1,720,956 research outputs found
Tip-Induced Dissociation of Diethyl Ether on Si(001)─Influence of Molecular Structure on Final Reaction Products
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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
Elektronentransferprozesse und Funktionalisierung von Organik/Anorganik-Grenzflächen
No full textIm Rahmen dieser Arbeit wurde die Funktionalisierung von Organik/Anorganik-Grenzflächen anhand von elektronisch induzierten Oberflächenreaktionen und Ladungstransferprozessen an Grenzflächen untersucht. In Experimenten zum Einfluss der molekularen Struktur von Adsorbaten auf die Produkte einer elektronisch induzierten Oberflächenreaktion wurde zunächst dativ gebundener Diethylether auf Si(001) untersucht. Es konnte gezeigt werden, dass ein temporäres Besetzen des LUMO und damit des antibindenden C-O σ*-Orbitals der Moleküle durch Tunnelelektronen eine STM-spitzeninduzierte Etherspaltung hervorrufen kann. Dieser Mechanismus wird nicht durch die starken Restriktionen des Übergangszustands der thermisch aktivierten C-O-Dissoziation beschränkt, wodurch Wechselwirkungen zwischen Adsorbat und Substrat erhöhten Einfluss auf die Reaktionsprodukte nehmen können. Dies wirkt sich unter anderem darin aus, dass die kovalente Anbindung der Ethylgruppe in den finalen Konfigurationen vorwiegend an Si-Atome mit ursprünglich unbesetzten D_down-Zuständen stattfindet. Weiterhin ermöglicht die induzierte Etherspaltung in den Diethylether-Molekülen die Desorption der abgespaltenen Ethylgruppe. Ein Vergleich zu Tetrahydrofuran, welches eine ähnliche chemische Zusammensetzung, aber eine unterschiedliche räumliche Molekülgeometrie besitzt, zeigte, dass diese bestimmen kann, inwieweit die lokale elektronische Struktur der Oberflächenzustände Einfluss auf den Reaktionsprozess nimmt. Weiterhin wurde in Experimenten zur STM-spitzeninduzierten Modifikation von oberflächenreagiertem Diethylether auf Si(001) gezeigt, dass ausgehend von den kovalent gebundenen Ausgangskonfigurationen eine komplexe Oberflächenreaktion ausgelöst werden kann, bei welcher eine C-H-Dissoziation in der Ethylgruppe durch eine substratvermittelte und thermisch aktivierte Ein-Elektron-Anregung induziert wird. Die Produkte dieser Oberflächenreaktion binden brückenartig auf Si-Dimeren. Eine solche kontrollierte Verbindung von Dimeren über Alkane oder andere Kohlenwasserstoffketten ist unter anderem für den Bau logischer Architekturen auf Si(001) auf molekularer Skala von Interesse. Zur Untersuchung von Ladungstransferprozessen an Organik/Anorganik-Grenzflächen wurden Experimente mittels zeitaufgelöster Photoemissions-Orbitaltomografie an Kupfer-Phthalocyanin/Cu(001)-2O durchgeführt. Ladungstransfer über molekulare Grenzflächen hinweg spiegelt sich in der Besetzung elektronischer Orbitale wider. Durch die zeitabhängigen Änderungen der Impulsverteilung der Photoelektronen konnten unbesetzte molekulare Zustände charakterisiert sowie die zeitliche Entwicklung ihrer vorübergehenden Besetzung verfolgt werden. Am Beispiel des untersuchten Systems wurde zudem in einem proof-of-principle-Experiment demonstriert, dass in den gemessenen Impulsverteilungen auch eindeutige Signaturen kohärenter Zwei-Photonen-Photoemission beobachtet werden können. Die Identifizierung und Separation von kohärenten und inkohärenten Photoemissionsbeiträgen ist insbesondere für organische Systeme von großem Interesse, da diese in der Regel eine Vielzahl von räumlich lokalisierten und oftmals überlappenden Zuständen aufweisen, was eine eindeutige Zuordnung der Photoemissionsbeiträge hinsichtlich der Molekülorbitale erschwert. Durch sorgfältige Analyse konnten im untersuchten System die beiden beobachteten Anregungspfade, die Photoemission aus dem temporär besetzten LUMO und die kohärente Zwei-Photonen-Photoemission aus dem HOMO, voneinander getrennt und systematisch untersucht werden. Zur quantitativen Analyse wurden Dichtematrix-Berechnungen angestellt und die optischen Blochgleichungen für ein Dreiniveausystem numerisch gelöst. Schließlich konnte eine präferentielle Anregung von CuPc-Molekülen spezifischer Orientierung auf dem Substrat gezeigt werden, indem das elektrische Feld der