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Time-frequency and time-scale analysis of Barkhausen noise signals

Padovese, Linilson Rodrigues; MARTIN, N.; MILLIOZ, F.
Fonte: PROFESSIONAL ENGINEERING PUBLISHING LTD Publicador: PROFESSIONAL ENGINEERING PUBLISHING LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
65.78%
Carrying out information about the microstructure and stress behaviour of ferromagnetic steels, magnetic Barkhausen noise (MBN) has been used as a basis for effective non-destructive testing methods, opening new areas in industrial applications. One of the factors that determines the quality and reliability of the MBN analysis is the way information is extracted from the signal. Commonly, simple scalar parameters are used to characterize the information content, such as amplitude maxima and signal root mean square. This paper presents a new approach based on the time-frequency analysis. The experimental test case relates the use of MBN signals to characterize hardness gradients in a AISI4140 steel. To that purpose different time-frequency (TFR) and time-scale (TSR) representations such as the spectrogram, the Wigner-Ville distribution, the Capongram, the ARgram obtained from an AutoRegressive model, the scalogram, and the Mellingram obtained from a Mellin transform are assessed. It is shown that, due to nonstationary characteristics of the MBN, TFRs can provide a rich and new panorama of these signals. Extraction techniques of some time-frequency parameters are used to allow a diagnostic process. Comparison with results obtained by the classical method highlights the improvement on the diagnosis provided by the method proposed.; FAPESP[05/51100-9]; FAPESP[06/04935-0]

Towards the development of a two-time scale CUEP/BCU method

Theodoro, Edson Aparecido Rozas; Alberto, Luís Fernando Costa; Hsiao-Dong, Chiang
Fonte: IEEE; Manhattan Publicador: IEEE; Manhattan
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
65.71%
This paper proposes a new Two-Time Scale (TTS) BCU method, and reports the first ever known use of the TTSCUEP method in a multi-machine power system. The proposed TTS-BCU method is a numerical algorithm to correctly compute the slow and fast CUEPs of the TTS-CUEP method. It also provides a more robust algorithm to compute the CUEP of the original system.; FAPESP

Estudo de propriedades não-lineares de colóides magnéticos nas escalas de tempo de mili e femtossegundos; Study of Nonlinear Properties of Magnetic Colloids in the Milli- and Femtosecond Time Scales.

Soga, Diogo
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
Publicado em 07/12/2007 PT
Relevância na Pesquisa
55.82%
Neste trabalho, estudamos alguns colóides magnéticos dos tipos iônico e surfactado com partículas de estrutura tipo espinélio. Usamos a técnica de varredura-Z para investigar as amostras nas escalas de tempo de femtossegundos e milissegundos. Medimos o índice de refração não-linear nas duas escalas de tempo. Na escala de milissegundos todas as amostras apresentaram comportamento tipo lente divergente, e os valores obtidos são da ordem de 10^(-7) cm^2/W. Na escala de femtossegundos, as amostras iônicas apresentaram comportamento tipo lente convergente, com valores típicos do índice de refração não-linear da ordem de 10^(11) cm^2/W. Também medimos a absorção não-linear na escala de tempo de femtossegundos. Os valores obtidos são da ordem de 10^2 cm/GW. Com os dados obtidos na escala de femtossegundos calculamos a susceptibilidade elétrica de terceira ordem (chi(3)). O módulo de chi(3) encontrado é da ordem de 10^(-17) m^2/V^2 (ou 10^(-9) esu). Obtivemos evidências experimentais da contribuição da susceptibilidade elétrica de quinta-ordem nas medidas de absorção não-linear. Verificamos a presença do efeito de tamanho das partículas no valor de chi(3) ao estudar partículas de mesma composição e de diâmetros diferentes.; In this work...

