1,720,972 research outputs found
atomistische Modellierung der Adhesion von Epoxy-Beschichtungen Atomistic modelling of the interfacial adhesion mechanism of epoxy-based coatings
Full text linkKunststoffbeschichtungen sind ein weit verbreiteter Ansatz, zur Bekämpfung und Abschwächung der schädlichen und kostspieligen Auswirkungen von Korrosion. Sie schränken die Exposition von Metallen gegenüber aggressiven Umwelteinflüssen erheblich ein. Diese Beschichtungen bringen eine Vielzahl von positiven Eigenschaften mit sich, welche von besserer Hitzebeständigkeit und chemischer Beständigkeit bis hin zu erhöhter Kratzbeständigkeit und ausgezeichneter Adhäsion reichen. In dieser Arbeit wird ein Ansatz zur Simulation von Kunststoffbeschichtungen auf Epoxidharzbasis mit Hilfe von Molekulardynamiksimulation vorgestellt.Untersucht werden die molekularen Wechselwirkungen dieser Beschichtungen, die Beziehung zwischen den molekularen Wechselwirkungen und die Mikrostruktur der Beschichtung, sowie Transportprozesse, insbesondere die Diffusion von Wasser durch die Kunststoffbeschichtung. Durch die Veränderung der Kettenlänge von polyfluorierten Alkylverbindungen und dem Einsatz von Silane mit oder ohne Aminogruppen wird die Wirkung verschiedener funktioneller Gruppen auf diese Wechselwirkungen bestimmt. Diese polyfluorierten Alkylverbindungen verringern die Diffusion von Wasser, indem sie die Wassermoleküle behindern. Außerdem wird eine Anhäufung von Wasser in sauerstoffreichen Regionen beobachtet. Wasserstoffbrückenbindungen zwischen Wasser und der Epoxidharzbeschichtung deuten darauf hin, dass Wasser in die Beschichtung eingebaut wird, wodurch sich die strukturelle Integrität des Kunststoffes ändert und gleichzeitig die Diffusion verzögert wird. Der Diffusionskoeffizient wird durch Simulation im Equilibrium quantifiziert. Anzahldichteprofile der Beschichtungen zeigen hydrophile Gruppen in der Nähe der Eisenoxidoberfläche, was auf eine gute Adhäsion hinweist. Diese Ergebnisse ermöglichen eine Einschätzung der Struktureigenschaften und der Transporteigenschaften dieser Beschichtungen unter besonderer Berücksichtigung von Silane und polyfluorierten Alkylverbindungen undgeben Aufschluss über die Mikrostruktur und die Wechselwirkungen auf molekularer Ebene.Polymer coatings are a widely used approach to combat and mitigate the damaging and costly effects caused by corrosion. They significantly limit the exposure ofmetals to aggressive environmental influences. Polymer coatings introduce a variety of different beneficial properties ranging from better heat and chemical resistance to an increase in scratch resistance and excellent adhesion. In this thesis, an approach to simulate epoxy-based polymer coatings with molecular dynamics simulations is demonstrated. The molecular interactions of these coatings in bulk and applied on iron oxide surfaces and the relationship between the molecular interactions and the microstructure of the coating, as well as transport processes, in particular the diffusion of water through the coating, are investigated. By changing the chain length of polyfluorinated carbon chains and employing silanes with or without amine groups,the effect of different functional groups on these interactions is determined. These polyfluorinated carbon chains reduce the diffusion of water by obstructing the watermolecules. Furthermore, an accumulation of water in oxygen-rich regions is observed.Hydrogen bonds between water and the coating suggest that the water is incorporated into the coating, changing the structural integrity of the polymer and simultaneously delaying the diffusion. The diffusion coefficient is quantified by equilibrium bulk simulations. Number density profiles of the coatings show hydrophilic groups in the proximity of the iron oxide surface, indicating good adhesion. These findings provide an assessment of structure properties and the water transport inpolymer coatings, specifically considering silanes and polyfluorinated carbon chains and elucidate the microstructure and interactions on a molecular level
Molecular dynamics simulations of the adsorption of different alkali metals on muscovite mica surfaces
No full textInterplay of Structure, Dynamics and Energetics of Alkali Metal Ions on Muscovite Mica Surfaces: Molecular Dynamics Simulation
No full textRole of Surface Cation and Ion Concentration on the Adsorption Behavior at Water-mica Interfaces
No full textAdsorption of ions at the solid-liquid interface is central to many natural processes and applications such as corrosion of metals, electrochemical energy storage, and swelling of clays. In these processes, the composition of electrolyte has a profound influence on the structure, dynamics and energetics of the ions and water at interface. Atomistic simulations are practical to properly explore cation-specific effects and concentration-dependence at molecular level. We perform molecular dynamics (MD) simulations to examine the ion adsorption, hydration and electric double layer structures, and ion transport behavior in aqueous electrolytes (Cs+, Li+, and Ca+2 ions) confined between two negatively charged mica surfaces. Our simulation results show that Cs+ ions have the most prominent screening effect at the surface, indicating a stronger ion adsorption compared to Li+ and Ca+2 ions at the same concentration. Interestingly, the number of adsorbed Cs+ ions exceeds the surface charge of mica. This refers to a phenomenon called as “overscreening”. As a result, the surface becomes positively charged, and the diffuse layer of EDL becomes co-ion dominated. However, this is not the case for Li+ and Ca+2 which they attach less strongly to the surface and undercharge the mica. These ion adsorption directly affects the water structures. Although there are less Li+ ions at the surface compared to Cs+, more water molecules come near to the surface from the center of the channel for Li case. Water molecules can go through between adsorbed Li+ layer and the surface, strongly hydrating Li+ ions whereas this is not possible for Cs+. These indicate that hydration is the driving force in Li solution while surface forces are dominant in Cs case. By assessing the competitive behavior of charged species at the surface, the adsorption coverage is quantified as a function of ion concentration. Cs+ coverage significantly increase with the increase of concentration while a linear but less prominent increase is obtained for Li+ adsorption. On the other hand, increased ion concentration shows a negligible influence on the Ca+2 coverage. MD simulation results highlighting the ion adsorption as a function of ion type and concentration is critical to understand the interfacial thermodynamics directly from high resolution atomic force microscopy imaging
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
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
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