Simulation de phénomènes de fonte et solidification a l’aide d’une simulation par particules

La simulation de fluides extrêmement visqueux à l’aide d’une approche basée sur les SPH (Smoothed-particle Hydrodynamics) est une tâche fastidieuse. Le paramètre contrôlant la viscosité varie entre 0 (liquide) et +∞, il est donc difficile de trouver une valeur produisant le comportement visqueux désiré. De plus, puisque les équations sont posées sous la forme d’un problème raide, la simulation de fluides extrêmement visqueux implique l’application de très grandes forces sur les particules du fluide. Ces très grandes forces nécessitent un très petit pas de temps afin de conserver la stabilité de la simulation et produire de bons résultats. L’approche présentée dans ce mémoire utilise un intégrateur itératif de type prédiction-correction afin d’optimiser des forces de rigidité appliquées au sein du fluide, produisant ainsi un comportement variant de liquide à solide. À chaque itération de l’optimisation des forces, la position des particule est prédite. La déformation des particules est ensuite mesurée et comparée à une déformation cible et puis les forces de rigidité sont ajustées afin de contrer la différence entre celles-ci. Comparativement au paramètre de viscosité des approches typiques, le paramètre de rigidité proposé est plus facile à contrôler puisqu’il fournit une variation continue de la déformation dans l’intervalle de 0 (liquide) à 1 (solide). Puisque la simulation de fluides extrêmement visqueux est sujette à de grands temps de calculs et des instabilités, le modèle proposé est complémenté avec certaines améliorations importantes. Premièrement, une amélioration du calcul du pas de temps adaptatif est proposée résultant à la fois en une diminution des temps de calcul et une amélioration de la stabilité de la simulation. Deuxièmement, une approche implicite à la diffusion de température offre une stabilité accrue lors de la fonte et de la solidification peu importe la taille du pas de temps. Troisièmement, une propagation de contraintes permet une convergence plus rapide des forces de rigidité vers un comportement réaliste. Ensemble, ces améliorations et le modèle proposé permettent la simulation de comportements extrêmement visqueux qui étaient très difficiles, voire impossibles, à simuler à l’aide des approches actuelles basées sur les SPH

Systematic off-pump coronary artery revascularization in multivessel disease: Experience of three hundred cases

AbstractObjective: We sought to report our recent experience with off-pump coronary artery revascularization in multivessel disease. Methods: Between October 1996 and December 1998, 300 off-pump beating heart operations were performed at the Montreal Heart Institute by a single surgeon, representing 94% of all procedures undertaken during this same time frame (97% for 1998). This cohort of patients was compared with 1870 patients operated on with cardiopulmonary bypass from 1995 to 1996. Results: Mean age, sex distribution, and preoperative risk factors were comparable for the two groups. On average, 2.92 ± 0.8 and 2.84 ± 0.6 grafts per patient were completed in the beating heart and cardiopulmonary bypass groups, respectively. A majority of patients (70%) had either a triple or quadruple bypass. Coronary anastomoses were achieved with myocardial mechanical stabilization and heart “verticalization.” Ischemic time was shorter in the beating heart group (29.8 ± 0.9 vs 45 ± 0.4 minutes, P < .05). Similarly, the need for transfusion was significantly less in the beating heart group (beating heart operations, 34%; cardiopulmonary bypass, 66%; P < .005). Reduced use of postoperative intra-aortic counterpulsation, as well as a lower rise in creatine kinase MB isoenzyme, was observed in the beating heart group. Operative mortality rates (beating heart operations, 1.3%; cardiopulmonary bypass, 2%) and perioperative myocardial infarction (beating heart operations, 3.6%; cardiopulmonary bypass, 4.2%) were comparable for the two groups. Conclusion: In a majority of patients, off-pump complete coronary artery revascularization is an acceptable alternative to conventional operations, yielding good results given progressive experience, rigorous technique, and adequate coronary artery stabilization. (J Thorac Cardiovasc Surg 2000;119:221-9

Diagnosing performance variations by comparing multi-level execution traces

Tracing allows the analysis of task interactions with each other and with the operating system. Locating performance problems in a trace is not trivial because of their large size. Furthermore, deep knowledge of all components of the observed system is required to decide whether observed behavior is normal. We introduce TraceCompare, a framework that automatically identifies differences between groups of executions of the same task at the user space and kernel levels. Many performance problems manifest themselves as variations that are easily identified by our framework. Our comparison algorithm takes into account all threads that affect the completion time of analyzed executions. Differences are correlated with application code to facilitate the correction of identified problems. Performance characteristics of task executions are represented by a new data structure called enhanced calling context tree (ECCT). We demonstrate the efficiency of our approach by presenting four case studies in which TraceCompare was used to uncover serious performance problems in enterprise and open source applications, without any prior knowledge of their codebase. We also show that the overhead of our tracing solution is between 0.2 and 9 percent depending on the type of application

Travail pendant les études et abandon scolaire : Causes, conséquences et politiques d'intervention

