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Georges Debrégeas





CNRS Chargé de Recherche

Laboratoire de Physique Statistique
Ecole Normale Supérieure / CNRS / UPMC
24 rue Lhomond 75231 Paris cedex 05 France

Tel : +33 (0)1 44 32 35 90 33

Fax : +33 (0)1 44 32 34 33

Email : georges.debregeas [at] lps.ens.fr

Short CV

 

Habilitation à Diriger les Recherches (HDR) - Georges Debrégeas

 

Research Topics

 

Tactile perception -

 

The skin plays a major role in the sense of touch. It conveys information from the external world to the embedded mechanoreceptors. In doing so, it filters and shapes the tactile information thus effectively participating in the signal processing and tactile encoding processes. We investigate the mechanism of tactile transduction using a bioimimetic tactile sensor. This device, based on MEMS microchips embeded in an elastomeric skin, mimics the operation of mechanoreceptors within the fingertip. It allows us to probe how the transduction of tactile information depends on physiological parameters (such as the presence of epidermal ridges) as well as exploratory conditions (applied load for instance).

We have recently started a collaboration with Dan Shulz group in CNRS-Gif to compare peripheral tactile perception in humans and rats. In rodents, tactile perception is mediated principally by the deformation of the long facial whisker hair which are swept across the substrates. This project will associate optical measurements of whiskers deformation measurements in anesthized rats, as well as neurophysiological measurements in the in the cortical areas receiving sensory information from the whiskers.

References

 

 

Solid friction is an unusually longstanding problem in physics, whose difficulty mainly originates from the coupled energy dissipation mechanisms occurring at multiple length scales. Indeed, the roughness of the contacting surfaces implies that the contact between two macroscopic solids is generally made up of a myriad of micro‐contacts which are sheared continuously and renewed when both surfaces slide past one another.

We probe the local mechanisms of friction in a macroscopic sliding contact between an elastomer and a rigid surface. In addition to their technological importance for friction applications, highly deformable systems such as elastomers offer the possibility of performing in situ optical measurements of friction induced deformations. We have developed imaging techniques to measure the spatially resolved stress distribution within the contacts, down to the micrometer scale. We use surfaces roughened b y mechanical abrasion or patterned with well controlled geometrical features obtained through soft micro‐photolithographic techniques.

References

 

Foam rheology -

 

images and reconstructed profiles of two soap bubbles in contact. By varying the distance between the tubes supporting the bubbles, we probe the dynamical adhesion properties of the two bubbles.Liquid foams are concentrated dispersions of gas bubbles in a liquid matrix. They constitute a convenient model system for a larger class of materials, often refered to as soft glassy systems, which includes concentrated emulsions, colloidal suspensions, dense granular packings, etc. Because the thermal energy is effectively zero, in the absence of external forcing such systems are trapped in metastable configurations. As a consequence, they exhibit a finite yield stress below which the material responds elastically. When a larger stress is imposed, it triggers a series of plastic events which release the applied stress, yielding a macroscopic flow.

We have performed a series of experiments on 2D foams. This system, which  consistis of a monolayer of bubbles confined between two horizontal plates, allows for a direct observation of ~1000 individual bubbles. It allowed us to  precisely characterize the bubble-scale dynamics of motion and deformation during a shearing process, and in particular to understand the shear-banding instability. This experiment has been reinforced by numerical simulations of a large collection of bubbles under plain shear using Surface Evolver.

More recently, we have developed an experiment to measure adhesion forces between two soap bubbles (see figure). These local adhesive properties can be related to the macroscopic response of the foam under rapid shearing.

References

 

PhD thesis :

 

Propriétés adhésives entre deux bulles de savon


  • Julien Scheibert - defended 06/07 - now in Oslo University, Norway
Mécanique du contact aux échelles mésoscopiques


Désordre et plasticité dans les milieux divisés : mousses et matériaux granulaires


Publications :

 

Contact mechanics and solid friction -


  • Texture-induced modulations of the friction force: The fingerprint effect E. Wandersman, R. Candelier, G. Debrégeas and A. Prevost, Phys. Rev. Lett. 107, 164301 (2011) (PDF)
  • Mécanique du Contact Rugueux et Perception Tactile J. Scheibert, G. Debrégeas et A. Prevost, Reflets de la physique n°16, octobre 2009, pp. 17-19 (www.sfpnet.fr) (PDF)

  • Stress Field at a Sliding Frictional Contact: Experiments and Calculations J. Scheibert, E. Katzav, M. Adda-Bedia, A. Prevost et G. Debrégeas, in press, J. Mech. Phys. Solids doi:10.1016/j.jmps.2009.08.008  (PDF).

  • Micro-slip Field at a Rough Contact Driven Towards Macroscopic Sliding, J. Scheibert, G. Debrégeas et A. Prevost (Preprint).

  • Experimental Evidence of Non-Amontons Behaviour at a Multi-contact Interface, J. Scheibert, A. Prevost, J. Frelat, P. Rey and G. Debrégeas, Europhys. Lett. 83, 34003 (2008) (PDF).