Determinação de Escalas Temporais para Reações entre Íons-pesados Leves através de Medidas de Correlações a Momentos Relativos Pequenos; Time scale determination for light heavy-ion reactions through small relative momenta correlation measurements

Moura, Marcia Maria de
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
Publicado em 14/12/1999 PT
Relevância na Pesquisa
55.71%
Neste trabalho foram realizadas, no Laboratório Pelletron do Instituto de Física da Universidade de São Paulo, medidas de coincidência entre partículas com momentos relativos pequenos para os sistemas 160+10B e 160+ 12C nas energias de 62,5 e 64,0 MeV, respectivamente. Para isso, foi utilizado um hodoscópio composto de 14 telescópios do tipo E-E, capazes de medir a energia tanto de partículas pesadas (Z>2) como leves (Z2). A partir dessas medidas foram obtidos espectros de diferença dos módulos das velocidades (vdif) e funções correlação em momento relativo (prel) para vários pa res de partículas. A análise do espectro de vdif permite determinar a proporção relativa entre as duas seqüências de emissão possíveis para um dado par de partículas. A região da anticorrelação na função correlação permite obter informações sobre a escala temporal referente ao intervalo de tempo entre a emissão da primeira e da segunda partícula. Para o ajuste tanto do espectro de vdif como da função correlação foi utilizado um programa que simula a emissão sequencial de duas partículas a partir de um núcleo composto, no qual a fração das sequências de emissão e a escala temporal são parâmetros ajustáveis. Correlações envolvendo somente partículas leves forneceram resultados para as escalas temporais da ordem de 10-20 s a 10-19 s...

Contribuição à análise de estabilidade transitória, em duas escalas de tempo, de sistemas elétricos de potência via métodos diretos; Contribution to two-time scale transient stability assessment of power systems by direct methods

Theodoro, Edson Aparecido Rozas
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
Publicado em 25/03/2013 PT
Relevância na Pesquisa
65.85%
O presente trabalho tem como objetivo investigar a presença de diferentes escalas de tempo nos modelos matemáticos que descrevem a dinâmica dos sistemas elétricos de potência (SEPs), em particular a existência de duas escalas de tempo distintas: lenta e rápida, e explorá-las no estudo de estabilidade transitória destes sistemas através da utilização de métodos diretos (funções energia). Em particular, o método do Ponto de Equilíbrio Instável de Controle (CUEP) para modelos com duas escalas de tempo será estudado e aplicado na análise de estabilidade transitória de SEPs. As bases teóricas para a análise de estabilidade transitória, de sistemas com duas escalas de tempo, serão apresentadas, assim como funções energia e novos algoritmos numéricos para o cálculo do CUEP nestes sistemas, a fim de evidenciar as melhorias e possíveis limitações deste novo método CUEP em duas escalas de tempo quando comparado ao método CUEP tradicional. Explorando as escalas de tempo lenta e rápida na análise de estabilidade transitória, espera-se que novos algoritmos numéricos mais robustos para o cálculo do CUEP sejam obtidos, assim como a diminuição do conservadorismo dos resultados.; The main objective of this work is to investigate the existence of several time-scales in the mathematical models of electric power systems...

Discrete-time fractional variational problems

Bastos, N.R.O.; Ferreira, R.A.C.; Torres, D.F.M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
55.71%
We introduce a discrete-time fractional calculus of variations on the time scale (hℤ)a,a∈ℝ,h>0. First and second order necessary optimality conditions are established. Examples illustrating the use of the new Euler-Lagrange and Legendre type conditions are given. They show that solutions to the considered fractional problems become the classical discrete-time solutions when the fractional order of the discrete-derivatives are integer values, and that they converge to the fractional continuous-time solutions when h tends to zero. Our Legendre type condition is useful to eliminate false candidates identified via the Euler-Lagrange fractional equation. © 2010 Elsevier B.V. All rights reserved.

A time-scale variational approach to inflation, unemployment and social loss

Dryl, M.; Malinowska, A. B.; Torres, D. F. M.
Fonte: Polish Academy of Sciences Publicador: Polish Academy of Sciences
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
55.68%
Both inflation and unemployment inflict social losses. When a tradeoff exists between the two, what would be the best combination of inflation and unemployment? A well known approach in economics to address this question is writing the social loss as a function of the rate of inflation p and the rate of unemployment u, with different weights, and then, using known relations between p, u, and the expected rate of inflation π, to rewrite the social loss function as a function of π. The answer is achieved by applying the calculus of variations in order to find an optimal path π that minimizes total social loss over a given time interval. Economists dealing with this question use a continuous or a discrete variational problem. Here we propose to use a time-scale model, unifying the results available in the literature. Moreover, the new formalism allows for obtaining new insights into the classical models when applied to real data of inflation and unemployment.

