1,720,956 research outputs found
Structural, Thermodynamic and Photo-Physical Properties of Cesium Lead Halide Perovskites
No full textRecently, the emergence of metal halide perovskite solar cells as a contender for next-generation photovoltaics constitutes a paradigm shift in the field of solution-processed semiconductors. Increased understanding of the fundamental optoelectronic, and structural properties of these materials and advances in thin film processing over the last few years have led to a meteoric rise in power conversion efficiencies, exceeding 23%, now rivaling much more mature commercial technologies. While the vast majority of halide perovskite studies involve the prototypical organic-inorganic hybrid compound methylammonium lead iodide (MAPbI3), the volatile and hygroscopic organic cation is detrimental to its chemical stability. Thus, finding an alternative material system, which can mitigate these issues without diminishing the desirable optoelectronic properties, is necessary. This thesis focuses on understanding the thermodynamic and photo-physical properties of a promising all-inorganic alternative, perovskite-phase cesium lead iodide (CsPbI3). The perovskite ('black') phase of CsPbI3 spontaneously forms at elevated temperature (>320 °C). At room temperature (ambient condition) the thermodynamically favored phase is a non-perovskite structure ('yellow'), not useful for photovoltaic application. To develop a fundamental understanding of phase transitions in CsPbI3, and quantify the thermodynamic landscape of phase change, herein spectroscopy and calorimetry techniques have been employed. A reversible enthalpy difference of 14.2 (± 0.5) kJ/mol between the two phases is observed which is offset only by the similarly large entropic favorability of the desired phase. It has also been shown that by rapid cooling (quenching) the black phase of CsPbI3 can be kinetically trapped in a metastable state. It is demonstrated herein that the mechanistic role of atmospheric moisture in the phase transition is catalytic rather than enthalpic. These fundamental physicochemical insights are implemented to design stable derivatives. To enhance the phase stability of the black-CsPbI3 towards atmospheric moisture a chloride doping strategy has been devised and implemented herein. The conventional synthetic routes do not allow a significant amount of chloride doping due to limited miscibility of chloride in a CsPbI3 host lattice. A combined solution- and solid-state method has been adopted. Colloidal nanocrystals of pure CsPbCl3 and CsPbI3 are co-deposited and the resulting nanocrystal solid is subsequently fused into a polycrystalline thin film of CsPbI3-xClx by chemically-induced, room-temperature sintering. This approach ensures nanometer-scale mixing even at compositions that potentially exceed the bulk miscibility of the two phases. From theoretical calculations an atomistic insight into the formation of the mixed crystal phase has been obtained. In order to accept CsPbI3 as an alternative to MAPbI3, the optoelectronic parameters need to be comparable. Transient Absorption Spectroscopy (TA) and Time Resolved Terahertz Spectroscopy have been employed to reveal the recombination kinetics of CsPbI3. By developing a 1D finite difference diffusion-recombination model the recombination rate constants are estimated and the role of carrier diffusion deconvoluted. A nearly identical bimolecular rate constant, a fundamental property of the semiconducting materials, between CsPbI3 the most highly optimized MAPbI3 films in the literature has been observed. Such resemblance without the presence of molecular dipole infers that the organic cation does not provide any fundamental advantage in the slow radiative recombination kinetics of the hybrid perovskites.Ph.D., Chemical Engineering -- Drexel University, 201
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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