Página 1 dos resultados de 435 itens digitais encontrados em 0.020 segundos

## ‣ Regularity of generalized Daubechies wavelets reproducing exponential polynomials

Dyn, N.; Kounchev, O.; Levin, D.; Render, H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.727043%
We investigate non-stationary orthogonal wavelets based on a non-stationary interpolatory subdivision scheme reproducing a given set of exponentials. The construction is analogous to the construction of Daubechies wavelets using the subdivision scheme of Deslauriers-Dubuc. The main result is the smoothness of these Daubechies type wavelets.

## ‣ Super-wavelets on local fields of positive characteristic

Shukla, Niraj K.; Maury, Saurabh C.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.897788%
The concept of super-wavelet was introduced by Balan, and Han and Larson over the field of real numbers which has many applications not only in engineering branches but also in different areas of mathematics. To develop this notion on local fields having positive characteristic we obtain characterizations of super-wavelets of finite length as well as Parseval frame multiwavelet sets of finite order in this setup. Using the group theoretical approach based on coset representatives, further we establish Shannon type multiwavelet in this perspective while providing examples of Parseval frame (multi)wavelets and (Parseval frame) super-wavelets. In addition, we obtain necessary conditions for decomposable and extendable Parseval frame wavelets associated to Parseval frame super-wavelets.; Comment: arXiv admin note: text overlap with arXiv:1511.05703

## ‣ Wavelets in Banach Spaces

Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
37.737173%
We describe a construction of wavelets (coherent states) in Banach spaces generated by admissible'' group representations. Our main targets are applications in pure mathematics while connections with quantum mechanics are mentioned. As an example we consider operator valued Segal-Bargmann type spaces and the Weyl functional calculus. Keywords: Wavelets, coherent states, Banach spaces, group representations, covariant, contravariant (Wick) symbols, Heisenberg group, Segal-Bargmann spaces, Weyl functional calculus (quantization), second quantization, bosonic field.; Comment: 37 pages; LaTeX2e; no pictures; 27/07/99: many small corrections

## ‣ On the usefulness of Meyer wavelets for deconvolution and density estimation

Bigot, Jeremie
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
37.826187%
The aim of this paper is to show the usefulness of Meyer wavelets for the classical problem of density estimation and for density deconvolution from noisy observations. By using such wavelets, the computation of the empirical wavelet coefficients relies on the fast Fourier transform of the data and on the fact that Meyer wavelets are band-limited functions. This makes such estimators very simple to compute and this avoids the problem of evaluating wavelets at non-dyadic points which is the main drawback of classical wavelet-based density estimators. Our approach is based on term-by-term thresholding of the empirical wavelet coefficients with random thresholds depending on an estimation of the variance of each coefficient. Such estimators are shown to achieve the same performances of an oracle estimator up to a logarithmic term. These estimators also achieve near-minimax rates of convergence over a large class of Besov spaces. A simulation study is proposed to show the good finite sample performances of the estimator for both problems of direct density estimation and density deconvolution.

## ‣ Non-MSF wavelets for the Hardy space H^2(\R)

Behera, Biswaranjan
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.766992%
We prove three results on wavelets for the Hardy space H^2(\R). All wavelets constructed so far for H^2(\R) are MSF wavelets. We construct a family of H^2-wavelets which are not MSF. An equivalence relation on H^2-wavelets is introduced and it is shown that the corresponding equivalence classes are non-empty. Finally, we construct a family of H^2-wavelets with Fourier transform discontinuous at the origin.; Comment: 11 pages

## ‣ On Filter Banks and Wavelets Based on Chebyshev Polynomials

Cintra, R. J.; de Oliveira, H. M.; Soares, L. R.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.766992%
In this paper we introduce a new family of wavelets, named Chebyshev wavelets, which are derived from conventional first and second kind Chebyshev polynomials. Properties of Chebyshev filter banks are investigated, including orthogonality and perfect reconstruction conditions. Chebyshev wavelets have compact support, their filters possess good selectivity, but they are not orthogonal. The convergence of the cascade algorithm of Chebyshev wavelets is proved by using properties of Markov chains. Computational implementation of these wavelets and some clear-cut applications are presented. Proposed wavelets are suitable for signal denoising.; Comment: 18 pages, 6 figures

## ‣ Higher-Order Properties of Analytic Wavelets

Lilly, J. M.; Olhede, S. C.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
37.766992%
The influence of higher-order wavelet properties on the analytic wavelet transform behavior is investigated, and wavelet functions offering advantageous performance are identified. This is accomplished through detailed investigation of the generalized Morse wavelets, a two-parameter family of exactly analytic continuous wavelets. The degree of time/frequency localization, the existence of a mapping between scale and frequency, and the bias involved in estimating properties of modulated oscillatory signals, are proposed as important considerations. Wavelet behavior is found to be strongly impacted by the degree of asymmetry of the wavelet in both the frequency and the time domain, as quantified by the third central moments. A particular subset of the generalized Morse wavelets, recognized as deriving from an inhomogeneous Airy function, emerge as having particularly desirable properties. These "Airy wavelets" substantially outperform the only approximately analytic Morlet wavelets for high time localization. Special cases of the generalized Morse wavelets are examined, revealing a broad range of behaviors which can be matched to the characteristics of a signal.; Comment: 15 pages, 6 Postscript figures

