Página 1 dos resultados de 389 itens digitais encontrados em 0.008 segundos

Análise de distúrbios relacionados com a qualidade da energia elétrica utilizando a transformada Wavelet; Analysis of power quality disturbances using Wavelet transform

Arruda, Elcio Franklin de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 07/04/2003 Português
Relevância na Pesquisa
56.33%
O presente trabalho visa a utilização da transformada Wavelet no monitoramento do sistema elétrico no que diz respeito a problemas de qualidade da energia com o intuito de detectar, localizar e classificar os mesmos. A transformada Wavelet tem surgido na literatura como uma nova ferramenta para análise de sinais, utilizando funções chamadas Wavelet mãe para mapear sinais em seu domínio, fornecendo informações simultâneas nos domínios tempo e freqüência. A transformada Wavelet é realizada através de filtros decompondo-se um dado sinal em análise multiresolução. Por esta, obtém-se a detecção e a localização de distúrbios relacionados com a qualidade da energia decompondo-se o sinal em dois outros que representam uma versão de detalhes (correspondente as altas freqüências do sinal) e uma versão de aproximação (correspondente as baixas freqüências do sinal). A versão de aproximação é novamente decomposta obtendo-se novos sinais de detalhes e aproximações e assim sucessivamente. Sendo assim, os distúrbios podem ser detectados e localizados no tempo em função do seu conteúdo de freqüência. Estas informações fornecem também características únicas pertinentes a cada distúrbio, permitindo classificá-los. Desta forma...

Aplicação de wavelets na análise de gestos musicais em timbres de instrumentos acústicos tradicionais.; Wavelets application on the analysis of musical gestures in timbres of traditional acoustic instruments.

Faria, Regis Rossi Alves
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/09/1997 Português
Relevância na Pesquisa
56.21%
A expressividade é um elemento chave para o transporte de emoções em música, e seu modelamento, vital para a concepção de sistemas de síntese mais realistas. Gestos musicais executados durante a interpretação usualmente portam a informação responsável pela expressividade percebida, e podem ser rastreados por meio de padrões sônicos a eles associados em diversas escalas de resolução. Um conjunto relevante de gestos musicais expressivos foi estudado através de uma análise em multiresolução utilizando-se a transformada wavelet. A escolha deve-se principalmente à capacidade natural desta ferramenta em realizar análises de tempo-escala/frequência, e suas semelhanças com o processamento dos estágios primários do sistema auditivo. Vinte e sete eventos musicais foram capturados em interpretações de violino e flauta, e analisados com o objetivo de avaliar a aplicabilidade desta ferramenta na identificação e segregação de padrões sônicos associados a gestos musicais expressivos. Os algoritmos wavelet foram implementados na plataforma MATLAB utilizando-se bancos de filtros organizados em esquema piramidal. Rotinas para análises gráfica e sônica e uma interface ao usuário foram também implementadas. Verificou-se que as wavelets permitem a identificação de padrões sônicos associados a gestos expressivos exibindo diferentes propriedades em níveis diferentes da análise. A técnica mostrou-se útil para isolar ruídos oriundos de fontes diversas...

Classification of masses in mammographic image using wavelet domain features and polynomial classifier

Nascimento, Marcelo Zanchetta Do; Martins, Alessandro Santana; Neves, Leandro Alves; Ramos, Rodrigo Pereira; Flores, Edna Lúcia; Carrijo, Gilberto Arantes
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 6213-6221
Português
Relevância na Pesquisa
46.34%
Breast cancer is the most common cancer among women. In CAD systems, several studies have investigated the use of wavelet transform as a multiresolution analysis tool for texture analysis and could be interpreted as inputs to a classifier. In classification, polynomial classifier has been used due to the advantages of providing only one model for optimal separation of classes and to consider this as the solution of the problem. In this paper, a system is proposed for texture analysis and classification of lesions in mammographic images. Multiresolution analysis features were extracted from the region of interest of a given image. These features were computed based on three different wavelet functions, Daubechies 8, Symlet 8 and bi-orthogonal 3.7. For classification, we used the polynomial classification algorithm to define the mammogram images as normal or abnormal. We also made a comparison with other artificial intelligence algorithms (Decision Tree, SVM, K-NN). A Receiver Operating Characteristics (ROC) curve is used to evaluate the performance of the proposed system. Our system is evaluated using 360 digitized mammograms from DDSM database and the result shows that the algorithm has an area under the ROC curve Az of 0.98 ± 0.03. The performance of the polynomial classifier has proved to be better in comparison to other classification algorithms. © 2013 Elsevier Ltd. All rights reserved.

