21 research outputs found

    Instabilité et turbulence dans des écoulements bidimensionnels MHD

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    We create two-dimensional flows within a thin horizontal mercury layer subjected to a vertical uniform magnetic field. The fluid is set in motion by injecting electrical currents.The first considered flow is a couple of vortices which signs is alternated. We study through visualizations. They reveal the spatial distribution of the velocity field. We calculate the vorticity and stream function by numerical processing of digitized velocity field. These two variables allow us to characterize the encountered stationary vortex structures.Then we turn to a hexagonal network of forced vortex, and we follow the destabilization of this periodic network. We show that even well beyond the transition, destabilized flow is governed by the interaction of nonlinear waves that appeared at times of transition.When disrupting the previous flow on a large scale before the spatial period of the network, a disorganized motion appears. We show that the fluctuating velocity component is quasi homogeneous and isotropic. Velocity fluctuations play an active role in transfers of inertial energy. We check that these transfers are described by the phenomenological laws of two-dimensional turbulence.Nous créons des écoulements bidimensionnels à l’intérieur d’une couche de mercure mince, horizontale et soumise à un champ magnétique uniforme vertical. Le fluide est mis en mouvement en injectant des courants électriques.Le premier type d’écoulements considéré est un couple de tourbillons de signes alternés. Nous l’étudions au moyen de visualisations. Elles révèlent la répartition spatiale du champ de vitesse. Nous calculons la vorticité et la fonction de courant par un traitement numérique du champ de vitesse digitalisé. Ces deux grandeurs nous permettent de caractériser les structures tourbillonnaires stationnaires rencontrées.Nous nous intéressons ensuite à un réseau hexagonal de tourbillons forcé, et suivons la déstabilisation de ce réseau périodique. Nous montrons que même bien au-delà de la transition, l’écoulement déstabilisé est gouverné par les interactions d’ondes non linéaires qui sont apparues aux moments de la transition. Lorsqu’on perturbe l’écoulement précédent à une échelle grande devant la période spatiale du réseau, un mouvement plus désorganisé apparaît. Nous montrons que la composante fluctuante de la vitesse est quasi homogène isotrope. Les fluctuations de la vitesse jouent le rôle actif dans les transferts inertiaux d’énergie. On vérifie que ces transferts sont décrits par les lois phénoménologiques de la turbulence bidimensionnelle

    Mutations in TUBG1, DYNC1H1, KIF5C and KIF2A cause malformations of cortical development and microcephaly.

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    International audienceThe genetic causes of malformations of cortical development (MCD) remain largely unknown. Here we report the discovery of multiple pathogenic missense mutations in TUBG1, DYNC1H1 and KIF2A, as well as a single germline mosaic mutation in KIF5C, in subjects with MCD. We found a frequent recurrence of mutations in DYNC1H1, implying that this gene is a major locus for unexplained MCD. We further show that the mutations in KIF5C, KIF2A and DYNC1H1 affect ATP hydrolysis, productive protein folding and microtubule binding, respectively. In addition, we show that suppression of mouse Tubg1 expression in vivo interferes with proper neuronal migration, whereas expression of altered Îł-tubulin proteins in Saccharomyces cerevisiae disrupts normal microtubule behavior. Our data reinforce the importance of centrosomal and microtubule-related proteins in cortical development and strongly suggest that microtubule-dependent mitotic and postmitotic processes are major contributors to the pathogenesis of MCD

    Colonic Biopsies to Assess the Neuropathology of Parkinson's Disease and Its Relationship with Symptoms

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    The presence of Lewy bodies and Lewy neurites (LN) has been demonstrated in the enteric nervous system (ENS) of Parkinson's disease (PD) patients. The aims of the present research were to use routine colonoscopy biopsies (1) to analyze, in depth, enteric pathology throughout the colonic submucosal plexus (SMP), and (2) to correlate the pathological burden with neurological and gastrointestinal (GI) symptoms.A total of 10 control and 29 PD patients divided into 3 groups according to disease duration were included. PD and GI symptoms were assessed using the Unified Parkinson's Disease Rating Scale part III and the Rome III questionnaire, respectively. Four biopsies were taken from the ascending and descending colon during the course of a total colonoscopy. Immunohistochemical analysis was performed using antibodies against phosphorylated alpha-synuclein, neurofilaments NF 220 kDa (NF) and tyrosine hydroxylase (TH). The density of LN, labeled by anti-phosphorylated alpha-synuclein antibodies, was evaluated using a quantitative rating score. Lewy pathology was apparent in the colonic biopsies from 21 patients and in none of the controls. A decreased number of NF-immunoreactive neurons per ganglion was observed in the SMP of PD patients compared to controls. The amount of LN in the ENS was inversely correlated with neuronal count and positively correlated with levodopa-unresponsive features and constipation.Analysis of the ENS by routine colonoscopy biopsies is a useful tool for pre-mortem neuropathological diagnosis of PD, and also provides insight into the progression of motor and non-motor symptoms

    Sequential positron emission tomography using [18F]fluorodeoxyglucose for monitoring response to chemotherapy in metastatic breast cancer.

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    peer reviewedPURPOSE: To evaluate the clinical value of positron emission tomography (PET) for monitoring chemotherapy in metastatic breast cancer. EXPERIMENTAL DESIGN: Twenty patients with hormonorefractory or hormonoreceptor-negative multimetastatic breast cancer were prospectively included. PET studies were done at baseline, at day 21 after the first cycle and at day 21 after the third cycle of chemotherapy. Metabolic response was defined based on visual and various modes of standardized uptake value (SUV) analysis of sequential PET studies. RESULTS: After one cycle, PET indicated a partial response in 12 patients, stable disease in 7 patients, and progressive disease in 1 patient, according to the visual analysis. After three cycles, PET showed a complete response in 5 patients, partial response in 11 patients, stable disease in 3 patients, and progressive disease in 1 patient. Seventy-five percent of the patients showing a metabolic response on visual analysis effectively responded to the treatment. The average SUV decreased on both the second and the third PET study, but only changes measured after three cycles of chemotherapy predicted the clinical response to chemotherapy and the overall survival. All methods for calculating the SUV (normalized for body weight, body surface area, or lean body mass) provided similar results. CONCLUSION: Semiquantitative analysis of [18F]fluorodeoxyglucose-PET studies done after three cycles of chemotherapy is useful for monitoring the response to chemotherapy in metastatic breast cancer

    Sequential Positron Emission Tomography Using [ 18

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    Platinum Doped Hydrotreating Catalysts for Deep Hydrodesulfurization of Diesel Fuels

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    International audienceTwo-stage processes are possible solutions for reaching 10 ppm sulfur in gas oil without severe running conditions. First, most of the sulfur is removed by using a CoMo conventional catalyst. Second, after H2S removal, the treated oil, with a remaining S content below 500 ppm, is again hydrotreated. In this latter case, the use of noble metal catalysts can be envisaged. In the present study dealing with this second stage reactor, we examined a catalytic system based on the addition of a low content of Pt to a commercial sulfide catalyst. An enhancement in catalytic activity can be obtained in the conversion of model molecules (tetralin and dibenzothiophene) as well as a hydrotreated straight run gas oil. The promotion effect strongly depends on the preparation procedure which requires the impregnation of Pt on a presulfided commercial HDT catalyst. Advanced EXAFS and HRTEM characterizations were used to characterize the active phases
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