Sur une Resolution Stochastique de l'Equation de Schrödinger à Coefficients Analytiques

Under some hypotheses of analyticity and integrability we show the existence and uniqueness of a strong regular solution of the Schrödinger equation using a natural generalisation to the complex case of the Feynman-Kac formula. This explicit representation allows us to study in certain cases the asymptotic behavior of the solution when the Planck constanth tends to zero. The same method can be used for the solution of more general Schrödinger equations.

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Membre du Laboratoire Associé au C.N.R.S., n° 224 Processus Stochastiques et Applications     

Identification du coefficient de transfert thermique sur la surface externe d'un échangeur de chaleur à tubes et ailettes planes en fonction de l'humidité de l'air,en l'absence de condensation

The following study, which is rather oriented towards experimentation, shows the influence of the humidity content of air on heat transfer. This first article concerns heat transfer between the external fluid (moist air) and the internal fluid (water containing glycol, whose thermal behavior inside circular tubes is well-known) in a heat exchanger of the same type as those used in automotive air conditioning (horizontal copper tubes and plane aluminium fins), in the absence of condensation. The most difficult part of this experimental work is the measurement and control of the air humidity, since one has to make sure that the measurement incertainties are not significant compared to the precision of the calculation of the heat transfer coefficient. The conclusion is that, for this type of exchanger, the heat transfer coefficient decreases with air humidity in the absence of condensation (dry wall). Some correlations have been developed with respect to the relative air humidity. An analog experimental investigation, but this time carried out in the presence of condensation (partially or completely wetted wall), is about to be completed; the obtained results will be communicated later on.     

Comparaison de deux approches d'optimisation. Application à une thermopompe

Comparison between two optimization approaches. Application to a heat pump. An energy flux consists of two parts; an available part, the exergy, and a non-available part, the anergy. The functional diagram of an energetic system is a schematic representation of fluxes for these two compounds. On this diagram, we define the products and ressources of exergy and anergy for each unit of the system as interactions with the external environment and/or with an internal network using two loops: an exergy loop and an anergy loop. This internal circuit could be represented by a server managing the use of exergy and anergy by the various units of the system. We associate to the exergy and anergy fluxes, unit costs defined through an approach called decomposition [1]. This study is concerned with the comparison of results when optimization is based on an objective function, that is one side the investment cost of the system and on the other side the coefficient of performance (COP). In both cases, the work downstream consists in optimizing the unit cost of the main product of each component using the decomposition approach. We will compare the COP, the investment cost, the annual cost and the thermodynamic states of the system.     

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.     

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 %.     

Amélioration du coefficient de qualité de résonateurs à ondes transverses sur plaques fines de quartz

Resonators based on transverse waves propagating in thin quartz plates have been optimized using a specific fabrication step in order to improve their quality coefficient and to minimize their insertion losses. Systematic measurements have been performed, allowing to emphasize the efficiency of the proposed approach. The possibility to fabricate resonators operating in the frequency range 100–250 MHz and exhibiting quality coefficient times frequency product greater than 10 ¹³ is there demonstrated. This last figure corresponds to more than the state of the art in surface acoustic wave resonators.     

Thermo-frigopompe à absorption pour production simultanée de chaleur et de fraîcheur utiles

Absorption heat-cold-pump for simultaneous production of useful heat and coolness. A new absorption heat-cold-pump for the simultaneous production of useful cold (12 °C – 7 °C) and of useful heat (80 °C – 85 °C) is presented. The system operates with a couple of components with comparable volatilities, for example the following saturated hydrocarbons, butane + hexane, butane + octane, butane + decane, propane + octane. The working pair is separated in a rectification column. The components are remixed in a reverse-rectification column fitted with an incorporated heat exchanger. The COP and the exergy efficiency are presented for a number of modelized internal structures of the heat-cold-pump.     

Développement de lasers visibles pompés par diode à base de cristaux de Nd:GdCOB autodoubleurs de fréquence

We present the performances of a diode-pumped solid-state laser operating in the visible by self-frequency-doubling. A cw output power of 115 mW at 545 nm has been obtained in a stable concave–concave cavity by using a crystal of Nd:GdCa₄O(BO₃)₃ pumped by a 2 W high-brightness laser diode. In a plano–plano cavity, similar to a microchip laser, we have obtained, for the first time to our knowledge, an output power of 22 mW in the green.     

Modélisation de séchoirs à tapis. Utilisation des réseaux de neurones

Modelling of convective layer dryers. Using neural networks. Dryer modelling is considered in this paper. A dryer scale approach is implemented in order to write the classical differential equations through parameters such as the heat transfer coefficient or drying kinetics. The behaviour of the dryers is described by a non-linear system which integrates these equations in a transfer network using the finite difference method. The finite difference method is easy to implement, but appears to be too slow for dryer designing. So, in the second part of the study, neural networks are used to model drying process in steady state. When applying neural networks method to the design of dryers, one of the main problems is to find necessary and sufficient inputs so that the neural networks can learn transfers laws. To reduce the problem, each output is defined by a single neural network and non-dimensional numbers are used. The following step deals with the determination of the number of neurones and the minimization of output error for each efficiency (change of training points). Then, neural networks are used to simulate different configurations of dryers. Results are compared with the finite difference method and an industrial application is studied in the last chapter.     

Mesures spectroscopiques de constituants et de polluants atmosphériques par techniques in situ et à distance,au sol ou embarquées

Infrared spectroscopy is a powerful tool for precise measurements of atmospheric trace species concentrations through the use of characteristic spectral signatures of the different molecular species and their associated vibration–rotation bands in the mid- or near-infrared. Different methods based on quantitative spectroscopy permit tropospheric or stratospheric measurements: in situ long path absorption, atmospheric absorption/emission by Fourier transform spectroscopy with high spectral resolution instruments on the ground, airborne, balloon-borne or satellite-borne.     

