Wake instabilities behind an axisymmetric bluff body at low Reynolds numbers

This paper aims at understanding the dynamical process that leads to the onset of chaos in the flow past a blunt based axisymmetric bluff body. On the ba- sis of direct numerical simulations, conducted for Reynolds numbers ranging from 100 to 800, we show that the flow undergoes multiple transitions, successively giv- ing rise to the SS, RSPa, RSPb and RSPc wake states. In particular, the RSPc state, revealed in this work via long-term computations, is characterized by intermittent vortex stretching denoting the onset of chaos and the potential occurence of a third instability that superimposes to the first and second instability associated with state RSPa and RSPb respectively. Interestingly, the reflectional symmetry plane that characterizes the RSP states is still retained. Hence, chaos is triggered before the symmetry breaking and the occurence of the RSB state observed at higher Reynolds numbers

Volumineux kystes mandibulaires : à propos de 2 cas

Les kystes odontogènes représentent une pathologie relativement fréquente mais posent de nombreux problèmes en pratique clinique, notamment en raison des difficultés de diagnostic. La découverte de ces kystes est généralement fortuite au cours d’un examen radiologique de routine et impose, quand cela est possible, le recours à une chirurgie énucléatrice. Des formes atypiques peuvent être rencontrées, soulignant l’intérêt majeur de l’histologie et de l’analyse anatomopathologique dans la pose du diagnostic. Deux cas cliniques viendront illustrer notre propos, à travers l’étude de deux formes de kératokystes odontogéniques

Turbulence and Interactions: Proceedings of the TI 2018 Conference, June 25-29, 2018, Les Trois-Îlets, Martinique, France

International audienc

Fluid-Structure Interactions in Discrete Mechanics

The primary objective of discrete mechanics is to unify various laws fromdifferent areas of physics, such as fluid mechanics and solid mechanics. The sameobjective was also pursued by continuum mechanics, but the latter has not been en-tirely successful in accomplishing it. The Galilean invariance and the principle ofequivalence make it possible to rewrite the law of dynamics as an equality betweenaccelerations, the one undergone by the medium and the external accelerations ap-plied to it. The derivation of the equation of discrete motion leads to writing theacceleration as a Hodge-Helmholtz decomposition,i.e.the sum of a gradient of ascalar potential and the rotational of a vector potential. By choosing the accelerationas being a primary variable, we can express the velocity and the displacement simplyas quantities that accumulate over time. Potentials represent energies per unit massand are also stored over time. The resulting formulation is able to describe the mo-tion and dynamics of complex media, that can be both fluid and solid, under largedeformations and large displacements. Two examples of fluid-structure coupling,an analytical solution and a numerical solution used for a benchmark, are presentedhere. They show the ability of the model to reproduce the behavior of interactingfluid and solid medi

Meloidogyne-SP4 effector gene silencing reduces reproduction of root-knot nematodes in rice (Oryza sativa)

International audienceThe root-knot nematodes (RKN) Meloidogyne graminicola and M. incognita are responsible for rice yield losses worldwide, particularly in Asia and Africa. Previous studies demonstrated that nematode-secreted proteins are crucial for root invasion and establishment in the host. We present some characteristics of a pioneer effector, M. incognita- secreted protein 4 (Mi-SP4), which is conserved in RKN and required for infection in compatible rice-RKN interactions. In situ hybridisation assays revealed Mi-SP4 expression in the dorsal pharyngeal gland of M. incognita second-stage juveniles (J2). Meloidogyne - SP4 transcripts strongly accumulated in pre-parasitic J2 and decreased in later parasitic stages of M. incognita and M. graminicola . Transient expression of the nematode effector gene in Nicotiana benthamiana leaves and onion cells indicated that GFP-tagged Mi-SP4 was present in the cytoplasm and accumulated in the nucleus of the plant cells. In vitro RNA interference (RNAi) gene silencing, obtained by soaking J2 with small-interfering (si)RNA si4-1, decreased Mi - SP4 expression in J2 by 35% and significantly reduced M. incognita reproduction in rice by at least 30%. Similarly, host-mediated gene silencing of the nematode SP4 effector candidate gene in transgenic rice plants significantly reduced M. graminicola reproduction by 26% to 47%. The data obtained demonstrate that Mi -SP4 is a pioneer virulence effector, which plays an essential role in both M. incognita and M. graminicola pathogenicity on rice