Ecriture de l'énergie cinétique à l'aide d'opérateurs quasi-moments

Cet article concerne l'utilisation des quasi-moments ?π _m , définis par

,

pour exprimer l'opérateur correspondant à l'énergie cinétique de N particules en Mécanique Quantique. La condition de Wilson-Howard portant sur les coefficients s^ml est interprétée comme la condition pour que les opérateurs ?π _m soient hermitiques quand on utilise l'élément de volume s dq ₁ … dq ₃ N (s=[dét {s^ml }]^-1). La condition générale pour qu'il soit possible de trouver un élément de volume avec lequel les opérateurs ?π _m sont hermitiques est donnée et différentes expressions de l'opérateur énergie cinétique sont établies quand cette condition est remplie et quand elle ne l'est pas.     

Densité des vecteurs propres généralisés d'une classe d'opérateurs compacts non auto-adjoints et applications

We consider a closed densely defined linear operatorT in a Hilbert spaceE, and assume the existence of ₀ (T) such thatK = (T - ₀ I)^-1 is compact and the existence ofp>0 such thats _n (K)=o((n ^–1/p)), whereS _n (K) denotes the sequence of non-zero eigenvalues of the compact hermitian operator . In this work, sufficient conditions (announced in [1]) are introduced to assure that the closed subspace ofE spanned by the generalized eigenvectors ofT coincides withE. These conditions are in particular verified by a family of non-self-adjoint operators arising in reggeon's field theory.     

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.     

Etude numérique des effets de densité dans un jet de mélange turbulent en microgravité

Numerical study of density effects on a turbulent mixing jet in microgravity. The aim of this paper is to present density effects on a turbulent heterogeneous mixing free jet in microgravity. The influence of the inlet density ratio S between the jet and the surrounding gas is pointed out from numerical simulations based on second order single point closure schemes. The mean quantities, entrainment, expansion and second order moments are presented. The density ratio varies from 0,14 to 5,11. Results are discussed in comparison with both experimental data and asymptotical considerations. It is shown that the density ratio effects on the jet development vanish far from the exit leading to self-similar profiles (full self-preservation according to George [1]).     

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.     

Étude d'une nouvelle technique de mesure des températures dans le sol

The measure of soil temperatures is generally achieved by implanting thermocouples at different depths. For the setting up of these thermocouples, and in order to resist the constraints of shearing, some rigid pegs were employed as supports. The utilization of these pegs, which are generally in metal, introduces some soil thermal perturbations. In order to minimize this kind of perturbation, a new technique of temperature measurements in soil is presented. The principle of this technique consists of replacing the peg by a removable stem which could be removed after setting up thermocouples in the soil. Apart from the thermal aspect, some mechanical tests of the new technical device are achieved. In order to notice the effects of the pegs, a qualitative study is carried out. It concerns, in particular, depths of 20, 30 and 50 cm and shows gaps in temperatures between the two techniques.     

Evolution avec la température de la réflectivité, de l'indice complexe et de la sélectivité spectrale du nitrure de zirconium

The reflectance of zirconium nitride has been measured at 20, 500 and 700°C, within the range 0.22 to 5.50 μ m. The optical constants have been determined using Kramers-Kronig analysis. The spectral selectivity of this compound noticeably depends on temperature; the absorptance increases from 0.28 at 20°C to 0.36 at 700°C while the emittance increases from 0.06 to 0.14.     

Etude des mouvements moléculaires en milieu liquide à partir du profil des bandes de vibration dans l'infrarouge et des fonctions de corrélation

We have studied the fundamental bands of chloroform and bromoform, both pure and in solution in various solvents; also the first harmonics of v ₁, and a few other harmonics and combination bands. The correlation functions of v ₁ and v ₂ and band moments of v ₁ have been calculated. The comparison of our results with those obtained in microwave and far IR and Raman spectra offers an opportunity to discern, in widths and correlation functions, what can be attributed to vibration and what originates in rotational diffusion. Our results are interpreted with the assumption that rotational diffusion is produced by small angles jumps and that the vibrational effect is very important. The v ₁ band shows an additional widening not accounted for in existing theories.     

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.     

Comportement non lorentzien de la raie Rayleigh dépolarisée dans quelques liquides. Discussion des théories ‘à trois variables’

Nous considérons en général le spectre Rayleigh dépolarisé des liquides simples constitués de molécules anisotropes comme la superposition d'une raie lorentzienne de réorientation, comportant une structure fine dûe au couplage entre orientation et modes hydrodynamiques, et d'une aile lointaine d'origine collisionnelle. Par une analyse détaillée des spectres d'un certain nombre de liquides constitués de molécules isotropes (CCl₄) ou anisotropes (benzène, pyridine, cyanopropyne, 2-butyne, iodopropyne), cet article met en évidence pour ces derniers une quatrième ‘composante’, bien représentée par une lorentzienne de demi-largeur comprise entre 3 et 10 cm^-1. Cette deuxième lorentzienne peut représenter jusqu'à 30 pour cent de l'intensité totale du spectre. Nous montrons qu'elle ne peut être dûe à une simple anisotropie réorientationnelle décrite par la variable tensorielle i. Elle implique donc l'existence d'une seconde variable tensorielle d'anisotropie locale g, attribuée à l'anisotropie d'ordre translationnel.

