Modeling of Nucleation Processes

Nucleation is the onset of a first-order phase transition by which a metastable phase transforms into a more stable one. Such a phase transition occurs when an initial system initially in equilibrium is destabilized by the change of an external parameter like the temperature or the pressure. If the perturbation is small enough, the system does not become unstable but rather stays metastable. In diffusive transformations, the system then evolves through the nucleation, the growth and the coarsening of a second phase. Such a phase transformation is found in a lot of situations in materials science like condensation of liquid droplets from a supersaturated vapor, solidification, precipitation from a supersaturated solid solution, ... The initial stage of all these different processes can be well described within the same framework. Since its initial formulation in 1927 by Volmer, Weber and Farkas and its modification in 1935 by Becker and D\"oring the classical nucleation theory has been a suitable tool to model the nucleation stage in phase transformations. In this article, we first describe this theory. A kinetic approach, the cluster dynamics, can also be used to describe nucleation. This constitutes the second part of this article. The links as well as the difference between both descriptions are emphasized. Since its initial formulation, the classical nucleation theory has been enriched, so as to take into account the fact that clusters other than monomers can migrate and react. It has been also extended to multi-component systems. These generalizations of the initial formalism are also presented

Thermodynamics of greenhouse systems : a new approach leading to new proposals for sustainable production

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Greenhouse production systems produce in the Netherlands and Flanders economical important quantities of vegetables, fruit and ornamentals. Control of the crop environment has led to a high primary energy use (1500MJ/m²/year). This high primary energy use affects the economical and environmental sustainability. Research projects in the Netherlands and Flanders are launched to achieve sustainable greenhouse systems with high crop yields and low primary energy use. Until now, these projects didn’t result in the desired primary energy savings. On the contrary, the civil building industry succeeds by the passive house technology in a magnitude’s reduction for primary energy use. The primary energy saving research in greenhouse systems was mainly based on analysis of energy balances. However, the thermodynamic theory indicates that an analysis based on the concept of exergy (free energy) and energy is preferred. Such analysis could reveal possibilities for primary energy savings. The different processes and in/outputs of the greenhouse system are outlined. The appropriate equations for exergy calculations are developed. First, analyses are performed on the processes of transpiration and ventilation. Further, a total system assessment is performed. The exergy analysis indicates that primary energy saving in greenhouse systems could be the same as in the building industry, but adapted technologies need to be developed. The Institute for Agricultural and Fisheries Research (ILVO) will use this exergy analysis as a basis for the development of an exergy efficient greenhouse prototype (EXEkas).mp201

Composantes transférables en EPS. Judo, lutte, sambo : même combat

Bronchart Bernard. Composantes transférables en EPS. Judo, lutte, sambo : même combat. In: Les Cahiers de l'INSEP, n°12-13, 1996. Arts martiaux, sports de combat. pp. 137-143

Advancing towards climate-neutral greenhouses : thermodynamic analyses of greenhouse systems and of dehumidification pathways and vapor transport through screens

Op weg naar een klimaatneutrale glastuinbouw De glastuinbouw is een grootverbruiker van primaire energie in de Vlaamse landbouw. Dit werk heeft antwoorden hoe dit komt, wat de wetenschappelijke lacunes zijn en schets mogelijke oplossingen voor een succesvolle transitie van de glastuinbouwsector. Het vertrekt van een thermodynamische analyse van een kas. Hieruit blijkt dat het gebruik van betere schermen de eerste stap zijn om het primaire energieverbruik te reduceren. Daarnaast wordt aangetoond dat ontvochtigen en CO2 voorziening met geschikte apparatuur een laag primair energieverbruik heeft. Dit wijst op een haalbare toekomst voor de transitie van de glastuinbouw. Het tweede deel spits zich dan toe op efficiënt ontvochtigen en ontwerpt een nieuw device: de dampwarmtepomp. Het derde deel behandelt het transport van damp doorheen schermen, een cruciaal aspect voor het behoud van een optimaal kasklimaat. Eerdere studies in de wetenschappelijke literatuur hebben hieromtrent fouten gemaakt die gereproduceerd werden door latere studies. Dit onderzoek corrigeert deze fouten en presenteert nauwkeurige correlaties voor het berekenen van damptransport doorheen schermen. Dit werk vormt daarmee een onmisbaar fundament voor iedereen die geïnteresseerd is in de transitie van de glastuinbouwsector en dient als het wetenschappelijke referentiewerk voor massatransport door niet-uniforme structuren zoals schermen

Age-related scopolamine effects on social and individual behaviour in rats.

The modulation of spontaneous (social and individual) behaviour as a function of the age of the rat (1, 3, 6, 12, 18 and 24 months) and of scopolamine dose (0.1, 0.2, 0.3 and 0.5 mg/kg) was studied. Observations were conducted during the dark phase of the reverse light/dark schedule using a reintroduction procedure. Results showed a marked effect of scopolamine on most of the behavioural patterns considered. Environmental interaction was enhanced whilst agonistic and social active interactions (social grooming) and play fighting were reduced by the drug. A slight hyposensitivity in the youngest rats and a marked hyposensitivity to the drug in the oldest ones were observed. The relationship to biochemical data and human sensitivity on the one hand and to learning and memory tasks and cholinergic specificity on the other hand, are discussed

Développement de méthodes de champs de phase quantitatives et applications à la précipitation homogène dans les alliages binaires

Nous développons ici des méthodes de Champ de Phase quantitatives sur les échelles de temps et d espace. Le but est de prédire à l échelle mésoscopique les évolutions microstructurales liées à la précipitation homogène dans un alliage binaire faiblement sursaturé. Tout d abord, nous présentons les fondements statistiques des approches purement phénoménologiques. Dans ce cadre, nous considérons deux cas distincts. Premièrement, nous calibrons une équation d évolution stochastique du type Allen-Cahn sur une dynamique Monte Carlo. Deuxièmement, nous calibrons une équation d évolution stochastique du type Cahn-Hilliard sur des données expérimentales définissant un alliage donné. Ensuite, nous abandonnons l approche phénoménologique et présentons une procédure de moyenne locale permettant d obtenir, à partir d une cinétique définie à l échelle atomique, une formulation nouvelle des méthodes de champ phase et de leurs ingrédients: densité d énergie libre, mobilités, terme stochastique.In this study, quantitative phase field modelings are developped. The quantitative aspect concerns the time and space scales. The aim is to predict at the mesoscale the microstructural evolutions of a homogeneous precipitation in a weakly supersaturated binary alloy. In a first part, the statistical basements of the phenomenological approaches are presented. In this phenomonological framework, we analyse two different cases. First, we calibrate the stochastic equation of evolution of the Allen-Cahn type on a Monte Carlo kinetic. Second, we calibrate the stochastic equation of evolution of the Cahn-Hilliard type on some experimental data that characterize the considered alloy. Finally, the purely phenomenological approach is abandoned and we present a coarse-graining procedure which allows to obtain, starting from a kinetic model defined at the atomic scale, a new formulation for the phase field modeling and its ingredients: density of free energy, mobilities, stochastic terms.CERGY PONTOISE-BU Neuville (951272102) / SudocSudocFranceF