Etude de l'énergie de désorption des substances polaires

Polar substance energy desorption study. This study suggests an extension of the Dubinin-Radushkevich and Gibbs-Helmholtz equations, by using adsorption forces in microporous composites. These forces, mainly those of Van der Waals, have been set up in three groups of components according to their effects :

• •unspecified forces,
• •dispersion-perturbation forces,
• •quadrupole and dipole interaction forces.

The suggested models take into account the different forces and present a good coherence with the experiment.     

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.     

Amélioration de la sensibilité de détection dans un sous-sol

Ground penetrating radar is a technique wich offers a way of viewing shallow soil. The areas of application for geophysical radar are divers and the associated electromagnetic phenomenology has been investigated for detecting targets buried within a realistic model ground environment. The continuous backscatter of field from soil gives rise to clutter, which limits the contrast of near-surface underground target reflections and, therefore, decreases the detection sensitivity of the radar. In this paper, a novel detection scheme is introduced in order to improve the detection sensitivity. This new approach is based on a frequency modulation by a micro-wave signal.     

Gestion de la thermique dans les procédés d'adsorption de gaz

Thermal aspects of gas adsorption processes. The adsorption of gases is an exothermal phenomenon, and fixed bed adsorption operations produce high thermal effects. Similarly, applying temperature changes to a process can modify adsorption.The purpose of this paper is to illustrate the basic features of non-isothermal adsorption, the most salient of which is the effect of relative velocities of heat and concentration waves. It is shown that there may exist a temperature at which a reversal occurs in the order of those velocities. A simple purification process is suggested, based on the temperature modulation of the gas mixture fed to the column. Examples are calculated with data corresponding to carbon dioxide adsorption on 13X molecular sieves.     

Quelques problèmes posés par les découvertes de Pluton et de Neptune

This Note reviews the history of the discovery of the planets Pluto and Neptune. To cite this article: V. Kourganoff, C. R. Physique 4 (2003).     

Modélisation de la décharge luminescente dans un écoulement de gaz en régime turbulent

In this paper we propose a model of a glow discharge in a turbulent flow. The electron density is calculated using a conservation equation. We assume that the gas glow acts on the electron density and the Shwartz model is used to model the change of diffusivity due to turbulence. In order to show the effects of the turbulence on the electron density, we use a 1D model of a stable electric discharge in to a turbulent flow. The model shows that the increase in turbulent diffusivity at high Reynolds numbers tends to flatten the electron density profiles. Theoretical results are in good agreement with the reported measures. Next, the model was applied to a 2D argon axisymmetric turbulent compressible steady flow. This study shows that when plasma oscillations and turbulence fluctuations of the neutral gas are correlated the temperature profile flattens. Finally, we study electronic distribution into a 3D plasma column in a dissymmetrical flow.     

Sur la remanence de la magnétisation par déplacement des parois de Bloch et la cinétique de sa desaimantation

Sans résumé

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Identification des propriétés thermiques de composites fibres de verre/résines thermodurcissables: Application à l'optimisation des procédés de moulage

Identification of glass fiber/thermosetting resins composites thermal properties. Application to the optimization of molding processes. A procedure has been developed to optimize molding processes of thermosetting composite materials. Three stages have been distinguished. In the first one, some thermal and kinetic properties have been measured by differential scanning calorimetry. Thermal conductivities have been identified afterwards in thick instrumented pieces, placed in a thermally regulated press. High dependences of thermal conductivities on temperature and transformation degree have been shown. Secondly, coupled heat transfers have been numerically simulated and results have been satisfactorily compared with experimental thermograms. Finally, optimization technics based on effective inverse methods have been used.These points have been illustrated with two examples : glass fiber/epoxy resin and glass fiber/polyester. Sufficient mechanical characteristics of the first one, which is cured in oven, and good surface aspect of the second, that is made by injection in heated and closed molds, had to be obtained. The results let foresee real improvement of the corresponding molding processes.     