Adaptive multiresolution analysis based on anisotropic triangulations

Cohen, Albert; Dyn, Nira; Hecht, Frédéric; Mirebeau, Jean-Marie
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/01/2011 Português
Relevância na Pesquisa
56.17%
A simple greedy refinement procedure for the generation of data-adapted triangulations is proposed and studied. Given a function of two variables, the algorithm produces a hierarchy of triangulations and piecewise polynomial approximations on these triangulations. The refinement procedure consists in bisecting a triangle T in a direction which is chosen so as to minimize the local approximation error in some prescribed norm between the approximated function and its piecewise polynomial approximation after T is bisected. The hierarchical structure allows us to derive various approximation tools such as multiresolution analysis, wavelet bases, adaptive triangulations based either on greedy or optimal CART trees, as well as a simple encoding of the corresponding triangulations. We give a general proof of convergence in the Lp norm of all these approximations. Numerical tests performed in the case of piecewise linear approximation of functions with analytic expressions or of numerical images illustrate the fact that the refinement procedure generates triangles with an optimal aspect ratio (which is dictated by the local Hessian of of the approximated function in case of C2 functions).; Comment: 19 pages, 7 figures

Multiresolution Analysis of Incomplete Rankings

Clémençon, Stéphan; Jakubowicz, Jérémie; Sibony, Eric
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/03/2014 Português
Relevância na Pesquisa
46.32%
Incomplete rankings on a set of items $\{1,\; \ldots,\; n\}$ are orderings of the form $a_{1}\prec\dots\prec a_{k}$, with $\{a_{1},\dots a_{k}\}\subset\{1,\dots,n\}$ and $k < n$. Though they arise in many modern applications, only a few methods have been introduced to manipulate them, most of them consisting in representing any incomplete ranking by the set of all its possible linear extensions on $\{1,\; \ldots,\; n\}$. It is the major purpose of this paper to introduce a completely novel approach, which allows to treat incomplete rankings directly, representing them as injective words over $\{1,\; \ldots,\; n\}$. Unexpectedly, operations on incomplete rankings have very simple equivalents in this setting and the topological structure of the complex of injective words can be interpretated in a simple fashion from the perspective of ranking. We exploit this connection here and use recent results from algebraic topology to construct a multiresolution analysis and develop a wavelet framework for incomplete rankings. Though purely combinatorial, this construction relies on the same ideas underlying multiresolution analysis on a Euclidean space, and permits to localize the information related to rankings on each subset of items. It can be viewed as a crucial step toward nonlinear approximation of distributions of incomplete rankings and paves the way for many statistical applications...

Adaptive Directional Subdivision Schemes and Shearlet Multiresolution Analysis

Kutyniok, Gitta; Sauer, Tomas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/10/2007 Português
Relevância na Pesquisa
56.34%
In this paper, we propose a solution for a fundamental problem in computational harmonic analysis, namely, the construction of a multiresolution analysis with directional components. We will do so by constructing subdivision schemes which provide a means to incorporate directionality into the data and thus the limit function. We develop a new type of non-stationary bivariate subdivision schemes, which allow to adapt the subdivision process depending on directionality constraints during its performance, and we derive a complete characterization of those masks for which these adaptive directional subdivision schemes converge. In addition, we present several numerical examples to illustrate how this scheme works. Secondly, we describe a fast decomposition associated with a sparse directional representation system for two dimensional data, where we focus on the recently introduced sparse directional representation system of shearlets. In fact, we show that the introduced adaptive directional subdivision schemes can be used as a framework for deriving a shearlet multiresolution analysis with finitely supported filters, thereby leading to a fast shearlet decomposition.; Comment: 35 pages, 7 figures

Wavelets, Curvelets and Multiresolution Analysis Techniques Applied to Implosion Symmetry Characterization of ICF Targets

