Essai d'interprétation des déplacements et élargissements par la pression des raies du spectre de vibration-rotation des molécules diatomiques

An interpretation is given of the dependence on the rotational quantum number J of the pressure shift and broadening of the lines of the vibration-rotation band of a hydracide molecule perturbed by a noble gas. It is shown that, with the fundamental hypothesis of adiabatic collisions between the absorbing molecule and the noble gas atoms, the impact theory can describe the J dependence. This results from the fact that one introduces the average over the sine of the phase shift η, which is J dependent, and not the average of the phase shift itself which is vanishing. With a hard-sphere model good agreement is obtained between the calculated and the observed shifts. Further, a rough estimation of the breadth is made.     

Détermination des caractéristiquesd'une colonne chromatographique pour le fractionnement der isotopes par analyse frontale

La technique de la chromatographie frontale est utilisée pour la séparation des isotopes de l'hydrogène et du néon. Les chromatogrammes abtenus sont utiles au caleul du facteur de séparation élémentaire pour ces isotopes ainsi qu'à la détermination des hauteurs équivalentes à un plateau théorique. Ces grandeurs sont importantes pour l'élaboration d'un project des installations correspondantes à l'échelle de production     

Propriétés d'extinction des fumées produites par le fioul domestique en combustion vive

A study dealing with the opacity and radiating power of smoke produced during flame combustion of heating oil is conducted. A quantity combining the smoke extinction coefficient, fuel-mass-loss rate and smoke volume flow rate is defined. This quantity, called specific extinction area, is shown to be conserved when varying combustion parameters. Its dependence with respect to radiation wavelength is derived through extinction measurements and compared to the theoretical evolution. Finally, smoke particles are characterized by size and concentration and the possible changes in size and structure of particles, in relation to modifications in environmental conditions, are discussed.     

Polarisation de la lumière diffusée par des particules agrégées fractales

Some of the dust particles present in the solar system are likely to be aggregates. The study of polarization of the light scattered by such aggregated particles is performed for the six main formation processes. The analysis of the results shows that an irregular and fluffy structure of the particles allows a better understanding of the light scattering observations.     

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.     

Modélisation d'un échangeur de chaleur compact à courants croisés séparés par des couches de matériau à changement de phase

A mathematical model was developed to predict the thermal behaviour of a crossflow compact heat exchanger with layers of phase change material (PCM) operating under winter conditions. The model is validated and a parametric study is conducted to determine the design and operating conditions that promote condensation and may lead eventually to the frosting of the exchanger. The transient and steady-state thermal efficiency of the exchanger are also predicted as a function of the number of thermal units NTU_f, of the ratio of the products of the mass flow rate by the heat capacity on the cold and hot sides C and of the Biot number Bi. Results indicate that for Bi = 0.6 (which corresponds to a 3 mm thick PCM layer), condensation occurs when NTU_f ≥ 2.0 for C = 1.0 and when NTU_f ≥ 5.0 for C = 0.5. If the thickness of the PCM layer increases, condensation is avoided and the duration of the heat recovery period is prolonged. At the same time however, the steady state thermal efficiency diminishes. A heat exchanger for which Bi = 0.6, C = 0.5 and NTU_f = 4.0 appears to be a good compromise for acceptable heat recovery and efficiency. In this case, the heat recovery period lasts 1.6 h and the steady state thermal efficiency levels off at 64 %.     

Etude des mouvements moléculaires du furanne en phases plastique et liquide par relaxation magnétique nucléaire

Les temps de relaxation spin-réseau du proton ont été mesurés dans les phases liquide et plastique du furanne pur et en solution dans le furanne perdeutéré, les relaxations nucléaires d'origine intra et inter-moléculaire ont été ainsi séparées. Des temps de corrélation pour le second harmonique sphérique τ₂ ont été déduits de ces mesures et comparés aux temps de corrélation du premier harmonique sphérique τ₁ obtenus par des mesures antérieures d'absorption micro-onde ; les valeurs du coefficient de diffusion translationnelle sont estimées en phase liquide.