Time scale differential, integral, and variational embeddings of Lagrangian systems

Cresson, J.; Malinowska, A. B.; Torres, D. F. M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
55.68%
We introduce differential, integral, and variational delta embeddings. We prove that the integral delta embedding of the Euler-Lagrange equations and the variational delta embedding coincide on an arbitrary time scale. In particular, a new coherent embedding for the discrete calculus of variations that is compatible with the least-action principle is obtained. © 2012 Elsevier Ltd. All rights reserved.

Calculus of variations on time scales and applications to economics; Cálculo das variações em escalas temporais e aplicações à economia

Dryl, Monika
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
55.79%
We consider some problems of the calculus of variations on time scales. On the beginning our attention is paid on two inverse extremal problems on arbitrary time scales. Firstly, using the Euler-Lagrange equation and the strengthened Legendre condition, we derive a general form for a variation functional that attains a local minimum at a given point of the vector space. Furthermore, we prove a necessary condition for a dynamic integro-differential equation to be an Euler-Lagrange equation. New and interesting results for the discrete and quantum calculus are obtained as particular cases. Afterwards, we prove Euler-Lagrange type equations and transversality conditions for generalized infinite horizon problems. Next we investigate the composition of a certain scalar function with delta and nabla integrals of a vector valued field. Euler-Lagrange equations in integral form, transversality conditions, and necessary optimality conditions for isoperimetric problems, on an arbitrary time scale, are proved. In the end, two main issues of application of time scales in economic, with interesting results, are presented. In the former case we consider a firm that wants to program its production and investment policies to reach a given production rate and to maximize its future market competitiveness. The model which describes firm activities is studied in two different ways: using classical discretizations; and applying discrete versions of our result on time scales. In the end we compare the cost functional values obtained from those two approaches. The latter problem is more complex and relates to rate of inflation...

Time-frequency and time-scale characterisation of the beat-by-beat high-resolution electrocardiogram

Ortigueira, M.D.; Batista, A. G.; Rodrigues, J. Machado
Fonte: Universidade Nova de Lisboa Publicador: Universidade Nova de Lisboa
Tipo: Trabalho em Andamento
Publicado em /06/2001 ENG
Relevância na Pesquisa
55.7%
Proceedings of the Sixth Portuguese Conference on Bioemedical Engineering faro, Portugal; Time-Frequency and Time-Scale distributions of sequential ST segments the High-Resolution Electrocardiogram, are represented using both the Morlet Wavelet based scalogram and the Zhao-Atlas-Marks representation. Resolution and representation readability, concerning the Ventricular Late Potentials are compared. The beat-tobeat variation of one VLP case is examined.

Time-scale invariance as an emergent property in a perceptron with realistic, noisy neurons

Buhusi, Catalin V.; Oprisan, Sorinel A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
45.88%
In most species, interval timing is time-scale invariant: errors in time estimation scale up linearly with the estimated duration. In mammals, time-scale invariance is ubiquitous over behavioral, lesion, and pharmacological manipulations. For example, dopaminergic drugs induce an immediate, whereas cholinergic drugs induce a gradual, scalar change in timing. Behavioral theories posit that time-scale invariance derives from particular computations, rules, or coding schemes. In contrast, we discuss a simple neural circuit, the perceptron, whose output neurons fire in a clockwise fashion (interval timing) based on the pattern of coincidental activation of its input neurons. We show numerically that time-scale invariance emerges spontaneously in a perceptron with realistic neurons, in the presence of noise. Under the assumption that dopaminergic drugs modulate the firing of input neurons, and that cholinergic drugs modulate the memory representation of the criterion time, we show that a perceptron with realistic neurons reproduces the pharmacological clock and memory patterns, and their time-scale invariance, in the presence of noise. These results suggest that rather than being a signature of higher-order cognitive processes or specific computations related to timing...

The Ediacaran Period: A New Addition to the Geologic Time Scale

Knoll, Andrew; Christie-Blick, Nicholas; Walter, Malcolm R.; Narbonne, Guy M.
Fonte: Blackwell Publishing Publicador: Blackwell Publishing
EN_US
Relevância na Pesquisa
65.71%
The International Union of Geological Sciences has approved a new addition to the geologic time scale: the Ediacaran Period. The Ediacaran is the first Proterozoic period to be recognized on the basis of chronostratigraphic criteria and the first internationally ratified, chronostratigraphically defined period of any age to be introduced in more than a century. In accordance with procedures established by the International Commission on Stratigraphy, the base of the Ediacaran Period is defined by a Global Stratotype Section and Point (GSSP) placed at the base of the Nuccaleena Formation cap carbonate directly above glacial diamictites and associated facies at Enorama Creek in the Flinders Ranges of South Australia. Its top is defined by the initial GSSP of the Cambrian Period. The new Ediacaran Period encompasses a distinctive interval of Earth history that is bounded both above and below by equally distinctive intervals. Both chemostratigraphic and biostratigraphic data indicate that the subdivision of the period into two or more series is feasible, and this should be a primary objective of continuing work by the Ediacaran Subcommission of the ICS.; Organismic and Evolutionary Biology

