1,720,966 research outputs found
Parametric analysis of extended hemispherical dielectric lenses fed by a broadband connected array of leaky-wave slots
No full textIn this study, the authors examine the properties of a broadband array of leaky-wave slots located in the focal plane of an extended hemispherical dielectric lens, to generate several independent beams for imaging applications. The array performance is investigated over a 4:1 band. Parametric analyses are performed by varying the extension length of the lens and the off-axis distance of the feed point. The results of these analyses provide useful guidelines for the lens design. A spectral domain approach is used to characterise the field generated by the array, while a numerically efficient physical optics algorithm is employed for the analysis of the lens. Simulations performed with Computer Simulation Technology Microwave Studio are used for the validation of the combined analysis methods
Extended hemispherical lens fed by wideband arrays of connected leaky-wave slots
No full textWe propose an array of connected leaky-wave slots as feed of an extended hemispherical dielectric lens, for broadband imaging applications. Simulations of the entire structure, including array and lens, are performed by combining a spectral Green's function approach and an accelerated physical optics method. The antenna characteristics are investigated over a 4:1 bandwidth parametrically varying the feed off-axis distance (x/R, y/R) and the lens extension length (L). Measurements from prototype demonstrator are also presented to validate the method of analysis. © 2013 IEEE
Çift periyodik yapıların analizi ve tasarımı
No full textFrekans Seçici Yüzey, Yapay Manyetik İletken,
Metamalzeme vb. yapılar sivil ve askeri sektörlerde birçok uygulama alanı bulmaktadır. Her iki
yönde periyodiklik gösteren bu düzlemsel yapıların tasarımı, çoğunlukla önceki deneyimlere
dayalı ve deneme-yanılma tabanlı bir süreçtir. Sürecin zamansal ve parasal maliyetinin
düşürülmesi için genellikle simülasyon-prototipleme-ölçümleme döngüsü içerisinde bir iş akışı
uygulanmaktadır. Bu projede de amaç, literatürdeki öncü çalışmalardan yola çıkılarak ilgili
yapıların incelenmesi, özgün bir takım yapıların da sözü edilen süreç dâhilinde tasarlanmasıdır.
Analysis and Design of Double-Periodic Structures: Structures such as Frequency Selective
Surfaces, Artificial Magnetic Conductors, Metamaterials, etc. find various applications in
commercial and military sectors. The design of these planar structures with double-periodicity
is usually a trial-and-error based process relying on past experiences. In order to decrease the
monetary and temporal cost of this process, an iterative flow of simulation-prototypingmeasurement cycles is generally applied. In this project, the main aim is to investigate the
relevant structures departing from the pioneering studies in the literature, and to design some
novel structures via the aforementioned process
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
Quasi-optical system for the DESHIMA spectrometer
No full textDESHIMA is a superconducting on-chip spectrometer using MKIDs in the sub-mm wavelength regime (240-720 GHz, 1:3 bandwidth). This thesis presents (1) an analysis of the quasi-optical system used for DESHIMA on the ASTE telescope in Chile (2) design of the room-temperature optics of this design and (3) a preliminary investigation into an ultra-wideband leaky-lens antenna suitable for multi-pixel, constant aperture efficiency operation to be used as a feed to high f-number (>2) reflectors. The designed and analyzed optics show good performance and tolerance for the fall 2017 campaign of DESHIMA-on-ASTE. The wideband investigation leads to constant, >70% optical efficiency over the 1:3 bandwidth for a single pixel design (f-num=3.7) or >55% optical efficiency with multiple pixels spaced at 2*\lambda*f-number (f-num=5). Future work must be done to optimize the radiation efficiency of the antenna over the whole bandwidth, which is now the largest obstacle to frequency-dispersion free aperture efficiency.DESHIMAElectrical Engineerin
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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