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Cubic mean

From Wikipedia, the free encyclopedia
Cubic root of the mean of the cubes

Thecubic mean (written asx¯cubic{\displaystyle {\bar {x}}_{\mathrm {cubic} }}) is a specific instance of thegeneralized mean withp=3{\displaystyle p=3}.

Definition

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Forn{\displaystyle n}real numbersxiR{\displaystyle x_{i}\in \mathbb {R} } the cubic mean is defined as:

x¯cubic=1ni=1nxi33=x13+x23++xn3n3.{\displaystyle {\bar {x}}_{\mathrm {cubic} }={\sqrt[{3}]{{\frac {1}{n}}\sum _{i=1}^{n}{x_{i}^{3}}}}={\sqrt[{3}]{{x_{1}^{3}+x_{2}^{3}+\cdots +x_{n}^{3}} \over n}}.}   [1][2][3]

For example, the cubic mean of two numbers is:

x13+x2323{\displaystyle {\sqrt[{3}]{\frac {x_{1}^{3}+x_{2}^{3}}{2}}}}.

Applications

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The cubic mean is used to predict thelife expectancy of machine parts.[3][4][5][6]

The cubic mean wind speed has been used a measure of local potential forwind energy.[7]

The cubic mean is also used inbiology to measure the mean dimensions of sphericalbacteria (cocci)[8] and of larger animals that are approximately spheroidal in shape.[9] In this case using the conventionalarithmetic mean will not give an accurate result because the size of a spherical bacterium increases as thecube of the radius.

References

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  1. ^"calculation formulas"(PDF).
  2. ^Svarovski, Ladislav (31 October 2000).Solid-Liquid Separation. Elsevier.ISBN 9780080541440. Retrieved2015-01-20.
  3. ^ab"Equivalent Load".Creative Motion Control. Archived fromthe original on 2015-01-20. Retrieved2015-01-19.
  4. ^"ISO 4301-1-1986 Cranes and lifting appliances; Classification; Part 1 : General".www.iso.org. 1986. also available from"freestd.us". Retrieved2015-01-20.
  5. ^Babu & Sridhar (2010).Design of Machine Elements. McGraw-Hill Education (India) Pvt Limited.ISBN 9780070672840. Retrieved2015-01-20.
  6. ^Harris, Tedric A.; Kotzalas, Michael N. (9 October 2006).Essential Concepts of Bearing Technology, Fifth Edition. CRC Press.ISBN 9781420006599. Retrieved2015-01-20.
  7. ^Da Rosa, Aldo Vieira (2013).Fundamentals of renewable energy processes. Academic Press. p. 696.ISBN 9780123972194.
  8. ^Rodina, Antonina Gavrilovna (1972).Methods in aquatic microbiology. University Park Press. p. 158.ISBN 083910071X.
  9. ^Rice, Dale W.; Wolman, Allen A. (1971).The life history and ecology of the gray whale (Eschrichtius robustus).Stillwater, Oklahoma: American Society of Mammalogists. p. 34.
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