2,565 research outputs found
A Bayesian approach for inferring the dynamics of partially observed endemic infectious diseases from space-time-genetic data
We describe a statistical framework for reconstructing the sequence of transmission events between observed cases of an endemic infectious disease using genetic, temporal and spatial information. Previous approaches to reconstructing transmission trees have assumed all infections in the study area originated from a single introduction and that a large fraction of cases were observed. There are as yet no approaches appropriate for endemic situations in which a disease is already well established in a host population and in which there may be multiple origins of infection, or that can enumerate unobserved infections missing from the sample. Our proposed framework addresses these shortcomings, enabling reconstruction of partially observed transmission trees and estimating the number of cases missing from the sample. Analyses of simulated datasets show the method to be accurate in identifying direct transmissions, while introductions and transmissions via one or more unsampled intermediate cases could be identified at high to moderate levels of case detection. When applied to partial genome sequences of rabies virus sampled from an endemic region of South Africa, our method reveals several distinct transmission cycles with little contact between them, and direct transmission over long distances suggesting significant anthropogenic influence in the movement of infected dogs
On the equivalence of the self-dual and Maxwell-Chern-Simons models coupled to Fermions
We study the exact equivalence between the self-dual model minimally coupled
with a Dirac field and the Maxwell-Chern-Simons model with non-minimal magnetic
coupling to fermions. We show that the fermion sectors of the models are
equivalent only if a Thirring like interaction is included. Using functional
methods we verify that, up to renormalizations, the equivalence persists at the
quantum level.Comment: 8 pages, revte
How important is the credit channel? An empirical study of the US banking crisis
We examine whether by adding a credit channel to the standard New Keynesian model we can account better for the behaviour of US macroeconomic data up to and including the banking crisis. We use the method of indirect inference which evaluates statistically how far a model's simulated behaviour mimics the behaviour of the data. We find that the model with credit dominates the standard model by a substantial margin. Credit shocks are the main contributor to the variation in the output gap during the crisis
The superspace geometry of gravitational Chern-Simons forms and their couplings to linear multiplets : a review
The superspace geometry of Chern-Simons forms is shown to be closely related
to that of the 3-form multiplet. This observation allows to simplify
considerably the geometric structure of supersymmetric Chern-Simons forms and
their coupling to linear multiplets. The analysis is carried through in U_K(1)
superspace, relevant at the same time for supergravity-matter couplings and for
chirally extended supergravity.Comment: 82 pages, LateX2
Bosonization and Duality in Arbitrary Dimensions: New Results
A generic massive Thirring Model in three space-time dimensions exhibits a
correspondence with a topologically massive bosonized gauge action associated
to a self-duality constraint, and we write down a general expression for this
relationship.
We also generalize this structure to dimensions, by adopting the
so-called doublet approach, recently introduced. In particular, a non-
conventional formulation of the bosonization technique in higher dimensions (in
the spirit of ), is proposed and, as an application, we show how fermionic
(Thirring-like) representations for bosonic topologically massive models in
four dimensions may be built up.Comment: Revised version, to appear in Phys. Rev.
On the measurement of inequalities in health
This paper offers a critical appraisal of the various methods employed to date to measure inequalities in health. It suggests that only two of these—the slope index of inequality and the concentration index—are likely to present an accurate picture of socioeconomic inequalities in health. The paper also presents several empirical examples to illustrate of the dangers of using other measures such as the range, the Lorenz curve and the index of dissimilarity
Emission-line stars discovered in the UKST H-alpha survey of the Large Magellanic Cloud; Part 1: Hot stars
We present new, accurate positions, spectral classifications, radial and
rotational velocities, H-alpha fluxes, equivalent widths and B,V,I,R magnitudes
for 579 hot emission-line stars (classes B0 - F9) in the Large Magellanic Cloud
which include 469 new discoveries. Candidate emission line stars were
discovered using a deep, high resolution H-alpha map of the central 25 deg2 of
the LMC obtained by median stacking a dozen 2 hour H-alpha exposures taken with
the UK Schmidt Telescope. Spectroscopic follow-up observations on the AAT,
UKST, VLT, the SAAO 1.9m and the MSSSO 2.3m telescope have established the
identity of these faint sources down to magnitude R~23 for H-alpha (4.5 x
10^-17 ergs cm^2 s^-1 Ang). Confirmed emission-line stars have been assigned an
underlying spectral classification through cross-correlation against 131
