Cascade of circulicity in compressible turbulence

The purpose of this work is to investigate whether a cascading process can be associated with the rotational motions of compressible three-dimensional turbulence. This question is examined through the lens of circulicity, a concept related to the angular momentum carried by large turbulent scales. By deriving a Monin-Yaglom relation for circulicity, we show that an ``effective'' cascade of this quantity exists, provided the flow is stirred with a force having a solenoidal component. This outcome is obtained independently from the expression of the equation of state. To supplement these results, a coarse-graining analysis of the flow is performed. This approach allows to separate the contributions of the transfer and production terms of circulicity and to discuss their respective effects in the inertial range

Diffusion limit of langevin pdf models in weakly inhomogeneous turbulence

In this work, we discuss the modelling of transport in Langevin probability density function (PDF) models used to predict turbulent flows. Our focus is on the diffusion limit of these models, i.e. when advection and dissipation are the only active physical processes. In this limit, we show that Langevin PDF models allow for an asymptotic expansion in terms of the ratio of the integral length to the mean gradient length. The main contribution of this expansion yields an evolution of the turbulent kinetic energy equivalent to that given by a k-epsilon model. In particular, the transport of kinetic energy is given by a gradient diffusion term. Interestingly, the identification between PDF and k-epsilon models raises a number of questions concerning the way turbulent transport is closed in PDF models. In order to validate the asymptotic solution, several numerical simulations are performed.Dans cet article, nous abordons la question de la modélisation du transport turbulent dans les modèles de turbulence basés sur les fonctions de densité de probabilité (PDF). Nous étudions la limite diffusive de ces modèles obtenue lorsque l'advection et la dissipation sont les seuls processus physiques actifs. Dans cette limite, nous montrons que les modèles PDF donnent lieu à un développement asymptotique selon un petit paramètre correspondant au rapport de l'échelle intégrale sur l'échelle du gradient moyen. La contribution principale de ce développement s'identifie avec un modèle k-epsilon classique. En particulier, le transport de l'énergie turbulente est donné par une diffusion en premier gradient. L'identification entre modèle k-epsilon et modèle PDF permet de soulever un certain nombre de questions sur la manière dont le transport est modélisé dans les approches PDF. La solution asymptotique est validée par des simulations numériques réalisées à l'aide d'un code Monte Carlo mais aussi d'un code déterministe

An early burst of IFN-γ induced by the pre-erythrocytic stage favours Plasmodium yoelii parasitaemia in B6 mice

<p>Abstract</p> <p>Background</p> <p>In murine models of malaria, an early proinflammatory response has been associated with the resolution of blood-stage infection. To dissect the protective immune mechanims that allow the control of parasitaemia, the early immune response of C57BL/6 mice induced during a non-lethal plasmodial infection was analysed.</p> <p>Methods</p> <p>Mice were infected with <it>Plasmodium yoelii </it>265BY sporozoites, the natural invasive form of the parasite, in order to complete its full life cycle. The concentrations of three proinflammatory cytokines in the sera of mice were determined by ELISA at different time points of infection. The contribution of the liver and the spleen to this cytokinic response was evaluated and the cytokine-producing lymphocytes were identified by flow cytometry. The physiological relevance of these results was tested by monitoring parasitaemia in genetically deficient C57BL/6 mice or wild-type mice treated with anti-cytokine neutralizing antibody. Finally, the cytokinic response in sera of mice infected with parasitized-RBCs was analysed.</p> <p>Results</p> <p>The early immune response of C57BL/6 mice to sporozoite-induced malaria is characterized by a peak of IFN-γ in the serum at day 5 of infection and splenic CD4 T lymphocytes are the major producer of this cytokine at this time point. Somewhat unexpected, the parasitaemia is significantly lower in <it>P. yoelii</it>-infected mice in the absence of IFN-γ. More precisely, at early time points of infection, IFN-γ favours parasitaemia, whereas helping to clear efficiently the blood-stage parasites at later time points. Interestingly, the early IFN-γ burst is induced by the pre-erythrocytic stage.</p> <p>Conclusion</p> <p>These results challenge the current view regarding the role of IFN-γ on the control of parasite growth since they show that IFN-γ is not an essential mediator of protection in <it>P. yoelii</it>-infected C57BL/6 mice. Moreover, the mice parasitaemia is more efficiently controlled in the absence of an early IFN-γ production, suggesting that this cytokine promotes parasite's growth. Finally, this early burst of IFN-γ is induced by the pre-erythrocytic stage, showing the impact of this stage on the immune response taking place during the subsequent erythrocytic stage.</p