Optimal Detection Using Bilinear Time Frequency and Time Scale Representations

Sayeed, Akbar M.; Jones, Douglas L.; Sayeed, Akbar M.; Jones, Douglas L.
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
65.78%
Journal Paper; Bilinear time-frequency representations (TFRs) and time-scale representations (TSRs) are potentially very useful for detecting a nonstationary signal in the presence of nonstationary noise or interference. As quadratic signal representations, they are promising for situations in which the optimal detector is a quadratic function of the observations. All existing time-frequency formulations of quadratic detection either implement classical optimal detectors equivalently in the time-frequency domain, without fully exploiting the structure of the TFR, or attempt to exploit the nonstationary structure of the signal in an ad hoc manner. We identify several important nonstationary composite hypothesis testing scenarios for which TFR/TSR-based detectors provide a "natural" framework; that is, in which TFR/TSR-based detectors are both optimal and exploit the many degrees of freedom available in the TFR/TSR. We also derive explicit expressions for the corresponding optimal TFR/TSR kernels. As practical examples, we show that the proposed TFR/TSR detectors are directly applicable to many important radar/sonar detection problems. Finally, we also derive optimal TFR/TSR-based detectors which exploit only partial information available about the nonstationary structure of the signal.

Nature and time-scale of bed morphological adjustments towards equilibrium in meandering streams: an experimental study

BINNS, ANDREW
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
55.77%
This thesis concerns the nature and time-scale of bed morphological adjustments towards equilibrium in alluvial meandering streams. Following the prevailing approach, the stream centrelines are assumed to follow sine-generated curves, the banks are fixed, and the flow is turbulent and sub-critical. The movable bed is flat at time t = 0; at t = Tb, the bed reaches its equilibrium or developed state. The specific objectives of this thesis are: 1) to develop a predictive equation for the bed development time Tb; 2) to determine the rate of growth of pool-bar complexes in meandering streams; and 3) to determine whether or not the large-scale, curvature-induced erosion-deposition zones of developing beds migrate upstream or downstream throughout their development. This thesis builds on the preliminary work and experimental tests by Binns (2006). The duration of bed development is found to be proportional to the square of the flow width B and inversely proportional to the channel-averaged bed-load rate (qsb)av, the proportionality factor being a function of the initial deflection angle (i.e., stream sinuosity). The form of this function is revealed on the basis of an extensive series of experimental runs carried out in meandering channels of varying values of the initial deflection angle (i.e....

Fractional viscoelastic models on time scales

Ribeiro, Carolina Paula Baptista; Antunes, P. J.
Fonte: WSEAS Publicador: WSEAS
Tipo: Conferência ou Objeto de Conferência
Publicado em 29/12/2011 ENG
Relevância na Pesquisa
55.68%
The main goal of this work is the generalisation of fractional viscoelastic models on Time Scales, applying the Riemann-Liouville derivative to the Maxwell's viscoelastic constitutive law. We show that, in time scale, the solution found is also expressed through the Miller-Ross function.; Fundação para a Ciência e a Tecnologia (FCT); CMAT

Global time scale and regional stratigraphic reference scales of Central and West Europe, East Europe, Tethys, South China, and North America as used in the Devonian-Carboniferous-Permian Correlation Chart 2003 (DCP 2003)

Menning, M; Alekseev, A.S.; Chuvashov, B; Davydov, V.I.; Devuyst, F-X; Forke, H C; Grunt, T.A.; Hance, L.; Heckel, P.H.; Izokh, N.G.; Jin, Y-G; Jones, Peter; Kotlyar, G.V.; Kozur, H.W.; Nemyrovska, T I; Schneider, J.W.; Wang, X-D; Weddige, K; Weyer, D; Wo
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
55.71%
The boundaries of the Devonian, Carboniferous, and Permian stages of the Global Stratigraphic Reference Scale (abbreviated to Global Stratigraphic Scale-GSS) are described in relation to the biostratigraphic and/or lithostratigraphic units of the Regional

