Capillary pinching in a pinched microchannel

We report a study of the capillary pinching of a gas bubble by a wetting liquid inside a pinched channel. The capillary pinching induces very reproducible bubbling, at a very well-defined frequency. There are two regimes associated with drip and jet bubbling. In the latter, we show that highly monodispersed bubbles are formed by our pinched channel. The dynamics of the bubble formation also shows two distinct regimes: a long-duration elongation of the air bubble and a rapid relaxation of the interface after interface breakup. The slow regime depends on the flux imposed and the channel geometry. The rapid deformation dynamic regime depends very weakly on the boundary conditions. Scaling arguments are proposed in the context of the lubrication approximation to describe the two regimes

Quasi-static liquid–air drainage in narrow channels with variations in the gap

This paper studies the shape of an air bubble quasi-statically flowing in the longitudinal direction of narrow channels. Two bottom topographies are treated, i.e., linear and quadratic variations of the gap along the transverse direction. This work analyses the main characteristics of the gas–liquid interface with respect to the wedge aspect ratio. From the convergence of asymptotic, numerical and experimental analyses, we found simple dependences for the finger width and total curvature as a function of channel aspect ratio. These results provide simple and general expressions for the pressure drop needed to overcome capillary forces and push the air finger inside the channel

Deep Convolutional Variational Autoencoder as a 2D-Visualization Tool for Partial Discharge Source Classification in Hydrogenerators

International audienceHydrogenerators are strategic assets for power utilities. Their reliability and availability can lead to significant benefits. For decades, monitoring and diagnosis of hydrogenerators have been at the core of maintenance strategies. A significant part of generator diagnosis relies on Partial Discharge (PD) measurements, because the main cause of hydrogenerator breakdown comes from failure of its high voltage stator, which is a major component of hydrogenerators. A study of all stator failure mechanisms reveals that more than 85 % of them involve the presence of PD activity. PD signal can be detected from the lead of the hydrogenerator while it is running, thus allowing for on-line diagnosis. Hydro-Québec has been collecting more than 33 000 unlabeled PD measurement files over the last decades. Up to now, this diagnostic technique has been quantified based on global PD amplitudes and integrated PD energy irrespective of the source of the PD signal. Several PD sources exist and they all have different relative risk, but in order to recognize the nature of the PD, or its source, the judgement of experts is required. In this paper, we propose a new method based on visual data analysis to build a PD source classifier with a minimum of labeled data. A convolutional variational autoencoder has been used to help experts to visually select the best training data set in order to improve the performances of the PD source classifier

Role of prey subcellular distribution on the bioaccumulation of yttrium (Y) in the rainbow trout

Our knowledge of the processes leading to the bioaccumulation of rare earth elements (REE) in aquatic biota is limited. As the contamination of freshwater ecosystems by anthropogenic REE have recently been reported, it becomes increasingly urgent to understand how these metals are transferred to freshwater organisms in order to develop appropriate guidelines. We exposed rainbow trout (Oncorhynchus mykiss) to an REE, yttrium (Y), to either a range of Y-contaminated prey (Daphnia magna) or a range of Y-contaminated water. For the feeding experiment, the relationship between the Y assimilation by O. mykiss and the Y subcellular fractionation in D. magna was evaluated. Assimilation efficiency of Y by O. mykiss was low, ranging from 0.8 to 3%. These values were close to the proportion of Y accumulated in D. magna cytosol, 0.6–2%, a theoretical trophically available fraction. Moreover, under our laboratory conditions, water appeared as a poor source of Y transfer to O. mykiss. Regardless of the source of contamination, a similar pattern of Y bioaccumulation among O. mykiss tissues was revealed: muscles < liver < gills < intestine. We conclude that the trophic transfer potential of Y is low and the evaluation of Y burden in prey cytosol appears to be a relevant predictor of Y assimilation by their consumers

Transient myocardial tissue and function changes during a marathon in less fit marathon runners

