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Photoionization and photoexcitation of free silicon dioxide nanoparticles
No full textIm Rahmen dieser Arbeit wurde die Photoionisation von freien Siliziumdioxid- Nanopartikeln unter Verwendung verschiedener Lichtquellen untersucht. Dabei wurde zur Probenpräparation ein kontinuierlicher Nanopartikelstrahl verwendet, der mittels einer aerodynamischen Linse ins Hochvakuum überführt wurde. Die Vorteile dieser Präparationsmethode liegen zum einen in der Vermeidung von Strahlenschäden durch ständiges Erneuern der Partikel im Wechselwirkungszen- trum. Zum anderen können Wechselwirkungen mit der Umgebung ausgeschlossen werden, wie es für deponierte Partikel der Fall ist.
Der erste Teil der Arbeit beschäftigt sich mit der Untersuchung der Winkelvertei- lung der Photoemission von freien SiO2-Nanopartikeln nach Ionisation mit wei- cher Röntgenstrahlung. Durch Variation der Photonenenergie und der Polarisati- on der ionisierenden Strahlung konnte der Anisotropieparameter für die Si 2p-, die O 1s- und die Valenzemission für kinetische Energien von bis zu 250 eV bestimmt werden. Verglichen mit der Winkelverteilung der Photoemission der isolierten Silizium- und Sauerstoffatome konnte eine Reduzierung der Anisotropie für die untersuchten Nanopartikel beobachtet werden, die durch das Auftreten elasti- scher Streuprozesse an Nachbaratomen innerhalb des Partikels erklärbar ist.
Im zweiten Teil wurde die Photoionisation der freien SiO2-Nanopartikel durch intensive ultrakurze Laserpulse im infraroten Spektralbereich untersucht. Die Energie- und Winkelverteilungen der emittierten Photoelektronen wurden im Zusammenhang mit den Mechanismen der Erzeugung und Beschleunigung von Elektronen in Nanopartikeln diskutiert. Zusätzlich konnte die Dynamik des ex- pandierenden Nanoplasmas mit Hilfe von Anregungs-Nachweis-Experimenten un- tersucht werden.
Der dritte Teil beschreibt Experimente, die am Freie-Elektronen-Laser FLASH durchgeführt wurden. Dabei wurde eine größen- und intensitätsabhängige Ver- änderung der Winkelverteilung der Ionenemission von SiO2-Nanopartikeln nach Ionisation mit intensiven ultrakurzen Röntgenpulsen beobachtet. Diese konnte durch die asymmetrische Absorption der Röntgenstrahlung und das bei der Ioni- sation entstehende Nanoplasma erklärt werden.Within the scope of this work, photoionization of free silicon dioxide nanoparti- cles irradiated by different light sources was studied. The sample was prepared in a continuous beam of nanoparticles that was transferred via an aerodynamic lens into high vacuum. The advantages of this preparation method are on the one hand the avoidance of radiation damage due to continuous exchange of the particles in the interaction region. On the other hand one can exclude interaction processes with a surrounding medium, as it is the case for deposited particles. In the first part of this work, the angular distribution of the photoemission from free SiO2 nanoparticles was studied after ionization by soft X-rays. By variation of the photon energy and the polarization of the ionizing radiation the anisotropy parameter of the Si 2p, the O 1s and the valence photoemission for kinetic en- ergies up to 250 eV could be determined. Compared to the angular distribution of the photoemission from isolated silicon and oxygen atoms a reduced angular anisotropy was found for the nanoparticles under study. This was explained by elastic scattering of the outgoing photoelectrons from neighboring atoms inside the nanoparticle.
In the second part, photoionization of free SiO2 nanoparticles by intense ultra- short laser pulses in the infrared regime was studied. The energy and angular distributions of the emitted photoelectrons were discussed in the context of ge- neration and acceleration mechanisms of electrons in nanoparticles. Further, the dynamics of the expanding nanoplasma was studied by pump-probe experiments. In the third part, experiments are introduced which are conducted at the free- electron laser FLASH. A size and intensity dependent change in the angular distribution of the ion emission from SiO2 nanoparticles after ionization by in- tense ultrashort X-ray pulses was found. This was explained by asymmetric X-ray absorption and the generated nanoplasma after ionization
Photoionisation und Photoanregung von freien Siliziumdioxid-Nanopartikeln
No full textWithin the scope of this work, photoionization of free silicon dioxide nanoparti-cles irradiated by different light sources was studied. The sample was preparedin a continuous beam of nanoparticles that was transferred via an aerodynamiclens into high vacuum. The advantages of this preparation method are on theone hand the avoidance of radiation damage due to continuous exchange of theparticles in the interaction region. On the other hand one can exclude interactionprocesses with a surrounding medium, as it is the case for deposited particles.In the first part of this work, the angular distribution of the photoemission fromfree SiO2nanoparticles was studied after ionization by soft X-rays. By variationof the photon energy and the polarization of the ionizing radiation the anisotropyparameter of the Si 2p, the O 1s and the valence photoemission for kinetic en-ergies up to 250 eV could be determined. Compared to the angular distributionof the photoemission from isolated silicon and oxygen atoms a reduced angularanisotropy was found for the nanoparticles under study. This was explained byelastic scattering of the outgoing photoelectrons from neighboring atoms insidethe nanoparticle.In the second part, photoionization of free SiO2nanoparticles by intense ultra-short laser pulses in the infrared regime was studied. The energy and angulardistributions of the emitted photoelectrons were discussed in the context of ge-neration and acceleration mechanisms of electrons in nanoparticles. Further, thedynamics of the expanding nanoplasma was studied by pump-probe experiments.In the third part, experiments are introduced which are conducted at the free-electron laser FLASH. A size and intensity dependent change in the angulardistribution of the ion emission from SiO2nanoparticles after ionization by in-tense ultrashort X-ray pulses was found. This was explained by asymmetric X-rayabsorption and the generated nanoplasma after ionization
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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