46,703 research outputs found
Finite Element Maximum Entropy Method for Approximating Absolutely Continuous Invariant Measures
In a chaotic dynamical system, the eventual behavior of iterates of initial points of a map is unpredictable even though the map is deterministic. A system which is chaotic in a deterministic point of view may be regular in a statistical viewpoint. The statistical viewpoint requires the study of absolutely continuous invariant measure (ACIM) of a map with respect to the Lebesgue measure. An invariant density of the Frobenius-Perron (F-P) operator associated with a nonsingular map is employed to evaluate an ACIM of the map. The ACIM is a key factor for studying the eventual behavior of iterates of almost all initial points of the map. It is difficult to obtain an invariant density of the F-P operator in an exact mathematical form except for some simple maps. Different numerical schemes have been developed to approximate such densities. The maximum entropy principle gives a criterion to select a least-biased density among all densities satisfying a system of moment equations. In this principle, a least-biased density maximizes the Boltzmann entropy. In this dissertation, piecewise quadratic functions and quadratic splines are used in the maximum entropy method to calculate the L1 errors between the exact and the approximate invariant densities of the F-P operator associated with nonsingular maps defined from [0;1] to itself. The numerical results are supported by rigorous mathematical proofs. The L1 errors between the exact and approximate invariant densities of the Markov operator associated with Markov type position dependent random maps, defined from [0;1] to itself, are calculated by using the piecewise linear polynomials maximum entropy method
Sunyaev-Zel'dovich clusters reconstruction in multiband bolometer camera surveys
We present a new method for the reconstruction of Sunyaev-Zel'dovich (SZ)
galaxy clusters in future SZ-survey experiments using multiband bolometer
cameras such as Olimpo, APEX, or Planck. Our goal is to optimise SZ-Cluster
extraction from our observed noisy maps. We wish to emphasize that none of the
algorithms used in the detection chain is tuned on prior knowledge on the SZ
-Cluster signal, or other astrophysical sources (Optical Spectrum, Noise
Covariance Matrix, or covariance of SZ Cluster wavelet coefficients). First, a
blind separation of the different astrophysical components which contribute to
the observations is conducted using an Independent Component Analysis (ICA)
method. Then, a recent non linear filtering technique in the wavelet domain,
based on multiscale entropy and the False Discovery Rate (FDR) method, is used
to detect and reconstruct the galaxy clusters. Finally, we use the Source
Extractor software to identify the detected clusters. The proposed method was
applied on realistic simulations of observations. As for global detection
efficiency, this new method is impressive as it provides comparable results to
Pierpaoli et al. method being however a blind algorithm. Preprint with full
resolution figures is available at the URL:
w10-dapnia.saclay.cea.fr/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=728Comment: Submitted to A&A. 32 Pages, text onl
Entropy computing via integration over fractal measures
We discuss the properties of invariant measures corresponding to iterated
function systems (IFSs) with place-dependent probabilities and compute their
Renyi entropies, generalized dimensions, and multifractal spectra. It is shown
that with certain dynamical systems one can associate the corresponding IFSs in
such a way that their generalized entropies are equal. This provides a new
method of computing entropy for some classical and quantum dynamical systems.
Numerical techniques are based on integration over the fractal measures.Comment: 14 pages in Latex, Revtex + 4 figures in .ps attached (revised
version, new title, several changes, to appear in CHAOS
An Independent Component Analysis Based Tool for Exploring Functional Connections in the Brain
This thesis describes the use of independent component analysis (ICA) as
a measure of voxel similarity, which allows the user to find and view
statistically independent maps of correlated voxel activity.
The tool developed in this work uses a specialized clustering technique,
designed to find and characterize clusters of activated voxels, to
compare the independent component spatial maps across patients. This
same method is also used to compare SPM results across patients
Extending emission line Doppler tomography ; mapping modulated line flux
Emission line Doppler tomography is a powerful tool that resolves the
accretion flow in binaries on micro-arcsecond scales using time-resolved
spectroscopy. I present an extension to Doppler tomography that relaxes one of
its fundamental axioms and permits the mapping of time-dependent emission
sources. Significant variability on the orbital period is a common
characteristic of the emission sources that are observed in the accretion flows
of cataclysmic variables and X-ray binaries. Modulation Doppler tomography maps
sources varying harmonically as a function of the orbital period through the
simultaneous reconstruction of three Doppler tomograms. One image describes the
average flux distribution like in standard tomography, while the two additional
images describe the variable component in terms of its sine and cosine
amplitudes. I describe the implementation of such an extension in the form of
the maximum entropy based fitting code MODMAP. Test reconstructions of
synthetic data illustrate that the technique is robust and well constrained.
Artifact free reconstructions of complex emission distributions can be achieved
under a wide range of signal to noise levels. An application of the technique
is illustrated by mapping the orbital modulations of the asymmetric accretion
disc emission in the dwarf nova IP Pegasi.Comment: 8 pages, 4 figures; accepted for publication in MNRA
Weak Lensing Mass Reconstruction using Wavelets
This paper presents a new method for the reconstruction of weak lensing mass
maps. It uses the multiscale entropy concept, which is based on wavelets, and
the False Discovery Rate which allows us to derive robust detection levels in
wavelet space. We show that this new restoration approach outperforms several
standard techniques currently used for weak shear mass reconstruction. This
method can also be used to separate E and B modes in the shear field, and thus
test for the presence of residual systematic effects. We concentrate on large
blind cosmic shear surveys, and illustrate our results using simulated shear
maps derived from N-Body Lambda-CDM simulations with added noise corresponding
to both ground-based and space-based observations.Comment: Accepted manuscript with all figures can be downloaded at:
http://jstarck.free.fr/aa_wlens05.pdf and software can be downloaded at
http://jstarck.free.fr/mrlens.htm
On the concept of complexity in random dynamical systems
We introduce a measure of complexity in terms of the average number of bits
per time unit necessary to specify the sequence generated by the system. In
random dynamical system, this indicator coincides with the rate K of divergence
of nearby trajectories evolving under two different noise realizations.
The meaning of K is discussed in the context of the information theory, and
it is shown that it can be determined from real experimental data. In presence
of strong dynamical intermittency, the value of K is very different from the
standard Lyapunov exponent computed considering two nearby trajectories
evolving under the same randomness. However, the former is much more relevant
than the latter from a physical point of view as illustrated by some numerical
computations for noisy maps and sandpile models.Comment: 35 pages, LaTe
- …