1,721,229 research outputs found
Trace element mobility during interaction between rain and volcanic ash on Mt. Etna
No full textVolcanic emissions represent one of the most relevant natural sources of trace elements to the troposphere, both during and between eruptions. Due to their potential toxicity they may have important environmental impacts from the local to the global scale.
Atmospheric precipitation was collected approximately every two weeks, from April 2006 to December 2007, using a network of five rain gauges, located at various altitudes on the upper flanks around the summit craters of Etna volcano. The collected samples were analysed for major (Ca, Mg, K, Na, F, SO4, Cl, NO3) and a large suite of trace elements (Ag, Al, As, Au, B, Ba, Be, Bi, Cd, Co, Cr, Cs, Cu, Fe, Hg, La, Li, Mn, Mo, Ni, Pb, Rb, Si, Sb, Sc, Se, Sr, Th, Ti, Tl, U, V, Zn) by using different techniques (IC and ICP-MS ). The raingauges occasionally collected also fresh volcanic ashes emitted by the volcano during paroxysmal events. The ashes were retained by the filter-system used to block the coarse material. More than twenty events of ashfall were collected, but only half of these samples were suitable for a complete chemical analysis, due to the small amount of sample. In order to obtain elemental chemical composition of ashes, powdered samples were analysed by a combination of methods, including XRF, total digestion ICP-MS, INAA, and IR.
The chemistry of rainwater reveals that most of the investigated elements (both major and trace elements) have higher concentrations close to the emission vent of the volcano, confirming the prevailing volcanic contribution. Rainwater composition clearly reflects the volcanic plume input. Ash-normalised rainwater composition indicates a contrasting behaviour between volatile elements, which are highly-enriched in rainwater, and refractory elements, which have low rainwater/ash concentration ratios. The degree of interaction between collected ash and rainwater was variable, depending on several factors: (i) the length of the period in which tephra was present in the sampler (the ash fall may have occurred any day from the first to the last day of the rain collecting period); (ii) the amount of rainwater fallen on the collectors after the ash-fall event, and its acidity; (iii) the granulometry of the ash samples that was widely variable (from few centimetres to micrometric particles) with increasing interaction due to the decreasing dimensions of the tephra grains; (iv) the distance of collector with respect to the craters. All these factors govern the efficiency of the dissolution processes of the volcanic ash, and the amount of elemental leaching from their surface.
The results suggest that sulphate and halide salt aerosols are adsorbed onto ash particles, and their rate of dissolution in rainwater depends on solubility. Moreover, rapid chemical weathering of the silicate glass by the corrosive volcanic acid (SO2, HCl and HF) can also explain the enrichment of several refractory elements (Na, K, Ca, Mg, Si, Al, Fe, Ti, Sc)
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
Final report of Research Unit V3_7/02
No full textINGV-DPC Project V3_7 - PantelleriaUnpublished1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attiveope
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
Estimation of the magmatic gas and heat flux through the Etnean volcanic aquifer
No full textEtna volcano, Italy, hosts one of the major groundwater systems of the island of Sicily. Waters circulate within
highly permeable fractured, mainly hawaiitic, volcanic rocks. Aquifers are limited downwards by the underlying
impermeable sedimentary terrains. Thickness of the volcanic rocks generally does not exceed some 300 m,
preventing the waters to reach great depths. This is faced by short travel times (years to tens of years) and low
thermalisation of the Etnean groundwaters. Measured temperatures are, in fact, generally lower than 25 °C. But
the huge annual meteoric recharge (about 0.97 kmˆ3) with a high actual infiltration coefficient (0.75) implies a
great underground circulation. During their travel from the summit area to the periphery of the volcano, waters
acquire magmatic heat together with volcanic gases and solutes through water-rock interaction processes.
In the last 20 years the Etnean aquifers has been extensively studied. Their waters were analysed for dissolved
major, minor and trace element, O, H, C, S, B, Sr and He isotopes, and dissolved gas composition. These data have
been published in several articles. Here, after a summary of the obtained results, the estimation of the magmatic
heat flux through the aquifer will be discussed.
To calculate heat uptake during subsurface circulation, for each sampling point (spring, well or drainage gallery)
the following data have been considered: flow rate, water temperature, and oxygen isotopic composition. The
latter was used to calculate the mean recharge altitude through the measured local isotopic lapse rate. Mean
recharge temperatures, weighted for rain amount throughout the year, were obtained from the local weather station
network. Calculations were made for a representative number of sampling points (216) including all major issues
and corresponding to a total water flow of about 0.315 kmˆ3/a, which is 40% of the effective meteoric recharge.
Results gave a total energy output of about 140 MW/a the half of which is ascribable to only 13 sampling points.
These correspond to the highest flow drainage galleries with fluxes ranging from 50 to 1000 l/s and wells with
pumping rates from 70 to 250 l/s. Geographical distribution indicates that, like magmatic gas leakage, heat flow
is influenced by structural features of the volcanic edifice. The major heat discharge through groundwater are all
tightly connected either to the major regional tectonic systems or to the major volcanic rift zones along which
the most important flank eruptions take place. But rift zones are much more important for heat upraise due to the
frequent dikes injection than for gas escape because generally when dikes have been emplaced the structure is no
more permeable to gases because it becomes sealed by the cooling magma.PublishedVienna, Austria1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attiveope
Final report of Research Unit V3_7/02
No full textINGV-DPC Project V3_7 - PantelleriaUnpublished1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attiveope
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
- …
