1,720,956 research outputs found
Réseau-réflecteur entièrement diélectrique fonctionnant dans la bande de fréquence millimétrique
No full textéquipe ISAencadré par Claire Migliaccio et jérôme LanteriLes réseaux-réflecteurs classiques sont constitués d'éléments imprimés sur un substrat diélectrique et ont un plan de masse métallique. Dans ce travail nous proposons de supprimer toutes les pièces métalliques et de les remplacer par une structure entièrement en diélectrique utilisant la technologie d'impression 3
Conception d'un système focalisant pour les communications point-à-point en bande millimétrique
No full textAs global wireless data demand continues to increase, more than one billion households around the world still lack access to reliable broadband connectivity. Fixed Wireless Access (FWA), especially when operating in millimeter-wave frequency bands, presents a compelling alternative to fiber and copper in underserved areas. However, millimeter-wave FWA faces considerable technical challenges, including high free-space path loss, limited beam-steering agility, and increased RF power consumption due to large phased array architectures. This thesis investigates a compact, high-gain antenna system that combines a 8 × 8 phased array with a Bragg-based dielectric reflectarray. This hybrid configuration enables efficient beam steering over a ± 15° angular range at 27 GHz, while requiring only a limited number of active RF chains. For operation at 39 GHz, a conventional circularly polarized reflectarray is used, positioned behind the Bragg-based reflectarray. Thanks to its engineered bandgap characteristics, the Bragg reflectarray becomes transparent at this frequency, enabling dual-band operation within a single radiating aperture.By selectively activating only a 2 x 2 sub-array for each beam, the system reduces power consumption and thermal load compared to traditional fully active phased arrays. Moreover, polarization diversity is integrated to strengthen link robustness and mitigate path loss effects in non-line-of-sight and multipath environments. The proposed antenna system has been validated through both simulation and experimental measurements. The results demonstrate that the proposed system meets the requirements of next-generation millimeter-wave FWA applications, where energy efficiency, spectral versatility, and compactness are critical design criteria.Alors que la demande mondiale en données sans fil ne cesse de croître, plus d'un milliard de foyers dans le monde restent privés d'un accès fiable à une connexion haut débit. L'Accès Fixe Sans Fil (FWA), notamment dans les bandes de fréquences millimétriques, constitue une alternative pertinente aux réseaux filaires (fibre optique ou cuivre) dans les zones mal desservies. Toutefois, le FWA en bande millimétrique se heurte à plusieurs défis techniques importants, tels que de fortes pertes de propagation en espace libre, une agilité limitée du dépointage de faisceau, ainsi qu'une consommation énergétique accrue liée aux architectures à réseaux phasés de grande taille. Cette thèse propose un système d'antenne compact et à gain élevé, combinant un réseau phasé 8 × 8 avec un réseau-réflecteur diélectrique à miroir de Bragg. Cette architecture hybride permet un balayage efficace du faisceau sur un secteur angulaire de ± 15° à 27 GHz, tout en ne nécessitant qu'un nombre limité de chaînes RF actives. À 39 GHz, un réseau-réflecteur conventionnel à polarisation circulaire est utilisé, positionné derrière le réseau-réflecteur à miroir de Bragg. Grâce à ses propriétés de bande interdite, celui-ci devient transparent à cette fréquence, permettant un fonctionnement bi-bande avec une seule ouverture rayonnante. En activant uniquement un sous-réseau 2 × 2 par faisceau, le système permet de réduire considérablement la consommation de puissance et la charge thermique par rapport aux réseaux phasés entièrement actifs. Par ailleurs, l'intégration d'une diversité de polarisation améliore la robustesse des liaisons et atténue les pertes en environnements complexes ou sans visibilité directe. Le système proposé a été validé par des simulations et des mesures expérimentales, confirmant sa pertinence pour les futures applications FWA en bande millimétrique, où efficacité énergétique, flexibilité spectrale et compacité sont des critères déterminants
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
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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