1,720,997 research outputs found
Radar cross section analysis of various objects and RCS optimisation [Muhtelif cisimlerin radar kesit alani analizleri ve RKA optimizasyonu]
No full textThis work is based on the analysis and optimization of the radar cross section that is indispensable for today's defense industry. In this study, radar cross section analysis of many objects from simple geometric structures to military vehicles are made. Nowadays, when the electronic war technology is growing rapidly in, the stealth technology in radar systems became one of the indispensable factors of the defence industry and is used widely in air, land, sea and undersea platforms. Usuage of these techniques that reduces the dedection probability of vehicles that are very important for a country such as ship, plane, helicopter, submarine, etc. is a very important technology in defence industry. On this scope by working on stealth technolgy the methods for reducing radar cross section was investigated detailed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Wideband Integrated Lens Antennas for Terahertz Deep Space Investigation
No full textThe Terahertz (THz) band is the portion of the spectrum that covers a frequency range from 300 GHz to 3 THz. The potential of this band has been proven for numerous type of applications including medical imaging, non-destructive testing, space observation, spectroscopy and security screening, thanks to its good compromise between the spatial resolution and penetration. Most of these applications demand for high spatial and range resolution of the images, as well as fast acquisition time. To fulll such requirements, focal plane arrays (FPAs) need to comprise a large number of elements and be able to operate over broad bandwidths. Moreover, fabrication of the FPAs with thousands of antenna elements becomes a real issue at such frequencies due to the fabrications constraints and immense manufacturing costs.This doctoral thesis consists of two parts: Part I focuses on the design of the lens antennas using a multiple feed per lens scenario, specically aiming at imaging for security and the telecommunication systems as potential applications. The aim of the study is to design integrated lens antennas to achieve frequency stable radiation characteristics either to obtain an ecient reflector illumination or to be used directly as an imager over a wideband operation, typically more than one octave. In the literature, double slot antennas have been widely proposed as an ecient lens feeder, yet they are able to operate within a very narrow bandwidth, in the order of 10 - 15%. Due to its wideband characteristics connected array of leaky slot antenna concept has been used as a lens feeder. Depending on the application type, two dierent approaches have been implemented to achieve frequency independent lens radiation: A coherently fed connected leaky slot array based design with a traditional extended hemi-spherical lens for phased array antenna applications and an integrated double shell lens based design where each source element is associated to an independent beam for telecommunication and security systems.Part II of the thesis focuses on a single feed per lens scenario, specifically aiming at Terahertz (THz) astronomy applications. Such applications mostly require antennas consist of multi-pixels with large operational bandwidths. Many of the sub-mm wave instruments done for this kind of applications are envisioned to have large format focal plane arrays (FPA) that are based on single beam per feed and tight sampling and are coupled to reflector systems with large F/D ratios. Future satellite based, astronomic THz radiometers will be most likely based on cryogenically cooled detectors to reach the highest sensitivities, will consist of tens of thousands receivers to provide a broad eld of view and could address simultaneously a broad portion of the THz band. Several type of reflector feeds have been proposed in the literature including the Vivaldi antennas, horn antennas and the eleven antennas. These antennas, however, are typically optimized to maximize the reflector illumination eciencies as a single reflector feed. As a result, they suer fromthe feed taper eciency which is crucial to characterize the total system performance for tightly packed FPAs. No need to mention about the feasibility issues when it comes to the fabrication of the thousands of array elements with the manufacturing techniques available nowadays in sub-mm band. Integrated lens antennas, on the other hand, are widely used in sub-mm band since they allow the integration of the antenna and the detector on the same chip. Space instruments based on cryogenic power detectors often use focal plane arrays based on dielectric lenses. In the literature, the most commonly used lens feed is a double slot antenna, which typically operates in a bandwidth much less than one octave and with single polarization. Sinuous and spiral antennas have been also proposed as wideband lens antenna solutions. However, the fabrication of the feeding lines integrated to the antenna becomes challenging at sub-mm band since they have to be extremely tiny in order not to disturb the radiated elds. To overcome these issues, we propose a highly ecient, dual-polarized wideband leaky lens antenna design that can be integrated to planar feeding lines on the same chip. To our knowledge, the proposed design is the only practical wideband dual polarized antenna solution presently available at sub-mm wave frequencies which lends itself as an extremely useful alternative for next generation sub-mm wave space astronomical instruments.Tera-Hertz Sensin
Variations on the Author
Get PDF“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
Get PDFWe 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
Convex parabolic reflector antenna design with cosecant-squared radiation pattern for microwave radar systems [Mikrodalga radar sistemleri i̇çin kosekant-kare işima desenli dişbükey parabolik yansitici anten tasarimi]
No full textIn this paper, symmetric and cosecant-squared radiation patterns are obtained by using parabolic reflector antennas which have different geometrical structres. The analytical regularization method (ARM) is used to solve the problem of E-polarized wave diffraction by parabolic shaped perfectly electrical conductive (PEC) cylindrical reflector with finite thickness. The initial boundry value problem is reduced to the infinite algebraic system of the second kind, which is an equation that can in principal be solved with any predetermined accuracy by means of the truncation number. The parabolic reflector is fed by a horn antenna which is designed to illuminate the reflector aperture efficiently. In contrast to traditional parabolic reflector structure that is used to obtain pencil beam, the upper side of the reflector geometry is designed as convex to obtain cosecant-squared radiation pattern and the obtained far-field radiation patterns are investigated
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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