The GRASP investigates the physical properties of disordered and fluctuating systems such as granular materials and complex fluids. The systems currently under investigations are : antibubbles, compaction of granular systems, bouncing droplets, dense bubble flows, fish tracking, foams in microgravity, ... The group has also developped many activities in physics education.
News
The Tibetan singing bowl [05/07/2011]
The Tibetan singing bowl is a type of standing bell originating from Himalaya. A singing bowl is played by striking or rubbing its rim with a wooden or leather-wrapped mallet. The sides and rim of the bowl then vibrate to produce a rich sound. When the bowl is filled with water, this excitation can cause crispation of the water surface that can be followed by more complicated surface wave patterns and ultimately the creation of droplets. We present an extensive investigation of the acoustics and the fluid dynamics of the bowl in a paper published in Nonlinearity journal (Recommended by D Lohse). A video of the Tibetan singing bowl is presented here.
A droplet made of water and oil, a water core and oil layer, is laid on a vibrating liquid surface. Above an acceleration threshold of the bath, the compound droplet periodically bounces on it. Above another threshold the droplet emulsifies. Tiny oil droplets coming from the oil layer enter in the water core producing a double emulsion. We can thus perform micro-emulsion in a droplet without touching it !
Here is a movie illustrating the emulsification. This movie won the 2nd Prize of the Gallery of Nonlinear Images videos contest at the APS March meeting in Pittsburg (USA) in 2009. The related publication was the most downloaded paper during two successive months in Chaos Journal.
The complete study of the mayonnaise droplet was published in Langmuir journal, here is a link to the paper.
Effect of an electric field on an intermittent granular flow [12/04/2010]
What is the effect of an electric field on the flowing properties of granular materials?
In a recent experimental study, we applied an high electric field on a granular material flowing through a silo. By this means, we are able to induce an interaction between grains that initially only interact with contact and frictional forces. We observed a transition of the geometry of the flow. Some flow intermittences are also induced. A regular article was recently accepted for publication in PRE. An open e-print version is already available on arXiv.
Droplets sliding on fibers [12/04/2010]
The behaviour of oil droplets released on nylon fibres has been investigated experimentally. Permanent regimes, transitions and instabilities are observed. An intersection between two fibres behaves like a diod that only let large droplets pass through.The droplet dynamics is rationalised thanks to scaling laws and differential equations.
This work has just been published in this issue of the European Physical Journal E (vol. 31 - 3, pp. 253-262, march 2010), and has been selected for the cover of the journal.
Faraday instability inside a newtork [22/03/2010]
Our video entitled "Cellular Faraday instability" won the first prize at the 2010 Gallery of NonLinear Images (GLNP) during the March APS Meeting. This experiment emphasizes the appearance of a collective behavior of adjacent cells experiencing Faraday instablity. A drastic change in the characteristic length is observed and the waves are spanding over the different cells. This new set of waves appears at the dual newtork length. You can see this video on the GNLP site at http://apps3.aps.org/gsnp/upload7/delon_mpeg1.mpg. More information on the university can also be found here.
What is the effect of an electric field on the flowing properties of granular materials?
Our video entitled "Cellular Faraday instability" won the first prize at the 2010 Gallery of NonLinear Images (