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.     

Etude de l’effet des dimensions des cristallites sur l’observation des raies du spectre excitonique de CuI

Previous investigations [1] have suggested the possibility of an effect of the sizes of the grains of a thin layer on the intensity of the exciton lines which can be observed at low temperatures. An experimental study of this effect has been carried out with CuI. It is possible to show that for thin layers formed of very small crystals, the exciton lines do not appear at all in the spectrum. The first line (n=1) appears in thin layers formed of crystals which have a size about of 860 Å, but the second line (n=2) appears only when the size of the grains is about 1000 Å. Finally, the third line (n=3) is observed only in single crystals or in thin layers which have crystals about 2000 Å?3000 Å [3]. The theory of this effect will presumably be mathematically very complicated but the physical principles implied in the described observations have been examined qualitatively in a previous paper [4] and are in good agreement with the observations.     

Etude de l'intensité d'oscillateur de la raie d'absorption quadrupolairen=1 de la série jaune de Cu2O à 4,2°K

The oscillator strength of the orthoexcitonicn=1 line of the yellow series of Cu₂O has been measured at 4,2°K. Its value for a polycrystalline sample and for unpolarized light isf=1,3·10^?9. The variation of intensity of the line as a function of the orientation of the light vectorq with respect to the symmetry axes of the crystal has been determined with natural, oriented single crystals. The results obtained are in good agreement withElliott's theory. According to this theory, this line corresponds to an excitonic electric quadrupole transition. The transition takes place from a ground level of representationΓ ₁ ⁺ towards an excitonic level of representationΓ ₂₅ ⁺. In the red part of the spectrum, we have observed with thick oriented monocrystalline samples of natural Cu₂O two new lines of weak intensity. The origin of these lines is discussed.     

Effets comparés des impuretés de terres rares sur la résonance ferrimagnétique et la relaxation nucléaire dans le grenat de fer et d’yttrium

The anomalous properties of impure yttrium iron garnet are related to the susceptibilities of the rare earth ions which it contains. The susceptibilities are calculated assuming a slow relaxation. It is shown that the success of the theory of “slow relaxation” requires the existence of a coupling between the transverse magnetization of the iron lattice on the one hand, and components of the magnetic moments of the rare earth ions, with non zero diagonal matrix elements, on the other hand. The temperature variations of the ferrimagnetic linewidth and the nuclear relaxation time are compared.     

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.     

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

Sans résumé

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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.     

Etude du spectre de l'holmium atomique: II. Interprétation paramétrique des niveaux d'énergie et des structures hyperfines

Energy levels of neutral holmium have been interpreted by means of parametric studies of the groups of configurations (4f¹¹6s² + 4f¹⁰6s²6p + 4f¹¹5d6s) and (4f¹⁰5d6s² + 4f¹¹6s6p), taking into account the mixing effects due to electrostatic interactions. Both real and effective parameters have been fitted from 71 odd and 70 even levels, respectively. The eigen-functions have been used for a determination of the magnetic dipole A and electric quadrupole B hyperfine constants. Values of the parameters obtained from various configurations are compared. Results of parametric studies are also reported for 4f¹⁰(⁵I)5d²6s.     

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.     

Analyse de la conduction de la chaleur aux temps ultra-courts dans un solide par la thermodynamique irréversible étendue et la dynamique moléculaire

Instantaneous heat propagation and thermodynamic local equilibrium cannot be assumed when solving space and time microscale problems. Therefore, we reconsider the thermodynamics basis of the Fourier law in order to obtain the new heat conduction models: the hyperbolic heat equation (EH) and the modified hyperbolic equation (EHM). We have performed molecular dynamics (DM) experiments which are independent of any thermodynamic model, to test the macroscopic approaches. We show that the solutions of the EH and the EHM do not agree with the numerical experiments and that the MD results are strongly dependent on the way from which the macroscopic conditions are simulated in the microscopic point of view.     

