1,721,052 research outputs found
Effiziente Ansätze zur Modellierung und Charakterisierung der Selbstorganisation von Nanomaterialien
Get PDFThe design of innovative materials poses an ongoing challenge to researchers around the world. Nowadays, many disciplines are involved in this process: engineering, physics, chemistry, biology, and computer science, amongst others.
Looking back to the beginning of materials research, in the early eighteenth century, chemists started to classify materials according to their origin. They introduced three different kingdoms: vegetables/plants, animals, and minerals. More criteria were applied to further subdivide these classes into a full taxonomy, such as the mode of extraction and preparation, and what it could be applied for.
Apart from the manifold of forms and structures in the inanimate world, in living nature, evolution has created a rich pool of specialized materials. These include functional tissue, serving specific purposes: spider silk is strong but preserves a high elasticity whilst being adhesive to insects; the cornea refracts light whilst being able to bend to focus on objects at varying distances; horn features specific shapes and surfaces, being stiff enough to endure fights in the animal kingdom; bone and teeth are even harder than horn, but nevertheless not too brittle. Besides a very high availability of the resources required for their synthesis, many of these materials feature built-in repair mechanisms.
The appealing properties of biomaterials serve as inspiration for man-made materials. The use of bio-inspired processes and systems for engineering purposes is called biomimetics, or bionics. Naturally, the biological systems have to be well-understood to serve as template for the industry.
The present work aims to establish a new level of understanding of solid materials, their principles of self-organization, along with their intrinsic physicochemical properties. Within chapter 1, a short introduction to the topics and systems under investigation will be given, with references to works published in the respective field by the author. Chapter 2 deals with a novel method of quantitatively and qualitatively analyzing atomistic structures, and applications for rationalizing the evolution of forming crystal nuclei. In chapter 3, we shift to composite materials, and provide insights into two different model systems of high complexity. Chapter 4 describes the modelling of a functionalized ZnO nanoparticle, and methods of analyzing its stabilization in solution. Finally, a summary of the results and gained insights, along with an outlook on future perspectives, is given in chapter 5
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
Bildung, Charakterisierung und Anwendung Selbstorganisierter Monolagen aus Phosphons¨auren auf Aluminiumoxid
Get PDFComputational methods have helped a great deal in finding explanations for formerly inscrutable observations, as they provide atomic-level resolution. With respect to self-assembled monolayers (SAMs), both density functional theory (DFT) of individual surfactant-surface interactions and force field calculations of nm-scale SAM patches have made significant contributions towards the understanding of SAM formation and their properties. In the present work, we will apply force field based molecular dynamics (MD) simulations to study the system of phosphonic acids/phosphonates on aluminum oxide surfaces. The main advantages of this combination are the cheap materials and the robustness of the resulting SAMs. An overview of this and various other SAM systems is given in chapter 2 along with the state of the art of research on the formation mechanism and properties.
In the first part of the results in chapter 4, the focus is on the self-assembly of phosphonic acids (PAs) on alumina surfaces and the ordering of their alkyl-chain acting as spacers. The main challenge here is the glaring discrepancy between the timescales in SAM formation and MD simulations. In order to obtain well-ordered monolayers, the alumina substrate is typically immersed for several hours due to the slow diffusion of the surfactant molecules towards and on the surface, whereas \ac{MD} simulations usually range on the ns-scale. An iterative approach to overcome this gap using steered molecular dynamics (SMD) is presented in section 4.1 and applied in vacuo. In section 4.2 this method is applied in three solvents of different polarity to study the influence of solvent polarity on the growth mechanism.
To conclude the part on SAM formation, section 4.3 shows that surfactant molecules can also be incorporated into the monolayer in inverted geometry during the monolayer growth. Such inversion defects may have a very long lifetime and affect the quality of the resulting SAM, as they are removed upon proper rinsing of the SAM. A post-assembly treatment with repeated wetting/drying cycles reverses these molecules by a quasi-Langmuir-Blodgett transfer and can thus significantly improve the ordering and/or reduce immersion-time.
