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In Richtung ultraschneller zeitaufgelöster Experimente mit nanoskaligen Objekten und Oberflächen
No full textAttosecond streaking is an established technique for the investigation of ultrafast phenomena in atomic and molecular physics. The demonstration of attosecond streaking on solid surfaces revealed ultrafast dynamics in the electron transport properties already. However, only a few single crystalline materials have been investigated so far. The potential applicability to plasmonic nanostructured or thin film samples maintaining ultrafast electron oscillations on the time-scale of attosecond has not been realized yet. In this thesis proof-of-principle experiments on gold and tungsten trioxide demonstrate, that surface contaminated and polycrystalline or amorphous samples are applicable for the investigation with attosecond streaking. In these experiments, a broadening of the photoelectron wavepackets compared to the laser pulse was found. Furthermore, a sample cleaning procedure is established to prepare nanostructured samples nondestructively. Simulations are performed for the design and optimisation of vertical disk resonators. Special attention was turned on the orientation of the electric field to make the plasmonic field accessible in the streaking experiments. Additionally, the appearance of ultrafast surface modes is investigated. The realisation of the nanodisk resonators has been started by preparation of thin film triple layers and first characterisation measurements. For ultrafast time-resolved measurements on the simulated nanostructures and thin films a beamline for the generation of isolated attosecond pulses by high harmonic generation was built.Attosekunden-zeitaufgelöstes Photoelektronen Streaking ist eine etablierte Methode für die Untersuchung von extrem schnellen Prozessen in Atomen und Molekülen. Durch die Anwendung dieser Technik auf Festkörperproben konnten auch in solchen Systemen ultraschnelle Dynamiken beim Elektronentransport nachgewiesen werden. Jedoch wurden bislang nur wenige einkristalline Materialien untersucht. Auf nanostrukturierte plasmonische Proben oder dünne Filme, die ebenfalls elektronische Dynamiken auf einer ähnlichen Zeitskala aufweisen, wurde die Streaking-Technik bisher noch nicht angewendet.
Im Rahmen dieser Dissertation wurden Streaking-Experimente an Gold- und Wolframtrioxid Proben durchgeführt, die die prinzipielle Anwendbarkeit dieser Technik auf polykristalline und amorphe Proben mit Oberflächenkontamination zeigen. In diesen Experimenten wurde eine Verbreiterung des Photoelektronen-Wellenpackets relativ zur Laserpulsdauer nachgewiesen. Weiterhin wurde eine Präparationsprozedur entwickelt, mit deren Hilfe nanostrukturierte Proben zerstörungsfrei von Oberflächenkontaminationen gereinigt werden können. Mit Hilfe von Simulationen wurden Mehrschicht-Resonatoren bestehend aus drei Scheiben entworfen und optimiert, die eine Orientierung des elektrischen Feldes senkrecht zur Oberfläche aufweisen. Damit erfüllen sie eine wichtige Anforderung, um in einem modifizierten plasmonischen Streaking-Experiment analysiert zu werden, da nur der Einfluss elektrischer Felder in Richtung des Elektronendetektors messbare Beiträge liefert. Außerdem wurde die Erzeugung von unterschiedlichen Oberflächen-Moden untersucht. Mit der Präparation von solchen Nanodisk-Resonatoren wurde bereits begonnen. Ein dreilagiges Schichtsystem wurde präpariert und daran erste Charakterisierungsmessungen durchgeführt. Um zeitaufgelöste Experimente an den simulierten Nanostrukturen durchführen zu können wurde außerdem eine Apparatur zur Erzeugung von isolierten Attosekunden Pulsen auf Basis der hohen harmonischen Erzeugung aufgebaut, die die beschriebenen Experimente ermöglichen soll
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
Assembly and application of an instrument for attosecond time-resolved ionization chronoscopy
Get PDFUphues T. Assembly and application of an instrument for attosecond time-resolved ionization chronoscopy. Bielefeld (Germany): Bielefeld University; 2006.In the framework of this thesis a new setup for attosecond time-resolved measurements has been built and observations of ionization dynamics in rare gas atoms have been made. This new technique is entitled Ionization Chronoscopy and gives further evidence that time-resolved experiments in the attosecond regime will become a powerful tool for investigations in atomic physics
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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