Página 1 dos resultados de 20683 itens digitais encontrados em 0.084 segundos

- Biblioteca Digitais de Teses e Dissertações da USP
- Biblioteca Digital da Unicamp
- Springer Verlag
- Elsevier
- http://www.osa.org/
- Monterey, California. U.S. Naval Postgraduate School
- Monterey, California. Naval Postgraduate School
- Quens University
- Universidade de Medellín
- Cambridge University Press
- Universidade Cornell
- Rochester Instituto de Tecnologia
- Optical Society of America
- Mais Publicadores...

## Utilização de análise de componentes principais em séries temporais; Use of principal component analysis in time series

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 12/04/2013
PT

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#Análise de componentes principais#Análise de componentes principais para domínio da frequência#MSSA#MSSA#Principal Component Analysis#Principal Component Analysis in the Frequency Domain#SSA#SSA

Um dos principais objetivos da análise de componentes principais consiste em reduzir o número de variáveis observadas em um conjunto de variáveis não correlacionadas, fornecendo ao pesquisador subsídios para entender a variabilidade e a estrutura de correlação dos dados observados com uma menor quantidade de variáveis não correlacionadas chamadas de componentes principais. A técnica é muito simples e amplamente utilizada em diversos estudos de diferentes áreas. Para construção, medimos a relação linear entre as variáveis observadas pela matriz de covariância ou pela matriz de correlação. Entretanto, as matrizes de covariância e de correlação podem deixar de capturar importante informações para dados correlacionados sequencialmente no tempo, autocorrelacionados, desperdiçando parte importante dos dados para interpretação das componentes. Neste trabalho, estudamos a técnica de análise de componentes principais que torna possível a interpretação ou análise da estrutura de autocorrelação dos dados observados. Para isso, exploramos a técnica de análise de componentes principais para o domínio da frequência que fornece para dados autocorrelacionados um resultado mais específico e detalhado do que a técnica de componentes principais clássica. Pelos métodos SSA (Singular Spectrum Analysis) e MSSA (Multichannel Singular Spectrum Analysis)...

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## Um estudo de vazão em redes oportunistas; Throughput analysis in opportunistic networks

Fonte: Biblioteca Digital da Unicamp
Publicador: Biblioteca Digital da Unicamp

Tipo: Dissertação de Mestrado
Formato: application/pdf

Publicado em 18/12/2009
PT

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#Redes de comunicação#Sistemas de comunicação sem fio#Analise espectral#Radio - Transmissores e transmissão - Desvanecimento#Radio#Communication networks#Wireless communication systems#Spectrum analysis#Radio

A evidente subutilização dos recursos de freqüência tem incentivado discussões e trabalhos visando propor uma transformação no uso do espectro. O acesso oportunista ao espectro é uma proposta bastante atraente nessa busca pelo uso mais eficiente dos recursos de freqüência e propõe o compartilhamento do espectro por redes licenciadas e redes oportunistas. As redes oportunistas utilizam os recursos com restrição espaço-temporal, enquanto as redes licenciadas são protegidas de possíveis danos causados por interferência. Este trabalho considera uma rede sem fio dotada de características cognitivas para a detecção de oportunidades de transmissão em um canal compartilhado com uma rede licenciada. São apresentados um estudo sobre o sensoriamento do espectro em ambientes com desvanecimento e um estudo de vazão nessa rede, determinando as probabilidades de colisão de pacotes e adotando um modelo de captura. Os resultados são validados por simulação de eventos discretos; The apparent underutilization of frequency resources has encouraged several research works on innovative spectrum usage schemes. The opportunistic spectrum access is an attractive proposal aiming at an efficient use of frequency resources by spectrum sharing among licensed and unlicensed networks. The unlicensed opportunistic networks use the spectrum with geographical and temporal constraints...

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## Can multiscale traffic analysis be used to differentiate Internet applications

Fonte: Springer Verlag
Publicador: Springer Verlag

Tipo: Artigo de Revista Científica

ENG

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#Application identification#Cluster analysis#Download#Multifractal behavior#Multiscale analysis#Upload#Wavelets#Cryptography#Internet#Internet protocols#Network management

An accurate mapping of Internet traffic to applications can be important for a broad range of network management and measurement tasks, including traffic engineering, service differentiation, performance/failure monitoring and security. Traditional mapping approaches have become increasingly inaccurate because many applications use nondefault or ephemeral port numbers, use well-known port numbers associated with other applications, change application signatures or use traffic encryption. In this paper we will demonstrate that multiscale traffic analysis based on multi-order wavelet spectrum can be used as a discriminator of Internet applications traffic profiles. By performing clustering analysis over the multiscale wavelet spectrum coefficients that are inferred from the measured traffic, the proposed methodology is able to efficiently differentiate different IP applications without using any payload information. This characteristic will allow the differentiation of traffic flows in unencrypted and encrypted scenarios. In order to compare the differentiating potential of different traffic application data, upload, download and joint upload and download flow statistics are considered to evaluate the identification approach for each selected protocol. Moreover...

