[Tracking dysplasia and congenital luxation of the hip].
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Hip Dislocation, Congenital↗
Biomedical subjects
M de Billy
Publications and source records attributed to M de Billy.
On the splitting of aspherical structure submitted to an acoustic polarized excitation.
We experimentally show how the deviations from spherical symmetry such as the inhomogeneity, the removal mass or the asphericity affect the frequency spectrum of a single elastic sphere. The recorded spectrograms point out the great influence of the polarization of the source on the splitting and the shift of the peaks. Qualitatively, the results are consistent with the data reported in Geophysics although the present study is concerned with a low degree and low- [Formula: see text] modes in contrast to those usually encountered in seismic investigations. From a practical point of view, this study suggests that Geophysics phenomena could be analyzed through spherical beads reproducing the imperfections encountered in the mantle and in the core of the earth.
Journal Article↗
Experimental study of sound propagation in a chain of spherical beads.
In this paper are described experimental observations which are concerned by the propagation of pulsed ultrasonic waves transmitted through a limited one dimensional periodic granular medium submitted to a static force. This study--which is limited to a time domain analysis--exhibits experimental results which depend on the polarization of the acoustic excitation. In the case of compressional excitation, spherical Rayleigh type surface waves propagate around the beads. In the case of shear excitation, the experimental recordings point out the existence of a very low signal, the frequency of which is equal to the cut-off frequency of the chain. Moreover it is established that the frequency value varies with the radius of the bead, the normal force applied to the beads, and the mechanical properties of the material.
Acoustics↗
Methods of analysis for backscattering from tissues.
Two techniques for tissue characterization by ultrasonic analysis are described. In the first, using narrow-band pulses, the angular variation I (theta) of the ultrasonic intensity back-scattered by vegetal or animal targets is analysed. We examine how it is possible to estimate the surface roughness and the average spatial periodicity d characteristic of the tissues, by calculating the Fourier transform or the autocorrelation function of I (theta). In the second technique the sample is insonified with a broadband pulse at a fixed angle. A value of the mean periodicity can be obtained directly from the frequency spectrum of the echo for tissues of fairly regular structure.
Animals↗