1,720,974 research outputs found
Friction and Wear: From Elementary Mechanisms to Macroscopic Behavior
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
TIRE WEAR PARTICLE HOT SPOTS – REVIEW OF INFLUENCING FACTORS
Get PDFAutomotive tires have played an important role in land-based transportation and will probably continue to do so for many years to come. During their service lifetime, parts of the outer protector layer are worn off and discarded into the environment. A typical passenger car emits about 120 micrograms of rubber per meter but the exact current value depends on a multitude of influencing factors and varies greatly. We review available data on the wear rate (or inverse expected lifetime) of automotive rubber tires and extract qualitative estimations on how the most important parameters alter the deposition rate on a given road section. Local hot spots of increased tire wear particle occurrence can be identified from these parameters. It is concluded that generally subjecting tires to milder usage conditions can reduce tire wear by substantial amounts. Reducing vehicle speeds is identified as the most effective general measure
Normalsteifigkeit mehrskaliger rauer Oberflächen in elastischem Kontakt
No full textTechnische Oberflächen sind rau. Werden zwei raue Oberflächen mittels wirkender Normalkraft zusammengebracht, so werden Sie sich in der Nähe der Rauheitsspitzen (Asperiten) deformieren und so ihre Form angleichen. Zum theoretischen Verständnis der Kontaktmechanik ist das elastische Eindruckverhalten fraktaler Oberflächen von großem Interesse. Solche Oberflächen besitzen Rauheiten auf mehreren Skalen, ggf. von Nanometern bis Metern. Der Eindruckvorgang kann beschrieben werden durch die Abhängigkeit der Kontaktsteifigkeit von der wirkenden Normalkraft. In der Vergangenheit wurde hierfür durch verschiedene theoretische und numerische Ansätze allgemein eine Potenzabhängigkeit vorgeschlagen. So ergaben verbesserte Asperitenmodelle mit elastischer Interaktion Exponenten zwischen 0.6 und 1. Die Diffusionstheorie nach Bo Persson, angewendet auf nominell glatte fraktale Oberflächen, ergibt eine lineare Abhängigkeit, entsprechend Exponent 1. Die Diskrepanz zwischen den verschiedenen Ansätzen ist bisher nicht geklärt worden. Die hier präsentierte Arbeit behandelt das Problem ebenfalls numerisch mit Hilfe der Randelementemethode und findet eine Potenzabhängigkeit. Dabei wird eine Abhängigkeit des Exponenten vom geometrischen Rauheitsparameter Hurst Exponent festgestellt und diese quantifiziert. Es werden auch Studien mit der Methode der Dimensionsreduktion durchgeführt, mit gleichem Ergebnis. Eine besondere Erkenntnis stellt die Herleitung einer analytischen Formel zur Beschreibung der o.g. Abhängigkeit dar. Sie wird im Wesentlichen erreicht durch Herstellen einer Analogie zum Eindruckverhalten eines rotationssymmetrischen Indenters, wie es bereits in den 1950er/60er Jahren von Galin/Sneddon gelöst wurde. Die hier neu gewonnenen Erkenntnisse werden auf makroskopisch glatte und gekrümmte Oberflächen angewendet, wobei geschlossene Lösungen gefunden werden.Engineering surfaces are rough. When two rough surfaces are brought into contact by applying a normal force, these surfaces will deform in the vicinity of the opposing top peaks (asperities). For both theoretical understanding and analysis the indentation of fractal rough surfaces has caught researchers’ interest. These surfaces include roughness features at multiple length scales, possibly ranging from nanometers to meters. The actual indentation process can be characterized by the dependency of the contact stiffness on the applied normal force. In the past, researchers have suggested a general power-law dependency using different analytical and numerical approaches. For examples, advanced multi-asperity-models including elastic interaction suggested an exponent between 0.6 and 1. According to the diffusion theory by Bo Persson, the dependence should be linear, thus have the exponent 1. The discrepancy between different approaches has not been entirely resolved. The present work introduces numerical results obtained by means of the boundary element method and finds a power-law behavior. A clear dependency of the exponent on the Hurst exponent is found and described quantitatively. Studies conducted with the method of dimensionality reduction confirm these results. Special insight is given by the derivation of an analytical formula describing this dependency. It is based mainly on the analogy between a fractal roughness and rotational symmetric indenter shape. The indentation of the latter had been solved in the 1950s and 60s by Galin/Sneddon. The results obtained in this thesis are applied to nominally flat and curved surfaces, where closed-form solutions are found. In the past, researchers have suggested a general power-law dependency using different analytical and numerical approaches. For examples, advanced multi-asperity-models including elastic interaction suggested an exponent between 0.6 and 1. According to the diffusion theory by Bo Persson, the dependence should be linear, thus have the exponent 1. The discrepancy between different approaches has not been entirely resolved. The present work introduces numerical results obtained by means of the boundary element method and finds a power-law behavior. A clear dependency of the exponent on the Hurst exponent is found and described quantitatively. Studies conducted with the method of dimensionality reduction confirm these results. Special insight is given by the derivation of an analytical formula describing this dependency. It is based mainly on the analogy between a fractal roughness and rotational symmetric indenter shape. The indentation of the latter had been solved in the 1950s and 60s by Galin/Sneddon. The results obtained in this thesis are applied to nominally flat and curved surfaces, where closed-form solutions are found
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Friction Influenced by Vibrations: A Refined Contact-Mechanics View on Lateral and Rotational Oscillations
Get PDFIt is known that superposed movements can lower the friction felt at the macroscale. This is well documented for in-plane and normal translatory oscillations. Contact mechanics are a suitable approach to model this effect but so far have not gone beyond single-slider dynamics. In this study, we make use of 3D Boundary Elements Simulations to study the macroscopic friction reduction. This approach allows us to take into account also partial sliding of the contact zone. We first revisit the case of transversal in-plane translatory oscillations. Here, we argue that the behavior at small velocities can best be described when partial slip is indeed taken into account. Next, we investigate the frictional response of a Hertzian indenter when the lateral movement is superposed with a rotational bore movement. An analytical approximation is given for the steady state solution with constant angular velocity. The third case under investigation is an oscillating bore rotation. We present numerical results for the reduction of the macroscopic friction. In two limiting cases, an analytical prediction is given, following the lines used in the translatory case. For extremely large amplitudes, it is based on the idea that a rotational steady state is assumed at every instant. For small velocities we adapt our new approach including partial sliding. We find these predictions to be good but not perfect, slightly underestimating the reduction that rotational oscillations can provide.TU Berlin, Open-Access-Mittel – 202
- …
