38,952 research outputs found
Sequential Empirical Bayes method for filtering dynamic spatiotemporal processes
We consider online prediction of a latent dynamic spatiotemporal process and
estimation of the associated model parameters based on noisy data. The problem
is motivated by the analysis of spatial data arriving in real-time and the
current parameter estimates and predictions are updated using the new data at a
fixed computational cost. Estimation and prediction is performed within an
empirical Bayes framework with the aid of Markov chain Monte Carlo samples.
Samples for the latent spatial field are generated using a sampling importance
resampling algorithm with a skewed-normal proposal and for the temporal
parameters using Gibbs sampling with their full conditionals written in terms
of sufficient quantities which are updated online. The spatial range parameter
is estimated by a novel online implementation of an empirical Bayes method,
called herein sequential empirical Bayes method. A simulation study shows that
our method gives similar results as an offline Bayesian method. We also find
that the skewed-normal proposal improves over the traditional Gaussian
proposal. The application of our method is demonstrated for online monitoring
of radiation after the Fukushima nuclear accident
Some statistical and computational challenges, and opportunities in astronomy
The data complexity and volume of astronomical findings have increased in recent decades due to major technological improvements in instrumentation and data collection methods. The contemporary astronomer is flooded with terabytes of raw data that produce enormous multidimensional catalogs of objects (stars, galaxies, quasars, etc.) numbering in the billions, with hundreds of measured numbers for each object. The astronomical community thus faces a key task: to enable efficient and objective scientific exploitation of enormous multifaceted data sets and the complex links between data and astrophysical theory. In recognition of this task, the National Virtual Observatory (NVO) initiative recently emerged to federate numerous large digital sky archives, and to develop tools to explore and understand these vast volumes of data. The effective use of such integrated massive data sets presents a variety of new challenging statistical and algorithmic problems that require methodological advances. An interdisciplinary team of statisticians, astronomers and computer scientists from The Pennsylvania State University, California Institute of Technology and Carnegie Mellon University is developing statistical methodology for the NVO. A brief glimpse into the Virtual Observatory and the work of the Penn State-led team is provided here
Adaptive Langevin Sampler for Separation of t-Distribution Modelled Astrophysical Maps
We propose to model the image differentials of astrophysical source maps by
Student's t-distribution and to use them in the Bayesian source separation
method as priors. We introduce an efficient Markov Chain Monte Carlo (MCMC)
sampling scheme to unmix the astrophysical sources and describe the derivation
details. In this scheme, we use the Langevin stochastic equation for
transitions, which enables parallel drawing of random samples from the
posterior, and reduces the computation time significantly (by two orders of
magnitude). In addition, Student's t-distribution parameters are updated
throughout the iterations. The results on astrophysical source separation are
assessed with two performance criteria defined in the pixel and the frequency
domains.Comment: 12 pages, 6 figure
Low energy recoil detection with a spherical proportional counter
We present low energy recoil detection results in the keV energy region, from
measurements performed with the Spherical Proportional Counter (SPC). An
fast neutron source is used in order to obtain
neutron-nucleus elastic scattering events inside the gaseous volume of the
detector. The detector performance in the energy region was resolved by
observing the line of a X-ray source, with energy
resolution of (). The toolkit GEANT4 was used to simulate the
irradiation of the detector by an source, while SRIM
was used to calculate the Ionization Quenching Factor (IQF). The GEANT4
simulated energy deposition spectrum in addition with the SRIM calculated
quenching factor provide valuable insight to the experimental results. The
performance of the SPC in low energy recoil detection makes the detector a good
candidate for a wide range of applications, including Supernova or reactor
neutrino detection and Dark Matter (WIMP) searches (via coherent elastic
scattering).Comment: 16 pages, 16 figures, preprin
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