1,721,137 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
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
Kohärente Röntgenbildgebung von Dotierstoffstrukturen in superflüssigen Helium-Nanotröpfchen
No full textSuperfluide Helium-Nanotröpfchen weisen einzigartige Eigenschaften auf, die sie für verschiedene Anwendungen wertvoll machen, beispielsweise als kryogene Matrix in der Molekularspektroskopie oder als Wachstumszellen für neuartige Nanopartikel. Das Auftreten von Wirbeln mit quantisiertem Drehimpuls ist ein faszinierender mesoskopischer Quanteneffekt, der aber auch die Anordnung von Dotierstoffen vorbestimmt, wenn diese vorhanden sind. Diese Arbeit beschäftigt sich mit der Frage, ob und wie wirbelfreie Heliumtröpfchen erzeugt werden können und wie sich dies auf die Anordnung von Dotierstoffen mit unterschiedlichen chemischen Bindungsarten auswirkt. Zu diesem Zweck wurde im Rahmen dieser Arbeit ein modulares System entworfen und gebaut, das eine Clusterquelle zur Erzeugung von Heliumtröpfchen und anderen Clustern durch Düsenexpansion sowie ein Dotiersystem mit einer Gaszelle und einem Verdampfungsofen umfasst. Das System steht nun für Benutzerexperimente am Europäischen Röntgen-Freie-Elektronen-Laser (EuXFEL) zur Verfügung, wo es auch für die Messung der Daten für diese Studie verwendet wurde. Einzelne Heliumtröpfchen wurden mit den ultrakurzen Röntgenpulsen des EuXFEL beleuchtet und das gestreute Licht aufgezeichnet. Mithilfe iterativer Algorithmen konnten Bilder der Tröpfchen und der darin enthaltenen Dotierstoffstrukturen rekonstruiert werden. Es konnte gezeigt werden, dass Tröpfchen mit einem geringeren Drehimpuls erzeugt werden können als vergleichbare Quellen, was zur Erzeugung von wirbelfreien Tröpfchen führt. Überraschenderweise zeigte das Auftreten von Wirbeln nur eine geringe Abhängigkeit von den Stagnationsbedingungen und der Dotierkonzentration, sondern in erster Linie von der Tröpfchengröße. Der Vergleich mit einem einfachen statistischen Modell legt nahe, dass der Drehimpuls aus Zusammenstößen der Tropfen während der Erzeugung stammen könnte. Die Analyse von Xenon- und Silberdotanten zeigt, dass sich zwar in beiden Fällen kompakte Strukturen bilden können, kompakte Silberkerne jedoch eine höhere Dichte aufweisen und in größeren Tröpfchen zu beobachten sind. Dies wird auf die Art der Bindung zurückgeführt und lässt auf partielles Schmelzen während der Aggregation schließen. Angesichts des grundlegenden Einflusses von Wirbeln auf das Wachstum von Dotierstoffstrukturen haben die Ergebnisse dieser Arbeit das Potenzial, die bestehenden Grenzen auf dem Gebiet der Nanopartikelsynthese zu erweitern und somit einen wichtigen Beitrag zur Erforschung neuartiger Materialien zu leisten.Superfluid helium nanodroplets exhibit unique properties that make them valuable for various applications, such as cryogenic matrix in molecular spectroscopy and growth cells for novel nanoparticles. The occurrence of vortices with quantized angular momentum is a fascinating mesoscopic quantum effect but also dictates the arrangement of dopants when they are present. This work addresses the question of whether and how vortex-free helium droplets can be created and how this affects the ordering of dopants with different types of chemical bonding. For this purpose, a modular system was designed and built within the scope, comprising a cluster source for producing helium droplets and other clusters by jet expansion, and a doping system with a gas cell and evaporation oven. The system is now available for user experiments at the European x-ray free-electron laser (EuXFEL), where it was utilized to record data for this study. Individual helium droplets were illuminated with the ultrashort x-ray pulses of the EuXFEL, capturing the diffracted light. Using iterative algorithms, images of the droplets and the contained dopant structures could be reconstructed. It was demonstrated that droplets could be produced with less angular momentum than comparable sources, resulting in the production of vortex-free droplets. Surprisingly, occurrence of vortices showed little dependence on stagnation conditions and dopant concentration, but primarily on droplet size. Comparison with a simple statistical model suggests that the angular momentum may have been generated by collisions of the droplets during generation. The analysis of xenon and silver dopants reveals that while compact structures may be formed in both cases, compact silver cores have a higher density and can be observed in larger droplets, which can be attributed to the type of bond and suggests partial melting during aggregation. Given the fundamental influence of vortices on dopant structure growth, the results of this work hold the potential to push the existing frontiers in the field of nanoparticle synthesis and thus to contribute significantly to the exploration of novel materials.BMBF Forschungsschwerpunkt Freie-Elektronen-Laser FSP-30
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