Página 1 dos resultados de 72 itens digitais encontrados em 0.075 segundos

## ‣ Computational aspects of harmonic wavelet Galerkin methods and an application to a precipitation front propagation model

BARROS, Saulo R. M.; PEIXOTO, Pedro S.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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This article is dedicated to harmonic wavelet Galerkin methods for the solution of partial differential equations. Several variants of the method are proposed and analyzed, using the Burgers equation as a test model. The computational complexity can be reduced when the localization properties of the wavelets and restricted interactions between different scales are exploited. The resulting variants of the method have computational complexities ranging from O(N(3)) to O(N) (N being the space dimension) per time step. A pseudo-spectral wavelet scheme is also described and compared to the methods based on connection coefficients. The harmonic wavelet Galerkin scheme is applied to a nonlinear model for the propagation of precipitation fronts, with the front locations being exposed in the sizes of the localized wavelet coefficients. (C) 2011 Elsevier Ltd. All rights reserved.; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq

## ‣ O método multigrid algébrico na resolução de sistemas lineares oriundos do método dos elementos finitos.; The algebric multigrid method for solving linear systems issued from the finite element method.

Pereira, Fábio Henrique
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
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## ‣ Tratamento e análise de sinais neurológicos visuais com wavelets; Treatment and analysis of visual neurological signals with wavelets

Weiderpass, Heinar Augusto
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
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## ‣ Resolução numérica de EDPs utilizando ondaletas harmônicas; Numerical resolution of partial differential equations using harmonic wavelets

Peixoto, Pedro da Silva
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
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Métodos de resolução numérica de equações diferenciais parciais que utilizam ondaletas como base vêm sendo desenvolvidos nas últimas décadas, mas existe uma carência de estudos mais profundos das características computacionais dos mesmos. Neste estudo analisou-se detalhadamente um método espectral de Galerkin com base de ondaletas harmônicas. Revisou-se a teoria matemática referente às ondaletas harmônicas, que mostrou ter grande similaridade com a teoria referente à base trigonométrica de Fourier. Diversos testes numéricos foram realizados. Ao analisarmos a resolução da equação do transporte linear, e também de transporte não linear (equação de Burgers), obtivemos boas aproximações da solução esperada. O custo computacional obtido foi similar ao método com base de Fourier, mas com ondaletas harmônicas foi possível usar a localidade das ondaletas para detectar características de localidade do sinal. Analisamos ainda uma abordagem pseudo-espectral para os casos não lineares, que resultaram em um expressivo aumento de eficiência. Tendo em vista o uso das propriedades de localidade das ondaletas, usamos o método de Galerkin com base de ondaletas harmônicas para resolver um sistema de equações referente a um modelo de propagação de frentes de precipitação. O método mostrou boas aproximações das soluções esperadas...

## ‣ Detecção e avaliação de impactos em mecanismos de direção automotivo servo-assistido através do uso da Transformada de Wavelets.; Impacts detection and evaluation of steering system with servo assistance by the use of Wavelet Transform.

Tsuchie, Marcos Jun
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
Relevância na Pesquisa
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## ‣ 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
Relevância na Pesquisa
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## ‣ Harmonics filtering and detection of disturbances using wavelets

Alves, Alceu F.; da Costa, P.; Fraga, Jose R P; Pires, Francisca Ap C
Tipo: Conferência ou Objeto de Conferência Formato: 1168-1173
Português
Relevância na Pesquisa
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Traditional mathematical tools, like Fourier Analysis, have proven to be efficient when analyzing steady-state distortions; however, the growing utilization of electronically controlled loads and the generation of a new dynamics in industrial environments signals have suggested the need of a powerful tool to perform the analysis of non-stationary distortions, overcoming limitations of frequency techniques. Wavelet Theory provides a new approach to harmonic analysis, focusing the decomposition of a signal into non-sinusoidal components, which are translated and scaled in time, generating a time-frequency basis. The correct choice of the waveshape to be used in decomposition is very important and discussed in this work. A brief theoretical introduction on Wavelet Transform is presented and some cases (practical and simulated) are discussed. Distortions commonly found in industrial environments, such as the current waveform of a Switched-Mode Power Supply and the input phase voltage waveform of motor fed by inverter are analyzed using Wavelet Theory. Applications such as extracting the fundamental frequency of a non-sinusoidal current signal, or using the ability of compact representation to detect non-repetitive disturbances are presented.

