Elastic properties of TeO2-B2O3-Ag2O glasses.

A series of glasses [(TeO2) x (B2O3)1−x ]1−y [Ag2O] y with x = 70 and y = 10, 15, 20, 25 and 30 mol% were synthesised by rapid quenching. Longitudinal and shear ultrasonic velocity were measured at room temperature and at 5 MHz frequency. Elastic properties, Poisson's ratio, microhardness, softening temperature and Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental results indicate that the elastic constants depend upon the composition of the glasses and the role of the Ag2O inside the glass network is discussed. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Comparison between the experimental elastic moduli data obtained in the study and the calculated theoretically by the mentioned above models has been discussed

Propagation et diffraction d'une onde electromagnetique dans des structures aperiodiques

SIGLECNRS TD 14957 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Scattering by anisotropic rough layered 2D interfaces

International audienceWe propose a statistical study of the scattering of an incident plane wave by a stack of two two-dimensional rough interfaces. The interfaces are characterized by Gaussian height distributions with zero mean values and Gaussian correlation functions. The electromagnetic fields are represented by Rayleigh expansions, and a perturbation method is used for solving the boundary value problem and determining the firstorder scattering amplitudes. For slightly rough interfaces with a finite extension, we show that the modulus of the co- and crosspolarized scattering amplitudes follows a Hoyt law and that the phase is not uniformly distributed. For interfaces with an infinite extension, the modulus follows a Rayleigh law and the phase is uniformly distributed. We show that these results are true for correlated or uncorrelated interfaces and for isotropic or anisotropic interfaces

Scattering from a slightly rough chiral surface: analysis with the small perturbation method and the small slope approximation

International audienceWe study the scattering of a linearly polarized electromagnetic plane wave by a two-dimensional random slightly rough surface separating the vacuum from a chiral medium. We implement the first-order small perturbation method (SPM) and the first-order small slope approximation (SSA) and determine the analytical expressions of the coherent and incoherent intensities. The effects of chirality on the polarization of the wave scattered within the vacuum are analyzed. The coherent intensity has a cross-polarized component as well as the incoherent intensity in the incidence plane. We show that there are configurations for which a total polarization coupling occurs with the co-polarized incoherent intensity equal to zer

Statistics of the Stokes parameters for the signal scattered by layered structures with an arbitrary number of slightly rough interfaces

International audienceHorizontally stratified structures are commonly used to represent naturally occurring structures, such as soils. The electromagnetic signature of such a medium illuminated by a radar and the polarization state of the scattered wave are fully determined by the knowledge of the four Stokes parameters. In this paper, we determine the statistics of the four Stokes parameters for the signal scattered by layered structures with an arbitrary number of slightly rough interfaces. The rough interfaces are realizations of second-order stationary centered Gaussian stochastic processes and the layered structure is illuminated by an elliptically polarized monochromatic wave. The zenithal and azimuthal components of the far scattered electric field are derived from the first-order small perturbation method. The derivation leads to a multivariate Gaussian model for the underlying complex scattered amplitudes and we establish the closed-form expressions of the probability density function, the cumulative density function and the first- and second-order moments for the four Stokes parameters. For an observation direction outside the incidence plane, we establish the condition on the incidence wave parameters for which the zenithal and azimuthal components are uncorrelated. For an air / snow cover / frozen soil / unfrozen soil structure, we analyze the marginal probabilities and validate the theory by comparison with Monte-Carlo simulations. More generally, when the two complex components of the field scattered by the illuminated zone are Gaussian random variables, these statistics offer possibilities for in-depth investigating the polarization of scattering processes from random media

Multilook Intensity Ratio Distribution for 3-D Layered Structures with Slightly Rough Interfaces

International audienceWe derive the statistics for the multilook intensity ratio for a multilayered medium bounded by randomly rough surfaces. Calculations are carried out in the context of the first-order small perturbation method and assume slightly rough surfaces of infinite extent and centered Gaussian height distributions. We show that the probability distributions for the co-polar and cross-polarized intensity ratios for n-look data are functions of three parameters and that the mean exists for n > 1 and the variance for n > 2 The obtained theoretical expressions are verified by comparison with Monte-Carlo results

Statistics of the Stokes parameters for multilook signals scattered by layered structures with slightly rough random interfaces

International audienceThe polarization state of waves scattered from multi-layered structures with randomly rough boundaries is given by the Stokes vector and its four components. Polarimetric radars use multilook processing to reduce statistical fluctuations by spatially averaging the scattered signals. In this paper, we obtain and express in closed-form the probability density function, the cumulative density function, the expected value and the variance for each Stokes parameter in the multilook case. The slightly rough boundaries are realizations of second-order stationary centered Gaussian bi-dimensional spatial random processes and the layered structure is illuminated by a monochromatic plane wave. The zenithal and azimuthal components of the far scattered electric field are obtained from the first-order small perturbation method. The theory leads to a multivariate Gaussian model. Finally, we obtain a universal function for the probability distribution for the last three Stokes parameters. Numerical simulations are performed and coincide with the theoretical derivations. For a ground snow system represented by three interfaces air / snow cover / frozen soil / unfrozen soil, we obtain the marginal probabilities and compare the theoretical results with Monte-Carlo simulations. We show that the marginal probability distributions for multilook data are very different from those for single-look returns. Some features of coherent phenomena are observed since multilook processing reduced statistical fluctuations

Loi de probabilité du rapport des intensités en approche multivisée pour des milieux stratifiés à interfaces faiblement rugueuses

International audienceNous déterminons l'expression analytique de la loi de probabilité du rapport des intensités diffusées par un milieu stratifié présentant deux interfaces faiblement rugueuses éclairé par une onde plane électromagnétique. Les formules obtenues sont valides pour des intensités en polarisations directes et croisées et en approche simple visée et en multivisées. Les calculs sont menés dans le cadre de la méthode des petites perturbations à l'ordre 1 et suppose que les scènes éclairées sont d'extensions infinies et que les interfaces présentent des distributions des hauteurs gaussiennes. Nous montrons que pour les signatures électromagnétiques basées sur plus de deux visées, la loi de probabilité a une moyenne finie et une variance finie. Les lois de probabilité théoriques sont validées par comparaison avec des histogrammes issus de tirages de Monte-Carlo. Mots clés-Rapport d'intensités, amplitude de diffraction, simple visée, multivisée, densité de probabilité, milieu stratifié, surface aléatoire, méthode des petites perturbations

Universal Statistics for the Three Normalized Stokes Parameters for Multilook Data— Application to Signals Scattered by Layered Structures With Slightly Rough Interfaces

International audienceThe polarization state of electromagnetic (EM) waves scattered from a random medium is given within the Poincaré space by the three normalized Stokes parameters. Polarimetric radar data are frequently multilook processed to reduce signal fluctuations by spatially averaging the scattered signals. In this article, a universal probability law is established, applicable to each of the three normalized Stokes parameters for multilook configurations and valid for a multivariate Gaussian model. As an application case, we consider the scattering of a polarized monochromatic plane wave from a stratified ground with an arbitrary number of slightly rough interfaces. Resulting expressions are studied for a snowy ground in L-band and are validated by comparison with Monte Carlo simulations