27 resultados para Transdutor de 5 a 10 MHz
em Repositório Institucional UNESP - Universidade Estadual Paulista "Julio de Mesquita Filho"
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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This paper presents an ultrasonic method to measure small concentrations of water in lubricating oil. It uses an ultrasonic measurement cell composed by a piezoceramic emitter (5 and 10 MHz), and a large aperture PVDF receiver that eliminates diffraction effects. The propagation velocity, attenuation coefficient and density of several samples of water-in-oil emulsion were measured. The concentrations of water of the samples were in the range of 0 to 5% in volume, and the results showed that these low concentrations can be discriminated within a resolution of 0.2% in the studied range, using the measurement of the propagation velocity.
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Polycrystalline Ba0.5Sr0.5(Ti0.80Sn0.20)O-3 (BST:Sn) thin films with a perovskite structure were prepared by the soft chemical method on a platinum-coated silicon substrate from spin-coating technique. The resulting thin films showed a dense structure with uniform grain size distribution. The dielectric constant of the films estimated from C-V curve is around 1134 and can be ascribed to a reduction in the oxygen vacancy concentration. The ferroelectric nature of the film indicated by butterfly-shaped C-V curves and confirmed by the hysteresis curve, showed remnant polarization of 14 mu C/cm(2) and coercive field of 74 kV/cm at frequency of 1 MHz. At the same frequency, the leakage current density at 1.0 V is equal to 1.5 x 10(-7) A/cm(2). This work clearly reveals the highly promising potential of BST:Sn for application in memory devices. (c) 2006 Elsevier B.V. All rights reserved.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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This study aimed to describe and compare the ultrasonographic alterations in dogs' eyes submitted to facectomy with or without intraocular lens implant (IOL), to assist in the diagnosis of possible alterations related to the surgical procedure and IOL implantation. Nineteen dogs with cataract (21 eyes) were submitted to phacoemulsification and late postoperative evaluation (at five years). The animals were initially submitted to complete ophthalmological exams which preceded the sonogram. Dogs were divided in three groups: (CA) aphakic dogs (n= 11); (PP) pseudophakic dogs with implantation of two IOLs in piggyback (n=5) and (PL) pseudophakic dogs with implantation of a veterinary IOL (n = 5). The ultrasound was carried under the administration of a topic local anesthetic, with a multi frequency linear transducer of 10 MHz. Biometric eye measurements were also performed. The clinical alterations observed were IOL dislocation, retinal detachment, asteroid hyalosis, and vitreous degeneration. Ultrasound examination was an excellent diagnostic tool, as it was possible to confirm and classify these changes. The piggyback implant reduced the measurements between the ciliary body and the vitreous chamber obtained from the ocular biometry when compared to other usual procedures, with no difference between the axial length and the anterior chamber.
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Pós-graduação em Ginecologia, Obstetrícia e Mastologia - FMB
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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This work describes the use of a large-aperture PVDF receiver in the measurement of liquid density and composite material elastic constants. The density measurement of several liquids is obtained with accuracy of 0.2% using a conventional NDE emitter transducer and a 70-mm-diameter, 52-mu m P(VDF-TrFE) membrane with gold electrodes. The determination of the elastic constants is based on the phase velocity measurement. Diffraction can lead to errors around 1% in velocity measurement when using alternatively the conventional pair of ultrasonic transducers (1-MHz frequency and 19-mm-diameter) operating in through-transmission mode, separated by a distance of 100 mm. This effect is negligible when using a pair of 10-MHz, 19-mm-diameter transducers. Nevertheless, the dispersion at 10 MHz can result in errors of about 0.5%, when measuring the velocity in composite materials. The use of an 80-mm diameter, 52-mu m-thick PVDF membrane receiver practically eliminates the diffraction effects in phase velocity measurement. The elastic constants of a carbon fiber reinforced polymer were determined and compared with the values obtained by a tensile test. (C) 2009 Elsevier B. V. All rights reserved.
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The isotherms of adsorption of CuX2 (XCl-, Br-, ClO4-) by silica gel chemically modified with 5-amino-1,3,4-thiadiazole-2-thiol were studied in acetone and ethanol solutions, at 25 degrees C. The following equilibria constants (in L mol(-1)) were determined: (a) CuCl2, 3.2 x 10(3) (ac), 2.5 x 10(3) (eth); (b) CuBr2, 2.9 x 10(3) (ac), 2.3 x 10(3) (eth); (c) Cu(ClO4)(2), 1.8 x 10(3) (ac), 1.2 x 10(3) (eth); ac, acetone; eth, ethanol. The electron spin resonance spectra of the surface complexes indicated a tetragonal-distorted structure in the case of lower degrees of metal loading on the chemically modified surface. The d-d electronic transition spectra showed that for the ClO4- complex, the peak of absorption did not change for any degree of metal loading and for Cl- and Br- complexes, the peak maxima shifted to higher energy with lower metal loadings. (C) 1998 Academic Press.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
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Thin films of lithium niobate were deposited on Pt/Ti/SiO2 (111) substrates by spin coating from the polymeric precursor method (Pechini process). Annealing in static air was performed at 500 degreesC for 3 h. The obtained films were characterized by X-ray diffraction and atomic force microscopy. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz and the hysteresis loop was obtained. The influence of number of layers on crystallization, morphology and properties of LiNbO3 thin films is discussed. (C) 2003 Elsevier B.V. All rights reserved.
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OBJETIVO: Avaliar o efeito do 5-fluorouracil (5FU) injetado intralesionalmente na cabeça do pterígio no período pré-operatório. MÉTODOS: Foram estudados 53 olhos (52 pacientes), sendo 28 pterígios primários e 25 recidivados, divididos em dois grupos: grupo 1 (G1), composto por indivíduos que receberam a injeção de 5-fluorouracil 30 dias antes do procedimento cirúrgico e grupo 2 (G2), no qual o 5-fluorouracil foi injetado 10 dias antes da cirurgia. Todas as cirurgias foram realizadas seguindo-se a mesma técnica cirúrgica, pelo mesmo cirurgião. Os pacientes foram reavaliados 7, 30 e 60 dias após a cirurgia. Os resultados observados foram submetidos à análise estatística. RESULTADOS: A amostra estudada foi constituída por 52,8% de pterígios primários e 47,2% de recidivados, sendo composta igualmente por indivíduos de ambos os sexos. Não ocorreram complicações decorrentes da infiltração da droga. A recidiva foi mais freqüente nos pterígios recidivados e no G1. CONCLUSÃO: O uso intralesional de 5-fluorouracil no pré-operatório do pterígio não provocou efeitos deletérios aos olhos estudados. Houve menor recorrência quando usado o 5-fluorouracil 10 dias antes da exérese cirúrgica, em relação à aplicação 30 dias antes do procedimento.
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The dielectric permittivity of Na0.80K0.20NbO3 ceramic was investigated by impedance spectroscopy. The dielectric characterization was performed from room temperature to 800 degreesC, in the frequency range 5 Hz-13 MHz. The bulk permittivity was derived by the variation of the imaginary part of the impedance as a function of reciprocal angular frequency. The permittivity values as a function of temperature showed two maxima. The first maximum is very similar at 200degreesC and the second one positioned at around 400degreesC, which was associated to Curie's temperature. The evolution of the complex permittivity as a function of frequency and temperature was investigated. At low frequency dispersion was investigated in terms of dielectric loss. The Na0.80K0.20NbO3 showed a dissipation factor between 5 and 40 over a frequency range from 1 to 10(2) kHz. (C) 2002 Elsevier B.V. B.V. All rights reserved.