1,721,006 research outputs found
Advances in the metrological traceability and performance of X-ray computed tomography
No full textX-ray computed tomography (XCT) is increasingly being used for evaluating quality and conformance of complex products, including assemblies and additively manufactured parts. The metrological performance and traceability of XCT nevertheless remains an important research area that is reviewed in this paper. The error sources influencing XCT measurement results are discussed, along with related qualification, calibration and optimization procedures. Moreover, progress on performance verification testing and on the determination of task-specific measurement uncertainty is covered. Results of interlaboratory comparisons are summarized and performance in various dimensional measurement fields is illustrated. Conclusions and an outlook for future research activities are also provided
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
Electrical energy analysis and potential environmental improvements of sheet metal punching processes
No full textDiscrete part manufacturing processes, in particular non-conventional production processes, are still poorly documented in terms of environmental footprint. Within the separating processes, sheet metal punching processes have not been analyzed yet from environmental point of view. The present paper aims to contribute to filling this knowledge gap. In particular, two different punching machine tool architectures were analyzed. Following the previously developed CO2PE methodological approach, power studies and a preliminary time study have been performed in order to understand the contribution of each sub-unit towards the total energy demand. The influence of the most relevant process parameters (e.g. sheet thickness and punch perimeter) are analyzed regarding the required punching energy. Finally, several potential improvement strategies to reduce the punching energy consumption are reported
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
A Novel Tomographic Characterisation Approach for Sag and Dross Defects in Metal Additively Manufactured Channels
No full textChannels and bores in metal components produced by laser powder bed fusion (LPBF) are internal features that are typically affected by defects such as dross and sag formation, dimensional errors and global deformations in different proportions. Such deviations from the ideal geometry may strongly limit the functionality of the channels, but are difficult to prevent, due to complex multi-physical production aspects. Different destructive and non-destructive approaches are available to investigate the geometry of the internal features and possibly correlate their results to the LPBF process parameters; however, such approaches do not offer a systematic method to derive key characteristics of the main contributors for channel deviations. Hence, this work proposes a novel tomographic non-destructive analysis of LPBF channels and bores, focusing on the derivation of sag and dross key parameters. The methodology works on polar-transformed profiles obtained from image stacks which are extracted perpendicularly to the channel axis from the X-ray computed tomography (CT) reconstructed volume. The method allows for the clear determination of surface characteristics and includes the quantitative evaluation of descriptors through an algorithm specifically developed for the purpose. In particular, general form deviations are addressed by fitting sinusoidals on the unwrapped mean surface profile, to tackle deviations induced by thermal residual stresses. Proposed descriptors of sag and dross are the onset angle of protrusions, separation criteria between sag and dross effects, and the peak analysis of the mean profile after approximation with a least squares spline. The developed algorithm is tested in the case study of a LPBF AlSi7Mg0.6 benchmark part comprising hollow cylinders and inter-connecting frusta with different diameters. The resulting evaluation of the benchmark part also corroborates how the proposed methodology can help to obtain more precise information regarding the correlation of LPBF fabrication conditions and obtained channels geometrical deviations. Furthermore, the results show possible routes to enable an a-priori compensation of the nominal channel design for first-time right LPBF manufacturing.sponsorship: This research was funded by the EU Framework Programme for Research and Innovation -Horizon 2020 -Grant Agreement No 721383 within the PAM2 (Precision Additive Metal Manufacturing) research project. Umberto Paggi and Lore Thijs (3D Systems) are kindly acknowledged for the fabrication of the spyglass benchmark at the 3D Systems Leuven facilities. (EU Framework Programme for Research and Innovation -Horizon 2020 within the PAM2 (Precision Additive Metal Manufacturing) research project|721383)status: Published onlin
Geometrical metrology for metal additive manufacturing
No full textThe needs, requirements, and on-going and future research issues in geometrical metrology for metal additive manufacturing are addressed. The infrastructure under development for specification standards in AM is presented, and the research on geometrical dimensioning and tolerancing for AM is reviewed. Post-process metrology is covered, including the measurement of surface form, texture and internal features. In-process requirements and developments in AM are discussed along with the materials metrology that is pertinent to geometrical measurement. Issues of traceability, including benchmarking artefacts, are presented. The information in the review sections is summarized in a synthesis of current requirements and future research topics
Unravelling the dependency of dross formations in metal additively manufactured channels as a function of channel diameter and inclination angle
Full text linkIn recent years, the non-destructive characterisation via X-ray computed tomography of internal features, often produced with novel manufacturing methods, has gained increasing attention. Reducing the rate of defects during the production of internal features is of particular interest since post-processing steps are highly cumbersome, or removal of defects is, in many cases, even impossible for complex channels or bores. However, it is not sufficient to characterise the defects solely, but their root causes need to be understood in depth to allow for a-priori compensation approaches fostering first-time right part production. To achieve this, it is imperative to fully understand the connections and influences between the different factors, to enable the creation of versatile and scalable correction and compensation approaches. Within this scope, this work presents a characterisation of additively manufactured internal channels, focussing on dross defects encountered in overhang regions of the channel and their dependency as a function of a broad range of channel diameters and inclination angles. The extraction of the required information from the channels is based on cross-sectional images along the channel’s axis of the reconstructed 3D volume, obtained with high-resolution X-ray computed tomography. With the data obtained through an analysis algorithm presented in an earlier publication, it is possible to extract characteristic identifiers that can be used to calculate potential compensations counteracting the defects emerging during the printing. With the aid of these identifiers, it is possible to chart out general trends of the channel defects as a function of channel diameter and inclination angle. Therefore, the results allow to identify parameters where certain defects remain almost constant for a variation of the channel diameter.sponsorship: This research was funded by the EU Framework Programme for Research and Innovation-Horizon 2020-Grant Agreement No 721383 within the PAM2 (Precision Additive Metal Manufacturing) research project. (EU Framework Programme for Research and Innovation-Horizon 2020|721383)status: Publishe
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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