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Very long period volcanic tremor at Stromboli volcano, Italy
No full textWe analyze a long time–space series of Stromboli volcanic tremors. A
very-low-frequency content in the range of 0.02–0.5 Hz has been found by using
spectral analysis and independent component analysis. Independent component analysis
is an entropy-based technique. We observe the occurrence of a component having
a period of 30 sec. Polarization analysis shows that the wave field comes mainly
from the crater area, well evidenced by seismometers located around the summit
ring, whereas the radiation becomes increasingly scattered at stations located around
the base of this volcano. Based on its apparent velocity, the 30-sec component appears
to be a slow wave, related to inhomogeneities of the source and/or gas-pressure
fluctuations inside the shallow plumbing system.
Introduction
Stromboli is one of the most active volcanoes in the
world, characterized by persistent explosive activity superimposed
on a background volcanic tremor.
During recent years, Strombolian events, particularly at
high frequencies (0.5 Hz), have been studied by different
authors (Del Pezzo et al., 1992; Chouet et al., 1997; Saccorotti
and Del Pezzo, 2000; Acernese et al., 2003). Many
results have been extracted concerning spectral features, polarization
analysis, location, and modeling of the source,
leading to the general agreement that tremor and explosions
seem to be generated by the same dynamic source process;
namely, the source of tremor and explosions at high frequency
seems to be located at a shallow depth beneath the
active craters.
A preliminary study carried out by Neuberg et al. (1994)
on broadband observations showed that Strombolian eruptions
can produce signals with periods of 10 sec or longer.
Moreover, very-long-period events have been revealed on
other volcanoes in the world (Rowe et al. 1998; Ohminato
et al., 1998). Since then, much attention has been devoted
to the study of the broadband nature of Strombolian events
and, recently, explosion quakes at low frequency (0.02–0.5
Hz) have been analyzed, constraining the geometry and the
dynamics of the source (Chouet et al., 1999, 2003); namely,
the source associated with explosions (whose time length
ranges from 5 to 15 sec) is localized below the same crater
area previously recognized for the high-frequency seismograms.
On the contrary, the characteristics of tremor at low
frequency are still unknown, so the aim of our work is to
study a long series of tremors in the range of 0.02–0.5 Hz.
This could give new insight into the fluid-dynamic mechanisms
involved i
Logarithmic Schroedinger-like equation as a model for magma transport
No full textWe show that, under a suitable assumption on the pressure tensor, the mass
and momentum balance equations ofh ydrodynamical theory, introduced in the early 1980s by
many authors to describe matrix separation, yield the equations ofthe Madelung fluid that are
equivalent to the Schr ̈odinger-like equation with logarithmic nonlinearity. This equation has
solitary-waves solutions as required by many experimental volcanic model
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
Analisi di polarizzazione della componente fondamentale degli eventi a bassa frequenza di Stromboli (Isole Eolie Italia)
No full text- …
