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Predicting Extreme Events
Experiments using electronic circuits as models of complex systems show that a special class of extreme, catastrophic events (“dragon kings”) can be predicted and prevented.
In many complex systems, catastrophic events (such as financial crises, earthquakes or power blackouts) are assumed to be unpredictable. But a study by researchers from Brazil, Switzerland and the US now suggests a special class of extreme events may be forecasted. Following a recently proposed theory, the authors argue extreme events can be of two types: 1) Events generated through the same mechanisms as non-extreme events, but amplified to a larger scale. 2) “Dragon Kings”: large-scale events (“kings”) that belong to a completely different species (“dragons”), thus carrying special signatures that could help identify them while they develop. The authors show that an experimental model of complex systems based on coupled electrical oscillators exhibits extreme events (large deviations from the normal circuit behavior) that can be classified as Dragon Kings and can be reliably predicted and prevented. The approach may suggest similar strategies for more complex real-world applications.
* Hugo LD de S Cavalcante (contact author) et al, “Predictability and suppression of extreme events in a chaotic system”, Physical Review Letters (expected publication date: Oct 30)
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Atomic Butterflies
Researchers have engineered a lattice of cold atoms that could be used to see Hofstadter’s butterfly – a beautiful, butterfly-shaped structure in the atoms’ energy spectrum.
In 1976, Douglas Hofstadter (the author of “Gödel, Escher, Bach”) predicted that electrons experiencing both the periodic electric field in a crystal and a magnetic field would have an energy spectrum with a beautiful fractal shape reminiscent of a butterfly. The effect has only been seen in a small number of materials because large magnetic fields are needed. Two independent teams in Germany and the US have now engineered an analogous system, based on cold atoms trapped in the lattice created by the superposition of several lasers. With additional lasers, they forced the atoms to undergo circular motion, mimicking the motion of electrons in a magnetic field. These atomic systems, essentially free of defects, realize the physics described by Hofstadter and, at colder temperature, may provide the cleanest view of Hofstadter’s butterfly.
* M Aidelsburger, Julio T Barreiro (contact author) et al, “Realization of the Hofstadter Hamiltonian with ultracold atoms in optical lattices”, Physical Review Letters (expected publication date: Oct 28)
** H Miyake, Colin J Kennedy (contact author), Wolfgang Ketterle et al, “Realizing the Harper Hamiltonian with laser-assisted tunneling in optical lattices”, Physical Review Letters (expected publication date: Oct 28)
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Surfaces that Control Gas Flow
Researchers at Virginia Tech have demonstrated a new method for controlling how gas flows through a narrow channel. The scheme works thanks to a thin organic film whose roughness depends on temperature. The researchers deposited the film on two nearly-touching glass surfaces and measured the flow of gas in the channel between them. Heating the film made it smoother and thus eased the gas flow. The results indicate that raising the temperature from 18 C to 40 C could double the flow rate in a micron-wide tube. The authors suggest the principle could be used to control the flight of microrobotic aircraft or to throttle the flow of gas or fluids in micron-sized “labs-on-a-chip” for biological and chemical applications.
* Dongjin Seo, William A Ducker (contact author), “In-Situ Control of Gas Flow by Modification of Gas–Solid Interactions”, Physical Review Letters (expected publication date: Oct 25)
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Journal articles and preprints are available to journalists on request.
Matteo Rini, PhD
Deputy Editor, Physics
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