Two-Time-Scale Approximation for Wonham Filters

Zhang, Qing; Yin, George; Moore, John
Fonte: Institute of Electrical and Electronics Engineers (IEEE Inc) Publicador: Institute of Electrical and Electronics Engineers (IEEE Inc)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.81%
This paper is concerned with approximation of Wonham filters. A focal point is that the underlying hidden Markov chain has a large state space. To reduce computational complexity, a two-time-scale approach is developed. Under time scale separation, the st

Canonical time-frequency, time-scale, and frequency-scale representations of time-varying channels

Rickard, Scott T.; Balan, Radu V.; Poor, H. Vincent; Verdu, Sergio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/10/2005
Relevância na Pesquisa
45.92%
Mobile communication channels are often modeled as linear time-varying filters or, equivalently, as time-frequency integral operators with finite support in time and frequency. Such a characterization inherently assumes the signals are narrowband and may not be appropriate for wideband signals. In this paper time-scale characterizations are examined that are useful in wideband time-varying channels, for which a time-scale integral operator is physically justifiable. A review of these time-frequency and time-scale characterizations is presented. Both the time-frequency and time-scale integral operators have a two-dimensional discrete characterization which motivates the design of time-frequency or time-scale rake receivers. These receivers have taps for both time and frequency (or time and scale) shifts of the transmitted signal. A general theory of these characterizations which generates, as specific cases, the discrete time-frequency and time-scale models is presented here. The interpretation of these models, namely, that they can be seen to arise from processing assumptions on the transmit and receive waveforms is discussed. Out of this discussion a third model arises: a frequency-scale continuous channel model with an associated discrete frequency-scale characterization.; Comment: To appear in Communications in Information and Systems - special issue in honor of Thomas Kailath's seventieth birthday

A Diagrammatic Kinetic Theory of Density Fluctuations in Simple Liquids in the Overdamped Limit. I. A Long Time Scale Theory for High Density

Pilkiewicz, Kevin R.; Andersen, Hans C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.86%
Starting with a formally exact diagrammatic kinetic theory for the equilibrium correlation functions of particle density and current fluctuations for a monatomic liquid, we develop a theory for high density liquids whose interatomic potential has a strongly repulsive short ranged part. We assume that interparticle collisions via this short ranged part of the potential are sufficient to randomize the velocities of the particles on a very small time scale compared with the fundamental time scale defined as the particle diameter divided by the mean thermal velocity. When this is the case, the graphical theory suggests that both the particle current correlation functions and the memory function of the particle density correlation function evolve on two distinct time scales, the very short time scale just mentioned and another that is much longer than the fundamental time scale. The diagrams that describe the motion on each of these time scales are identified. When the two time scales are very different, a dramatic simplification of the diagrammatic theory at long times takes place. We identify an irreducible memory function and a more basic function, which we call the irreducible memory kernel. This latter function evolves on the longer time scale only and determines the time dependence of the density and current correlation functions of interest at long times. In the following paper...

Continuous-Time Tracking Algorithms Involving Two-Time-Scale Markov Chains

Yin, George; Zhang, Qing; Moore, John; Liu, Y J
Fonte: Institute of Electrical and Electronics Engineers (IEEE Inc) Publicador: Institute of Electrical and Electronics Engineers (IEEE Inc)
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
65.78%
This work is concerned with least-mean-squares (LMS) algorithms in continuous time for tracking a time-varying parameter process. A distinctive feature is that the true parameter process is changing at a fast pace driven by a finite-state Markov chain. The states of the Markov chain are divisible into a number of groups. Within each group, the transitions take place rapidly; among different groups, the transitions are infrequent. Introducing a small parameter into the generator of the Markov chain leads to a two-time-scale formulation. The tracking objective is difficult to achieve. Nevertheless, a limit result is derived yielding algorithms for limit systems. Moreover, the rates of variation of the tracking error sequence are analyzed. Under simple conditions, it is shown that a scaled sequence of the tracking errors converges weakly to a switching diffusion. In addition, a numerical example is provided and an adaptive step-size algorithm developed.