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A numerical algorithm for the solution of two-dimensional rough contact problems
No full textIn this paper, a numerical algorithm is developed to solve the elastic contact problem accurately for two-dimensional rough surfaces. A first version of the method gives a full numerical solution for the discrete problem with all the details of the profile included, and the second version simulates approximately the roughness on a smaller scale with the presence of a non-linear elastic layer (as in the classical Winkler foundation model). In the literature, usually the solution of line contact is given by assuming displacements relative to a datum point, to overcome the difficulty that in two dimensions the displacements are undefined to an arbitrary constant. In the present work, the compliance matrix of the elastic half-plane is calculated starting from a self-equilibrated load distribution with periodic boundary conditions. Some examples are shown to validate the methods. Finally, the method is applied to discuss previous results by the present authors on rough contact problems defined by Weierstrass series profiles, and a discussion follows. In particular, it is found that the Winkler non-linear layer model is surprisingly useful for evaluating the electrical conductance, since (at least in the limited case of two superposed sinusoids) it does not require the wavelength and amplitude of the microscopic component of roughness to be much smaller than the macroscopic component. Some aspects of the mutual role of various components of roughness in the compliance and conductance are elucidated by means of example cases
On the elastic contact of rough surfaces: Numerical experiments and comparisons with recent theories
No full textSome numerical experiments are conducted for studying the decrease of the elastic contact area in the elastic contact of fractal random surfaces when adding components of roughness of progressively smaller wavelengths. In particular, Fourier and Weierstrass random series are used, and a recent accurate and efficient method developed by the authors is used, involving superpositions of overlapping triangles. Some comparisons are made using two recent theories, that of Ciavarella et al. published in 2000 on the deterministic Weierstrass fractal profile, and that of Persson published in 2001 on random generic contact. We show that both theories tend to underpredict the contact area by a significant (and similar) factor in these representative cases in the region of light loads (partial contact), where the non-linearities of the contact mechanics are not included in neither of the formulations. In Persson's theory case, the discrepancy is particularly large at high fractal dimensions of the profile, where in theory the numerical experiments should be more closely reproducing a true Gaussian process. The Ciavarella et al. "Archard-like" theory, is only accurate when the parameter gamma (the ratio of successive wavelengths) is unrealistically large. However, we only tested the Ciavarella et al. theory in the simplified "Hertzian approximation" form assuming partial contact at the peaks of contact, although we don't expect the full version to improve dramatically the results. (c) 2006 Elsevier B.V. All rights reserved
Risposta del fagiolo borlotto all’irrigazione con acque a diverse concentrazioni saline e SAR.
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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
Patients with ovarian lesions: spectrum of diseases evaluated with contrast enhanced ultrasound
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