136,078 research outputs found
A continuous contact force model for impact analysis in multibody dynamics
No full textA new continuous contact force model for contact problems with complex geometries and energy dissipations in multibody systems is presented and discussed in this work. The model is developed according to the Hertz law, and a hysteresis damping force is introduced for modeling the energy dissipation during the contact process. As it is almost impossible to obtain an analytical solution based on the system dynamic equation, an approximate dynamic equation for the collision system is proposed, achieving a good approximation of the system dynamic equation. An approximate function relating the deformation velocity and indentation depth is determined based on the approximate dynamic equation and is utilized to calculate the energy loss due to the damping force. Then, a primary formula of the hysteresis damping parameter is derived by combining energy balance and the law of conservation of linear momentum. The new model is developed by modifying the primary formula through nondimensional analysis. The comparison with published experimental data and the analysis of the simulation data of eight different continuous contact models reveal the capability and high precision of the new model as well as the effect of the geometry of the contacting surfaces on the dynamic system response. (c) 2020 Elsevier Ltd. All rights reserved
A continuous contact force model for impact analysis
No full textHunt and Crossley proposed a general expression of the contact force in 1975. The dissipative force term of the general expression has two exponents: the exponent of indentation depth and that of velocity. Because it is almost impossible to obtain an analytical solution based on the general expression, more than twenty continuous contact models have been developed based on the simplification of the general expression. In these studies, the exponent of the indentation depth was set as 0.25, 0.5, 0.65, 1.0 or 1.5, and the exponent of the velocity was set to 1.0. This paper proposes a new continuous contact force model with arbitrary values of the exponents of the indentation depth and velocity. The model is based on the general expression of the contact force. Considering the rule of energy equivalence, an approximate dynamic equation is developed by introducing the equivalent indentation and equivalent velocity. Subsequently, a new contin-uous contact force model is constructed based on the system dynamic equation and approximate dynamic equation. The influences of the two exponents on the performance of the continuous contact force models are investigated by analyzing the simulation results. Moreover, the validity of the new model is demonstrated by comparing the simulation results with two published experimental datasets. The comparison also indicates that the performance of the continuous contact model can be enhanced by selecting appropriate values of the two exponents
Protecting Animals 36: Author Witi Ihimaera
No full textIn this very special episode of Knowing Animals I am joined by beloved New Zealand author Witi Ihimaera. Witi has written many books featuring nonhuman animals. He offers us a non-colonial lens through which to think about the human/nonhuman relationship
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
Dynamics and Robust Control of an Underactuated Torsional Vibratory Gyroscope Actuated by Electrostatic Actuator
No full textIt has been shown that the underactuated MEMS gyroscopes provide inherent robustness against structural and environmental parameter variations. To further improve the performance of the systems, the electrical and mechanical coupling dynamics of the underactuated torsional gyroscopes with double oscillators actuated by a single electrostatic actuator is investigated in this paper. It is shown that the highly nonlinear coupling dynamics of the underactuated gyroscope systems can be transformed into the fifth-order linear systems even though the electrical uncertainties of the systems are considered. For the purpose of simplifying the structures of the underactuated torsional MEMS gyroscopes, an observer-based robust controller with considering structural uncertainties is presented on the basis of linear matrix inequalities (LMIs). The robust stability of the presented controller is also demonstrated by some numerical simulations on a three-degree-of-freedom underactuated MEMS gyroscope. It is shown that the LMI-based robust controller can accommodate both large initial errors in the system state and bounded uncertainties in the structural parameters of the system.National Natural Science Foundation of China [51375016]SCI(E)[email protected]; [email protected]
Dynamics synthesis and control for a hopping robot with articulated leg