Afeyan, Bedros; Won, Kirk; Starck, Jean Luc; Cuneo, Michael
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/11/2012 Português
Relevância na Pesquisa
56.17%
We introduce wavelets, curvelets and multiresolution analysis techniques to assess the symmetry of X ray driven imploding shells in ICF targets. After denoising X ray backlighting produced images, we determine the Shell Thickness Averaged Radius (STAR) of maximum density, r*(N, {\theta}), where N is the percentage of the shell thickness over which to average. The non-uniformities of r*(N, {\theta}) are quantified by a Legendre polynomial decomposition in angle, {\theta}. Undecimated wavelet decompositions outperform decimated ones in denoising and both are surpassed by the curvelet transform. In each case, hard thresholding based on noise modeling is used. We have also applied combined wavelet and curvelet filter techniques with variational minimization as a way to select the significant coefficients. Gains are minimal over curvelets alone in the images we have analyzed.; Comment: 6 pages, 4 figures, IFSA Conference 2003 Proceedings, p107, B. A. Hammel, D. D. Meyerhofer, J. Meyer-ter-Vehn and H. Azechi, editors, American Nuclear Society, 2004

Wavelets, Curvelets and Multiresolution Analysis Techniques in Fast Z Pinch Research

Afeyan, Bedros; Won, Kirk; Starck, Jean Luc; Cuneo, Michael
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/11/2012 Português
Relevância na Pesquisa
56.17%
Z pinches produce an X ray rich plasma environment where backlighting imaging of imploding targets can be quite challenging to analyze. What is required is a detailed understanding of the implosion dynamics by studying snapshot images of its in flight deformations away from a spherical shell. We have used wavelets, curvelets and multiresolution analysis techniques to address some of these difficulties and to establish the Shell Thickness Averaged Radius (STAR) of maximum density, r*(N, {\theta}), where N is the percentage of the shell thickness over which we average. The non-uniformities of r*(N, {\theta}) are quantified by a Legendre polynomial decomposition in angle, {\theta}, and the identification of its largest coefficients. Undecimated wavelet decompositions outperform decimated ones in denoising and both are surpassed by the curvelet transform. In each case, hard thresholding based on noise modeling is used.; Comment: 11 pages, 17 figures, Volume 5207 Wavelets: Applications in Signal and Image Processing X. 10.1117/12.506243

Spectral Models for Orthonormal Wavelets and Multiresolution Analysis of $L^2({\mathbb R})$

Gómez-Cubillo, F.; Suchanecki, Z.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/05/2009 Português
Relevância na Pesquisa
56.17%
Spectral representations of the dilation and translation operators on $L^2({\mathbb R})$ are built through appropriate bases. Orthonormal wavelets and multiresolution analysis are then described in terms of rigid operator-valued functions defined on the functional spectral spaces. The approach is useful for computational purposes.; Comment: 26 pages

Multiresolution wavelet analysis of Bessel functions of scale $\nu +1$

Jorgensen, P. E. T.; Paolucci, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.45%
We identify multiresolution subspaces giving rise via Hankel transforms to Bessel functions. They emerge as orthogonal systems derived from geometric Hilbert-space considerations, the same way the wavelet functions from a multiresolution scaling wavelet construction arise from a scale of Hilbert spaces. We study the theory of representations of the C*-algebra O_{\nu+1} arising from this multiresolution analysis.; Comment: 19 pages, REVTeX v. 3.1, submitted to J. Math. Phys., PACS 02.30.Nw, 02.30.Tb, 03.65.-w, 03.65.Bz, 03.65.Db. In the revision, the title is changed (from "Deformed multiresolution wavelet analysis of scale $\nu +1$"), some more introductory material is added, and some points both in the statements of results and their proof have been clarified

Multiresolution analysis for Markov Interval Maps

Bohnstengel, Jana; Kesseböhmer, Marc
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/07/2011 Português
Relevância na Pesquisa
56.41%
We set up a multiresolution analysis on fractal sets derived from limit sets of Markov Interval Maps. For this we consider the $\mathbb{Z}$-convolution of a non-atomic measure supported on the limit set of such systems and give a thorough investigation of the space of square integrable functions with respect to this measure. We define an abstract multiresolution analysis, prove the existence of mother wavelets, and then apply these abstract results to Markov Interval Maps. Even though, in our setting the corresponding scaling operators are in general not unitary we are able to give a complete description of the multiresolution analysis in terms of multiwavelets.; Comment: 31 pages, 4 figures

