A new twist on a twist

By Rachel Courtland, 12:54 PM May 30, 2014

Nature abounds with perfect helices. They show up in animal horns and seashells, in DNA and the young tendrils of plants. But helix formation can get complicated: In some cases, the direction of rotation can reverse as a helix grows. The resulting structure has been dubbed the hemihelix, and you may have made one yourself by untwisting part of a telephone cord so much that it flips and spirals in the other direction.

Katia Bertoldi, a professor of applied mechanics at Harvard University, and h...

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