La thermoluminescence de la glace; Les effects de la deformation plastique

We have studied the thermoluminescence of polycrystalline ices irradiated by ultraviolet light at liquid-nitrogen temperature. The effect of plastic deformation and annealing has been confirmed. The trap depth calculated from the law of light intensity variation with temperature, is sensibly equal to 0.09 eV.     

Comportement anelastique de la glace ih dopee avec HF

Modifications of mechanical damping of HF doped ice crystal are studied in a lower frequency range. Three effects are observed: (1) The relaxation peak appeared in a lower temperature range than that of pure ice. (2) High temperature internal friction is increased. (3) High temperature internal friction becomes more amplitude dependant. These effects are interpreted in terms of increase of the content of Bjerrum defects according to the assumption about the substitutional position of fluorine atome in the ice lattice.     

Etude du comportement électrique de la glace pure en basse température — ferroélectricité et charge d'espace

The existing results on polarization- and depolarization currents in ice are reviewed. New low temperature measurements of the depolarization currents using blocking and non blocking electrodes are presented and interpreted. The results are not in contradiction with the assumption of a ferroelectric state.

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Résumé Après un rappel des résultats existant en basse température sur la glace et des interprétations contradictoires qui en sont données on présente quelques expériences de courant de dépolarisation effectuées dans différentes conditions (électrodes ohmiques, bloquantes ...). On montre que ces expériences permettent d'infirmer certaines des hypothèses avancées et d'expliquer certains résultats rapportés par différents auteurs.

     

Calcul semi-empirique de la temperature de transition des superconducteurs et de l'effet de la pression sur la transition

A method is developed to take into account the contribution of the Umklapprozesse to the electron-phonon interaction in polyvalent metals. This method is used to compute—from first principles—the high-temperature resistivity of non-transition metals as well as the transition temperature T_c of non-transition superconductors along the lines of , and 's theory of superconductivity (Phys. Rev. 108, 1175 (1957)). The effect of pressure on T_c is also computed and its dependence upon the band structure is stressed.     

Analyse de la symetrie de αU Au moyen de la diffraction des neutrons

Using polycristalline samples of αU, careful experiments yield precise neutron diffractograms, taking advantage of a linear multiwire detector. We could refine profile and integrated intensities of very weak satellite reflections of first and for some of them of second order. The modulated structure is re-examined. The structure at room temperature may be non centred.     

Etude de la structure du tellure liquide par diffraction de neutrons au voisinage de la temperature de fusion

The structure factor of liquid tellurium has been measured by neutron diffraction at the melting temperature and in the supercooled state. These results are a confirmation of the existence of an A₇ type stable configuration in a large range of temperature between 400 and 1100°C.     

Etude de la cinetique de la reaction de polymerisation de resines epoxy et polyester par analyse du comportement dielectrique

In this piece of research, we have chosen to study the dielectric behaviour of different resins while in process of polymerization and determine the dielectric parameters most relevant to the monitoring of the kinetic process taking place; our aim being to design electromagnetic sensors which will enable us to monitor the polymerization process thoroughout.Consequently we have confined ourselves to carrying out radiofrequency measurements by using only a few set frequencies, without attempting to monitor, as many researchers have tried to, the evolution of dielectric relaxation [1, 5].We have studied two types of resins, one of them being epoxy-based and the other polyester-based. We have succeeded in demonstrating that the perception of the real terms of the complex dielectric constant as well as of the evolution of the loss tangent angle, both complementary elements, are essential for a thorough analysis of the kinetic process.Whereas ε is most suitable for the monitoring of the concluding phase of the polymerization, tan δ is more appropriate to the study of the opening stage of the process, while allowing us to define with great accuracy the exothermicity point reached after gel time [6, 7, 8].     

Reconstruction de la forme de polarisation par holographie

With a reference beam diffused by a depolarizing diffuser, we reconstruct holographically the polarization form which existed at each object point.     

Examen de la loi d'arrhenius de la diffusion dans les solides

Validity of the Arrhenius law has been investigated by measuring the influence of temperature on the transport processes in very pure single crystals of sodium iodide. For the first time, due to the high experimental accuracy and the precision of the temperature control, diffusion coefficients could be measured in a solid in steps of a few degrees up to a few tenths of a degree of the temperature of fusion. We have studied: (a) ionic conductivity, (b) self-diffusion of the cation Na⁺ and (c) self-diffusion of the anion I^?. The three transport processes follow the same temperature dependence: (a) strict verification of the Arrhenius law over several orders of magnitude up to about thirty degrees below the melting point and (b) in the last thirty degrees a positive departure from the simple exponential law is observed which increases rapidly to reach 50% at fusion. The different possible reasons of this departure are discussed. The phenomenon seems to be connected with the lattice dynamics before melting.     

