Subject transport properties, dependence

The rational application of these molecules to in vivo studies with human subjects requires a detailed knowledge of their behavior in the body, including modes of metabolism and elimination, sites of accumulation, and time dependence. Developing a radiopharmaceutical having desirable biological transport properties is often a matter of much experimentation (e.g., to find conditions for chemical modification of a protein that do not alter its biological activity). The studies with albumin that are discussed below provide some insight into this process. 

The impact of fillers on the ionic conductivity of solid PEO-based systems has been a subject of discussion for quite many years. The literature shows that for some systems the enhancement of conductivity is tremendous, although for some others it is very limited or there is even no enhancement of transport properties at aU. Some systems are stable, some are not, although they differ only slightly. A deeper look into the subject, combined with extended laboratory practice prove that ceramic fillers work, but the extent to which it happens depends a lot on the preparation conditions. 

Measurement of exposure can be made by determining levels of toxic chemicals in human serum or tissue if the chemicals of concern persist in tissue or if the exposure is recent. For most situations, neither of these conditions is met. As a result, most assessments of exposure depend primarily on chemical measurements in environmental media coupled with semi-quantitative assessments of environmental pathways. However, when measurements in human tissue are possible, valuable exposure information can be obtained, subject to the same limitations cited above for environmental measurement methodology. Interpretation of tissue concentration data is dependent on knowledge of the absorption, excretion, metabolism, and tissue specificity characteristics for the chemical under study. The toxic hazard posed by a particular chemical will depend critically upon the concentration achieved at particular target organ sites. This, in turn, depends upon rates of absorption, transport, and metabolic alteration. Metabolic alterations can involve either partial inactivation of toxic material or conversion to chemicals with increased or differing toxic properties. 

Either a liquid or a gas can be used as the carrier fluid, depending on the size and properties of the particles, but there are important differences between hydraulic (liquid) and pneumatic (gas) transport. For example, in liquid (hydraulic) transport the fluid-particle and particle-particle interactions dominate over the particle-wall interactions, whereas in gas (pneumatic) transport the particle-particle and particle-wall interactions tend to dominate over the fluid-particle interactions. A typical practical approach, which gives reasonable results for a wide variety of flow conditions in both cases, is to determine the fluid only pressure drop and then apply a correction to account for the effect of the particles from the fluid-particle, particle-particle, and/or particle-wall interactions. A great number of publications have been devoted to this subject, and summaries of much of this work are given by Darby (1986), Govier and Aziz (1972), Klinzing et al. (1997), Molerus (1993), and Wasp et al. (1977). This approach will be addressed shortly. 

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