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## Singular spectrum analysis for an automated solvent artifact removal and baseline correction of 1D NMR spectra

Fonte: Elsevier
Publicador: Elsevier

Tipo: Artigo de Revista Científica

ENG

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#AUREMOL-SSA/ALS#Singular Spectrum Analysis#Solvent suppression#Baseline correction#Oversampled digitally filtered data#Group delay#Finite response filter

NMR spectroscopy in biology and medicine is generally performed in aqueous solutions, thus in 1H NMR spectroscopy, the dominant signal often stems from the partly suppressed solvent and can be many orders of magnitude larger than the resonances of interest. Strong solvent signals lead to a disappearance of weak resonances of interest close to the solvent artifact and to base plane variations all over the spectrum. The AUREMOL-SSA/ALS approach for automated solvent artifact removal and baseline correction has been originally developed for multi-dimensional NMR spectroscopy. Here, we describe the necessary adaptations for an automated application to one-dimensional NMR spectra. Its core algorithm is still based on singular spectrum analysis (SSA) applied on time domain signals (FIDs) and it is still combined with an automated baseline correction (ALS) in the frequency domain. However, both steps (SSA and ALS) have been modified in order to achieve optimal results when dealing with one-dimensional spectra. The performance of the method has been tested on one-dimensional synthetic and experimental spectra including the back-calculated spectrum of HPr protein and an experimental spectrum of a human urine sample. The latter has been recorded with the typically used NOESY-type 1D pulse sequence including water pre-saturation. Furthermore...

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## Terahertz bandwidth RF spectrum analysis of femtosecond pulses using a chalcogenide chip

Fonte: http://www.osa.org/
Publicador: http://www.osa.org/

Tipo: Journal article; Published Version; Optical Society of America
Formato: 9 pages

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#nonlinear optical signal processing#spectrum analysis#nonlinear optics, devices#ultrafast nonlinear optics

We report the first demonstration of the use of an RF spectrum
analyser with multi-terahertz bandwidth to measure the properties of
femtosecond optical pulses. A low distortion and broad measurement
bandwidth of 2.78 THz (nearly two orders of magnitude greater than
conventional opto-electronic analyzers) was achieved by using a 6 cm long
As2S3 chalcogenide waveguide designed for high Kerr nonlinearity and near
zero dispersion. Measurements of pulses as short as 260 fs produced from a
soliton-effect compressor reveal features not evident from the pulse’s
optical spectrum. We also applied an inverse Fourier transform numerically
to the captured data to re-construct a time-domain waveform that resembled
pulse measurement obtained from intensity autocorrelation.

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## The determination of the dynamic response of a small swept wing jet fighter to atmospheric turbulence using the power spectrum method of analysis

Fonte: Monterey, California. U.S. Naval Postgraduate School
Publicador: Monterey, California. U.S. Naval Postgraduate School

Tipo: Tese de Doutorado
Formato: 96 p.: ill.

EN_US

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Approved for public release; distribution is unlimited; The power spectral techniques of generalized harmonic analysis were applied to determine the phase and amplitude of the transfer function between the vertical component of turbulence and the resultant pitch rate of a small swept wing jet fighter. The power spectrum analysis was based on actual flight test data. In addition the amplitude and phase of the aircraft's transfer function are determined theoretically by two different methods and compared with the results of the power spectrum analysis. It was established that the power spectrum method, as applied to random turbulence, can be used to determine an aircraft's response to this random input on a ocntinuous basis and that power spectrum techniques have considerable potential value in the study of aircraft gust loading; http://www.archive.org/details/determinationofd00nort; Lieutenant, United States Navy

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## Spectrum receiver and signal selection unit designs for the Naval Postgraduate School SATCOM signal analyzer

Fonte: Monterey, California. Naval Postgraduate School
Publicador: Monterey, California. Naval Postgraduate School

Tipo: Relatório
Formato: 79 p. : ill. ; 28 cm.

