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F G Mitri - One of the best experts on this subject based on the ideXlab platform.
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optical bessel tractor Beam on active dielectric rayleigh prolate and oblate spheroids
Journal of The Optical Society of America B-optical Physics, 2017Co-Authors: F G MitriAbstract:Optical Bessel tractor Beams, designed to produce a negative pulling force on a particle, are gaining increased attention for applications in noncontact remote sampling, particle manipulation, and handling, to name some examples. In the long-wavelength (Rayleigh) limit, known also as the electric dipole approximation, earlier investigations demonstrated that a zeroth-order Bessel Beam incident upon a passive dielectric sphere (i.e., no radiating sources in its core) always acts as a repulsor Beam, which causes the particle to be pushed away from the source in the forward direction of the linear momentum. In contrast to what has already been established, this work shows that the incident wave field can act as a tractor Beam (where a small spheroid is pulled backwards towards the source due to a negative attractive force) in the dipole approximation (Rayleigh) limit, provided that the particle is made of an active material, i.e., a dielectric spheroid acting as an oscillating source for which the extinction energy efficiency is negative. Numerical computations for the Cartesian components of the optical radiation force on active prolate and oblate spheroids with arbitrary orientation are performed. Emphasis is placed on the emergence of the tractor Beam Behavior and its dependence upon the half-cone angle, the polarization type of the incident Beam, the spheroid aspect ratio, as well as its orientation in space. The analysis is extended to calculate the Cartesian components of the spin radiation torque, which causes a rotation of the spheroid around its center of mass in either the counterclockwise or the clockwise (negative) direction of spinning. Unlike the case of a sphere, the optical spin torque arises for a nonabsorptive oblate or prolate spheroid with arbitrary orientation in the field of a zeroth-order Bessel Beam. Potential applications in optically engineered metamaterials, optical tractor Beams, tweezers, particle manipulation, rotation, and handling would benefit from the results of this study.
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axial acoustic radiation force on rigid oblate and prolate spheroids in bessel vortex Beams of progressive standing and quasi standing waves
Ultrasonics, 2017Co-Authors: F G MitriAbstract:The analysis using the partial-wave series expansion (PWSE) method in spherical coordinates is extended to evaluate the acoustic radiation force experienced by rigid oblate and prolate spheroids centered on the axis of wave propagation of high-order Bessel vortex Beams composed of progressive, standing and quasi-standing waves, respectively. A coupled system of linear equations is derived after applying the Neumann boundary condition for an immovable surface in a non-viscous fluid, and solved numerically by matrix inversion after performing a single numerical integration procedure. The system of linear equations depends on the partial-wave index n and the order of the Bessel vortex Beam m using truncated but converging PWSEs in the least-squares sense. Numerical results for the radiation force function, which is the radiation force per unit energy density and unit cross-sectional surface, are computed with particular emphasis on the amplitude ratio describing the transition from the progressive to the pure standing waves cases, the aspect ratio (i.e., the ratio of the major axis over the minor axis of the spheroid), the half-cone angle and order of the Bessel vortex Beam, as well as the dimensionless size parameter. A generalized expression for the radiation force function is derived for cases encompassing the progressive, standing and quasi-standing waves of Bessel vortex Beams. This expression can be reduced to other types of Beams/waves such as the zeroth-order Bessel non-vortex Beam or the infinite plane wave case by appropriate selection of the Beam parameters. The results for progressive waves reveal a tractor Beam Behavior, characterized by the emergence of an attractive pulling force acting in opposite direction of wave propagation. Moreover, the transition to the quasi-standing and pure standing wave cases shows the acoustical tweezers Behavior in dual-Beam Bessel vortex Beams. Applications in acoustic levitation, particle manipulation and acousto-fluidics would benefit from the results of the present investigation.
Mark F Green - One of the best experts on this subject based on the ideXlab platform.
