Conjugaisons finies et milieux continus en relativité générale

We present here the main elements of a mechanics of relativistic continua relying upon a concept of 《finite conjugacy》 between two relativistic motions described by two unit vector-fields u and u' defined on two different relativistic manifolds $\text{M}$-and $\text{M}$'.This purely relativistic, global, and intrinsic theory leads, together with a new approach of the deformation tensors in relativity, to a differential system of equations for the conjugacies which is neither under-determined nor over-determined. A rough study of the propagation of the conjugacy-waves shows then that it is advisable to consider the notion of a finite conjugacy as a satisfying relativistic extension of the classical and tridimensional notion of a finite deformation in mechanics, and to identify the spatial conjugacy-waves obtained with the ordinary acoustic waves.Drastic particularizations of the space-times $\text{M}$ and $\text{M}$', of the motions u and u', of the admissible types of conjugacies and of the elastic behaviour of the continua under study allow to recover, as very important but particular cases, the tridimensional non-relativistic theory of elasticity for finite deformations and non-linear behaviour, as well as the main theories of relativistic elasticity already proposed by Mmes Choquet-Bruhat and Lamoureux-Brousse, Rayner, Carter and Carter-Quintana, Grot-Eringen…. The obtained system of equations generalizes also to the finite case some aspects of the infinitesimal theory of Weber and Papapetrou.     

MODICS. Généralisation de la méthode d'optimisation systémique aux systèmes thermiques avec échangeurs imposés

We present here the generalization of the systemic optimization method for complex thermal installations, based on the thermal integration, that was the subject of a previous publication in the October 1995 (n^o 406) issue of the Revue Générale de Thermique. The proposed method allows to distinguish component irreversibilities, that are linked to the internal functioning of a component alone, independently of the rest of the considered system, and systemic irreversibilities that can only be modified by changing the configuration of the system. It constitutes a tool for design engineers, the originality and the power of which are to give them systemic insights on the installation under study.The general method MODICS is obtained by mixing on the one hand the previously described method and on the other hand an analogous approach adapted to the case when heat exchangers are imposed. The article details the totality of procedures to follow to implement this method and gives various examples.     

Termes de signe positif et négatif en analyses exergétiques des flux de chaleur

Positive and negative terms in the exergetic analysis of heat fluxes. In various technical plants heat transfer rates at temperatures above that of the environment and heat transfer rates at temperatures below the temperature of the environment can be simultaneously observed. This is the case in cryogenic industrial processes where a cooling effect is produced from a heat source. This is also the case for all absorption refrigeration plants or absorption plants that provide refrigeration and heat pumping, in particular for air-conditioning of buildings. In these cases exergetic analysis leads to equations in which some terms are positive and others are negative. This can generate difficulties in the definition of exergetic, or rational, efficiencies. In this paper ways of resolving these difficulties are discussed.     

Efficacité des techniques de régénération d'eau pour une usine de fabrication de papier intégrée sans effluent. Analyse exergétique

Water regeneration efficiency for pulp and paper plant. Exergy analysis. The water network of a pulp and paper mill is contaminated by a large number of components which are brought into the system as wood constituants or process additives. Keeping the contaminant concentrations below certain limits, to safeguard paper quality and process runnability, must be part of any systems closure strategy. This can be achieved by purging contaminants using well known separation techniques such as evaporation, freeze crystallization and membrane filtration. The purpose of this study was to compare the thermodynamic efficiency of these techniques by means of an advanced exergy analysis. The contaminated stream was modelled using key components for both organic and inorganic contaminants. The activity coefficients were calculated using the Chen algorithm. The approach developed by Brodyanski, Sorin and Le Goff was used to determine the exergy efficiency. This analysis shows that freeze crystallisation is the most efficient technique when the exergy of the output stream is considered as a useful effect. When only the useful work obtained by separation is considered, membrane separation becomes the most efficient process. The analysis of the process incorporating a separation operation produces the actual efficiency. This example illustrates the advantage of using exergy methods to determine the efficiency of processes based on different physico-chemical phenomena.     