Les théories dites ‘à trois variables’, supposant g directe (primaire) ou indirecte (secondaire), sont comparées à la lumière de ces résultats expérimentaux, sans qu'il soit possible de trancher définitivement cette question. En particulier, nous montrons que dans le cas le plus général — g à la fois directe et indirecte-il existe plus de paramètres théoriques que de paramètres déductibles de l'expérience.     

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.     

Transfert de chaleur par rayonnement dans un four d'incinération industriel: application de la méthode des zones

In the context of resource conservation, incineration of domestic wastes is a technique allowing an interesting potential in energy valorization. However, because of the variability (annual, monthly) in quality and quantity of raw material, one of the characteristics of waste incineration cogeneration power plants is their frequent partial or excess loading. In order to describe their behaviour at these non-nominal loads, there is a need for simulation tools which predict with accuracy the behaviour of the principal components of the plant at these loads. This paper presents an original approach for predicting the heat transfer in a waste incinerator. In particular, the model developed is applied to and validated with measurements from a waste incinerator located at the Cottendart waste incineration cogeneration power plant in Switzerland. The part of the incinerator studied is characterized by high gas temperatures (1 000-500 °C) for which radiative heat transfer represents the most important part of the global heat exchange. A three-dimensional model using nodal analysis is proposed. The radiative heat exchange is treated using the zone method. With a fine enough mesh, the behaviour of the system in regions far from the nominal point can be predicted with very high accuracy. This paper describes the model and the simulation results.     

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

Sans résumé

---

,

     

L'origine des régularités constatées dans les observations interférométriques de Dayton C. Miller 1925–1926 : variations de température ou anisotropie de l'espace

It is utterly impossible to consider that the regularities displayed in Miller's interferometric observations can be explained by temperature effects. As a result the light velocity is not invariant whatever its direction and consequently the principle of invariance of light velocity on which fundamentally does rest the special theory of relativity is invalidated by the observation data.     

Mesures thermiques et profilométriques 3D pour étudier l'influence de la pression apparente sur la résistance thermique et la microgéométrie des contacts métalliques

Load effects on thermal resistance and on microgeometry of metal contacts : thermal and profilometric study. Thermal contact resistances R_c between pairs of metallic samples have been measured, depending on the pressure P as well as on the maximum pressure P^* reached during the evolution of the stress. Moreover, microgeometry measurement of surfaces in contact have been performed by 3D optical analysis. Metals of different compositions and machined differently were considered. Finally we suggest: lg R_c = K₁ + K₂.lg P + K₃.lg P^* with constants depending on the nature of the metal and the way it has been machined.We find that P^* neither changes too much the roughness parameters nor the Abbott's curve of the variation of the bearing area with the displacement of the plan of contact. On the other hand, the size of contact sports and their surface density are strongly modified as the bearing area changes; their modifications are almost independent of P^*, and are specific to each material.     

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.     

Mise en œuvre d'une méthode d'approximation diffuse adaptative pour la résolution des équations de diffusion et de transport

An adaptative diffuse approximation method for convection diffusion problems has been developed. The grid refinement method is first described and two examples are reported to illustrate the validity of the proposed method. The first one is a two-dimensionnal diffusion problem and the second one is a one-dimensionnal convection-diffusion problem.     

Auto-inflammation de substances explosives. Comparaison entre calcul analytique et numérique en vue d'une optimisation dans le domaine de la pyrotechnie

Self-ignition of energetic material was investigated in order to optimize safety in the field of pyrotechnic applications. Two approaches were used; the first one is relative to Frank-Kamenetskii stationary thermal explosion theory. The second approach consists of a choice of some numerical solutions of heat conduction equations in a non-stationary state. Comparison between these results was carried out in order to find the numerical scheme which is the most compatible with Frank-Kamenetskii stationary thermal explosion theory. Numerical data were used for three explosive substances. One of them was studied by the author. In all cases, the numerical stationary state is in agreement with the Frank-Kamenetskii stationary thermal explosion theory, more or less accurately. From this comparison, it may be concluded that it is preferable, for this kind of problem, to use an implicit scheme with linearization of the heat source term. Explicit numerical methods, with or without the addition of the heat term with the Zinn and Mader scheme are revealed to be less accurate and to need a greater optimization of spatial and temporal meshing.