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Rautananorakenteiden reaktiivisuus tiheysfunktionaaliteoriaan pohjautuen
No full textMost chemical processes rely on heterogeneous catalysis. The role of a catalyst is to provide an environment for more facile breaking and making of chemical bonds without being consumed itself. Catalytic performance is determined by the electronic structure, which can be modified by changing the atomic structure and composition. Conventional heterogeneous catalysis takes place on large crystal surfaces where the catalytic activity is determined mostly by the surface structure. However, catalyst particles smaller than 10 nm exhibit finite-size effects and the catalytic properties become very dependent on the size and geometry of the particle.
The size- and geometry-dependent properties allow the modification of nanostructures towards specific catalytic applications. To reach this goal the relationships between catalytic performance and atomic and electronic factors must be understood. In this thesis a quantum mechanical approach within density functional theory is employed to obtain an atomic level understanding of CO dissociation on iron nanostructures. This is an important initial step for the total efficiency and selectivity in, e.g., Fischer-Tropsch synthesis for hydrocarbons and synthesis of carbon nanotubes.
Results on 0.5-1.5 nm icosahedral, BCC, and amorphous iron nanoparticles show that the larger particles are more reactive towards CO dissociation. The presence of particle edges is essential for facile CO dissociation and on BCC particles very low dissociation barriers are observed even without atomic steps, which are the active sites on crystal surfaces. The reactivity of particle edges is explained by favorable orbital interactions between the metal surface and CO's LUMO orbital stabilizing the transition state. An optimal site for facile CO dissociation needs to fulfil several requirements: 1) CO is adsorbed at a BCC(100) like four-fold hollow site in the initial state,2) CO breaks over an atomic step, and 3) C is adsorbed in a fourfold site and O in a three-fold site in the final state.
All properties of magnetic materials depend on their magnetic state but the effect of different magnetic states on catalytic activity has been largely ignored. In this thesis it is shown that the electron donation and reactivity of FCC(111) iron surface can be modified by changing the magnetic state. This gives a justification for magnetically controlled catalysis.
Besides studies on reactivity of nanostructures, a general algorithm for improving transition state methods used in computational nanocatalysis was developed. The method removes external degrees of freedom using quaternion algebra and the new NEB-TR and DIMER-TR methods were shown to use fewer iterations to converge to a saddle point and describe minimum energy pathways more accurately in the case of NEB-TR.Suurin osa kemiallisista prosesseista perustuu heterogeeniseen katalyysiin, jossa katalyytin tehtävä on kiihdyttää kemiallisten sidosten muodostumista ja hajoamista kulumatta itse reaktion aikana. Katalyytin tehokkuus on suoraan sidoksissa sen elektronirakenteeseen, joka puolestaan riippuu sekä atomitason rakenteesta että koostumuksesta. Perinteiset heterogeeniset katalyytit ovat suuria metallipintoja, joiden aktiivisuus riippuu lähinnä katalyyttipinnan rakenteesta. Alle 10 nm katalyyttipartikkelien aktiivisuus on puolestaan hyvin riippuvainen partikkelin koosta ja geometriasta. Koko- ja geometriariippuvuus mahdollistaa katalyyttien muokkaamisen erilaisia sovelluksia varten. Tämä vaatii kuitenkin syvällisen ymmärryksen atomi- ja elektronirakenteen vaikutuksesta katalyyttiseen aktiivisuuteen.
Tässä väitöskirjassa on hyödynnetty kvanttimekaniikkaan pohjautuvaa tiheysfunktionaaliteoriaa antamaan atomitason ymmärrystä hiilimonoksidin hajoamisesta erilaisten rautananorakenteiden pinnalla. Tämän reaktioaskeleen on esitetty olevan keskeinen sekä selektiivisyyden että aktiivisuuden kannalta mm. pitkin hiilivetyjen Fischer Tropsch -synteesissä sekä hiilinanoputkien synteesissä.
Tutkimalla hiilimonoksidin hajoamista 0.5-1.5 nm rautananopartikkelien pinnalla havaittiin, että suuremmat partikkelit ovat reaktiivisempia ja että partikkelien reunat ovat keskeisiä reaktiivisuuden kannalta. Etenkin BCC-rakenteisten partikkelien reunat ovat hyvin reaktiivisia, mikä osoittaa, että katalyytti voi olla hyvin aktiivinen ilman atomikokoisia askelmia. Reunojen reaktiivisuus johtuu matalaenergisestä siirtymätilasta, mikä voitiin osoittaa orbitaaliteorian avulla. Hiilimonoksidin hajottamiseen vaadittavan aktiivisen kohdan tulee täyttää useita vaatimuksia:1) CO on sitoutunut BCC(100)-tyyppiseen kuoppapaikkaan, 2) CO hajoaa atomikokoisen askelman yli ja 3) hiili ja happi ovat vastaavasti neljän tai kolmen atomikuoppapaikoissa.
Magneettisten materiaalien ominaisuudet ovat hyvin riippuvaisia niiden magneettisesta rakenteesta. Magnetismin hyödyntämistä katalyysissä ei ole kuitenkaan juuri tutkittu. Tässä väitöskirjassa on osoitettu, että FCC(111) rautapinnan reaktiivisuus ja kyky luovuttaa elektroneja riippuu hyvin paljon sen magneettisesta rakenteesta. Tämä tulos osoittaa, että reaktiivisuutta voidaan muokata magnetismin avulla.
Reaktiivisuustutkimusten lisäksi tässä väitöskirjassa on kehitetty algoritmi, joka tehostaa siirtymätilojen etsintää laskennallisessa nanokatalyysissa. Menetelmä perustuu ulkoisten vapausasteiden eliminointiin kvaternioalgebran avulla. Uudet NEB-TR ja DIMER-TR menetelmät ovat tehokkaampia ja tarkempia kuin alkuperäiset menetelmät
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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