1,720,957 research outputs found
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
Manganmischoxide als biomimetische Wasseroxidationskatalysatoren: vielversprechende Materialien für die Herstellung eines solaren Brennstoffs durch künstliche Photosynthese
Full text linkTo take full advantage of the enormous potential of the sun as sustainable energy source, solutions to the capture of solar energy and its conversion into readily utilizable and storable forms are urgently required. Against this background, light-driven water-splitting is an intensely discussed approach for the generation of a so called solar fuel. In reaction sequences for the production of such solar fuels, the catalysis of the water-oxidation half-reaction represents one of the major challenges.
In nature, solar energy is captured and converted during photosynthesis. In this fundamental biological process CO2, H2O and light energy are used to form biomass and O2. The water-oxidation reaction is catalyzed within the enzyme photosystem II (PSII) by a μ-oxido bridged CaMn4 cluster, the oxygen-evolving-complex (OEC).
Inspired by the composition of the OEC, layered calcium manganese oxides of the birnessite family have been prepared prior to this work and showed promising activities in water-oxidation catalysis by far exceeding the activity of pure manganese oxides. These results raised questions concerning the role of Ca2+ ions in these catalytic reactions by synthetic Ca-birnessites. In case of PSII, the enzyme is known to be virtually inactive if Ca2+ is removed from the OEC. But the catalytic activity can be restored not only by the addition of Ca2+ but also Sr2+ ions, albeit at a reduced rate.
In the research project presented in this thesis, various layered manganese oxides were synthesized containing intercalated Ca2+ ions in different concentrations or K+, Sr2+, Mg2+, Cd2+, Al3+, Zn2+, Pb2+ and Fe3+, respectively. A detailed analysis by EDX, AAS, thermogravimetry, SEM, N2 adsorption/desorption isotherms, IR spectroscopy and XRD revealed insights into properties of the prepared materials. A relatively high amount of water and hydroxide molecules is placed in between layers build up from edge-sharing MnO6 octahedra. The morphology of the oxide materials is influenced by their compositions, as higher amounts of additional cations incorporated in the structures are resulting in the formation of smaller, less ordered particles, exhibiting a larger specific surface area. X-ray absorption spectroscopy (XAS) carried out at the Mn K-edge of Ca-, Sr- and Mg-birnessites showed that these materials have similar atomic structures despite differences in their compositions and morphologies. Furthermore, the oxides contain structural units, resembling the μ-oxido CaMn4 core of the OEC.
In water-oxidation experiments carried out using the prepared M-birnessites as catalysts and CeIV as well as photochemically generated [Ru(bpy)3]3+ as oxidants, all probed materials showed catalytic activity. However, reactivity correlated with the type of the intercalated cation and can best be formulated as Ca2+ > Sr2+ > Mg2+/Cd2+/Al3+/Zn2+/ Pb2+/Fe3+. Also less pronounced dependencies of the reactivity on the concentration of the additional cations and the ripening periods used during the oxide syntheses could be observed. Interestingly, the relative reactivities of Ca-, Sr- and Mg-birnessites are similar to the activities in water-oxidation reported for the Ca2+, Sr2+ and Mg2+ reactivated OEC. Based on these findings, mechanistic scenarios proposed for the O−O bond formation catalyzed by the OEC were adopted to M-birnessites. In these mechanistic scenarios, Ca2+ (or Sr2+) ions may act as binding and activation site for substrate water molecules. Overall, the results presented in this thesis are demonstrating that M-birnessites are promising candidates to be utilized as water-oxidation catalysts in artificial photosynthesis for sustainable energy production. Furthermore, Ca-birnessites in particular are outstanding OEC model compounds, as they mimic both structure and function of the biological paragon.Die Sonne bietet ein schier unbegrenztes Potential, um als saubere und nachhaltige Energiequelle zu dienen. Um dieses Potential jedoch uneingeschränkt nutzen zu können, ist es nötig, Wege zu finden, um Sonnenenergie zu absorbieren und in speicherbare, leicht zugängliche Formen zu überführen. In diesem Zusammenhang ist die lichtgetriebene Spaltung von Wasser zur Herstellung eines sogenannten solaren Brennstoffs ein vielfach diskutierter Ansatz. In solch einem Szenario stellt die katalytische Wasseroxidation einen der zentralen und besonders herausfordernden Reaktionsschritte dar.
Die Natur bedient sich hierfür der Photosynthese, während der Lichtenergie aufgenommen und zur Umwandlung von CO2 und H2O in Biomasse und O2 eingesetzt wird. Die Wasseroxidation findet dabei im Enzym Photosystem II (PSII), genauer in dessen aktiven Zentrum, einem μ-oxido verbrückten CaMn4-Komplex statt. Dieser Komplex wird als OEC (von oxygen-evolving-complex) bezeichnet.