The deterioration of the wage conditions of non-qualified workers has been the subject of considerable attention over the past few years. Unfortunately, it is not the sole preoccupation of public decision-makers. In this class of workers, the employment rate is particularly low, while unemployment tends to remain rather high. The first cause of non-qualification of young workers being their dropping out of school (the Canadian rate of dropouts from high school is 18%), any policy likely to reduce the dropout rates will be an effective means of improving the working situation of the youth. Our research identifies several determinants of dropping out and different policies which can be put into action by the governments in order to reduce dropout. We mention particularly the role played by the minimum wage in the dropout phenomenon: it is clear that a high minimum wage tends to increase dropout significantly La détérioration des conditions salariales des travailleurs non qualifiés sur le marché du travail a été l'objet d'une attention considérable au cours des dernières années. Malheureusement, elle n'est pas la seule source de préoccupations pour les décideurs publics. S'agissant de cette catégorie de travailleurs, le ratio emploi/population demeure singulièrement bas et le taux de chômage se0501ntient à des niveaux le plus souvent élevés. La première source de la non qualification des jeunes travailleurs étant l'abandon des études secondaires (à l'échelle canadienne, le taux d'abandon au secondaire est estimé à 18 %), toute politique susceptible de réduire les taux d'abandon représentera un moyen efficace d'améliorer la situation des jeunes sur le marché du travail. Notre recherche identifie plusieurs déterminants de l'abandon et différentes politiques qui pourront être mises de l'avant par les gouvernements pour réduire l'abandon scolaire. En particulier, mentionnons le rôle du salaire minimum dans le phénomène du décrochage : il est clair que le salaire minimum, quand il est élevé, contribue de façon significative à accroître l'abandon scolaire.School dropout, hours of work during study, minimum wage, Abandon scolaire, heures travaillées pendant les études, salaire minimum

Postoperative atrial fibrillation predicts long-term survival after aortic-valve surgery but not after mitral-valve surgery: a retrospective study

Background: Postoperative atrial fibrillation (POAF) has been reported to be associated with reduced long-term survival after isolated coronary artery bypass grafting surgery. The objective of this study was to determine the impact of POAF on long-term survival after valvular surgery. Methods: The authors retrospectively analysed the preoperative and operative data of 2986 consecutive patients with no preoperative history of atrial fibrillation undergoing first valvular surgery (aortic-valve replacement (AVR), mitral valve replacement or mitral valve repair (MVR/MVRp) with or without coronary artery bypass grafting surgery) in their institution between 1995 and 2008 (median follow-up 5.31 years, range 0.1-15.0). The authors investigated the impact of POAF on survival using multivariable Cox regression. Results: Patients with POAF were older, and were more likely to have hypertension or renal failure when compared with patients without POAF. The 12-year survival in patients with POAF was 45.7±2.8% versus 61.4±2.1% in patients without POAF (p<0.001). On a multivariable analysis, when adjusting for age and other potential confounding factors, POAF tended to be associated with lower long-term survival (HR for all-cause death (HR)=1.17, 95% CI 1.00 to 1.38, p=0.051). The authors also analysed this association separately in patients with AVR and those with MVR/MVRp. In the multivariable analysis, POAF was a significant predictor of higher long-term mortality in patients with AVR (HR=1.22, CI 1.02 to 1.45, p=0.03) but not in patients with MVR/MVRp (HR=0.87, CI 0.58 to 1.29, p=0.48). Conclusions: POAF is significantly associated with long-term mortality following AVR but not after MVR/MVRp. The underlying factors involved in the pathogenesis of POAF after MVR/MVRp may partially account for the lack of association between POAF and survival in these patients

Impact of Prosthesis-Patient Mismatch on Long-Term Survival After Aortic Valve Replacement Influence of Age, Obesity, and Left Ventricular Dysfunction

ObjectivesThis study was designed to evaluate the effect of valve prosthesis-patient mismatch (PPM) on late survival after aortic valve replacement (AVR) and to determine if this effect is modulated by patient age, body mass index (BMI), and pre-operative left ventricular (LV) function.BackgroundWe recently reported that PPM is an independent predictor of operative mortality after AVR, particularly when associated with LV dysfunction.MethodsThe indexed valve effective orifice area (EOA) was estimated in 2,576 patients having survived AVR and was used to define PPM as not clinically significant if it was >0.85 cm2/m2, as moderate if >0.65 and ≤0.85 cm2/m2, and severe if ≤0.65 cm2/m2.ResultsAfter adjustment for other risk factors, severe PPM was associated with increased late overall mortality (hazard ratio [HR]: 1.38; p = 0.03) and cardiovascular mortality (HR: 1.63; p = 0.0006) in the whole cohort. Severe PPM was also associated with increased overall mortality in patients <70 years old (HR: 1.77; p = 0.002) and in patients with a BMI <30 kg/m2 (HR: 2.1; p = 0.006), but had no impact in older patients or in obese patients. Moderate PPM was a predictor of mortality in patients with LV ejection fraction <50% (HR: 1.21; p = 0.01), but not in patients with preserved LV function.ConclusionsModerate PPM is associated with increased late mortality in patients with LV dysfunction, but with normal prognosis in those with preserved LV function. Notwithstanding the previously demonstrated deleterious effect of severe PPM on early mortality, this factor appears to increase late mortality only in patients <70 years old and/or with a BMI <30 kg/m2 or an LV ejection fraction <50%

