954 resultados para Spherical elastic shells


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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Restoring a misaligned tooth with an inadequate contact point is a challenge to the practitioner. In some instances, teeth that could be repositioned and adequately restored are extracted. Thus, the aim of this article was to describe a treatment using orthodontic and prosthetic techniques to restore esthetics and function in a patient with a distally drifted maxillary lateral incisor. The patient's functional and esthetic expectations were successfully met with the outlined treatment.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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We study the elastic scattering of positronium atoms by hydrogen atoms at medium energies using partial-wave Born-Oppenheimer (BO) exchange amplitudes and report accurate BO cross sections in the energy range 0 to 60 eV. The present BO results agree with a 22-state R-matrix and a five-state coupled-channel model potential calculation, but disagree strongly with a conventional close-coupling calculation as well as its input BO amplitudes at medium energies.

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We study the propagation of waves in an elastic tube filled with an inviscid fluid. We consider the case of inhomogeneity whose mechanical and geometrical properties vary in space. We deduce a system of equations of the Boussinesq type as describing the wave propagation in the tube. Numerical simulations of these equations show that inhomogeneities prevent separation of right-going from left-going waves. Then reflected and transmitted coefficients are obtained in the case of localized constriction and localized rigidity. Next we focus on wavetrains incident on various types of anomalous regions. We show that the existence of anomalous regions modifies the wavetrain patterns. (c) 2007 Elsevier B.V. All rights reserved.

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Scattering of positronium (Ps) by a helium atom has been investigated in a three-Ps-state coupled-channel model including Ps(1s,2s,2p) states using a recently proposed time-reversal-symmetric regularized electron-exchange model potential. Specifically, we report results of differential cross sections for elastic scattering and target-elastic Ps excitations. We also present results for total and different partial cross sections and compare them with experiment and other calculations.

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Elastic and inelastic positron-helium scattering have been investigated in different partial waves at medium energies using the close-coupling approximation with realistic wavefunctions employing the following states: He(1s1s), He(1s2s), He(1s2p), He(1s3s), He(1s3p), Ps(1s), Ps(2s) and Ps(2p). All excitations of the helium atom are in the spin-singlet electronic state. Calculations are reported of cross sections to He(1s1s), He(1s2s), and He(1s2p) transitions for incident positron energies up to 200 eV. These cross sections are in good agreement with experimental results.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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The purpose of this work is to obtain spherical particles YIG from micrometric to nanometric scales. The spherical particles were obtained from cation hydrolysis in acid medium by adding urea or ammonia in order to carry out a homogeneous nucleation process up to 90 degrees C. Different composition and morphology were achieved by changing reactant concentrations, precipitation agent and stabilizing agent. X-ray diffractometry, electrophoretic mobility, transmission and scanning electron microscopies were carried out on these particles to investigate the phase identification, mobility, morphology and particle size. Crystalline YIG, with spherical characteristics, was obtained. The surface potential presented different characteristics for different dispersion media.

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This study aimed at determining the minimum time required for the penetration of Salmonella Heidelberg inside the eggs after contact with contaminated material. Recently-collected brown and white eggs from laying hens between 45-50 weeks of age, reared in a commercial poultry house, were artificially contaminated by contact with wood shavings moistened with liquid inoculum of Salmonella Heidelberg in stationary-growth phase (10³-10(4) CFU g-1). According to type (white or brown), eggs were distributed into three different groups, with four replicates each: negative control group (no artificial contamination), positive control group (analyzed externally immediately after contamination and internally after the maximum storage period of the test group) and test group. Eggs were stored at controlled environmental temperature varying from 25ºC to 30ºC. In the test group, eggs contents (yolk and albumen) were pooled and analyzed after 1:00, 1:30, 2:00, 2:30, 3:00, 3:30, and 4:00 hours after contamination for the presence of Salmonella Heidelberg in 25g of this pool. The experimental unit consisted of five eggs in each test. The analysis protocol included pre-enrichment, selective enrichment, plating on selective agar, and biochemical and serological tests. The results obtained were submitted to logistic regression, which indicated that the presence of Salmonella Heidelberg was verified after 2:16 h and 2:44 h of contact with white and brown eggs, respectively.