1,720,998 research outputs found
Diffraction Tomographic Imaging of Shallowly Buried Targets using Ground Penetrating Radar
No full textThe problem of subsurface imaging with Ground Penetrating Radar (GPR) is a challenging one. Due to the low-pass nature of soil sensors must utilise wave-lengths that are of the same order of magnitude as the object being imaged. This makes imaging difficult as straight ray approximations commonly used in higher frequency applications cannot be used. The problem becomes even more challenging when the target is shallowly buried as in this case the ground surface reflection and the near-field parameters of the radar need to be considered. This thesis has investigated the problem of imaging shallowly buried targets with GPR. Two distinct problems exist in this field radar design and the design of inverse scattering techniques. This thesis focuses on the design of inverse scattering techniques capable of taking the electric field measurements from the receiver and providing accurate images of the scatterer in real time.\ud
\ud
\ud
\ud
The thesis commences with a brief introduction to GPR theory. It then provides an extensive review of linear inverse scattering techniques applied to raw GPR data. As a result of this review the thesis draws the conclusion that, due to its strong foundations in Maxwell's equations, diffraction tomography is the most appropriate approach for imaging shallowly buried targets with GPR. A three-dimensional diffraction tomographic technique is then developed. This algorithm forms the primary contribution of the thesis.\ud
\ud
\ud
\ud
The novel diffraction tomography technique improves on its predecessors by catering for shallowly buried targets, significant antenna heights and evanescent waves. This is also the first diffraction tomography technique to be derived for a range of antenna structures. The advantages of the novel technique are demonstrated first mathematically then on synthetic and finally practical data. The algorithm is shown to be of high practical value by producing accurate images of buried targets in real time
Imaging of buried targets with ground penetrating radar
No full textDiffraction tomographic imaging is applied to the imaging of shallowly buried targets with multi-bistatic arrays of transmitters and receivers
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
Predicting software change coupling
Full text linkThis project was an exploratory study of techniques for predicting future change coupling among a program's source code les. Two source code les are change coupled if programmers edit them together frequently, and separately infrequently. Speci cally, this project investigated the predictive power of three approaches: mining of software change logs, software similarity detection, and software proximity detection.Software mining extracts patterns from source code databases, that is, version control systems containing source code and change histories. This project explored whether identi cation of past change coupling among source code les can predict future change coupling among those les. Software similarity detection nds les that contain similar, alias cloned, code. This project explored whether identi cation of similar code among source code les can predict future change coupling among those les. Finally, software proximity detection nds les that reference each other heavily. This project explored whether identi cation of proximity among source code les can predict future change coupling among those les.This project performed the study applied a software miner (created speci cally for this project), three preexisting similarity detectors, and two proximity detectors (created speci cally for this project) to four large open source code databases at multiple points in time. It determined that software mining generally generated the best predictions of the three approaches, followed by similarity detection, followed by proximity detection.Excessive source code change coupling can be a serious maintenance problem. So the prediction of future change coupling is an important challenge in software engineering. The results of this project shed light on the abilities of the three approaches, both in the absolute and relative senses, to predict change coupling. So the results of this project hold promise for decreasing program maintenance costs.Ph.D., Information Science and Technology -- Drexel University, 200
- …
