Chemical Evolution in the Substrate due to oxidation: A Numerical Model with Explicit Treatment of Vacancy Fluxes

To get a better understanding of oxidation behavior of Ni-base alloys in PWR primary water, a numerical model for oxide scale growth has been developed. The final aim of the model is to estimate the effects of possible changes of experimental conditions. Hence, our model has not been restricted by the classical hypothesis of quasi-steady state and can consider transient stages. The model calculates the chemical species concentration profiles, but also the vacancy concentration profiles evolution in the oxide and in the metal as a function of time. It treats the elimination of the possible supersaturated vacancies formed at the metal/oxide interface by introducing a dislocation density at the interface and in the metal bulk. This latter density can be related to the cold-working state. Its effect on the vacancy profile evolution is studied in the case of a pure metal. Eventually an extension of the present model to the oxidation of Ni-base alloys is discussed regarding a recent vacancy diffusion model adjusted on Ni-base alloys

Organic carbon decomposition rates with depth under an agroforestry system in a calcareous soil

The aims of this study were: (i) assess soil organic carbon (SOC) mineralisation potential as a function of soil depth in an agroforestry (AF) plot compared to an agricultural plot (ii) estimate the contribution of soil inorganic carbon (SIC) to CO2 emissions at different depths. Soils were collected in an 18-year-old AF (tree rows and alleys) and in an adjacent agricultural plot. The incubation comprised four soil replicates per location (control, tree row, alley) and per depth (0-10, 10-30, 70-100 and 160-180 cm). Soil samples were moistened to reach field capacity, at pF 2.5, and were then incubated at 20°C in the dark. The CO2 concentration and the δ13C of the CO2 were measured after 1, 3, 7, 14, 21, 28, 35 and 44 days. The microbial biomass was measured at the end of the incubation. Decomposition rates were calculated, as well as the metabolic quotient. The cumulated total CO2, SIC-derived CO2 and SOC-derived CO2 emissions were only significantly higher in tree row than in the alley or in the control plot at 0-10 cm. SOC decomposition rates decreased with increasing depth. Contributions of SIC to total CO2 emissions according were comprised between 0.15 and 0.30 in topsoil layers and between 0.50 and 0.70 in subsoil layers. The higher emission in the tree row at 0-10 cm was related to a large amount of labile particulate organic matter. SOC did not seem to be more stabilized in AF compared to the control. SIC-derived CO2 must be taken into account on calcareous soils

Specificity determinants for lysine incorporation in staphylococcus aureus peptidoglycan as revealed by the structure of a MurE enzyme ternary complex

Background: MurE controls stereo chemical incorporation of Lysine or diaminopimelate into peptidoglycan stem peptides Results: The structure of S.aureus MurE reveals an unexpected lack of specificity for Lysine within the active site. Conclusion: Incorporation of Lysine is supported by the comparatively high concentration of cytoplasmic lysine, not enzyme specificity. Significance: This study provides new perspectives in targeting Gram-positive peptidoglycan assembly for antimicrobial discovery

Contribution à l’étude du comportement au feu de câbles électriques par simulation numérique et par développement d’un banc d’essai à échelle réduite

L'objectif de ce travail de thèse est d’étudier le comportement au feu de câbles électriques par deux approches, la première consistant à développer des méthodes de caractérisation des propriétés des gaines externes de câbles afin d’en modéliser le comportement au feu. Parallèlement, une approche basée sur le développement d’un banc d'essai original à échelle réduite a été étudiée. La caractérisation des propriétés thermo-physique des matériaux a permis la prédiction de la température et de la perte de masse lors d'expériences thermogravimétriques, de gazéification et de combustion. Il a été montré que tester de mince spécimen de gaine de câbles dans une enceinte à échelle réduite permettait la prédiction des résultats de la norme EN 50399. Ce nouveau test de l'échelle du laboratoire a ensuite utilisé avec succès pour le développement de nouveaux câbles présentant des propriétés feu améliorées.The aim of this PhD work is to study the behavior of cables following two approaches: numerical modelling and small scale testing. First, methodologies to characterize the properties of the cables jacket materials were developed to further model their fire behavior. Concurrently, an approach was followed by developing a novel bench-scale fire test. Innovative methodologies using simultaneous thermal analyzer, Hot Disc apparatus were developed and so, the thermo-physical properties of the materials were characterized both as a function of temperature and of the decomposition state. Using these parameters as inputs data for a pyrolysis model, the temperature and mass loss rate were well predicted in case of thermo-gravimetric experiments, gasification and mass loss calorimeter. Moreover, it was shown that testing thin specimen of cables jacket materials in a reduced scaled enclosure of the EN 50399 test allowed the prediction of the results obtained on the large scale test carried out on whole cables. This new bench scale test was then successfully to develop new material that can be used as jacket for halogen-free electrical cable

Characterization of Thermo-Physical Properties of EVA/ATH: Application to Gasification Experiments and Pyrolysis Modeling

