Shear-induced crystallization of polypropylene: Influence of molecular structure

International audienceThe isothermal crystallization of isotactic polypropylenes has been studied under static conditions and under shear flow. The shear was induced by displacement of a glass fibre in the molten polymer. An α-monoclinic crystalline phase was formed with a columnar organization at the surface of the glass fibre, which did not appear under static conditions. The growth rate, constant during shear-induced crystallization experiments, is compared with the results obtained from static crystallizations. An important increase of the growth rate due to the shear flow is observed. This increase depends on the molecular weight and the tacticity of the polypropylene. Actually, the molecular weight and the isotactic index seem to be the most important molecular parameters. Their augmentation leads to a significant increase of the growth rate, which can be increased by a factor of seven, under the present conditions

Shear-induced crystallization of polypropylene. Growth enhancement and rheology in the crystallization range

International audienceCrystallization under shear of many different polypropylenes has been studied using a fiber pull-out device. It appears that growth can be considerably enhanced by flow. The best correlation is obtained with weight average molecular weight. Modeling the flow pattern gives access to the mechanical parameters at the growth front (shear rate and shear stress) as well as to the total strain applied to the polymer. The residual strain can be calculated taking into account relaxation processes

Shear-induced crystallization of polypropylene: Influence of molecular weight

International audienceThree series of isotactic polypropylene characterized by different molecular weights and the same isotactic index have been studied during crystallization under static and shearing conditions. The shear is induced by the displacement of a glass fiber in the molten polymer. The monoclinic α-phase is here formed under shear with a columnar organization at the surface of the glass fiber, and does not appear under static condition. The growth-rate, constant during the shear-induced crystallization experiment, is compared with the result obtained from static crystallization. An important increase of the growth-rate due to the shear flow is observed. This increase depends on the molecular structure. The average molecular weights M̄w and M̄z seem to be the most important molecular parameters, for which an excellent correlation is obtained. The increase of these parameters M̄w and M̄z leads to a significant enhancement of the growth-rate, which can be multiplied by a factor of 10 in the present conditions

Évolution thermique des séries sédimentaires de la Marge ardéchoise : étude pétrographique de la matière organique et des argiles. Thermal evolution of the sedimentary series of the Ardèche Margin: petrological studies of organic matter and clays

Two wells, Balazuc (BA1) and Morte-Mérie (MM1), located in a confined area (1200 m apart) and separated by the Uzer fault (a Liassic structure with a dip fault of 1300 m) were analysed using conventional methodologies and techniques (PRV, TAI, XRD, STEM) in order to compare the diagenetic evolution of clays and organic matter. The thermal convective process allows the circulation of hot fluids and the oxidation of organic matter. The conductive process allows the maturation of the organic matter, the expulsion of hydrocarbons and the deposit of pyrobitumes in the migration channel

Pathologie de l’homme du Lazaret

Pathologie de l’homme du Lazare

Dok-1 and Dok-2 Regulate the Formation of Memory CD8 + T Cells

International audienceDiverse signals received by CD8+ T cells are integrated to achieve the required magnitude of cell expansion and the appropriate balance of effector/memory CD8+ T cell generation. Notably, the strength and nature of TCR signaling influence the differentiation and functional capacity of effector and memory CD8+ T cells. Dok-1 and Dok-2, the two members of the Dok family expressed in T cells, negatively regulate TCR signaling in vitro. However, the role of Dok proteins in modulating T cell function in vivo has not yet studied. We studied the function of Dok-1 and Dok-2 proteins in the regulation of the CD8+ T cell response to vaccinia virus infection. Comparison of responses to vaccinia virus expressing OVA peptide SIINFEKL by wild-type and Dok-1/2−/− CD8+ OT-I cells showed that the absence of Dok-1 and Dok-2 slightly reduced the magnitude of virus-specific effector CD8+ T cell expansion. This was not due to reduced proliferation or enhanced apoptosis of effector CD8+ T cells. Dok-1/2–deficient effector CD8+ T cells showed increased cell surface TCR expression following virus infection in vivo and increased expression of granzyme B and TNF upon stimulation with peptide Ag ex vivo. Finally, Dok-1/2–deficient effector CD8+ T had a severe defect in survival that resulted in impaired generation of memory CD8+ T cells. These results reveal the critical involvement of Dok-1 and Dok-2 in a negative-feedback loop that prevents overactivation of CD8+ T cells and promotes memory formation