1,720,969 research outputs found
Experimental investigation on the influence of detector misalignment on X-ray CT measurement accuracy
No full textIn X-ray computed tomography (CT), measurement accuracy and image quality are strongly affected by the presence of geometrical
misalignments and/or the wrong estimation of CT system geometry . In this work, the effects of detector misalignment are
experimentally investigated. CT measurements of a calibrated ball bar were acquired first with the system aligned according to the
manufacturer’s guidelines, and then after that the flat-panel detector was physically misaligned. The experimental results were
compared to show the effects of detector misalignment on CT measurement errors
Computed tomography helical scanning for dimensional metrology: Evaluation of measurement errors
No full textIn industrial X-ray computed tomography, it is frequently necessary to scan long objects that exceed the dimensions of the detector, while meeting dimensional accuracy requirements (for example, in automotive and aerospace fields). Conventional scans using circular trajectories face limits when dealing with internal and complex features on elongated work pieces. To this extent helical scanning is a valuable solution that also enables obtaining a strong improvement on image quality, eliminating the cone beam artifacts that characterize conventional scans. To use helical scanning for dimensional quality control, the assessment of metrological performances is needed. In this work, metrological performances for helical scanning are investigated and compared with those of conventional circular scans. Repeated helical scans are performed to investigate the influence of main helical scans parameters when performing dimensional measurements. Experimental results show that helical scanning, with appropriate scan parameters, performs better than traditional circular scans with a strong improvement on image quality
Investigation on scan parameters for accurate dimensional measurements by CT helical scanning
No full textIn industrial X-ray computed tomography (CT), conventional scans using circular trajectories face limits when dealing with internal and complex features on elongated workpieces, mainly due to the dimensions of the detector. To this extent, helical scanning is a powerful solution that enhances flexibility of the system and, when using suitable parameters, enables obtaining a strong improvement on image quality, eliminating the cone-beam artifacts that characterize conventional scans. In this work, metrological performances in CT helical scanning are experimentally investigated and compared with those of conventional circular scans. The influence of main helical scan parameters are studied to enhance accuracy of dimensional measurements by CT helical scanning
Investigation on the effects of X-ray CT system geometrical misalignments on dimensional measurement errors
No full textX-ray CT measurements are affected by a multitude of influence factors, among which the correct estimation of the CT system geometry is of major importance. The presence of geometrical misalignment and/or the wrong estimation of system geometry, indeed, leads to artifacts and distortions in the measured volume, and to measurement errors when performing metrological tasks. That is why it is important to quantify the effects of geometrical misalignments or misestimation on CT measurement accuracy. In this work, the effects of detector misalignment are experimentally investigated on a metrology CT system. Physical misalignments were purposefully induced on a flat-panel detector for investigating the influence of a detector out of plane rotation on measurement results. The experimental results show the effects of the induced detector misalignment on center-to-center measurements, diameter and form measurements on a calibrated ball bar. The effects of the amplitude of the angular misalignment induced are also shown
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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