## ‣ $p$-Adic multidimensional wavelets and their application to $p$-adic pseudo-differential operators

Khrennikov, A. Yu.; Shelkovich, V. M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.951929%
In this paper we study some problems related with the theory of multidimensional $p$-adic wavelets in connection with the theory of multidimensional $p$-adic pseudo-differential operators (in the $p$-adic Lizorkin space). We introduce a new class of $n$-dimensional $p$-adic compactly supported wavelets. In one-dimensional case this class includes the Kozyrev $p$-adic wavelets. These wavelets (and their Fourier transforms) form an orthonormal complete basis in ${\cL}^2(\bQ_p^n)$. A criterion for a multidimensional $p$-adic wavelet to be an eigenfunction for a pseudo-differential operator is derived. We prove that these wavelets are eigenfunctions of the Taibleson fractional operator. Since many $p$-adic models use pseudo-differential operators (fractional operator), these results can be intensively used in applications. Moreover, $p$-adic wavelets are used to construct solutions of linear and {\it semi-linear} pseudo-differential equations.

## ‣ Diffusive wavelets on the Spin group

Bernstein, Swanhild; Ebert, Svend; Sommen, Franciscus
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
37.883525%
The first part of this article is devoted to a brief review of the results about representation theory of the spin group Spin(m) from the point of view of Clifford analysis. In the second part we are interested in Clifford-valued functions and wavelets on the sphere. The connection of representations of Spin(m) and the concept of diffusive wavelets leads naturally to investigations of a modified diffusion equation on the sphere, that makes use of the Gamma operator. We will achieve to obtain Clifford-valued diffusion wavelets with respect to a modified diffusion operator. Since we are able to characterize all representations of Spin(m) and even to obtain all eigenvectors of the (by representation) regarded Casimir operator in representation spaces, it seems appropriate to look at functions on Spin(m) directly. Concerning this, our aim shall be to formulate eigenfunctions for the Laplace-Beltrami operator on Spin(m) and give the series expansion of the heat kernel on Spin(m) in terms of eigenfunctions.; Comment: 28 pages. arXiv admin note: text overlap with arXiv:0809.1408 1 reference added, motivation part rewritten

## ‣ Uncertainty constants and quasispline wavelets

Lebedeva, E. A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.951929%
In 1996 Chui and Wang proved that the uncertainty constants of scaling and wavelet functions tend to infinity as smoothness of the wavelets grows for a broad class of wavelets such as Daubechies wavelets and spline wavelets. We construct a class of new families of wavelets (quasispline wavelets) whose uncertainty constants tend to those of the Meyer wavelet function used in construction.; Comment: 27 pages

## ‣ Continuous Wavelets on Compact Manifolds

Geller, Daryl; Mayeli, Azita
Tipo: Artigo de Revista Científica
Let $\bf M$ be a smooth compact oriented Riemannian manifold, and let $\Delta_{\bf M}$ be the Laplace-Beltrami operator on ${\bf M}$. Say $0 \neq f \in \mathcal{S}(\RR^+)$, and that $f(0) = 0$. For $t > 0$, let $K_t(x,y)$ denote the kernel of $f(t^2 \Delta_{\bf M})$. We show that $K_t$ is well-localized near the diagonal, in the sense that it satisfies estimates akin to those satisfied by the kernel of the convolution operator $f(t^2\Delta)$ on $\RR^n$. We define continuous ${\cal S}$-wavelets on ${\bf M}$, in such a manner that $K_t(x,y)$ satisfies this definition, because of its localization near the diagonal. Continuous ${\cal S}$-wavelets on ${\bf M}$ are analogous to continuous wavelets on $\RR^n$ in $\mathcal{S}(\RR^n)$. In particular, we are able to characterize the H$\ddot{o}$lder continuous functions on ${\bf M}$ by the size of their continuous ${\mathcal{S}}-$wavelet transforms, for H$\ddot{o}$lder exponents strictly between 0 and 1. If $\bf M$ is the torus $\TT^2$ or the sphere $S^2$, and $f(s)=se^{-s}$ (the Mexican hat'' situation), we obtain two explicit approximate formulas for $K_t$, one to be used when $t$ is large, and one to be used when $t$ is small.
We give a characterization of a class of band-limited wavelets of $L^2({\mathbb R})$ and show that none of these wavelets come from a multiresolution analysis (MRA). For each $n\geq 2$, we construct a subset $S_n$ of ${\mathbb R}$ which is symmetric with respect to the origin. We give necessary and sufficient conditions on a function $\psi\in L^2({\mathbb R})$ with supp $\hat\psi\subseteq S_n$ to be an orthonormal wavelet. This result generalizes the characterization of a class of wavelets of E. Hern\'andez and G. Weiss. The dimension functions associated with these wavelets are also computed explicitly. Starting from the wavelets we have constructed, we are able to construct examples of wavelets in each of the equivalence classes of wavelets defined by E. Weber.; Comment: AMS Latex, 17 pages