1,720,975 research outputs found
Insights of the Nanoscale Compositional Variations in Dental Enamel Revealed by Statistical Atom Probe Tomography
Get PDFThesis (Ph.D.)--University of Washington, 2025Dental enamel is a critical tissue in the body, acting as the primary surface for mastication as well as serving an aesthetic role in a smile. Enamel is also an inspirational material from a materials science perspective, as it endures decades in a challenging and complex oral environment whilst being subjected to cyclic loads. For these reasons, it is worthwhile to develop a thorough understanding of the microstructural and compositional features that provide this tissue its longevity, and how those features can be altered as a function of location within the tooth, age, or external factors such as disease or lifestyle choices. This dissertation is concerned with exploring the composition of the hydroxyapatite nanocrystals that constitute enamel at the smallest scale, elucidating where changes take place at a nanometric level and providing a perspective as to how those changes occur. Atom probe tomography (APT) is a powerful tool that is well suited to this investigation. Over the past decade, APT has had a significant impact on the study of enamel structure, however small sample sizes and inconsistent use of parameters have limited its ability to make rigorous comparisons between samples from distinct locations, age groups, or conditions. To address these issues, we have developed a routine for atom probe data analysis which enables more granular and robust statistical tests to provide a measure of confidence when comparing multiple groups. The routine is strengthened by complimentary analysis with other techniques such as TEM and Raman spectroscopy. Applied to human enamel from young and senior age groups, this routine reveals an enrichment of fluorine with age in the outer shell of nanocrystals, but not in the nanocrystal core or the intergranular space between nanocrystals. This reflects the culmination of decades of cyclical de- and re-mineralization during which fluorine is incorporated into the nanocrystal shells, though the nanocrystals themselves become slightly smaller and the separation between them slightly larger. The routine described above was also applied to “aprismatic” crocodilian enamel (i.e. without rods), complimenting a broader investigation of the sharp gradient in mechanical properties, composition, and nanocrystal morphology that arises at the outermost enamel surface.
Parameter selection during atom probe experimentation and choices made during analysis can have a substantial impact on the reported results. In pursuit of improved accuracy, precision, and repeatability for these and future experiments, this dissertation also includes a systematic exploration of the parameter space for atom probe experiments on synthetic hydroxyapatite. As part of this, we present a facile and automated approach to ranging of the mass-to-charge spectrum, from which the composition is derived. The significance of the wavelength of the laser pulse used during APT is also studied, with evidence indicating that hydroxyapatite is photoionized by the deep ultraviolet wavelength laser which comes equipped on the newest generation of commercial laser pulsed atom probe systems.
Finally, this dissertation incorporates the developments described above to compare inner enamel from primary, young, and senior age groups, with a particular focus on the presence of nanoscale organic precipitates that reside between some nanocrystals. Statistical analysis of these precipitates allows for the confident differentiation between organic (e.g., CO) and inorganic (e.g., CO2H) carbon-containing signals in atom probe reconstructions, which can then be applied to better understand the variations in both mineral and organic components between age groups. Additionally, retention of some precipitates after exposure of the enamel to a prolonged bleaching solution indicates that these organic features can be occluded by mineral and thus are resistant to change under attack by external threats.
Altogether, this research advances both our understanding of dental enamel as well as the measurement science required to explore nanoscale features in this and other material systems. We envision that future investigations will be able to delve deeper into specific conditions of global and clinical concern, such as aging populations, environmental exposures, caries, molar-incisal hypomineralization, and amelogenesis imperfecta
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
- …
