Coupling changes in cell shape to chromosome segregation

Animal cells undergo dramatic changes in shape, mechanics and polarity as they progress through the different stages of cell division. These changes begin at mitotic entry, with cell–substrate adhesion remodelling, assembly of a cortical actomyosin network and osmotic swelling, which together enable cells to adopt a near spherical form even when growing in a crowded tissue environment. These shape changes, which probably aid spindle assembly and positioning, are then reversed at mitotic exit to restore the interphase cell morphology. Here, we discuss the dynamics, regulation and function of these processes, and how cell shape changes and sister chromatid segregation are coupled to ensure that the daughter cells generated through division receive their fair inheritance

Thermal Evolution of Crude Oils in Sedimentary Basins: Experimental Simulation in a Confined System and Kinetic Modeling

A detailed knowledge of the cracking mechanisms of crude oils should highly improve the understanding of geochemical reactions involved in hydrocarbon degradation into lighter oil and gas and consequently the applicability of kinetic models currently used for prediction of gas formation. Although the mechanisms of cracking are well known for several model compounds or simple mixtures, there is, to date, no available method to model complex mixtures, especially when they contain heavy compounds, except by using empirical approaches. During thermal cracking, oil will produce both lighter and heavier molecules than those present in the initial sample. Thus, the pyrolysate will be a mixture of both new compounds and compounds not yet degraded. In order to discriminate between reactants and products, we have chosen to fractionate each oil into two classes : the first one (distillate 300-) comprising light hydrocarbons ranging from C6 to C16 the second one (residue 300+) comprising both hydrocarbons and polar compounds. For simulation of thermal evolution of crude oils, about 100 experiments were carried out on two oils (Boscan and Pematang), in a closed pyrolysis system, over a wide range of heating times (few minutes to 1 month) and temperatures (335 to 500°C). The pyrolysate is represented by 10 chemical fractions (C1, C2, C3-C5, C6-C13 saturates, benzene + toluene + xylenes + naphthalene, C9-C13 alkyl aromatics, C14+ saturates, C14+ condensed aromatics, C14+ alkyl and/or naphtheno aromatics + resins + asphaltenes and coke). For kinetic modeling, the degradation of each fraction, except for C1, C6-C13 aromatic mixture comprising benzene, toluene, xylenes and naphthalene, and coke considered as stable compounds, is described by a balanced elementary reaction governed by first order kinetics and obeying Arrhenius law. For a given oil, the kinetic parameters of the model (apparent activation energies Ei, preexponential factor A and stoichiometric coefficients alphaij) were optimized with reference to a dataset comprising the final compositions resulting from oil pyrolysis experiments. This optimization was carried out successively on each distillate and each residue, on both distillate and residue from the same oil, then on the two distillates and two residues altogether. The model accounts satisfactorily for the specific kinetics of cracking of both each oil and of the two oils together, suggesting that it is now possible to predict the thermal behavior of a given oil provided the proportions of the ten fractions selected for the model are known. The wide temperature range in which the model is valid, supports its extrapolation to the temperature range of sedimentary basins

Thermal Evolution of Crude Oils in Sedimentary Basins: Experimental Simulation in a Confined System and Kinetic Modeling Evolution thermique des huiles dans les bassins sédimentaires : simulation expérimentale par pyrolyse en milieu confiné et modélisation cinétique

