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This paper presents the design, development, and testing of a novel three-degree-of-freedom compliant parallel-kinematic active constant-force stage. The active constant-force property enables a large travel and constant driving p...
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This paper presents the design, development, and testing of a novel three-degree-of-freedom compliant parallel-kinematic active constant-force stage. The active constant-force property enables a large travel and constant driving property, which is enabled by introducing symmetrical bistable flexure hinges. The folded flexure mechanism is adopted to guide the driving input and to balance the stiffness of the stage to zero. Besides, leaf flexure hinges are employed to decouple the cross-axis motion of the three-degree-of-freedom parallel stage. Analytical modeling is conducted to evaluate the stage performances of constant-force property and motion decoupling, which is verified by performing finite-element analysis simulation study. Design optimization of the stage parameters is implemented for minimizing the fluctuation of the constant-force value via multi-objective genetic algorithm. Moreover, a prototype is fabricated and experimental study is carried out to validate the analytical modeling results and performances of the proposed stage design. (C) 2019 Elsevier Ltd. All rights reserved.
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Kachanov's simplified model of microcrack interaction is applied to an investigation of the behaviour of a cracked body under predominantly compressive periodic loading, so that the cracks experience periods of closure and slip, w...
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Kachanov's simplified model of microcrack interaction is applied to an investigation of the behaviour of a cracked body under predominantly compressive periodic loading, so that the cracks experience periods of closure and slip, with frictional dissipation. The model is shown to be equivalent to a discrete elastic frictional system with each crack representing one node. Theorems and algorithms from such systems are applied to determine the conditions under which the system shakes down to a state with no slip and hence no energy dissipation in friction. For conditions not too far beyond the shakedown state, the dissipation is significantly affected by the initial conditions, but with larger oscillating loads, it becomes a unique and increasing function of load amplitude. The effect of crack interaction is assessed by comparison with an uncoupled model, for which the dissipation is obtained as a summation of closed form expressions over the crack population. For small numbers of cracks, the results are significantly dependent on the randomly chosen crack locations and sizes, but with larger populations, a statistically significant decrease in dissipation is observed with increasing interaction terms.
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We use a Hamiltonian interacting particle system to derive a stochastic mean field system whose McKean-Vlasov equation yields the incompressible Navier-Stokes equation. Since the system is Hamiltonian, the particle relabeling symm...
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We use a Hamiltonian interacting particle system to derive a stochastic mean field system whose McKean-Vlasov equation yields the incompressible Navier-Stokes equation. Since the system is Hamiltonian, the particle relabeling symmetry implies a Kelvin Circulation Theorem along stochastic Lagrangian paths. Moreover, issues of energy dissipation are discussed and the model is connected to other approaches in the literaturature.
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A configuration of near-equilibrium liquid droplets sitting on a precursor film which wets the entire substrate can coarsen in time by two different mechanisms: collapse or collision of droplets. The collapse mechanism, i.e., a la...
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A configuration of near-equilibrium liquid droplets sitting on a precursor film which wets the entire substrate can coarsen in time by two different mechanisms: collapse or collision of droplets. The collapse mechanism, i.e., a larger droplet grows at the expense of a smaller one by mass exchange through the precursor film, is also known as Ostwald ripening. As was shown by K. B. Glasner and T. P. Witelski (‘Collision versus collapse of droplets in coarsening of dewetting thin films’, Phys. D 209(1–4), 2005, 80–104) in case of a one-dimensional substrate, the migration of droplets may interfere with Ostwald ripening: The configuration can coarsen by collision rather than by collapse. We study the role of migration in case of a two-dimensional substrate for a whole range of mobilities. We characterize the velocity of a single droplet immersed into an environment with constant flux field far away. This allows us to describe the dynamics of a droplet configuration on a two-dimensional substrate by a system of ODEs. In particular, we find by heuristic arguments that collision can be a relevant coarsening mechanism.
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This paper presents a novel study on the analysis and design of a new type compliant spatial four-bar (RSSR) mechanism. To the best of our knowledge, any research on compliant spatial mechanisms which possesses out of plane motion...
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This paper presents a novel study on the analysis and design of a new type compliant spatial four-bar (RSSR) mechanism. To the best of our knowledge, any research on compliant spatial mechanisms which possesses out of plane motions is not available in the literature. This study introduces enumeration and novel approach for the analysis and design of such mechanisms. The analysis and design are performed with the pseudo-rigid-body model (PRBM). Since there are numerous applications of rigid spatial four bar mechanisms, it is strongly believed that a compliant version of such mechanisms may find many applications.
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This paper presents a novel study on the analysis and design of a new type compliant spatial four-bar (RSSR) mechanism. To the best of our knowledge, any research on compliant spatial mechanisms which possesses out of plane motion...
