Migration radial

This consists in spotting the separation mixture at intervals on a chromatographic plate and then applying the selected solvents in the center of each spot by means of a thin capillary. The spots migrate radially, and different chromatographic behavior of spotted rnixmre can be observed [16,59]. 

At the time of laying, the chick embryo is a flat disk consisting of about 60,000 cells. It is made up of two layers, the hypoblast ventrally, lying in close association with the yolk, and the epiblast dorsally, facing the vitelline membrane, the membrane which surrounds the yolk. The disk has a translucent iimer core, the area pellucida, from which the embryo will form, and a denser outer ring of mainly yolk-containing cells, the area opaca. Only the cells at the periphery of the blastoderm are attached to the vitelline membrane, and as they migrate radially, the blastoderm expands. 

The advantage of circular development, where the solvent system migrates radially from the center of the plate to the periphery, is well known for the separation of compounds in the lower Rj range yi,52). Working with the same mobile phase the resolution, particularly in the lower /iy range, is about 4-5 times greater in circular than in the linear development mode. It can be stated that the separation power of the circular development mode can be better exploited if the samples are spotted near to the center (41,52). 

Figure 2 Two measured pulses from a 25 fim diameter sphere which is reversed back and forth through a 70 /im diameter and 570 m long glass capillary. The particle migrates radially in Poiseuille flow from the axis (short transit time) towards the wall (long transit time) and the pulse height increases when the particle moves closer to the wall. Approximately 20 reversals separate the two realizations.

Cross-flow-elec trofiltratiou (CF-EF) is the multifunctional separation process which combines the electrophoretic migration present in elec trofiltration with the particle diffusion and radial-migration forces present in cross-flow filtration (CFF) (microfiltration includes cross-flow filtration as one mode of operation in Membrane Separation Processes which appears later in this section) in order to reduce further the formation of filter cake. Cross-flow-electrofiltratiou can even eliminate the formation of filter cake entirely. This process should find application in the filtration of suspensions when there are charged particles as well as a relatively low conduc tivity in the continuous phase. Low conductivity in the continuous phase is necessary in order to minimize the amount of elec trical power necessaiy to sustain the elec tric field. Low-ionic-strength aqueous media and nonaqueous suspending media fulfill this requirement. 

FIG. 22-29 Qualitative effects of Reynolds number and applied-electric-field strength on the filtration permeate flux J. Dashed lines indicate large particles (radial migration dominates) solid lines, small particles (particle diffusion dominates). 

Influent water enters one end of the pressure vessel and is evenly distributed along the length of the vessel by a concentric distributor tube. As the water migrates out radially, some of it permeates the fibers and exits the pressure vessel via the tube sheet on the opposite end. The direction of permeate flow is from outside to inside the fibers. The concentrated solution, or reject, completes its radial flow path and leaves the vessel at the same end at which it entered. 

As can be seen from this expression, there is no radial migration for Newtonian fluid (n = 1) for pseudoplastic fluid (n < 1), the migration occurs from the tube centre for dilatant fluid (n > 1), the migration is directed towards the tube centre. 

Gauthier et al. [38] studied radial migration of spherical particles with a concentration of 5% by volume in the mixture for the following values of parameters a = 0.019 cm R = 0.4 cm V = 0.127 cm3/s, n = 0.64. At the start of the time period, a particle deficit was observed at the channel walls, three minutes later the particles were uniformly distributed in the channel, ten minutes later 75 % of particles... 

Saito Y, Sharer LR, Epstein LG, Michaels J, Mintz M, Louder M, Golding K, Cvetkovich TA, Blumberg BM (1994) Overexpression of nef as a marker for restricted HIV-1 infection of astrocytes in postmortem pediatric central nervous tissues. Neurology 44 474-481 Sargeant TJ, Day DJ, Mrkusich EM, Eoo DE, Miller JH (2007) Mu opioid receptors are expressed on radial glia but not migrating neuroblasts in the late embryonic mouse brain. Brain Res 1175 28-38... 

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