1,720,959 research outputs found
Integrated measurement system for high speed unsteady plasma flow and its application to electric arcs
No full textAn integrated measurement system for the study of high speed and high temperature unsteady plasma flows, such as those found in the vicinity of high current switching arcs, is presented. An optical high-speed imaging system is integrated with pressure sensing and spectroscopic measurement to gain insight into the complex unsteady flows in applications such as circuit breakers and internal combustion engines. The system permits direct and non-intrusive measurement to obtain new data on these transient events, which occur over a period of a few milliseconds. The imaging system captures at a rate of 1000 000 images per second. Software techniques have been developed to control light sensitivity, to generate dynamic images of the high-speed flows; to measure trajectories, times, velocities, pressure change, and to analyse gaseous composition in the tested device simultaneously. The range of applications for this system is very wide. For demonstration purposes, a study of the electric arcing process within a low-voltage circuit breaker and an aeroplane engine ignition unit is presented. This is the first time that a system has been developed to provide detailed measurement of arc root immobility time and arc motion
Evaluation of various fluid-film models for use in the analysis of squeeze film dampers with a central groove
Full text linkExperimental vibration responses of squeeze film dampers (SFDs) are obtained with four different central groove depths, two types of lubricant and various unbalance levels. Highly non-linear fluid stiffness and damping are observed, the damping being sensitively related to oil viscosity and unbalance. Existing oil film models are applied to predict the SFD behaviour. A special groove-two land model is able to predict the vibration behaviour of a very shallow grooved SFD and the conventional two-land theory is applicable to a SFD with a very deep groove. These observations provide useful guidelines for designing a shallow or deep grooved SFD-rotor assembly
Reduced order modelling methods to assess the overall vibration response of a flexible rotor-squeeze film damper assembly
No full textThis paper uses two reduced-order methods to calculate the overall non-linear vibration response of a multi-mode rotor-squeeze film damper (SFD) bearing assembly. Good agreement has been found between their computed results and those calculated by the conventional Runge-Kutta-Merson method (RKMM), yet they require less than 5 per cent of the computing time consumed by the RKMM. They are applied to compute the vibration response, three-dimensional deflection shape and the overall vibrational kinetic energy of the rotor-bearing assembly. The assembly is simulated under various operating conditions including different unbalances, oil viscosities, static misalignments and damper factors. It is concluded that effective vibration control of a flexible rotor-SFD bearing assembly can be achieved when the vertical static eccentricity ratio of the SFD is set to a certain limit
A theoretical and experimental investigation into the vibration response of a flexible rotor and squeeze film damper assembly
No full textThis paper presents two efficient methods to calculate the unbalance vibration response of a flexible rotor provided with a squeeze-film damper (SFD) with retainer springs. Both methods are iterative and combine the harmonic balance and receptance approaches. The first method, called the modified iteration method (MIM), is suitable for predicting the three-dimensional mode shapes of a concentric SFD-rotor system. The second method, called the modified harmonic balance method (MHBM), is developed to calculate the non-linear vibration response of a flexible shaft provided with either a concentric or eccentric SFD. The system is also investigated experimentally under different conditions. The predictions computed by these methods are compared with experimental measurements and reasonably good agreement is obtained
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
- …