Chapter 5 describes properties and applications of the fully-grown SAMs. The self-healing after plastic deformation of a SAM of octadecyl phosphonic acid (ODPA) molecules on alpha-Al2O3 is investigated in section 5.1. Indentation of the SAM with a micro-lens leads to the formation of gauche-defects in the alkyl-chains. After release of pressure, the healing process begins at the fringe area of the disturbance and proceed towards its center. The ion-doping of an oligoethyleneglycol (OEG)-functionalized SAM is studied in 5.2. Here we explore the simulation-based design of SAMs and electronic devices.Rechnergestützte Methoden haben durch ihre inhäret atomare Auflösung bei der Aufklärung vormals rätselhafter Beobachtungen sehr geholfen. Bezogen auf selbstogranisierte Monolagen (SAMs) haben sowohl Rechnungen zur Wechselwirk einzelnder Adsorbtiv-Moleküle mit der Oberfläche mittels Dichtefunktionaltheorie (DFT) als auch Kraftfeldrechnungen auf der Nanometer-Skala einen großen Beitrag zum Verständnis der Bildung und Eigenschaften von SAMs geleistet. In dieser Arbeit werden kraftfeldbasierte Moleküldynamik-Simulationen (MD) angewendet, um SAMs von Phosphonsäuren auf Aluminiumoxid zu untersuchen. Die größten Vorteile dieser Kombination sind die günstigen Ausgangsmaterialien und die hohe Stabilität der entstehenden Monolage. Ein Überblick über dieses und andere SAM-Systeme ist in Kapitel 2 gegegen.
Im ersten Ergebnisteil (Kapitel 4) liegt der Fokus auf der Selbstorganisation der Phosphonsäuren (PAs) auf Aluminiumoxid-Oberflächen und dem Ausordnen der Alkylketten. Die größte Herausforderung bei der Modellierung ist hierbei die große Diskrepanz zwischen den Zeitskalen der SAM-Bildung und den Simulationen. Um wohlgeordnete Monolagen zu erhalten werden die Aluminiumoxid-Substrate aufgrund der langsamen Diffusion der Moleküle zur und auf der Oberfläche in der Regel für mehrere Stunden in eine PA-Lösung getaucht, während typische MD-Simulationen im Bereich von Nanosekunden liegen. Um diese Lücke zu überbrücken wird in Abschnitt 4.1 ein iterativer Ansatz unter Verwendung von Steered MD (SMD) entwickelt und in Vakuum-Simulationen getestet. In Abschnitt 4.2 wird diese Methode auch in drei Lösungsmitteln unterschiedlicher Polarität angewendet, um den Einfluss der Polarität auf das Wachstum zu untersuchen.
In Abschnitt 4.3 wird schließlich gezeigt, dass Phosphonsäure-Moleküle während des Wachstums auch in invertierter Geometrie in die SAM gebunden werden können. Solche Inversionsdefekte haben eine hohe Lebensdauer und beeinträchtigen die Qualität der SAM, da sie beim Spülen herausgelöst werden. Eine nachträgliche Behandlung mit wiederholtem Benetzen und Trocknen ist in der Lage diese Moleküle durch einen quasi-Langmuir-Blodgett-Transfer umzuderehen und so die Ordnung in der SAM signifikant zu erhöhen und/oder die Immersionszeit zu reduzieren.
Kapitel 5 beschäftigt sich mit Anwendungen wohlgeordneter SAMs. Die Selbstheilungseigenschaften einer SAM aus Octadecylphosphonsäure (ODPA) auf alpha-Al2O3 nach plastischer Verformung wird in Abschnitt 5.1 thematisiert. Eindrücken der SAM mit eine Mikrolinse führt hier zur Bildung von gauche-Defekten in den Alkylketten. Nach Wegnehmen des Drucks beginnt der Selbstheilungsprozess am Rande des gestörten Bereichs und pflanzt sich zu dessen Zentrum fort. In Abschnitt 5.2 wird das Dotieren einer SAM aus Oligoethylenglycol-funktionalisierten (OEG) Phosphonsäuren mit Ionen untersucht. Ausgehend von den Ergebnissen der MD Simulationen werden zudem elektronische Bauteile entwickelt
Molekulardynamik-Simulationen zur Selbstassemblierung und deren Auswirkungen auf optische Eigenschaften
Get PDFComputer simulations on the atomic/molecular scale have become a powerful tool for modern research in all fields of chemistry and related subjects such as material science or molecular biology. This progression was facilitated by ongoing improvements of computational capacities and the development of sophisticated algorithms. The great benefit of computational methods is their capability of gathering insights on time- and length-scales, that are experimentally hardly or not at all accessible. On one hand, these insights may help to interpret experimental results and to establish new theoretical concepts. On the other hand, predictions based on computational studies, such as reaction mechanisms or material properties, are
increasingly serving as input for synthetic and analytic strategies. This mutuality makes computer simulations highly suitable for interdisciplinary applications with experimental studies and vice versa.
Most of the computational studies presented in this thesis were carried out in close cooperation with experimentalist, resulting in comprehensive studies of the investigated systems. Altogether, our results enable a deeper understanding of the mechanisms controlling the optical properties of self-assembled systems and represent an important contribution to this field of research
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
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