New approach smooths wrinkle analysis. (Physics).

From furrowed brows to mountain-forming ripples in Earth's crest, wrinkles are ubiquitous. To better understand these widespread phenomena (SN: 6/15/96, p. 3763, scientists would like to predict certain topographical properties of wrinkles, such as the heights of their folds and how close together those folds lie.

A simple new theory does just that. In the Feb. 21 Physical Review Letters, Enrique Cerda of the University of Santiago in Chile and Lakshminarayanan Mahadevan of the University Cambridge in England mathematically analyze wrinkles. They report a straightforward relationship between elasticities of materials and the topographies of the wrinkles that form in them

In their report, Cerda and Mahadevan focus on membranes, such as the skins of apples and people, in which a thin, pliant layer overlies thicker, stiffer tissue, Because the thin surface tends to bow smoothly when compressed whereas the stiffer substrate prefers to crinkle, the wrinkle pattern comes out somewhere in between, the scientits say. That analysis seems to work--at least for some examples. The scientists accurately predicted creases spaced like barcode lines in a drying apple's skin. Moreover, the analysis correctly predicted the wider spacings that occurred in pinched human skin. In both cases, the researchers note, the heights of the folds were roughly equal to their spacings. The new wrinkle-prediction technique could be useful for studying the mechanics of skin and cell motility, the researchers say. --P.W.