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David Keen, British physicist and president of the British Crystallographic Association. David Keen studies crystal structures that behave in unusual ways when their atoms become disordered; for example, substances which unexpectedly melt, change into a glass, or start conducting electricity. He is photographed on Porthcawl Beach, South Wales, where a pattern of holes in the sand around him portray the neutron diffraction pattern from a quartz crystal. Quartz is a common component of sand, and a subject of Keen's research.
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