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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, ...
Some density-gradient work for purifying cells and organelles can be carried out in swinging-bucket rotors, or in the case of Percoll gradients in fixed-angle rotors. [9] High-speed or superspeed centrifuges can handle larger sample volumes, from a few tens of millilitres to several litres.
The sample is put on top of the solution, and then the tube is spun at a very high speed for an extended time, at times lasting days. The CsCl molecules become densely packed toward the bottom, so a continuous gradient of layers of different densities (and CsCl concentrations) form.
The difference between differential and density gradient centrifugation techniques is that the latter method uses solutions of different densities (e.g. sucrose, Ficoll, Percoll) or gels through which the sample passes.
In the square gradient approximation a strong non-uniform density contributes a term in the gradient of the density. In a perturbation theory approach the direct correlation function is given by the sum of the direct correlation in a known system such as hard spheres and a term in a weak interaction such as the long range London dispersion ...
Semiconservative replication would result in double-stranded DNA with one strand of 15 N DNA, and one of 14 N DNA, while dispersive replication would result in double-stranded DNA with both strands having mixtures of 15 N and 14 N DNA, either of which would have appeared as DNA of an intermediate density. The authors continued to sample cells ...
The simplest example of a stably stratified flow is an incompressible flow with density decreasing with height. [citation needed] In a compressible gas such as the atmosphere, the relevant measure is the vertical gradient of the entropy, which must increase with height for the flow to be stably stratified. [citation needed]
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]