1,697 research outputs found
Predictions for ASKAP Neutral Hydrogen Surveys
The Australian Square Kilometer Array Pathfinder (ASKAP) will revolutionise
our knowledge of gas-rich galaxies in the Universe. Here we present predictions
for two proposed extragalactic ASKAP neutral hydrogen (HI) emission-line
surveys, based on semi-analytic models applied to cosmological N-body
simulations. The ASKAP HI All-Sky Survey, known as WALLABY, is a shallow 3 Pi
survey (z = 0 - 0.26) which will probe the mass and dynamics of over 600,000
galaxies. A much deeper small-area HI survey, called DINGO, aims to trace the
evolution of HI from z = 0 - 0.43, a cosmological volume of 40 million Mpc^3,
detecting potentially 100,000 galaxies. The high-sensitivity 30 antenna ASKAP
core (diameter ~2 km) will provide an angular resolution of 30 arcsec (at z=0).
Our simulations show that the majority of galaxies detected in WALLABY (87.5%)
will be resolved. About 5000 galaxies will be well resolved, i.e. more than
five beams (2.5 arcmin) across the major axis, enabling kinematic studies of
their gaseous disks. This number would rise to 160,000 galaxies if all 36 ASKAP
antennas could be used; the additional six antennas provide baselines up to 6
km, resulting in an angular resolution of 10 arcsec. For DINGO this increased
resolution is highly desirable to minimise source confusion; reducing confusion
rates from a maximum of 10% of sources at the survey edge to 3%. We estimate
that the sources detected by WALLABY and DINGO will span four orders of
magnitude in total halo mass (from 10^{11} to 10^{15} Msol) and nearly seven
orders of magnitude in stellar mass (from 10^{5} to 10^{12} Msol), allowing us
to investigate the process of galaxy formation across the last four billion
years.Comment: 21 pages, accepted for publication in MNRAS, minor updates to
published version and fixed links. Movies and images available at
http://ict.icrar.org/store/Movies/Duffy12c
A method for exploratory repeated-measures analysis applied to a breast-cancer screening study
When a model may be fitted separately to each individual statistical unit,
inspection of the point estimates may help the statistician to understand
between-individual variability and to identify possible relationships. However,
some information will be lost in such an approach because estimation
uncertainty is disregarded. We present a comparative method for exploratory
repeated-measures analysis to complement the point estimates that was motivated
by and is demonstrated by analysis of data from the CADET II breast-cancer
screening study. The approach helped to flag up some unusual reader behavior,
to assess differences in performance, and to identify potential random-effects
models for further analysis.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS481 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Large deviations for a damped telegraph process
In this paper we consider a slight generalization of the damped telegraph
process in Di Crescenzo and Martinucci (2010). We prove a large deviation
principle for this process and an asymptotic result for its level crossing
probabilities (as the level goes to infinity). Finally we compare our results
with the analogous well-known results for the standard telegraph process
The Frailty Matters Project:coproducing a coaching and educational intervention for integrated community teams alongside older people with lived experience of frailty.
Informant-based screening tools for dementia: an overview of systematic reviews
Background:
Informant-based questionnaires may have utility for cognitive impairment or dementia screening. Reviews describing the accuracy of respective questionnaires are available, but their focus on individual questionnaires precludes comparisons across tools. We conducted an overview of systematic reviews to assess the comparative accuracy of informant questionnaires and identify areas where evidence is lacking.
Methods:
We searched six databases to identify systematic reviews describing diagnostic test accuracy of informant questionnaires for cognitive impairment or dementia. We pooled sensitivity and specificity data for each questionnaire and used network approaches to compare accuracy estimates across the differing tests. We used grading of recommendations, assessment, development and evaluation (GRADE) to evaluate the overall certainty of evidence. Finally, we created an evidence ‘heat-map’, describing the availability of accurate data for individual tests in different populations and settings.
