Slow avalanches oscillate in new experiment

Oct 25, 2012 by Anne Ju
A microcrystal array for which extremely small forces and motions are tracked with atomic-scale precision to probe and model the avalanche response at slow driving rates. Within the image, a view of the San Andreas fault, where such effects can be seen in the world. Credit: Stefanos Papanikolaou

"Avalanches"—the crackling behavior of materials under slowly increasing stress, like crumpling paper or earthquakes—may have a novel facet previously unknown, say Cornell researchers.

A study led by former postdoctoral associate Stefanos Papanikolaou employs both theory and experiment to describe never-before-seen oscillatory behavior of microcrystal plastic bursts at very small scales, under highly controlled conditions.

The study, co-authored by James Sethna, professor of physics, is featured on the cover of the journal Nature, Oct. 25.

The experiments were done by co-author Dennis M. Dimiduk of the Air Force Research Laboratory, using microfabricated nickel microcrystals. They recorded individual microcrystals' behavior as they were slowly crushed, causing microscale avalanches. What emerged was a new power law that determined the probability of crackles of different sizes.

Analyzing the data, Papanikolaou and found that slowing the crushing of microcrystals led to an of avalanches themselves—large then small, in a repeating pattern, and with time periods between the large events roughly periodic. This was different from previous experiments and theories of crackling noise and avalanches.

Avalanches have previously been known to happen at random times following a power law behavior, in that the number of avalanches is given by a power of the avalanches' size. The new experiments not only display oscillations, but also give a markedly different power law—a "new route to criticality, with a perpetual cycle leading to the emergence of self-similarity," Sethna said.

They explain and model the oscillations and this new law by including other smooth "oozing" processes that compete with the avalanches; oozing becomes important when the are crushed nearly as slowly as they ooze.

It's a theory the scientists think could apply to many intermittent that become oscillatory as "relaxation" increases—earthquakes deep in the earth crust, for one, but even less conventional ones—like the low-frequency oscillations of brain waves during sleep.

"We could maybe open a window to actually starting to model accurately the emergence of such phenomena in large collections of neurons," Papanikolaou said.

Explore further: Experiment with speeding ions verifies relativistic time dilation to new level of precision

Related Stories

Physicists study mechanics of 'crackling'

Jan 27, 2011

(PhysOrg.com) -- Everywhere around us, things "crackle" -- from Rice Krispies in a puddle of milk, to crumpled pieces of paper, to the Earth's crust from earthquakes. Physics is helping us understand what this familiar noise ...

Wired for avalanches -- and learning

May 02, 2012

The brain's neurons are coupled together into vast and complex networks called circuits. Yet despite their complexity, these circuits are capable of displaying striking examples of collective behavior such as the phenomenon ...

Engineers model the threat of avalanches

Jul 25, 2012

(Phys.org) -- Snow avalanches, a real threat in countries from Switzerland to Afghanistan, are fundamentally a physics problem: What are the physical laws that govern how they start, grow and move, and can theoretical modeling ...

Recommended for you

How Paramecium protozoa claw their way to the top

Sep 19, 2014

The ability to swim upwards – towards the sun and food supplies – is vital for many aquatic microorganisms. Exactly how they are able to differentiate between above and below in often murky waters is ...

User comments : 0