42,621 research outputs found
Unsupervised non-parametric change point detection in quasi-periodic signals
We propose a new unsupervised and non-parametric method to detect change
points in intricate quasi-periodic signals. The detection relies on optimal
transport theory combined with topological analysis and the bootstrap
procedure. The algorithm is designed to detect changes in virtually any
harmonic or a partially harmonic signal and is verified on three different
sources of physiological data streams. We successfully find abnormal or
irregular cardiac cycles in the waveforms for the six of the most frequent
types of clinical arrhythmias using a single algorithm. The validation and the
efficiency of the method are shown both on synthetic and on real time series.
Our unsupervised approach reaches the level of performance of the supervised
state-of-the-art techniques. We provide conceptual justification for the
efficiency of the method and prove the convergence of the bootstrap procedure
theoretically.Comment: 8 pages, 7 figures, 1 tabl
Systematic search for gamma-ray periodicity in active galactic nuclei detected by the Fermi Large Area Telescope
We use nine years of gamma-ray data provided by the Fermi Large Area
Telescope (LAT) to systematically study the light curves of more than two
thousand active galactic nuclei (AGN) included in recent Fermi-LAT catalogs.
Ten different techniques are used, which are organized in an automatic
periodicity-search pipeline, in order to search for evidence of periodic
emission in gamma rays. Understanding the processes behind this puzzling
phenomenon will provide a better view about the astrophysical nature of these
extragalactic sources. However, the observation of temporal patterns in
gamma-ray light curves of AGN is still challenging. Despite the fact that there
have been efforts on characterizing the temporal emission of some individual
sources, a systematic search for periodicities by means of a full likelihood
analysis applied to large samples of sources was missing. Our analysis finds 11
AGN, of which 9 are identified for the first time, showing periodicity at more
than 4sigma in at least four algorithms. These findings will help in solving
questions related to the astrophysical origin of this periodic behavior.Comment: 16 pages, 5 figures, 4 tables. Accepted by Ap
Systemic: A Testbed For Characterizing the Detection of Extrasolar Planets. I. The Systemic Console Package
We present the systemic Console, a new all-in-one, general-purpose software
package for the analysis and combined multiparameter fitting of Doppler radial
velocity (RV) and transit timing observations. We give an overview of the
computational algorithms implemented in the Console, and describe the tools
offered for streamlining the characterization of planetary systems. We
illustrate the capabilities of the package by analyzing an updated radial
velocity data set for the HD128311 planetary system. HD128311 harbors a pair of
planets that appear to be participating in a 2:1 mean motion resonance. We show
that the dynamical configuration cannot be fully determined from the current
data. We find that if a planetary system like HD128311 is found to undergo
transits, then self-consistent Newtonian fits to combined radial velocity data
and a small number of timing measurements of transit midpoints can provide an
immediate and vastly improved characterization of the planet's dynamical state.Comment: 10 pages, 5 figures, accepted for publication on PASP. Additional
material at http://www.ucolick.org/~smeschia/systemic.ph
An empirical Bayesian analysis applied to the globular cluster pulsar population
We describe an empirical Bayesian approach to determine the most likely size
of an astronomical population of sources of which only a small subset are
observed above some limiting flux density threshold. The method is most
naturally applied to astronomical source populations at a common distance
(e.g.,stellar populations in globular clusters), and can be applied even to
populations where a survey detects no objects. The model allows for the
inclusion of physical parameters of the stellar population and the detection
process. As an example, we apply this method to the current sample of radio
pulsars in Galactic globular clusters. Using the sample of flux density limits
on pulsar surveys in 94 globular clusters published by Boyles et al., we
examine a large number of population models with different dependencies. We
find that models which include the globular cluster two-body encounter rate,
, are strongly favoured over models in which this is not a factor. The
optimal model is one in which the mean number of pulsars is proportional to
. This model agrees well with earlier work by Hui et al.
