Traduction humaine et traduction automatique : entre erreur et errance

Nous présentons ici quelques réflexions issues d’un projet de recherche de l’Université de Pise visant à élaborer une approche linguistique à la traduction automatique. Notre contribution est centrée sur la traduction du français vers l’italien et concerne tout spécialement les erreurs humaines de traduction : par l’analyse des traductions pédagogiques nous essayons de comprendre quelles sont les unités problématiques qui amènent à l’erreur et quels sont les principaux facteurs qui la déterminent. En comparant les erreurs produites par des étudiants au cours d’exercices de traduction avec les erreurs relevables en traduction automatique, nous essayons ensuite de juger si l’identification des problèmes de la traduction humaine peut contribuer à une amélioration des résultats de la traduction automatique

Large Eddy Simulation of combustion instabilities in a lean partially premixed swirled flame

This paper investigates one issue related to Large Eddy Simulations (LES) of self- excited combustion instabilities in gas-fueled swirled burners: the effects of incom- plete mixing between the gas injection and the combustion chamber. For simplicity reasons, many LES assume perfect premixing of the gases entering the combustion chamber. In practice this is rarely the case and this study addresses the question by comparing LES assuming perfect premixing and LES where the fuel jets are resolved and fuel/air mixing is explicitely computed. This is done for the Preccin- sta swirled burner which has been carefully studied experimentally at DLR. All previous LES studies of Preccinsta have assumed perfect premixing and this work demonstrates that this assumption is reasonable for stable flows but is not accept- able to predict self-excited unstable cases. This is shown by comparing LES and experimental fields in terms of mean and RMS fields of temperature, species and velocities as well as mixture fraction pdfs and unsteady activity for two regimes: a stable one at equivalence ratio 0.83 and an unstable one at 0.7

A conservative model for high-throughput synthesis of nanoparticles in reacting gas flows

Considerable progress has been made over the past decades in the modeling of gas-phase synthesis of nanoparticles. However, when the nanoparticles mass fraction is large representing up to 50 % of the mixture mass fraction, some issues can be observed in the self-consistent modeling of the production process. In particular, enthalpy exchanges between gas and particle phases and differential diffusion between the two phases are usually neglected, since the particle mass fraction is generally very small. However, when high nanoparticle mass fractions are encountered, these simplifications may cause non conservation of the total enthalpy or the total mass. In the present paper, we propose a conservative model for nanoparticles production from gas-phase processes with a high throughput of nanoparticles. The model is derived in order to satisfy conservations of both enthalpy and mass and is validated on laminar one-dimensional premixed and non-premixed flames. In particular, it is shown that the enthalpy of the particle phase as well as the differential diffusion of the gas phase with respect to the particle phase cannot be generally neglected when the nanoparticles concentration is high to preserve the accuracy of the numerical results

A conservative model for high-throughput synthesis of nanoparticles in reacting gas flows

Considerable progress has been made over the past decades in the modeling of gas-phase synthesis of nanoparticles. However, when the nanoparticles mass fraction is large representing up to 50 % of the mixture mass fraction, some issues can be observed in the self-consistent modeling of the production process. In particular, enthalpy exchanges between gas and particle phases and differential diffusion between the two phases are usually neglected, since the particle mass fraction is generally very small. However, when high nanoparticle mass fractions are encountered, these simplifications may cause non conservation of the total enthalpy or the total mass. In the present paper, we propose a conservative model for nanoparticles production from gas-phase processes with a high throughput of nanoparticles. The model is derived in order to satisfy conservations of both enthalpy and mass and is validated on laminar one-dimensional premixed and non-premixed flames. In particular, it is shown that the enthalpy of the particle phase as well as the differential diffusion of the gas phase with respect to the particle phase cannot be generally neglected when the nanoparticles concentration is high to preserve the accuracy of the numerical results

Impact of the chemical description on direct numerical simulations and large eddy simulations of turbulent combustion in industrial aero-engines

