Here is another intriguing article about geometries creating focussed
cavities
http://www.sciencenews.org/sn_edpik/ps_1.htm
This recent work involves placing a random array of small obstacles
inside a rectangular cavity in order to study the connection between
chaos and disorder in quantum systems. It's like observing the effect
of impurities on the movement of electrons in tiny, two-dimensional
structures.
The experiments reveal that these obstacles force the eigenfunctions
to concentrate themselves in certain areas of the cavity. They no
longer spread themselves throughout the entire container.
"You see enormous localization in certain regions," Sridhar says. "The
waves are happy just to sit there." By changing the number of
obstacles and the microwave frequency, the researchers can increase or
decrease the degree of localization at will, thus making it possible
to explore the link between chaos and disorder.
Sridhar and Kudrolli described their work in March at an American
Physical Society meeting held in San Jose, Calif. Such findings may
help explain the results of experiments involving electron and photon
activity in disordered solids (SN: 4/20/91, p.248).
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