1,721,005 research outputs found
An investigation into the surface characteristics of three-dimensional objects
No full textThis thesis presents three-dimensional surface metrology techniques suitable for the appraisal 'of curved surfaces. Instrument requirements for measuring 3-D curved surfaces are discussed and four instruments selected which meet these requirements. These instruments are a Laser Radius-scope, Fizeau Interferometer, Laser Ranging Probe and a Stylus Profilometer.Numerical algorithms for assessing the data from these instruments are then considered, with particular emphasis being placed on the evaluation of the radius of curvature of the surface, removal of this best-fit sphere from the data and visualisation of the resulting errors of form. New circle and sphere-fitting algorithms are presented for radius of curvature analysis. These numerical methods, together with a number of standard, well documented routines (least-squares circle and sphere) are then tested for their sensitivity to a number of sample parameters on ideal, computer generated data sets. The parameters tested are sample length/area, radius of curvature, centre offset and surface roughness.The new techniques show a considerable improvement in estimating the radius of the test data; in the presence of + I0.00/*m peak-to-valley surface roughness, the new circle-fit routine produced a radius error of 0.32/xm as opposed to -0.85/*m for the least-squares circle routine, whilst the new sphere-fit had a radius error of 2.29jum compared to the least-squares sphere's error of -3.64/xm. The new sphere-fit also reduces the computation times on a 66MHz. 486DX2 Personal Computer from 14.89 seconds for least-squares sphere to 0.66 seconds.Four studies are then carried out on nominally spherical samples of varying dimensions, radius of curvature and surface finish. The studies assess the radius of curvature of the samples, either directly for the Laser Radius-scope and Fizeau Interferometer or, in the case of the Laser Ranging Probe and the Stylus Profilometer, by the application of the numerical routines previously tested.The advantages, limitations and faults of each instrument are discussed and it is concluded that despite the stylus profiler's instrumentational flaws, it offers the most flexible method of measuring the three-dimensional surface profiles of curved surfaces
The surface area and localised 3D roughness of a highly structured surface using X-Ray Computed tomography (XCT)
No full textThe characterisation of a highly structured surface is explored. The surface investigated has both high aspect ratio and hidden features. A regular AgNi (80/20) electrical contact has been structured using a scanning electron-beam, with the objective of wear reduction during arcing events. An X-Ray Computed tomography system (XCT) is used to provide data of the whole surface and the data then referenced against a standard calibrated high gauge confocal optical surface metrology system using standard surface metrology software. To allow the surface analysis of the XCT data, the workflow and associated data processing steps are described. The results show that the XCT method provides surface data on the whole surface area including the hidden features, but that the data resolution and associated uncertainty, limits the accuracy of the roughness evaluation. The full surface area is determined using a combination of optical and XCT data
Volumetric erosion of a structured electrical contact surface using X-Ray Computed Tomography
No full textThe use of 3D optical scanning methods is well established for the evaluation of volumetric wear on electrical contact surfaces. A longstanding limitation of these methods has been the accuracy to which the underlying form of the surface prior to the wear process is determined. Electrical contact surfaces are never perfectly flat, in many applications the underlying surface is nominally spherical or a freeform surface. This paper introduces newly developed methodes to enhance the capability of resolving volumetric wear on a surface with complex shape (form). These methods are applicable to a wide range of applications, but the focus here is on arcing elec-trical contacts. The paper investigates wear on a nominally spherical AgNi contact used in low voltage switch-ing applications and compares this to the wear on a surface modified using electron beam process to create a highly structured surface; under the same switching conditions. The spherical contact is analysed using a new 3D optical metrology solution using a data fusion method, which combines both metrology data and surface photographic image data. The 3D optical scanning data is then compared with surface data from X-Ray comput-ed tomography (X-CT) of the structured electrical contact surface
Agent-based Traffic Operator Training Environments for Evacuation Scenarios
No full textRealistic simulation environments play a vital role in the effective training of traffic controllers to respond to large-scale events such as natural disasters or terrorist threats. BAE SYSTEMS is developing a training environment that comprises of: a physical traffic control centre environment, a 3D visualisation and a traffic behaviour model. In this paper, we describe how an agent-based approach has been essential in the development of the traffic operator training environment, especially for constructing the required behavioural models. The simulator has been applied to an evacuation scenario, for which an agent-based model has been developed which models a variety of relevant driver evacuation behaviours. These unusual behaviours have been observed occurring in real-life evacuations but to date have not been incorporated in traffic simulators. In addition, our agent-based approach includes flexibility within the simulator to respond to the variety of decisions traffic controllers can make, as well as achieving a strong degree of control for the scenario manager
The uncertainty of radius estimation in least-squares sphere-fitting, with an introduction to a new summation based method
No full textThis paper considers the sensitivity of three sphere-fitting algorithms to real-world measurement errors. It pays particular attention to nominally spherical surfaces, such as those typically measured by tactile and optical profilometers, addressing the limitations of sensor gauge range and angular tolerance. A recently proposed linear circle-fitting algorithm is extended to a sphere-fitting algorithm and its performance compared to two long standing sphere-fitting algorithms; namely linear and non-linear least-squares. Sources of measurement error in optical profilometers are discussed, and user defined scan parameters are optimised based on the results of a designed experiment. The performance of all three sphere-fitting algorithms are tested on a sphere superimposed with varying degrees of surface irregularities in a Monte Carlo simulation; this study shows that both linear routines display a negative skewness in their radius error distribution. Finally, a method of predicting radius uncertainty is offered that considers the surface residual that remains after sphere-fitting and relates this to the radius uncertainty of the chosen algorithm
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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