Spotting evidence of directed percolation

Nov 17, 2009
This is an illustration of directed percolation in 1+1 dimensions: Activity percolates through open bonds (red lines), activating nearest neighbors and giving rise to a cluster of activity. Credit: Illustration: Alan Stonebraker

A team of physicists has, for the first time, seen convincing experimental evidence for directed percolation, a phenomenon that turns up in computer models of the ways diseases spread through a population or how water soaks through loose soil. Their observation strengthens the case for directed percolation's relevance to real systems, and lends new vigor to long-standing theories about how it works. Their experiment is reported in Physical Review E and highlighted with a Viewpoint in the November 16 issue of Physics.

While directed percolation models are handy for describing things as diverse as sand flow and dynamics in cells, no one had managed to find clear, reproducible evidence of the phenomenon in a controlled experiment.

Now a team of physicists from the University of Tokyo, in Japan, and CEA-Saclay, in France, have seen directed percolation in a layer of liquid crystals about a hundredth of a millimeter thick sandwiched between two glass plates connected to electrodes. When they increased the voltage above a threshold, they saw gray spots appearing. A spot could disappear spontaneously but also cause spots to pop up around it, similar to the way a virus can die in one individual after infecting people nearby. The team showed that the system exhibited many of the mathematical hallmarks of directed percolation—convincing evidence that the long-theorized phenomenon occurs in real systems.

More information: Experimental realization of directed percolation criticality in turbulent liquid crystals, Kazumasa A. Takeuchi, Masafumi Kuroda, Hugues Chaté, and Masaki Sano, Phys. Rev. E 80, 051116 (2009) - Published November 16, 2009, Download PDF (free)

Source: American Physical Society

Explore further: The unifying framework of symmetry reveals properties of a broad range of physical systems

add to favorites email to friend print save as pdf

Related Stories

Making monster waves

Oct 19, 2009

Rogue waves -- giant waves that spring up suddenly and tower over the seas around them—have inspired physicists to look for an analogue in light. These high-intensity pulses can cross large distances without ...

Slipper-shaped blood cells

Oct 26, 2009

Red blood cells, which make up 45 percent of blood, normally take the shape of circular cushions with a dimple on either side. But they can sometimes deform into an asymmetrical slipper shape. A team of physicists ...

Flipping a photonic shock wave

Nov 02, 2009

A team of physicists has directly observed a reverse shock wave of light in a specially tailored structure known as a left-handed metamaterial. Although it was first predicted over forty years ago, this is ...

Growing geodesic carbon nanodomes

Oct 12, 2009

Researchers analyzing the assembly of graphene (sheets of carbon only one atom thick) on a surface of iridium have found that the sheets grow by first forming tiny carbon domes. The discovery offers new insight ...

Recommended for you

What time is it in the universe?

Aug 29, 2014

Flavor Flav knows what time it is. At least he does for Flavor Flav. Even with all his moving and accelerating, with the planet, the solar system, getting on planes, taking elevators, and perhaps even some ...

Watching the structure of glass under pressure

Aug 28, 2014

Glass has many applications that call for different properties, such as resistance to thermal shock or to chemically harsh environments. Glassmakers commonly use additives such as boron oxide to tweak these ...

Inter-dependent networks stress test

Aug 28, 2014

Energy production systems are good examples of complex systems. Their infrastructure equipment requires ancillary sub-systems structured like a network—including water for cooling, transport to supply fuel, and ICT systems ...

Explainer: How does our sun shine?

Aug 28, 2014

What makes our sun shine has been a mystery for most of human history. Given our sun is a star and stars are suns, explaining the source of the sun's energy would help us understand why stars shine. ...

User comments : 0