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Occurrence and implications of secondary olivine veinlets in lunar highland breccia Northwest Africa 11273
No full textLunar breccias preserve the records of geologic processes on the Moon. In this study, we report the occurrence, petrography, mineralogy, and geological significance of the observed secondary olivine veinlets in lunar feldspathic breccia meteorite Northwest Africa (NWA) 11273. Bulk-rock composition measurements shown that this meteorite is geochemically similar to other lunar highland meteorites. In NWA 11273, five clasts are observed to host veinlets that are dominated by interconnecting olivine mineral grains. The host clasts mainly composed of mafic minerals (i.e., pyroxene and olivine) and probably sourced from a basaltic lithology. The studied olivine veinlets (~5 to 30 μm in width) are distributed within the mafic-mineral host, but do not extend into the adjacent plagioclase. Chemically, these olivine veinlets are Fe-richer (Fo41.4–51.9), compared with other olivine grains (Fo54.3–83.1) in lithic clasts and matrix of NWA 11273. By analogy with the secondary olivine veinlets observed in meteorites from asteroid Vesta (HED-group samples) and lunar mare samples, our study suggests that the newly observed olivine veinlets in NWA 11273 are likely formed by secondary deposition from a lunar fluid, rather than by crystallization from a high-temperature silicate melt. Such fluid could be sulfur- and phosphorous-poor and likely had an endogenic origin on the Moon. The new occurrence of secondary olivine veinlets in breccia NWA 11273 reveals that the fluid mobility and deposition could be a previously underappreciated geological process on the Moon
Procesos geoquímicos de alteración en el patrimonio natural: las especificidades del Meteorito Lunar NWA 11273
Get PDF46 p. : il. -- Bibliogr: pp. 43-46En el Trabajo Fin de Máster “PROCESOS GEOQUÍMICOS DE ALTERACIÓN EN EL
PATRIMONIO NATURAL: las especificidades del Meteorito Lunar NWA 11273” se han
resuelto los principales objetivos planteados.
El primero era completar la caracterización geoquímica del meteorito mediante dos
técnicas analíticas no destructivas complementarias, la micro-fluorescencia de rayos
X y la espectroscopia Raman. Con ellas se identificaron los minerales: anortita, olivino,
piroxeno, zircón, hematita, calcita, camacita, anatasa, cuarzo, ilmenita, troilita,
ilmenita, enstatita, rozenita y retgersita.
El segundo consistía en estudiar las principales alteraciones o procesos de
meteorización a los que se había visto sujeto el Patrimonio Natural, concretamente,
el meteorito lunar NWA 11273. Para ello se establecieron relaciones entre las distintas
fases minerales encontradas a lo largo de la caracterización. Pudiéndose distinguir tres
tipos de alteraciones: las de por presión, por oxidación y por meteorización terrestre.
La posición de la banda principal de zircón reveló que se trataba de un zircón de
impacto y que el meteorito salió eyectado de la Luna con una presión de 20 GPa. Esta
presión provocó la meteorización de algunos olivinos a, principalmente, enstatita,
entre otros minerales secundarios.
Debido a la entrada del meteorito en una atmósfera oxidante, algunos minerales se
oxidaron, como lo hizo la ilmenita, generando anatasa y hematita. Así mismo, algunos
de los olivinos que quedaron sin alterarse debido a la presión, se oxidaron generando
como subproductos cuarzo y hematita.
Finalmente, se detectaron algunas de los procesos de meteorización terrestre más
comunes, como lo son la precipitación de carbonato cálcico en forma de calcita y la
generación de sulfatos.
Se pretende trasladar la información generada acerca de las alteraciones del
meteorito lunar NWA 11273 a cualquier tipo de patrimonio sometido a condiciones
iguales o similares que la muestra estudiada
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
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