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Image processing analysis in reconstructing fragmentation and transportation mechanisms of pyroclastic deposits. The case of Monte Pilato-Rocche Rosse eruptions, Lipari (Aeolian islands, Italy)
No full textA quantitative study of particle morphology of samples from Monte Pilato-Rocche Rosse deposits, Lipari (Aeolian islands, Italy) shows a significant variability in particle structure and texture. The study consisted of image processing techniques and multivariate statistical methods in analysis of the quantitative particle morphology data, with the goal of identifying the genetic processes responsible for the formation of the deposits. From these investigations we numerically define the form of the clasts, thus avoiding subjectivity in the classification of clast morphology, Starting from this clast definition, we then construct diagrams in which clasts due to different genetic processes (i.e., magmatic vs. hydromagmatic fragmentation), are discriminated based on simple nondimensional parameters, The application of the methods used seems to be of general interest in discriminating the fragmentation and transportation dynamics responsible for the formation of pyroclastic deposits
FRAGMENTATION VERSUS TRANSPORTATION MECHANISMS IN THE PYROCLASTIC SEQUENCE OF MONTE-PILATO ROCCHE-ROSSE (LIPARI, ITALY)
No full textMonte Pilato is a rhyolitic pumice cone formed about 1400 years ago during the last volcanic activity which occurred at Lipari. Its activity consisted of numerous explosive episodes, ending with the extrusion of the Rocche Rosse obsidian lava flow. We have identified nine different pyroclastic lithofacies, of which four main lithofacies represent 90% of the erupted products; they include: (1) deposits consisting of decimeters- to meters-thick well-sorted, graded beds of pumice lapilli, which are of fall origin; (2) massive deposits consisting of decimeters-thick beds of pumice lapilli in an ash matrix, interpreted as being of pyroclastic flow origin; (3) deposits of centimeters-thick ash beds of surge origin; (4) decimeter-thick fine ash layers with scattered subcentimetric accretionary lapilli of turbulent ''flow'' origin.
The complex grain size distributions of the main lithofacies were distinguished using a multivariate statistic analysis (R-mode factor analysis). Variations of the grain size characteristics in relation to the distance from the vent area have been investigated in order to discriminate the roles played by fragmentation and transportation processes. In the lithofacies 1 fall deposits, the grain size distribution is always unimodal and varies from a Rosin-type distribution near the vent to a Gaussian one in the distal outcrops. This is caused by the transport process and the different particle trajectories. In lithofacies 2, 3 and 4, the grain size distributions are always polymodal. The polymodality is not caused by preferential processes occurring during transportation, but seems, rather, to be connected with the original fragmentation of the pyroclastic material. The pumice lapilli present both in lithofacies 1 and 2 have mean vesicularity index values always in excess of 65%, and the value is homogeneous throughout the sample. These data suggest that for these two lithofacies, the pumice lapilli originated from exsolution of magmatic gases. In contrast, the fine ash particles in lithofacies 2, and also the main mode of lithofacies 3 and 4 deposits, show typical features of hydromagmatic fragmentation processes. The grain size population is always centered at 4-5 phi (0.032-0.064 mm) and, interestingly, the same grain size has been obtained recently (Zimanowski et al., 1991) for fragments produced by experimental magma/water interaction. Field and laboratory data suggest that during Monte Pilato-Rocche Rosse eruptions magmatic and hydromagmatic mechanisms were frequently operative at the same time
Eruptive and emplacement mechanisms of widespread fine-grained pyroclastic deposits on Vulcano Island (Italy)
No full textTufi di Grotte dei Rossi Inferiori are thick ash deposits, representing the most voluminous stratigraphic unit on Vulcano Island. The deposits are related to hydromagmatic eruption which occurred under shallow water inside a caldera depression. Grain-size data and results of SEM investigation allow the character of the transporting medium, solid material concentration in the cloud during the lateral expansion, and the nature and role of the fluids present at the time of deposition to be constrained. We suggest that the eruption was characterized by closely timed hydromagmatic pulses giving rise to eruption clouds rich in water vapor and steam. The coarser material was not significantly transported in the eruptive cloud and it probably deposited in the caldera depression area. The finer material was extensively transported in the cloud, creating turbulent flows which surmounted the caldera rim barrier and dispersed in a southward direction, forming widespread deposits in the Piano area. Lower concentrated flows produced laminated deposits of more limited dispersion, whereas higher concentrated flows formed more dispersed thicker massive layers
MINERAL CHEMISTRY OF MONTE VULTURE VOLCANICS - PETROLOGICAL IMPLICATIONS RID A-1229-2011
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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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