Daily Physics

Nanocluster Simulations Show Counterintuitive Results

In simulations involving collisions of nanoclusters, hundreds of atoms packed together into a single unit, an unexpected result has come to light: There is a non-zero probability that the nanoclusters will leave the collision with more energy than they started it with. Researchers Hisao Hayakawa, of Kyoto University, and Hiroto Kuninaka, of Chuo University in Tokyo, produced the computer modeling and have published results of their nanocluster collision simulations in March’s Physical Review E.

The system parameters were simple, with the few-hundred-atom nanoclusters moving at speeds of 3 to 5 m/s. While most nanoclusters were simulated to simply stick together or bounce apart with less-than-initial energy, a small number (~5%) were simulated to actually gain energy in collision! Another way to describe this is that the “restitution coefficient is larger than unity.”

This result would be incredible it it were to occur on a macro-scale - It would be breaking one of the fundamental laws of physics. However, at the micro-scale, one has to take the effect of having so few atoms and having the wavefunctions of these atoms so close together in to account. Also, this “super-rebound” effect has been observed in several systems.

This >1 restitution coefficient is achieved by random internal energy fluctuations found in each atom that makes up the nanoclusters. I would expect that when a large enough number of these internal energy fluctuations occur in roughly the same direction as the resultant motion, at the same time as the impulse is imparted from collision, the restitution coefficient has the greatest probability of being >1. However, the initial collision would have to be almost perfectly elastic. The greater the number of atoms a given nanocluster, the less probability of >1 restitution coefficients.

While this was only a simulation, it delves into a phenomenon that would be nearly impossible to investigate otherwise. This furthers the amount of knowledge we have gathered about nanoscale structures, most likely allowing for a greater possibility of real-world applications of such structures.

Resources:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PLEEE8000079000003031309000001&idtype=cvips&gifs=Yes
http://www.sciencenews.org/view/generic/id/42877/title/Nanoclusters_seem_to_skirt_physics_law

Posted in: Condensed Matter, Quantum Physics

Tags: nano, nanoclusters, thermodynamics

This entry was posted on Sunday, April 19th, 2009 at 10:32 am and is filed under Condensed Matter, Quantum Physics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.