~~Robot Ups and Downs~~ Space and military planners are keen on using small, cheap robots for planetary exploration, battlefield defenses, and other jobs. But little robots on wheels or treads get stuck too easily in rough terrain. Recently, robot designers have unveiled doll-size robots that hurdle obstacles much larger than themselves. Here, a hopper rights itself after a leap. (Photos: Jet Propulsion Laboratory-NASA/Caltech)

In multiple-exposure photograph, robot prototype created by Sandia National Laboratories leaps over the head of Gary J. Fischer, one of its designers. Inset: The device on the ground.
Credit: Randy Montoya/Sandia; inset: Gaye Garrison/Sandia

A fallen frogbot pushes with plastic levers to right itself after a hop.
Credit: JPL-NASA/Caltech

In a polymer blend between two quartz disks, tiny droplets of one polymer (top) coalesce into strings (bottom) as the upper disk's rotation slows. Microscope lens below the disks provides a view.
Credit: Migler/NIST

Competition from a superbee may have driven to extinction the species of these bees, which were trapped in amber millions of years ago.
Credit: Engel

A chip with a see-saw plate suspended parallel to its surface (left) is pushed up (right) toward a ball. Quantum fluctuations in empty space produce a force that tilts the plate.
Credit: Adapted from Chan et al./Science

A Nasonia wasp, about 3 millimeters long, injects an egg into a fly pupa.
Credit: (c) Werren

Researchers detected uranium for the first time in an ancient star's absorption spectra.
Credit: R. Cayrel et al./Nature

BCR-ABL (magenta) can be trapped in leukemia-cell nuclei, where it forces the cells to commit suicide.
Credit: Vigneri, Wang, Jim Feramisco

An original design by Robert Longhurst, carved in wood.
Credit: Longhurst

Computer-generated image of the minimal-surface cousin of Longhurst's sculpture, created by Matthias Weber.
Credit: Weber

White Narcissus.
Credit: Photo by Stan Wagon

Example of a graph with one token poised to take a random walk.