1,720,970 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
Investigating the emergence of electronic and atomic structure during the synthesis of transition-metal sulfides
Full text linkThe synthesis of nanomaterials in solution often involves multiple intermediate steps from the precursor to the final product, as outlined in the non-classical nucleation theory. The first step in a one-pot reaction typically begins with the dissolution of the precursors in a solvent, often promoted by the coordination of metal ions with specific ligands. Upon heating, a series of chemical reactions are triggered, leading to the nucleation and growth of the desired nanoparticles. Understanding all steps in the synthesis of nanomaterials is essential for controlling and designing their formation mechanism.
Especially transition metal oxide and sulfide nanomaterials are used in a variety of applications. While mechanistic studies are often reported for the case of metal oxides, the key reaction pathways influencing the synthesis of many transition metal sulfides are still under debate. This thesis elucidates the formation of ZnS nanomaterials in solvothermal reactions through in situ X-ray spectroscopy and scattering techniques as a benchmark and shows preliminary characterization of FexSy nanomaterial synthesis.
We utilized in situ valence-to-core X-ray emission spectroscopy (vtc-XES) combined with in situ high-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) supported by density functional theory (DFT) calculations to resolve the metal-ligand coordination during the synthesis of sphalerite ZnS nanorods (s-ZnS). The study elucidates the dissolution of Zn(Ac)2 in oleylamine (OA), proposing [Zn(OA)4]2+ and [Zn(OA)6]2+ complexes, and detailing the ligand exchange towards oleylthioamide (SOA) upon the addition of elemental sulfur to the reaction mixture at room temperature. Throughout the synthesis of s-ZnS, in situ vtc-XES and HERFD-XAS analyses were employed to calculate an in situ HOMO/LUMO gap, showing the emergence of a band structure during the synthesis of s-ZnS. This enables the size prediction of the intermediate structure, the ZnS nanoparticle in the wurtzite phase (w-ZnS), based on their band gap. Complementary in situ powder X-ray diffraction (PXRD) and small angle X-ray scattering (SAXS) analysis confirm the identity of w-ZnS and s-ZnS and provide additional information about their size and morphology.
We also propose and study the synthesis of ZnS nanoparticles using a two-phase water-toluene solvothermal reaction. The method allows the obtaining of colloidally stable monodispersed ZnS nanoparticles in the sphalerite phase. The diffusion of Zn2+ ions at the water-toluene interface was monitored by spatially resolved HERFD-XAS analysis, where the coordination of Zn2+ ions in each phase was resolved using DFT calculations. The dissolution of Zn(Ac)2 in water leads to the formation of a [Zn(H2O)6]2+ complex. The Zn2+ ion diffuses into the toluene phase already at room temperature, forming a [Zn(OA)6]2+ complex. In situ HERFD-XAS during the heating of the reaction solution up to 155°C reveals the formation of ZnS nanoparticles in the sphalerite phase, undergoing a [Zn(RS)4]2+ cluster and ZnS nuclei as intermediate structures. The findings were complemented by in situ PXRD and total X-ray scattering (TS) analysis, which verified the occurrence of these intermediates and assigned domain sizes to them. To validate the versatility of the method, we applied the complementary analysis to understand the formation of Fe3S4 nanomaterials in a solvothermal reaction. Since the reaction of Fe(acac)3 with elemental sulfur and oleylamine dissolved in toluene failed to achieve the required reaction temperature (180°C) to yield Fe3S4 nanomaterials, the solvent was exchanged to benzyl alcohol (BA) and the sulfur source to thioacetamide. In this reaction, no addition of oleylamine was required. BA is well known as a solvent that promotes the formation of ultrasmall and monodisperse nanoparticles.
The preliminary analysis of in situ HERFD-XAS and vtc-XES data of the synthesis of Fe3S4 nanomaterials uncovers the formation of an intermediate structure above 50°C, which can be attributed to the coordination of Fe(acac)3 by BA under the formation of a [Fe(acac)2(BA)2] complex, as resolved by HERFD-XAS analysis and supported by DFT calculations. Furthermore, the formation of Fe3S4 nanocrystals undergoes an intermediate formation of FeS nanocrystals, as revealed by combined HERFD-XAS and FEFF analysis.