absorption line template spectra covering the range O1 to F8. We confirm 111
previously identified emission line stars and 64 previously known variable
stars with spectral types hotter than F8. The majority of hot stars identified
(518 stars or 89%) are class B. Of all the hot emission-line stars in classes
B-F, 130 or 22% are type B[e], characterised by the presence of forbidden
emission lines such as [SII], [NII] and [OII]. We report on the physical
location of these stars with reference to possible contamination from ambient
HII emission. Along with flux calibration of the H-alpha emission we provide
the first H-alpha luminosity function for selected sub-samples after correction
for any possible nebula or ambient contamination. We find a moderate
correlation between the intensity of H-alpha emission and the V magnitude of
the central star based on SuperCOSMOS magnitudes and OGLE-II photometry where
possible. Cool stars from classes G-S, with and without strong H-alpha
emission, will be the focus of part 2 in this series.Comment: 24 pages (main paper) 36 figures, 6 tables; Appendix Tables: 22
pages, MNRAS, 201
Cyclic Variability of the Circumstellar Disc of the Be Star Tau. II. Testing the 2D Global Disc Oscillation Model
Aims. In this paper we model, in a self-consistent way, polarimetric,
photometric, spectrophotometric and interferometric observations of the
classical Be star Tauri. Our primary goal is to conduct a critical
quantitative test of the global oscillation scenario. Methods. We have carried
out detailed three-dimensional, NLTE radiative transfer calculations using the
radiative transfer code HDUST. For the input for the code we have used the most
up-to-date research on Be stars to include a physically realistic description
for the central star and the circumstellar disc. We adopt a rotationally
deformed, gravity darkened central star, surrounded by a disc whose unperturbed
state is given by a steady-state viscous decretion disc model. We further
assume that disc is in vertical hydrostatic equilibrium. Results. By adopting a
viscous decretion disc model for Tauri and a rigorous solution of the
radiative transfer, we have obtained a very good fit of the time-average
properties of the disc. This provides strong theoretical evidence that the
viscous decretion disc model is the mechanism responsible for disc formation.
With the global oscillation model we have successfully fitted spatially
resolved VLTI/AMBER observations and the temporal V/R variations of the
H and Br lines. This result convincingly demonstrates that the
oscillation pattern in the disc is a one-armed spiral. Possible model
shortcomings, as well as suggestions for future improvements, are also
discussed.Comment: 14 pages, 9 figures, accepted to A&
Motion frozen 18F-FDG cardiac PET
BackgroundPET reconstruction incorporating spatially variant 3D Point Spread Function (PSF) improves contrast and image resolution. "Cardiac Motion Frozen" (CMF) processing eliminates the influence of cardiac motion in static summed images. We have evaluated the combined use of CMF- and PSF-based reconstruction for high-resolution cardiac PET.MethodsStatic and 16-bin ECG-gated images of 20 patients referred for (18)F-FDG myocardial viability scans were obtained on a Siemens Biograph-64. CMF was applied to the gated images reconstructed with PSF. Myocardium to blood contrast, maximum left ventricle (LV) counts to defect contrast, contrast-to-noise (CNR) and wall thickness with standard reconstruction (2D-AWOSEM), PSF, ED-gated PSF, and CMF-PSF were compared.ResultsThe measured wall thickness was 18.9 ± 5.2 mm for 2D-AWOSEM, 16.6 ± 4.5 mm for PSF, and 13.8 ± 3.9 mm for CMF-PSF reconstructed images (all P < .05). The CMF-PSF myocardium to blood and maximum LV counts to defect contrasts (5.7 ± 2.7, 10.0 ± 5.7) were higher than for 2D-AWOSEM (3.5 ± 1.4, 6.5 ± 3.1) and for PSF (3.9 ± 1.7, 7.7 ± 3.7) (CMF vs all other, P < .05). The CNR for CMF-PSF (26.3 ± 17.5) was comparable to PSF (29.1 ± 18.3), but higher than for ED-gated dataset (13.7 ± 8.8, P < .05).ConclusionCombined CMF-PSF reconstruction increased myocardium to blood contrast, maximum LV counts to defect contrast and maintained equivalent noise when compared to static summed 2D-AWOSEM and PSF reconstruction
On the maximal superalgebras of supersymmetric backgrounds
In this note we give a precise definition of the notion of a maximal
superalgebra of certain types of supersymmetric supergravity backgrounds,
including the Freund-Rubin backgrounds, and propose a geometric construction
extending the well-known construction of its Killing superalgebra. We determine
the structure of maximal Lie superalgebras and show that there is a finite
number of isomorphism classes, all related via contractions from an
orthosymplectic Lie superalgebra. We use the structure theory to show that
maximally supersymmetric waves do not possess such a maximal superalgebra, but
that the maximally supersymmetric Freund-Rubin backgrounds do. We perform the
explicit geometric construction of the maximal superalgebra of AdS_4 x S^7 and
find that is isomorphic to osp(1|32). We propose an algebraic construction of
the maximal superalgebra of any background asymptotic to AdS_4 x S^7 and we
test this proposal by computing the maximal superalgebra of the M2-brane in its
two maximally supersymmetric limits, finding agreement.Comment: 17 page
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