1,720,964 research outputs found
The effect of iron on the rheological properties of silicate melts.
No full textAs the viscosity is probably one of the most important properties governing the dynamics of magmas at all the scales, its investigation is fundamental to provide importantconstraints on all the magmatic processes such as crystallization, magma differentiation and eruption dynamics on terrestrial planets. Igneous provinces have been found on Earth, Moon, Venus, Io and Mars. As matter of fact, it is generally accepted, that Martian rocks have a higher Fe content than rocks on Earth. Unfortunately, existing models of the physico-chemical properties of silicate melts are not calibrated for the high Fe contents. In order to adapt these models to high Fe-content compositions, we have developed a new experimental approach from which the physico-chemical properties of both iron components (FeO and Fe2O3) will be derived. Therefore, viscosity measurements have been conducted in this study over the whole temperature liquid range. High-T viscosities (1594-1275_C) have been measured in air using the concentric cylinder (CC) method. Low-T viscosities (817-711_C) have been measured under argon using the micro-penetration method (MP) for the melts that could be quenched to glasses. The oxidation state of Fe has been determined on quenched glasses at regular T steps by wet chemistry method. Two different simple Fe-bearing systems have been studied to date: (i) anorthite-diopside eutectic composition (AnDi) with variable amount of Fe (up to 30 wt%) as described in the literature as -a basalt analogue- and (ii) sodium disilicate (NS2 up to 20 wt% of Fe). In addition, the compositional range has been extended to include a Martian mantle composition based on the model of [1]. The high T viscosity data obtained for the AnDi-eutectic in this study are in good agreement with the data provided by previous authors [2] on the same composition. Since no previous studies have dealt with the low T viscosity of the AnDi-eutectic composition, our experimental data were compared with viscosity of Etna lava [3] taken as an example of natural basaltic composition. In fact, whereas the high T viscosities are similar to each other, this is not true at low temperature (i.e., the Etna basalt shows a much lower activation energy with respect to our AnDi-eutectic composition). High-T viscosities of SNC shows a good agreement with viscosities obtained for a natural peridotite from Balmuccia (Earth mantle analogue) [Dingwell - personal communication]. Low-T viscosities of SNC could not be measured due to the occurrence of crystallization. All the materials exhibit non-Arrhenian behaviour when observed within the complete range of the experimental determinations. Therefore, a Vogel Fulcher Tammann (VFT) form of equation was used to characterize the variation of the viscosity with temperature. In addition, the present results suggest that the effect of iron on decreasing the viscosity at isothermal temperatures (more effective at low T) is linear for AnDi samples containing up to 10 wt% of Fe, while this behaviour becomes non-near for higher Fe-content.[1] Dreibus, G., Waenke, H., (1985) Mars, A Volatile-Rich Planet, Meteoritics 20, 367-381. [2] Scarfe et al., (1983) Viscosity-tempearture relationship at 1 atm in the system diopside-anortite, Am.Mineral. 68, 1083-1088. [3] Giordano, D., Dingwell, D.B., (2003) Viscosity of hydrous Etna basalt: implications for Plinian-style basaltic eruptions, Bull.Volcanol. 65, 8-14
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
Viscosity of a molten mantle: insights from a combination of experimental techniques on liquid peridotite
No full textExistence of molten peridotite in the early history of the Earth has long been the subject of debate and conjecture. Interest in the physical properties stems from a number of sources but was re-focussed in the wake of the proposal for the existence of a ̧Smagma ocean ¡T in the evolution of the moon, the Earth and other terrestrial planets. The application of phase equilibrium, buoyancy, thermodynamic and fluid dynamic constraints on the behaviour of molten mantle all rely on adequate characterisation ofthe properties of molten peridotite, largely lacking to date. The viscosity in particular, has received too little attention. A big experimental effort has been provided to obtain the dependence on temperature (T) of viscosity at ambient pressure (P) for the natural peridotite collected at Balmuccia, Italy. High-T measurements were performed by using concentric cylinder (CC). The high-T viscometry was started at 1600_C and proceeded at 10_C intervals, separated by cooling stages at 5_C/min, each one held for 1 hour. No measurements were possible below 1570 _C, because crystallization had occurred. All standard attempts to obtain a homogeneous glass failed. A new technique was therefore used. Small 1-2 mm chips were hung in Pt loops suspended from a long Pt wire and the loops lowered by hand into the high-T viscosity furnace until the chips fused into a bead of liquid held in the loop by surface tension. These samples were then left to quench and placed aside to be used in the splat-quenching device (SQD) (which allows quench rates on the order of 10exp4 _C/s) to finallyobtain a supercooled liquids by squeezing and rapidly quenching a falling liquid drop, through a joint action of a complex photoelectric-driven electromagnetic device. Electron microprobe analysis revealed that only a few vol% of the obtained glasses crystallized in isochemical crystals, whereas the homogeneity of the glassy matrix composition was found to be excellent. As the amount of glass obtained was too small to be used in the micropenetration technique we used differential scanning calorimetry (DSC) to derive the viscosity at low-T. DSC allowed us to unequivocally determine glass transition temperatures (Tg) for cooling/heating rates of 20, 15, 10, 8 and 5 K/min, as the peak of the Cp curves. At this point we used a recent method developed by [1] that, on the basis of the equivalence of the shear stress and the enthalpic relaxation time, allow to predict the low-T viscosity. The combined results obtained by using the different techniques above mentioned were fit by VFT equation with the high-T limiting value (viscosity value at infinite temperature) being fixed at a value of 10exp-4.31 Pas [2]. A comparison between the data obtained here with the recent model from [3] (calibrated with melts as basic as basanite), have shown that in the range 900 to 1600 _C, the viscosity calculated according to [3] is very similar to those measured or calculated by the VFT fit, if A = -4.31; the discrepancy becoming significant at T<900 _C. The very low T dependence of viscosity at superliquidus conditions obtained from the fitting here, indicates that at putative temperatures of the core-mantle boundary, near 5000 _C, the viscosity will decrease up to 10exp-3.5 Pa s. [1] J. Gottsmann et al. (2002), EPSL, 198, 417;. [2] J.K. Russell et al. (2003), Am. Mineral., 88, 1390;. [3] D. Giordano & D.B. Dingwell (2003), EPSL, 208, 337 and Errata Corrige, in press
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
Evidence of Al/Si tetrahedral network in aluminosilicate glasses from Al K-edge X-ray Absorption Spectroscopy
No full textThe structure of aluminosilicate melts and/or glasses plays a key role in the earth sciences for the understanding of rock-forming igneous processes, as well as in the materials sciences for their technical applications. In particular, the alkaline-earth aluminosilicate glasses are an extremely important group of materials, with a wide range of commercial application, as well as serving as an analog for natural basaltic melts. However, definition of their structure and properties is still controversial, and in particular the role and effect of Al has long been a subject of debate. Here we report a series of experimental x-ray absorption near-edge structure spectra at the Al K edge on a series of synthetic glasses of peralkaline composition in the CaO-Al2O3-SiO2 system, together with a general theoretical framework for data analysis based on an nb initio full multiple-scattering theory. We propose an Al/Si tetrahedral network model for aluminosilicate glasses based on distorted polyhedra, with varying both the T-O (T=Al or Si) bond lengths and the T-O-T angles, and with different Al/Si composition. This model achieves a significant agreement between experiments and simulations. In these glasses, experimental data and theoretical results concur to support a model in which Al is network former with a comparatively well ordered local medium-range order (up to 5 Angstrom)
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
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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