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Cover: The water stream pictured here, roughly 8 mm across and flowing slower than 1 m/s, is being destabilized by a faster, coaxial stream of air flowing around it at 50 m/s. The formation and breakup of the thin filaments are dynamical consequences of capillary forces. Understanding such phenomena may have broad applications, from diesel engines to high-tech windshields to improved blood circulation. For more on capillarity, turn to the article by Yves Pomeau and Emmanuel Villermaux on page 39.
