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Strontian fluoro-magnesiohastingsite in Alban Hills lavas (Central Italy): constraints on crystallization conditions
No full textA magmatic calcic amphibole (Ca-M4 greater than or equal to1.50) characterized by large Sr and F contents (SrO >1 wt.%, F >2.5 wt.%) is described. According to the crystal-chemical formula, the amphibole can be classified as a strontian fluoro-magnesiohastingsite and the presence of Sr cations in the A sites is suggested. The amphibole occurs in the groundmass of ultrapotassic lavas from the Alban Hills Volcanic District (Central Italy). This peculiar chemical composition is due to the lavas' groundmass compositional trend occurring under low silica-activity conditions. We suggest that the occurrence of F amphiboles allows us to consider the Alban Hills Volcanic District magmas to be as rich in F as other ultrapotassic magmas
Volcanic history and magmatic evolution of Southern Vulsini (Central Italy): preliminary data.
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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
Water diffusion in natural potassic melt. In Volcanic Degassing: experiments, models, observations and impacts
No full textWater diffusion experiments were performed on a trachytic melt from the Agnano-Monte Spina explosive eruption (Phlegrean Fields, South Italy). Experiments were run in a piston cylinder apparatus at 1 GPa pressure, at temperatures from 1373 to 1673 K and for durations of 0 to 255 s, using the diffusion-couple technique. Water concentration profiles were measured by Fourier transform infrared spectrometry. Water diffusion coefficients at different temperatures and water concentrations were calculated from the total water profiles, using the Boltzmann-Matano technique.
Over the investigated range of temperatures and water concentrations, the diffusivity of water in potassic melts (Dwater), m2/s can be described by Arrhenius equations that can be generalized for water concentrations between 0.25 and 2 wt% as follows: Formula where CH2O is the water concentration in wt%, R is 8.3145 (J K−1 mol.−1) and T is the temperature in Kelvin. Water diffusivities in trachytic melts were compared with water diffusivities in rhyolitic and basaltic melts. The activation energies for water diffusivity in trachyte and basalt are comparable, and higher than the haplogranitic melt. This results in a convergence of water diffusion coefficients in all melts at lower (magmatic) temperatures
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
The Villa Senni eruption (Alban Hills, Central Italy): volatiles control on magma chamber system and on eruptive mechanism.
No full textCatching a collapsing solidification front through thermal gradient experiments
No full textLarge explosive eruptions commonly emplace differentiated (i.e. rhyolite, phonolite), crystal-poor juveniles. This is a well-known paradox in volcanology, considering that magmatic differentiation implies crystallization and that crystal-melt separation processes (e.g. crystal settling) are more efficient in high-temperature, primitive magmas. Conversely, differentiated, crystal-poor juveniles are usually associated to shallow, thermally-zoned feeding systems. Here, the generation of differentiated, crystal-poor magmas may be explained throughout the development of a “solidification front” at the roof of the chamber. Although natural evidences and theoretical models support the solidification front concept, its capability to originate differentiated, crystal- poor magmas remains unconstrained.
By experimentally investigating the formation of a solidification front in a thermally zoned environment we demonstrate its capability to originate glassy belts and pockets phonolitic in composition. We recognize in the instability and collapse of rigid crystal frame the driving mechanism producing segregation and upward accumulation of crystal-poor melts and suggest this model may apply to thermally zoned magma chambers
Highly stereoregular polymerization of 1,3-cyclohexadiene in the presence of Cp2Ni-MAO catalyst
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