Etude de l'instabilité barocline symétrique entre deux sphères concentriques en rotation

Notre travail essentiellement à caractère expérimental est mené à l'aide d'un dispositif expérimental inclinable, constitué de deux sphères concentriques en rotation. On vise à mettre en évidence les effets de l'inclinaison et de la hauteur H du fluide dans l'espace annulaire de largeur d sur les conditions d'apparition et la taille l'instabilité barocline. Les résultats montrent que l'instabilité barocline symétrique apparaît pour un facteur d'aspect H/d < 18 et un angle d'inclinaison compris entre 75° et 82°

Experimental investigations of the spherical Taylor-Couette flow

Transition to turbulence of a viscous incompressible fluid flow between two concentric spheres with the innerone rotating and the outer stationary was investigated experimentally. The flow modes were studied using theflow visualization and electrochemical technique. Different flow states were obtained for the gap/radius ratio0.107 in function of the Taylor number in the interval (22 - 1500) and aspect ratio (17 - 21). Observed stateswere classified into: Taylor Vortex Flow (TVF), Spiral Mode (SM), Spiral Mode Wavy Mode (SM+WM),Spiral Wavy Mode (SWM), Wavy Mode (WM) and Chaos. The variations of the flow patterns were reflectedby the wall velocity gradient, its fluctuation and spectral analysis. Fast Fourier transform applied on the timeseries of the wall velocity gradient allowed for the analysis and identification of the fundamental frequenciesand their evolutions associated with each flow state

Experimental investigations of the spherical taylor-couette flow using electrodiffusion technique

In this paper, we study the hydrodynamic instabilities between two concentric spheres, the inner rotating while the outer is at rest, through visualization and electrodiffusion technique. The exploration of the flow regimes is carried out for different values of the Taylor number Ta and the aspect ratio Gamma, but with one dimensionless gap width delta = 0.107. The bifurcation diagram of the flow is determined by classical visualization. On the other hand, by means of electrodiffusion technique, we measured the friction factor at the inner wall of the outer sphere. Time series obtained by the electrodiffusion technique, using FFT, permitted the identification of the fundamental frequencies and confirmed part of the bifurcation diagram obtained by the classical visualization

Variety of flow regimes in Taylor-Couette-Poiseuille flow

Taylor-Couette-Poiseuille (TCP) flow was studied in a wide range of Taylor numbers and low axial Reynolds numbers. The experimental set-up was characterized by a radius ratio of 0.8 and an aspect ratio of 44. The electrodiffusion method with a three-segment probe and an array of simple probes was used for mapping the components of wall shear rate at the outer fixed cylinder. The filling experiments were carried out consisting in adjusting the rotation rate of the inner cylinder and than filling the annular gap with liquid at the prescribed flowrate. Flow patterns were registered using a movie camera. Taylor vortex flow, wavy vortex flow, helical flow having screw opposite to the basic Couette Poiseuille (CT) flow and moving in the direction of the Poiseuille flow, steady and moving helical flow having screw coinciding with the basic CP flow and wavy helical flow was observed at low Taylor numbers. Laminar wavy vortex flow with 2, 3 and 4 waves was observed at moderate Taylor numbers. Vortices with turbulent flow either with straight or wavy boundaries and turbulent helical flow with screw coinciding with the basic flow and axial movement opposite to the axial basic flow were observed at higher Taylor numbers. Different time histories of axial and azimuthal wall shear rate components correspond to each flow pattern. The axial and azimuthal celerity of flow patterns and their size were evaluated from limiting diffusioncurrents and movies

Prediction of all-cause mortality in haemodialysis patients using a Bayesian network

BACKGROUND: All-cause mortality in haemodialysis (HD) is high, reaching 15.6% in the first year according to the European Renal Association. METHODS: A new clinical tool to predict all-cause mortality in HD patients is proposed. It uses a post hoc analysis of data from the prospective cohort study Photo-Graph V3. A total of 35 variables related to patient characteristics, laboratory values and treatments were used as predictors of all-cause mortality. The first step was to compare the results obtained using a logistic regression to those obtained by a Bayesian network. The second step aimed to increase the performance of the best prediction model using synthetic data. Finally, a compromise between performance and ergonomics was proposed by reducing the number of variables to be entered in the prediction tool. RESULTS: Among the 9010 HD patients included in the Photo-Graph V3 study, 4915 incident patients with known medical status at 2 years were analysed. All-cause mortality at 2 years was 34.1%. The Bayesian network provided the most reliable prediction. The final optimized models that used 14 variables had areas under the receiver operating characteristic curves of 0.78 ± 0.01, sensitivity of 72 ± 2%, specificity of 69 ± 2%, predictive positive value of 70 ± 1% and negative predictive value of 71 ± 2% for the prediction of all-cause mortality. CONCLUSIONS: Using artificial intelligence methods, a new clinical tool to predict all-cause mortality in incident HD patients is proposed. The latter can be used for research purposes before its external validation at: https://www.hed.cc/? a=twoyearsallcausemortalityhemod&n=2-years%20All-cause%20Mortality%20Hemodialysis.neta

Longitudinal lung function and structural changes in children with primary ciliary dyskinesia.

Functional and structural lung evaluations are part of the follow-up of patients with primary ciliary dyskinesia (PCD). We aimed to evaluate transversal and longitudinal relationships between lung function test (LFT) and chest computed tomography (CT) in children with PCD, in stable clinical condition. Data from children followed in the French National Center were retrospectively collected. Inclusion criteria were (i) definitive diagnosis of PCD, (ii) age less than 15 years at the beginning of follow-up, (iii) at least 8 years of follow-up, (iv) at least two couples of concurrent CT and LFT available in a phase of clinical stability of the lung disease without modification of the treatment regimen in the last 4 weeks. Twenty children (median age at entry 4.6 years, median follow-up 15.4 years) were included. Concurrent LFT (blood gas and spirometry) and CT (score) results were recorded. LFT indices (PaO(2) (n = 210), FVC, FEV(1) , FEF(2575%) (n = 195)) significantly decreased with age, and the mean annual decrease (z-score (% predicted)) was -0.17 (-0.49%), -0.09 (-0.50%), -0.10 (-0.89%), and -0.07 (-1.73%), respectively. First CT (median age 8.7 years) revealed bronchiectasis (70%), mucous plugging (70%), peribronchial thickening (90%), parenchymal abnormalities (65%), and hyperinflation (50%). CT scores (n = 74) significantly increased with age, and was negatively correlated to PaO(2), FVC, FEV(1), and FEF(2575%) longitudinal changes. In stable clinical condition, functional, and structural progressive impairments significantly correlated in children with PCD. Further prospective studies, including large populations of patients with various levels of disease severity, are needed to confirm whether lung function follow-up can be used to adjust CT frequency and help at minimizing the radiation burden in children with a good life expectancy