Differential activity of methylene blue against erythrocytic and hepatic stages of Plasmodium

Background: In the context of malaria elimination/eradication, drugs that are effective against the different developmental stages of the parasite are highly desirable. The oldest synthetic anti-malarial drug, the thiazine dye methylene blue (MB), is known for its activity against Plasmodium blood stages, including gametocytes. The aim of the present study was to investigate a possible effect of MB against malaria parasite liver stages. Methods: MB activity was investigated using both in vitro and in vivo models. In vitro assays consisted of testing MB activity on Plasmodium falciparum, Plasmodium cynomolgi and Plasmodium yoelii parasites in human, simian or murine primary hepatocytes, respectively. MB in vivo activity was evaluated using intravital imaging in BALB/c mice infected with a transgenic bioluminescent P. yoelii parasite line. The transmission-blocking activity of MB was also addressed using mosquitoes fed on MB-treated mice. Results: MB shows no activity on Plasmodium liver stages, including hypnozoites, in vitro in primary hepatocytes. In BALB/c mice, MB has moderate effect on P. yoelii hepatic development but is highly effective against blood stage growth. MB is active against gametocytes and abrogates parasite transmission from mice to mosquitoes. Conclusion: While confirming activity of MB against both sexual and asexual blood stages, the results indicate that MB has only little activity on the development of the hepatic stages of malaria parasites

Approches PDF pour la combustion turbulente, prise en compte d un spectre d échelles turbulentes dans la modélisation du micromélange et élaboration d une méthode de Monte Carlo eulérienne

La première partie de cette thèse concerne la modélisation du micromélange. Deux nouveaux modèles ont été proposés par Sabel'nikov et Gorokhovski (2001) afin de prendre en compte un spectre d'échelles de fréquence turbulent. Leurs propriétés sont ici analysées dans le cas de la décroissance d'un scalaire homogène en turbulence homogène. Les PDF transitoires sont calculées numériquement et comparées aux résultats des calculs DNS de Eswaran et Pope (1988). Les solutions asymptotiques sont également étudiées. Nous montrons que les modèles donnent des résultats satisfaisants par rapport à la DNS, et qu'ils donnent lieu à des solutions asymptotiques non-nécessairement gaussiennes. La seconde partie traite de la résolution numérique de l'équation de transport de la PDF de scalaires réactifs. Une nouvelle méthode de Monte Carlo eulérienne, basée sur des équations aux dérivées partielles stochastiques hyperboliques, est proposée. Ces équations sont analysées et illustrées sur des exemples simples. Des schémas numériques sont proposés pour les résoudre. La méthode est alors évaluée sur des cas mono-dimensionnels et finalement appliquée au calcul d'une flamme de prémélange 2D.The first part of this thesis deals with micromixing models. Two new models have been proposed by Sabel'nikov and Gorokhovski (2001), in order to account for a turbulent frequency scale spectrum. Their properties are analyzed here in the case of the decay of a homogeneous scalar in homogeneous turbulence. Transient PDF are numerically computed and evaluated against the DNS data of Eswaran and Pope (1988). Besides, asymptotic solutions are also examined. We show that the models compare well against the DNS results, and that they yield asymptotic solutions which are not necessarily Gaussian. The second part focuses on numerical methods for solving the transport equation of the PDF of turbulent scalars. A new Eulerian Monte Carlo method is proposed. It is based on hyperbolic stochastic partial differential equations. These equations are analysed and illustrated on simple examples. Numerical schemes are proposed for solving them. The Monte Carlo method is then assessed on one-dimensional tests. Finally, it is applied to compute a 2D premixed flame.ROUEN-BU Sciences Madrillet (765752101) / SudocROUEN-BU Sciences (764512102) / SudocSudocFranceF

Petites et grandes exploitations agricoles en région Occitanie-Pyrénées-Méditerranée. Une analyse ville-campagne à partir du recensement agricole

National audienc

Petites et grandes exploitations agricoles en région Occitanie-Pyrénées-Méditerranée. Une analyse ville-campagne à partir du recensement agricole

National audienc