The in situ approach of vtc-XES reveals changes in donor orbitals during the first 50 minutes of the reaction, confirming the emergence of the [Fe(acac)2(BA)2] complex. Through complementary in situ PXRD analyses, we identified the formation of FeS nanosheets and their conversion into Fe3S4 nanocrystals, which are approximately 22 nm in size.
This thesis presents an analysis of the coordination chemistry and structural evolution during the synthesis of ZnS and FexSy nanomaterials. It aims to propose reaction mechanisms for transition metal sulfides under solvothermal conditions by combining in situ X-ray spectroscopy and scattering analysis with quantum-mechanical calculations. This complementary approach offers insights into the formation of transition metal sulfide molecular clusters, the emergence of transition metal sulfide nuclei, and the crystallization processes of transition metal sulfide nanoparticles, nanorods, and nanosheets.Die Synthese von Nanomaterialien in Lösung umfasst oft mehrere Zwischenschritte vom Vorläufer bis zum Endprodukt, wie es die nicht-klassische Nukleationstheorie beschreibt. Der erste Schritt in einer One-Pot-Reaktion beginnt typischerweise mit der Auflösung der Vorläufer in einem Lösungsmittel, was oft durch die Koordination von Metallionen mit spezifischen Liganden gefördert wird. Beim Erhitzen wird eine Reihe von chemischen Reaktionen ausgelöst, die zur Nukleation und zum Wachstum der gewünschten Nanopartikel führen. Das Verständnis aller Schritte bei der Synthese von Nanomaterialien ist entscheidend für die Kontrolle und Anpassung ihres Formationsmechanismus. Übergangsmetalloxide und -sulfide werden in einer Vielzahl von Anwendungen eingesetzt. Während zahlreiche mechanistische Studien für Metalloxide in der Literatur verfügbar sind, ist der Reaktionsmechanismus, der Herstellung vieler Übergangsmetallsulfide, noch nicht im Detail verstanden. Diese Dissertation beleuchtet die Bildung von ZnS-Nanomaterialien in solvothermalen Reaktionen durch in situ Röntgenspektroskopie und Streutechniken als Blaupause für andere Syntheserouten und zeigt eine vorläufige Charakterisierung der FexSy-Nanomaterial-Synthese.
Wir nutzten in situ Valenz-zu-Kern-Röntgenemissionsspektroskopie (vtc-XES) kombiniert mit in situ hochenergetischer Fluoreszenz-detektierten Röntgenabsorptionsspektroskopie (HERFD-XAS), unterstützt durch Dichtefunktionaltheorie (DFT)-Berechnungen, um die Metall-Ligand-Koordination während der Synthese von Sphalerit ZnS-Nanorods (s-ZnS) aufzuklären. Die Studie erläutert die Auflösung von Zn(Ac)2 in Oleylamin (OA) und schlägt die Bildung von [Zn(OA)4]2+ und [Zn(OA)6]2+ Komplexen vor, sowie den Ligandenaustausch zu Oleylthioamid (SOA) bei Zugabe von elementarem Schwefel zur Reaktionsmischung bei Raumtemperatur. Während der Synthese von s-ZnS wurden in situ vtc-XES und HERFD-XAS Analysen eingesetzt, um eine in situ HOMO/LUMO-Lücke zu berechnen, welche das Entstehen einer Bandstruktur während der Synthese von s-ZnS aufzeigt und die Größenbestimmung der Zwischenstruktur, des ZnS-Nanopartikels in der Wurtzit-Phase (w-ZnS), basierend auf ihrer Bandlücke ermöglicht. Ergänzende in situ Pulverdiffraktometrie (PXRD) und Kleinwinkel-Röntgenstreuungsanalysen (SAXS) bestätigen die Identität von w-ZnS und s-ZnS und liefern zusätzliche Informationen über deren Größe und Morphologie.
