Synopsis: Gravity organizes sediment

Sedimenting particles subjected to periodic shear are used to demonstrate a link between self-organized criticality and nonequilibrium phase transitions.
Synopsis figure
Illustration: L. Corté et al., Phys. Rev. Lett. (2009)

Self-organized criticality (SOC), proposed by Per Bak, Chao Tang, and Kurt Wiesenfeld, is a property of dynamical systems that leads to scale-invariant behavior without the need to fine tune parameters to precise values as required in an ordinary phase transition. The ideas have been applied to study diverse phenomena ranging from the power-law distribution of earthquake intensities to forest fires and even biological evolution. SOC has inspired countless numerical and theoretical studies, but the few experimental characterizations such as liquid 4He near the superfluid transition, or rice piles, do not elucidate how criticality arises far from equilibrium.

In a recent work to appear in Physical Review Letters, Laurent Corté and collaborators from Mines-ParisTech, France, and New York University, Cornell University, and San Francisco State University, all in the US, report self-organized criticality in suspensions of sedimenting particles undergoing periodic shear. The new experiment builds on an earlier observation of a continuous phase transition between an absorbing state (at small shear rates and/or low concentrations) where particles return to their original positions after each shear cycle and an active state (in the opposite limit) where particle positions change randomly. Corté et al. use particles slightly denser than the surrounding fluid; in the absence of shear, a dense sediment forms at the bottom. Applying shear, the suspension is attracted to its critical state since, when the concentration is less than critical, particles are inactive and sediment, increasing the concentration, whereas for concentrations above critical, activity tends to spread the particles over a larger range of heights, reducing the density. This observation of SOC opens a new route to explore properties of out-of-equilibrium critical phenomena. – Ronald Dickman


Features

More Features »

Announcements

More Announcements »

Subject Areas

Statistical Physics

Previous Synopsis

Next Synopsis

Related Articles

Viewpoint: Squeezed Environment Boosts Engine Performance
Nanophysics

Viewpoint: Squeezed Environment Boosts Engine Performance

A tiny engine can surpass the Carnot limit of efficiency when researchers engineer the thermal properties of the environment. Read More »

Synopsis: Subway Stats
Statistical Physics

Synopsis: Subway Stats

A comparison of the arrival-time statistics of New York City’s subway trains indicates that some train lines may be more efficiently run than others. Read More »

Viewpoint: The Thermodynamic Cost of Measuring Time
Quantum Physics

Viewpoint: The Thermodynamic Cost of Measuring Time

A simple model of an autonomous quantum clock yields a quantitative connection between the clock’s thermodynamic cost and its accuracy and resolution. Read More »

More Articles