1,720,991 research outputs found
IL PARCO DI VILLA TORRIGIANI (CAMIGLIANO – LU): APPLICAZIONE DEL VTA PER LA GESTIONE DEGLI ESEMPLARI ARBOREI E PER LA SICUREZZA DEI FRUITORI
No full textPractical range of applicability of a linear stiffness model of an elliptical flexure hinge
No full textThis paper presents the analysis of a linear stiffness model of an elliptical flexure hinge. The purpose of the study is to support the mechanical designer in choosing the geometric dimensions of the hinge based on design specifications, driven by the accuracy that can later be achieved in planning its motion using the related stiffness model. Results are presented as a comparison between the analytical model and a finite element model of the flexure hinge, showing the practical range of applicability of the analytical model and its limitations. A case study show how to design a flexure hinge of small size for micro scale robotic or mechatronic operations
TOWARDS THE SYNTHESIS OF PLANAR BEAMS WHOSE DEFORMATION ENERGY DEPENDS ON THE THIRD GRADIENT OF DISPLACEMENT
No full textWe exhibit a planar truss structure that, once homogenised at a macro-level, can be regarded (i.e., will need to be modelled) as a third-gradient beam, meaning a one dimensional continuum whose deformation energy depends on the third derivative of its displacement. We call it a ZAPAB structure, for z igzaged a rticulated p arallelograms with a rticulated b races. The idea of the construction is simple: we look for a planar mechanism formed by rigid bars and interconnecting terminal pivots (thus, a type of linkage) satisfying the following properties: (i) it has one degree of freedom characterised by one Lagrange parameter u ; (ii) in it, a specific set of material points initially lies on a straight line; (iii) when u varies, the positions of these points are equidistant and belong to circumferences whose radius depends on u ; (iv) their distance is a function of u . Suitably constraining the mechanism and assuming that the bars are elastic, the linkage becomes a planar ZAPAB truss structure. Since, in the configurations described in (ii), (iii) and (iv), no constituting bar is deformed, the class of zero- energy placements (floppy modes) for the ZAPAB structure, as a whole, consists exactly of circumferences with different radiuses. This implies that a planar one-dimensional continuum capable of describing as a whole the mechanical behaviour of ZAPAB structure must have a deformation energy depending on the derivative (with respect to its curvilinear abscissa) of the curvature. We present a first piece of evidence for this statement, by using numerical simulations based on a novel code that efficiently calculates the minimum deformation energy for ZAPAB structures. This promising result motivates future investigations and proves how artificial is the (typically bureaucratic and Italian) split between structural mechanics and mechanics applied to machines design: Lagrangian mechanics is their common conceptual basis
Insights into Bending Stiffness Modeling of Elementary Flexure Hinges
Full text linkFlexure hinges are widely used in mechanical devices, especially for micro- or even nano-scale applications, where conventional joints based on conjugate surfaces prove unsuitable. However, to achieve accurate motion of devices whose joints are flexure hinges, knowledge of stiffness models that correlate applied forces or bending moments with the resulting displacements is required. Nonlinear bending models are typically too complex and difficult to implement. Therefore, it is preferred to use linear models, which admit analytical solutions. The purpose of this paper is to show what is lost in terms of accuracy in reducing a nonlinear bending stiffness model associated with a flexure hinge when simplifications are made to obtain an analytical solution. An analysis of the simplification process leading to a linear stiffness model and its analytical solution is presented. From this study arises an increased awareness of flexure joints in terms of the accuracy obtained with their stiffness models, suggesting important information to the user in choosing the level of complexity required to model them in a specific application. A comparison between analytical and numerical results is provided in the form of maps and tables so as to make that choice as clear as possible
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
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