Wir entwickelten außerdem die Synthese von ZnS-Nanopartikeln in einer Wasser-Toluol-Solvothermalsynthese und untersuchen diese. Die Methode ermöglicht es, kolloidal stabile monodisperse ZnS-Nanopartikel in der Sphalerit-Phase zu erhalten. Die Diffusion von Zn2+-Ionen an der Wasser-Toluol-Grenzfläche wurde durch ortsaufgelöste HERFD-XAS-Analysen untersucht, wobei die Koordination der Zn2+-Ionen in jeder Phase mithilfe von DFT-Berechnungen aufgelöst wurde. Die Auflösung von Zn(Ac)2 in Wasser führt zur Bildung eines [Zn(H2O)6]2+-Komplexes. Die Zn2+-Ion wandern bereits bei Raumtemperatur in die Toluol-Phase und bilden einen [Zn(OA)6]2+-Komplex. In situ HERFD-XAS während des Erhitzens der Reaktionslösung bis zu 155°C zeigt die Bildung von ZnS-Nanopartikeln in der Sphalerit-Phase, die ein [Zn(RS)4]2+-Cluster und ZnS Nukleationskeime als Zwischenstrukturen durchlaufen. Die Erkenntnisse wurden durch in situ PXRD und Totalen Streuungsanalyse (TS) ergänzt, die das Auftreten dieser Zwischenstrukturen bestätigen und ihnen Domänengrößen zuweisen. Um die Vielseitigkeit der Methode zu validieren, wendeten wir die komplementäre Analyse an, um die Bildung von Fe3S4-Nanomaterialien in einer solvothermalen Reaktion zu verstehen. Da die Reaktion von Fe(acac)3 mit elementarem Schwefel und in Toluol gelöstem Oleylamin die erforderliche Reaktionstemperatur (180°C) zur Erzeugung von Fe3S4-Nanomaterialien nicht erreichte, wurde das Lösungsmittel durch Benzylalkohol (BA) und die Schwefelquelle durch Thioacetamid ersetzt. In dieser Reaktion war keine Zugabe von Oleylamin erforderlich. BA ist bekannt als Lösungsmittel, das die Bildung kleiner und monodisperse Nanopartikel fördert.
Die vorläufige Analyse von in situ HERFD-XAS und vtc-XES Daten der Synthese von Fe3S4-Nanomaterialien deckt die Bildung einer Zwischenstruktur oberhalb von 50°C auf, die der Koordination von Fe(acac)3 durch BA mit der Bildung eines [Fe(acac)2(BA)2]-Komplexes zugeschrieben werden kann, wie durch HERFD-XAS-Analyse aufgelöst und durch DFT-Berechnungen unterstützt. Darüber hinaus durchläuft die Bildung von Fe3S4-Nanokristallen eine Zwischenbildung von FeS-Nanokristallen, wie durch kombinierte HERFD-XAS und FEFF-Analyse aufgezeigt. Der in situ Ansatz von vtc-XES zeigt Änderungen in den Donor-Orbitalen während der ersten 50 Minuten der Reaktion, was das Auftreten des [Fe(acac)2(BA)2]-Komplexes bestätigt. Durch ergänzende in situ PXRD-Analysen identifizierten wir die Bildung von FeS-Nanosheets und deren Umwandlung in Fe3S4-Nanokristalle, die ungefähr 22 nm groß sind.
Diese Arbeit präsentiert eine Analyse der Koordinationschemie und der strukturellen Evolution während der Synthese von ZnS- und FexSy-Nanomaterialien. Ziel ist es, Reaktionsmechanismen für Übergangsmetallsulfide unter solvothermalen Bedingungen vorzuschlagen, indem in situ Röntgenspektroskopie und Streuanalyse mit quantenmechanischen Berechnungen kombiniert werden. Dieser komplementäre Ansatz bietet Einblicke in die Bildung von Übergangsmetall-Sulfid-Molekülclustern, das Entstehen von Übergangsmetall-Sulfid-Kernen und die Kristallisationsprozesse von Übergangsmetall-Sulfid-Nanopartikeln, -Nanorods und -Nanosheets
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
Nucleation and growth of ferroelectric thin films studied by total X-ray scattering.
No full textIn this work, the synthesis of ferroelectric PbZrTiO (PZT) thin films by chemical solution deposition (CSD) and their investigation by atomic pair distribution function (PDF), which is a total X-ray scattering method, are described. The PZT thin films are fabricated at different temperatures to analyse temperature-induced phase transitions. PDF analysis and further characterisation methods like energy-dispersive X-ray spectroscopy (EDX) suggest a formation of a tetragonal zirconium dioxide phase on the glass substrate. This is in contradiction to previous results on a metallic substrate where a tetragonal PZT phase was formed. An other aim of the work is to optimise the performed synthesis and to test the PDF Method for applicability on ferroelectric thin films. Additionally, the discrepancies to the expected crystal structure are discussed by means of a structural model. In conclusion, possible improvements of the synthesis route are proposed, and possible further investigations of the samples are discussed
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
- …
