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  1. Earth

    An Ounce of Prevention

    Fresh approaches may cut back greenhouse-gas emissions.

    By Sid Perkins
  2. Earth

    The Motion in the Ocean

    Scientists dive deep to learn how the sea circulates.

    By Kathryn Brown
  3. Math

    The Tangled Task of Distinguishing Knots

    Consider the plight of a gardener struggling with a recalcitrant tangle of garden hose. Sometimes, no amount of pulling or twisting unsnarls the coils. At other times, the tangles readily come apart, and the hose emerges unknotted. Trefoil knot. Different views of the figure-eight knot. Robert Scharein Braid (left) and its closed form (right). Robert […]

    By Ivars Peterson
  4. Physics

    Electronic Acrobats: Tidily tweaking electrons’ twirls

    The first demonstration of three-dimensional, electrical control of a quantum property of electrons known as spin marks an important step toward a new type of spin-based electronics and, possibly, quantum computers.