EN_US

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The design and construction of a Signal Selection Unit
and four Spectrum Receivers for use in the Naval Postgraduate
School's SATCOM Signal Analyzer are presented. The purpose
of the SATCOM Signal Analyzer is to provide high-speed spectrum
analysis and characterization of the outputs of UHF
communication satellite transponders in orbit. It is constructed
around a PDP-11/34 minicomputer which provides the
necessary control for most of the equipment of the system.
Extremely accurate frequency measurement is provided by the
frequency receivers and signals for multi-channel spectrum
analyses are provided by the Spectrum Receivers. The Signal
Selection Unit routes signals to the Spectrum, AM/FM, and
Frequency Receivers. This report documents the design and
development of the Spectrum Receivers and the Signal Selection Unit.; Prepared for: Naval Electronic Systems Command, PME-106-1, Washington, D.C. 20360.; http://archive.org/details/spectrumreceiver00ohls

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## Process Analysis and Performance Assessment for Sheet Forming Processes

Fonte: Quens University
Publicador: Quens University

Tipo: Tese de Doutorado

EN; EN

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#Singular Spectrum Analysis#controller performance assessment#minimum-variance#sheet forming process

Process monitoring and controller performance assessment are essential tools for ensuring that manufacturing processes operate safely, predictably, meet quality targets and operate profitably. Efficient techniques for process analysis and controller assessment facilitates are important for identifying areas for process and control improvement. Sheet- and film-forming processes pose special challenges for these techniques, because they often have periods of non-steady-state operation, and can exhibit both spatial and temporal variations. Existing process evaluation and analysis methodologies are oriented primarily for processes under steady operation, and focus on temporal variations.
New tools are proposed to address limitations on the application of minimum-variance-based controller performance assessment to metal rolling processes. Extensions are proposed which address: 1) non-constant deadtime that arises from changes in rolling speed during startup, steady operation and wind down in the rolling process; 2) constraints on control actions; and 3) different sampling intervals for the manipulated variable input and the process output. The efficacy of the proposed extensions are demonstrated using an aluminum rolling mill and simulation examples.
Singular Spectrum Analysis (SSA) is a promising technique for analyzing time series that decomposes data into a number of interpretable frequency components. New filtering and spectral interpretations of SSA are proposed in this work...

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## A wave parameters and directional spectrum analysis for extreme winds

Fonte: Universidade de Medellín
Publicador: Universidade de Medellín

Tipo: Article; info:eu-repo/semantics/article

ENG

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#Directional spectrum#Gulf of Mexico#Hurricane waves#Moored buoys#Wind speed#Directional spectra#Directional wave spectrum#Gulf of Mexico#Hurricane katrina#Significant wave height#Spatial representations

In this research a comparison between two of the most popular ocean wave models, WAVEWATCH III™ and SWAN, was performed using data from hurricane Katrina in the Gulf of Mexico. The numerical simulation of sea surface directional wave spectrum and other wave parameters for several parameter-izations and its relation with the drag coefficient was carried out. The simulated data were compared with in-situ NOAA buoy data. For most of the buoys, WAVEWATCH III™ presented the best statistical comparisons for the main wave parameters, such as significant wave height and peak period. The SWAN model tends to overestimate the maximum values for significant wave height for some buoys and the peak period for almost all the buoys. Both models tend to overestimate the value of peak direction, presenting an area of greater energy to the south. The WAVEWATCH III™ model performs best for buoys located in right forward quadrant, which generally has higher winds and waves. This indicates a better spatial representation of wave parameters in the higher energy areas for the WAVEWATCH III™ model. Results based on the quadrant location for most of the analyzed cases, are in agreement with the results from other sources such as the Scanning Radar Altimeter (SRA). © 2013 Elsevier Ltd. All rights reserved.

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## Quantum Chaos Analysis of the Ideal Interchange Spectrum in a Stellarator

Fonte: Cambridge University Press
Publicador: Cambridge University Press

Tipo: Artigo de Revista Científica

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#Keywords: Chaos theory#Magnetic fields#Plasma confinement#Plasma stability#Plasma turbulence#Quantum theory#Spectrum analysis#Statistical methods#Eigenmode spectrum#Eigenvalue spacings#Quantum chaos theory

The eigenmode spectrum is a fundamental starting point for the analysis of plasma stability and the onset of turbulence. Quantum chaos theory provides tools for characterizing the spectrum statistically, from the regular spectrum of the separable case (in

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## Spectrum analysis for the Vlasov-Poisson-Boltzmann system

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 14/02/2014

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By identifying a norm capturing the effect of the forcing governed by the
Poisson equation, we give a detailed spectrum analysis on the linearized
Vlasov-Poisson-Boltzmann system around a global Maxwellian. It is shown that
the electric field governed by the self-consistent Poisson equation plays a key
role in the analysis so that the spectrum structure is genuinely different from
the well-known one of the Boltzmann equation. Based on this, we give the
optimal time decay rates of solutions to the equilibrium.

