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).     

Mesure du chaos dans les systèmes conservatifs en vue de l'étude des transferts dans les systèmes ouverts

Assessment of such a measure has been revealed to be especially difficult due to the lake of mathematical criteria applicable to conservative systems. Existing tools are mainly based on the characterization of the ‘strangeness’ of the attractors. These asymptotic measures are thus limited to dissipative systems. We have adapted some of these tools in order to apply them to conservative systems, based on short time observations of the system instead of asymptotic observations. In this study we have used the alternating Dean flow as a benchmark and on the basis of which the mathematical tools have been constructed. Instead of observing an attractor, we suggest observing the image formed by the cross section of a tracer filament injected upstream of the flow. Such an image is simulated by using a numerical model for the flow. With the image, we evaluate the ‘information dimension’ as well as the ‘integral correlation dimension’. Since we use short time observations, the dimensions depend on the initial position of the injected filament. However, their evolution follows the apparent disorder observed on the images. As a global measure of the chaotic behavior, we suggest calculating the mean value of the dimensions for all injection positions defined as ‘mean integral correlation dimensions’.     

Étude des phénomènes de transferts thermiques dans les stérilisateurs à vapeur

Study of heat transfer phenomena in a vapor sterilizer. Steam sterilization occupies a preferential place in the hospital hygiene. Hospital infection designates any sickness contracted in a hospital, allocated to microorganisms which affected sick people or hospital staff. The research work aims at studying heat transfer phenomena in a vapor sterilizer. The interactions between the different modes of heat transfer confer great complexity to this problem. The development of calculation method, zonal method, allowed to predict the field of temperature and heat transfer to optimise vapor sterilizers. This work presents the results of experiments carried out on a cycle of instrument sterilization. The main motivations of this study are the droplets of water which remain pasted to the load at the end of the drying process.     

Sur les algèbres de Lie nilpotentes de dimension ⩽ 7

We consider the embedding problem of a nilpotent Lie algebra into a stratified one; we construct all nilpotent Lie algebras of dimension ⩽ 7 having a fixed Lie algebra of codimension 1, and we get among other results, a new classification of 6-dimensional nilpotent Lie algebras. This study has applications on the analysis of deformations of the internal space of 11 dimensional Kaluza-Klein theories (non abelian theories) and in 11-dimensional supergravity.     

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.     

Calcul de fonctions de corrélation pour des modèles réorientationnels par sauts instantanes,en utilisant la théorie des groupes

On développe un formalisme permettant le calcul des fonctions de corrélations rotationnelles pour des modèles de réorientation moléculaires par sauts instantanés, en utilisant le formalisme de la théorie des groupes. Les mouvements sont décrits par des rotations appartenant à un sous-groupe (continu ou fini) du groupe des rotations, mais les probabilités par unité de temps ne sont pas nécessairement des fonctions centrales (constantes sur les classes du groupe). On traite un cas où le mouvement est décrit par la superposition d'une diffusion rotationnelle et de sauts discrets autour d'axes cristallographiques. Ce cas est appliqué à la diffusion inélastique incohérente de neutrons sur le néopentane plastique.     

Determination de bases de gaussiennes optimales pour les molécules

On montre que l'optimisation des exposants et des paramètres géométriques a une grande importance. En particulier la barrière de rotation de CH₃OH (exp. 1,07 kcal/mole) passe, par optimisation complète en restant dans le cadre du modèle à particules indépendantes de 2,2 kcal/mole à la valeur remarquable de 1,078 kcal/mole.     

L'asymptotique de Weyl pour les bouteilles magnétiques

Nous prouvons une formule pour le comportement asymptotique de la fonctionN() de dénombrement des valeurs propres de l'opérateur de Schrödinger avec un champ magnétique qui tend vers l'infini `a l'infini de ^d . La preuve utilise un résultat précis sur l'estimation des valeurs propres pour un champ magnétique constant dans un cube de ^d.     

Lumière diffusée par les particules solides éjectées du noyau de la comète 81P/Wild 2

Comet 81P/Wild 2, target of the Stardust mission, has been observed in 1997, through an imaging polarimetry technique. Intensity and polarization images, retrieved for 9 000 to 26 000 km wide fields, imply a value of the decrease of the intensity with increasing distance to the nucleus, and a decrease of the polarization in the inner coma, in agreement with previous observations of other comets. The averaged polarization values have been determined for the first time on this comet. The results suggest that it could belong to the class of comets with a low polarization at large phase angles and an absence of silicate emission features.     