Results:
We identified 25 reviews, consisting of 93 studies and 13 informant questionnaires. Pooled analysis (37 studies; 11 052 participants) ranked the eight-item interview to ascertain dementia (AD8) highest for sensitivity [90%; 95% credible intervals (CrI) = 82–95; ‘best-test’ probability = 36]; while the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) was most specific (81%; 95% CrI = 66–90; ‘best-test’ probability = 29%). GRADE-based evaluation of evidence suggested certainty was ‘low’ overall. Our heat-map indicated that only AD8 and IQCODE have been extensively evaluated and most studies have been in the secondary care settings.
Conclusions:
AD8 and IQCODE appear to be valid questionnaires for cognitive impairment or dementia assessment. Other available informant-based cognitive screening questionnaires lack evidence to justify their use at present. Evidence on the accuracy of available tools in primary care settings and with specific populations is required
A WKB approach to scalar fields dynamics in curved space-time
Quantum fields exhibit non-trivial behaviours in curved space-times,
especially around black holes or when a cosmological constant is added to the
field equations. A new scheme, based on the Wentzel-Kramers-Brillouin (WKB)
approximation is presented. The main advantage of this method is to allow for a
better physical understanding of previously known results and to give good
orders of magnitude in situations where no other approaches are currently
developed. Greybody factors for evaporating black holes are rederived in this
framework and the energy levels of scalar fields in the Anti-de Sitter (AdS)
spacetime are accurately obtained. Stationary solutions in the
Schwarzschild-Anti-de Sitter (SAdS) background are investigated. Some
improvements and the basics of a line of thought for more complex situations
are suggested.Comment: Accepted for publication in Nucl. Phys.
Genome-wide association studies identify multiple genetic loci influencing eyebrow color variation in Europeans
Pairing, Charge, and Spin Correlations in the Three-Band Hubbard Model
Using the Constrained Path Monte Carlo (CPMC) method, we simulated the
two-dimensional, three-band Hubbard model to study pairing, charge, and spin
correlations as a function of electron and hole doping and the Coulomb
repulsion between charges on neighboring Cu and O lattice sites. As a
function of distance, both the -wave and extended s-wave pairing
correlations decayed quickly. In the charge-transfer regime, increasing
decreased the long-range part of the correlation functions in both
channels, while in the mixed-valent regime, it increased the long-range part of
the s-wave behavior but decreased that of the d-wave behavior. Still the d-wave
behavior dominated. At a given doping, increasing increased the
spin-spin correlations in the charge-transfer regime but decreased them in the
mixed-valent regime. Also increasing suppressed the charge-charge
correlations between neighboring Cu and O sites. Electron and hole doping away
from half-filling was accompanied by a rapid suppression of anti-ferromagnetic
correlations.Comment: Revtex, 8 pages with 15 figure
Antigenic diversity is generated by distinct evolutionary mechanisms in African trypanosome species
Antigenic variation enables pathogens to avoid the host immune response by continual switching of surface proteins. The protozoan blood parasite Trypanosoma brucei causes human African trypanosomiasis ("sleeping sickness") across sub-Saharan Africa and is a model system for antigenic variation, surviving by periodically replacing a monolayer of variant surface glycoproteins (VSG) that covers its cell surface. We compared the genome of Trypanosoma brucei with two closely related parasites Trypanosoma congolense and Trypanosoma vivax, to reveal how the variant antigen repertoire has evolved and how it might affect contemporary antigenic diversity. We reconstruct VSG diversification showing that Trypanosoma congolense uses variant antigens derived from multiple ancestral VSG lineages, whereas in Trypanosoma brucei VSG have recent origins, and ancestral gene lineages have been repeatedly co-opted to novel functions. These historical differences are reflected in fundamental differences between species in the scale and mechanism of recombination. Using phylogenetic incompatibility as a metric for genetic exchange, we show that the frequency of recombination is comparable between Trypanosoma congolense and Trypanosoma brucei but is much lower in Trypanosoma vivax. Furthermore, in showing that the C-terminal domain of Trypanosoma brucei VSG plays a crucial role in facilitating exchange, we reveal substantial species differences in the mechanism of VSG diversification. Our results demonstrate how past VSG evolution indirectly determines the ability of contemporary parasites to generate novel variant antigens through recombination and suggest that the current model for antigenic variation in Trypanosoma brucei is only one means by which these parasites maintain chronic infections
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