1,721,016 research outputs found
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
Ultra-high solar concentration for ultra-efficient photovoltaics: 1,000 suns and beyond
No full textNational audiencePhotovoltaic conversion under high solar flux concentration (1000 suns and more) has been popular for many years, because of the prospects it offers in terms of solar-to-electric conversion efficiency, but also because of the lower cost of the electricity produced by these systems (the cell surface area required being considerably reduced compared with conventional PV systems). However, the interest aroused by very high solar concentrations a few years ago now seems to be fading, despite its proven theoretical interest.In this presentation, we will try to take a step back from this technology by reviewing the physical principles justifying the development of PV cells under ultra-high solar flux (UH-CPV), discuss the limiting mechanisms leading to a degradation of actual cell performance, and establish an overview of cell technologies likely to benefit from ultra-high solar concentrations. We will begin with a few reminders related to the theoretical motivations underlying the development of PV cells for ultra-high solar concentrations. The second part of this presentation will review the principal limiting mechanisms that are likely to impact the efficiency of UH-CPV cells in practice. We will then examine the various solutions that have been developed to address these limitations. Particular attention will be paid to the subject of resistive losses, which is one of the most significant limiting mechanisms under high solar flux concentration, and which has inspired a great deal of work aimed at reducing their amplitude.The final section of this presentation will provide a review of solar cell technologies compatible with ultra-high solar concentrations, recalling the physical principles underlying each of these technologies, discussing the role of ultra-high solar concentrations in their operation, and listing the scientific and technological challenges to be overcome for each of them
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
COMPACT HYBRID SOLAR PHOTOVOLTAIC/THERMAL SYSTEMS: RECENT PROGRESS AND REMAINING CHALLENGES
No full textInternational audienceCompact hybrid PV/CSP systems have been suggested as a promising strategy to combine the high dispatchability of CSP systems, together with the high efficiency and the affordability of PV converters. Different approaches have been proposed, each one having its own system architecture, operating conditions, and light manipulation strategies. However, despite the significant amount of work dedicated to these systems in the last 5 years, it is still unclear whether this strategy may outperform conventional hybrid plants consisting of PV and CSP systems independently operated. Here, we’ll first review the recent work devoted to these systems, before addressing some key issues to be tackled toward ensuring an efficient operation of these systems in real operating conditions
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
Conversion haut-rendement de l’énergie solaire concentrée: de la théorie à la pratique
No full textCe manuscrit synthétise les travaux de recherche effectués au cours des 12 années qui se sont écoulées depuis ma soutenance de thèse. Les technologies photovoltaïques ont subi d'importants bouleversements au cours de cette période: la filière photovoltaïque à concentration, qui a constitué le fil conducteur de mes travaux de recherche depuis douze ans, fait indéniablement partie des filières sur le déclin. Les motivations scientifiques sous-jacentes, ainsi que les raisons qui ont probablement conduit à un désintérèt progressif de la communauté solaire et de l'industrie pour cette technologie, sont discutées dans le deuxième chapitre. Par essence, les systèmes photovoltaïques à concentration sont exposés à des conditions opératoires extrêmes (en termes de température de fonctionnement, ou de densité de puissance lumineuse absorbée), et la compréhension des mécanismes limitant susceptibles de conduire a une dégradation de leur performances en conditions réelles de fonctionnement est donc primordiale. Cette thématique de recherche a fait l'objet de nombreux travaux qui sont détaillés dans le troisième chapitre de ce manuscrit. L'optimisation et l'adaptation des architectures de cellules solaires aux conditions extrêmes de fonctionnement caractéristiques des systèmes CPV sous très hautes concentrations a également fait l'objet de travaux de recherches, dont les principaux résultats sont présentés dans le quatrième chapitre. L'hybridation de systèmes PV ou CPV conventionnels avec des systèmes de conversion thermodynamiques de l'énergie solaire pourrait apporter une solution à l'absence de pilotabilité des technologies PV conventionnelles. L'étude des différents systèmes hybrides PV/CSP a constitué un axe de recherche important au cours des 5 dernières années, dont les principaux résultats sont discutés dans le chapitre 5. Le dernier chapitre est consacré aux thématiques de recherche qui seront développées dans les années à venir. Celles-ci s'articuleront essentiellement autour de 2 axes distincts, 1) La place de l'énergie solaire dans la transition énergétique 2) La concentration solaire comme moyen de caractérisation et de synthèse
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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