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Pearls Are Self-Organized Natural Ratchets

Abstract : Pearls, the most flawless and highly prized of them, are perhaps the ă most perfectly spherical macroscopic bodies in the biological world. How ă are they so round? Why are other pearls solids of revolution (off-round, ă drop, ringed pearl), and yet others have no symmetry (baroque pearls)? ă We observe that with a spherical pearl the growth fronts of nacre are ă spirals and target patterns distributed across its surface, and that ă this is true for a baroque pearl, too, but that in pearls with ă rotational symmetry spirals and target patterns are found only in the ă vicinity of the poles; elsewhere the growth fronts are arrayed in ă ratchet fashion around the equator. We argue that pearl rotation is a ă self-organized phenomenon caused and sustained by physical forces from ă the growth fronts, and that rotating pearls are an example-perhaps ă unique-of a natural ratchet.
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Submitted on : Friday, February 10, 2017 - 1:23:54 PM
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Julyan H. E. Cartwright, Antonio G. Checa, Marthe Rousseau. Pearls Are Self-Organized Natural Ratchets. Langmuir, American Chemical Society, 2013, 29 (26), pp.8370-8376. ⟨10.1021/la4014202⟩. ⟨hal-01464673⟩



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