Multiresolution Analysis Based on Coalescence Hidden-variable FIF

Kapoor, G. P.; Prasad, Srijanani Anurag
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/01/2012 Português
Relevância na Pesquisa
46.4%
In the present paper, multiresolution analysis arising from Coalescence Hidden-variable Fractal Interpolation Functions (CHFIFs) is accomplished. The availability of a larger set of free variables and constrained variables with CHFIF in multiresolution analysis based on CHFIFs provides more control in reconstruction of functions in L2(\mathbb{R})than that provided by multiresolution analysis based only on Affine Fractal Interpolation Functions (AFIFs). In our approach, the vector space of CHFIFs is introduced, its dimension is determined and Riesz bases of vector subspaces Vk, k \in \mathbb{Z}, consisting of certain CHFIFs in L2(\mathbb{R}) \cap C0(\mathbb{R}) are constructed. As a special case, for the vector space of CHFIFs of dimension 4, orthogonal bases for the vector subspaces Vk, k \in \mathbb{Z}, are explicitly constructed and, using these bases, compactly supported continuous orthonormal wavelets are generated.; Comment: 19 Pages, 3 Figures

A new multiresolution finite element method based on a multiresolution quadrilateral plate element

Xia, YiMing
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.54%
A new multiresolution quadrilateral plate element is proposed and a multiresolution finite element method is hence presented. The multiresolution analysis (MRA) framework is formulated out of a mutually nesting displacement subspace sequence, whose basis functions are constructed of scaling and shifting on the element domain of basic node shape function. The basic node shape function is constructed by extending shape function around a specific node. The MRA endows the proposed element with the resolution level (RL) to adjust the element node number, thus modulating structural analysis accuracy accordingly. As a result, the traditional 4-node quadrilateral plate element and method is a monoresolution one and also a special case of the proposed element and method. The meshing for the monoresolution plate element model is based on the empiricism while the RL adjusting for the multiresolution is laid on the rigorous mathematical basis. The accuracy of a structural analysis is actually determined by the RL, not by the mesh. The rational MRA enable the implementation of the multiresolution element method to be more rational and efficient than that of the conventional monoresolution plate element method or other corresponding MRA methods such as the wavelet finite element method...

A Multiresolution Ensemble Kalman Filter using Wavelet Decomposition

Hickmann, Kyle S.; Godinez, Humberto C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/11/2015 Português
Relevância na Pesquisa
46.35%
We present a method of using classical wavelet based multiresolution analysis to separate scales in model and observations during data assimilation with the ensemble Kalman filter. In many applications, the underlying physics of a phenomena involve the interaction of features at multiple scales. Blending of observational and model error across scales can result in large forecast inaccuracies since large errors at one scale are interpreted as inexact data at all scales. Our method uses a transformation of the observation operator in order to separate the information from different scales of the observations. This naturally induces a transformation of the observation covariance and we put forward several algorithms to efficiently compute the transformed covariance. Another advantage of our multiresolution ensemble Kalman filter is that scales can be weighted independently to adjust each scale's effect on the forecast. To demonstrate feasibility we present applications to a one dimensional Kuramoto-Sivashinsky (K-S) model with scale dependent observation noise and an application involving the forecasting of solar photospheric flux. The latter example demonstrates the multiresolution ensemble Kalman filter's ability to account for scale dependent model error. Modeling of photospheric magnetic flux transport is accomplished by the Air Force Data Assimilative Photospheric Transport (ADAPT) model.

Fault Analysis Using Gegenbauer Multiresolution Analysis

Soares, L. R.; de Oliveira, H. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/02/2015 Português
Relevância na Pesquisa
56.34%
This paper exploits the multiresolution analysis in the fault analysis on transmission lines. Faults were simulated using the ATP (Alternative Transient Program), considering signals at 128/cycle. A nonorthogonal multiresolution analysis was provided by Gegenbauer scaling and wavelet filters. In the cases where the signal reconstruction is not required, orthogonality may be immaterial. Gegenbauer filter banks are thereby offered in this paper as a tool for analyzing fault signals on transmission lines. Results are compared to those ones derived from a 4-coefficient Daubechies filter. The main advantages in favor of Gegenbauer filters are their smaller computational effort and their constant group delay, as they are symmetric filters.; Comment: 6 pages, 12 figures. In: Transmission and Distribution IEEE/PES/T&D Latin America, Sao Paulo, Brazil, 2004

