAP sky maps
We apply a previously developed Gibbs sampling framework to the foreground
corrected 3-yr WMAP polarization data and compute the power spectrum and
residual foreground template amplitude posterior distributions. We first
analyze the co-added Q- and V-band data, and compare our results to the
likelihood code published by the WMAP team. We find good agreement, and thus
verify the numerics and data processing steps of both approaches. However, we
also analyze the Q- and V-bands separately, allowing for non-zero EB
cross-correlations and including two individual foreground template amplitudes
tracing synchrotron and dust emission. In these analyses, we find tentative
evidence of systematics: The foreground tracers correlate with each of the Q-
and V-band sky maps individually, although not with the co-added QV map; there
is a noticeable negative EB cross-correlation at l <~ 16 in the V-band map; and
finally, when relaxing the constraints on EB and BB, noticeable differences are
observed between the marginalized band powers in the Q- and V-bands. Further
studies of these features are imperative, given the importance of the low-l EE
spectrum on the optical depth of reionization tau and the spectral index of
scalar perturbations n_s.Comment: 5 pages, 4 figures, submitted to ApJ
A Markov Chain Monte Carlo Algorithm for analysis of low signal-to-noise CMB data
We present a new Monte Carlo Markov Chain algorithm for CMB analysis in the
low signal-to-noise regime. This method builds on and complements the
previously described CMB Gibbs sampler, and effectively solves the low
signal-to-noise inefficiency problem of the direct Gibbs sampler. The new
algorithm is a simple Metropolis-Hastings sampler with a general proposal rule
for the power spectrum, C_l, followed by a particular deterministic rescaling
operation of the sky signal. The acceptance probability for this joint move
depends on the sky map only through the difference of chi-squared between the
original and proposed sky sample, which is close to unity in the low
signal-to-noise regime. The algorithm is completed by alternating this move
with a standard Gibbs move. Together, these two proposals constitute a
computationally efficient algorithm for mapping out the full joint CMB
posterior, both in the high and low signal-to-noise regimes.Comment: Submitted to Ap
Bayesian Power Spectrum Analysis of the First-Year WMAP data
We present the first results from a Bayesian analysis of the WMAP first year
data using a Gibbs sampling technique. Using two independent, parallel
supercomputer codes we analyze the WMAP Q, V and W bands. The analysis results
in a full probabilistic description of the information the WMAP data set
contains about the power spectrum and the all-sky map of the cosmic microwave
background anisotropies. We present the complete probability distributions for
each C_l including any non-Gaussianities of the power spectrum likelihood.
While we find good overall agreement with the previously published WMAP
spectrum, our analysis uncovers discrepancies in the power spectrum estimates
at low l multipoles. For example we claim the best-fit Lambda-CDM model is
consistent with the C_2 inferred from our combined Q+V+W analysis with a 10%
probability of an even larger theoretical C_2. Based on our exact analysis we
can therefore attribute the "low quadrupole issue" to a statistical
fluctuation.Comment: 5 pages. 4 figures. For additional information and data see
http://www.astro.uiuc.edu/~iodwyer/research#wma
A re-analysis of the three-year WMAP temperature power spectrum and likelihood
We analyze the three-year WMAP temperature anisotropy data seeking to confirm
the power spectrum and likelihoods published by the WMAP team. We apply five
independent implementations of four algorithms to the power spectrum estimation
and two implementations to the parameter estimation. Our single most important
result is that we broadly confirm the WMAP power spectrum and analysis. Still,
we do find two small but potentially important discrepancies: On large angular
scales there is a small power excess in the WMAP spectrum (5-10% at l<~30)
primarily due to likelihood approximation issues between 13 <= l <~30. On small
angular scales there is a systematic difference between the V- and W-band
spectra (few percent at l>~300). Recently, the latter discrepancy was explained
by Huffenberger et al. (2006) in terms of over-subtraction of unresolved point
sources. As far as the low-l bias is concerned, most parameters are affected by
a few tenths of a sigma. The most important effect is seen in n_s. For the
combination of WMAP, Acbar and BOOMERanG, the significance of n_s =/ 1 drops
from ~2.7 sigma to ~2.3 sigma when correcting for this bias. We propose a few
simple improvements to the low-l WMAP likelihood code, and introduce two
important extensions to the Gibbs sampling method that allows for proper
sampling of the low signal-to-noise regime. Finally, we make the products from
the Gibbs sampling analysis publically available, thereby providing a fast and
simple route to the exact likelihood without the need of expensive matrix
inversions.Comment: 14 pages, 7 figures. Accepted for publication in ApJ. Numerical
results unchanged, but interpretation sharpened: Likelihood approximation
issues at l=13-30 far more important than potential foreground issues at l <=
12. Gibbs products (spectrum and sky samples, and "easy-to-use" likelihood
module) available from http://www.astro.uio.no/~hke/ under "Research
Optically pumped magnetometry in arbitrarily oriented magnetic fields
Optically pumped atomic magnetometers (OPMs) offer highly sensitive magnetic measurements using compact hardware, offering new possibilities for practical precision sensors. Double-resonance OPM operation is well suited to unshielded magnetometry, due to high sensor dynamic range. However, sensor response is highly anisotropic with variation in the orientation of the magnetic field. We present data quantifying these effects and discuss implications for the design of practical sensors
Medical student assessments-frequency of radiological images used : a national study