Contribution a la theorie atomique de la diffusion chimique

Here we present an analysis and a development of the atomic theory of chemical diffusion as proposed by Manning for a binary system a/b.The general expression for the flux of a tracer in a concentration gradient is first established. This expression of the flux is identified with that deduced in the phenomenological theory. Thus a relationship between the partial correlation factors of vacancies with each of the a and b species is obtained.The effect of “vacancy flow” can be described in terms of these correlation factors. Thus the vacancy flow on species A leads to a correlation of the vacancy jumps with species B and vice versa.We shall see that the Nernst-Einstein equation can be extended to the case of chemical diffusion and that the ratio of the intrinsic diffusion coefficients is equal to the ratio of the mean jump frequencies W_A and W_B.Also, the activation energies of intrinsic diffusion coefficients are related very simply to the activation enthalpies of atomic jumps.In conclusion, we shall see that chemical diffusion in a binary system a/b can be completely described if either the thermodynamic factor and the coefficients of self diffusion, or the thermodynamic factor and the coefficients of intrinsic diffusion are known as functions of the concentration.     

Emploi quantitatif de la spectroscopie Auger; Étalonnage de la méthode

A calibration is presented for the measurement, by Auger electron spectroscopy, of sulphur adsorbed on nickel. The Auger emission from the metal is used as a reference. The use of radioactive sulphur permits a direct measurement of the quantity of adsorbed sulphur.     

Etude par correlation de photons de la raie depolarisee dans la glycerine a basse temperature

The depolarized light scattered by glycerol at low temperature has been studied using a digital clipped correlator. The data are fitted to a Cole-Davidson distribution of relaxation times. Comparison of the polarized and depolarized spectra indicates that large step reorientational motions take place. This confirms the results obtained at higher temperature by Pinnow, Candau and Litovitz.     

Determination de la temperature d'une flamme de diffusion methane-fluor au moyen du spectre de vibration-rotation de la molecule HF

Taking into account self-absorption and a thermal gradient, the thermal gradient alone, and none of these effects, in rotational-temperature determinations involving the 1–0 and 3–0 bands of the vibration-rotation system of HF and the 0–1 band of the ²δ⁺-²δ⁺ system of CN, we observed good agreement between three measured rotational temperatures.     

Les methodes de determination de la sonie des bruits

For some considerable time now specialists have taken an interest in the measurement and analysis of noise. They quickly understood that the process of perception of sounds by the ear was very complex and that it was difficult to relate a physical level or a sound level to people's impression of nuisance or loudness. Therefore several authors such as, for example, Stevens, Kryter and Zwicker, proposed different methods and different units. In a general way, these methods apply to continuous noise but they cannot be applied without care to discontinuous impulsive or transitory noise. Speech and music come into this latter category. The known methods according to the present author cannot be used for dealing with this type of noise.     

Sur la restitution du signe de la phase en interferometrie

Phase variations are transformed into intensity variations by means of interferometry. It is then possible to form a visible image of a pure phase object. But then information on the sign of the phase or the direction of surface relief is lost. Principles of a method for extracting only the imaginary part of the complex amplitude of the object, which is an odd function of the phase, are studied. From this it is possible to obtain the sign of the phase.     

Détermination de la forme de la section d'une fibre optique non gainée à l'aide de l'analyse harmonique de son diagramme de rayonnement

Résumé Dans cet article, on étudie le diagramme de diffusion vers l'avant d'une fibre optique d'indice uniforme éclairée par un faisceau laser perpendiculaire à son axe lorsqu'elle tourne sur elle-même. On montre qu'il existe une relation linéaire entre les coefficients des développements en série de Fourier des fonctions représentant le déplacement angulaire d'une frange brillante et le contour de la section. Le mesure du déplacement d'une seule frange permet de connaître avec une excellente approximation la forme de la section.

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In this paper, the movement of the forward scattering pattern of an unclad fibre illuminated by a laser beam perpendicular to its axis is studied when the fibre is rotated. The existence of a linear relation between the coefficients of the Fourier series which represent the angular shift of a bright fringe and the fibre cross-section is shown. Thus it is possible to know to an excellent approximation the shape of the cross-section by monitoring the fringe movement.

     

Etude de la structure magnetique et de la transition de typr “spin-flop” de Rb2FeF5

The nature of the magnetic interactions in the chain compound Rb₂FeF₅ has been investigated using neutron diffraction and magnetic measurements under high applied fields. Rb₂FeF₅ orders antiferromagnetically at T_N = 8.0 ± 0.5 K; the magnetic structure is of the A_Z + G_X mode and the moment of the Fe³⁺ ion extrapoled to 0K is 3.5 ± 0.2 μ_B, this low value being due to zero-point spin reduction. Within a chain the Fe³⁺ ions are antiferromagnetically coupled with an exchange constant of J/k = ?8.8 K. A spin-flop behavior has been observed and interpreted on the basis of the molecular field theory. The critical field was found to be H_C = 65 kOe at 1.7 K.