Atomistic simulations of molten carbonates: Thermodynamic and transport properties of the Li2CO3-Na2CO3-K2CO3 system.

Although molten carbonates only represent, at most, a very minor phase in the Earth's mantle, they are thought to be implied in anomalous high-conductivity zones in its upper part (70-350 km). Besides, the high electrical conductivity of these molten salts is also exploitable in fuel cells. Here, we report quantitative calculations of their properties, over a large range of thermodynamic conditions and chemical compositions, which are a requisite to develop technological devices and to provide a better understanding of a number of geochemical processes. To model molten carbonates by atomistic simulations, we have developed an optimized classical force field based on experimental data of the literature and on the liquid structure issued from ab initio molecular dynamics simulations performed by ourselves. In implementing this force field into a molecular dynamics simulation code, we have evaluated the thermodynamics (equation of state and surface tension), the microscopic liquid structure and the transport properties (diffusion coefficients, electrical conductivity, and viscosity) of molten alkali carbonates (Li2CO3, Na2CO3, K2CO3, and some of their binary and ternary mixtures) from the melting point up to the thermodynamic conditions prevailing in the Earth's upper mantle (∼1100-2100 K, 0-15 GPa). Our results are in very good agreement with the data available in the literature. To our knowledge, a reliable molecular model for molten alkali carbonates covering such a large domain of thermodynamic conditions, chemical compositions, and physicochemical properties has never been published yet.

The MgCO3-CaCO3-Li2CO3-Na2CO3-K2CO3 melts: Thermodynamics and transport properties by atomistic simulations.

Atomistic simulations provide a meaningful way to determine the physicochemical properties of liquids in a consistent theoretical framework. This approach takes on a particular usefulness for the study of molten carbonates, in a context where thermodynamic and transport data are crucially needed over a large domain of temperatures and pressures (to ascertain the role of these melts in geochemical processes) but are very scarce in the literature, especially for the calcomagnesian compositions prevailing in the Earth's mantle. Following our work on Li2CO3-Na2CO3-K2CO3 melts, we extend our force field to incorporate Ca and Mg components. The empirical interaction potentials are benchmarked on the density data available in the experimental literature [for the crystals and the K2Ca(CO3)2 melt] and on the liquid structure issued from ab initio molecular dynamics simulations. Molecular dynamics simulations are then performed to study the thermodynamics, the microscopic structure, the diffusion coefficients, the electrical conductivity, and the viscosity of molten Ca,Mg-bearing carbonates up to 2073 K and 15 GPa. Additionally, the equation of state of a Na-Ca-K mixture representative of the lavas emitted at Ol Doinyo Lengai (Tanzania) is evaluated. The overall agreement between the MD results and the existing experimental data is very satisfactory and provides evidence for the ability of the force field to accurately model any MgCO3-CaCO3-Li2CO3-Na2CO3-K2CO3 melt over a large T-P range. Moreover, it is the first report of a force field allowing us to study the transport properties of molten magnesite (MgCO3) and molten dolomite [CaMg(CO3)2].

Breaking of Henry's law for noble gas and CO2 solubility in silicate melt under pressure.

Degassing of the Earth is still poorly understood, as is the large scatter in He/Ar ratios observed in mid-ocean ridge basalts. A possible explanation for such observations is that vesiculation occurs at great depths with noble-gas solubilities different from those measured at 1 bar (ref. 1). Here we develop a hard-sphere model for noble-gas solubility and find that, owing to melt compaction, solubility may decrease by several orders of magnitude when pressure increases, an effect subtly overbalanced by the compression of the fluid phase. Our results satisfactorily explain recent experimental data on argon solubility in silicate melts, where argon concentration increases almost linearly with pressure, then levels off at pressures of 50-100 kbar (refs 2-5). We also model vesiculation during magma ascent at ridges and find that noble-gas partitioning between melt and CO2 vesicles at depth differs significantly from that at low pressure. Starting at 10 kbar (approximately 35 km depth), several stages of vesiculation occur followed by vesicle loss, which explains the broad variability of He-Ar concentration data in mid-ocean ridge basalts. 'Popping rocks', exceptional samples with high vesicularity, may represent fully vesiculated ridge magma, whereas common samples would simply have lost such vesicles.

Information contextualization in decision support modules for adverse drug event prevention.

This paper presents an analysis of hospitals' organization and Hospital Information Systems' features which can contribute in contextualization of Clinical Decision Support Systems (CDSS) for Adverse Drug Event (ADE) prevention. We identified four categories of contextualization: ENVIRONMENT, TASKS, USERS and TEMPORAL ASPECTS. Based on this analysis, we studied the technical possibilities at the architectural level to determine which component(s) of a standalone knowledge platform could technically handle contextualization. The results impact three types of components of this platform: (1) a CDSS providing decision support based on ADE signals mined in large data repositories; (2) a Connectivity Platform providing transformation and routing services (enabling any application to connect to the CDSS); (3) three prototype applications for accessing the decision support services realized within an industrial Computerized Physician Order Entry, an industrial Electronic Health Record and in an independent Web prototype, respectively. In each of the above components we present the dimension(s) of contextualization that has/have been determined to cope with and the design followed in the implementation phase.

Three different cases of exploiting decision support services for adverse drug event prevention.

Clinical Decision Support Systems (CDSSs) are implemented in clinical settings in order to improve patient outcomes and/or clinical practices. However, they are still not widely accepted by healthcare professionals due to over-alerting. The aim of the "Patient Safety through Intelligent Procedures in medication" (PSIP) project is to develop and demonstrate innovative tools so as to generate and provide relevant knowledge to healthcare professionals and patients for Adverse Drug Event (ADE) prevention by means of Information and Communication Technologies (ICT). PSIP employs a Knowledge Base (KB) as the core of its CDSS. This KB encapsulates signals capable of automatically detecting potential ADEs and contextualizing the CDSS output to the patient and healthcare professionals. To exploit the KB, a Global Knowledge Platform (GKP) has been created comprising of a KB system, a Connectivity Platform and appropriate user interface modules. The GKP has been tested to demonstrate integration of the KB in different work situations and it has been deployed in three different medical applications. The first is a Web application; the second involves a commercial French EHR (Electronic Health Record) and the third is a Danish CPOE (Computerised Physician Order Entry) system. This paper presents recent progress as regards the exploitation of the PSIP KB and the results obtained in the three different medical applications.

Investigation of vapor-deposited amorphous ice and irradiated ice by molecular dynamics simulation.

With the purpose of clarifying a number of points raised in the experimental literature, we investigate by molecular dynamics simulation the thermodynamics, the structure and the vibrational properties of vapor-deposited amorphous ice (ASW) as well as the phase transformations experienced by crystalline and vitreous ice under ion bombardment. Concerning ASW, we have shown that by changing the conditions of the deposition process, it is possible to form either a nonmicroporous amorphous deposit whose density (approximately 1.0 g/cm3) is essentially invariant with the temperature of deposition, or a microporous sample whose density varies drastically upon temperature annealing. We find that ASW is energetically different from glassy water except at the glass transition temperature and above. Moreover, the molecular dynamics simulation shows no evidence for the formation of a high-density phase when depositing water molecules at very low temperature. In order to model the processing of interstellar ices by cosmic ray protons and heavy ions coming from the magnetospheric radiation environment around the giant planets, we bombarded samples of vitreous ice and cubic ice with 35 eV water molecules. After irradiation the recovered samples were found to be densified, the lower the temperature, the higher the density of the recovered sample. The analysis of the structure and vibrational properties of this new high-density phase of amorphous ice shows a close relationship with those of high-density amorphous ice obtained by pressure-induced amorphization.