1,721,010 research outputs found
Viscosities of granitic (sensu lato) melts: influence of the anorthite component
No full textThe viscosities of a series of granitic (sensu lato) melts have been determined in the range of 103 to 1012 Pa·s. The anhydrous melt compositions are based on the addition of 10, 20, 50, and 75 wt% of the anorthite component (CaAl2Si2O8) to a haplogranitic melt (HPG8) whose composition lies near
the 2 kbar water-saturated minimum melt composition in the system NaAlSi3O8-KAlSi3O8-SiO2. Melts with 10 and 20 wt% normative anorthite were subjected to high-pressure hydration syntheses using a piston-cylinder apparatus to generate water contents up to 2 wt%. Viscosities were determined for the anhydrous melts using the concentric cylinder method in the viscosity range of 102 to
105 Pa·s, and for both anhydrous and hydrated melts in the range of 109 to 1012 Pa·s. The results for the temperature dependence of viscosity in the anhydrous system indicate that the
influence on melt viscosity, caused by the addition of normative anorthite to the haplogranitic melt
composition, is strongly temperature-dependent. Viscosity-temperature relationships of the melts
become much more non-Arrhenian with addition of normative anorthite. The addition of water to
melts with 10 and 20 wt% normative anorthite results in strong nonlinear decreases in viscosity. In the high viscosity range, the results for hydrous melts with 10% normative anorthite are adequately reproduced using the calcalkaline melt viscosity model of Hess and Dingwell (1996), whereas those
for hydrous melts with 20 wt% normative anorthite are higher than the model predictions by amounts
that depend on the water content. It appears that, at the higher temperatures anticipated for intermediate
granitic magmatism, the calcalkaline model can adequately deal with up to 15 wt% normative anorthite in the melt composition in the range of temperatures relevant for intermediate magmas in nature
The effect of water on the viscosity of a haplogranitic melt under P-T-X- conditions relevant to silicic volcanism
No full textThe viscosities of hydrous haplogranitic melts synthesized by hydrothermal fusion at 2 kbar pressure and 800 to 1040°C have been measured at temperatures just above the glass transition and at a pressure of 1 bar using micropenetration techniques.
The micropenetration viscometry has been performed
in the viscosity range of 109 Pa s to 1012 Pa s. The
samples ranged in water content from 0.4 to 3.5 wt%.
For samples with up to 2.5 wt% H2O, the water contents
have been determined using infrared spectroscopy
obtained before and after each viscometry experiment
to be constant over the duration of the measurements.
Above this water content a measurable loss of water
occurs during the viscometry.
The viscosity data illustrate an extremely nonlinear
decrease in viscosity with added water. The viscosity
drops drastically with the addition of 0.5 wt% of water
and then shallows out at water contents of 2 wt%. An
additional viscosity datum point obtained from the
analysis of ßuid inclusions in a water-saturated HPG8
confirms a near invariance of the viscosity with the
addition of water between 2 and 6 wt%. These
measurements may be compared directly with the data
of Hess et al. (1995, in press) for the effects of excess alkali and alkaline earth oxides on the viscosity of HPG8 (also obtained at 1 bar). The viscosity of the
melts, compared on an equivalent molar basis, increases in the order H2O<(Li
2O<Na2O<K2O<Rb2O,Cs2O<BaO<SrO<CaO<MgO<BeO). The extraordinary decrease in melt viscosity with added water is poorly reproduced by the calculation scheme of Shaw (1972) for the range of water contents
investigated here. The speciation of water in the quen-ched glasses can be used to quantify the dependence of
the viscosity on hydroxyl content. Considering only the
hydroxyl groups as active ßuidizers in the hydrous
melts the nonlinearity of the viscosity decrease and the
di¤erence with the e¤ects of the alkali oxides becomes
larger. Consequences for degassing calcalkaline
rhyolite are discussed
Extremely fluid behavior of Hydrous Peralkaline Rhyolites
No full textThe viscosities of a series of water-bearing peralkaline rhyolitic melts have been experimentally determined. The dry melt compositions are composed of a series of additions of Na2O to a metaluminous base composition. The melts, initially hydrated at high pressures and quenched isobarically, have been prepared by cutting and polishing, then reheating across the glass transition at 1 atm where they are annealed to a relaxed metastable state and then investigated dilatometrically
using micropenetration methods. The measurements have been performed in the viscosity range of 108.5–1011.5 Pa s which
corresponds to temperatures in the range of 675–220oC for these compositions. Despite the relatively low viscosities of dry
peralkaline melts in comparison with metaluminous melts of similar SiO2 content, the viscosities of peralkaline rhyolitic
melts also decrease strongly and non-linearly with the addition of water. The resulting viscosity–temperature relationships
for water-bearing peralkaline rhyolitic melts are shifted to much lower temperatures such that glass transition temperatures for moderate cooling rates correspond to extraordinarily low temperatures. A model is presented for the calculation of melt viscosities in the range of 108.5–1011.5 Pa s for peralkaline rhyolites with up to 7 wt% H2O. The very fluid nature of
these peralkaline rhyolites over a wide range of water contents may facilitate a very efficient degassing history of glassy
peralkaline rhyolites in nature. Efficient degassing might explain the apparent contradiction of the presence of common water-rich melt inclusions in phenocryst phases hosted in water-free glassy rhyolites, versus the absence of vesicular layers
or textural evidence for a vesicular past for the glassy rocks
The Viscosities of dry and hydrous XAlSi3O8 (X=Li, Na, K, Ca0.5, Mg0.5) melts
No full textThe low-temperature viscosities of dry and hydrous X (X=Li, Na, K, Ca0.5, Mg0.5)AlSi3O8 melts have been investigated. The samples were hydrated via piston cylinder synthesis, and the water contents were subsequently determined
by Karl-Fischer titration (KFT) and IR spectroscopy. Both the anhydrous and hydrous viscosities were measured using the
micropenetration technique in the range of viscosities between 108.5 to 1011.9 Pa s, at 1 atm pressure and in the temperature ranges of 745–990 °C and 400–790°C for the dry and wet melts, respectively. The range of water content varied for all of the
samples from 0.70 to 3.13 wt.% H2O. The viscosities of dry melts vary, at fixed temperature, as a complex function of the identity of the cation in the order Li<Na<Ca<Mg<K. This trend is interpreted as due to the combined effects of cation
field strength and (Si, Al) distribution in these melts.
With the introduction of water into these melts, the viscosity decreases for all of the compositions investigated. As water
is further dissolved, the array of anhydrous viscosities converges into two distinct curves, for alkali-bearing and
alkaline-earth-bearing aluminosilicate liquids, respectively. In contrast to the insensitivity of viscosity to alkali cation
identity for hydrous melts, the alkali-aluminium ratio remains a sensitive control on viscosity. Thus, the viscosities of a
slightly peralkaline albite glass (Naexc)are lower than all of the others, both for the dry and the hydrous systems. We suggest that, in the case of alkaline-earth-bearing melts, an aluminium pair must be closely related to a doubly charged cation, to maintain electrostatic neutrality. The increase in the size of smallest rearranging species, which participates in the viscous flow process, as well as clustering of silica-rich and alumina-rich domains on an Aintermediate-rangeB scale, may be the factors resulting in the higher viscosities of Ca- and Mg-bearing compared to alkali-bearing liquids
Fe K-Edge XANES of Synthetic and Natural Silicate Glasses: Composition and fO2 Dependent Structural Properties
No full text
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
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