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## Filter characteristics in image decomposition with singular spectrum analysis

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 07/05/2015

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Singular spectrum analysis is developed as a nonparametric spectral
decomposition of a time series. It can be easily extended to the decomposition
of multidimensional lattice-like data through the filtering interpretation. In
this viewpoint, the singular spectrum analysis can be understood as the
adaptive and optimal generation of the filters and their two-step
point-symmetric operation to the original data. In this paper, we point out
that, when applied to the multidimensional data, the adaptively generated
filters exhibit symmetry properties resulting from the bisymmetric nature of
the lag-covariance matrices. The eigenvectors of the lag-covariance matrix are
either symmetric or antisymmetric, and for the 2D image data, these lead to the
differential-type filters with even- or odd-order derivatives. The dominant
filter is a smoothing filter, reflecting the dominance of low-frequency
components of the photo images. The others are the edge-enhancement or the
noise filters corresponding to the band-pass or the high-pass filters. The
implication of the decomposition to the image denoising is briefly discussed.

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## The 2dF Galaxy Redshift Survey: Power-spectrum analysis of the final dataset and cosmological implications

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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We present a power spectrum analysis of the final 2dF Galaxy Redshift Survey,
employing a direct Fourier method. The sample used comprises 221,414 galaxies
with measured redshifts. We investigate in detail the modelling of the sample
selection. A new angular mask is derived, based on revisions to the photometric
calibration. The redshift selection function is determined by dividing the
survey according to rest-frame colour, and deducing a self-consistent treatment
of k-corrections and evolution for each population. The covariance matrix for
the power-spectrum estimates is determined using two different approaches to
the construction of mock surveys which are used to demonstrate that the input
cosmological model can be correctly recovered. We are confident that the 2dFGRS
power spectrum can be used to infer the matter content of the universe. On
large scales, our estimated power spectrum shows evidence for the `baryon
oscillations' that are predicted in CDM models. Fitting to a CDM model,
assuming a primordial $n_{s}=1$ spectrum, $h=0.72$ and negligible neutrino
mass, the preferred parameters are $\Omega_{M} h = 0.168 \pm 0.016$ and a
baryon fraction $\Omega_{b} /\Omega_{M} = 0.185\pm0.046$ (1$\sigma$ errors).
The value of $\Omega_{M} h$ is $1\sigma$ lower than the $0.20 \pm 0.03$ in our
2001 analysis of the partially complete 2dFGRS. This shift is largely due to
the signal from the newly-sampled regions of space...

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## Application of Bryan's algorithm to the mobility spectrum analysis of semiconductor devices

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 21/08/2003

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A powerful method for mobility spectrum analysis is presented, based on
Bryan's maximum entropy algorithm. The Bayesian analysis central to Bryan's
algorithm ensures that we avoid overfitting of data, resulting in a physically
reasonable solution. The algorithm is fast, and allows the analysis of large
quantities of data, removing the bias of data selection inherent in all
previous techniques. Existing mobility spectrum analysis systems are reviewed,
and the performance of the Bryan's Algorithm Mobility Spectrum (BAMS) approach
is demonstrated using synthetic data sets. Analysis of experimental data is
briefly discussed. We find that BAMS performs well compared to existing
mobility spectrum methods.; Comment: 9 pages, 4 figures. Submitted to Journal of Applied Physics

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## Power-spectrum analysis of Super-Kamiokande solar neutrino data, taking into account asymmetry in the error estimates

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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The purpose of this article is to carry out a power-spectrum analysis (based
on likelihood methods) of the Super-Kamiokande 5-day dataset that takes account
of the asymmetry in the error estimates. Whereas the likelihood analysis
involves a linear optimization procedure for symmetrical error estimates, it
involves a nonlinear optimization procedure for asymmetrical error estimates.
We find that for most frequencies there is little difference between the
power spectra derived from analyses of symmetrized error estimates and from
asymmetrical error estimates. However, this proves not to be the case for the
principal peak in the power spectra, which is found at 9.43 yr-1. A likelihood
analysis which allows for a "floating offset" and takes account of the start
time and end time of each bin and of the flux estimate and the symmetrized
error estimate leads to a power of 11.24 for this peak. A Monte Carlo analysis
shows that there is a chance of only 1% of finding a peak this big or bigger in
the frequency band 1 - 36 yr-1 (the widest band that avoids artificial peaks).
On the other hand, an analysis that takes account of the error asymmetry leads
to a peak with power 13.24 at that frequency. A Monte Carlo analysis shows that
there is a chance of only 0.1% of finding a peak this big or bigger in that
frequency band 1 - 36 yr-1. From this perspective...

