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Influência dos parâmetros de usinagem no brochamento de um bloco em ferro fundido; Influence of the machining parameters on the broaching of a casting iron block

Zappalenti, Artur
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 08/08/2007 PT
Relevância na Pesquisa
35.93%
O objetivo do presente trabalho é analisar a influência de alguns parâmetros de usinagem na qualidade geométrica e superficial da peça. O brochamento é uma operação de usinagem antiga, a qual se desenvolveu com a indústria automobilística, mas que atualmente pode ser encontrada em diversos segmentos industriais. O processo consiste em uma remoção progressiva do material pela ação de uma ferramenta de corte multi-arestas. Este processo é capaz de, em um único ciclo, realizar as operações de desbaste e acabamento da peça em virtude da combinação de uma geometria adequada da ferramenta, tornando esta uma importante característica deste processo. Para o trabalho em questão, foi analisado um processo brochamento de acabamento na usinagem de blocos fabricados em ferro fundido. Este material foi escolhido por estar bastante presente na indústria de transformação devido à boa usinabilidade. Os resultados foram obtidos em medições com aparelhos eletrônicos e através de análise estatística foi avaliado o grau de interferência dos fatores para as características estudadas. Os resultados mostraram que os fatores e suas combinações interferem de forma diferente para cada característica analisada. Na maioria das situações analisadas...

Ensaios geoelétricos 2D no antigo lixão de Ribeirão Preto-SP: avaliação de parâmetros de aquisição e monitoramento ambiental do problema; Geoelectrical 2D investigations in the old landfill site at Ribeirão Preto city, São Paulo, Brazil: Acquisition parameters evaluation and environmental monitoring.

Fachin, Sérgio Junior 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
Publicado em 14/09/2007 PT
Relevância na Pesquisa
35.81%
Em razão da crescente preocupação com a proteção ao meio ambiente e preservação da qualidade das águas superficiais e subterrâneas, as áreas de disposição de resíduos, tanto domésticos como industriais, têm merecido especial atenção das instituições de pesquisa ligadas à proteção ambiental. Atualmente o uso dos métodos geoelétricos vem se destacando como metodologia indireta de investigação de áreas afetadas pela disposição inadequada de resíduos sólidos urbanos e industriais pois fornecem, desde que adequadamente escolhidas as técnicas e os parâmetros de aquisição, informações importantes com respeito à localização e geometria dos depósitos de resíduos, extensão da pluma de contaminação, posição da zona saturada e sentido do fluxo subterrâneo, características litológicas e presença de estruturas geológicas. A integração de ferramentas como simulações e métodos de interpretação qualitativa e quantitativa também auxiliam na caracterização e monitoramento ambiental de áreas de disposição de resíduos sólidos. O objetivo principal deste trabalho foi a avaliação de alguns parâmetros de aquisição 2D (arranjos eletródicos, espaçamento entre eletrodos e níveis de investigação) com os métodos da Eletrorresistividade e da Polarização Induzida...

Estimação de modelos de duração condicional estocástica por meio da função característica empírica; Estimation of stochastic conditional duration models by means of the empirical characteristic function.

Ferraz, Jose Euclides de Melo
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 27/03/2008 PT
Relevância na Pesquisa
35.92%
Neste trabalho propomos a utilização do método da função característica empírica (ECF - empirical characteristic function), para estimação do modelo de duração condicional estocástica (SCD - stochastic conditional duration). Para determinação das variáveis latentes do processo utilizamos três alternativas: um filtro de Kalman, um filtro obtido por integração numérica e um filtro baseado na expansão de Gram-Charlier até 4ª ordem. Os resultados são então aplicados em séries de duração da GE, Microsoft e USD/EUR.; We propose the use of the empirical characteristic function (ECF) method to estimate the parameters of the stochastic conditional duration (SCD) model. In order to estimate the latent variables we propose the use of three alternatives: a Kalman filter, a filter based on numerical integration (quadrature) and a filter based on the 4th-order Gram-Charlier expansion. The results are applied to the estimation of the parameters of the duration process for GE, Microsoft and USD/EUR.

Identificação de parâmetros de motor de indução linear tubular para extração de petróleo.; Identification of parameters of the tubular linear induction motor for the extraction of oil.

