Turbulent Couette-Taylor flows with endwall effects: a numerical benchmark

International audienceThe accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of rotating machineries. The selection of a suitable model to account for the effects of turbulence on such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of different approaches available within commercial CFD solvers together with results obtained by means of in-house developed or open-source available research codes exploiting a suitable Reynolds Stress Model (RSM) closure, Large Eddy Simulation (LES) and a direct numerical simulation (DNS). The predictions are compared to the experimental data of Burin et al. (2010) in an original enclosed Couette-Taylor apparatus with endcap rings. The results are discussed in details for both the mean and turbulent fields. A particular attention has been turned to the scaling of the turbulent angular momentum G with the Reynolds number Re. By DNS, G is found to be proportional to Rea, the exponent a = 1.9 being constant in our case for the whole range of Reynolds numbers. Most of the approaches predict quite well the good trends apart from the k-w SST model, which provides relatively poor agreement with the experiments even for the mean tangential velocity profile. Among the RANS models, even though no approach appears to be fully satisfactory, the RSM closure offers the best overall agreement

Caractérisation de l'influence des instabilités de surface d'un film d'eau ruisselant sur le transfert de chaleur pariétal

Les films d'eau ruisselants sont utilisés dans un grand nombre d'applications industrielles. Ils permettent en impliquant une faible masse de fluide d'obtenir des transferts de chaleur importants. En général, ces films sont sujets à des instabilités de surface. Nous proposons ici une étude de l'influence de celles-ci sur le transfert convectif pariétal. Le problème est abordé numériquement en utilisant un maillage mobile épousant la forme de la surface libre. Une étude statistique nous permet de conclure sur l'importance des fluctuations de hauteur du film sur le flux pariétal transféré

Transferts de chaleur et de masse dans de ecoulements turbulents de Taylor-Couette avec flux axial

International audienceNous nous intéressons ici aux transferts de chaleur et de masse dans unsys eme de Taylor-Couette avec flux axial. Un dispositif permettant des mesures de vitesse et de coefficients de transferts á eté développé. Les régime etudiés sont turbulents : nombre de Reynolds axial entre 5600 et 11200 et entre 7900 et 79 millios pour le nombre de Taylor. Nous reportons le nombre de Nusselt en fonction du nombre de Reynolds axial et du nombre de Taylor ainsi que des mesures de vitesse. La présence de structures organisées proche du rotor á eté observée, ce qui est confirmé par un calcul DNS

Developmental motor problems and health-related quality of life in 5-year-old children born extremely preterm:A European cohort study

Aim: To measure the association between cerebral palsy (CP) and non-CP-related movement difficulties and health-related quality of life (HRQoL) among 5-year-old children born extremely preterm (&lt;28 weeks gestational age). Method: We included 5-year-old children from a multi-country, population-based cohort of children born extremely preterm in 2011 to 2012 in 11 European countries (n = 1021). Children without CP were classified using the Movement Assessment Battery for Children, Second Edition as having significant movement difficulties (≤5th centile of standardized norms) or being at risk of movement difficulties (6th–15th centile). Parents reported on a clinical CP diagnosis and HRQoL using the Pediatric Quality of Life Inventory. Associations were assessed using linear and quantile regressions. Results: Compared to children without movement difficulties, children at risk of movement difficulties, with significant movement difficulties, and CP had lower adjusted HRQoL total scores (β [95% confidence interval] = −5.0 [−7.7 to −2.3], −9.1 [−12.0 to −6.1], and − 26.1 [−31.0 to −21.2]). Quantile regression analyses showed similar decreases in HRQoL for all children with CP, whereas for children with non-CP-related movement difficulties, reductions in HRQoL were more pronounced at lower centiles. Interpretation: CP and non-CP-related movement difficulties were associated with lower HRQoL, even for children with less severe difficulties. Heterogeneous associations for non-CP-related movement difficulties raise questions for research about mitigating and protective factors.</p

Impact of parental lifestyle patterns in the preconception and pregnancy periods on childhood obesity

