1,720,955 research outputs found
Analytical Models for Large Displacement Behavior of Elliptical Flexure Joints
No full textI meccanismi flexure, noti anche come compliant mechanisms, forniscono un movimento guidato tramite deformazione elastica. La loro capacità di produrre un movimento ripetibile/preciso senza attrito li rende una scelta comune nei dispositivi di posizionamento di precisione, cuscinetti senza attrito, dispositivi biomedici e protesi. Tradizionalmente, la progettazione di meccanismi a flessione è stata condotta in modo intuitivo, utilizzando modelli lineari semplicistici. Per i meccanismi a flessione in cui sono presenti effetti non lineari che contribuiscono ai movimenti di errore e alle variazioni di rigidità, i progettisti hanno dovuto utilizzare metodi computazionali come la modellazione a elementi finiti, che fornisce una visione relativamente limitata della progettazione. Questa tesi mira a creare un modello che catturi gli effetti non lineari in modo semplice e chiuso, in modo da poter studiare facilmente la variazione parametrica di vari attributi prestazionali nei meccanismi a flessione. Di conseguenza, diversi meccanismi complessi potrebbero essere analizzati accuratamente senza ricorrere a tecniche computazionali/numeriche o limitare le condizioni di carico. Data la generalità dei modelli analitici degli elementi flexure, questa formulazione può essere utilizzata in futuro per l'ottimizzazione dei meccanismi di flessione. Questa formulazione può essere utilizzata in futuro per l'ottimizzazione dei meccanismi di flessione in termini di forma/tipo/numero degli elementi di flessione e della loro disposizione spaziale. Inoltre, questo lavoro può fornire una base per un nuovo approccio di sintesi basato su vincoli non lineari. Flexure mechanisms, also known as compliant mechanisms, provide guided motion via elastic deformation. Their ability to produce repeatable and precise frictionless motion makes them a common choice in precision positioning devices, frictionless bearings, biomedical devices and prosthetics.
Traditionally, design of flexure mechanisms has been conducted in an intuitive manner using simplistic linear models. For flexure mechanisms where nonlinear efects that contribute to error motions and stifness variations are present, designers have had to use computational methods such as fnite elements modeling, which provides relatively limited design insight. This dissertation aims to create simple analytical models that capture nonlinear efects in closed form, so that the parametric variation of various performance attributes in fexure mechanisms can be easily studied.
As a result, several complex mechanisms could be analyzed accurately without resorting to computational and numerical techniques or restricting the loading conditions.
Given the generality of the proposed analytical models, the latter can be used in the future for optimization of fexure mechanisms in terms of shape,type and number of fexure joints as well as their spatial arrangement. Furthermore, this work can provide a foundation for a new nonlinear constraint based synthesis approach
A Dimensionless Large Displacement Model for Flexure Hinges of Elliptical Geometry
No full textFlexure hinges are joints typically used in the design and manufacturing of compliant mechanisms, especially when small dimensions do not allow for conventional mechanical devices. In this paper, a closed-form solution is proposed for a nonlinear stiffness model used to describe the static displacements obtained on a flexure hinge of elementary geometry as a function of applied loads. A comparison with the most widely used linear model demonstrates the effectiveness of the proposed nonlinear approach, highlighting the advantages of its use in its scope of application. The obtained results are verified by finite element (FE) simulations, taken as a reference of the actual behavior assumed for the joints studied
Kinematics of Zigzagged Articulated Parallelograms with Articulated Braces (ZAPAB) mechanisms
No full textWe study the kinematics of Zigzagged Articulated Parallelograms with Articulated Braces (ZAPAB) mechanisms, a modular-based bars linkage characterized by a single Lagrange parameter, aimed to supply the microstructure for a third-gradient planar one-dimensional continuum after homogenization. We choose a specific geometry for the constituent planar modules of the ZAPAB mechanism, where each module is built upon rigid bars and hinges (nodes). The hinges are arranged in three layers: upper, middle, and lower. Thus, when perfect constraints are imposed, the placement and the length of each module depend uniquely on the selected Lagrangian parameter: the distance between adjacent, nonconnected nodes associated with the middle layer hinges. In this way, we introduce a mechanism in which a designated set of material points belong to a family of circumferences parameterized by a unique degree of freedom, when neglecting the global rigid motions. We prove, following a symmetry argument, that the allowed configurations for the considered ZAPAB mechanism are circumferences of different radii. Furthermore, given a reference length of the mechanism, we prove that, in the limit of a large number of modules, the length of the mechanism does not vary as the Lagrange parameter changes: the mechanism is inextensible. We give the analytical expression for the curve traced by the terminal point of ZAPAB mechanism. Therefore, this configuration of ZAPAB structure is a candidate to represent a synthesis for a particular class of third-gradient one-dimensional continua: those that are inextensible and whose deformation energy depends on the derivative of the curvature, with respect to its curvilinear abscissa
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
- …
