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  1. Math

    Completing Latin Squares

    Using only the numbers 1, 2, 3, and 4, arrange four sets of these numbers into a four-by-four array so that no column or row contains the same two numbers. The result is known as a Latin square. Here are two examples of Latin squares of order 4: 1 2 3 4 2 1 4 […]

    By Ivars Peterson
  2. Earth

    Shifting Sands

    Sand dunes can provide scientists with clues about ancient patterns of wind and precipitation.

    By Sid Perkins
  3. Physics

    Ring around the proton

    An orbiting electron accelerated to relativistic velocities by a laser in a strong magnetic field can behave like a ring-shaped electron cloud spinning around the nucleus.