1,720,958 research outputs found
Synthese und Charakterisierung neuartiger molekularer Schalter auf Basis von Bisthiophenethenen
Get PDFDie Bisthiophenethene (kurz BTEs) gehören der Klasse der photochromen Moleküle an, welche durch äußere Stimuli (hier Bestrahlung) reversibel zwischen zwei Zuständen wechseln können. Diese beiden Zustände unterscheiden sich in ihren physikalischen Eigenschaften sowie den geometrischen und elektronischen Strukturen. Das Ziel dieser Arbeit war der Aufbau eines push-pull-Systems unter Verwendung der bisher kaum untersuchten Methoxymethyl-Gruppe (MOM). Die synthetisierten BTEs sollten ein hohes Ansprechverhalten in Bezug auf Bestrahlung mit UV- und visuellem Licht sowie eine hohe Anzahl an Schaltzyklen aufweisen. Für letztere Untersuchung wurden die BTEs mittels Rotationsbeschichtung in eine PMMA-Matrix eingebettet und mit zwei verschiedenen Lasern in die geschlossene oder offene Form überführt. Es erfolgte die Synthese von fünf neuartigen BTE-Typen, dessen MOM-Gruppe unter Optimierung der Reaktion deutlich zeitsparender eingeführt werden konnte. Zudem konnte ein linearer Zusammenhang zwischen den Substituenten und den zugehörigen UV/Vis-Spektren ermittelt werden. Für diesen Zusammenhang wurde die spektroskopische HAMMETT-Funktion eingesetzt, weshalb durch Verwendung von HAMMETT- und HAMMETT-BROWN-Konstanten die spektroskopischen Eigenschaften der BTEs prognostiziert werden können. Das Stabilitätsverhalten der BTEs in Lösung oder in kristalliner Phase war nicht auf die PMMA-Matrix übertragbar, weshalb nach Einführung von stabilitätsfördernden Substituenten oder Einheiten ein gegensätzliches Verhalten deutlich wurde. Die 1,3-Dioxanyl-Ringe zeigten zwar einen stabilisierenden Einfluss auf die nichtsymmetrischen Systeme, dennoch erwiesen sich die symmetrischen BTEs deutlich stabiler, wenn sie eine Erweiterung des aromatischen Systems aufzeigten. Damit einhergehend wirken sich die erweiterten π-Systeme positiv auf die spektroskopischen Eigenschaften aus und bewirken einen bathochromen Shift. Es wurden Beschichtungen gänzlich ohne PMMA-Anteil hergestellt und untersucht. Weiterführend wurde PMMA in der Matrix durch andere Polymere, wie z.B. Polystyrol, Polycarbonat und Polyvinylpyrrolidon ersetzt, um den Einfluss auf die Schichtdicke sowie die Stabilität zu untersuchen. Hierbei erwiesen sich BTEs in der PVP-Matrix als deutlich stabiler als in der PMMA-Umgebung.Bisthiophenethenes (BTEs) belong to the class of photochromic molecules that can switch reversibly between two states in response to external stimuli (in this case irradiation). These two states differ in their physical properties as well as their geometric and electronic structures. The aim of this work was to construct a push-pull system using the methoxymethyl group (MOM), which has barely been investigated to date. The synthesised BTEs should exhibit a high response to irradiation with UV and visual light as well as a high number of switching cycles. For the latter investigation, the BTEs were embedded in a PMMA matrix using the process of spin coating and converted into the closed or open form using two different lasers. Five new types of BTE were synthesised, the MOM group of which could be introduced in a significantly less time-consuming manner by optimising the reaction. In addition, a linear relationship between the substituents and the corresponding UV/Vis spectra was determined. The spectroscopic HAMMETT function was used for this relationship, which is why the spectroscopic properties of the BTEs can be predicted by using HAMMETT and HAMMETT-BROWN constants. The stability behaviour of the BTEs in solution or in the crystalline phase could not be transferred to the PMMA matrix, which is why a contrasting behaviour became apparent after the introduction of stability-promoting substituents or units. Although the 1,3-dioxanyl rings showed a stabilising effect on the non-symmetrical systems, the symmetrical BTEs proved to be significantly more stable when they exhibited an extension of the aromatic system. As a result, the extended π-systems have a positive effect on the spectroscopic properties and cause a bathochromic shift. Coatings without any PMMA content were produced and analysed. In addition, PMMA was replaced in the matrix by other polymers, such as polystyrene, polycarbonate and polyvinylpyrrolidone, in order to investigate the influence on the coating thickness and stability. BTEs proved to be significantly more stable in the PVP matrix than in the PMMA environment
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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