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This paper presents a novel study on the analysis and design of a new type compliant spatial four-bar (RSSR) mechanism. To the best of our knowledge, any research on compliant spatial mechanisms which possesses out of plane motions is not available in the literature. This study introduces enumeration and novel approach for the analysis and design of such mechanisms. The analysis and design are performed with the pseudo-rigid-body model (PRBM). Since there are numerous applications of rigid spatial four bar mechanisms, it is strongly believed that a compliant version of such mechanisms may find many applications.
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In this study, a novel compliant mechanism, "partially compliant spatial slider-crank (RSSP)" is proposed. All possible configurations of compliant RSSP mechanisms are classified and discussed. A method is derived to determine def...
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In this study, a novel compliant mechanism, "partially compliant spatial slider-crank (RSSP)" is proposed. All possible configurations of compliant RSSP mechanisms are classified and discussed. A method is derived to determine deflection of the multiple-axis flexural hinge for all positions of the crank. A design procedure for partially compliant RSSP mechanisms is introduced. In order to prove the feasibility of the proposed mathematical model, a real model is built and it is shown that results are consistent.
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Attending in-class paper demonstrations and performing experiments in solid mechanics courses are very effective ways for students to gain an understanding of the complicated concepts of mechanics. This paper explores a few applic...
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Attending in-class paper demonstrations and performing experiments in solid mechanics courses are very effective ways for students to gain an understanding of the complicated concepts of mechanics. This paper explores a few applications of dogbone tensile tests, stress concentrations and crack kinking or mixed-mode fracture. Furthermore, this handy technique can be extended to other broader areas of mechanics education. Since only simple materials and supplies are used: copy paper, staples, scissors and a paper punching machine, students can repeat these typical mechanics experiments in future in other locations, such as in an office or at home. Therefore, this simple and effective technique can have a remarkable influence on the student's long-term career.
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This paper presents a design methodology for mechanisms consisting of a single continuous structure, continuum mechanisms, that blends the kinematic synthesis of rigid-body mechanisms with topology optimization for compliant mecha...
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This paper presents a design methodology for mechanisms consisting of a single continuous structure, continuum mechanisms, that blends the kinematic synthesis of rigid-body mechanisms with topology optimization for compliant mechanisms. Rather than start with a generic structure that is shaped to achieve a required force-deflection task for a compliant mechanism, our approach shapes the initial structure based on the kinematic synthesis of a rigid-body mechanism for the required movement, then the structure is shaped using finite element analysis to achieve the required force-deflection relationship. The result of this approach is a continuum mechanism with the same workpiece movement as the rigid link mechanism when actuated. An example illustrates the design process to obtain an eight-bar linkage that guides its workpiece in straight-line rectilinear movement. We show that the resulting continuum mechanism provides the desired rectilinear movement. A 210 mm physical model machined from Nylon-6 is shown to achieve 21.5 mm rectilinear movement with no perceived deviation from a straight-line.
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Xylella fastidiosa is a xylem-limited bacterium that causes citrus variegated chlorosis (CVC), Pierce's disease of grapevine, and leaf scald of coffee and plum and many other plant species. This pathogen is vectored by sharpshoote...
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Xylella fastidiosa is a xylem-limited bacterium that causes citrus variegated chlorosis (CVC), Pierce's disease of grapevine, and leaf scald of coffee and plum and many other plant species. This pathogen is vectored by sharpshooter leafhoppers (Hemiptera: Cicadellidae: Cicadellinae) and resides in the insect foregut. Scanning electron microscopy was used to determine the retention sites of X. fastidiosa for the most common vector species in Brazilian citrus groves, Acrogonia citrina, Bucephalogonia xanthophis, Dilobopterus costalimai, and Oncometopia facialis. After a 48-h acquisition access period on infected citrus or plum, adult sharpshooters were kept on healthy citrus seedlings for an incubation period of 2 weeks to allow for bacterial multiplication. Then the vector heads were incubated for 24 h in a fixative and transferred into a cryoprotector liquid. Bacterial rod cells exhibiting similar X. fastidiosa morphology were found laterally attached to different regions inside the cibarial pump chamber (longitudinal groove, lateral surface, cibarial diaphragm and apodemal groove) of A. citrina, O. facialis, and D. costalimai, and polarly attached to the precibarium channel of O. facialis. Polymerase chain reactions of vector's heads were positive for the presence of X. fastidiosa. No X. fastidiosa-like cells were detected in B. xanthophis. A different type of rod-shaped bacterium was found on B. xanthophis cibarium chamber and images suggest that the cibarium wall was degraded/digested by these bacteria. Colonization patterns of X. fastidiosa in their vectors are fundamental aspects to be explored toward understanding acquisition, adhesion, and transmission mechanisms for development of X. fastidiosa control strategies.
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