Tactile perception -


  • Pre-neural texture-to-whisker transduction in rats: a predictive model of whisker deflections. Yves Boubenec, Daniel E. Shulz and Georges Debrégeas, submitted (PDF)
  • The role of exploratory conditions in bio-inspired tactile sensing of single topological features. Raphaël Candelier, Alexis Prevost and Georges Debrégeas, Sensors 11, 7934-7953 (2011) (abstract, PDF)

  • Effect of fingerprints orientation on skin vibrations during tactile exploration of textured surfaces. Alexis Prevost, Julien Scheibert and Georges Debrégeas, Communicative and Integrative Biology 2(5) (2009) (abstract, PDF)

  • The role of fingerprints in the coding of tactile information probed with a biomimetic sensor, J. Scheibert, S. Leurent, A. Prevost et G. Debrégeas, Science 323 1503-1506 (2009) (abstract, PDF)

(see also : Nature news, Science news, Nature Research highlights, Science signaling, Nature Methods, analytical chemistry, science news magazine, Atten. Percept & Psych.)

 

Foam rheology -


  • Dissipation in a Sheared Foam: From Bubble Adhesion to Foam Rheology, S. Besson, G.  Debrégeas, S. Cohen-Addad and R. Höhler, Phys. Rev. Lett. 101, 214504(2008) (PDF).

  • Statics and dynamics of adhesion between two soap bubbles. S. Besson and G. Debrégeas, Eur. Phys. J. E 24, 109-117 (2007) (PDF)

  • Quasi-static rheology of foams. Part 1. Oscillating strain, A. Kabla and G. Debrégeas, Journal of Fluid Mechanics, 587 (2007), pp 23-44(PDF).

  • Quasi-static rheology of foams. Part 2. Continuous shear flow, A. Kabla, J. SCcheibert and G. Debrégeas, Journal of Fluid Mechanics 587 (2007), pp 45-72(PDF)

  • Local Stress Relaxation and Shear Banding in a Dry Foam under Shear. A. Kabla and G. Debrégeas, Phys. Rev. Lett. 90(25) 258303 (2003) (PDF)

  • Deformation and Flow of a Two-Dimensional Foam under Continuous Shear. G. Debrégeas, H. Tabuteau, and J.-M di Meglio, Phys. Rev. Lett. 87(17) 178305 (2001) (PDF)


Dynamics of granular systems and soft glasses -


  • X-ray observation of micro-failures in granular piles approaching an avalanche, A. Kabla, G. Debrégeas, J.-M. di Meglio and T. J. Senden, Europhys. Lett. 71 932-937 (2005) (PDF)

  • Contact Dynamics in a Gently Vibrated Granular Pile. A. Kabla and G. Debrégeas, Phys. Rev. Lett. 92(3), 035501(2004) (PDF)

  • Partial rejuvenation of a colloidal glass. F. Ozon, T. Narita, A. Knaebel, G. Debrégeas, P. Hébraud and J.-P. Munch, Phys. Rev. E 68, 032401 (2003) (PDF)

  • Rheology of soft glassy materials. D. Bonn, P. Coussot, H. Huynh, F. Bertrand and G. Debrégeas, Europhys. Lett., 59 (5), pp. 786-792 (2002) (PDF)

  • A self-similar model for shear flows in dense granular materials. G. Debrégeas and C. Josserand, Europhys. Lett., 52 (2), pp. 137-143 (2000) (PDF)

  • Signatures of granular microstructure in dense shear flows. D. Mueth, G. Debregeas*, G. Karczmar, P. Eng, S. Nagel & H. Jaeger, Nature 406, 385-388 (2000) (pdf)


 

    Hydrodynamics of thin films, wetting and capillarity -

 

  • Stick-slip instability for viscous fingering in a gel. N. Puff, G. Debrégeas, J.-M. di Meglio, D. Higgins, D. Bonn, C. Wagner, Europhys. Lett. 58(4), p. 524 (2002) (pdf)

  • The Life and Death of "Bare" Viscous Bubbles. G. Debrégeas, P.-G. de Gennes, F. Brochard-Wyart, Science 279, 1704 (1998) (pdf)

  • Dewetting of Supported Viscoelastic Polymer Films: Birth of Rims. F. Brochard-Wyart, G. Debrégeas, R. Fondecave, and P. Martin, Macromolecules, 30(4) pp 1211-1213 (1997)

  • Nucleation radius and growth of a liquid meniscus. G. Debrégeas, F. Brochard-Wyart,  Journal of colloid and interface science 190(1) pp.134-141(1997)

  • Spreading of viscous droplets on a non viscous liquid F. Brochard-Wyart, G. Debrégeas, P.-G. de Gennes,  Colloid and polymer science 274(1) pp.70-72 (1996)

  • Experimental Study of the Spreading of a Viscous Droplet on a Nonviscous Liquid. L. Bacri, G. Debrégeas, and F. Brochard-Wyart, Langmuir 12(26), pp 6708-6711 (1996)

  • Viscous Bursting of Suspended Films. G. Debrégeas, P. Martin and F. Brochard-Wyart, Phys. Rev. Lett. 75(21) 3886 (1995) (pdf)


Talks (ppt)

 

"The role of fingerprints in tactile perception probed with a biomimetic sensor", ENS Physics Departement seminar,  2009 (PPT)

 


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