and provides strong support to the idea that the two-body encounter rate
directly impacts the number of neutron stars in a cluster. Our model predicts
that the total number of potentially observable globular cluster pulsars in the
Boyles et al. sample is 1070, where the uncertainties signify
the 95% confidence interval. Scaling this result to all Galactic globular
clusters, and to account for radio pulsar beaming, we estimate the total
population to be 2280.Comment: 8 pages, 6 figures, 3 tables, corrected a few minor formatting errors
which have also been submitted as an erratum to MNRA
Quantile-based bias correction and uncertainty quantification of extreme event attribution statements
Extreme event attribution characterizes how anthropogenic climate change may
have influenced the probability and magnitude of selected individual extreme
weather and climate events. Attribution statements often involve quantification
of the fraction of attributable risk (FAR) or the risk ratio (RR) and
associated confidence intervals. Many such analyses use climate model output to
characterize extreme event behavior with and without anthropogenic influence.
However, such climate models may have biases in their representation of extreme
events. To account for discrepancies in the probabilities of extreme events
between observational datasets and model datasets, we demonstrate an
appropriate rescaling of the model output based on the quantiles of the
datasets to estimate an adjusted risk ratio. Our methodology accounts for
various components of uncertainty in estimation of the risk ratio. In
particular, we present an approach to construct a one-sided confidence interval
on the lower bound of the risk ratio when the estimated risk ratio is infinity.
We demonstrate the methodology using the summer 2011 central US heatwave and
output from the Community Earth System Model. In this example, we find that the
lower bound of the risk ratio is relatively insensitive to the magnitude and
probability of the actual event.Comment: 28 pages, 4 figures, 3 table
Simultaneous Selection of Multiple Important Single Nucleotide Polymorphisms in Familial Genome Wide Association Studies Data
We propose a resampling-based fast variable selection technique for selecting
important Single Nucleotide Polymorphisms (SNP) in multi-marker mixed effect
models used in twin studies. Due to computational complexity, current practice
includes testing the effect of one SNP at a time, commonly termed as `single
SNP association analysis'. Joint modeling of genetic variants within a gene or
pathway may have better power to detect the relevant genetic variants, hence we
adapt our recently proposed framework of -values to address this. In this
paper, we propose a computationally efficient approach for single SNP detection
in families while utilizing information on multiple SNPs simultaneously. We
achieve this through improvements in two aspects. First, unlike other model
selection techniques, our method only requires training a model with all
possible predictors. Second, we utilize a fast and scalable bootstrap procedure
that only requires Monte-Carlo sampling to obtain bootstrapped copies of the
estimated vector of coefficients. Using this bootstrap sample, we obtain the
-value for each SNP, and select SNPs having -values below a threshold. We
illustrate through numerical studies that our method is more effective in
detecting SNPs associated with a trait than either single-marker analysis using
family data or model selection methods that ignore the familial dependency
structure. We also use the -values to perform gene-level analysis in nuclear
families and detect several SNPs that have been implicated to be associated
with alcohol consumption
Detecting Unspecified Structure in Low-Count Images
Unexpected structure in images of astronomical sources often presents itself
upon visual inspection of the image, but such apparent structure may either
correspond to true features in the source or be due to noise in the data. This
paper presents a method for testing whether inferred structure in an image with
Poisson noise represents a significant departure from a baseline (null) model
of the image. To infer image structure, we conduct a Bayesian analysis of a
full model that uses a multiscale component to allow flexible departures from
the posited null model. As a test statistic, we use a tail probability of the
posterior distribution under the full model. This choice of test statistic
allows us to estimate a computationally efficient upper bound on a p-value that
enables us to draw strong conclusions even when there are limited computational
resources that can be devoted to simulations under the null model. We
demonstrate the statistical performance of our method on simulated images.
Applying our method to an X-ray image of the quasar 0730+257, we find
significant evidence against the null model of a single point source and
uniform background, lending support to the claim of an X-ray jet
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