Modélisation du comportement thermique d'un espace urbain: Calcul de la réponse en température des structures et de l'air ambiant

This paper presents theoretical modelling works on the thermal behaviour of an urban space (street). A calculation code, named Codyflow, has been developed in order to simulate the thermal response of an urban system to climatic solicitations. The model allows us to take into consideration, on the one hand, the radiative flux soliciting the urban canyon, on the other hand, heat transfers inside the system. The airflow solicitation, which plays a part in the convective exchanges and in the ambient air temperature, is calculated by the CFD code Fluent. Some simulation results, obtained by the code Codyflow, are presented. They bring to the fore the influence of many factors on the thermal response of the urban canyon: the geometrical configuration, the used materials (through their thermophysical characteristics) and the airflow solicitation. These results allow us to predict the thermal behaviour of urban spaces for the benefit of architects and urban designers in the conception phase of an urban plan.     

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.     

Dynamique non-linéaire d'instabilités de surface : gouttes et colonnes liquides formées par ruissellement de films

The destabilization of a thin film by gravity is of central importance in many industrial devices, especially those involved in Thermics (film boiling, heat exchangers). In the simplest case of a liquid film hanging below a solid ceiling, spatial structures are forced by the destabilizing action of gravity (Rayleigh-Taylor instability): one observes regular lattices of pendant drops, that in turn become instable by coalescences and falling of the drops. When the film is supplied with liquid at a constant rate, other flow regimes are observed: periodic emission of drops, formation of regular arrays of liquid columns, liquid sheet. Liquid columns exhibit a collective dynamics that is typical of non-linear systems: modulations of their spatial periodicity, diffusion of the perturbations, self-sustained oscillations, propagation of solitary dilation waves, coalescences and nucleations of the columns, etc.     

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.     

Contamination par le nickel et d'autres métaux lors de la manipulation des pièces de monnaie – comparaison entre francs français et euros

The introduction of the euro has revived the interest for potential nickel allergies. We show that the handling of a single used nickel coin releases an average of 0.45 μg of nickel, 0.26 μg of copper and 0.08 μg of zinc, whereas a euro coin composed of nickel alloys releases 0.25 μg of nickel, 1.3 μg of copper and 0.17 μg of zinc. These levels of contamination, favored by friction during handling, differ from those obtained on the basis of the EN 1811 test applicable to solubilisation in artificial sweat. The evaluation of allergy risks following the introduction of the euro may require the consideration of potential synergies between the metals mentioned above. To cite this article: P.-G. Fournier et al., C. R. Physique 3 (2002) 749–758.     

Influence des phénomènes d'hystérésis sur les propriétés hydriques de matériaux poreux: Comparaison de deux modèles de simulation du comportement thermohydrique de parois de bâtiment

Porous materials hysteretic moisture characteristics : influence on water content distributions in buildings walls. Comparison of two simulation models. Two models for determining the temperature and moisture distributions within a wall are presented. The first one is a direct application of the classical Philip and de Vries model. The second one, using the suction potential, is derived from Milly's researches and is more efficient because it allows the hysteresis phenomena to be taken into account. First, the different equilibrium and transfer parameters used in the models are reviewed. Indications are given on how they can be experimentally determined and results for two cement pastes and a cellular concrete are illustrated. Then, calculation results of water content distributions for the two models are presented for an homogeneous cellular concrete wall in steady environmental conditions. In that particular case, the two models estimations are in good agreement despite different numerical treatments and experimental procedures. Using Milly's model with cyclic boundaries conditions, a significant influence of hysteresis phenomena is clearly shown.     

Influence des différents scénarios techniques, énergétiques et économiques sur la décision d'installer un nouvel échangeur de chaleur

Influence of different technical, energetic and economic scenarios on the decision of installing a new heat exchanger. This article proposes to examine the decision of installing a new heat exchanger in a working industrial unit in order to improve its energy performances. This examination is based on a new graphical method permitting us to approach the decision while taking into consideration the operating, technological and conjunctural variables.The analysis of the results shows that improvement in energy performances of an industrial unit does not always contribute to improving its economic performances. Factors that govern this contribution are in increasing importance: the choice of heat exchanger's configuration, the energy scenarios, the energy to be saved and the choice of the construction material of the heat exchanger.