1,721,142 research outputs found
Merapi Volcano: Geology, Eruptive Activity, and Monitoring of a High-Risk Volcano
No full textThis book provides the first comprehensive compilation of cutting-edge research on Merapi volcano on the island of Java, Indonesia, one of the most iconic volcanoes in the world. It integrates results from both the natural (geology, petrology, geochemistry, geophysics, physical volcanology) and social sciences, and provides state-of-the-art information on volcano monitoring, the assessment of volcanic hazards, and risk mitigation measures.As one of Indonesia’s most active and dangerous volcanoes, Merapi is perhaps best known for its pyroclastic density currents, which are produced by gravitational or explosive lava dome failures (commonly referred to as Merapi-type nuées ardentes). Merapi’s eruptions have posed a persistent threat to life, property and infrastructure within the densely populated areas on the volcano’s flanks, as demonstrated most recently by catastrophic eruptions, which attracted worldwide media interest
Three-dimensional geometry of concentric intrusive sheet swarms in the Geitafell and the Dyrfjöll Volcanoes, Eastern Iceland
No full textSheet intrusions (inclined sheets and dykes) in the deeply eroded volcanoes of Geitafell and Dyrfjöll,eastern Iceland, were studied at the surface to identify the location, depth, and size of their magmaticsource(s). For this purpose, the measured orientations of inclined sheets were projected in three dimensionsto produce models of sheet swarm geometries. For the Geitafell Volcano, the majority of sheetsconverge toward a common focal area with a diameter of at least 4 to 7 km, the location of which coincideswith several gabbro bodies exposed at the surface. Assuming that these gabbros represent part of the magmachamber feeding the inclined sheets, a source depth of 2 to 4 km below the paleoland surface is derived.A second, younger swarm of steeply dipping sheets crosscuts this gabbro and members of the first swarm.The source of this second swarm is estimated to be located to the SE of the source of Swarm 1, below thepresent‐day level of exposure and deeper than the source of the first swarm. For the Dyrfjöll Volcano,we show that the sheets can be divided into seven different subsets, three of which can be interpretedas swarms. The most prominent swarm, the Njardvik Sheet Swarm, converges toward a several kilometerswide area in the Njardvik Valley at a depth of 1.5 to 4 km below the paleoland surface. Two additionalmagmatic sources are postulated to be located to the northeast and southwest of the main source. Crosscuttingrelationships indicate contemporaneous, as well as successive activity of different magma chambers,but without a resolvable spatial trend. The Dyrfjöll Volcano is thus part of a complex volcanic cluster thatextends far beyond the study area and can serve as fossil analog for nested volcanoes such as Askja, whereasin Geitafell, the sheet swarms seem to have originated from a single focus at one time, thus defining a singlecentral volcanic complex, such as Krafla Volcano
Weibull-distributed dyke thickness reflects probabilistic character of host-rock strength
Full text linkMagmatic sheet intrusions (dykes) constitute the main form of magma transport in the Earth’s crust. The size distribution of dykes is a crucial parameter that controls volcanic surface deformation and eruption rates and is required to realistically model volcano deformation for eruption forecasting. Here we present statistical analyses of 3,676 dyke thickness measurements from different tectonic settings and show that dyke thickness consistently follows the Weibull distribution. Known from materials science, power law-distributed flaws in brittle materials lead to Weibull-distributed failure stress. We therefore propose a dynamic model in which dyke thickness is determined by variable magma pressure that exploits differently sized host-rock weaknesses. The observed dyke thickness distributions are thus site-specific because rock strength, rather than magma viscosity and composition, exerts the dominant control on dyke emplacement. Fundamentally, the strength of geomaterials is scale-dependent and should be approximated by a probability distribution
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
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