Etude du désenfumage par extraction mécanique dans un local siège d'un feu: expériences en grandeur et simulations numériques par modèles de zones et de champs

This study regards conditions of control of fire-induced smoke in a 7-m × 7-m rectangular cell, for an ‘intermediate configuration’ of a volume larger than that of an apartment room but smaller than that of an entrance hall, of a fire source a little less powerful than ‘design fires’ considered in standard approaches, of a fan-powered exhaust rate a little higher than rates typically required in regulations.From case to case were experimentally modified the following parameters: ceiling height (3 m, or 6.4 m), source type and power (between 100 and 500 kW), exhaust volume flow rate (from a few tenths of m³.s⁻¹ to a few m³.s⁻¹). Each experiment was supposed to reach a steady-state configuration, which has proved more or less true in practice. Smoke stratification within the cell has proved less sharp for a fire source non located in the centre of the cell, and the mean temperature of gases in the exhaust inlet has proved lower than under the cell ceiling, which suggested a phenomenon of ‘plugholing’ (air mixing upstream). In spite of the weaknesses of the computer models, and of a certain unaccuracy of measurements, plugholing phenomenon could be recognized in simulation results yielded by the zone model (which were in a better accordance with test results for higher exhaust rates), since the field model gave rise to a better agreement between computed and measured results for lower heat release rates and/or higher rates of smoke exhaust.     

Sur les intégrales de mouvement du système de sinus-Gordon discret – On Integrals of Motion of the discrete sine-Gordon System

We give explicit formulas for some densities of integrals of motion for the discrete sine-Gordon system (quantum or not). The generating function for the densities of integrals of motion may be seen as the expansion of the logarithm of a certain continued fraction (possibly quantum). In the case of q root of the unity, we show that these integrals of motion can be identified to the classical integrals of motion.     

Sur les possibiliti es de l'analyse par activation appliquée en médecine

An fur et à mesure que l'analyse par activation se développe dans toutes les branches de l,industric et de la science, en tant que méthode analytique actuelle, son application devient det plus en plus importante dans les domaines de la médecine, de la biologie et de la biochimie, ainsi que dans les domaines des recherches et des contrôles des radioéléments destinés à usage médical.     

Comportement thermique d'un matériau de référence poreux soumis à des atmosphères de chauffe différentes

This study presents an analysis of the temperature evolution in a porous sample. Various situations have been examined: the porous solid is initially dry or water saturated, and the heating fluid is dry air or steam. This analysis showed experimentally the optimal phases of using steam to heat a material. Moreover, as humidity in the solid considerably modifies the heating kinetics, the study has also been carried out on a non-porous solid. The treatment of the temperature curves under an adimensionnal form shows a singular behaviour of those temperatures following the heating fluid nature and its temperature. Equations giving temperature versus time have been proposed. They are based on the definition of a time lag and a time constant, both being defined as a function of the single fluid temperature parameter. Finally, in the particular case of the non-porous solid heated by dry air, with additional approximations, it has been possible to check that the experimental time constant is very close to a fundamental time constant.     

Modélisation numérique des écoulements réactifs dans les foyers de turboréacteurs

Some assumptions have to be made to deal with combustion and aerodynamical phenomena simultaneously. We propose a turbulent combustion model where we consider a one step reaction for chemical modelling. Consequently, only two variables are sufficient to describe the problem. In fact, the combustion can be characterized by the consumption of one of the two reactive species. In a first step, to obtain the instantaneous consumption rate, we model the Lagrangian equation of the fuel mass fraction by considering only the equilibrium state. This state is calculated in order to obtain the same temperature as with a detailed kinetic scheme. In a second step, the mean consumption rate is calculated with the instantaneous consumption rate and a presumed probability density function. This model has been tested on many configurations, particularly, on a non-premixed flame and an experimental industrial combustor. Results from these validations show that this model can be used to predict temperature level in an industrial combustor.     

Les systèmes hétérogènes « eau–zéolithe hydrophobe »: de nouveaux ressorts moléculaires

Pressure–volume isotherms have been determined for three heterogeneous ‘water–zeolite’ systems. The first two concern hydrophobic purely siliceous zeolites: silicalite-1 (F⁻) and zeolite β (F⁻); the third comprises a more hydrophilic commercial zeolite of the type ZSM-5. The P–V diagram for the water–silicalite-1 (F⁻) system is characterized by a plateau corresponding to the intrusion of water inside the pores of the solid. During the release the phenomenon is reversible. This system, which is able to accumulate and restore superficial energy, constitutes a molecular spring. For zeolite β, the P–V curve displays a plateau during the compression, but during the release, the phenomenon is not reversible. In that case, the system absorbs mechanical energy and acts as a bumper. The third system, based on the more hydrophilic ZSM-5 zeolite shows a linear isotherm without any plateau. These results open new applications perspectives in the field of the energetics for hydrophobic zeolites in contact with water. To cite this article: V. Eroshenko et al., C. R. Physique 3 (2002) 111–119