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prestressed carbon fiber reinforced polymer sheets for strengthening concrete Beams at room and low temperatures
Journal of Composites for Construction, 2004Co-Authors: Raafat Elhacha, Gordon R Wight, Mark F GreenAbstract:A technique for strengthening damaged concrete Beams using prestressed carbon fiber reinforced polymer (CFRP) sheets was developed at Queen’s University and the Royal Military College of Canada. As part of this study, an anchorage system was developed to directly prestress the CFRP sheets by jacking and reacting against the strengthened concrete Beam itself. The feasibility and effectiveness of using bonded prestressed CFRP sheets to strengthen precracked concrete Beams at both room (+22°C,+72°F) and low (-28°C,-20°F) temperatures have been investigated experimentally. Materials and prestress changes due to temperature variations that would affect and cause changes in flexural Behavior were studied. The strengthened Beams showed significant increases in flexural stiffness and ultimate capacity as compared to the control-unstrengthened Beams. The flexural Behavior of the strengthened Beams was not adversely affected by short-term exposure to reduced temperature (-28°C,-20°F). In addition to the experimental investigation, analytical models were developed to predict the overall flexural Behavior of the strengthened Beams during prestressing of the CFRP sheets and under external loading at both room and low temperatures. The model accurately predicted the flexural Beam Behavior. Improved serviceability Behavior and higher strength were predicted for Beams strengthened with the bonded prestressed CFRP sheets.
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prestressed frp sheets for poststrengthening reinforced concrete Beams
Journal of Composites for Construction, 2001Co-Authors: R G Wight, Mark F Green, Ma ErkiAbstract:Four large-scale reinforced concrete Beams were constructed and tested to investigate the effectiveness of external poststrengthening with prestressed fiber reinforced polymer (FRP) sheets. One of the Beams served as a control specimen, another was strengthened with nonprestressed carbon FRP sheets, and the remaining two were strengthened with prestressed carbon FRP sheets. Presented is a method of prestressing multiple layers of the carbon fiber sheets during the application process and the experimental and analytical Behavior of the Beams under quasi-static loading. Comparisons are made between the control Beam, the Beam reinforced with nonprestressed carbon FRP sheets, and the Beams strengthened with prestressed sheets. Serviceability and ultimate conditions are considered in the theoretical prediction of Beam Behavior, including the effects of multiple layer prestressing and external loading. The bonding of prestressed FRP sheets to the tensile face of concrete Beams improved both the serviceability a...
Adil K Altamimi - One of the best experts on this subject based on the ideXlab platform.
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Behavior of reinforced concrete Beams strengthened with externally bonded hybrid fiber reinforced polymer systems
Materials & Design, 2014Co-Authors: Rami A Hawileh, Hayder A Rasheed, Jamal A Abdalla, Adil K AltamimiAbstract:Abstract This paper presents an experimental and an analytical investigation of the Behavior of Reinforced Concrete (RC) Beams strengthened in flexure by means of different combinations of externally bonded hybrid Glass and Carbon Fiber Reinforced Polymer (GFRP/CFRP) sheets. In order to obtain the mechanical properties of the hybrid sheets, multiple tensile coupon tests were conducted. In addition, an experimental program consisting of a control Beam and four Beams strengthened in flexure with GFRP, CFRP and hybrid FRP sheets was conducted. The series of the RC Beams were tested under four point bending to study the flexural effectiveness of the proposed hybrid FRP sheets. The load–deflection response, strain readings at certain locations and associated failure modes of the tested specimens had been recorded. It is observed that the increase in the load capacity of the strengthened Beams ranged from 30% to 98% of the un-strengthened control RC Beam depending on the combination of the Carbon/Glass sheets. It was also observed that the ductility at failure loads of the Beams strengthened with glass and hybrid sheets is higher than that with a single carbon sheet. Hence, the selection of the optimum combination of hybrid sheets can lead to a strengthening material which provides an improved ductility and strength in Beam Behavior. The load carrying capacity of the tested specimens was then predicted by the ACI 440.2R-08 guidelines. The predicted and measured results were in good agreement, within 5% for the control Beam and for Beams with one layer of strengthening sheet and between 13% and 17% for Beams with two or more layers of hybrid strengthening sheets. Furthermore, an analytical model was developed to predict the load–deflection response of the tested specimens and the results were compared with the measured experimental data. The results showed that the developed analytical model predicted the response of the tested Beam specimens with reasonable accuracy.
Ma Erki - One of the best experts on this subject based on the ideXlab platform.