Rossini, Wagner Marques
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 22/02/2008 PT
Relevância na Pesquisa
35.81%
O presente trabalho apresenta a identificação de parâmetros de motor de indução linear tubular para a extração de petróleo, denominado de MATÆOS -- Motor Assíncrono Tubular para Aplicação na Extração de Óleo Subterrâneo. O primeiro passo para a identificação de parâmetros do motor foi a implementação da bancada de testes com o seu sistema de controle e supervisório. O modelo adotado corresponde à situação de operação em regime estacionário e consiste no circuito contendo resistores e indutores tradicionalmente utilizado para representar motores de indução. A identificação dos parâmetros foi realizada por meio de um procedimento de otimização tomando por base o balanço de potência do motor. Para isso, em função dos parâmetros do modelo, definiu-se e minimizou-se uma medida de erro entre as potências medidas e as calculadas pelo modelo para um conjunto pré-fixado de escorregamentos. A solução desse problema de otimização foi obtida por meio de uma busca exaustiva, uma vez que o número de variáveis independentes do problema é pequeno e uma região contendo o ponto de mínimo é conhecida com razoável confiança. Os resultados obtidos indicam que os valores dos parâmetros nominais a quente apresentam algumas diferenças em relação àqueles produzidos pelo método de identificação. Essas diferenças se devem possivelmente a variações nas características térmicas do motor e a erros introduzidos pelos instrumentos de medida. O modelo identificado apresentou uma menor disponibilidade de força e um pior rendimento quando comparado com os valores de projeto do modelo nominal a quente. Apesar disto...

A simplified method for determining the high frequency induction motor equivalent electrical circuit parameters to be used in EMI effect

Riehl, Rudolf Ribeiro; Ruppert Filho, Ernesto
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 1244-1248
ENG
Relevância na Pesquisa
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The aim of this paper is to present a simple method for determining the high frequency parameters of a three-phase induction motor to be used in studies involving variable speed drives with PWM three-phase inverters, in which it is necessary to check the effects caused to the motor by the electromagnetic interference, (EMI) in the differential mode, as well as in the common mode. The motor parameters determination is generally performed in adequate laboratories using accurate instruments, such as very expensive RLC bridges. The method proposed here consists in the identification of the motor equivalent electrical circuit parameters in rated frequency and in high frequency through characteristic tests in the laboratory, together with the use of characteristic equations and curves, shown in the references to be mentioned for determining the motor high frequency parasite capacitances and also through system simulations using dedicated software, like Pspice, determining the characteristic waveforms involved in the differential and common mode phenomena, comparing and validating the procedure through published papers [01].

Study on characteristic parameters influencing laser-induced damage threshold of KH2PO4 crystal surface machined by single point diamond turning

Chen, Mingjun; Li, Mingquan; Cheng, Jian; Jiang, Wei; Wang, Jian; Xu, Qiao
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.04%
It has fundamental meaning to find the elements influencing the laser-induced damage threshold (LIDT) of KH2PO4 (KDP) crystal and to provide suitable characterization parameters for these factors in order to improve the LIDT of KDP. Using single-point diamond turning (SPDT) to process the KDP crystal, the machined surface quality has important effects on its LIDT. However, there are still not suitable characteristic parameters of surface quality of KDP to correspond with the LIDT nowadays. In this paper, guided by the Fourier model theory, we study deeply the relationship between the relevant characteristic parameters of surface topography of KDP crystal and the experimental LIDT. Research results indicate that the waviness rather than the roughness is the leading topography element on the KDP surface machined by the SPDT method when the LIDT is considered and the amplitude of micro-waviness has greater influence on the light intensity inside the KDP crystal within the scope of dangerous frequencies between (180 μm)−1 and (90 μm)−1; with suitable testing equipment, the characteristic parameters of waviness amplitude, such as the arithmetical mean deviation of three-dimensional profile Sa or root mean square deviation of three-dimensional contour Sq...