## ‣ Multi-resolution Shape Analysis via Non-Euclidean Wavelets: Applications to Mesh Segmentation and Surface Alignment Problems

Kim, Won Hwa; Chung, Moo K.; Singh, Vikas
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The analysis of 3-D shape meshes is a fundamental problem in computer vision, graphics, and medical imaging. Frequently, the needs of the application require that our analysis take a multi-resolution view of the shape’s local and global topology, and that the solution is consistent across multiple scales. Unfortunately, the preferred mathematical construct which offers this behavior in classical image/signal processing, Wavelets, is no longer applicable in this general setting (data with non-uniform topology). In particular, the traditional definition does not allow writing out an expansion for graphs that do not correspond to the uniformly sampled lattice (e.g., images). In this paper, we adapt recent results in harmonic analysis, to derive Non-Euclidean Wavelets based algorithms for a range of shape analysis problems in vision and medical imaging. We show how descriptors derived from the dual domain representation offer native multi-resolution behavior for characterizing local/global topology around vertices. With only minor modifications, the framework yields a method for extracting interest/key points from shapes, a surprisingly simple algorithm for 3-D shape segmentation (competitive with state of the art), and a method for surface alignment (without landmarks). We give an extensive set of comparison results on a large shape segmentation benchmark and derive a uniqueness theorem for the surface alignment problem.

## ‣ Nonlinear system response to nonstationary input processes using harmonic wavelets

Tezcan, Jale
Português
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Thorough understanding of dynamic system behavior is of major importance in many fields in science and engineering. When the spectral content of a process is changing with time, neither the time nor the frequency domain alone is sufficient to describe the process accurately. It is clearly recognized that a method to analyze excitation and response processes in both time and frequency domains is needed. This dissertation introduces a method to estimate the response of nonlinear systems to non-stationary excitations described by their wavelet coefficients. Time-frequency localization properties of wavelets are utilized to capture the evolutionary behavior of the spectral characteristics of the non-stationary processes and to describe the time dependent behavior of a nonlinear system. The wavelets-based approach developed in this thesis employs harmonic wavelets due to their concise form in the frequency domain, where each point in the frequency domain belongs to one particular scale only, thereby allowing one to use the terms "scale" and "frequency band" interchangeably. Utilizing this attractive property of the harmonic wavelets, an explicit relationship between the harmonic wavelet coefficients of a process and its time dependent spectral content is derived. To estimate the response of a nonlinear system...

## ‣ Harmonic Wavelets Procedures and Wiener Path and Integral Methods for Response Determination and Reliability Assessment of Nonlinear Systems/Structures

Kougioumtzoglou, Ioannis A.
Português
Relevância na Pesquisa
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In this thesis a novel approximate/analytical approach based on the concepts of stochastic averaging and of statistical linearization is developed for the response determination of nonlinear/hysteretic multi-degree-of-freedom (MDOF) systems subject to evolutionary stochastic excitation. The significant advantage of the approach relates to the fact that it is readily applicable for excitations possessing even non-separable evolutionary power spectra (EPS) circumventing ad hoc pre-filtering and pre-processing excitation treatments associated with existing alternative schemes of linearization. Further, the approach can be used, in a rather straightforward manner, in conjunction with recently developed design spectrum based analyses for obtaining peak response estimates without resorting to numerical integration of the nonlinear equations of motion. Furthermore, a novel approximate/analytical Wiener path integral based solution (PIS) is developed and a numerical PIS approach is extended to determine the response and first-passage probability density functions (PDFs) of nonlinear/hysteretic systems subject to evolutionary stochastic excitation. Applications include the versatile Preisach hysteretic model, recently applied in modeling systems equipped with smart material (shape memory alloys) devices used for seismic hazard risk mitigation. The approach is also applied to determine the capsizing probability of a ship...

## ‣ Harmonic analysis on the Möbius gyrogroup

Ferreira, Milton
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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In this paper we propose to develop harmonic analysis on the Poincaré ball $B_t^n$, a model of the n-dimensional real hyperbolic space. The Poincaré ball $B_t^n$ is the open ball of the Euclidean n-space $R^n$ with radius $t>0$, centered at the origin of $R^n$ and equipped with Möbius addition, thus forming a Möbius gyrogroup where Möbius addition in the ball plays the role of vector addition in $\mathbb{R}^n$. For any $t>0$ and an arbitrary parameter $\sigma \in R$ we study the $(\sigma,t)$-translation, the $( \sigma,t)$-convolution, the eigenfunctions of the $(\sigma,t)$-Laplace-Beltrami operator, the $(\sigma,t)$-Helgason Fourier transform, its inverse transform and the associated Plancherel's Theorem, which represent counterparts of standard tools, thus, enabling an effective theory of hyperbolic harmonic analysis. Moreover, when $t \rightarrow +\infty$ the resulting hyperbolic harmonic analysis on $B_t^n$ tends to the standard Euclidean harmonic analysis on $R^n$, thus unifying hyperbolic and Euclidean harmonic analysis. As an application we construct diffusive wavelets on $B_t^n$.

