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Natural gadolinium discharge from volcanic sources
No full textAlthough a large fraction of chemicals is provided from volcanic fluids to the environment (Oppenheimer et al., 2014) only a scarce literature was focused on the Rare Earth elements (REE) release from high temperature fumaroles (Möller et al., 2003; Gilbert & Williams-Jones, 2008; Zelenski et al., 2013). In order to fill this gap, this research was carried out mainly taking in account the REE partitioning during the emissions of fumarolic fluid between newly-forming sublimates and the remaining gas phase. The latter was collected as alkaline condensates according to Sortino et al. (2006). The investigated high temperature fumaroles (95-450°C) occur in several volcanic systems at Vulcano (Aeolian Islands) and Phlegrean Fields (Italy), Santorini (Cyclades Islands, Greece), Canary Islands (Spain) and Cape Verde where strong passive emission of fluids occur.
Fumarolic sublimates show higher lanthanide contents, whereas alkaline condensates represent the most volatile fractions of these fluids. The analysis of geochemical behaviour of these elements was investigated studying the features observed in shale-normalised REE patterns (vs. PAAS, Taylor and McLennan, 1995). This analysis indicates that Gd is preferentially partitioned in the vapour phase during the sublimation of less volatile fluid fractions. Consequently, positive Gd anomalies occur in alkaline condensates with respect to coexisting solid sublimates. The amplitudes of these anomalies can be assessed according to the equation:
(Moller et al., 2007) where n-suffix indicates normalised lanthanide concentrations and Gd* is the expected normalised Gd concentration according to Tb and Ho contents. Comparing the amplitudes of these anomalies with the temperatures of investigated fumaroles larger Gd/Gd* values are mainly found in higher temperature fumaroles (450-250°C) in Vulcano (1.5 ≤ Gd/Gd* ≤ 6.8) and less in lower temperature fumaroles (285-82°C) studied in Phlegrean Fields, Canary and Cape Verde islands (1.1 ≤ Gd/Gd* ≤ 2.7).
Moreover, comparing the amplitudes of Gd/Gd* and related HCl/HF ratio values of alkaline condensates a significant positive relationship is observed only in alkaline condensates collected from higher temperature fumaroles (T > 200 °C). This evidence is consistent with a preferential REE complexation via Cl-complexes in vapour phase and can be considered a consequence of nephelauxetic effect. According to this suggestion the growth of positive Gd anomalies is a consequence of changes of the first Gd hydration sphere during the formation of Gd-chloride complexes at higher temperature and does not occur if complexes are formed at temperatures up to 200 °C (Mayanovic et al., 2007).
Being REE-chloride complexes highly soluble species quickly removed from the atmosphere by water droplets, Gd coming from volcanic gas phase could represent a significant component of the geochemical Gd cycle in aqueous media
Possible role of fluid overpressure in the generation of earthquake swarms in active tectonic areas: The case of the Peloritani Mts. (Sicily, Italy)
Full text linkThe Peloritani Mts. (NE Sicily) are characterized by frequent seismicity. Between 1994 and 2006 more than 1000 earthquakes (1.0 <= M-L <= 3.3) occurred, mostly as highly clustered swarms located at shallow depth near the villages of Castroreale and Rod! Milici (western part of Peloritani Mts.). The same area is also characterized by some geothermal springs and gas vents. Using a multidisciplinary approach, data were collected on the tectonic setting, seismicity pattern and geochemical characteristics of fluid emissions, with the aim of understanding the process of earthquake swarm generation beneath the investigated area. Most of the gases emitted in the study area. in terms of focused and/or diffuse gas emissions often associated with thermal fluids, is of mantle origin, as shown by their He isotopes ratio. On approaching the surface. deep gases interact strongly with local aquifers. An estimate of both the surface efflux of mantle-derived gases measured in focused emissions and of the P-T conditions of fluids in the local crust point to a pressurised gas source that would be located at depth of 7-12 km, corresponding to the range of hypocentral depths of seismic swarms. The complex network of tectonic structures in the area would act as high-permeability pathways for the migration of sub-crustal fluids towards the surface. This scenario could be compatible with a close interplay between pressurised mantle fluids at depth, nucleation of earthquakes due to higher-thanhydrostatic pore pressure and release of mantle-derived gases at the surface. This sequence would be repeated in time, thus producing the observed cycles in the local seismic activity
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
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