Anregeimpulse an den Molekülachsen ausgerichtet wurde. Die Ergebnisse dieser Arbeit erweitern das Verständnis von gezielter Funktionalisierung von Siliziumoberflächen mit organischen Molekülen und der optischen Anregung organischer Systeme mittels zeitaufgelöster Impulsmikroskopie und bieten vielversprechende Anknüpfungspunkte für zukünftige Experimente in komplexeren Systemen wie organischen Heterostrukturen.In this thesis, the functionalization of organic/inorganic interfaces was studied. To this end, electronically induced surface reactions as well as charge transfer processes at molecular interfaces were measured and analyzed. The influence of the molecular structure of adsorbates on the products of electronically induced surface reactions was studied on datively bound diethyl ether on Si(001). Transient occupation of the LUMO and therefore the antibonding C-O σ* orbital of the molecules by tunneling electrons was found to induce ether cleavage. While thermally activated C-O dissociation is governed by strong restrictions in the transition state, the reaction products of STM tip-induced ether cleavage were significantly influenced by adsorbate-substrate interaction. In particular, the ethyl group of the final state configurations was found to predominantly form covalent bonds with Si atoms with originally unoccupied D_down states. Tip-induced ether cleavage also allows for the desorption of the ethyl group as it was split off. A comparison with tetrahydrofuran, a molecule of similar chemical composition but different spatial geometry, demonstrated that the molecular structure may determine to what extend the local electronic structure of the surface states influences the reaction process. Furthermore, tip-induced modification of surface-reacted diethyl ether on Si(001) was studied by means of STM, where covalently bound initial states were modified by a complex surface reaction. C-H dissociation in the ethyl group was induced by substrate mediated and thermally activated one electron excitation. The products of this type of surface reaction were found to form bridge-like configurations on the Si dimers. The controlled bridging of Si dimers with alkanes or other hydrocarbon chains might be considerably useful for building logical architectures on Si(001) on the molecular scale. For the investigation of charge transfer processes across organic/inorganic interfaces, experiments on copper(II) phthalocyanine on Cu(001)-2O were performed by means of time-resolved photoemission orbital tomography. Charge transfer across molecular interfaces is reflected in the population of electronic orbitals. Making use of the time-dependent evolution of the momentum distribution of the photoelectrons, unoccupied electronic states could be characterized and the temporal evolution of their distribution could be traced. It was demonstrated in a proof of principle experiment, that in the measured momentum distributions, signatures of coherent two-photon photoemission may also be observed. The separation and identification of coherent and incoherent photoemission contributions is of particular advantage when applied to organic systems as they are often characterized by many spatially localized electronic states that sometimes overlap and render the unambiguous assignment of photoemission contributions difficult. With a careful analysis of the different excitation pathways, coherent two-photon photoemission from the HOMO and photoemission from the transiently populated LUMO could be disentangled and systematically investigated in the studied system. In addition, it was demonstrated that a preferential excitation of CuPc molecules of specific orientation on the substrate could be realised by aligning the electric field of the pump pulse along the molecular axes. The insights on the functionalization of silicon surfaces with organic molecules and on optical excitation by means of time-resolved photoemission orbital tomography which were gained in this work offer possible use for future experiments on even more complex systems like organic heterostructures
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
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