## ‣ El problema de tomografía local utilizando wavelets [recurso electrónico] / Wilmar Alberto Díaz Ossa, Harold Vacca González

Díaz Ossa, Wilmar A.; Vacca González, Harold
Tipo: masterThesis; Tesis de Maestría; acceptedVersion
Português
Relevância na Pesquisa
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## ‣ Método Wavelet-Petrov-Galerkin en la solución numérica de la ecuación KdV

Duarte Vidal, Julio César; Fierro Yaguara, Esper Andrés
Tipo: masterThesis; Tesis de Maestría; acceptedVersion
Português
Relevância na Pesquisa
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## ‣ Compresión de imágenes usando wavelets

Puetamán Guerrero, Gloria; Salazar Escobar, Hernán
Tipo: masterThesis; Tesis de Maestría; acceptedVersion
Português
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Las wavelets y el análisis de multirresolución constituyen una potente herramienta para afrontar problemas fundamentales en el tratamiento de señales. Entre ellos se encuentran la reducción del ruido, la compresión de señales (de mucha importancia tanto en la transmisión de grandes cantidades de datos como en su almacenamiento) o la detección de determinados patrones o irregularidades locales en ciertos tipos de señales (electrocardiogramas, huellas digitales, vibraciones de motores, defectos de soldadura entre placas de acero, entre otras) (ver, p.e., [1], [7], [9], [11], [12], [18], [20], [23], [24], [30], [42], [47]). Esta moderna teoría ha experimentado un gran desarrollo en las dos últimas décadas mostrándose muy eficiente donde otras técnicas, como por ejemplo, la transformada rápida de Fourier no resultaban satisfactorias.; v, 95 p.; Contenido parcial: Introducción a las wavelets -- Compresión de imágenes usando wavelets -- El problema de la compresión de imágenes -- Manual del usuario y anexos.

## ‣ Locally Supported Wavelets for the Separation of Spherical Vector Fields with Respect to their Sources

Gerhards, Christian
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We provide a space domain oriented separation of magnetic fields into parts generated by sources in the exterior and sources in the interior of a given sphere. The separation itself is well-known in geomagnetic modeling, usually in terms of a spherical harmonic analysis or a wavelet analysis that is spherical harmonic based. In contrast to these frequency oriented methods, we use a more spatially oriented approach in this paper. We derive integral representations with explicitly known convolution kernels. Regularizing these singular kernels allows a multiscale representation of the internal and external contributions to the magnetic field with locally supported wavelets. This representation is applied to a set of CHAMP data for crustal field modeling.

## ‣ Wavelets and wavelet-like transforms on the sphere and their application to geophysical data inversion

Simons, Frederik J.; Loris, Ignace; Brevdo, Eugene; Daubechies, Ingrid C.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Many flexible parameterizations exist to represent data on the sphere. In addition to the venerable spherical harmonics, we have the Slepian basis, harmonic splines, wavelets and wavelet-like Slepian frames. In this paper we focus on the latter two: spherical wavelets developed for geophysical applications on the cubed sphere, and the Slepian "tree", a new construction that combines a quadratic concentration measure with wavelet-like multiresolution. We discuss the basic features of these mathematical tools, and illustrate their applicability in parameterizing large-scale global geophysical (inverse) problems.; Comment: 15 pages, 11 figures, submitted to the Proceedings of the SPIE 2011 conference Wavelets and Sparsity XIV

## ‣ Compactly Supported Wavelets Derived From Legendre Polynomials: Spherical Harmonic Wavelets

Lira, M. M. S.; de Oliveira, H. M.; Carvalho Jr, M. A.; de Souza, R. M. Campello
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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A new family of wavelets is introduced, which is associated with Legendre polynomials. These wavelets, termed spherical harmonic or Legendre wavelets, possess compact support. The method for the wavelet construction is derived from the association of ordinary second order differential equations with multiresolution filters. The low-pass filter associated with Legendre multiresolution analysis is a linear phase finite impulse response filter (FIR).; Comment: 6 pages, 6 figures, 1 table In: Computational Methods in Circuits and Systems Applications, WSEAS press, pp.211-215, 2003. ISBN: 960-8052-88-2

## ‣ Harmonic Singular Integrals and Steerable Wavelets in $L_2(\mathbb{R}^d)$

Ward, John Paul; Unser, Michael
Tipo: Artigo de Revista Científica
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Here we present a method of constructing steerable wavelet frames in $L_2(\mathbb{R}^d)$ that generalizes and unifies previous approaches, including Simoncelli's pyramid and Riesz wavelets. The motivation for steerable wavelets is the need to more accurately account for the orientation of data. Such wavelets can be constructed by decomposing an isotropic mother wavelet into a finite collection of oriented mother wavelets. The key to this construction is that the angular decomposition is an isometry, whereby the new collection of wavelets maintains the frame bounds of the original one. The general method that we propose here is based on partitions of unity involving spherical harmonics. A fundamental aspect of this construction is that Fourier multipliers composed of spherical harmonics correspond to singular integrals in the spatial domain. Such transforms have been studied extensively in the field of harmonic analysis, and we take advantage of this wealth of knowledge to make the proposed construction practically feasible and computationally efficient.; Comment: 27 pages, 2 figures

## ‣ Flaglets: Exact Wavelets on the Ball

Leistedt, Boris; McEwen, Jason D.
Tipo: Artigo de Revista Científica