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Density gradient is a spatial variation in density over an area. The term is used in the natural sciences to describe varying density of matter, but can apply to any quantity whose density can be measured.[1][2]


In the study of supersonic flight, Schlieren photography observes the density gradient of air as it interacts with aircraft. [3]

Also in the field of Computational Fluid Dynamics, Density gradient is used to observe the acoustic waves, shock waves or expansion waves in the flow field.


A steep density gradient in a body of water can have the effect of trapping energy and preventing convection, such a gradient is employed in solar ponds. In the case of salt water, sharp gradients can lead to stratification of different concentrations of salinity. This is called a Halocline. [4]


In the life sciences, a special technique called density gradient separation is used for isolating and purifying cells, viruses and subcellular particles.[5] Variations of this include Isopycnic centrifugation, Differential centrifugation, and Sucrose gradient centrifugation. A blood donation technique called Pheresis involves density gradient separation.


The understanding of what is at the centre of the earth, the earth core, requires the framework of density gradients in which elements and compounds then interact. Fast breeder nuclear reactor at the core of the earth is one theory by reason of density gradient and supported and espoused by J. Marvin Herndon (7 & 8).

Urban EconomicsEdit

In the study of population, the density gradient can refer to the change in density in an urban area from the center to the periphery. [6]


  1. ^ "Non-Destructive Testing Resource Center - Glossary".
  2. ^ "Chicago Wilderness Journal, Volume 1 - Number 1 - November, 2003" (PDF). Archived from the original (PDF) on 2006-09-28. Retrieved 2006-12-09.
  3. ^ "CFI-Shadowgraph/Schliren Photography for Aerodynamic Applications" (PDF). Archived from the original (PDF) on 2007-02-26. Retrieved 2006-12-09.
  4. ^ "Effects of sill processes and tidal forcing on exchange in eastern Long Island Sound".
  5. ^ "GE Healthcare Density Gradient Separation". Archived from the original on 2006-10-09. Retrieved 2006-12-09.
  6. ^ "The Spatial Distribution of Population in 48 World Cities: Implications for Economies in Transition" (PDF). Archived from the original (PDF) on 2006-09-05. Retrieved 2006-12-09.
  • 7. Herndon, J. Marvin (1994) Planetary and Protostellar Nuclear Fission: Implications for Planetary Change, Stellar Ignition and Dark Matter Proceedings: Mathematical and Physical Sciences, Vol. 445, No. 1924 (May 9, 1994), pp. 453–461
  • 8. Herndon, J. Marvin (1996) Substructure of the inner core of the Earth Vol. 93, Issue 2, 646-648, January 23, 1996, PNAS