Une politique concernant les données issues d’un programme de recherches interventionnelles en santé mondiale

ArticleLa recherche interventionnelle en santé mondiale est souvent effectuée au moyen de partenariats scientifiques internationaux. Mais la réalisation de telles recherches, notamment dans les pays à faible revenu où les enjeux de pouvoir, d’argent et de relations interculturelles sont exacerbés, soulève de nombreux défis éthiques, notamment concernant la conduite responsable lors des recherches collaboratives. L’un d’eux est la conservation, l’accès, l’utilisation et la publication des données. Malgré l’existence de multiples politiques et documents phares sur l’éthique et la conduite responsable de la recherche, les chercheurs en recherche interventionnelle sont encore peu outillés pour faire face à ce défi. Dans le contexte d’un programme de recherches interventionnelles réalisées au Burkina Faso, les auteurs souhaitent partager leur expérience dans le développement d’une politique interne concernant leurs données. Après avoir évoqué le contexte global et particulier, l’article présente le processus de formulation et d’adoption de cette politique par les chercheurs d’une équipe interdisciplinaire et internationale (Allemagne, Burkina Faso, Canada, France). Les valeurs qui enchâssent cette politique interne sont la transparence, la prévention, le consensus autour du processus de production, le respect des principes internationaux, l’accès libre aux connaissances produites et la préoccupation pour leur diffusion et utilisation. La politique se présente en plusieurs parties : objet, types et statuts des chercheurs impliqués, conservation des données, accès et utilisation des données, production scientifique et paternité. Les principaux défis rencontrés par les chercheurs pour formuler cette politique sont analysés dans un souci de partage pour susciter un débat rarement abordé. La confiance, la transparence et le respect mutuel doivent être au cœur de tout partenariat scientifique en recherche interventionnelle.Interventional global health research is often carried out through international scientific partnerships. However, the conduct of such research, especially in low-income countries where issues of power, money and intercultural relations are exacerbated, raises many ethical challenges particularly related to responsible conduct in collaborative research. One of these challenges is the storage, access, use and publication of data. Despite the existence of multiple influential policies and documents on ethics and the responsible conduct of research, researchers in intervention research are still not equipped to deal with such challenges. In the context of an intervention research program conducted in Burkina Faso, the authors would like to share their experience in the development of an internal policy concerning their data. After presenting the global and the particular context, the paper presents the process of policy formulation and its adoption by the researchers of an interdisciplinary and international team (Burkina Faso, Canada, France, Germany). The values that entrench this internal policy are: transparency, prevention, consensus about the production process, respect for international principles, free access to the knowledge produced and concerns regarding its dissemination and use. The policy is presented in several parts: aim, types and status of the participating researchers, data storage, access and use of data, scientific production and authorship. The main challenges faced by researchers in formulating this policy are analyzed in a shared desire to spark a debate that is rarely addressed. Trust, transparency and mutual respect should be central to any scientific partnership in intervention research

Assessing cardiometabolic parameter monitoring in inpatients taking a second-generation antipsychotic : the CAMI-SGA study – a crosssectional study

Objectives This study aims to determine the proportion of initial cardiometabolic assessment and its predicting factors in adults with schizophrenia, bipolar disorder or other related diagnoses for whom a second-generation antipsychotic was prescribed in the hospital setting. Design Cross-sectional study. Setting The psychiatry unit of a Canadian tertiary care teaching hospital in Montreal, Canada. Participants 402 patients with aforementioned disorders who initiated, restarted or switched to one of the following antipsychotics: clozapine, olanzapine, risperidone, paliperidone or quetiapine, between 2013 and 2016. Primary outcome measures We assessed the proportion of cardiometabolic parameters monitored. Secondary outcome measures We identified predictors that influence the monitoring of cardiometabolic parameters and we assessed the proportion of adequate interventions following the screening of uncontrolled blood pressure and fasting glucose or glycated haemoglobin (HbA1c) results. Results Only 37.3% of patients received monitoring for at least three cardiometabolic parameters. Blood pressure was assessed in 99.8% of patients; lipid profile in 24.4%; fasting glucose or HbA1c in 33.3% and weight or body mass index in 97.8% of patients while waist circumference was assessed in 4.5% of patients. For patients with abnormal blood pressure and glycaemic values, 42.3% and 41.2% subsequent interventions were done, respectively. The study highlighted the psychiatric diagnosis (substance induced disorder OR 0.06 95% CI 0.00 to 0.44), the presence of a court-ordered treatment (OR 0.79 95% CI 0.35 to 1.79) and the treating psychiatrist (up to OR 34.0 95% CI 16.2 to 140.7) as predictors of cardiometabolic monitoring. Conclusions This study reports suboptimal baseline cardiometabolic monitoring of patients taking an antipsychotic in a Canadian hospital. Optimising collaboration within a multidisciplinary team may increase cardiometabolic monitoring