The Effect of Metal-Semiconductor Contact on the Transient Photovoltaic Characteristic of HgCdTe PV Detector

Cui, Haoyang; Xu, Yongpeng; Yang, Junjie; Tang, Naiyun; Tang, Zhong
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Publicado em 30/09/2013 EN
Relevância na Pesquisa
35.78%
The transient photovoltaic (PV) characteristic of HgCdTe PV array is studied using an ultrafast laser. The photoresponse shows an apparent negative valley first, then it evolves into a positive peak. By employing a combined theoretical model of pn junction and Schottky potential, this photo-response polarity changing curves can be interpreted well. An obvious decreasing of ratio of negative valley to positive peak can be realized by limiting the illumination area of the array electrode. This shows that the photoelectric effect of Schottky barrier at metal-semiconductor (M/S) interface is suppressed, which will verify the correctness of the model. The characteristic parameters of transient photo-response induced from p-n junction and Schottky potential are extracted by fitting the response curve utilizing this model. It shows that the negative PV response induced by the Schottky barrier decreases the positive photovoltage generated by the pn junction.

Influence of Precision of Emission Characteristic Parameters on Model Prediction Error of VOCs/Formaldehyde from Dry Building Material

Wei, Wenjuan; Xiong, Jianyin; Zhang, Yinping
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 03/12/2013 EN
Relevância na Pesquisa
45.81%
Mass transfer models are useful in predicting the emissions of volatile organic compounds (VOCs) and formaldehyde from building materials in indoor environments. They are also useful for human exposure evaluation and in sustainable building design. The measurement errors in the emission characteristic parameters in these mass transfer models, i.e., the initial emittable concentration (C0), the diffusion coefficient (D), and the partition coefficient (K), can result in errors in predicting indoor VOC and formaldehyde concentrations. These errors have not yet been quantitatively well analyzed in the literature. This paper addresses this by using modelling to assess these errors for some typical building conditions. The error in C0, as measured in environmental chambers and applied to a reference living room in Beijing, has the largest influence on the model prediction error in indoor VOC and formaldehyde concentration, while the error in K has the least effect. A correlation between the errors in D, K, and C0 and the error in the indoor VOC and formaldehyde concentration prediction is then derived for engineering applications. In addition, the influence of temperature on the model prediction of emissions is investigated. It shows the impact of temperature fluctuations on the prediction errors in indoor VOC and formaldehyde concentrations to be less than 7% at 23±0.5°C and less than 30% at 23±2°C.

Performance Analysis of Metamaterials With Two-dimensional Isotropy

Yao, Hai-Ying; Li, Le-Wei
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 406675 bytes; application/pdf
EN_US
Relevância na Pesquisa
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A two-dimensional isotropic metamaterials formed by crossed split-ring resonators (CSRRs) are studied in this paper. The effective characteristic parameters of this media are determined by quasi-static Lorentz theory. The induced current distributions of a single CSRR at the resonant frequency are presented. Moreover, the dependence of the resonant frequency on the dimensions of single CSRR and the spaces of the array are also discussed.; Singapore-MIT Alliance (SMA)

Induction motor parameters estimation and faults diagnosis using optimisation algorithms.

Duan, Fang
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2015
Relevância na Pesquisa
45.97%
Induction motors are the most widespread rotating electric machines in industry due to their efficient and cost-effective performance. Induction motors are used to mainly operate at the constant speed since the rotor speed depends on the supply frequency. The development of power electronic devices and converter technologies has revolutionized the adjustable-speed induction motor drives. For most high-performance control methods, the effective motor control requires precise knowledge of the motor’s parameters, which are usually obtained from manufacturers. However, the manufacturers describe these parameters under starting or full-loading condition only, instead of the normal operating conditions. It is well known that motor parameters are influenced by not only the load level but also environmental factors, such as temperature, humidity and lubricant viscosity. The first part of the thesis describes the application of the sparse grid optimisation method in solving the induction motor parameter estimation problem. Kernel of the method is the efficient search in minimising the cost function on the grid created by using the Hyperbolic Cross Points (HCPs). The cost function quantifies the difference between simulation results and measurement results. Within model reference adaptive system (MRAS) framework...

