214 research outputs found
Na2O solubility in CaO–MgO–SiO2 melts
No full textThe sodium solubility in silicate melts in the CaO-MgO-SiO2 (CMS) system at 1400 C has been measured by using a closed thermochemical reactor designed to control alkali metal activity. In this reactor, Na-(g) evaporation from a Na2O-xSiO(2) melt imposes an alkali metal vapor pressure in equilibrium with the molten silicate samples. Because of equilibrium conditions in the reactor, the activity of sodium-metal oxide in the molten samples is the same as that of the source, i.e., aNa(2)O((sample)) = aNa(2)O((source)). This design also allows to determine the sodium oxide activity coefficient in the samples. Thirty-three different CMS compositions were studied. The results show that the amount of sodium entering from the gas phase (i.e., Na2O solubility) is strongly sensitive to silica content of the melt and, to a lesser extent, the relative amounts of CaO and MgO. Despite the large range of tested melt compositions (0 < CaO and MgO < 40; 40 < SiO2 < 100; in wt%), we found that Na2O solubility is conveniently modeled as a linear function of the optical basicity (A) calculated on a Na-free basis melt composition. In our experiments, gamma Na2O(sample) ranges from 7 x 10(-7) to 5 x 10(-6), indicating a strongly non-ideal behavior of Na2O solubility in the studied CMS melts (gamma Na2O(sample) << 1). In addition to showing the effect of sodium on phase relationships in the CMS system, this Na2O solubility study brings valuable new constraints on how melt structure controls the solubility of Na in the CMS silicate melts. Our results suggest that Na2O addition causes depolymerization of the melt by preferential breaking of Si-O-Si bonds of the most polymerized tetrahedral sites, mainly Q(4). (C) 2010 Elsevier Ltd. All rights reserved.ANR [BLAN06-3_134633
Systèmes d’information et observatoires
No full textContact: Jean Christophe Desconnets, [email protected] & Thérèse Libourel, [email protected] audienc
Systèmes d’information et observatoires
No full textContact: Jean Christophe Desconnets, [email protected] & Thérèse Libourel, [email protected] audienc
Systèmes d’information et observatoires
No full textContact: Jean Christophe Desconnets, [email protected] & Thérèse Libourel, [email protected] audienc
A measurement-oriented modelling approach: a step forward
No full textMeasurements represent a fundamental component of Enterprise Information Systems and they play a key role in organizations. Their own languages, concepts and techniques, concerning how to approach and solve problems in modern industrial scenarios, inevitably characterize these two disciplines. This is why the question we posed is to get a methodology that allows us to analyse, model and implement software subsystems able to render really usable information concerning measurements, keeping their informative peculiarities unchanged. The final goal of our research is to define a Use Case-based methodological proposal for modeling the informative content of measurements and their usage that starts from the business model of an enterprise subsystem and achieves a software model able to satisfy the users' need
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Gas-melt interactions and their bearing on chondrule formation
No full textInteractions between nebular gas and molten silictes or oxides coul have played a major role in the formation and differentiation of the first solids formed in the solar system. In order to simulate such interactions, we set up a new experimental device in which isothermal condensation experiments have been conducted. Partially molten chondrule-like samples have been exposed to high SiO(g) partial pressures, for intervals between 80 and 300 s and at temperatures ranging from 1600 to 1750 K. Results show that silica entering from the gas phase could be responsible for several textural and mineralogical featues observed in natural chondrules. For instance, these experiments reproduce not only the mineralogical zonation of porphyritic olivine-pyroxene chondrules with the peripheral location of pyroxenes, but also olivine resorption textures and the common poikilitical enclosure of olivines in pyroxenes. In the light of these similarities, we advocate that gas-melt interactions through condensation are viable mechanisms for chondrule formation and hence may place severe constrains on the history of these primitive objects. In the nebula, high SiO(g) partial pressures could have been established by the volatization of regions with high dust/gas ratio. A possible scenario for this stochastic thermal activity is the intense activity of the protosun in its young stellar object phase.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202
A Measurement-oriented Modelling Approach – basic concepts to be shared
No full textMeasurements represent a fundamental component of Enterprise Information Systems and they play a key role in organizations. Their own languages, concepts and techniques, concerning how to approach and solve
problems in modern industrial scenarios, inevitably characterize these two disciplines. This is why the
question we posed is to get a methodology that allows us to analyse, model and implement software
subsystems able to render really usable information concerning measurements, keeping their informative peculiarities unchanged. The final goal of our research is to define a Use Case-based methodological proposal for modeling the informative content of measurements and their usage that starts from the business
model of an enterprise subsystem and achieves a software model able to satisfy the users' needs
Asteroids: New Challenges, New Targets
No full textInternational audienceAt present, we know of ~600,000 asteroids in the asteroid belt, and there are very likely millions more. Orbiting the Sun between Mars and Jupiter, they are thought to be the shattered remnants of small bodies formed within the young Sun's solar nebula that never accreted enough material to become planets. These “minor bodies” are therefore keys to understanding how the Solar System formed and evolved. As leftover planetary building blocks, they are of great importance in understanding planetary compositions. They may also provide clues to the origin of life, as similar bodies may have delivered organics and water to the early Earth. For these reasons, several international space agencies have funded sample-return missions to asteroids
The effect of phosphorus on the iron redox ratio, viscosity, and density of an evolved ferro-basalt
No full textDespite the abundant evidence for the enrichment of phosphorus during the petrogenesis of natural ferro-basalts, the effect of phosphorus on the physical properties of these melts is poorly understood. The effects of phosphorus on the viscosity, density and redox ratio of a ferro-basaltic melt have been determined experimentally. The viscosity measurements were obtained using the concentric cylinder method on a ferro-basaltic melt above its liquidus, at 1 atm, in equilibrium with air and with CO2. The density measurements were performed using the double Pt-bob Archimedean method at superliquidus conditions under 1 atm of air. The redox ratio was obtained by wet chemical analysis of samples collected during physical property measurements. Phosphorus pentoxide reduces ferric iron in ferro-basaltic melt. The reduction due to P2O5 is much larger than that for most other oxide components in basaltic melts. A coefficient for the reduction of ferric iron has been generated for inclusion in calculation schemes. The effect of P2O5 on the viscosity is shown to be complex. The initial reduction of ferric iron with the addition of P2O5 results in a relatively small change in viscosity, while further addition of P2O5 results in a strong increase. The addition of phosphorus to a ferro-basaltic melt also reduces the density. A partial molar volume of 64.5±0.7 cm3/mol for P2O5 in this melt has been obtained at 1300° C, yielding a volume of 12.9 cm3/mol per oxygen, consistent with a tetrahedral coordination for this high field strength cation. The effects of P2O5 on redox state, density and viscosity provide constraints on the structural role of phosphorus in these melts. The results suggest a complex interaction of phosphorus with the aluminosilicate network, and tetrahedral ferric iron. In light of the significant effects of phosphorus on the physical and chemical properties of ferro-basaltic liquids, and the extreme enrichments possible in these liquids in nature, the role of phosphorus in these melts should, in future, be considered more carefully
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