Le développement de nouvelles technologies pour le transport aérien moins polluant est de plus en plus basé sur la simulation numérique, qui nécessite alors une description fiable de la chimie. Pour la plupart des carburants, la description de la combustion nécessite des mécanismes détaillés mais leur utilisation dans une simulation numérique de combustion turbulente est limitée par le coût calcul. Des mécanismes cinétiques réduits et des méthodes de tabulation ont été proposés pour surmonter ce problème. Ces descriptions chimiques simplifiées ayant été développées dans le cadre de configurations laminaires, cette thèse propose de les évaluer dans des configurations turbulentes: une DNS de flamme prémélangée méthane/air de type Bunsen et une LES d’un brûleur expérimental. Les mécanismes sont analysés en termes de structure de flamme, paramètres de flamme globaux, longuer de flamme, prediction des concentrations en espèces majoritaires et des émissions polluantes. Une méthodologie pour évaluer a priori la capacité d’un mécanisme à prédire correctement des phénomènes chimiques tridimensionnels est proposée en se basant sur les résultats de flammes laminaires monodimensionnelles non étirées et étirées. Il ressort que, d’une part, pour construire un mécanisme réduit, il est nécessaire de faire un compromis entre coût calcul, robustesse et qualité des résultats. D’autre part, la qualité des résultats de DNS et LES de configurations tridimensionnelles turbulentes peut être anticipée par une analyse du comportement des schémas réduits dans des configurations simplifiées de flammes monodimensionnelles laminaires non étirées et étirées. ABSTRACT : A growing need for numerical simulations based on reliable chemistries has been observed in the last years in order to develop new technologies which could guarantee the reduction of the enviromental impact on air transport. The description of combustion requires the use of detailed kinetic mechanisms for most hydro-carbons. Their use in turbulent combustion simulation is still prohibitive because of their high computational cost. Reduced chemistries and tabulation methods have been proposed to over-come this problem. Since all these reductions have been developed for laminar configurations, this thesis proposes to evaluate their performances in simulations of turbulent configurations such as a DNS of a premixed Bunsen methane/air flame and a LES of an experimental PREC-CINSTA burner. The mechanisms are analysed in terms of flame structure, global burning parameters, flame length, prediction of major species concentrations and pollutant emissions. An a priori methodology based on one-dimensional unstrained and strained laminar flames to evaluate the mechanism capability to predict three-dimensional turbulent flame features is therefore proposed. On the one hand when building a new reduced scheme, its requirements should be fixed compromising the computational cost, the robustness of the chemical description and the desired quality of results. On the other hand, the quality of DNS or LES results in three-dimensional configurations could be anticipated testing the reduced mechanism on laminar one-dimensional premixed unstrained and strained flames

Impact of the chemical description on a Large Eddy Simulation of a lean partially premixed swirled flame

International audienc

Stability and change of lifestyle profiles in cardiovascular patients after their first acute coronary event

Background: Acute coronary syndrome (ACS) is a major cause of morbidity and mortality. Lifestyle and health behavior changes play an important role in the primary and secondary prevention of ACS recurrence. Changes in unhealthy lifestyles after an acute coronary event have been analyzed by considering separate behaviors individually, even though research on the healthy population has demonstrated that unhealthy behaviors tend to co-occur. Purpose: The aim of this study was to identify lifestyle profiles of ACS patients and to explore their pathways of change for one year after their first coronary event by adopting a typological approach. Methods: Two hundred and twenty-three patients (84% male; mean age = 57.14) completed self-report measures of health-related behaviors at the beginning of cardiac rehabilitation, and six months and twelve months after. At each wave depression, anxiety and heart rate were also evaluated. Cluster analysis was performed to identify lifestyle profiles and to analyze their change over time. Differences in psychological factors and heart rate among clusters were assessed. Results: Patients’ diet, physical activity, and smoking behavior greatly improved six months after their first coronary event. No further improvements were detected after one year. At each wave specific lifestyle profiles were identified, ranging from more maladaptive to healthier clusters. Patients with multiple unhealthy behaviors experience greater difficulties in maintaining a healthier lifestyle over time. Moreover, the results demonstrated the association between lifestyle profiles at twelve months after the acute coronary event and depression measured six months earlier. Finally, the most maladaptive lifestyle profile had many members with elevated heart rate at twelve months after the cardiac rehabilitation. Conclusions: Current findings may have a strong practical impact in the development and implementation of personalized secondary prevention programs targeting lifestyles of ACS patients

Large-eddy simulation of spray combustion in a gas turbine combustor

The paper describes the results of a comprehensive study of turbulent mixing, fuel spray dispersion and evaporation and combustion in a gas-turbine combustor geometry (the DLR Generic Single Sector Combustor) with the aid of Large Eddy Simulation (LES). An Eulerian description of the continuous phase is adopted and is coupled with a Lagrangian formulation of the dispersed phase. The sub-grid scale (sgs) probability density function approach in conjunction with the stochastic fields solution method is used to account for sgs turbulence-chemistry interactions. Stochastic models are used to represent the influence of sgs fluctuations on droplet dispersion and evaporation. Two different test cases are simulated involving reacting and non-reacting conditions. The simulations of the underlying flow field are satisfying in terms of mean statistics and the structure of the flame is captured accurately. Detailed spray simulations are also presented and compared with measurements where the fuel spray model is shown to reproduce the measured Sauter Mean Diameter (SMD) and the velocity of the droplets accurately