Efficient estimation using the characteristic function : theory and applications with high frequency data

Kotchoni, Rachidi
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
Relevância na Pesquisa
35.85%
Nous abordons deux sujets distincts dans cette thèse: l'estimation de la volatilité des prix d'actifs financiers à partir des données à haute fréquence, et l'estimation des paramétres d'un processus aléatoire à partir de sa fonction caractéristique. Le chapitre 1 s'intéresse à l'estimation de la volatilité des prix d'actifs. Nous supposons que les données à haute fréquence disponibles sont entachées de bruit de microstructure. Les propriétés que l'on prête au bruit sont déterminantes dans le choix de l'estimateur de la volatilité. Dans ce chapitre, nous spécifions un nouveau modèle dynamique pour le bruit de microstructure qui intègre trois propriétés importantes: (i) le bruit peut être autocorrélé, (ii) le retard maximal au delà duquel l'autocorrélation est nulle peut être une fonction croissante de la fréquence journalière d'observations; (iii) le bruit peut avoir une composante correlée avec le rendement efficient. Cette dernière composante est alors dite endogène. Ce modèle se différencie de ceux existant en ceci qu'il implique que l'autocorrélation d'ordre 1 du bruit converge vers 1 lorsque la fréquence journalière d'observation tend vers l'infini. Nous utilisons le cadre semi-paramétrique ainsi défini pour dériver un nouvel estimateur de la volatilité intégrée baptisée "estimateur shrinkage". Cet estimateur se présente sous la forme d'une combinaison linéaire optimale de deux estimateurs aux propriétés différentes...

Crenças e representações dos professores sobre o construtivismo, os parâmetros currículares nacionais (PCN) e as inovações pedagógicas no contexto das diretrizes propostas para o ensino fundamental a partir da nova LDB; Beliefs and representations of teachers about constructivism, national curricular parameters and pedagogic innovations within the context of the directives proposed for basic teaching starting from the new LDB. 2002

Carraro, Patrícia Rossi
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 05/02/2003 PT
Relevância na Pesquisa
35.82%
O presente trabalho teve como objetivo investigar, a partir da linha de pesquisa “Pensamento do Professor”, as crenças e representações dos professores do ensino fundamental a respeito do construtivismo, dos parâmetros curriculares nacionais e das inovações pedagógicas decorrentes da nova LDB. Foi realizada entrevista de profundidade, semi-estruturada, com quarenta professores do ensino fundamental, em duas Escolas da Rede Pública de Ensino de uma cidade do interior de São Paulo, em duas sessões. A primeira buscava a contextualização da formação, história e prática profissional dos professores e teve, ainda, como objetivo, o estabelecimento de um vínculo mais favorável que facilitasse a participação dos entrevistados. A segunda sessão investigou as crenças e representações em relação ao construtivismo, aos PCN e as inovações do ensino atual. Os resultados das entrevistas gravadas e transcritas literalmente foram submetidos à Análise de Conteúdo. Revelaram que a maioria dos professores não é desfavorável às mudanças no cotidiano escolar, pois acreditam que estas são necessárias e importantes. O que não concordam é a maneira como estas transformações são implantadas e conduzidas. A grande maioria dos professores revelou ter uma noção imprecisa e...

Gait Characteristic Analysis and Identification Based on the iPhone's Accelerometer and Gyrometer

Sun, Bing; Wang, Yang; Banda, Jacob
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 12/09/2014 EN
Relevância na Pesquisa
35.92%
Gait identification is a valuable approach to identify humans at a distance. In this paper, gait characteristics are analyzed based on an iPhone's accelerometer and gyrometer, and a new approach is proposed for gait identification. Specifically, gait datasets are collected by the triaxial accelerometer and gyrometer embedded in an iPhone. Then, the datasets are processed to extract gait characteristic parameters which include gait frequency, symmetry coefficient, dynamic range and similarity coefficient of characteristic curves. Finally, a weighted voting scheme dependent upon the gait characteristic parameters is proposed for gait identification. Four experiments are implemented to validate the proposed scheme. The attitude and acceleration solutions are verified by simulation. Then the gait characteristics are analyzed by comparing two sets of actual data, and the performance of the weighted voting identification scheme is verified by 40 datasets of 10 subjects.