No full textTo investigate the design and the applications of elastic underactuated mechanisms for improving the energy efficiency of dynamic mechanical systems, the dynamics and control of a one-legged hopping robot with articulated leg is studied in this paper. To ensure the controllability of the elastic underactuated mechanism, a dynamics synthesis method is proposed for designing the underactuated mechanism so that the dynamics of the system can be transformed into the strict feedback normal form. To improve the energy efficiency of the one-legged locomotion system, an optimal motion planning method is presented to optimize the trajectories of the robot joints. A nonlinear controller is proposed to stabilize the hopping robot to its balance configuration in stance phase, and a switched linear controller is proposed to stabilize the continuous hopping movement. The stability of the presented controllers is analyzed in theory and verified by some numerical simulations. (C) 2011 Elsevier Ltd. All rights reserved.Engineering, MechanicalSCI(E)EI0ARTICLE111669-16884
Finite-Time Stabilization of a Comb-Drive Electrostatic Microactuator
No full textThe inherent nonlinear characteristic between the electrostatic force and the applied voltage causes electrostatic microactuators to show the pull-in bifurcation phenomenon. Exploiting a closed-loop control for stabilizing the electrostatic microactuators in its full travel range is the primary objective in the control of such devices. In this paper, the dynamics of a transverse comb-drive electrostatic microactuator is established with considering the presence of parasitic and parametric uncertainties, and it is shown that the dynamics can be transformed into the third-order Brunovsky's canonical form. Then, a finite-time stabilizing controller is proposed for the third-order Brunovsky's canonical form systems, and the finite-time stability of the presented controller is shown. The robust finite-time stability of the controller under the parasitic and parametric uncertainties is also verified using numerical simulations.Automation & Control SystemsEngineering, ManufacturingEngineering, Electrical & ElectronicEngineering, MechanicalSCI(E)EI0ARTICLE1107-1151
Retinitis Pigmentosa GTPase Regulator (RPGR) protein isoforms in mammalian retina:insights into X-linked Retinitis Pigmentosa and associated ciliopathies
No full textMutations in the cilia-centrosomal protein Retinitis Pigmentosa GTPase Regulator (RPGR) are a frequent cause of retinal degeneration. The RPGR gene undergoes complex alternative splicing and encodes multiple protein isoforms. To elucidate the function of major RPGR isoforms (RPGR 1-19 and RPGR ORF15), we have generated isoform-specific antibodies and examined their expression and localization in the retina. Using sucrose-gradient centrifugation, immunofluorescence and co-immunoprecipitation methods, we show that RPGR isoforms localize to distinct sub-cellular compartments in mammalian photoreceptors and associate with a number of cilia-centrosomal proteins. The RCC1-like domain of RPGR, which is present in all major RPGR isoforms, is sufficient to target it to the cilia and centrosomes in cultured cells. Our findings indicate that multiple isotypes of RPGR may perform overlapping yet somewhat distinct transport-related functions in photoreceptors
Investigation of Lagrangian coherent structures in a wake-induced boundary layer transition
No full textThe evolution of coherent structures in a flat plate boundary layer transition induced by the cylinder wake is investigated using the particle image velocimetry (PIV) technique. The finite-time Lyapunov exponent (FTLE), which characterizes the amount of stretching about the flow trajectory, is used to extract the Lagrangian coherent structures. It is revealed that secondary vortex is induced by the cylinder wake vortices in the near wall region,which would evolve into hairpin vortex as it convects downstream. The subsequent evolvement of the hairpin vortex, characterized by the regeneration of offspring hairpin vortex upstream of it, leads to the appearance of the hairpin packet and the boundary layer finally reaches a turbulent state
Taxonomy and nomenclature of Salix baileyi, S. rehderiana, and S. disperma
No full textResearchers have frequently misapplied the name Salix leveilleana C.K. Schneider to S. baileyi C.K. Schneider. After detailed study of the types, relevant specimens and literature, S. leveilleana is synonymized with S. disperma Roxb. ex D. Don. Salix dolia C.K. Schneider and S. rehderiana C.K. Schneider represent the same taxon; in this study, the later one is chosen. Furthermore, the author perfected the descriptions of S. baileyi, and amend its distribution area to include Hunan and Zhejiang, China.</jats:p
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