1,721,370 research outputs found
Source lithology of the Galápagos plume
No full textWe have measured the contents of Ni, Ca, and Mn in olivine phenocrysts from volcanoes in the Galápagos archipelago to infer the mantle source lithologies. Results show that peridotite is the dominant source lithology for Fernandina, Floreana, Genovesa, Marchena, Pinta, Wolf Island, and Darwin Island. These volcanoes largely characterize the PLUME, WD, FLO and DUM Nd, Sr, and Pb isotopic endmembers of Harpp and White (2001). Only a minor pyroxenite component contributes to Fernandina and Floreana. Peridotite is also the dominant source lithology for Volcan Wolf, Alcedo, and Cerro Azul, and that these have isotopic compositions that can be defined by mixing of the 4 endmembers. Peridotite is therefore the dominant source lithology of the Galápagos plume. However, pyroxenite melting is significant in two spatially separated domains which are also isotopically distinct: Roca Redonda, Volcan Ecuador, Sierra Negra in the enriched western part of the archipelago and Volcan Darwin, Santiago, Santa Cruz, and Santa Fe in the depleted east. An implication is that the western and eastern pyroxenite domains likely represent two separate bodies of recycled crust within the Galápagos mantle plume. Isotopically enriched and depleted domains of the archipelago melted from both peridotite and pyroxenite, and there is no relationship between source lithology and its isotopic characteristics. The identification of peridotite source melting in volcanoes with isotopic characteristics that have been attributed to recycled crust points to the importance of mixing in OIB genesis, in agreement with studies on the Canary Islands.M.S.Includes bibliographical referencesby Christopher Allen Vidit
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
Of pigeons, and mud, and streets, and clouds
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: S.M., Massachusetts Institute of Technology, Department of Architecture, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 127-129).Attending to nonhumans--the innumerable trees, rats, cows, copper, smog, clouds, bricks, oil, shade, doors, speed bumps, and others who must be omitted for the requisite brevity of an 'abstract'--orients the ecological problem per our everyday epistemology: how we relate with the world. In this domain, architecture, fundamentally an environmental medium, may operate as a fulcrum, shifting how we situate ourselves within the world.Yet, before we can design in such a way, we must first learn to witness the agency of nonhumans, a shift which demands expanded practices of attention and representation. This thesis focuses on a technique of mediated observation-simultaneously filmic, sonic, and textual-promoting an awareness of the multiple dimensions through which nonhumans constitute collectives. Playing upon the ubiquity of mobile devices, these techniques are brought together in the form of a smart phone application that prompts users to redirect their attention to the multitude of entities active around them. Participants' responses aggregate as a database of relational anecdotes, which is then choreographed into a series of episodic representations. Forgoing the human monopoly over the fabrication of worlds, these seek to foster an aesthetic "contact zone" whereby the agency of nonhumans is foregrounded. De-centering, yet not negating, the human.by Christopher Allen Weaver.S.M.S.M. Massachusetts Institute of Technology, Department of Architectur
Non-invasive recovery of gear rotation from machine vibration dc by Christopher Allen Lerch.
No full textThesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995.Includes bibliographical references (p. 102-103).M.S
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
African Perspectives. Papers in the History, Politics and Economies of Africa presented to Thomas Hodgkin, éd. by Christopher Allen and R. W. Johnson
No full textPerson Yves. African Perspectives. Papers in the History, Politics and Economies of Africa presented to Thomas Hodgkin, éd. by Christopher Allen and R. W. Johnson. In: Revue française d'histoire d'outre-mer, tome 59, n°215, 2e trimestre 1972. pp. 320-322
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
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