1,720,968 research outputs found
Paroxysm-induced early warning signals at Stromboli volcano, Italy
No full textMt. Stromboli is an iconic active volcano, located in the Aeolian Islands archipelago, off the north coast of Sicily (Italy), in the Mediterranean Sea. Its volcanic activity is characterized by mild and frequent explosions, sometimes interrupted by occasional episodes of more vigorous activity, which can be accompanied by lava flows and more energetic eruptions, known as "major" or "paroxysmal" eruptions, according to the energy dissipated during the event.
Stromboli produced vulcanian eruptions in 2003, 2007 and July-August 2019, which were well recorded by the INGV monitoring network. In particular the last three events were accompanied by a wide range of phenomena (pyroclastic flows which produced tsunami waves, lava flows, eruptive column several kilometers high) and have been studied through records from borehole strainmeters, which allow us to infer many details of source dynamics. These events are clearly preceded by an inflation phase of the volcanic building characterized by a slow strain buildup, starting several minutes before the paroxysms. These observations could be used in future for civil protection purposes. The recorded eruptions consist of two or more pulses, with oscillations ranging from several seconds, as in 2007, to some minutes, such as in 2019 and lasting from several minutes to one hour after the explosions.
Mechanisms involved in the triggering process of the vulcanian explosions include an increase of magma flux ascending from sources located from 2 to 5-7 km depths and morphological complexity in the upper feeding system.
A preliminary early-warning algorithm, based on an evaluation of strain rate change, has been defined: it has shown itself capable of ascertain the occurring eruptions minutes before their summit onset
Abrupt magma chamber contraction and microseismicity at Campi Flegrei, Italy: Cause and effect determined from strainmeters and tiltmeters
Full text linkIn March 2010 two borehole strainmeters and three Michelson tiltmeters within the Campi Flegrei volcanic system, Italy, registered an abrupt deformation signal that was followed 20 min later by seismic slip on a pair of onshore normal faults. We demonstrate that the observed strain changes were caused by a small but rapid volume decrease in a previously identified offshore ellipsoidal magma source or part of it. Although the total deflation was below the detectability of interferometric synthetic aperture radar and GPS, deflation observed rates were briefly 2 orders of magnitude more rapid than decadal inflation rates. We conclude that this high dilatational contraction rate was responsible for triggering seismicity and that this process may be responsible for the normal faulting often observed in the Campi
Flegrei region. Our study quantifies the crucial role played by a transient, minor reduction in dilatational stress, in triggering slip on a fault near critical failure. Our subsurface measurements of strain and tilt registered anomalous deformation three sigma above background noise levels 17 min before the onset of microseismicity suggesting strain measurements have potential utility as an early warning system for the city of Naples
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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