308 research outputs found
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
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
An impact and feasibility evaluation of a 6 week (9 hour) active play intervention on fathers' engagement with their preschool children: A feasibility study
Research has demonstrated the benefits of father involvement with their children and a link between uninvolved fatherhood and societal problems. Childrenâs Centres (n=15) received 6 x 90 minute active play sessions designed to foster six aspects of parental engagement. Fathersâ engagement and attitudes to child PA were measured pre- and post-intervention via questionnaire. Acceptability of the intervention was explored through participant and staff focus groups. Results showed no effect on overall time fathers spent with their child during the week (t (36) = 0.178, p = 0.860) and the weekend (t (36) =1.166, p = 0.252). Qualitative results demonstrated the sessions provided opportunities for fathers to spend quality time with their children. Parenting self-efficacy increased across the subscale control, t (36) = -2.97, p = 0.04. Fathers increased awareness of their role in motivating their child to play (z = -2.46, p = 0.01). Further longitudinal research is recommended.
Key Words: fathersâ engagement; childcare settings; parenting programmes; active play; parenting self-efficac
Improving Photoelectron Counting and Particle Identification in Scintillation Detectors with Bayesian Techniques
Many current and future dark matter and neutrino detectors are designed to
measure scintillation light with a large array of photomultiplier tubes (PMTs).
The energy resolution and particle identification capabilities of these
detectors depend in part on the ability to accurately identify individual
photoelectrons in PMT waveforms despite large variability in pulse amplitudes
and pulse pileup. We describe a Bayesian technique that can identify the times
of individual photoelectrons in a sampled PMT waveform without deconvolution,
even when pileup is present. To demonstrate the technique, we apply it to the
general problem of particle identification in single-phase liquid argon dark
matter detectors. Using the output of the Bayesian photoelectron counting
algorithm described in this paper, we construct several test statistics for
rejection of backgrounds for dark matter searches in argon. Compared to simpler
methods based on either observed charge or peak finding, the photoelectron
counting technique improves both energy resolution and particle identification
of low energy events in calibration data from the DEAP-1 detector and
simulation of the larger MiniCLEAN dark matter detector.Comment: 16 pages, 16 figure
Radon backgrounds in the DEAP-1 liquid-argon-based Dark Matter detector
The DEAP-1 \SI{7}{kg} single phase liquid argon scintillation detector was
operated underground at SNOLAB in order to test the techniques and measure the
backgrounds inherent to single phase detection, in support of the
\mbox{DEAP-3600} Dark Matter detector. Backgrounds in DEAP are controlled
through material selection, construction techniques, pulse shape discrimination
and event reconstruction. This report details the analysis of background events
observed in three iterations of the DEAP-1 detector, and the measures taken to
reduce them.
The Rn decay rate in the liquid argon was measured to be between 16
and \SI{26}{\micro\becquerel\per\kilogram}. We found that the background
spectrum near the region of interest for Dark Matter detection in the DEAP-1
detector can be described considering events from three sources: radon
daughters decaying on the surface of the active volume, the expected rate of
electromagnetic events misidentified as nuclear recoils due to inefficiencies
in the pulse shape discrimination, and leakage of events from outside the
fiducial volume due to imperfect position reconstruction. These backgrounds
statistically account for all observed events, and they will be strongly
reduced in the DEAP-3600 detector due to its higher light yield and simpler
geometry
- âŠ