Selected article

The three major types of atomic line filters are absorption-re-emission ALFs, Faraday filters and Voigt filters. Absorption-re-emission filters were the first type developed, and so are commonly called simply "atomic line filters"; the other two types are usually referred to specifically as "Faraday filters" or "Voigt filters". Atomic line filters use different mechanisms and designs for different applications, but the same basic strategy is always employed: by taking advantage of the narrow lines of absorption or resonance in a metallic vapor, a specific frequency of light bypasses a series of filters that block all other light.

Selected picture

Gallium (IPA: /ˈgaliəm/) is a chemical element that has the symbol Ga and atomic number 31. A rare, soft silvery metallic poor metal, gallium is a brittle solid at low temperatures but liquefies slightly above room temperature and will melt in the hand. It occurs in trace amounts in bauxite and zinc ores. An important application is in the compound gallium arsenide, used as a semiconductor, most notably in light-emitting diodes (LEDs).

Selected biography

Did you know...

• ...that the endangered golden lion tamarin (pictured) has a long, but not prehensile, tail?
• ...that the Witch's hat is the common name of a colourful orange-red toadstool?
• ...that Grandi's series 1 − 1 + 1 − 1 + • • • is divergent and appears to equal 0, yet in some sense "sums" to ¹⁄₂ — a paradox once linked to the creation ex nihilo of the universe?
• ...that Derek Freeman was an anthropologist whose refutation of Margaret Mead's work "ignited controversy of a scale, visibility, and ferocity never before seen in anthropology"?
• ...that the New Year's Eve snowstorm of 1963/1964 dropped over 17 inches of snow at Huntsville, Alabama, simultaneously setting new snowfall records for any day, week, or month in their history?

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