Catégorie : en

M. N. Ichchou, B. Jemai, L. Bellon and L. Jezequel, Smart Materials and Structures 10 1095-1099 (2001)

doi: 10.1088/0964-1726/10/5/401

This paper proposes an experimental mock-up which aims to validate a new concept of a piezo-rubber mount. This new concept is based upon the combination of an electrically-monitored active piezoelectric block with a passive rubber mount. An adaptive control law is then used for an off-line identification and control of the force transmissibility. The new hybrid mount is shown to be very efficient and significantly improves the transfer between disturbances and receiving components.

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L. Bellon, S. Ciliberto and C. Laroche, Europhysics Letters 53 511-517 (2001)

doi: 10.1209/epl/i2001-00182-9

The relationship between the conductivity and the polarization noise is measured in a colloidal glass as a function of frequency in the range 1 Hz-40 Hz. It is found that at the beginning of the transition from a fluid-like sol to a solid-like colloidal glass the fluctuation-dissipation relation is strongly violated. The amplitude and the persistence time of this violation are decreasing functions of frequency. At the lowest frequencies of the measuring range it persists for times which are about 5% of the time needed to form the colloidal glass. This phenomenology is quite close to the recent theoretical predictions done for the violation of the fluctuation-dissipation relation in glassy systems.

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L. Bellon, S. Ciliberto and C. Laroche, Europhysics Letters 51 551-556 (2000)

doi: 10.1209/epl/i2000-00368-1

Low-frequency dielectric measurements on plexiglass (PMMA) show that cooling and heating the sample at constant rate give a hysteretic dependence on temperature of the dielectric constant ε. A temporary stop of cooling produces a downward relaxation of ε. Two main features are observed: i) when cooling is resumed ε goes back to the values obtained without the cooling stop ( i.e. the low-temperature state is independent of the cooling history); ii) upon reheating ε keeps the memory of the aging history ( Memory ). The analogies and differences with similar experiments done in spin-glasses are discussed.

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L. Bellon, L. Fourtune, V. Ter Minassian and M. Rabaud, Physical Review E 58 565-574 (1998)

doi: 10.1103/PhysRevE.58.565

We present a mechanism of limitation for the possible wave numbers above an instability threshold. This mechanism is experimentally investigated in the interfacial instability of directional viscous fingering in a finite system. It is shown experimentally to be controlled by the divergence of a phase-diffusion constant. Theoretically, this limitation on the low value of the accessible wave numbers is a consequence of the interaction between the fundamental and the first harmonic modes. The analysis of coupled amplitude equations demonstrates theoretically the existence of a divergence of a phase-diffusion constant when approaching the threshold of a parity-breaking instability.

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A. Garcimartin, A. Guarino, L. Bellon and S. Ciliberto, Physical Review Letters 79 3202-3205 (1997)

doi: 10.1103/PhysRevLett.79.3202

We present the data of a mode-I fracture experiment. The samples are broken under imposed pressure. The acoustic emission of microfractures before the breakup of the sample is registered. From the acoustic signals, the position of microfractures and the energy released are calculated. A measure of the clustering of microfractures yields information about the critical load. The statistics from energy measurements strongly suggest that the fracture can be viewed as a critical phenomenon; energy events are distributed in magnitude as a power law, and a critical exponent is found for the energy near fracture.

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