
1) Concentration
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https://www.crosswordclues.com/clue/rarefaction

1) Expansion
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https://www.crosswordclues.com/clue/rarefaction

Rarefaction is the reduction of an item`s density, the opposite of compression. Like compression, which can travel in waves (sound waves, for instance), rarefaction waves also exist in nature. A common rarefaction wave is the area of low relative pressure following a shock wave (see picture). Rarefaction waves expand with time (much like sea wave....
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http://en.wikipedia.org/wiki/Rarefaction
[ecology] In ecology, rarefaction is a technique to assess species richness from the results of sampling. Rarefaction allows the calculation of species richness for a given number of individual samples, based on the construction of so-called rarefaction curves. This curve is a plot of the number of species as a function of the number of sam...
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http://en.wikipedia.org/wiki/Rarefaction_(ecology)

• (n.) The act or process of rarefying; the state of being rarefied; -- opposed to condensation; as, the rarefaction of air.
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http://thinkexist.com/dictionary/meaning/rarefaction/

in the physics of sound, segment of one cycle of a longitudinal wave during its travel or motion, the other segment being compression. If the prong ... [1 related articles]
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http://www.britannica.com/eb/a-z/r/13

The air particles being spread apart in the formation of a sound pressure wave.
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http://www.encyclo.co.uk/local/20447

The process of becoming light or less dense; the condition of being light; opposed to condensation. ... Origin: L. Rarus, thin, + facio, to make ... (05 Mar 2000) ...
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http://www.encyclo.co.uk/local/20973

(rar″ә-fak´shәn) the condition of being or becoming less dense.
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http://www.encyclo.co.uk/local/21001
Rar`e·fac'tion (răr`e*făk'shŭn)
noun [ Confer French
raréfaction . See
Rarefy .] The act or process of rarefying; the state of being rarefied; -- opposed to
condensation ; as, the
rarefaction of air.
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http://www.encyclo.co.uk/webster/R/12

Type: Term Pronunciation: rār′ĕ-fak′shŭn Definitions: 1. The process of becoming light or less dense; the condition of being light; opposed to condensation. 2. In vascular physiology, the process that results in a reduction in the density of capillaries in a tissue.
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http://www.medilexicon.com/medicaldictionary.php?t=75827

[
n] - a decrease in the density of something
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http://www.webdictionary.co.uk/definition.php?query=rarefaction

A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave. The opposite of compression. See also: Sound.
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https://www.encyclo.co.uk/local/20687
noun a decrease in the density of something; `a sound wave causes periodic rarefactions in its medium`
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https://www.encyclo.co.uk/local/20974

Region of a sound wave where the particles of the medium through which it is travelling are spread out, that is at a low density. Sound waves consist of alternate regions of compressions and rarefactions travelling away from the source
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https://www.encyclo.co.uk/local/21221

In sound waves, the opposite of compression. An area of decreased air pressure caused by a sound wav
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https://www.encyclo.co.uk/local/22369
No exact match found.