1,721,005 research outputs found
Effects of a fin edge close to a point caustic of a Gregorian antenna
No full textThe problem of edge diffraction close to a point caustic is analyzed in a typical dual-reflector Gregorian antenna in offset configuration. The diffraction phenomenon is produced by a perfectly conducting fin located between the feeder and the main reflector. This fin is sometimes used to reduce the coupling between the primary feed and the main reflector. For the sake of simplicity, the two-dimensional case is studied here, but the present technique can also be applied to practical three-dimensional configurations. (C) 1997 John Wiley & Sons, Inc
A multiresonant slotted patch
No full textA configuration of a slotted patch antenna is introduced, which allows two or more separate operating frequencies. Both of them are associated with a radiating mode almost identical to that of a standard patch. The two resonances are related to the patch width and the slot/patch length respectively
A CAD‐oriented approach for aperture‐coupled patch antennas
No full textA simplified model is suggested for describing aperture-coupled patch antennas in CAD applications. The scattering parameters of the antenna are calculated by assuming a single mode distribution for the currents on the slot and on the microstrip-line. The coupling between the slot and the patch is represented by superimposing a contribution from a fundamental mode and that from higher order modes. The former is described by a complex eigenvalue of a cavity model with impedance walls. The latter is described by a parallel plate waveguide model, which properly accounts for the storage of reactive energy close to the slot. Numerical results are presented and compared with experiments. In particular, S-band patches have been fabricated and tested to demonstrate the accuracy of the model
Soil erosion induced by land use changes as determined by plough marks and field evidence in the Aksum area (Ethiopia)
No full textThe aim of the research presented here was to analyse soil erosion in response to changes in agricultural
and soil conservation practices throughout history. The Aksum area (Tigray, northern Ethiopia) presents
favourable conditions for the development of a long-term approach for assessing soil conservation techniques
that have been applied for centuries (i.e., since the Aksumite kingdom, 400 BC to 800 AD). These
techniques have been maintained until the present day, and parts of the terraced systems of the area are
still in use. During the 1970s, social and political events led to a remarkable change in land use patterns,
and large arable areas were converted into grazing land, resulting in a significant increase in soil loss.
The rates of soil erosion were evaluated based on analyses of the deep scratches (plough marks) left on
stones in the soil by the maresha, the ard plough pulled by oxen used in agricultural practices of the
area, and the patinas, varnishes and weathering rinds exposed by soil loss after the abandonment of the
fields. The study results show average rates of soil erosion of 2.8 t ha−1 y−1 and 65.8 t ha−1 y−1 for the soil
conservation conditions under traditional agriculture (long-term observations) and accelerated erosion
after abandonment (short-term observations), respectively. A comparison using recently calibrated erosion
evaluation techniques conducted to support the field measurements revealed a close correlation
between the calculated and recorded data
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
- …
