1,720,995 research outputs found
Decreasing the bandwidth of linear and nonlinear Thomson scattering radiation for electron bunches with a finite energy spread
Full text linkRelative narrow bandwidth-high energy radiation can be produced through Thomson scattering, where highly relativistic electrons collide with a laser pulse. The bandwidth of such a source is determined, among others factors, by the bandwidth of the laser pulse and the energy spread of the electrons. Here we investigate how the bandwidth of such a source can be minimized, with a particular emphasis on electron bunches with a correlated energy spread of several percent, that are typical for plasma based accelerator schemes. We show that by introducing a chirp on the laser pulse it is possible to compensate the broadening effect due to the energy spread of the electrons, and obtain the same bandwidth as a quasi-monochromatic plane wave laser pulse colliding with a monoenergetic electron bunch. Ultimately, the bandwidth of a Thomson source is limited by the acceptance angle and the initial transverse momentum of electrons (emittance)
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
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
Generation of dense electron bunches by laser plasma accelerators for QED experiments in high fields
Full text linkDie Entwicklung von Laser-Plasma getriebenen Beschleunigern (LWFA) ist eine vergleichsweise neue Entwicklung. Durch die enormen Felder, die das Plasma zur Verfügung stellen kann, ist es möglich, ultrakurze und dichte Elektronenpulse über sehr kurze Strecken zu beschleunigen. In dieser Arbeit wird gezeigt, dass die Gasdynamik auf einer \sim 10\einh{\mu m}-Skala, die bisher nicht gemessen werden konnte, großen Einfluss auf den LWFA-Beschleunigungsprozess hat. Dichtemodulationen auf einer Skala von 10\einh{\mu m} wurden mithilfe eines ultrakurzen Laserpulses in Plasmen vermessen, die durch die Fokussierung des Hochintensitätslasers in einen Gasjet erzeugt wurden. Es wird gezeigt, dass diese Dichtemodulationen die Selbstinjektion in diesem Plasma auslösen. Die Resultate werden sowohl durch ein analytisches Modell sowie Particle-in-Cell (PIC) Simulationen bestätigt. Diese Erkenntnisse ebnen den Weg zu einem Plasmabeschleuniger bei dem Injektions- und Beschleunigsprozess unabhängig voneinander kontrolliert werden können. Darüber hinaus wurde in dieser Arbeit ein neues Kriterium für die Homogenität der Plasmadichte eingeführt, das auch in einem allgemeineren Kontext für Plasmabeschleuniger gilt. Im zweiten Teil der Dissertation wird untersucht, inwiefern kurze Elektronenpulse in Plasmen fokussiert werden können. In dieser Arbeit wird erstmalig das Konzept der passiven Plasmalinse mit ultrakurzen LWFA-Elektronenpulsen untersucht. Sowohl Experimente als auch Simulationen demonstrieren den Effekt der passiven Plasmalinse. Es wurde zudem ein analytisches Modell entwickelt, welches die experimentellen Ergebnisse beschreibt. Es ist hervorzuheben, dass die gemessene Fokussierstärke die eines konventionellen Quadrupolmagneten deutlich übersteigt. Das Modell sagt des Weiteren eine Steigerung der Fokussierstärke für Elektronenpulse mit größerer Ladung voraus
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