Sur la base de ces résultats et en utilisant, pour la phase plastique, les donnés cristallographiques, un modèle est proposé pour dépeindre les mouvements réorientationnels des molécules dans chacune des deux phases condensées.

Dans le liquide, près du point triple, un modèle de type Ivanov s'applique avec des angles moyens de saut voisins de 50° et des durées de piegeage orientationnel de l'ordre de 1,3 ps. En augmentant la température, les temps de résidence tendent à devenir comparables aux durées de saut ou même inférieurs.

Dans la phase plastique, les sauts réorientationnels ont lieu de façon concertée (simultanée) entre les quatre orientations permises. Un modèle analytique décrivant les mouvements d'un ensemble de rotateurs dans un potentiel de symétrie rectangulaire permet d'expliquer les résultats expérimentaux en supposant que les sauts ont lieu de façon privilégiée entre puits de potentiel non adjacents. Un calcul numérique confirme l'existence de quatre puits de potentiel séparés par de faibles barrières et montre que les corrélations d'orientation ont principalement pour origine des intéractions de type Van der Waals entre atomes d'hydrogène de molécules voisines.     

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.     

Effets produits par l'irradiation avec des neutrons et avec des rayons gammas sur la série jaune et la série verte du spectre d'absorption excitonique de la cuprite

The effects of irradiations in a reactor and in a Cobalt 60 source on the green and yellow series of the excitonic absorption spectrum of cuprous oxide are studied. In the reactor irradiation experiments, the effects of fast neutrons are separately studied from those of thermal neutrons and of gamma rays. It is shown that the perturbations of the absorption spectra of Cu₂O by fast neutrons are very similar to those produced by an external electric field. They are also similar to those produced by quenching which creates probably internal strains. Charged defects occur probably in the crystal during bombardment and these charged defects produce an internal electric field and strains. It is not possible to study separately the effects of the electric field and the effects of strains. The electric field can be evaluated by comparison of its effects on the excitonic spectrum with those of an external field. An evaluation of the rate of creation of defects by fast neutrons in the crystal is deduced. It is also shown that the effects of gamma-rays are very different from those of fast neutrons. It is possible with gamma-ray irradiations to decrease residual internal fields which may exist in a crystal.     

Conductivité thermique des feutres de carbone,isolants à forte anisotropie: modèle de conduction par la phase solide

Uses of carbon felts for high temperature insulation are reviewed. Effects of raw material and fabrication method on the felt properties are discussed. The connection between the thermal conductivity λ and the other felt properties are analysed. Evidence is given for the existence of three hierarchized anisotropy levels of λ: crystal lattice, fiber and felt. The two directional felt conductivities — the longitudinal λ_L and the transversal λ_T ones — are modelled using a definite geometry of the felt texture and a previously introduced expression for the constriction resistance of a fiber/fiber contact. λ_T depends on both components of fiber conductivity : axial λ_A (assumed to be equal to the longitudinal) and radial λ_R. The geometrical parameters considered are: felt porosity, fiber tortuosity, aspect ratio (fiber width to heigth), fiber mean size, contact spot size a and relative frequency of direct interlayer crossing, U. The experimental validation is currently only approximate, since measurements of λ_R, a and U are not accurate enough yet.     

Étude tridimensionnelle du transfert radiatif dans un milieu semi-transparent diffusant anisotrope par la méthode des transferts discrets modifiée

The development of the modified discrete transfer method (MDT) in a three-dimensional rectangular configuration allowed us to simulate the thermal behaviour of a semi-transparent, grey, absorbing emitting and anisotropically scattering medium at the radiative equilibrium. An internal source distributes heat uniformly in the medium while the walls of the enclosure that surround it, opaque, grey, diffuse for emission and reflection, are submitted to prescribed temperatures. A linear variation law of the temperature, as well as the scattered radiation intensity, within a grid cell associated with the direction set of the discrete ordinates method has been adopted. A grid close enough to each inner wall was necessary for a better estimation of the incident flux near the singularities of the considered system. These global improvements led to a new version of the stable MDT method, as accurate as the zonal method and as flexible as the discrete ordinates one.     