International audienceIntroduction High prevalence of overweight and obesity already observed in preschool children suggests the involvement of early-life risk factors. Preconception period and pregnancy are crucial windows for the implementation of child obesity prevention interventions with parental lifestyle factors as relevant targets. So far, most studies have evaluated their role separately, with only a few having investigated their potential synergistic effect on childhood obesity. Our objective was to investigate parental lifestyle patterns in the preconception and pregnancy periods and their association with the risk of child overweight after 5 years. Materials and methods We harmonized and interpreted results from four European mother-offspring cohorts participating in the EndObesity Consortium [EDEN, France; Elfe, France; Lifeways, Ireland; and Generation R, Netherlands] with data available for 1,900, 18,000, 1,100, and 9,500 families, respectively. Lifestyle factors were collected using questionnaires and included parental smoking, body mass index (BMI), gestational weight gain, diet, physical activity, and sedentary behavior. We applied principal component analyses to identify parental lifestyle patterns in preconception and pregnancy. Their association with risk of overweight (including obesity; OW-OB) and BMI z -scores between 5 and 12 years were assessed using cohort-specific multivariable logistic and linear and regression models (adjusted for potential confounders including parental age, education level, employment status, geographic origin, parity, and household income). Results Among the various lifestyle patterns derived in all cohorts, the two explaining the most variance were characterized by (1) “high parental smoking, low maternal diet quality (and high maternal sedentary behavior in some cohorts)” and, (2) “high parental BMI and low gestational weight gain.” Patterns characterized by high parental BMI, smoking, low diet quality or high sedentary lifestyle before or during pregnancy were associated with higher risk of OW-OB in children, and BMI z -score at any age, with consistent strengths of associations in the main cohorts, except for lifeways. Conclusion This project provides insight into how combined parental lifestyle factors in the preconception and pregnancy periods are associated with the future risk of child obesity. These findings are valuable to inform family-based and multi-behavioural child obesity prevention strategies in early life

Development of a Multivariate Prediction Model for Early-Onset Bronchiolitis Obliterans Syndrome and Restrictive Allograft Syndrome in Lung Transplantation.

Chronic lung allograft dysfunction and its main phenotypes, bronchiolitis obliterans syndrome (BOS) and restrictive allograft syndrome (RAS), are major causes of mortality after lung transplantation (LT). RAS and early-onset BOS, developing within 3 years after LT, are associated with particularly inferior clinical outcomes. Prediction models for early-onset BOS and RAS have not been previously described. LT recipients of the French and Swiss transplant cohorts were eligible for inclusion in the SysCLAD cohort if they were alive with at least 2 years of follow-up but less than 3 years, or if they died or were retransplanted at any time less than 3 years. These patients were assessed for early-onset BOS, RAS, or stable allograft function by an adjudication committee. Baseline characteristics, data on surgery, immunosuppression, and year-1 follow-up were collected. Prediction models for BOS and RAS were developed using multivariate logistic regression and multivariate multinomial analysis. Among patients fulfilling the eligibility criteria, we identified 149 stable, 51 BOS, and 30 RAS subjects. The best prediction model for early-onset BOS and RAS included the underlying diagnosis, induction treatment, immunosuppression, and year-1 class II donor-specific antibodies (DSAs). Within this model, class II DSAs were associated with BOS and RAS, whereas pre-LT diagnoses of interstitial lung disease and chronic obstructive pulmonary disease were associated with RAS. Although these findings need further validation, results indicate that specific baseline and year-1 parameters may serve as predictors of BOS or RAS by 3 years post-LT. Their identification may allow intervention or guide risk stratification, aiming for an individualized patient management approach

Deriving the dietary approaches to stop hypertension (DASH) score in women from seven pregnancy cohorts from the European alphabet consortium

The ALPHABET consortium aims to examine the interplays between maternal diet quality, epigenetics and offspring health in seven pregnancy/birth cohorts from five European countries. We aimed to use the Dietary Approaches to Stop Hypertension (DASH) score to assess diet quality, but different versions have been published. To derive a single DASH score allowing cross-country, cross-cohort and cross-period comparison and limiting data heterogeneity within the ALPHABET consortium, we harmonised food frequency questionnaire (FFQ) data collected before and during pregnancy in ≥26,500 women. Although FFQs differed strongly in length and content, we derived a consortium DASH score composed of eight food components by combining the prescriptive original DASH and the DASH described by Fung et al. Statistical issues tied to the nature of the FFQs led us to re-classify two food groups (grains and dairy products). Most DASH food components exhibited pronounced between-cohort variability, including non-full-fat dairy products (median intake ranging from 0.1 to 2.2 servings/day), sugar-sweetened beverages/sweets/added sugars (0.3–1.7 servings/day), fruits (1.1–3.1 servings/day), and vegetables (1.5–3.6 servings/day). We successfully developed a harmonized DASH score adapted to all cohorts being part of the ALPHABET consortium. This methodological work may benefit other research teams in adapting the DASH to their study’s specificities

Associations of maternal dietary inflammatory potential and quality with offspring birth outcomes: An individual participant data pooled analysis of 7 European cohorts in the ALPHABET consortium

