3,888 research outputs found
Observational bounds on the cosmic radiation density
We consider the inference of the cosmic radiation density, traditionally
parameterised as the effective number of neutrino species N_eff, from precision
cosmological data. Paying particular attention to systematic effects, notably
scale-dependent biasing in the galaxy power spectrum, we find no evidence for a
significant deviation of N_eff from the standard value of N_eff^0=3.046 in any
combination of cosmological data sets, in contrast to some recent conclusions
of other authors. The combination of all available data in the linear regime
prefers, in the context of a ``vanilla+N_eff'' cosmological model,
1.1<N_eff<4.8 (95% C.L.) with a best-fit value of 2.6. Adding data at smaller
scales, notably the Lyman-alpha forest, we find 2.2<N_eff<5.8 (95% C.L.) with
3.8 as the best fit. Inclusion of the Lyman-alpha data shifts the preferred
N_eff upwards because the sigma_8 value derived from the SDSS Lyman-alpha data
is inconsistent with that inferred from CMB. In an extended cosmological model
that includes a nonzero mass for N_eff neutrino flavours, a running scalar
spectral index and a w parameter for the dark energy, we find 0.8<N_eff<6.1
(95% C.L.) with 3.0 as the best fit.Comment: 23 pages, 3 figures, uses iopart.cls; v2: 1 new figure, references
added, matches published versio
Degeneracy of gravitational waveforms in the context of GW150914
We study the degeneracy of theoretical gravitational waveforms for binary
black hole mergers using an aligned-spin effective-one-body model. After
appropriate truncation, bandpassing, and matching, we identify regions in the
mass--spin parameter space containing waveforms similar to the template
proposed for GW150914, with masses and , using the cross-correlation coefficient as a measure of
the similarity between waveforms. Remarkably high cross-correlations are found
across broad regions of parameter space. The associated uncertanties exceed
these from LIGO's Bayesian analysis considerably. We have shown that waveforms
with greatly increased masses, such as and , and strong anti-aligned spins ( and )
yield almost the same signal-to-noise ratio in the strain data for GW150914.Comment: Accepted for publication in JCA
Approximate Inference for Constructing Astronomical Catalogs from Images
We present a new, fully generative model for constructing astronomical
catalogs from optical telescope image sets. Each pixel intensity is treated as
a random variable with parameters that depend on the latent properties of stars
and galaxies. These latent properties are themselves modeled as random. We
compare two procedures for posterior inference. One procedure is based on
Markov chain Monte Carlo (MCMC) while the other is based on variational
inference (VI). The MCMC procedure excels at quantifying uncertainty, while the
VI procedure is 1000 times faster. On a supercomputer, the VI procedure
efficiently uses 665,000 CPU cores to construct an astronomical catalog from 50
terabytes of images in 14.6 minutes, demonstrating the scaling characteristics
necessary to construct catalogs for upcoming astronomical surveys.Comment: accepted to the Annals of Applied Statistic
Semiparametric regression analysis via Infer.NET
© 2018, American Statistical Association. All rights reserved. We provide several examples of Bayesian semiparametric regression analysis via the Infer.NET package for approximate deterministic inference in Bayesian models. The examples are chosen to encompass a wide range of semiparametric regression situations. Infer.NET is shown to produce accurate inference in comparison with Markov chain Monte Carlo via the BUGS package, but to be considerably faster. Potentially, this contribution represents the start of a new era for semiparametric regression, where large and complex analyses are performed via fast Bayesian inference methodology and software, mainly being developed within Machine Learning
Contamination source inference in water distribution networks
We study the inference of the origin and the pattern of contamination in
water distribution networks. We assume a simplified model for the dyanmics of
the contamination spread inside a water distribution network, and assume that
at some random location a sensor detects the presence of contaminants. We
transform the source location problem into an optimization problem by
considering discrete times and a binary contaminated/not contaminated state for
the nodes of the network. The resulting problem is solved by Mixed Integer
Linear Programming. We test our results on random networks as well as in the
Modena city network
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