Publications

L. Bellon, L. Buisson, S. Ciliberto, F. Vittoz, Review of Scientific Instruments 73 3286-3290 (2002)

doi: 10.1063/1.1499210

In order to test the fluctuation-dissipation relation on rheological properties of soft materials, we built an experiment to measure thermally excited strain in a sample and compare it to the classical response to an external stress. The rheometer is based on a cylindrical Couette geometry. We use differential interferometry to achieve better than 1E-10 rad/root(Hz) sensitivity in angular position above 0.5 Hz. The forcing method, based on electrostatic interaction in a capacitor, generates torques comparable to that of thermal noise. Experiments on a calibrated silicon oil show good agreement between response and fluctuation measurements.

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L. Bellon and S. Ciliberto, Physica D-Nonlinear Phenomena 168 325-335 (2002)

doi: 10.1016/S0167-2789(02)00520-1

The validity of fluctuation dissipation relations (FDRs) in an aging system is studied in a colloidal glass during the transition from a fluid-like to a solid-like state. The evolution of the rheological and electrical properties is analyzed in the range 1-40 Hz. It is found that at the beginning of the transition the FDR is strongly violated in electrical measurements. 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 FDR in glassy systems. In contrast in the rheological measurements no violation of the FDR is observed. The reasons of this large difference between the electrical and rheological measurements are discussed.

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L. Bellon, S. Ciliberto, H. Boubaker and L. Guyon, Optics Communications 207 49-56 (2002)

doi: 10.1016/S0030-4018(02)01475-X

We present a new design of the Nomarski interferometer, which can measure displacements of several microns, with a resolution better than 1E-13 m/root(Hz). In the standard design this sensitivity can be achieved only within a 100 nm displacement range. One main advantage of this new set-up of the interferometer is the total independence of the measure sensitivity on the interferometer thermal drifts.

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L. Bellon, S. Ciliberto and C. Laroche, European Physical Journal B 25 223-231 (2002)

doi: 10.1140/epjb/e20020025

A new kind of memory effect oil low frequency dielectric measurements oil plexiglass (PMMA) is described. These measurements show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant epsilon. A temporary stop of cooling produces a downward relaxation of epsilon. Two main features are observed (i) when cooling is resumed epsilon 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 epsilon keeps the memory of all the cooling stops (Advanced memory). The dependence of this effect on frequency and oil the cooling rate is analyzed. The memory deletion is studied too. Finally the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.

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R. H. Hernandez, M. Vial, L. Bellon and C. Baudet,  in Instabilities and Nonequilibrium Structures IX, O. Descalzi, J. Martínez, S. Rica (Eds.), Kluwer Academic Publishers. Series: Nonlinear Phenomena and Complex Systems 9 195-205 (2004)

ISBN: 978-1-4020-1950-0

We report experimental measurements of the wake behavior of a thin flat plate submitted to an external harmonic forcing. Two slightly different configurations are examined. Classical hot wire measurements of the velocity field downstream the plate and sound scattering experiments of the near wake demonstrates that the flat plate wake displays a kind of inertial resonance when the inverse of the forcing frequency matches the flying time of fluid particles along the moving part of the plate.

Proceedings of the Ninth International Workshop on Instabilities and Nonequilibrium Structures, Viña del Mar, Chile, December 2001. 

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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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