La dépendance du pouvoir séparateur du systeme „Objectif-Émulsion photographique“ de l'ouverture relative de l'objectif

Résumé On étudie la qualité de l'image photographique, fournie par des objectifs entachés d'aberration sphérique et enregistrée sur la couche photographique, en fonction de l'ouverture relative de l'objectif. On trouve que l'ouverture relative optima, déterminée, photographiquement, était dans tous les cas bien plus petite que celle correspondant a l'aberration d'onde égale à /4. Elle ne Concorde pas aussi avec l'ouverture relative optima trouvée à l'aide du critérium de la qualité basé sur l'éclairage au centre de la tache de diffusion. On présente un essai d'expliquer des différences trouvées.     

Effet isotopique en relaxation magnétique nucléaire. Cas du système AX

La comparaison des vitesses de relaxation du proton dans les couples de molécules isotopomères ¹³C-¹HBr₃ et ¹²C-¹HBr₃, ²⁹Si-¹HCl₃ et ²⁸Si-¹HCl₃, C₆H₅ ⁷⁷Se-¹H et C₆H₅ ⁷⁶Se-¹H permet de déterminer indirectement le temps de relaxation spin-milieu des noyaux de ¹³C, ²⁹Si et ⁷⁷Se. Dans le cas de spins ½ couplés (A-X), l'analyse des courbes d'évolution des raies permet de préciser les mécanismes de relaxation qui interviennent. La méthode présente sur l'observation directe, l'avantage de la sensibilité du proton mais l'évolution des raies au cours du temps est assez compliquée. Toutefois, nous avons vérifié que les deux méthodes concordaient bien dans le cas du carbone 13 du bromoforme.     

Théorème du viriel et dynamique des supernovae

The use of the transformation groups leads to dynamical solutions of the nonlinear gravitational hydrodynamical equations. These solutions, combined with the virial theorem, generalise the Chandrasekhar's static relation between the total and the internal energies. The new relations describe a collapse, an expansion or the sequence collapse/expansion of the external layers of a star (case of a supernova, for example).     

Comportement transitoire d'une machine frigorifique à adsorption. Étude expérimentale du système alcool/charbon actif

The objective of this article is to present an experimental study of an adsorption refrigerator, accounting for the transient phenomena in each component of the machine, in particular in the adsorber. The couples adsorbate/adsorbent investigated (activated carbon/methanol or ethanol) have been chosen on the basis of an earlier comparative study. We have performed a full series of experiments to investigate the transient evolution of temperatures, pressures and the cycled mass, in a discontinuous cycle, and along the components of the refrigerating machine. The influence of various parameters is studied by varying one at a time: adsorbate/adsorbent couple, alcohol load in adsorber, alcohol flowrate, heating power, initial desorption temperature. All these experimental observations are discussed and compared to transient models developed in a separate article.     

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’.     

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.     

MODICS. Généralisation de la méthode d'optimisation systémique aux systèmes thermiques avec échangeurs imposés

We present here the generalization of the systemic optimization method for complex thermal installations, based on the thermal integration, that was the subject of a previous publication in the October 1995 (n^o 406) issue of the Revue Générale de Thermique. The proposed method allows to distinguish component irreversibilities, that are linked to the internal functioning of a component alone, independently of the rest of the considered system, and systemic irreversibilities that can only be modified by changing the configuration of the system. It constitutes a tool for design engineers, the originality and the power of which are to give them systemic insights on the installation under study.The general method MODICS is obtained by mixing on the one hand the previously described method and on the other hand an analogous approach adapted to the case when heat exchangers are imposed. The article details the totality of procedures to follow to implement this method and gives various examples.     

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     

Effets des radiofréquences sur le système nerveux central chez lʼhomme : EEG,sommeil, cognition,vascularisation

Most of clinical studies on radiofrequency electromagnetic fields (RF) were directed at mobile phone-related exposures, usually at the level of the head, at their effect on some physiological functions including sleep, brain electrical activity (EEG), cognitive processes, brain vascularisation, and more generally on the cardiovascular and endocrine systems. They were frequently carried out on healthy adults. Effects on the amplitude of EEG alpha waves, mainly during sleep, look reproducible. It would however be important to define more precisely whether and how the absence of electromagnetic disturbance between RF exposure and the recording systems is checked. No consensus arises about cognitive effects. Some effects on cerebral vascularisation need complementary work.     

De la microstructure du polymère à ses propriétés rhéologiques

We extend the previous work by Benallal et al. on the relationship between structure and rheological properties of linear polymer melts. The aim of this paper is to quantify the effect of the chemical structure on the viscoelastic properties. We show that these properties are governed by the monomer dimensions and the interaction energy. To cite this article: A. Allal et al., C. R. Physique 3 (2002) 1451–1458.     

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.     

Relaxation nucléaire de l'azote et du proton dans le cyanoacétylène liquide

On a étudié les temps de relaxation spin-réseau de l'azote et du proton du cyanoacétylène en phase liquide à différentes températures. La vitesse de relaxation du proton est décomposée en différentes contributions : spin-rotation, intra et intermoléculaire dipole-dipole. Les mouvements moléculaires de translation et de réorientation sont analysés en utilisant différents modèles (conditions aux limites de ‘glissement total’ et de ‘frottement total’, correction de Perrin …).     

Etude par résonance paramagnétique électronique de la variation en fonction de la température du couplage hyperfin du radical tert-butyle

Le radical tert-butyle obtenu par irradiation γ à 77°k du chlorure de tertiobutyle peut se présenter sous deux structures différentes. Une forme pyramidale, ayant pour origine les contraintes exercées par le réseau cristallin, et pour laquelle le couplage a ¹³C avec le carbone central est une fonction décroissante de la température. Une forme plane pour laquelle a ¹³C croît avec la température. L'étude du radical plan a permis de séparer les contributions relatives des vibrations, a ¹³C _v , et de la polarisation des électrons des couches internes et des liaisons, a ¹³C_pol, à la valeur du couplage a ¹³C. Le résultat obtenu confirme la relative insensibilité de a ¹³C_Pol, par rapport aux détails des substituants du carbone central, prévue par les calculs de Melchior.     

La filière thorium,une option intéressante pour le nucléaire du futur

To satisfy a significant part of the primary energy demand at the world level by 2050, fission nuclear energy production has to grow by a large factor (more than 10). Due to the natural limitations of Uranium reserves (at a reasonable price) such a development makes necessary the use of breeder reactors. A comparative study of such breeder reactors using Uranium or Thorium based fuels shows that the use of Thorium based fuel has clear advantages in terms of flexibility, of minor actinides contents in the fuel cycle as well as for the inventory and disposal radiotoxicities. To cite this article: J.-M. Loiseaux et al., C. R. Physique 3 (2002) 1023–1034.