1,720,968 research outputs found
The meteorite collection of the Museo Nazionale dell’Antartide in Siena – December 2002 update
No full textThe updated (December 2002) catalogue for the meteorite collection of the Museo Nazionale dell'Antartide is presented. The collection primarily contains meteorites recovered from Antarctica by the Italian Programma Nazionale di Ricerche in Antartide, but also includes specimens from various locations around the world. The collection totals 983 specimens representing 28 876 g of extraterrestrial material of asteroidal and planetary origin, including 920 chondrites, 51 achondrites, 3 stony-iron meteorites and 9 iron meteorites
The meteorite collection of the Museo Nazionale dell’Antartide in Siena
No full textThe catalogue for the meteorite collection of Siena's Museo Nazionale dell'Antartide is presented. The collection primarily contains meteorites recovered from the Antarctic by the Italian National Programme for Antarctic Research but also includes specimens from various locations around the world. To date (April 2000), the collection totals 722 specimens. Of these, 533 specimens are classified, including 500 chondrites, 21 achondrites, 3 stony-iron meteorites, and 9 iron meteorites
Metamorphic evolution of the Koettlitz Group in the Koettlitz-Ferrar Glaciers region (southern Victoria Land, Antarctica)
No full textPolyphase medium- to high-grade metamorphism is described in the Koettlitz Group in the region between the Koettlitz and Ferrar Glaciers (southern Victoria Land, Antarctica). The critical metamorphic mineral assemblages define five metamorphic zones: muscovite+sillimanite and K-feldspar+sillimanite (in metapelites), biotite+calcite, Ca-amphibole, and Ca-pyroxene (in calc-silicate rocks). This metamorphic zonation, with increasing grade from the southwest to the northeast, developed during a syn-D1 progressive intermediate-P metamorphism with metamorphic peak conditions of PH2O 540 Ma, followed by magmatic accretion and low P / high T metamorphism at c. 500 Ma. All events occurred within the broadly convergent Neoproterozoic/Early Palaeozoic regime of the Ross orogenic belt in the Ross Sea sector of the palaeo-Pacific margin of Gondwana
Magnetic petrology of the Ross Orogen in Oates Land (Antarctica)
No full textThis paper presents the results of a pilot study on the magnetic petrology of basement rock units in the Ross Orogen in Oates Land (Antarctica). Magnetic susceptibilities of migmatitic gneisses - the dominant lithology - are generally low (ilmenite+/-graphite-bearing rocks), with the exception of two occurrences (magnetite+/-green spinel-bearing rocks) at Harald Bay and Burnside Ridge. Similar low values are typical for most Granite Harbour Intrusives, except for the variably mylonitic Exiles Nunataks granite and the Archangel Nunataks gabbros and pyroxenites, which are among the most magnetic rock types in the area. Metamorphosed mafic and ultramafic rocks, occurring in outcrop as volumetrically minor bodies (lenses of 1 dm to 10 m size), are variably but generally about one order of magnitude more highly magnetic than country gneisses. Petrological investigations on representative samples indicate that nearly pure or low-Ti magnetite is the only ferrimagnetic phase, irrespective of lithologic type, and magnetic susceptibility values are always positively correlated with the modal amount of magnetite. The rare occurrence of magnetite in the opaque mineralogy of migmatitic gneisses indicates that appropriate chemical and fO2 conditions were only locally attained in the region, and microstructural evidence indicate that magnetite possibly formed at different metamorphic stages during the post-peak decompressional path at high T and/or the retrograde path. In variably magnetic ultramafic and mafic lenses magnetite (almost pure to low-Ti) typically occurs as very fine grained opaque inclusions in secondary hornblende and/or chlorite. This evidence indicates that a high proportion of magnetite is of secondary origin and related to amphibolite grade or lower grade metamorphic processes. Titanomagnetite and exolution features are documented in the gabbros from Archangel Nunataks, in which the decrease of magnetite content is inversely correlated with the extent of sub-solidus late-magmatic re-equilibration (replacement of pyroxene by hornblende). Similar microstructural evidence of re-equilibration during cooling was also found in the highly magnetic magnetite-bearing mylonitic hornblende-biotite granites from Exiles Nunataks. All highly magnetic rock units represent potential petrologic sources of regional crustal magnetic anomalies in the Oates Land region as revealed by aeromagnetic surveys. In particular, the Exiles Nunataks magnetite-bearing granites are clearly marked by aeromagnetic anomalies forming a small part of the "Matusevich Anomaly", a prominent magnetic anomaly, co-linear with the Matusevich Glacier. The gabbros as exposed in the southestermost Archangel Nunataks are correlated with a distinct high-amplitude anomaly that occurs at this location and delineates the extent of the gabbroic intrusion itself. Significant volumes of metamorphosed mafic/ultramafic rocks may account for the high-frequency anomaly chains flanking the main part of the Matusevich Anomaly in the Lazarev Mountains
High pressure metamorphism in the nappes of the valle dell'Orco traverse (Western Alps collisional belt)
No full textAbstract A detailed field and petrological study of rocks from nappes cut by the Valle dell'Orco (Italian Western Alps), in particular the Sesia–Lanzo composite unit, has revealed geological and metamorphic histories which started in pre‐alpine times and lasted up to the alpine subduction‐collisional processes. During these processes the nappes sustained an early high P–low T stage and a later low P greenschist facies stage, but followed partly distinctive P–T–time trajectories. This paper discusses the kinematic evolution and the thermal history of the alpine belt from the early subduction/underthrust to the later exhumation stage. The metamorphic crystallization is often governed by incomplete and/or local equilibrium, and the pervasive syn‐metamorphic deformation and the composition of the syn‐metamorphic fluid phase (if present) have exerted an effective local control on reaction kinetics. Copyright © 1987, Wiley Blackwell. All rights reserve
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
- …