Phénomènes de glissement à l'interface liquide–solide

The problem of liquid–solid slip is described here, in a simplified manner. Today, several experiments have shown that substantial slip appears when a non-wetting liquid flows along a surface which is smooth on an atomic scale. This phenomena is characterised by a length, called the slip length, or Navier length, generally denoted by L_s. A number of experiments indicate that this quantity may be as large as several hundreds of nanometers. Numerical simulations also show the existence of slip in non-wetting conditions, but the corresponding lengths found here are much smaller than those found experimentally. A theory, based on the existence of a gas film of nanometre thickness has been proposed, but has not yet been experimentally confirmed. Experiments on this are difficult, and sometimes controversial. To cite this article: P. Tabeling, C. R. Physique 5 (2004).     

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.     

Application, à un cristal de béryl,d'une nouvelle méthode d'étude par réflexion

The vibrational frequencies of beryl are determined from a measurement of the optical constants with a method utilizing reflexion from samples with and without an evaporated layer of an optically known substance.     

Modèle correctif de la mesure de la température d'un gaz par couple thermoélectrique. Application à une zone à fort gradient thermique

Corrective model of the gas temperature thermocouple measure. Application to an important thermal gradient zone. The gas temperature measurement with a thermocouple in important thermal gradient zones requires a corrective model. For example, such zones exist for thermal boundary layers near active walls. We have calculated these thermocouple thermal exchanges where connection wires are considered as fins with a variable ambient gas temperature. The heat exchanges by convection and radiation on the thermocouple head are analytically calculated, then a numerical method is used for fins where the space increment is the same as for the experimental measure. The corrective model in steady state is semi-analytical. Its validation is made with experimental results from studies of flows along a non-isothermal vertical wall in a cavity filled with wet air. Several applications are offered for many thermal curves, for more important gradient zones corrections are larger than 1.5 K for a K type thermocouple of 0.08 mm wire diameter.     

Dimérisation des sels de l'ion nitrosodisulfonate à l'état solide

La dimérisation de plusieurs sels du radical libre nitrosodisulfonate est étudiée par R.S.E. Les spectres d'échantillons polycristallins de deux formes cristallographiques des sels de sodium, potassium et rubidium, sont caractéristiques d'un état triplet accessible thermiquement. Ces spectres sont attribués à des paires de groupements NO radicalaires, couplés par échange et sont décrits par l'Hamiltonien de spin:

Les paramètres de déplacement en champ nul, les composantes du tenseur g le long des directions principales X, Y, Z du tenseur fin et la composante du tenseur A le long de l'axe Z (dans le cas où la structure hyperfine est résolue), ont été mesurés et discutés.

A partir de ces mesures, on montre que l'axe Z est dirigé suivant les orbitales 2p des atomes d'azote et d'oxygène, et que l'axe X est dirigé selon la liaison NO. Par suite, l'arrangement des deux groupements NO d'une paire est toujours sensiblement rectangulaire.

Dans le cas des deux formes cristallines du potassium et du rubidium, l'écart singulet triplet dépend de la température, ainsi que les paramètres de déplacement en champ nul, ces variations avec la température sont attribuées à l'expansion thermique du réseau.

La présence d'une structure hyperfine bien résolue dans certains de ces sels, et la forte anisotropie des largeurs de raies dans les autres sels, suggèrent que les excitations sont fortement localisées, et que si elle sont mobiles leur fréquence de saut est inférieure à 10⁷ Hz.     

Etude hydrodynamique et thermique d'un échangeur de chaleur à noyau tournant conique

Hydrodynamic and thermal study of a conical rotating heat exchanger. This work reports on a new heat exchanger for various food products (jam, sauces). The fluid flows between two coaxial parallel cones from the vertex to the base. The inner cone rotates and the outer is stationary. A uniform heat flux is delivered through the external wall. The numerical modelling is performed on a bidimensional configuration by the finite-volume method with Phoenics package. The model takes into account the rheological food products characteristics.The principal phenomenon, numerically and experimentally observed, is the appearance of the recirculation that renews the fluid on the heating wall, increases the heat transfer and has a mixing effect.     

Etude du comportement de radicaux libres à la transition de phase et en phase antiferroélectrique de NH4H2AsO4

Cet article décrit le comportement de radicaux libres dans le cristal antiferroélectrique de NH₄H₂AsO₄ et le compare à celui de ces mêmes radicaux dans le ferroélectrique KH₂AsO₄. A la transition de phase, les modifications que subissent les espèces radicalaires sont interprétées en liaison avec l'abaissement de symétrie et l'établissement de l'ordre antiferro-électrique. Des transformations interradicalaires thermiquement réversibles sont mises en évidence ; elles se caractérisent par une variation du nombre de protons en interaction avec l'électron non apparié.     

Les études Séismologiques en Tchécoslovaquie de 1951 à 1953

Ohne ZusammenfassungRapport national présenté devant l'Association Internationale de Séismologie et de Physique de l'Intérieur de la Terre pendant la 10ème Assemblée Générale de l'Union Géodésique et Géophysique Internationale (UGGI) à Rome en Septembre 1954.     

Facteur de bruit d'une chaı̂ne de cinématographie ultrarapide : application à la fusion par confinement inertiel

Inertial confinement fusion simulates in a laboratory the thermodynamic state of the center of stars, thus leading to the determination of stellar parameters. In order to reach that aim, high-speed cinematography brings up instruments specifically adapted to picosecond measurement, for which it is necessary to know the final precision. A model of the noise factor of the instruments under study is introduced and confronted to the experimental results obtained.