Étude théorique des transferts couplés de chaleur et de masse lors de la désorption du couple zéolithe 13X-eau

A mathematical model based on scale changing has been established, in order to study heat and mass transfers in a zeolithe bed during water desorption. The model has been solved numerically by the finite-volume method, for the case of two-dimensional transfers. The numerical simulation is used to present the time-space evolution of the solid temperature, the pressure and the moisture content in the reactor and to determine the sensitivity to some parameters (heating temperature, outlet temperature, heat coefficients and reactor geometry). The effects of the particle diameter, the kinetic constant of desorption as well as the effective thermal conductivity are discussed.     

Polarisabilités optiques moléculaires de dérivés benzèniques en solution déterminées par des mesures d'effet Kerr statique

Une expression théorique simplifiée de la constante de Kerr permet une comparaison cohérente des mesures d'effet Kerr statique et de diffusion Rayleigh dépolarisée. Cette comparaison ainsi que des mesures de moments dipolaires sont effectuées sur une série de composés benzèniques en solution diluée dans le tétrachlorure de carbone. La méthode d'exploitation des résultats expérimentaux conduit à la détermination du tenseur des polarisabilités optiques moléculaires α de ces composés. Un accord satisfaisant est obtenu en comparant la constante spécifique de Kerr S _k et l'anisotropie optique moléculaire γ², calculées à partir de ces polarisabilités, à leurs valeurs expérimentales.     

Contrôle de matériaux d'origine biologique par méthode photothermique: intérêt de la détection pyroélectrique

Photothermal methods are well adapted to thin multilayer material analysis. In the particular case of biological materials, which are thermally fragile, low excitation power is required. We have studied whole human blood sedimentation by using photothermal radiometry and a photopyroelectric technique. Results obtained with random- and sine-modulated excitation are discussed. Evolution laws of plasma thicknesses and optical absorption coefficients during the process have been determined by identifying the parameters using different estimation methods. It appears that results are consistent with theoretical predictions of our 2D-thermophysical model and also with the values measured by the well-known Westergreen reference method, usually used in clinical analysis. Finally, in order to extend the investigation field of the pyroelectric method, particularly in the domain of biological materials, we have analysed the possibility of using the sensitive pyroelectric sensors without direct thermal contact with the sample and detecting the temperature changes at the sample surface through a thin air monolayer.     

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₊.     

La dépendance du pouvoir séparateur du systeme „Objectif-Émulsion photographique“ de l'ouverture relative de l'objectif

Résumé On étudie la qualité de l'image photographique, fournie par des objectifs entachés d'aberration sphérique et enregistrée sur la couche photographique, en fonction de l'ouverture relative de l'objectif. On trouve que l'ouverture relative optima, déterminée, photographiquement, était dans tous les cas bien plus petite que celle correspondant a l'aberration d'onde égale à /4. Elle ne Concorde pas aussi avec l'ouverture relative optima trouvée à l'aide du critérium de la qualité basé sur l'éclairage au centre de la tache de diffusion. On présente un essai d'expliquer des différences trouvées.     

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 théorique de la durée de vie radiative du triplet métastable de quelques composés carbonylés

Les paramètres de phosphorescence (force d'oscillateur et durée de vie), sont déterminés théoriquement pour quelques composés carbonylés (formaldéhyde, benzaldéhyde, acétophénone, propiophénone, 2,4,5-triméthylbenzaldéhyde, et 3,4-diméthylacétophénone). La fonction d'onde de l'état singulet fondamental est obtenue à l'aide d'un calcul SCF utilisant la méthode CNDO/S de Del Bene et Jaffé. Les fonctions d'onde, les énergies et les moments de transition dipolaire électrique S_I ←S ₀ et T_J ←T ₁ sont déterminés à l'aide d'une interaction portant sur des configurations mono et diexcitées par rapport à l'état singulet fondamental.

Les paramètres de phosphorescence sont calculés en utilisant une approximation monocentrique et monoélectronique de l'opérateur hamiltonien de couplage spin-orbite. Cette approximation est justifiée par la comparaison des résultats obtenus avec les valeurs expérimentales, compte tenu de la concordance entre les conditions d'expérience et les hypothèses de calcul.