1,721,055 research outputs found
The volcanic ash problem
No full textExplosive volcanic eruptions are the result of intensive magma and rock fragmentation, and they produce volcanic ash, which consists of fragments < 2 min in average diameter. The problem with volcanic ash is that its formation is poorly understood from the standpoint of eruption energetics. Because the source of explosive eruption energy should be the thermal energy of magma, and because an explosion requires rapid conversion of energy into a mechanical form, and because of the physical properties of magma thermal energy is dominantly released by conduction, the energy release on a short time scale (explosion) in volcanic processes has to be the result of a special mechanism, probably a positive feedback mechanism of fragmentation and heat exchange. In fact, the most explosive volcanic explosions are characterized by the most intensive fragmentation. In any fragmentation mechanism the generated particle sizes reflect the kinetic energy available (i.e. the fragmentation energy density). Consequently, fine ash (less than or equal to 64 mum) provides information on fragmentation mechanisms that are the most energetic and related to the highest explosive energy release. In this letter we discuss mechanisms of formation of fine volcanic ash, using experimental results, theoretical considerations, and field observations. We focus on the potency of these mechanisms to explain fine ash produced by explosive volcanism. We conclude that quantitative analysis of fine ash particles is necessary to estimate the mechanical energy of volcanic explosions
Identifying magma-water interaction from the surface features of ash particles
No full textThe deposits from explosive volcanic eruptions (those eruptions that release mechanical energy over a short time span(1)) are characterized by an abundance of volcanic ash(2,3). This ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre-existing crust (host rocks). Interactions between rising magma and the hydrosphere (oceans, lakes, and ground water) play an important role in explosive volcanism(4,5), because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy, Although the relative proportion of magma to host-rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions, it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits(2-5). Here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments. We find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water, The abundance of such ash grains can then be related to the water/magma mass ratios during their interaction
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Great Sumatra Earthquake Registers on Electrostatic Sensor
No full textStrong electrical signals that correspond to
the Mw = 9.3 earthquake of 26 December 2004,
which occurred at 0058:50.7 UTC
off the west coast of northern Sumatra, Indonesia,
were recorded by an electrostatic sensor
(a device that detects short-term variations in
Earth’s electrostatic fi eld) at a seismic station
in Italy, which had been installed to study the
infl uence of local earthquakes on a new landslide
monitoring system
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