Old X-rays, new vision: A nano-focused X-ray laser

Imagine taking movies of the fastest chemical processes, or imaging atomic-scale detail of single virus particles without damaging them. Researchers from Japan have advanced the state-of-the-art in such endeavors, by enhancing ...

Impacts on asteroids produce regolith, erase small craters

Impact cratering both produces new regolith and causes seismic events that can degrade and erase small craters on the surface of asteroids, a paper by Planetary Science Institute Senior Scientist James Richardson says. 

Image: ESA's Large Diameter Centrifuge at full speed

ESA's Large Diameter Centrifuge at the Agency's technical heart in the Netherlands is seen running here at full speed. The 8-m diameter four-arm centrifuge gives researchers access to a range of hypergravity environments ...

Asteroids help scientists measure distant stars

Look up at the sky on a clear night, and you'll see lots of stars. Sometimes they seem almost within reach or at least a short rocket ride. But the closest star to Earth—not counting our sun—is more than four light years ...

Magnetic nanoparticles can 'burn' cancer cells

Unfortunately, cancer isn't simply a single disease, and some types, like pancreas, brain or liver tumours, are still difficult to treat with chemotherapy, radiation therapy or surgery, leading to low survival rates for patients. ...

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In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle. The word "diameter" derives from Greek διάμετρος (diametros), "diagonal of a circle", from δια- (dia-), "across, through" + μέτρον (metron), "a measure").

In more modern usage, the length of a diameter is also called the diameter. In this sense one speaks of the diameter rather than a diameter, because all diameters of a circle have the same length, this being twice the radius.

For a convex shape in the plane, the diameter is defined to be the largest distance that can be formed between two opposite parallel lines tangent to its boundary, and the width is defined to be the smallest such distance. For a curve of constant width such as the Reuleaux triangle, the width and diameter are the same because all such pairs of parallel tangent lines have the same distance. See also Tangent lines to circles.

This text uses material from Wikipedia, licensed under CC BY-SA