929 research outputs found
Present and future evidence for evolving dark energy
We compute the Bayesian evidences for one- and two-parameter models of
evolving dark energy, and compare them to the evidence for a cosmological
constant, using current data from Type Ia supernova, baryon acoustic
oscillations, and the cosmic microwave background. We use only distance
information, ignoring dark energy perturbations. We find that, under various
priors on the dark energy parameters, LambdaCDM is currently favoured as
compared to the dark energy models. We consider the parameter constraints that
arise under Bayesian model averaging, and discuss the implication of our
results for future dark energy projects seeking to detect dark energy
evolution. The model selection approach complements and extends the
figure-of-merit approach of the Dark Energy Task Force in assessing future
experiments, and suggests a significantly-modified interpretation of that
statistic.Comment: 10 pages RevTex4, 3 figures included. Minor changes to match version
accepted by PR
Two-Stage Two-Locus Models in Genome-Wide Association
Studies in model organisms suggest that epistasis may play an important role in the etiology of complex diseases and traits in humans. With the era of large-scale genome-wide association studies fast approaching, it is important to quantify whether it will be possible to detect interacting loci using realistic sample sizes in humans and to what extent undetected epistasis will adversely affect power to detect association when single-locus approaches are employed. We therefore investigated the power to detect association for an extensive range of two-locus quantitative trait models that incorporated varying degrees of epistasis. We compared the power to detect association using a single-locus model that ignored interaction effects, a full two-locus model that allowed for interactions, and, most important, two two-stage strategies whereby a subset of loci initially identified using single-locus tests were analyzed using the full two-locus model. Despite the penalty introduced by multiple testing, fitting the full two-locus model performed better than single-locus tests for many of the situations considered, particularly when compared with attempts to detect both individual loci. Using a two-stage strategy reduced the computational burden associated with performing an exhaustive two-locus search across the genome but was not as powerful as the exhaustive search when loci interacted. Two-stage approaches also increased the risk of missing interacting loci that contributed little effect at the margins. Based on our extensive simulations, our results suggest that an exhaustive search involving all pairwise combinations of markers across the genome might provide a useful complement to single-locus scans in identifying interacting loci that contribute to moderate proportions of the phenotypic variance
Direct reconstruction of the quintessence potential
We describe an algorithm which directly determines the quintessence potential
from observational data, without using an equation of state parametrisation.
The strategy is to numerically determine observational quantities as a function
of the expansion coefficients of the quintessence potential, which are then
constrained using a likelihood approach. We further impose a model selection
criterion, the Bayesian Information Criterion, to determine the appropriate
level of the potential expansion. In addition to the potential parameters, the
present-day quintessence field velocity is kept as a free parameter. Our
investigation contains unusual model types, including a scalar field moving on
a flat potential, or in an uphill direction, and is general enough to permit
oscillating quintessence field models. We apply our method to the `gold' Type
Ia supernovae sample of Riess et al. (2004), confirming the pure cosmological
constant model as the best description of current supernovae
luminosity-redshift data. Our method is optimal for extracting quintessence
parameters from future data.Comment: 9 pages RevTeX4 with lots of incorporated figure
A Prospective Study of Intraarterial Infusion Chemotherapy in Advanced WT BRAF Melanoma Patients.
ABSTRACT Background Treatment strategies for advanced cutaneous melanoma (CM) patients, resistant or not treatable with novel target and immunotherapeutic drugs, remain a significant challenge, particularly for patients with unresectable stage IIIC/D disease localized to inferior limbs and pelvis, for whom specific outcomes are rarely considered. Materials and methods This is a prospective study of multidisciplinary treatments, including locoregional melphalan chemotherapy, in 62 BRAF wild-type CM patients with locoregional metastases in the inferior limbs and pelvis, including inguinal regions. Patients were either in progression following or ineligible for, or not treatable with novel immunotherapy. For exclusively inferior limb-localised disease, patients received locoregional melphalan chemotherapy performed by hyperthermic isolated limb perfusion (n = 19) or isolated limb infusion (n = 19), and for synchronous lesions localised to inferior limbs and pelvis, received hypoxic pelvic and limb perfusion (n = 24). Additional multidisciplinary therapy included local, locoregional and systemic treatments and the primary endpoint was tumour response. Results The objective response rate following first cycle of locoregional chemotherapy was 37.1% at 3 mo and median progression-free survival was 4-mo, with 12.9% procedure-related complications, 30.6% low-grade haematological toxicity and 11.3% severe limb toxic tissue reactions. Multivariate logistic regression showed that the odds of response were significantly higher for patients ≤ 75 y of age and for patients with locoregional metastases exclusively located in the inferior limbs. Conclusion In this subgroup of CM patients with BRAF wild-type status, locoregional metastases localized to inferior limbs and pelvis, in progression following or ineligible for immunotherapy, melphalan locoregional chemotherapy demonstrated a safe and effective profile. Trial Registration ClinicalTrials.gov Identifier NCT01920516; date of trial registration: August 6, 2013
Yangians, Integrable Quantum Systems and Dorey's rule
We study tensor products of fundamental representations of Yangians and show
that the fundamental quotients of such tensor products are given by Dorey's
rule.Comment: We have made corrections to the results for the Yangians associated
to the non--simply laced algebra
Optimizing future dark energy surveys for model selection goals
We demonstrate a methodology for optimizing the ability of future dark energy
surveys to answer model selection questions, such as `Is acceleration due to a
cosmological constant or a dynamical dark energy model?'. Model selection
Figures of Merit are defined, exploiting the Bayes factor, and surveys
optimized over their design parameter space via a Monte Carlo method. As a
specific example we apply our methods to generic multi-fibre baryon acoustic
oscillation spectroscopic surveys, comparable to that proposed for SuMIRe PFS,
and present implementations based on the Savage-Dickey Density Ratio that are
both accurate and practical for use in optimization. It is shown that whilst
the optimal surveys using model selection agree with those found using the Dark
Energy Task Force (DETF) Figure of Merit, they provide better informed
flexibility of survey configuration and an absolute scale for performance; for
example, we find survey configurations with close to optimal model selection
performance despite their corresponding DETF Figure of Merit being at only 50%
of its maximum. This Bayes factor approach allows us to interpret the survey
configurations that will be good enough for the task at hand, vital especially
when wanting to add extra science goals and in dealing with time restrictions
or multiple probes within the same project.Comment: 12 pages, 16 figure
Model selection forecasts for the spectral index from the Planck satellite
The recent WMAP3 results have placed measurements of the spectral index n_S
in an interesting position. While parameter estimation techniques indicate that
the Harrison-Zel'dovich spectrum n_S=1 is strongly excluded (in the absence of
tensor perturbations), Bayesian model selection techniques reveal that the case
against n_S=1 is not yet conclusive. In this paper, we forecast the ability of
the Planck satellite mission to use Bayesian model selection to convincingly
exclude (or favour) the Harrison-Zel'dovich model.Comment: 4 pages RevTeX with one figure included. Updated to match PRD
accepted version. Improved likelihood function implementation; no qualitative
change to results but some tiny numerical shift
Warren McCulloch and the British cyberneticians
Warren McCulloch was a significant influence on a number of British cyberneticians, as some British pioneers in this area were on him. He interacted regularly with most of the main figures on the British cybernetics scene, forming close friendships and collaborations with several, as well as mentoring others. Many of these interactions stemmed from a 1949 visit to London during which he gave the opening talk at the inaugural meeting of the Ratio Club, a gathering of brilliant, mainly young, British scientists working in areas related to cybernetics. This paper traces some of these relationships and interaction
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