Factors That Affect Stopping

Retinoids are classed as morphogens, small molecnles released from one type of cells that can affect the growth and differentiation of neighboring cells. Their normal roles in the hnman body are to indnce differentiation of some cells, stop the differentiation of others, and both snppress and indnce apoptosis in different cell types. Their diverse actions come from the diversity of their receptors. The two classes of retinoid receptors are retinoid X receptors (RXRs) and retinoic acid receptors (RARs), each with a, P, and y snbclasses. RXRs are versatile they bind to RARs and to other nnclear receptors such as thyroid hormone receptors. Once activated, the receptors act as transcription factors that in turn regulate the expression of genes that control ceUnlar growth and differentiation. ... 

Heat losses in a propagating front have a significant effect on the front velocity. This is related to two factors the size of the tube that affects the surface-to-volmne ratio, and the medium outside the tube that affects the rate of heat conduction. If the tube diameter is decreased, the front travels slower. In tubes of the size we have used, the polymerization front stops when the vessel is placed in room-temperature water, because water conducts heat more effectively than air. 

The period that elapses before two or more solutions are thoroughly mixed in a chemical kinetic experiment. In most manually controlled chemical kinetic studies, the mixing time is rarely a factor affecting accurate data acquisition however, the mixing time can be significant in rapid kinetic processes studied by continuous and stopped-flow kinetic techniques. 

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