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Density gradient is a spatial variation in density over a region. 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 .
The Non-Covalent Interactions index, commonly referred to as simply Non-Covalent Interactions (NCI) is a visualization index based in the Electron density (ρ) and the reduced density gradient (s). It is based on the empirical observation that Non-covalent interactions can be associated with the regions of small reduced density gradient at low ...
Historically a cesium chloride (CsCl) solution was often used, but more commonly used density gradients are sucrose or Percoll.This application requires a solution with high density and yet relatively low viscosity, and CsCl suits it because of its high solubility in water, high density owing to the large mass of Cs, as well as low viscosity and high stability of CsCl solutions.
Differential centrifugation, on the other hand, does not utilize a density gradient, and the centrifugation is taken in increasing speeds. The different centrifugation speeds often create separation into not more than two fractions, so the supernatant can be separated further in additional centrifugation steps.
The region of rapid density change is known as the pycnocline, and it acts as a barrier to vertical water circulation; thus it also affects the vertical distribution of certain chemicals which play a role in the biology of the seas. The sharp gradients in temperature and density also may act as a restriction to vertical movements of animals. [6]
Over a long or fast centrifugation, particles travel to locations in the gradient where the density of the medium is the same as that of the particle density; (ρp – ρm) → 0. Therefore, a small, dense particle initially sediments less readily than a large, low density particle.
When DNA is extracted from these cells and made to undergo buoyant density centrifugation on a salt density gradient, the DNA separates out at the point at which its density equals that of the salt solution. The DNA of the cells grown in 15 N medium had a higher density than cells grown in normal 14 N medium.
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. An isopycnic surface is a surface of constant density inside a fluid.