1,721,041 research outputs found
Analysis of a 3D optical scanner based on photogrammetry suitable for industrial applications in close and micro-range
Full text linkThe new paradigm of Industry 4.0 encompasses the manufacturing metrology and the necessity for fast, flexible, reliable and holistic systems arises, in order to accompany the more advanced manufacturing technologies. The more extensive use of additive manufacturing techniques, which entail the realization of complex structures and freeform geometries, as well as, the use of new materials, enhances this concept.
These driving forces are the basis for the great interest towards 3D scanning systems because
they perfectly fit the key factors of the new manufacturing metrology 4.0. Among other things, they have the capacity to reconstruct complete and detailed 3D models in a very short time, which makes them suitable for on-machine verification.
In this context, close-range photogrammetry is recognized as a simple, versatile, and effective
methodology for 3D measurements of components, even if they are characterized by a prevailing dimension respect to the others (e.g. height is much higher than length or vice versa), complex free form geometry, and under-cuts. Moreover, it is able to provide accurate measurements and 3D photorealistic (thanks to the computation of the texture) surface reconstructions in a simple and inexpensive way, as well as in very short time. Photogrammetry-based systems and, generally, optical-based techniques, are flexible and holistic systems, but their strengths are also their weaknesses, because this complexity results in more variables involved and more sources of error affecting the results.
The present thesis is focused on the development and the analysis of an optical 3D scanner based on photogrammetry, suitable for measurements of complex parts in close and micro range. The analysis started from the identification of the main sources of error affecting the measuring system, with the final goal to include them in a proper uncertainty assessment. In particular, there are errors due to the measuring system itself, errors due to the object under measurement, i.e. errors due to the manufacturing process, as well as, errors due to the interaction of the specific system with the object (materials, colours and surface texture). Thus, the uncertainty evaluation of such systems is still an open issue.
The first chapters are dedicated to the state of the art of currently available measuring techniques, highlighting the main advantages and drawbacks, in order to explain the importance of developing a photogrammetry-based system for industrial application.
The third chapter is of fundamental importance since it describes the state of the art of the currently available standards in 3D optical scanning. They mainly refer to the VDI/VDE 2634 series, in the form of acceptance and reverification test. In addition, the standards usually used for the uncertainty assessment of the more reliable Coordinate Measuring Machine (CMMs), such as the ISO 15530-3, were described, highlighting the main criticalities and the possible adaptation for optical-based scanners.
The forth chapter is entirely dedicated to photogrammetry-based systems, with a brief introduction to the state of the art when applying photogrammetry in close and micro range, a description of the measuring principle through the mathematical models behind and the main advances carried out in the development of the reconstruction software algorithms. Then, the photogrammetry-based system is presented together with the sensors and the optical equipment used throughout the thesis. Finally, a summary of the main criticalities is reported.
The experimental investigations carried out during the PhD course are collected in the chapters from 5 to 11. Each chapter is dedicated to a specific measuring task, with the aim to analyse a specific aspect or a criticality of the photogrammetry- based system under exam.
The fifth chapter is focused on the analysis of repeatability of the photogrammetric reconstruction software used, which has proved to be a fundamental part of the system. The study was conducted on a pyramidal artefact already used in previous experiments.
In the sixth chapter, a new three-dimensional reference artefact was presented. The purpose was double: for the estimation of the external orientation, scale adjustment, and for the uncertainty assessment, calibration. The effectiveness of this reference artefact was proved through the reconstruction of the test object used in the previous chapter, the pyramidal artefact.
The capacity of the presented system to reconstruct free form geometries was analysed through a preliminary test in Chapter 7. The tests were performed through the use of three artefacts produced by additive manufacturing techniques, which were a customized version of the NPL free form artefact designed and developed by NPL institute. The need for the customization was mainly due to the necessity to resize the artefact to make it measurable with the optical equipment under exam.
In Chapter 8, the application of the photogrammetry-based system for measuring additive manufactured biomedical devices was reported, highlighting critical aspects due to their object and surface textures characteristics.
Chapters 9 and 10 report the work conducted during the external stay period at the Department of Mechanical Engineering of the Denmark Technical University. The introduction of a step gauge reference artefact was analysed, and the photogrammetry-based system was then compared with other non-contact measuring techniques, such as structured light scanner, laser based scanner and a computed tomography scanner. The performance verification of all those
3D non-contact measuring techniques was conducted through the step gauge reference artefact. In chapter 10, the investigation was focused on the analysis of the interaction between the 3D optical scanning systems and the materials and colours of the objects under measurements. For the purpose, five miniature step gauges made of different polymeric materials and colours were scanned and analyzed.
Finally, Chapter 11 is dedicated to the application of the photogrammetry to the microscopic range, for the acquisition of components realized through μEDM (Electro Discharge Machining). The optical equipment, used in this investigation, allowed to reach magnification levels higher than 2x, with optical resolutions up to 2,4 μm. The investigation was mainly focused on the verification of the reproducibility of the internal parameters estimated through the traditional mathematical models, for such magnification levels
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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