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

Sans résumé

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Comparaison des fonctions de corrélation mono- et multimoléculaires des liquides et des solutions

Le théorème de corrélation microscopique-macroscopique correspondante est redérivé à l'aide de la théorie des groupes. La démonstration est fondée sur l'invariance de l'hamiltonien d'un échantillon de liquide sous l'effet des permutations des molécules identiques. Les conséquences et les limitations du théorème sont examinées en détail.     

Etude par Spectrométrie Infrarouge et Raman des Phases Cristallines Basses Temperatures de (NH4)3H(SO4)2

The Raman and infrared spectra of (NH₄)₃H(SO₄)₂ crystal were investigated in the range 20–300 K. An assignment of bands due to internal and external vibrations is given. The crystalline phases designated II, III, V and VII were identified and characterized spectroscopically. Hydrogen bonding, the nature and degree of structural (dis)order and the mechanisms of the phase transitions are discussed. The NH₄⁺ ions show an important orientational disorder and become fully ordered in phase VII only. They are involved in all transitions and seem the main cause of the ferroelectricity at low temperature.     

Première détection d'un transfert d'aimantation entre du xénon polarisé par laser et des protons d'une protéine

The conditions of observation and characterization of magnetization transfert between laser-polarized xenon 129 and protein protons are addressed. This is experimentally illustrated by its first detection obtained on the wheat non-specific lipid transfer protein.     

Simulation des transferts de masse et de chaleur par modélisation à bas nombres de Reynolds dans un écoulement avec effusion locale en canalisation

The turbulence model developed by Lam and Bremhorst with low values of Reynolds numbers is used to simulate a flow between two impermeable plate walls. This model, corrected by Yap, is able to simulate flow inside the boundary layer on the part of porous walls submitted to the blowing. This model of flow inside a channel with local blowing is coupled with a model of transfers through the impermeable walls and the porous wall, and with the environment. The global model is validated by comparison between experimental results from the literature and those obtained by the authors from experiences carried out with the test facilities of a subsonic thermal wind tunnel.A simulation of non-isothermal flow inside a channel with local blowing shows the attractive way of wall cooling by blowing. The optimal injection ratio is found equal to 0.01.     

Etude de l'ammoniac par double irradiation infrarouge hertzien Mise en evidence des collisions pour lesquelles chaque molecule subit une transition de type ΔJ=0

Par une technique de double irradiation infrarouge hertzien, on étudie l'état des partenaires lors des chocs entre molécules. Après avoir mis en évidence les transitions par collisions entre doublets d'inversion de l'ammoniac (ΔJ=0), on montre par une étude systématique que les modifications d'intensité des transitions de sonde sont beaucoup plus importantes pour J?K que pour J?K et que la symétrie des molécules partenaires joue un rôle très important.     

Die Bestimmung des Kern-Quadrupolmomentes des 247 keV-Niveaus des Cadmium-111 durch Messung der zirkularen Polarisation der γ-Strahlung

The interaction of the nuclear electric quadrupolemoment with an electric field gradient at the position of the nucleus changes the angular correlation of two successiveγ-rays and should also produce a circular polarization of theγ-rays. By measuring this polarization it should be possible to distinguish between electric and magnetic attenuation of theγ-cascade. In the electric case this measurement leads to determine not only the absolute value of the interaction product\(Q \cdot \frac{{\partial E}}{{\partial z}}\) but also the sign of it and therefore the sign of the nuclear quadrupolemoment. In the following paper the measurement of the circular polarization of the 247 kevγ-ray of Cadmium-111 is described. A polarization ofP=(0.8±0.2)% leads to the determination of the quadrupolemoment of the first excited state toQ=+0·9·10^?24cm².