The pyrolysis of solid polymeric materials is a complex process that involves both chemical and physical phenomena such as phase transitions, chemical reactions, heat transfer, and mass transport of gaseous components. For modeling purposes, it is important to characterize and to quantify the properties driving those phenomena, especially in the case of flame-retarded materials. In this study, protocols have been developed to characterize the thermal conductivity and the heat capacity of an ethylene-vinyl acetate copolymer (EVA) flame retarded with aluminum tri-hydroxide (ATH). These properties were measured for the various species identified across the decomposition of the material. Namely, the thermal conductivity was found to decrease as a function of temperature before decomposition whereas the ceramic residue obtained after the decomposition at the steady state exhibits a thermal conductivity as low as 0.2 W/m/K. The heat capacity of the material was also investigated using both isothermal modulated Differential Scanning Calorimetry (DSC) and the standard method (ASTM E1269). It was shown that the final residue exhibits a similar behavior to alumina, which is consistent with the decomposition pathway of EVA/ATH. Besides, the two experimental approaches give similar results over the whole range of temperatures. Moreover, the optical properties before decomposition and the heat capacity of the decomposition gases were also analyzed. Those properties were then used as input data for a pyrolysis model in order to predict gasification experiments. Mass losses of gasification experiments were well predicted, thus validating the characterization of the thermo-physical properties of the material

CFD modelling of WUI fire behaviour in historical fire cases according to different fuel management scenarios

Background In most wildland–urban interface (WUI) fires, damage to buildings results from poor surrounding vegetation management. No simulation had been conducted yet on historical WUI fires with Computational Fluid Dynamics modelling. Aims It was interesting to check the feasibility of this modelling in simulating past fire cases for different scenarios of vegetation management and fire propagation. Methods We studied three cases of WUI dwellings surrounded by gardens (subject to French regulations on fuel reduction) adjacent to forest affected by a past fire. The 3D fire propagation was assessed using the Fire Dynamic Simulator model (FDS) and taking into account accurate fire environment (fine vegetation distribution, terrain, etc.). Key results Results showed that, in the current model state, brush-clearing mitigated fire intensity and propagation and damage to ornamental vegetation. However, it sometimes highlighted that this measure could be strengthened when the effects of topography and wind were combined. Conclusions FDS modelling at the WUI scale using accurate vegetation distribution proved to be functionally satisfactory, exhibiting realistic fire behaviour. Implications Once validated, this modelling will ultimately help to assess when fuel reduction is efficient in fire mitigation and to pinpoint possible limitations

Characterization of Thermo-Physical Properties of EVA/ATH: Application to Gasification Experiments and Pyrolysis Modeling

The pyrolysis of solid polymeric materials is a complex process that involves both chemical and physical phenomena such as phase transitions, chemical reactions, heat transfer, and mass transport of gaseous components. For modeling purposes, it is important to characterize and to quantify the properties driving those phenomena, especially in the case of flame-retarded materials. In this study, protocols have been developed to characterize the thermal conductivity and the heat capacity of an ethylene-vinyl acetate copolymer (EVA) flame retarded with aluminum tri-hydroxide (ATH). These properties were measured for the various species identified across the decomposition of the material. Namely, the thermal conductivity was found to decrease as a function of temperature before decomposition whereas the ceramic residue obtained after the decomposition at the steady state exhibits a thermal conductivity as low as 0.2 W/m/K. The heat capacity of the material was also investigated using both isothermal modulated Differential Scanning Calorimetry (DSC) and the standard method (ASTM E1269). It was shown that the final residue exhibits a similar behavior to alumina, which is consistent with the decomposition pathway of EVA/ATH. Besides, the two experimental approaches give similar results over the whole range of temperatures. Moreover, the optical properties before decomposition and the heat capacity of the decomposition gases were also analyzed. Those properties were then used as input data for a pyrolysis model in order to predict gasification experiments. Mass losses of gasification experiments were well predicted, thus validating the characterization of the thermo-physical properties of the material

Chemical Evolution in the Substrate due to oxidation: A Numerical Model with Explicit Treatment of Vacancy Fluxes

International audienceTo get a better understanding of oxidation behavior of Ni-base alloys in PWR primary water, a numerical model for oxide scale growth has been developed. The final aim of the model is to estimate the effects of possible changes of experimental conditions. Hence, our model has not been restricted by the classical hypothesis of quasi-steady state and can consider transient stages. The model calculates the chemical species concentration profiles, but also the vacancy concentration profiles evolution in the oxide and in the metal as a function of time. It treats the elimination of the possible supersaturated vacancies formed at the metal/oxide interface by introducing a dislocation density at the interface and in the metal bulk. This latter density can be related to the cold-working state. Its effect on the vacancy profile evolution is studied in the case of a pure metal. Eventually an extension of the present model to the oxidation of Ni-base alloys is discussed regarding a recent vacancy diffusion model adjusted on Ni-base alloys