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## Optimal Weighting Scheme in Redshift-space Power Spectrum Analysis and a Prospect for Measuring the Cosmic Equation of State

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Relevância na Pesquisa

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We develop a useful formula for power spectrum analysis for high and
intermediate redshift galaxy samples, as an extension of the work by Feldman,
Kaiser & Peacock (1994). An optimal weight factor, which minimizes the errors
of the power spectrum estimator, is obtained so that the light-cone effect and
redshift-space distortions are incorporated. Using this formula, we assess the
feasibility of the power spectrum analysis with the luminous red galaxy (LRG)
sample in the Sloan Digital Sky Survey as a probe of the equation of state of
the dark energy. Fisher matrix analysis shows that the LRG sample can be
sensitive to the equation of state around redshift z=0.13. It is also
demonstrated that the LRG sample can constrain the equation of state with
(1-sigma) error of 10% level, if other fundamental cosmological parameters are
well determined independently. For the useful constraint, we point out the
importance of modeling the bias taking the luminosity dependence into account.
We also discuss the optimized strategy to constrain the equation of state using
power spectrum analysis. For a sample with fixed total number of objects, it is
most advantageous to have the sample with the mean number density $10^{-4}
h^3{\rm Mpc}^{-3}$ in the range of the redshift $0.4 \simlt z\simlt 1$.; Comment: 27 pages...

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## Spectrum analysis and optimal decay rates of the bipolar Vlasov-Poisson-Boltzmann equations

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/11/2014

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In the present paper, we consider the initial value problem for the bipolar
Vlasov-Poisson-Boltzmann (bVPB) system and its corresponding modified
Vlasov-Poisson-Boltzmann (mVPB). We give the spectrum analysis on the
linearized bVPB and mVPB systems around their equilibrium state and show the
optimal convergence rate of global solutions. It was showed that the electric
field decays exponentially and the distribution function tends to the absolute
Maxwellian at the optimal convergence rate $(1+t)^{-3/4}$ for the bVPB system,
yet both the electric field and the distribution function converge to
equilibrium state at the optimal rate $(1+t)^{-3/4}$ for the mVPB system.; Comment: arXiv admin note: text overlap with arXiv:1410.3356

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## Short time spectrum analysis-synthesis of speech

Fonte: Rochester Instituto de Tecnologia
Publicador: Rochester Instituto de Tecnologia

Tipo: Tese de Doutorado

EN_US

Relevância na Pesquisa

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#Analysis-synthesis of speech#Electrical engineering#Fourier transform phase information#Short time spectrum#STSASS algorithm#Thesis#TK7882.S65 V8 1985#Speech synthesis#Fourier transformations

This thesis presents an extensive study of the short time spectrum analysis-synthesis of speech. This type of speech processing attempts to synthesize speech without the short time Fourier transform phase information. Several existing analysis-synthesis methods are presented. In addition, five other methods are attempted experimentally. The results of these experiments are explained, identifying some very important properties of the short time spectrum analysis-synthesis. One of the methods was shown to synthesize a high fidelity speech. Finally, a comparison is made between this method and other known methods which are based on short time Fourier transform approach.

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## Two-stage spatial-filtering for diffraction pattern-analysis

Fonte: Optical Society of America
Publicador: Optical Society of America

Tipo: Artigo de Revista Científica
Formato: 69352 bytes; application/pdf

EN_US

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#Apertures#Classifications#Diffraction patterns#Fourier transformation#Image processing#Optical filters#Pattern recognition#Power spectra#Spatial filtering#Spectrum analysis

The use of optical power spectrum analysis for feature detection and classification is often restricted by the superposition of the aperture spectrum. A spatial frequency filtering technique using a circular aperture and filters has been previously proposed to separate the object and aperture spectra. An adaptation of this technique using square apertures and an opaque cross spatial filter offers improved performance for some applications. Numerical calculations and experimental results are given comparing the two techniques.

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## Electricity consumption forecasting using singular spectrum analysis

Fonte: DYNA
Publicador: DYNA

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/04/2015
EN

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Singular Spectrum Analysis (SSA) is a non-parametric technique that allows the decomposition of a time series into signal and noise. Thus, it is a useful technique to trend extraction, smooth and filter a time series. The effect on performance of both Box and Jenkins' and Holt-Winters models when applied to the time series filtered by SSA is investigated in this paper. Three different methodologies are evaluated in the SSA approach: Principal Component Analysis (PCA), Cluster Analysis and Graphical Analysis of Singular Vectors. In order to illustrate and compare the methodologies, in this paper, we also present the main results of a computational experiment with the monthly residential consumption of electricity in Brazil.

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