A Family of Wavelets and a new Orthogonal Multiresolution Analysis Based on the Nyquist Criterion

de Oliveira, H. M.; Soares, L. R.; Falk, T. H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.19%
A generalisation of the Shannon complex wavelet is introduced, which is related to raised cosine filters. This approach is used to derive a new family of orthogonal complex wavelets based on the Nyquist criterion for Intersymbolic Interference (ISI) elimination. An orthogonal Multiresolution Analysis (MRA) is presented, showing that the roll-off parameter should be kept below 1/3. The pass-band behaviour of the Wavelet Fourier spectrum is examined. The left and right roll-off regions are asymmetric; nevertheless the Q-constant analysis philosophy is maintained. Finally, a generalisation of the (square root) raised cosine wavelets is proposed.; Comment: 8 pages, 14 figures

A hypergeometric basis for the Alpert multiresolution analysis

Geronimo, Jeffrey S.; Iliev, Plamen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.2%
We construct an explicit orthonormal basis of piecewise ${}_{i+1}F_{i}$ hypergeometric polynomials for the Alpert multiresolution analysis. The Fourier transform of each basis function is written in terms of ${}_2F_3$ hypergeometric functions. Moreover, the entries in the matrix equation connecting the wavelets with the scaling functions are shown to be balanced ${}_4 F_3$ hypergeometric functions evaluated at $1$, which allows to compute them recursively via three-term recurrence relations. The above results lead to a variety of new interesting identities and orthogonality relations reminiscent to classical identities of higher-order hypergeometric functions and orthogonality relations of Wigner $6j$-symbols.

Shannon Multiresolution Analysis on the Heisenberg Group

Mayeli, Azita
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.17%
We present a notion of frame multiresolution analysis on the Heisenberg group, abbreviated by FMRA, and study its properties. Using the irreducible representations of this group, we shall define a sinc-type function which is our starting point for obtaining the scaling function. Further, we shall give a concrete example of a wavelet FMRA on the Heisenberg group which is analogous to the Shannon MRA on $\RR$.; Comment: 17 pages

An adaptive numerical method for the Vlasov equation based on a multiresolution analysis

Besse, Nicolas; Filbet, Francis; Gutnic, Michael; Paun, Ioana; Sonnendrücker, Eric
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/04/2007 Português
Relevância na Pesquisa
56.17%
In this paper, we present very first results for the adaptive solution on a grid of the phase space of the Vlasov equation arising in particles accelarator and plasma physics. The numerical algorithm is based on a semi-Lagrangian method while adaptivity is obtained using multiresolution analysis.

Boundary element based multiresolution shape optimisation in electrostatics

Bandara, Kosala; Cirak, Fehmi; Of, G?nther; Steinbach, Olaf; Zapletal, Jan
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; published version
Português
Relevância na Pesquisa
46.35%
This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.jcp.2015.05.017; We consider the shape optimisation of high-voltage devices subject to electrostatic field equations by combining fast boundary elements with multiresolution subdivision surfaces. The geometry of the domain is described with subdivision surfaces and different resolutions of the same geometry are used for optimisation and analysis. The primal and adjoint problems are discretised with the boundary element method using a sufficiently fine control mesh. For shape optimisation the geometry is updated starting from the coarsest control mesh with increasingly finer control meshes. The multiresolution approach effectively prevents the appearance of non-physical geometry oscillations in the optimised shapes. Moreover, there is no need for mesh regeneration or smoothing during the optimisation due to the absence of a volume mesh. We present several numerical experiments and one industrial application to demonstrate the robustness and versatility of the developed approach.; We gratefully acknowledge the support provided by the EU commission through the FP7 Marie Curie IAPP project CASOPT (PIAP-GA-2008-230224). K.B. and F.C. thank for the additional support provided by EPSRC through #EP/G008531/1. J.Z. thanks for the support provided by the European Regional Development Fund in the IT4Innovations Centre of Excellence project (CZ.1.05/1.1.00/02.0070) and by the project SPOMECH ? Creating a Multidisciplinary R&D Team for Reliable Solution of Mechanical Problems...