1,721,043 research outputs found
Comparison of THz backward wave oscillators based on corrugated waveguides.
No full textThe backward wave oscillator is a promising and powerful source at THz frequencies. The rectangular corrugated waveguide is an effective solution as slow wave structure to design backward-wave oscillators (BWOs), suitable to be fabricated by photolithographic high-aspect ratio processes. However, assembling and vacuum pumping are a critical issue. In this paper, a corrugated waveguide with the width of the corrugation narrower than the waveguide width will be investigated as slow wave structure for BWOs. A relevant improvement from the point of view of the assembling, together with even better performance will be demonstrated. Two backward wave oscillators, at 1 THz central frequency, designed with conventional and narrow corrugated waveguide will be compared in terms of output power and frequency band of tuning
Corrugated Rectangular Waveguide Tunable Backward Wave Oscillator for Terahertz Applications
No full textA tunable backward wave oscillator (BWO) for terahertz applications is proposed. The use of a corrugated rectangular waveguide as the slow-wave structure permits relevant performance together with full compatibility with microfabrication technologies. The design, done using an analytical electromagnetic model, is fully verified by 3-D particle-in-cell simulations. A 20% tuning bandwidth is obtained at a central frequency of 1 THz, demonstrating more than 100-mW output power
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
Double-Corrugated Rectangular Waveguide Slow-Wave Structure for Terahertz Vacuum Devices
No full textA novel rectangular-corrugated waveguide is proposed for submillimeter and terahertz vacuum devices. Two parallel corrugations that are enclosed in a rectangular waveguide create a beam channel that supports an interaction with a cylindrical electron beam. A notable advantage of the double-corrugated rectangular waveguide slow-wave structure (SWS) is the extension of well-established cylindrical beam technology to corrugated waveguide SWSs. The structure is also fully realizable with the most recent microfabrication techniques and is easily assembled. A detailed study to describe the electromagnetic behavior of the presented SWS is performed by 3-D electromagnetic simulation. A 650-GHz backward-wave oscillator and a 227-GHz traveling-wave tube are designed and simulated, by 3-D particle-in-cell code, to highlight the great potential of the double-corrugated rectangular waveguide for submillimeter frequency vacuum devices
- …