BACKGROUND: Adverse birth outcomes are major causes of morbidity and mortality during childhood and associate with a higher risk of noncommunicable diseases in adult life. Maternal periconception and antenatal nutrition, mostly focusing on single nutrients or foods, has been shown to influence infant birth o

Cooperation stereo mouvement pour la detection des objets dynamiques

Un grand nombre d'applications de robotique embarquées pourrait bénéficier d'une détection explicite des objets mobiles. A ce jour, la majorité des approches présentées repose sur la classification, ou sur une analyse structurelle de la scène (la V-Disparité est un bon exemple de ces approches). Depuis quelques années, nous sommes témoins d'un intérêt croissant pour les méthodes faisant collaborer activement l'analyse structurelle et l'analyse du mouvement. Ces deux processus sont en effet étroitement liés. Dans ce contexte, nous proposons, à travers de travail de thèse, deux approches différentes. Si la première fait appel à l'intégralité de l'information stéréo/mouvement, la seconde se penche sur le cas des capteurs monoculaires, et permet de retrouver une information partielle.La première approche présentée consiste en un système innovation d'odométrie visuelle. Nous avons en effet démontré que le problème d'odométrie visuelle peut être posé de façon linéaire, alors que l'immense majorité des auteurs sont contraint de faire appel à des méthodes d'optimisation non-linéaires. Nous avons également montré que notre approche permet d'atteindre, voire de dépasser le niveau de performances présenté par des système matériels haut de gamme (type centrale inertielle). A partir de ce système d'odométrie visuelle, nous définissons une procédure permettant de détecter les objets mobiles. Cette procédure repose sur une compensation de l'influence de l'égo-mouvement, puis une mesure du mouvement résiduel. Nous avons ensuite mené une réflexion de fond sur les limitations et les sources d'amélioration de ce système. Il nous est apparu que les principaux paramètres du système de vision (base, focale) ont un impact de premier plan sur les performances du détecteur. A notre connaissance, cet impact n'a jamais été décrit dans la littérature. Il nous semble cependant que nos conclusions peuvent constituer un ensemble de recommandations utiles à tout concepteur de système de vision intelligent.La seconde partie de ce travail porte sur les systèmes de vision monoculaire, et plus précisément sur le concept de C-Vélocité. Alors que la V-Disparité a défini une transformée de la carte de disparité permettant de mettre en avant certains plans de l'image, la C-Vélocité défini une transformée du champ de flot optique, et qui utilise la position du FoE, qui permet une détection facile de certains plans spécifiques de l'image. Dans ce travail, nous présentons une modification de la C-Vélocité. Au lieu d'utiliser un a priori sur l'égo-mouvement (la position du FoE) afin d'inférer la structure de la scène, nous utilisons un a priori sur la structure de la scène afin de localiser le FoE, donc d'estimer l'égo-mouvement translationnel. Les premiers résultats de ce travail sont encourageants et nous permettent d'ouvrir plusieurs pistes de recherches futures.Many embedded robotic applications could benefit from an explicit detection of mobile objects. To this day, most approaches rely on classification, or on some structural scene analysis (for instance, V-Disparity). During the last few years, we've witnessed a growing interest for collaboration methods, that use actively btw structural analysis and motion analysis. These two processes are, indeed, closely related. In this context, we propose, through this study, two novel approaches that address this issue. While the first one use information from stereo and motion, the second one focuses on monocular systems, and allows us to retrieve a partial information.The first presented approach consists in a novel visual odometry system. We have shown that, even though the wide majority of authors tackle the visual odometry problem as non-linear, it can be shown to be purely linear. We have also shown that our approach achieves performances, as good as, or even better than the ones achieved by high-end IMUs. Given this visual odometry system, we then define a procedure allowing us to detect mobile objects. This procedure relies on a compensation of the ego-motion and a measure of the residual motion. We then lead a reflexion on the causes of limitation and the possible sources of improvement of this system. It appeared that the main parameters of the vision system (baseline, focal length) have a major impact on the performances of our detector. To the best of our knowledge, this impact had never been discussed, prior to our study. However, we think that our conclusion could be used as a set of recommendations, useful for every designer of intelligent vision system.the second part of this work focuses on monocular systems, and more specifically on the concept of C-Velocity. When V-Disparity defined a disparity map transform, allowing an easy detection of specific planes, C-Velocity defines a transform of the optical flow field, using the position of the FoE, allowing an easy detection of specific planes. Through this work, we present a modification of the C-Velocity concept. Instead of using a priori knowledge of the ego-motion (the position of the FoE) in order to determine the scene structure, we use a prior knowledge of the scene structure in order to localize the FoE, thus the translational ego-motion. the first results of this work are promising, and allow us to define several future works.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF