Isopycnic

Isopycnic
Viruses purified by isopycnic centrifugation— a density gradient was formed during high speed centrifugation of a solution of caesium chloride and the two virus types come to rest at points corresponding to their density. The tube is about 10cm long.

Isopycnic means "of the same density." In particular, an isopycnic surface is a surface of constant density. This term is a bit more obscure than the similar terms isobaric or isothermal surfaces, which describe surfaces of constant pressure and constant temperature respectively. It is common in conversational use to hear isopycnic surfaces referred to simply as "iso-density" surfaces, which while strictly incorrect, is nonetheless abundantly more clear.

The term "isopycnic" is commonly encountered in the fluid dynamics of compressible fluids, such as in meteorology and geophysical fluid dynamics, astrophysics, or the fluid dynamics of explosions or high Mach number flows. It may also be applied to other situations where a continuous medium has smoothly-varying density, such as in the case of an inhomogeneous colloidal suspension.

Isopycnic surfaces occur in geology, especially in connection with cratons which are very old geologic formations at the core of the continents, little affected by tectonic events. These formations are often known as shields or platforms. These formations are, relative to other lithospheric formations, cooler and less dense but much more isopycnic.[1]

Compare also with isochoric. Note that one may discuss isobaric surfaces or isobaric processes; likewise one may discuss isothermal surfaces or isothermal processes. However, the use of "isopycnic" is typically reserved for surfaces and not processes. In particular, unless there is a flux of mass into or out of a control volume, a process which occurs at a constant density also occurs at a constant volume and is called an isochoric process and not an isopycnic process.

The term Isopycnic is also encountered in biophysical chemistry and usually in reference to a process of separating particles, sub cellular organelles, or other substances on the basis of their density. Isopycnic centrifugation refers to a method wherein a density gradient is either pre-formed or forms during high speed centrifugation, after this gradient is formed particles move within the gradient to the position having a density matching their own (this is in fact an incorrect description of the exact physical process but does describe the result in a meaningful way). This technique is extremely powerful.

References

  1. ^ Charles Petit (18 December 2010). "Continental Hearts - Science News". Science News. pp. 22–26. http://www.sciencenews.org/view/feature/id/66927/title/Continental_Hearts. Retrieved 2011-01-08. 

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  • Isopycnic — I so*pyc nic, a. [Iso + Gr. pykno s dense.] (Physics) Having equal density, as different regions of a medium; passing through points at which the density is equal; as, an isopycnic line or surface. [1913 Webster] …   The Collaborative International Dictionary of English

  • Isopycnic — I so*pyc nic, n. (Physics) A line or surface passing through those points in a medium, at which the density is the same. [1913 Webster] …   The Collaborative International Dictionary of English

  • isopycnic — izopikna statusas T sritis Standartizacija ir metrologija apibrėžtis Brėžinio linija, jungianti vienodo tankio taškus. atitikmenys: angl. curve of constant density; equidense; isodense; isopycn; isopycnic; isopycnic line; line of equal density… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • isopycnic — izopikna statusas T sritis fizika atitikmenys: angl. isopycn; isopycnic; isopycnic line vok. Isodense, f; Isopykne, f; Linie gleicher Dichte, f rus. изопикна, f pranc. courbe d’égale densité, f; courbe isopycne, f; isopycne, f …   Fizikos terminų žodynas

  • isopycnic — Having equal density: thus in equilibrium density gradient centrifugation a particle (molecule) will cease to move when it reaches a level at which it is isopycnic with the medium …   Dictionary of molecular biology

  • Isopycnic centrifugation — Isopycnic centrifugation, also known as density gradient centrifugation or equilibrium sedimentation is a technique used to separate molecules on the basis of buoyant density. (The word isopycnic means equal density .) Typically, a self… …   Wikipedia

  • isopycnic centrifugation — isopycnic centrifugation. = density gradient centrifugation (см.). (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • isopycnic line — izopikna statusas T sritis Standartizacija ir metrologija apibrėžtis Brėžinio linija, jungianti vienodo tankio taškus. atitikmenys: angl. curve of constant density; equidense; isodense; isopycn; isopycnic; isopycnic line; line of equal density… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • isopycnic line — izopikna statusas T sritis fizika atitikmenys: angl. isopycn; isopycnic; isopycnic line vok. Isodense, f; Isopykne, f; Linie gleicher Dichte, f rus. изопикна, f pranc. courbe d’égale densité, f; courbe isopycne, f; isopycne, f …   Fizikos terminų žodynas

  • isopycnic — adjective Etymology: is + Greek pyknos dense Date: circa 1890 1. of, relating to, or marked by equal or constant density 2. being or produced by a technique (as centrifugation) in which the components of a mixture are separated on the basis of… …   New Collegiate Dictionary

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