Procédure rapide de choix de réseaux d'échangeurs de chaleur

A fast calculation of a reasonable solution for the choice of a heat exchanger network able to make some imposed cooling and warming up tasks, with the use of auxiliary utilities, is developed in this article.This problem boils down to the internal heat exchanger network choice with respect to a constraint limiting the exchange area, maximizing the heat recovery and minimizing the number of stream matching.These internal matches are made one by one with respect to the tasks to be effected at each step. Amongst the possible matches, we have retained the privilegied ones, ie matches saturating a maximum number of constraints. Some procedures are implemented so as to choose among this set of privilegied matches.The illustration with some literature problems shows that an algorithm made up with these procedures carries out a good compromise between the quality of the obtained solution and the computer time.     

Quelques nouvelles propriétés de régularité de l'opérateur de Gribov

In this work, we establish new regularity properties for Gribov's operator:H=A ^* A ₊ iA ^*(A+A ^*)A;(,)², whereA ^* andA are the creation and annihilation operators. Particularly, we prove that for all >0,H ^–1 is in the class of Carleman's operatorl ₁₊.     

Réflexions sur lʼavenir de lʼénergie nucléaire,de la France dʼaujourdʼhui au monde de demain : IIe à IVe générations

The recent events at the Fukushima power plants (PP) have brought to light key issues which have to be discussed concerning the position of nuclear energy in the energy mix, in the context of global warming, of waning petroleum resources, of an increasing world population, and of its industrial development. These questions are addressed here from the viewpoint of physical facts; and, without proposing definite choices, this article aims to provide information on the equipment required to benefit from the fission chain reaction, while explaining the possible incidents and accidents, and the possible hidden military misuse of nuclear matter. Specific issues, such as risk assessment and risk management, will be considered, under the constraints of dealing with international non-proliferation safeguards and France energy resources independence. A special emphasis will be given on the fuel cycle, on the variety of time scales involved, and on the requirements of developing the next generation of nuclear power plants, and more specifically the fast breeder option. The lessons to be drawn from the Fukushima accident, resulting mainly from the residual power of used fuel and the loss of cooling source, are outlined, and the consequences to be drawn about the various relevant time scales are emphasized.     

Instabilités de calibration de phase

In very long baseline interferometry, the image reconstruction procedures are very sensitive to the potential instabilities of the phase calibration operation. The analysis presented in this Note reveals that these instabilities are due to the existence of secondary minima (more or less critical) of the phase calibration objective functional. By resolving the corresponding integer ambiguity problems in an appropriate manner, these minima can be explicitly identified and compared. The stability of the self-calibration procedures can thus be easily controlled. To cite this article: A. Lannes, C. R. Physique 4 (2003).     

Etude expérimentale de la dévolatilisation rapide de charbons pulvérisés

Experimental study of the rapid devolatilization of pulverized coals. Rapid devolatilization of various pulverized coals have been studied in a laboratory bench constituted by a flat flame burner of propane which reproduces thermal conditions of an industrial flame. The particles, which undergo a heating rate of 6.10⁶ K⁻¹.s⁻¹ with a peak temperature of 1 100 °C, are completely devolatilized within 24 ms. Fifteen coals, included in a wide range (anthracite to subbituminous coal) have been tested. The coal weight loss is globally proportional to the normalized volatile matter content with some exceptions which confirm the advantage of this laboratory bench. The formation of tars or hydrocarbons has been related to the coal weight loss. Carbon, hydrogen and nitrogen devolatilized fraction have been followed with total mass weight loss. In spite of the fact that hydrogen and carbon devolatilized fractions present a good correlation with the total mass weight loss, the nitrogen devolatilized fraction have an anarchic evolution. For high heating rates, the devolatilization of tars observed for the bituminous coals seems to explain this unpredictable phenomenon. These results will be valorized in comparison with those obtained in industrial flame conditions.