Background : Although regular physical activity improves health, strenuous exercise might transiently increase cardiac risk. Training and fitness might provide protection. Methods : We prospectively studied 20 recreational marathon runners without known cardiovascular disease or symptoms: at peak training before, immediately after, and 3 months after a 42.2-km marathon. Changes in global/segmental myocardial function, edema, resting perfusion, and fibrosis were measured. Results : At peak training, runners exercised 8.1 ± 2.3 hours and 62 ± 18 km per week with mean maximal oxygen consumption (VO2max) of 53.2 ± 8.3 mL/kg/min. In response to the marathon, global left ventricular and right ventricular ejection fraction decreased in half of the runners; these runners had poorer peak training distance, training time, and fitness level. Change in global left ventricular ejection fraction was associated with VO2max. Overall, 36% of segments developed edema, 53% decreased function, and 59% decreased perfusion. Significant agreement was observed between segment decreasing function, decreasing perfusion, and developing edema. Myocardial changes were reversible at 3 months. Conclusions : Completing a marathon leads to localized myocardial edema, diminished perfusion, and decreased function occurring more extensively in less trained and fit runners. Although reversible, these changes might contribute to the transient increase in cardiac risk reported during sustained vigorous exercise.Introduction : Bien que l’activité physique régulière améliore la santé, l’exercice intense pourrait augmenter de façon passagère le risque de maladies du cœur. L’entraînement et la bonne forme physique pourraient apporter une protection contre ce risque. Méthodes : Nous avons étudié de façon prospective les coureurs récréatifs de marathon n’ayant pas de maladies ou de symptômes cardiovasculaires connus : au sommet de leur entraînement, avant, immédiatement après et 3 mois après un marathon de 42,2 km. Les changements dans le fonctionnement myocardique global et segmentaire, l’œdème, la perfusion au repos et la fibrose ont été mesurés. Résultats : Au sommet de leur entraînement, les coureurs ont accompli 8,1 ± 2,3 heures et 62 ± 18 km par semaine selon une consommation d'oxygène maximal (VO2 max) moyenne de 53,2 ± 8,3ml/kg/min. En réponse au marathon, la fraction d’éjection globale du ventricule gauche et du ventricule droit a diminué chez la moitié des coureurs; ces coureurs ont obtenu au sommet de leur entraînement une distance, une durée et un niveau de forme physique médiocres. La modification de la fraction d’éjection globale du ventricule gauche a été associée à la VO2 max. Dans l’ensemble, 36 % des segments ont développé un œdème, 53 % ont diminué le fonctionnement et 59 % ont diminué la perfusion. Une concordance significative a été observée entre le segment diminuant le fonctionnement, le segment diminuant la perfusion et le segment développant l’œdème. Les modifications du myocarde ont été réversibles à 3 mois. Conclusions : La réalisation d’un marathon mène à un œdème localisé du myocarde, à une perfusion réduite et à un fonctionnement diminué apparaissant davantage chez les coureurs moins entraînés et moins en forme. Bien que ces modifications soient réversibles, ils pourraient contribuer à l’augmentation passagère du risque de problèmes cardiaques signalés durant l’exercice intense soutenu

Predicting late myocardial recovery and outcomes in the early hours of ST-segment elevation myocardial infarction : traditional measures compared with microvascular obstruction, salvaged myocardium, and necrosis characteristics by cardiovascular magnetic resonance

Objectives : The aim of this study was to determine whether a very early imaging strategy improves the prediction of late systolic dysfunction and poor outcomes in ST-segment elevation myocardial infarction (STEMI) compared with traditional predictors. Background : Earlier prediction of poor outcomes after STEMI is desirable, because it will allow tailored therapy at the earliest possible time, when benefits might be greatest. Methods : One hundred and three patients with acute STEMI were studied by contrast-enhanced cardiovascular magnetic resonance within 12 h of primary angioplasty and at 6 months and followed >2 years. The primary end point was left ventricular (LV) dysfunction, whereas poor outcomes were a key secondary end point. Results : Traditional risk factors were only modest predictors of late LV dysfunction. Late gadolinium enhancement (LGE) volume maintained a stronger association to LV ejection fraction change than infarct transmurality, microvascular obstruction, or myocardial salvage during STEMI (p = 0.02). Multivariable logistic regression identified LGE volume during STEMI as the best predictor of late LV dysfunction (odds ratio: 1.36, p = 0.03). An LGE =23% of LV during STEMI accurately predicted late LV dysfunction (sensitivity 89%, specificity 74%). The LGE volume provided important incremental benefit for predicting late dysfunction (area under the curve = 0.92, p = 0.03 vs. traditional risk factors). Twenty-three patients developed poor outcomes (1 death, 2 myocardial infarctions, 5 malignant arrhythmias, 4 severe LV dysfunction <35%, 11 hospital stays for heart failure) over 2.6 ± 0.9 years; LGE volume remained a strong independent predictor of poor outcomes, whereas LGE =23% carried a hazard ratio of 6.1 for adverse events (p < 0.0001). Conclusions : During the hyperacute phase of STEMI, LGE volume provides the strongest association and incremental predictive value for late systolic dysfunction and discerns poor late outcomes