The question of “evidence” in the emergence of evidence-based or evidence-aware policies in agriculture

Evidence-based or evidence-aware policy approaches are used in many different sectors (health, education, etc.). These approaches are less common in agriculture but are gradually emerging. Analysis of debates surrounding this trend sheds light on the particular nature of the difficulties faced by public decision-makers who are willing to use available scientific knowledge. After examining certain misunderstandings which arise in the international debate over evidence-based policy approaches, this paper addresses two specific issues: (i) the problems of competing evidence for using knowledge in the design of public policies and (ii) the potential role of rationalization tools in a possible "depoliticisation" of public decision-making.knowledge, agriculture, policy, evidence, Agricultural and Food Policy, B29, D8, Q01, O3,

The evolution equation for the flame surface density in turbulent premixed combustion

The mean reaction rate in flamelet models for turbulent premixed combustion depends on two basic quantities: a mean chemical rate, called the flamelet speed, and the flame surface density. Our previous work had been primarily focused on the problem of the structure and topology of turbulent premixed flames, and it was then determined that the flamelet speed, when space-averaged, is only weakly sensitive to the turbulent flow field. Consequently, the flame surface density is the key quantity that conveys most of the effects of the turbulence on the rate of energy release. In flamelet models, this quantity is obtained via a modeled transport equation called the Sigma-equation. Past theoretical work has produced a rigorous approach that leads to an exact but unclosed formulation for the turbulent Sigma-equation. In the exact Sigma-equation, it appears that the dynamical properties of the flame surface density are determined by a single parameter, namely the turbulent flame stretch. Unfortunately, the turbulent flame stretch as well as the flame surface density is not available from experiments, and, in the absence of experimental data, little is known on the validity of the closure assumptions used in current flamelet models. Direct Numerical Simulation (DNS) is the alternative approach to get basic information on these fundamental quantities. In the present work, three-dimensional DNS of premixed flames in isotropic turbulent flow is used to estimate the different terms appearing in the Sigma-equation. A new methodology is proposed to provide the source and sink terms for the flame surface density, resolved both temporally and spatially throughout the turbulent flame brush. Using this methodology, our objective is to extract the turbulent flame stretch from the DNS data base and then perform extensive comparisons with flamelet models. Thanks to the detailed information produced by the DNS-based analysis, it is expected that this type of comparison will not only underscore the shortcomings of current models, but also suggest ways to improve them

KNOWLEDGE PRODUCTION, MULTIFUNCTIONALITY OF AGRICULTURE AND PUBLIC DECISIONS: CRITICAL ISSUES OF CONTEMPORARY CONTROVERSIES

Various theoretical models of public policy analysis are used to treat situations of decision-making in which public deciders have to take into account the multifunctionality of agriculture. For some, science-society relations are not really problematical. Others acknowledge the current attempts of these policy-makers to find adequate scientific knowledge, and the difficulties they encounter. These difficulties stem partly from the very content of knowledge produced by research. Could other modes of production be more efficient? The status of the knowledge produced by these approaches is a subject of debate. Bridging the divide between science and policy more effectively is not only a question of knowledge brokerage. Accessibility and reliability of the existing evidences are also problems to be addressed. The debates around evidence-based practices may provide some landmarks in this new situation although they also emphasize the limits of the tools that can be built for this purpose.Multifunctionality, Agriculture, Knowledge, Policy, Agribusiness, Community/Rural/Urban Development, Labor and Human Capital,

The evolution equation for the flame surface density in turbulent premixed combustion

One central ingredient in flamelet models for turbulent premixed combustion is the flame surface density. This quantity conveys most of the effects of the turbulence on the rate of energy release and is obtained via a modeled transport equation, called the Sigma-equation. Past theoretical work has produced a rigorous approach that leads to an exact, but unclosed, formulation for the turbulent Sigma-equation. In this exact Sigma-equation, it appears that the dynamical properties of the flame surface density are determined by a single parameter, namely the turbulent flame stretch. Unfortunately, the flame surface density and the turbulent flame stretch are not available from experiments and, in the absence of experimental data, little is known on the validity of the closure assumptions used in current flamelet models. Direct Numerical Simulation (DNS) is the obvious, complementary approach to get basic information on these fundamental quantities. Three-dimensional DNS of premixed flames in isotropic turbulent flow is used to estimate the different terms appearing in the Sigma-equation. A new methodology is proposed to provide the source and sink terms for the flame surface density, resolved both temporally and spatially throughout the turbulent flame brush. Using this methodology, the effects of the Lewis number on the rate of production of flame surface area are described in great detail and meaningful comparisons with flamelet models can be performed. The analysis reveals in particular the tendency of the models to overpredict flame surface dissipation as well as their inability to reproduce variations due to thermo-diffusive phenomena. Thanks to the detailed information produced by a DNS-based analysis, this type of comparison not only underscores the shortcomings of current models but also suggests ways to improve them

Cinq études sur Aragon. Théâtre Roman

Le dernier roman d’Aragon, dans lequel les commentateurs ont parfois cru discerner un affaiblissement de la veine littéraire, préfigure le nouveau millénaire en cours, marqué par les effondrements multiples et la révision des cadres de pensée qui avaient paru s’imposer jusqu’alors. Théâtre/Roman traite du théâtre au propre et au figuré, dans un jeu de miroir entre les protagonistes de la représentation – acteur, metteur en scène – et le théâtre intérieur de l’écriture romanesque. La voix tragique de l’Écrivain et de ses doubles, confrontés à la faillite d’un idéal révolutionnaire néanmoins réaffirmé, trouve des échos dans d’autres œuvres du passé et d’autres époques qui l’universalisent. Le face-à-face vertigineux entre roman et théâtre, par l’orchestration poétique de la composition d’ensemble, ouvre pour le lecteur un espace inédit d’exploration, nommé ici, avec l’assentiment tacite d’Aragon, arrière-texte. Un passage de relais est suggéré : « Dans ce que je vois, il y a toujours ce que je ne vois pas »

Various nonconforming approximation of thin shell problems and the question of their convergence

Projet MODULE