Homogeneity and heterogeneity

This article is about states of matter. For other meanings of heterogeneity, homogeneity, and related words, see Homogeneity (disambiguation) and Heterogeneity (disambiguation).
Clam chowder, a heterogeneous material

Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity in a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, size, weight, height, distribution, texture, language, income, disease, temperature, radioactivity, architectural design, etc.); one that is heterogeneous is distinctly nonuniform in one of these qualities.[1][2][3]

The words homogeneous and heterogeneous come from Medieval Latin homogeneus and heterogeneus, from Ancient Greek ὁμογενής (homogenēs) and ἑτερογενής (heterogenēs), from ὁμός (homos, “same”) and ἕτερος (heteros, “other, another, different”) respectively, followed by γένος (genos, “kind”); -ous is an adjectival suffix.[4]

The concepts are the same to every level of complexity, from atoms to populations of animals or people, and galaxies. Hence, an element may be homogeneous on a larger scale, compared to being heterogeneous on a smaller scale. This is known as an effective medium approach, or effective medium approximations.[5][6]

Heterogeneity

Heterogeneity is the state of being heterogeneous. It is the nature of opposition, or contrariety of qualities. It is diverse in kind or nature; composed of diverse parts, or resulting from differing causes. In general, a heterogeneous entity is composed of dissimilar parts, hence the constituents are of a different kind that can be distinguished from one another. The parts (or constituents) are connected, and of a conglomerate mass, and viewed in respect to the parts of which it is made up.[2][7]

Various disciplines understand heterogeneity, or being heterogeneous, in different ways. For example:

Homogeneity

Homogeneity is the state of being homogeneous. Pertaining to the sciences, it is a substance where all the constituents are of the same nature; consisting of similar parts, or of elements of the like nature. For example, homogeneous particles, homogeneous elements, homogeneous principles, or homogeneous bodies; or (algebra) possessing the same number of factors of a given kind as with a homogeneous polynomial.[3]

Chemistry

A heterogeneous mixture is a mixture of two or more compounds. Examples are: mixtures of sand and water or sand and iron filings, a conglomerate rock, water and oil, a salad, trail mix, and concrete (not cement).[10] During the sampling of heterogeneous mixtures of particles, the variance of the sampling error is generally non-zero. Gy's sampling theory [11] quantitatively defines the heterogeneity of a particle as:

h_i = \frac{(c_i - c_\text{batch})m_i}{c_\text{batch} m_\text{aver}} .
h_i, the heterogeneity of the ith particle of the population
c_i, the mass concentration of the property of interest in the ith particle of the population
c_\text{batch},the mass concentration of the property of interest in the population
m_i, the mass of the ith particle in the population
m_\text{aver}, the average mass of a particle in the population

Homogenization is the process of causing a heterogeneous mixture to become homogeneous, as is done with the making of homogenized milk.

Homogeneous and heterogeneous reactions

Homogeneous reactions are chemical reactions in which the reactants and products are in the same phase, while heterogeneous reactions have reactants in two or more phases. Reactions that take place on the surface of a catalyst of a different phase are also heterogeneous. A reaction between two gases or two miscible liquids is homogeneous. A reaction between a gas and a liquid, a gas and a solid or a liquid and a solid is heterogeneous.

A mixture can be determined to be homogeneous when everything is settled and equal, and the liquid, gas, object is one color or the same form. Various models have been proposed to model the concentrations in different phases. The phenomena to be considered are mass rates and reaction .

Spelling

The alternate spellings "homogenous" and "heterogenous" are commonly, but incorrectly, used to refer to the above. The word "homogenous" strictly speaking is a biological term which has largely been replaced by "homologous", though its use to mean "homogeneous" has seen a rise, since 2000, which makes it an "established variant".[12] "Heterogenous" meanwhile is a term primarily confined to pathology which refers to the property of an object in the body having its origin outside the body.[13]

See also

References

  1. Heterogeneous Mixtures, in chemistry, is where certain elements are unwillingly combined and, when given the option, will separates completely. "Webster's Revised Unabridged Dictionary (1913 + 1828)" (Part of this paragraph is public domain material copyright 1828 and 1913). Heterogeneity. The ARTFL Project, University of Chicago. September 2010. Retrieved 2010-09-10.
  2. 1 2 "Webster's Revised Unabridged Dictionary (1913 + 1828)" (Part of this paragraph is public domain material copyright 1828 and 1913). Heterogeneous. The ARTFL Project, University of Chicago. September 2010. Retrieved 2010-09-10.
  3. 1 2 "Webster's Revised Unabridged Dictionary (1913 + 1828)" (This is public domain material copyright 1828 and 1913). Homogeneous. The ARTFL Project, University of Chicago. September 2010. Retrieved 2010-09-10.
  4. http://www.oxforddictionaries.com/definition/english/heterogeneous
  5. 1 2 Guéguen,, Yves; Palciauskas, Victor (May 1994). Introduction to the physics of rocks. Princeton University Press. pp. 53–72 (Chapter 3). ISBN 978-0-691-03452-2.Google Books preview download available
  6. Shadrivov, Ilya V.; Kozyrev, AB; Van Der Weide, DW; Kivshar, YS (2008-11-24). "Nonlinear magnetic metamaterials" (Introduction section. Free PDF download). Optics Express 16 (25): 20266–71. Bibcode:2008OExpr..1620266S. doi:10.1364/OE.16.020266. PMID 19065165. Retrieved 2009-11-26.
  7. Heterogeneous Mixtures, in chemistry, is where certain elements are unwillingly combined and, when given the option, will separate. "Webster's Revised Unabridged Dictionary (1913 + 1828)" (Part of this paragraph is public domain material copyright 1828 and 1913). Heterogeneity. The ARTFL Project, University of Chicago. September 2010. Retrieved 2010-09-10.
  8. http://mmc2.igeofcu.unam.mx/cursos/gest/Articulos/Reservoir%20Caracterization/Multiple-point%20geostatistics%20a%20quantitative%20vehicle%20for%20integrating%20geologic%20analogs%20into%20multiple%20reservoir%20models.pdf
  9. Bhatia, Sangeeta; John V Frangioni; Robert M Hoffman; A John Iafrate; Kornelia Polyak (10 July 2012). "The challenges posed by cancer heterogeneity". Nature Biotechnology 30: 604–610. doi:10.1038/nbt.2294.
  10. Gamow, George (April 1967). "Chapter VI, "Descending Staircase"". One Two Three... Infinity (Mass market paperback) (Bantam Science and Mathematics, 5th printing ed.). Bantam. p. 117. [Clam chowder] represents a nice example of what is known as a heterogeneous material.
  11. Gy, P. (1979), Sampling of Particulate Materials: Theory and Practice, Elsevier: Amsterdam, 431 pp.
  12. http://www.oxforddictionaries.com/definition/english/homogeneous
  13. http://grammarist.com/usage/heterogeneous-heterogenous/

External links

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