Differential retardation

The gel-like, bead nature of wet Sephadex enables small molecules such as inorganic salts to diffuse freely into it while, at the same time, protein molecules are unable to do so. Hence, passage through a Sephadex column can be used for complete removal of salts from protein solutions. Polysaccharides can be freed from monosaccharides and other small molecules because of their differential retardation. Similarly, amino acids can be separated from proteins and large peptides. 

Circular birefringence will induce a differential retardation in the phase of the orthogonal states of circularly polarized light. Circular dichroism, on the other hand, results in anisotropic attenuation of left- and right-circularly polarized light. The Jones matrix of circularly dichroic materials is normally written as ... 

The Tswett procedure is only one of hundreds that has now inherited the name chromatography. All these methods depend upon the basic chromatographic mechanism a differential retardation caused by unequal degrees of sorption of substances washed along in a stream of fluid. However there are numerous variations in the procedure as suggested below. 

DIA (differentiation inhibitory activity)/DRF (differentiation retarding factor)... 

Another aspect of LIF was revealed by studies on the activity that prevents differentiation of totipotent ES cells derived from normal blastocysts (Williams et al., 1988 Smith et al., 1988 Gough et al., 1989 Smith et al., 1992). It is known that to maintain the totipotency of ES cells, they must be grown on a feeder layer of fibroblasts. The activity secreted by the feeder layer fibroblasts, termed DIA (differentiation inhibitory activity) or DRF (differentiation retarding factor), has been purified, and its characteristics suggest that DIA/DRF may be identical to LIF. Indeed, not only does LIF exhibit the same activities as DIA and DRF in vitro, but also ES cells cultured with LIF can retain their totipotency. When the ES cells treated with LIF are injected into mouse blastocysts and then introduced into pseudo-pregnant females, they contribute extensively to the development of all of the somatic tissues (Williams et al., 1988 Gough et al., 1989). 

Because the radius, r, is expressed as a reduced distance (relative to unit radius inclusion) in Figs. 2-4, the physical path length is given by R dh, where R is a scale factor representing the actual radius of the inclusion. Thus, the differential retardation, dP, caused by an element of swollen rubber at point J is given by dP = v (np - n )R dh... 

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