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prestressed frp sheets for poststrengthening reinforced concrete Beams
Journal of Composites for Construction, 2001Co-Authors: R G Wight, Mark F Green, Ma ErkiAbstract:Four large-scale reinforced concrete Beams were constructed and tested to investigate the effectiveness of external poststrengthening with prestressed fiber reinforced polymer (FRP) sheets. One of the Beams served as a control specimen, another was strengthened with nonprestressed carbon FRP sheets, and the remaining two were strengthened with prestressed carbon FRP sheets. Presented is a method of prestressing multiple layers of the carbon fiber sheets during the application process and the experimental and analytical Behavior of the Beams under quasi-static loading. Comparisons are made between the control Beam, the Beam reinforced with nonprestressed carbon FRP sheets, and the Beams strengthened with prestressed sheets. Serviceability and ultimate conditions are considered in the theoretical prediction of Beam Behavior, including the effects of multiple layer prestressing and external loading. The bonding of prestressed FRP sheets to the tensile face of concrete Beams improved both the serviceability a...
Catoia Bruna - One of the best experts on this subject based on the ideXlab platform.
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Comportamento de vigas protendidas pré-moldadas com ligações semi-rígidas
Programa de Pós-graduação em Estruturas e Construção Cívil, 2007Co-Authors: Catoia BrunaAbstract:The behaviour of prestressed precast Beams is directly affected by the rotational stiffness of the end connections. Although the prestressed Beam presents a linear behaviour in service, the effective behaviour of the precast Beam depends on the interaction of the Beam with the behaviour of its connections. The majority of the experimental investigations on semi-rigid connections in precast concrete structures are focused on the testing of isolated models of connections aiming to the characterization of their moment-rotation relationships. However, the effective behaviour of precast Beams with semi-rigid connections can only be determined through tests of precast subframes, wherein the interaction of the Beam with its connections can be evaluated. The present research presents a development of an experimental procedure for testing of precast subframes with semi-rigid connections, which integrates analytical equations, allowing estimate the partial restrained moment at the Beam-column connections. Using this approach, this research presents the results of an experimental investigation. With the experimental inquiry of the prestressed Beam Behavior together with the Beam-column connections of extremity, through physical tests, was possible esteem the partial restrained in the Beam-column connections, despite in exploratory character. Were testing two models, being one compose for a prestressed Beam with semi-rigid connections, and the other compose for a simply supported prestressed Beam With the analyses of the experimental results for the studied models, the effective restrained of the connections, in other words, the capacity of restriction to the rotation of Beam-column connections of extremity in the U.L.S, was esteem as being a value between 60% and 70%, presenting, thus, a good performance. Although these results are restricted to the negative moments, it gives credit that these connections possess one high potential for application in porches, because the detail used in the interface between the Beam and the column made possible a bigger capacity of restriction to the rotation of the connectionUniversidade Federal de Minas GeraisO comportamento das vigas pré-moldadas de concreto protendido é diretamente afetado pela relação momento-rotação do apoio. Dessa forma, embora a viga protendida apresente um comportamento linear, o comportamento conjunto viga e ligações, é determinado pela não linearidade das ligações. Os estudos experimentais existentes sobre o comportamento das ligações semi-rígidas em estruturas pré-moldadas têm se restringido a caracterização da rigidez à flexão de maneira isolada, devido principalmente à falta de uma metodologia experimental que integre parâmetros teóricos de controle, como o fator de restrição à rotação αR e o procedimento Beam-line. Na presente pesquisa, desenvolveu-se um procedimento experimental, através do qual foi possível integrar diversos equacionamentos teóricos, que levam em consideração diferentes parâmetros para a análise dos resultados. Com a investigação experimental do comportamento conjunto de uma viga pré-moldada de concreto protendido e de suas ligações viga-pilar de extremidade, a partir de ensaios físicos de dois modelos, foi possível estimar o engastamento parcial nas ligações viga-pilar. Foram ensaiados dois modelos, sendo um composto por uma viga protendida com ligações semirígidas, e o outro composto por uma viga protendida bi-apoiada, ainda que em caráter exploratório Com base nas análises dos resultados experimentais obtidos para os modelos estudados, o engastamento parcial efetivo da ligação, ou seja, a capacidade de restrição à rotação da ligação viga-pilar de extremidade, no Estado Limite Último, foi estimada como sendo um valor entre 60% e 70%, apresentando, assim, um bom desempenho. Embora tais resultados sejam restritos aos momentos negativos, acredita-se que essa ligação possui um elevado potencial para aplicação em pórticos, na medida em que o detalhe utilizado na interface entre a viga e o pilar possibilitou uma maior capacidade de restrição ao giro da ligaçã