4,818 research outputs found
Multifractal Fluctuations in Seismic Interspike Series
Multifractal fluctuations in the time dynamics of seismicity data have been
analyzed. We investigated the interspike intervals (times between successive
earthquakes) of one of the most seismically active areas of central Italy by
using the Multifractal Detrended Fluctuation Analysis (MF-DFA). Analyzing the
time evolution of the multifractality degree of the series, a loss of
multifractality during the aftershocks is revealed. This study aims to suggest
another approach to investigate the complex dynamics of earthquakes
Joint Clustering and Registration of Functional Data
Curve registration and clustering are fundamental tools in the analysis of
functional data. While several methods have been developed and explored for
either task individually, limited work has been done to infer functional
clusters and register curves simultaneously. We propose a hierarchical model
for joint curve clustering and registration. Our proposal combines a Dirichlet
process mixture model for clustering of common shapes, with a reproducing
kernel representation of phase variability for registration. We show how
inference can be carried out applying standard posterior simulation algorithms
and compare our method to several alternatives in both engineered data and a
benchmark analysis of the Berkeley growth data. We conclude our investigation
with an application to time course gene expression
The changing ideas about valuation mechanisms in the interwar period: Toeplitz, Marlio and the 'Great Trasformation'
The Classical Analogue of CP-violation
The phenomenological features of the mixing in the neutral pseudoscalar
mesons K0-K0bar can be illustrated in the classical framework of mechanics and
by means of electromagnetic coupled circuits. The time-reversed not-invariant
processes and the related phenomenon of CP-nonconservation can be induced by
dissipative effects which yield a not vanishing imaginary part for the relevant
Hamiltonian. Thus, two coupled dissipative oscillators can resemble the
peculiar asymmetries which are so common in the realm of high energy particle
physics.Comment: 12 pages, Latex, 2 figures available by fa
Bayesian Inference for Latent Biologic Structure with Determinantal Point Processes (DPP)
We discuss the use of the determinantal point process (DPP) as a prior for
latent structure in biomedical applications, where inference often centers on
the interpretation of latent features as biologically or clinically meaningful
structure. Typical examples include mixture models, when the terms of the
mixture are meant to represent clinically meaningful subpopulations (of
patients, genes, etc.). Another class of examples are feature allocation
models. We propose the DPP prior as a repulsive prior on latent mixture
components in the first example, and as prior on feature-specific parameters in
the second case. We argue that the DPP is in general an attractive prior model
for latent structure when biologically relevant interpretation of such
structure is desired. We illustrate the advantages of DPP prior in three case
studies, including inference in mixture models for magnetic resonance images
(MRI) and for protein expression, and a feature allocation model for gene
expression using data from The Cancer Genome Atlas. An important part of our
argument are efficient and straightforward posterior simulation methods. We
implement a variation of reversible jump Markov chain Monte Carlo simulation
for inference under the DPP prior, using a density with respect to the unit
rate Poisson process
Optimization of the relative calibration for a visible bremsstrahlung Zeff diagnostic on TEXTOR via requirements of profile consistency
Large-Scale information extraction from textual definitions through deep syntactic and semantic analysis
We present DEFIE, an approach to large-scale Information Extraction (IE) based on a syntactic-semantic analysis of textual definitions. Given a large corpus of definitions we leverage syntactic dependencies to reduce data sparsity, then disambiguate the arguments and content words of the relation strings, and finally exploit the resulting information to organize the acquired relations hierarchically. The output of DEFIE is a high-quality knowledge base consisting of several million automatically acquired semantic relations
Comparison of Clustering Methods for Time Course Genomic Data: Applications to Aging Effects
Time course microarray data provide insight about dynamic biological
processes. While several clustering methods have been proposed for the analysis
of these data structures, comparison and selection of appropriate clustering
methods are seldom discussed. We compared probabilistic based clustering
methods and distance based clustering methods for time course microarray
data. Among probabilistic methods, we considered: smoothing spline clustering
also known as model based functional data analysis (MFDA), functional
clustering models for sparsely sampled data (FCM) and model-based clustering
(MCLUST). Among distance based methods, we considered: weighted gene
co-expression network analysis (WGCNA), clustering with dynamic time warping
distance (DTW) and clustering with autocorrelation based distance (ACF). We
studied these algorithms in both simulated settings and case study data. Our
investigations showed that FCM performed very well when gene curves were short
and sparse. DTW and WGCNA performed well when gene curves were medium or long
( observations). SSC performed very well when there were clusters of gene
curves similar to one another. Overall, ACF performed poorly in these
applications. In terms of computation time, FCM, SSC and DTW were considerably
slower than MCLUST and WGCNA. WGCNA outperformed MCLUST by generating more
accurate and biological meaningful clustering results. WGCNA and MCLUST are the
best methods among the 6 methods compared, when performance and computation
time are both taken into account. WGCNA outperforms MCLUST, but MCLUST provides
model based inference and uncertainty measure of clustering results
Reconstruction of Zeff profiles at TEXTOR through Bayasian source separation
The understanding of the behaviour of impurities is a critical issue in
tokamak physics. The ion effective charge Zeff provides a measure for impurity
concentration. On the TEXTOR tokamak (Julich, Germany), we run a diagnostic to
determine Zeff from the bremsstrahlung emissivity E. From radial profiles of E,
electron density ne and temperature Te, profiles for Zeff can be reconstructed.
However, their interpretation is difficult outside the plasma centre, because
of various uncertainties in E, ne and Te at the edge, which render the radial
matching of the different profiles problematic. Conversely, if it were possible
to obtain a set of line-integrated values for Zeff directly from the
line-integrated measurements of E, ne and Te, then these problems would be
avoided. Now, recent advances in the field of statistical signal processing
allow the extraction of an unknown signal from a signal mixture. In particular,
we describe a procedure for the single-channel Bayesian source separation of a
line-integrated Zeff signal from a line-integrated emissivity source, using as
a forward model a linearized version of the known functional dependence of Zeff
on E, ne and Te. Here, a line-integral over a traditionally obtained Zeff
profile may serve as a prior for the line-integrated Zeff signal. In this way,
precise information on the electron density and temperature may even become
superfluous for the determination of Zeff.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
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