Assessments are a key part of life for medical students at University. We know there is variation in these assessments across Universities. The aims of this study were to expatiate summative assessments in Scottish Medical Schools and to examine how frequently radiological images feature in them. All Scottish medical schools were invited to participate in the study. Data on objective structured clinical examinations (OSCEs; 5 years) and written assessments (3 years) were retrospectively collected for each university and results were collated. Each University was randomly assigned a letter from A to E and anonymised for data presentation. 10,534 multiple choice questions (MCQ) and 1083 OSCE stations were included in this study. There was wide variation in the number, type and timing of assessments across Scottish medical schools. There were highly significant differences in the number of OSCE stations and the number of MCQs set over the study period ( <0.0001). Radiological images were used on average 0.6 times (range 0-1.1) in each OSCE examination and 2.4 times (range 0.1-3.7) for written assessments. In this detailed study, we demonstrated significant differences in medical student assessments across Scottish Universities. Given the importance of Radiology in modern medicine, the frequency and differences in which radiological images were used in assessments across Universities should be addressed. This is the first national longitudinal study to quantify the role of radiological images in summative Medical Student Assessments. Great variability exists in the extent and how (clinical versus written assessments) radiological images are used to assess Scottish medical students. Radiological images are used infrequently in clinical assessments, but are present in every written assessment. These findings could help inform medical schools and academic radiologists as they prepare medical students for the imminent unified medical licensing examination, where Clinical Imaging is a subject with one of the highest number of associated conditions examinable. [Abstract copyright: © 2020 The Authors. Published by the British Institute of Radiology.]Publisher PDFPeer reviewe
Attitudes towards attrition among UK trainees in obstetrics and gynaecology
Physician dissatisfaction in the workplace has consequences for patient safety. Currently in the UK, 1 in 5 doctors who enter specialist training in obstetrics and gynaecology leave the programme before completion. Trainee attrition has implications for workforce planning, organization of health-care services and patient care. The authors conducted a survey of current trainees' and former trainees' views concerning attrition and âperi-attritionâ â a term coined to describe the trainee who has seriously considered leaving the specialty.
The authors identified six key themes which describe trainees' feelings about attrition in obstetrics and gynaecology: morale and undermining; training processes and paperwork; support and supervision; workâlife balance and realities of life; NHS environment; and job satisfaction. This article discusses themes of an under-resourced health service, bullying, lack of workâlife balance and poor personal support
Bayesian component separation and CMB estimation for the 5-year WMAP temperature data
A well-tested and validated Gibbs sampling code, that performs component
separation and CMB power spectrum estimation, was applied to the {\it WMAP}
5-yr data. Using a simple model consisting of CMB, noise, monopoles and
dipoles, a ``per pixel'' low-frequency power-law (fitting for both amplitude
and spectral index), and a thermal dust template with fixed spectral index, we
found that the low- () CMB power spectrum is in good agreement
with the published {\it WMAP}5 results. Residual monopoles and dipoles were
found to be small (K) or negligible in the 5-yr data. We
comprehensively tested the assumptions that were made about the foregrounds
(e.g. dust spectral index, power-law spectral index prior, templates), and
found that the CMB power spectrum was insensitive to these choices. We confirm
the asymmetry of power between the north and south ecliptic hemispheres, which
appears to be robust against foreground modeling. The map of low frequency
spectral indices indicates a steeper spectrum on average ()
relative to those found at low (GHz) frequencies.Comment: 18 pages, 19 figures, submitted to Ap
Angular power spectrum of the FastICA CMB component from BEAST data
We present the angular power spectrum of the CMB component extracted with
FastICA from the Background Emission Anisotropy Scanning Telescope (BEAST)
data. BEAST is a 2.2 meter off-axis telescope with a focal plane comprising 8
elements at Q (38-45 GHz) and Ka (26-36 GHz) bands. It operates from the UC
White Mountain Research Station at an altitude of 3800 meters. The BEAST CMB
angular power spectrum has been already calculated by O'Dwyer et.al. using only
the Q band data. With two input channels FastICA returns two possible
independent components. We found that one of these two has an unphysical
spectral behaviour while the other is a reasonable CMB component. After a
detailed calibration procedure based on Monte-Carlo (MC) simulations we
extracted the angular power spectrum for the identified CMB component and found
a very good agreement with the already published BEAST CMB angular power
spectrum and with the WMAP data.Comment: 9 pages, 5 figures. Accepted for publication in MNRA
'Treatment of the Sportsman's groin': British Hernia Society's 2014 position statement based on the Manchester Consensus Conference
<b>Introduction</b> The aim was to produce a multidisciplinary consensus to determine the current position on the nomenclature, definition, diagnosis, imaging modalities and management of Sportsman's groin (SG).<p></p>
<b>Methods</b> Experts in the diagnosis and management of SG were invited to participate in a consensus conference held by the British Hernia Society in Manchester, UK on 11â12 October 2012. Experts included a physiotherapist, a musculoskeletal radiologist and surgeons with a proven track record of expertise in this field. Presentations detailing scientific as well as outcome data from their own experiences were given. Records were made of the presentations with specific areas debated openly.<p></p>
<b>Results</b> The term âinguinal disruptionâ (ID) was agreed as the preferred nomenclature with the term âSportsman's herniaâ or âgroinâ rejected, as no true hernia exists. There was an overwhelming agreement of opinion that there was abnormal tension in the groin, particularly around the inguinal ligament attachment. Other common findings included the possibility of external oblique disruption with consequent small tears noted as well as some oedema of the tissues. A multidisciplinary approach with tailored physiotherapy as the initial treatment was recommended with any surgery involving releasing the tension in the inguinal canal by various techniques and reinforcing it with a mesh or suture repair. A national registry should be developed for all athletes undergoing surgery.<p></p>
<b>Conclusions</b> ID is a common condition where no true hernia exists. It should be managed through a multidisciplinary approach to ensure consistent standards and outcomes are achieved
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