Hydrophobicity Classification of Polymeric Insulators Based on Embedded Methods

Dong,Zhengcheng; Fang,Yanjun; Wang,Xianpei; Zhao,Yu; Wang,Quande
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2015 EN
Relevância na Pesquisa
45.81%
Hydrophobicity is an important parameter to characterize electrical properties of insulated materials. Therefore, it is an urgent task to develop on-line instruments to identify the hydrophobicity of insulated material's surface conveniently, quickly and accurately. For this purpose, a novel evaluation system with image processing and decision tree is proposed which is based on embedded platform. For obtaining satisfactory results, we first propose a mixed image segmentation method to overcome the complex conditions outside, concerning non-controlled illumination, nonstandard surfaces and unfixed shooting angle. Then we adopt four new characteristic parameters to describe the image of each sample. Finally, a classification method based on MultiBoost decision tree is conducted which synthesizes the merits of both AdaBoost and Wagging algorithm. Results indicate the procedures can be applied in the DSP (Digital Signal Processor) platform perfectly and better results can be obtained than those did in our previous study or that of some other research.

Comparison of lattice-fluid binary parameters for mixtures and block copolymers

Riccardi, Carmen Cristina; Schroeder, Walter Fabian; Serrano, Elena; Mondragon, Iñaki
Fonte: Taylor Publicador: Taylor
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
Relevância na Pesquisa
35.96%
The aim of this report is to discuss the method of determination of lattice-fluid binary interaction parameters by comparing well characterized immiscible blends and block copolymers of poly(methyl methacrylate) (PMMA) and poly(ε−caprolactone) (PCL). Experimental pressure-volume-temperature (PVT) data in the liquid state were correlated with the Sanchez-Lacombe (SL) equation of state with the scaling parameters for mixtures and copolymers obtained through combination rules of the characteristic parameters for the pure homopolymers. The lattice-fluid binary parameters for energy and volume were higher than those of block copolymers implying that the copolymers were more compatible due to the chemical links between the blocks. Therefore, a common parameter cannot account for both homopolymer blend and block copolymer phase behaviors based on current theory. As we were able to adjust all data of the mixtures with a single set of lattice-binary parameters and all data of the block copolymers with another single set we can conclude that both parameters did not depend on the composition for this system. This characteristic, plus the fact that the additivity law of specific volumes can be suitably applied for this system, allowed us to model the behavior of the immiscible blend with the SL equation of state. In addition...

A Constraint between Noncommutative Parameters of Quantum Theories in Noncommutative Space

Zhang, Jian-Zu
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.79%
In two-dimensional noncommutive space for the case of both position - position and momentum - momentum noncommuting, a constraint between noncommutative parameters is investigated. The related topic of guaranteeing Bose - Einstein statistics in noncommutive space in the general case are elucidated: Bose - Einstein statistics is guaranteed by the deformed Heisenberg - Weyl algebra itself, independent of dynamics. A special character of a dynamical system is represented by a constraint between noncommutative parameters. The general feature of the constraint for any system is a direct proportionality between noncommutative parameters with a proportional coefficient depending on characteristic parameters of the system under study. The constraint for a harmonic oscillator is illustrated.; Comment: 13 pages

Spheroid's Panchromatic Investigation in Different Environmental Regions (SPIDER) - I. Sample and galaxy parameters in the grizYJHK wavebands

La Barbera, F.; de Carvalho, R. R.; de la Rosa, I. G.; Lopes, P. A. A.; Kohl-Moreira, J. L.; Capelato, H. V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.81%
This is the first paper of a series presenting a Spheroid's Panchromatic Investigation in Different Environmental Regions (SPIDER). The sample of spheroids consists of 5,080 bright (Mr<-20) Early-Type galaxies (ETGs), in the redshift range of 0.05 to 0.095, with optical (griz) photometry and spectroscopy from SDSS-DR6 and Near-Infrared (YJHK) photometry from UKIDSS-LAS (DR4). We describe how homogeneous photometric parameters (galaxy colors and structural parameters) are derived using grizYJHK wavebands. We find no systematic steepening of the CM relation when probing the baseline from g-r to g-K, implying that internal color gradients drive most of the mass-metallicity relation in ETGs. As far as structural parameters are concerned we find that the mean effective radius of ETGs smoothly decreases, by ~30%, from g through K, while no significant dependence on waveband is detected for the axis ratio, Sersic index, and a4 parameters. Also, velocity dispersions are re-measured for all the ETGs using STARLIGHT and compared to those obtained by SDSS. We compare our (2DPHOT) measurements of total magnitude, effective radius, and mean surface brightness with those obtained as part of the SDSS pipeline (Photo). Significant differences are found and reported...