Der Zusammensetzung des OEC folgend wurden bereits geschichtete Calcium-Manganoxide synthetisiert, die dem natürlich vorkommenden Mineral Birnessit ähneln. Hinsichtlich der Wasseroxidation zeigten diese Materialien eine vielversprechende katalyti- sche Aktivität, die bei weitem die von reinen Manganoxiden überstieg. Daher stellte sich die Frage, welche Rolle die Ca2+ Ionen bei dieser Reaktion spielen. Über den OEC ist bekannt, dass die Aktivität praktisch verloren geht, wenn Ca2+ aus dem Enzym entfernt wird. Jedoch kann die katalytische Aktivität wieder hergestellt werden, indem Ca2+ oder auch Sr2+ Ionen hinzugegeben werden. Allerdings erfolgt die Reaktivierung des Enzyms im Falle des Sr2+ nur in deutlich geringerem Umfang.
Im Rahmen der hier präsentierten Forschungsarbeit wurden verschiedene geschichtete Manganoxide synthetisiert, die Ca2+ Ionen in unterschiedlichen Konzentrationen, oder auch K+, Sr2+, Mg2+, Cd2+, Al3+, Zn2+, Pb2+ und Fe3+ enthielten. Die ausführliche Analyse der Materialien mittels EDX, AAS, Thermogravimetrie, SEM, N2 sorptions Isothermen, IR Spektroskopie und XRD ergab, dass eine relativ große Anzahl an Wasser- und Hydroxidmolekülen zwischen den Oxidschichten gebunden ist. Die Schichten selbst werden aus kantenverknüpften MnO6 Oktaedern gebildet. Es konnte gezeigt werden, dass der Einbau von größeren Mengen an zweiwertigen Kationen zur Ausbildung von Schichten führt, die eine höhere Anzahl an Fehlstellen aufweisen. Zusätzlich nimmt die Größe der Partikel ab und deren spezifische Oberfläche zu. Röntgenabsorptionsspektroskopische Messungen, die an der Mn K-Kante an Ca-, Sr- und Mg-Birnessiten durchgeführt wurden, zeigten, dass sich die Strukturen dieser Materialien auf der atomaren Ebene praktisch nicht unterscheiden. Des weiteren konnten anhand dieser Messungen Strukturmotive identifiziert werden, die dem μ-oxido CaMn4 Zentrum des OEC stark ähneln.
In Experimenten zur katalytischen Wasseroxidation, in denen CeIV beziehungsweise photochemisch generiertes [Ru(bpy)3]3+ als Oxidationsmittel und die Birnessite als Katalysatoren verwendet wurden, zeigten alle Oxide Aktivität. Beim Vergleich der Katalyseraten konnten dann aber verschiedene Tendenzen ausgemacht werden. Am deutlichsten erschien hierbei ein Trend in Abhängigkeit der Art des interkalierten Kations, der wie folgt formuliert werden kann: Ca2+ > Sr2+ > Mg2+/Cd2+/Al3+/Zn2+/Pb2+/Fe3+. Auch weniger deutliche Tendenzen wurden beobachtet, die in Zusammenhang mit der Konzentration der interkalierten Kationen oder der Dauer des Reifeprozesses der Materialien während der Synthese stehen. Besonders interessant ist an dieser Stelle, dass die relativen Katalyseraten, die für die Ca-, Sr- und Mg-Birnessite bestimmt wurden, gut mit denen übereinstimmen, die in der Literatur für den Ca2+-, Sr2+- und Mg2+-reaktivierten OEC zu finden sind. Bestärkt durch diese Ergebnisse wurden mechanistische Modelle, die für die O−O Bindungsbildung während der Wasseroxidation am OEC vorgeschlagen worden sind, auf M-Birnessite übertragen. In diesen Szenarien spielen Ca2+ (oder Sr2+) Ionen möglicherweise eine entscheidende Rolle als Aktivierungs- und Bindungsstelle für Substrat-Wasser Moleküle.
Alles in allem zeigen die vorgestellten Ergebnisse, dass M-Birnessite vielversprechende Wasseroxidationskatalysatoren sind, die in künstlichen Photosyntheseprozessen ihre Anwendung finden könnten. Des weiteren sind vor allem Ca-Birnessite besonders interessante Modellverbindung für den OEC, da sie dieses Vorbild sowohl strukturell, als auch funktionell nachahmen
Mixed Manganese Oxides as Biomimetic Water Oxidation Catalysts promising Materials for the Production of Solar Fuels by Artificial Photosynthesis
No full textDispelling 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
- …
