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Physics News Update
The American Institute of Physics Bulletin of Physics News

Number 459 (Story #2), November 29, 1999 by Phillip F. Schewe and Ben Stein

SWIRLED SPHERE MAGIC NUMBERS. Physicists love to detect patterns in nature, whether in the crystalline structures of atoms in solids, or the groupings into "shells" of electrons inside atoms or protons and neutrons within nuclei. Even in a system as simple as a bunch of spheres swirled around in a dish patterns can emerge. Scientists at the Max Planck Institute in Dortmund, Germany (Karsten Kotter,, and Mario Markus), and the University of Chile (Eric Goles) have determined that for certain "magic" numbers of spheres, such as 19, 21, or 30, the spheres congregate into solid-like shell structures with stable rings. The swirled balls are a form of granular material. Studies of agitated grains had uncovered stable structures before (such as "oscillons") but not any that had depended on the number of particles present. The researchers noticed that when they increased the size of the dish a puzzling transition between stable and disordered states would occur intermittently. (Kötter et al., Physical Review E, December 1999; Select Article.)

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