An improved interface model for molten corium-concrete interaction

In the field of research for Severe Accidents of PWRs, calculation results are needed to estimate when corium achieves basemat melt-through. In this framework, knowledge of the heat transfer coefficient as well as the temperature at the interface between the melt and the solid are key issues. It has been previously emphasized that physico-chemistry of the melt (composition) affects the temperature. However, the effect of gas sparging and liquid concrete release on the mechanical stability of the solid layer and on the interface temperature has not been analysed in detail. ARTEMIS 1D tests were launched to analyse the phenomenology at the interface. A general conclusion for all these tests is that a solid medium enriched in refractory species exists at the interface between the pool and the concrete.Tests 2 and 6, which are close to reactor representative conditions, could be well described with the assumption T_interface = T_liquidus. The analysis of tests 3 and 4 revealed that the interfacial medium is thicker by a factor of 4-5 times than calculated with the assumption of pure conduction heat transfer. Detailed analysis leads to the conclusion that the interfacial medium is made of a porous layer of refractory particles embedded in a liquid phase. The liquid density difference, between the porous medium and chimneys, results in recirculation of the liquid in the porous layer. This recirculation is responsible for a convective contribution to heat transfer through the porous layer. The convective heat flux is partly linked to cooling of the recirculating liquid, but also to its partial solidification. The solidification results in gradual plugging and enrichment of the porous layer in refractory species and in the increase of the resistance to heat transfer. The phenomena have been modelled and ARTEMIS tests 3 and 4 are well reproduced. The complete plugging of the porous medium, associated with thermodynamic equilibrium at the interface between the solid medium and the pool leads naturally to the solid crust model implemented in TOLBIAC-ICB. The latter model appears, thus, as a simplification of the porous medium approach described here.Thick interfacial layers, which have composition between refractory and corium mixture, have been observed in ACE and MACE tests with LCS (Limestone-Common Sand) or Limestone concrete and can be explained with the proposed model approach. For siliceous concrete, convection within a porous medium is not possible due to the large viscosity.     

Preparation, electrical conductivity, and magnetic susceptibility of (Ba1 − x Bi x )(Mn0.5 + x/2Nb0.5 − x/2)O3

(Ba_{1 ? x} Bi _x )(Mn_{0.5 + x/2}Nb_{0.5 ? x/2})O₃ perovskite solid solutions have been prepared by solid-state reactions and their physicochemical properties have been investigated. We have studied the influence of bismuth substitution for barium cations on the phase composition of the samples. Their magnetic susceptibility and electrical conductivity have been measured as functions of temperature. The composition dependence of the antiferromagnetic ordering temperature is presented.     

Assigning multiple activities to work shifts

In some companies such as large retail stores, the employees perform different activities (e.g., cashier or clerk in a specific department) to respond to a customer demand for each activity that varies over the planning horizon and must be fulfilled as soon as possible. For a given time period, this demand translates into an ideal number of employees required for the corresponding activity. During a work shift, an employee can be assigned to several activities that are interruptible at any time and subject to operational constraints (required skills, minimum and maximum assignment durations). Given work shifts already assigned to the employees, the multi-activity assignment problem (MAAP) consists of assigning activities to the shifts such that the activity demands are satisfied as best as possible over the planning horizon. In this paper, we propose three integer programming models for the MAAP and develop various heuristics based on mathematical programming techniques. Computational results obtained on randomly generated MAAP instances show that a heuristic column generation method embedded into a rolling horizon procedure provides the best results in general.     

Preliminary investigations of weak non-adiabatic effects in materials from simulations on model clusters

According to earlier work, excited electronic states, despite their very small concentrations in wide-gap systems, might be involved in the initiation of energetic materials. To get further insight into the non-adiabatic electronic behaviour under intense mechanical perturbations, a simple approach is suggested, using finite clusters as models for materials. Preliminary calculations are carried out for isolated clusters undergoing vibrations. Electronic populations in excited states obtained from these simulations are much larger than expected on the basis of statistical mechanics. Therefore, an extension of the present scheme to the canonical NVT ensemble would be desirable.     

Genotype-phenotype analysis in four families with mutations in beta-myosin heavy chain gene responsible for familial hypertrophic cardiomyopathy

The effects of two progestogen-only pills containing either 75 microgram desogestrel (DSG) or 30 microgram levonorgestrel (LNG) on hemostasis were investigated in a double-blind, randomized, controlled study of seven treatment cycles in 78 healthy women. DSG reduced factor VII activity (p < 0.05) and prothrombin fragment 1+2 (p < 0.05) and increased protein S (p < 0.001). LNG reduced factor VII activity (p < 0.01) and plasminogen activity (p < 0.01) and increased tissue-plasminogen activator (t-PA) (p < 0.05). At the end of the post-treatment cycle with DSG, protein S (p < 0.01) and t-PA (p < 0.05) were increased and plasminogen activity was decreased (p < 0.05), whereas with LNG, t-PA was increased (p < 0.001) and prothrombin fragment 1+2 (p < 0.05) and plasminogen activity (p < 0.001) were decreased. Between-group comparisons revealed higher values for DSG regarding the anticoagulatory parameter protein S at cycle 7 (p < 0.01) and post-treatment assessments (p < 0.05), and the fibrinolytic parameter plasmin-antiplasmin complex was higher with DSG at cycle 7 (p < 0.05) and at post-treatment (p < 0.05). Both preparations had comparable and potentially favorable effects of hemostasis, and may offer suitable hormonal contraception to women with a personal or family history of venous thromboembolic diseases.     

Constant-distance mode scanning potentiometry. 1. Visualization of calcium carbonate dissolution in aqueous solution

Constant-distance mode scanning potentiometry was established by integrating potentiometric microsensors as ion-selective scanning probes into a SECM setup that was equipped with a piezoelectric shear force-based tip-to-sample distance control. The combination of specially designed micrometer-sized potentiometric tips with an advanced system for tip positioning allowed simultaneous acquisition of both topographic and potentiometric information at solid/liquid interfaces with high spatial resolution. The performance of the approach was evaluated by applying Ca(2+)-selective constant-distance mode potentiometry to monitor the dissolution of calcium carbonate occurring either at the (104) surface of calcite crystals or in proximity to the more complex surface of cross sections of a calcium carbonate shell of Mya arenaria exposed to slightly acidic aqueous solutions. Micrometer-scale heterogeneities in the apparent calcium activity profiles have successfully been resolved for both samples.