Etude de la propagation d'une onde du type Franz sur des cylindres

A “Franz-type” wave was generated on the outside of solid cylinders immersed in water with “ka” values ranging from 25 to 800. In this investigation, the velocity and the attenuation of this wave have been obtained for different materials. Good agreement is obtained with the theory and other experiments.     

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.     

Influence des brandons sur la propagation d'un feu de forêt

A two-dimensional weighed-site small-world network is proposed to study the action of firebrands (lofted flaming or glowing debris) on fire spread through homogeneous or heterogeneous systems. The firebrand emission distance obeys an exponentially-decreasing distribution law. For homogeneous systems, the effect of firebrands is strengthened when the fire impact length decreases and the characteristic firebrand emission distance increases. As a result, jumps in the rate of spread appear and time oscillations in the burning area can occur. For heterogeneous systems, this effect becomes weaker as the degree of disorder and the distance of firebrand emission increase. The influence of characteristic lengths of radiation, firebrand emission, and medium heterogeneity on fire spread is discussed. To cite this article: B. Porterie et al., C. R. Physique 6 (2005).     

Influence de la temperature sur les intensites des raies Raman de resonance

Using an analytical expression for the resonance Raman scattering tensor, the influence of the temperature on the scattered intensities is studied.The variation of the intensities as a function of the temperature is different from the result given by the polarisability theory. However, it is shown that the usual ratio $\text{I}{}_{\mathrm{<mtext>Stokes</mtext>}}\text{I}{}_{\mathrm{<mtext>antiStokes</mtext>}}$ is still valid with a good approximation.     

Le théorème de réduction de Marsden-Weinstein en géométrie cosymplectique et de contact

We show that the classical Marsden-Weinstein Reduction theorem for Hamiltonian systems with symmetries is still true for contact manifolds and cosympletic manifolds (i.e. canonical manifolds in the sense of A. Lichnerowicz).

In fact, we precise the notion of transitive almost contact structure, which enables us to consider the cosymplectic geometry as a limit of the contact geometry when a certain parameter goes to zero. This point of view unifies both theories.

However, we have to give two distinct proofs for the contact Reduction theorem and the cosymplectic one.     

Influence des parametres experimentaux sur la restitution du sinus de la phase en interferometrie

Combination of phase-modulation interferometry and scanning of the object is capable of restoring the sine of the phase everywhere in the object field. So, information on the direction of the surface relief is obtained. The influences of the analysing surface characteristics and of the process of scanning are studied.     

Determination de la longueur de covariance d'une surface rugueuse par l'etude de la diffusion residuelle a l'infini

We propose a simple method for directly measuring the correlation length of a slightly rough surface by using the residual scattered light. As in a previous work about strong diffusors, we use the experimental results to discuss the validity of Beckmann's theory on surface scattering, now in the case of weak diffusors.     

Experiences sur l'anisotropie de la resistance de surface des supraconducteurs pres de Hc3

In this paper we present some experimental results in the anisotropy of the surface resistance near H_c3. The materials used in this work have values of κ between 1.2 and 4.6. The results seem to indicate that the actual theories are incomplete due to the fact that the influence of the κ parameter is not sufficiently taken into account.     

Influence des impuretes et de l'inhomogeneite d'un plasma sur la mesure de sa temperature electronique

The effect of impurities on soft X-ray continuum radiation emitted from a high-temperature deuterium plasma has been studied. The results of these calculations are useful in the determination of the electronic temperature of a laser-created plasma. Such a plasma is inhomogenous and contains impurities.     

Influence de la teneur en halogene sur les proprietes cathodochromiques des sodalites

The influence of the preparative methods upon the number of vacancies in sodalites Na_4-x(AlSiO₄)₃Br_1-x (0.07 ? x ? 0.86) was investigated. A relation has been found between the bromine content and the number of optically erasable F centers induced by an electron beam. Conversely to some previous hypotheses it is possible to conclude that the halogen is the electron donor.     

Effets d'irradiation sur les proprietes magnetiques des alliages de fer-nickel dans la region invar

We have undertaken the irradiation of iron-nickel alloys of 30, 32, 35 and 40% nickel content to study its influence on the magnetic properties of invar. The initial results obtained from measurements of the magnetization and from the Mössbauer effect, show that electron irradiation could lead to the appearance of an ordered phase.     

Étude théorique de la diffusion quasi-libre des pions sur les noyaux

The experimental results of the reaction ¹²C(π⁺, π⁺ p)¹¹B at about 130 MeV can be explained satisfactorily by using a modified distorted wave impulse approximation. The strong inelasticity in the elastic channel at these energies makes the knock-out reaction essentially peripheral. We show that under these circumstances the knock-out reaction can be used to obtain information about the off-shell pion-nucleon scattering amplitude. Future experiments in this direction are suggested. We have introduced an invariant half-off-shell pion-nucleon scattering amplitude and have re-examined the DWIA method in a relativistic way.     

