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When a drop of coffee dries, a halo of particles accumulates at the drops edge. This coffee-ring effect, first described formally in a Nature paper in 1997, is a common occurrence when a solution of suspended colloidal particles evaporates. Far from being just a household curiosity, it has turned out to have relevance for many applications in which a uniform particle deposition is required, such as inkjet printing, assembly of photonics components and manufacture of DNA chips. In this issue, Peter Yunker and colleagues show that ellipsoidal particles suppress the coffee-ring effect. Attractive interparticle interactions between ellipsoids are sufficiently strong to counteract the forces that drive spherical particles towards the drop's edge as the drop evaporates. The coffee-ring effect can be restored for ellipsoids in solution containing surfactant, and designed mixtures of spheres and ellipsoids can lead to uniform deposition. Cover photo: Annthea Lewis.
Daphne Sheldrick was the first person to rear baby elephants successfully by hand, and has worked with animals for 50 years in Kenya. As she stars in an IMAX film chronicling her efforts, she describes her experience of conservation and animal husbandry.
The well-known boundaries of coffee stains are caused by the outward flow of particles suspended in the liquid. Experiments show that ellipsoidal particles can prevent the formation of such boundaries. See Letter p.308
The protein Lgr5 has been valuable as the undisputed marker of intestinal and other stem cells. It emerges that Lgr5 and its relatives also have essential signalling roles of relevance to health and disease. See Article p.293
Polarized emission has been detected from the largest Lyman-α gas cloud, known as blob 1. This result strongly suggests that such clouds are powered by a central source of ionizing radiation. See Letter p.304
Images of the sea floor in Pine Island Bay, West Antarctica, reveal impressive evidence that a massive ice-shelf break-up occurred before about 12,000 years ago, and point to a tidal influence on sea-floor features produced during deglaciation.
Tracing a common ancestry between languages becomes harder as the connection goes further back in time. A new test has revealed a surprisingly ancient relationship between a central Siberian and a North American language family.