A detailed knowledge of the cracking mechanisms of crude oils should highly improve the understanding of geochemical reactions involved in hydrocarbon degradation into lighter oil and gas and consequently the applicability of kinetic models currently used for prediction of gas formation. Although the mechanisms of cracking are well known for several model compounds or simple mixtures, there is, to date, no available method to model complex mixtures, especially when they contain heavy compounds, except by using empirical approaches. During thermal cracking, oil will produce both lighter and heavier molecules than those present in the initial sample. Thus, the pyrolysate will be a mixture of both new compounds and compounds not yet degraded. In order to discriminate between reactants and products, we have chosen to fractionate each oil into two classes : the first one (distillate 300-) comprising light hydrocarbons ranging from C6 to C16 the second one (residue 300+) comprising both hydrocarbons and polar compounds. For simulation of thermal evolution of crude oils, about 100 experiments were carried out on two oils (Boscan and Pematang), in a closed pyrolysis system, over a wide range of heating times (few minutes to 1 month) and temperatures (335 to 500°C). The pyrolysate is represented by 10 chemical fractions (C1, C2, C3-C5, C6-C13 saturates, benzene + toluene + xylenes + naphthalene, C9-C13 alkyl aromatics, C14+ saturates, C14+ condensed aromatics, C14+ alkyl and/or naphtheno aromatics + resins + asphaltenes and coke). For kinetic modeling, the degradation of each fraction, except for C1, C6-C13 aromatic mixture comprising benzene, toluene, xylenes and naphthalene, and coke considered as stable compounds, is described by a balanced elementary reaction governed by first order kinetics and obeying Arrhenius law. For a given oil, the kinetic parameters of the model (apparent activation energies Ei, preexponential factor A and stoichiometric coefficients alphaij) were optimized with reference to a dataset comprising the final compositions resulting from oil pyrolysis experiments. This optimization was carried out successively on each distillate and each residue, on both distillate and residue from the same oil, then on the two distillates and two residues altogether. The model accounts satisfactorily for the specific kinetics of cracking of both each oil and of the two oils together, suggesting that it is now possible to predict the thermal behavior of a given oil provided the proportions of the ten fractions selected for the model are known. The wide temperature range in which the model is valid, supports its extrapolation to the temperature range of sedimentary basins. Une meilleure connaissance des mécanismes du craquage thermique des huiles doit permettre de mieux comprendre leur évolution naturelle dans les bassins sédimentaires et donc d'améliorer les modèles actuels utilisés pour prédire la formation du gaz. Bien que les mécanismes de craquage soient bien connus pour des composés modèles ou des mélanges simples d'hydrocarbures, il n'existe pas à l'heure actuelle, à l'exception des modèles empiriques, de méthode pour rendre compte de la dégradation thermique des mélanges complexes, surtout, lorsque ces derniers sont enrichis en produits lourds. Au cours du craquage thermique, une huile produira à la fois des composés plus légers et des composés plus lourds que la charge initiale. En conséquence, les produits de pyrolyse seront un mélange complexe contenant des produits nouveaux et des composés non encore dégradés. Afin de pouvoir faire la distinction entre réactifs et produits, nous avons choisi de fractionner chaque huile en deux grandes fractions : la première (distillat 300- ) contenant des hydrocarbures légers de C6 à C16 et la seconde (résidu 300+) contenant des hydrocarbures et des produits polaires. Afin de simuler l'évolution thermique des huiles, nous avons réalisé une centaine d'expériences de pyrolyse en milieu fermé sur deux huiles; l'une enrichie en composés aromatiques (Boscan) et l'autre enrichie en structures aliphatiques (Pematang). La gamme de température explorée est comprise entre 335 et 540°C et celle des temps de séjour entre quelques minutes et quelques semaines. Les huiles, ainsi que les produits de pyrolyse sont représentés par 10 classes chimiques (C1, C2, C3-C5, C6-C13 saturés, benzène + toluène + xylènes + naphtalène, C9-C13 aromatiques alkylés, C14+ saturés, C14+ aromatiques condensés, C14+ alkyl et/ou naphténo aromatiques + résines + asphaltènes et coke). Pour les modèles cinétiques, le craquage de chacune des fractions, à l'exception du méthane, du mélange aromatique comprenant le benzène, le toluène, les xylènes et le naphtalène et du coke considérés comme produits stables, est décrit par une réaction élémentaire pondérée, gouvernée par une cinétique d'ordre 1 et obéissant à la loi d'Arrhénius. Pour chaque huile étudiée, les paramètres cinétiques (énergies d'activation apparentes Ei, facteur préexponentiel A et coefficients stoechiométriques alphaij) sont optimisés à partir d'un jeu de données expérimentales sur la composition des produits finaux résultant des expériences. Cette optimisation a été réalisée successivement sur chaque distillat et sur chaque résidu, sur le distillat et sur le résidu provenant d'une même huile, puis sur l'ensemble des deux distillats et des résidus. Les modèles obtenus rendent compte de façon satisfaisante de la cinétique de craquage de chacune des 2 huiles modélisées séparément ainsi que de la cinétique de craquage de l'ensemble des 2 huiles. En conséquence, il semble possible maintenant de prédire à priori le comportement thermique d'une huile donnée, à condition de connaître au départ, les proportions respectives des 10 classes chimiques définies pour la modélisation. Par ailleurs, la large gamme de températures explorées dans laquelle ces modèles sont valables, a permis leur extrapolation dans la gamme de températures des bassins sédimentaires