1,721,129 research outputs found
Fluids in early stage hydrothermal alteration of high-sulfidation epithermal systems: A view from the Vulcano active hydrothermal system (Aeolian Island, Italy)
No full textHigh-sulfidation (HS) epithermal systems have elements in common with passively degassing volcanoes associated with high T,
acid fumarole fields or acid crater lakes. They are considered to form in two stages, the first of which involves advanced argillic
alteration resulting from intense, strongly acidic fluid–rock interaction. The La Fossa hydrothermal system (Vulcano Island)
represents a classic example of such an active HS system and can be considered as a modern analogue of this early stage of
alteration, resulting in a core of intense silicic (90–95% pure SiO2) alteration surrounded by alunitic alteration zones.
This paper focuses on a geochemical and stable isotope study of the surficial alteration facies of Vulcano – particularly the horizon
characterized by strong silicic alteration – and on deep seated xenoliths ejected during the last eruption of La Fossa volcano (1888–90)
that can be considered as representative of fragments of the deep conduit system of La Fossa volcano. Using directly measured
temperatures at the sites of sampling, we have calculated fluid composition in isotopic equilibrium with the alteration products. The
large range of measured silica δ18O (12.3 to 29‰) reflects the wide range of formation temperatures (80–240 °C). The fluid
compositions calculated for intense silicic alteration vary from −0.9 to +6.5‰. These are significantly heavier than local meteoric
water (−6‰), and are consistent with derivation from the condensation of high-temperature fumarolic gases, dominated by magmatic
fluids and rich in acid gases (SO2, H2S, HCl, HF), into shallow groundwaters of meteoric origin, with dynamically variable ratios of
fumarolic steam/meteoric water. The calculated δ18O and δD of water in equilibrium with alunite also suggest the mixing of magmatic
and meteoric waters for the fluids involved in the genesis of advanced argillic alteration facies.
The calculated δ18Oofwater in equilibrium with hedenbergitic clinopyroxene, found in a veinlet in ametasomatized xenolith is +8.9‰.
This value cannot reasonably result from water–rock interaction between the host volcanic rocks and surface water. Instead, it most likely
represents a fluid (brine) exsolved from magma, which was responsible for high temperature metasomatism in the deep conduit system.
© 2007 Elsevier B.V. All rights reserved
Sulphur, sulphate oxygen and strontium isotopic composition of Cenozoic Turkish evaporates
No full textSulphur (δ34S) and strontium isotope (87Sr/86Sr) ratios have been measured in 37 sulphate minerals (gypsum, celestite and thenardite) and 4 sulphide samples (δ34S only) from 9 Cenozoic marine and nonmarine evaporites located in Anatolia, Turkey. Oxygen isotope (δ18Osulphate) ratios were also measured in 25 gypsum and 1 anhydrite sample from these deposits. These data have been used to determine the origin of dissolved sulphate in the brines that precipitated these minerals. They show that seawater was the dominant source of sulphate and Sr in the marine evaporites, but that perturbations from contemporaneous seawater Sr and sulphur isotope compositions result from recycling of older evaporites and sulphate reduction. Although continental geothermal fluids played an important role in supplying the dissolved salts that formed the nonmarine evaporites, the δ18Osulphate, δ34S and Sr isotope compositions of many of these nonmarine evaporites are indistinguishable from the marine evaporites. As well as suggesting that recycling of marine evaporites was important for controlling the composition of the nonmarine evaporites, it also suggests that δ18Osulphate, δ34S and Sr isotope compositions are not unequivocal tracers in distinguishing between these two types of evaporite. For the Turkish evaporites considered here, the major difference between marine and nonmarine evaporites that contain similar δ34S – δ18Osulphate – 87Sr/86Sr relationships is that the latter contain high concentrations of boron that reflect a geothermal contribution to the deposits
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Speleothem evidence of late glacial and Early Holocene Preboreal and Boreal hydro-climate changes in western Mediterranean (Corchia Cave, Italy)
No full textThis paper explores the rainfall variability across the western Mediterranean area from ca. 12 to 9 ka, and its
climate teleconnection within the northern Hemisphere realm. A high-resolution stable isotope (δ18O, δ13C) and
growth rate record from a Corchia Cave stalagmite (Apuan Alps, Central Italy) shows evidence of: 1) increased
rainfall during the transition from the late Younger Dryas (YD) to the Holocene; and 2) two Early Holocene
episodes of reduced rainfall during the so-called Preboreal and Boreal Oscillations (PBO and BO respectively).
The YD to Holocene transition occurs at Corchia from 11.91+0.10/-0.11 to 11.33+0.07/-0.07 ka, in agreement with
other Mediterranean records. The expression of PBO is constrained in Central Italy between 11.19+0.09/-0.08 and +0.09 +0.13 +0.27
11.04 /-0.09 ka, while the BO from 10.42 /-0.27 to 10.19 /-0.24 ka, contemporaneous with a significant reduction of the Lago dell’ Accesa lake levels (Central Italy).
The new record suggests that the increase of rainfall at Corchia during the deglaciation is connected to the enhanced evaporation from a warming north Atlantic and the higher moisture amount across the Mediterranean delivered by the westerlies. Reduced rainfall is instead attested during PBO/BOs. The latter are often associated with fluxes of ice-sheet meltwaters into the Atlantic, which trigger a deficit in moisture availability resulting in lower humidity reaching the Mediterranean area. This work confirms that the PBO/BO relative aridity is restricted to the Mediterranean area, while mid-European records point to moister conditions within the same events. Thus, our results imply that future – even subtle - polar ice sheet instabilities, boosted by the ongoing climate crisis, might amplify the change of rainfall dynamics across the western Mediterranean, a hot-spot area for climatic change that is already experiencing an increasing number of drought years
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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