1,721,045 research outputs found
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
Wear and elastohydrodynamic lubrication studies of cams and followers
No full textThe concentrated non-conformal contact between the cam and the follower is one of the most severe working tribological components in the internal combustion engine. Due to the continuous variation of load, speed and geometry, this contact is very difficult to be investigated.
This work is mainly devoted to review the wear and elastohydrodynamic film thickness studies related to this important engine mechanism and is divided into two parts.
In the first part a review is made of theoretical/numerical studies addressed to predict the film thickness, pressure distribution and their relations with the most common surface failures as pitting and scuffing.
The second part is committed to show the experimental efforts that have been carried out to estimate the real film thickness and the force friction in order to improve the durability of mating cam/follower surfaces under elastohydrodynamic lubricating regimen. A new versatile experimental apparatus under development is also presented
Experimental apparatus for film thickness and friction measurements on gear teeth and cam-follower contacts
No full textGear teeth and cam-follower couplings are typical non-conformal contacts working under transient elastohydrodynamic conditions undergoing variations of load, speed and geometry. Therefore, both numerical and experimental simulation of these contacts are difficult. Experimental results can validate numerical results and furnish useful indications for design optimization of gears and cam systems.
In this work, a new test rig is presented that has been purposely designed for investigations on lubricated contacts working under transient conditions, as gear teeth and cam-follower contacts.
Some theoretical/numerical simulations has been performed to investigate the dynamic behaviour of the apparatus to obtain important indications for its design.
The contact is formed between a specimen of suitable shape moved by an electric motor and a flat counterface. The load is applied thanks to a lever system and calibrated springs. Film thickness and contact forces are the main quantities measured by the experimental apparatus. Film thickness and shape are estimated using optical interferometry; interference images are recorded using a microscope connected with a computer controlled high-speed camera when using glass counterfaces. A complex dynamometric system with load cells has been realised for measuring all components of the contact force. An air cooled insulated base is used for thermal insulation. A real-time controller and data acquisition system are used
Sviluppo di un’attrezzatura per la simulazione di contatti fra camma e piattello e fra denti di ingranaggi
No full textI sistemi costituiti da camma-piattello e denti di ingranaggi sono tipici contatti non conformi, che lavorano sotto condizioni elastoidrodinamiche transitorie a causa della variazione di carichi, velocità e geometria. Per questo motivo sia la simulazione numerica che quella sperimentale di tali contatti sono difficoltose. I risultati sperimentali sono fondamentali per validare quelli numerici e fornire utili indicazioni per l'ottimizzazione dei sistemi a camme.
In questo lavoro è descritta una nuova attrezzatura sperimentale, progettata per lo studio di contatti lubrificati in condizioni di transitorio, proprio come il contatto camma-piattello e quello fra denti di ingranaggi. Sono state effettuate alcune simulazioni teorico-numeriche per studiare il comportamento dinamico dell'attrezzatura utilizzando profili di camme diversi e variando velocità di rotazione
Dynamic aspects of a new experimental apparatus for tribological investigations on cam-follower pairs
No full textThe cam-follower mechanism is one of the most complex lubricated contacts, due to its continuous variations of load, velocity and geometry. Both theoretical-numerical and experimental studies are very difficult to perform and need to be often done in parallel. Numerical simulations need an experimental verification and experiments need often a dynamic simulation for a better interpretation of the experimental results and also for design purposes. In this work the importance of the dynamic behaviour of the whole system connected to a cam-follower pair is evidenced. A new experimental apparatus has been designed with the aid of a simulation programme contemporaneously developed. Different versions of the apparatus have been analysed with purposely developed versions of the programme, particularly for a correct estimation of the contact load. Some sample results obtained for a cam with a spline profile used with two versions of the apparatus are presented. The influence of the dynamic effects particularly on the contact load is shown
Experimental study of engine cam-followers
No full textThe cam-follower pair is a very complex lubricated contact because its continuous variation of load, speed and radius of curvature. Experimental verification are necessary but very difficult to perform. After a literature review of the existing test rigs for cam-follower simulation, the main aspects of a new versatile apparatus are presented. Several design variations are presented, each one with its advantages and drawbacks. The final project will take into account some of the presented design solutions and the results of dynamic simulations of the rigs currently under elaboration
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
- …