Higher order bulk characteristic parameters of asymmetric nuclear matter

Chen, Lie-Wen
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.1%
The bulk parameters characterizing the energy of symmetric nuclear matter and the symmetry energy defined at normal nuclear density $\rho_0 $ provide important information on the equation of state (EOS) of isospin asymmetric nuclear matter. While significant progress has been made in determining some lower order bulk characteristic parameters, such as the energy $E_0(\rho_0)$ and incompressibility $K_0$ of symmetric nuclear matter as well as the symmetry energy $E_{sym}(\rho_0)$ and its slope parameter $L$, yet the higher order bulk characteristic parameters are still poorly known. Here, we analyze the correlations between the lower and higher order bulk characteristic parameters within the framework of Skyrme Hartree-Fock energy density functional and then estimate the values of some higher order bulk characteristic parameters. In particular, we obtain $J_0=-355 \pm 95$ MeV and $I_0=1473 \pm 680$ MeV for the third-order and fourth-order derivative parameters of symmetric nuclear matter at $\rho_0 $ and $K_{sym} = -100 \pm 165$ MeV, $J_{sym} = 224 \pm 385$ MeV, $I_{sym} = -1309 \pm 2025$ MeV for the curvature parameter, third-order and fourth-order derivative parameters of the symmetry energy at $\rho_0 $, using the empirical constraints on $E_0(\rho_0)$...

Characteristic Parameters in Integrated Photoelasticity: An Application of Poincare's Equivalence Theorem

Hammer, Hanno
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.96%
The Poincare Equivalence Theorem states that any optical element which contains no absorbing components can be replaced by an equivalent optical model which consists of one linear retarder and one rotator only, both of which are uniquely determined. This has many useful applications in the field of Optics of Polarized Light. In particular, it arises naturally in attempts to reconstruct spatially varying refractive tensors or dielectric tensors from measurements of the change of state of polarization of light beams passing through the medium, a field which is known as Tensor Tomography. A special case is Photoelasticity, where the internal stress of a transparent material may be reconstructed from knowledge of the local optical tensors by using the stress-optical laws. - We present a rigorous approach to the Poincare Equivalence Theorem by explicitly proving a matrix decomposition theorem, from which the Poincare Equivalence Theorem follows as a corollary. To make the paper self-contained we supplement a brief account of the Jones matrix formalism, at least as far as linear retarders and rotators are concerned. We point out the connection between the parameters of the Poincare-equivalent model to previously introduced notions of the Characteristic Parameters of an optical model in the engineering literature. Finally...

Sensitivity analysis and non linear parameters estimation of porous materials from normal sound coefficient absorption measurements

Garoum, M.; Idchabani, R.; Tajayouti, M.; Rhachi, M.; Moreno, Antonio
Fonte: Société française d'acoustique; Acoustical Society of America; European Acoustics Association Publicador: Société française d'acoustique; Acoustical Society of America; European Acoustics Association
Tipo: Comunicación de congreso Formato: 29167 bytes; application/pdf
ENG
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35.92%
Communication presented at: Acoustics '08 (Paris, France, June 29-July 4, 2008), comprising: 5th Forum Acusticum, 155th ASA Meeting, 9e Congrès Français d'Acoustique, 7th European Conference on Noise Control (Euronoise), 9th European Conference on Underwater Acoustics (ECUA).-- Book of abstracts published in Vol. 94 Suppl.1: S1-S1020 (May/June 2008) of Acta Acustica united with Acustica: The Journal of the European Acoustics Association (ISSN 1610-1928).; In literature, various models have been proposed in order to predict characteristic impedance Zc and wave number kc of porous materials. To use these models their involved nonacoustical parameters (i. e. flow resistivity, tortuosity porosityoe) are usually measured. Unfortunately measurements require specialised equipments and are often difficult on loose porous materials leading most often to erroneous values. Moreover, the inverse estimation of theses parameters from experimental data is not an easy task as believed. This is due to the non linearity of models and the presence of some parameters with weak and/or linearly dependent influences. In this work an approach based on the tradeoff between magnitude and linear independence of the sensitivity matrix components is presented in order to achieve an efficient ranking of parameters according to their inherent ease of estimation. Next this approach is associated to Genetic Algorithms to minimize the least squares norm between measured and modelled normal sound absorption coefficient. For five widely used models in literatures...