Distribution Radiale de la Densité des Atomes Métastables dans les Plasmas Produits par un Champ Electrique Continu ou de Haute-Fréquence

The radial density distribution of metastable Ar(³P₂) and resonant Ar(¹P₁) atoms is determined experimentally in two types of electrical discharges of cylindrical shape: the positive column plasma of a DC discharge and the plasma produced by an electromagnetic surface wave. The exitation and deexcitation rates for Ar(³P₂) by electron collisions are determined as a function of radius from the measured radial population density profile using a population density balance equation. These rate coefficients are obtained for various electron density values on the axis. The published values for these coefficients in the positive column plasma assume that they are independent of the discharge current. In this work, it is shown that these coefficients actually decrease as the electron density increases. In a more general way, the results obtained indicate that the examination of the radial density distributions of exited atoms is a powerful method for determining the kinetics of their creation and destruction.     

Interprétation de la susceptibilité magnétique de l'oxysulfure de samarium par un modèle de champ cristallin

The paramagnetic susceptibility of polycrystalline samarium oxysulfide has been measured between 3° and 300°K. The data are interpreted with an approximation to the crystal potential of the form

V_c = _JV₂⁰O₂⁰ + β_JV₄⁰O₄⁰ + β_JV₄³O₄³

and correction taking into account exchange is made. The energy levels and crystal fields parameters have been calculated. Fluorescence studies of Gd₂O₂S: Sm³⁺ and Y₂O₂S: Sm³⁺ have confirmed these results.     

Étude par la diffraction des électrons lents et la spectroscopie auger de l'adsorption du soufre sur le platine

The adsorption of sulphur on the (111), (100) and (110) faces of platinum has been studied by LEED and Auger spectroscopy. By the combined use of radioactive S³⁵ the contents of the surface unit meshes were determined “in situ” for each state of adsorption. On the (111) face one observes a preliminary adsorption with localization of sulphur atoms at sites of maximum coordination of the metal. At higher pressures and temperatures, S-S distance contracts and a compact hexagonal arrangement, with sulphur atoms outside sites, is obtained. The thermal stability of the various structures was studied as a function of sulphur coverage. During adsorption on the (100) and (110) faces, two steps may be distinguished: the first one seems to correspond to an adsorption in sites, the second corresponds to the formation of a two-dimensional compound whose square mesh is slightly different on the two faces.     

Glissement de gouttes de liquide sur des solides mous

Viscoelastic braking due to the motion of the wetting ridge during spreading of a liquid drop on a soft, viscoelastic solid is now established in axisymmetric conditions where only capillary forces cause motion of the triple wetting (or dewetting) line. We consider here preliminary results where this same phenomenon of slowing down prevents rapid flow of the liquid on an inclined elastomeric plane.     

Décomposition du fibré des spineurs d''une variété spin Kähler-quanternionenienne sous l''action de la 4-forme fondamentale

On a spin quaternionic-Kähler manifold M^4m, we give the spectral decomposition of the spin bundle the action of the fundamental 4-form Ω. Moreover, we compute the eigenvalues of Ω which, in the compact case, play an essential role in the problem of estimating the eigenvalues of the Dirac operator. The proof is based on the decomposition of the spin representation into irreducible components under the action of the group Sp(1) × Sp(m). We show that this algebraic results induces a Whitney decomposition of the spin bundle which, when restricted to the fibres, is the spectral decomposition under the action of Ω.     

Influence des marches atomiques sur le transport de matière à la surface du nickel

Surface atomic transport on Ni was measured by mass transport technique on a sinusoidal profile. One of the studied surfaces was within 15' of a singular (001) orientation. Others were vicinal surfaces. Kinetic damping coefficients $\text{1}\text{τ}$ are shown to be dependent on the profile parameters, i.e. of the density n_tot, of all the monoatomic steps and also of the density σ_c of kinks of the monoatomic steps. If the parameter describes the random motion of adatoms on isolated terraces and if α and k are two coefficients linked to adsorption/emission processes from steps and kinks, a sinusoidal profile with 5 μm periodicity obeys to the relation: $\text{1}\text{τ}\text{= (}\text{1}\text{τ}\text{)}{}_{\mathrm{T}}\text{[1+αn}{}_{\mathrm{tot}}{}^2\text{(1+ kσ}{}^2{}_{\mathrm{c}}\text{)]}$. This result demonstrates the importance of surface atomic structure which has been neglected in Mullins' theory, which may be non-negligible in all processes where surface mass transport is involved.     

Déformations covariantes sur les orbites polarisées d''un groupe de Lie

We prove the existence of covariant star-products on the orbits of the coadjoint representation of a Lie group which admits polarisations.