Biokinetic models performance

Information on the transplacental transfer of americium in humans is not available directly, but the information from experiments with americium and other actinides has been used to derive biokinetic models and perform dosimetric models for the human (NCRP 1998 NRC 1996 Sikov and Kelman 1989). Studies in animals that received parenteral injections of americium have shown that absorbed americium is transferred to the fetus (Hisamatsu and Takizawa 1983 Paquet et al. 1998 Sasser at al. 1986 Schoeters et al. 1990 Weiss et al. 1980) (see Section 3.4.2.1). Limited reports indicate that241 Am may induce fetal death and teratogenic effects in rodents (Moskalev et al. 1969 Rommerein and Sikov 1986). 

Modifications of biokinetic models can be included in the CSTR performance equation. 

Indirect measurements generally interfere less with worker assignments, but require access to a radiochemical analytical laboratory such a laboratory may also be used for measttring environmental samples, but high level (e g. reactor water chemistry) and low level (e g. bioassay or environmental samples) measurements should be performed in separate laboratories. Excreta measurements determine the rate of loss of radioactive materials from the body by a particular route, and must be related to the body content and intake by a biokinetic model. Because of the ability of radiochemical analyses to detect low levels of activity, measrrrements of excreta usually give sensitive detection of activity in the body. 

The biokinetic models developed by the ICRP are intended for use in normal situations for example for the evaluation of doses fiom measurements performed aeeording to routine monitoring programmes. The evaluation of doses in accident situations needs more specific information about the time and pattern of intake, about the physicochemieal form of the radionuctides and about the eharacteristics of the individual (e.g. body mass). Individual spedfie data on the biokinetics of radio-nuclide(s) may be obtained through speeial monitoring, i.e. by repeated direct measurements of the whole body or speeifie sites and measurements of excretion. 

There are several software packages for modehng chemical and biochemical systems. They simulate the kinetics of systems of chemical and biochemical reactions, providing tools to fit models to data, estimate parameters and perform simulations and optimizations, among other options. In the general purpose software, the task of the user is to develop a mathematical model and rewrite a model in the format expected by the software. Specific programs devoted to biokinetics have the most often appHed biokinetic models already implemented. 

Until recently, reactor design, selection of suitable operating conditions, and scale up were performed using either rules of thumb [80] or different kinds of compartment models [36,81 -83].With the exponential increase in computing power, hard- and software tools became available to successfully implement simulation strategies based on integration of computational fluid dynamics (CFD) and structured biokinetics. 

There are three major points to be stressed. First, the Hquid/ceUular interface may contribute significantly to mass transfer limitations. Second, when mass transfer Hmitations exist the intrinsic biokinetics parameters cannot be determined. In biochemical reactor design, intrinsic parameters are essential to model adequately the system performance. Furthermore, without an understanding of the intrinsic biokinetics, one cannot accurately study transport mechanisms across biological membranes. The determination of passive or active transport across membranes is strongly affected by the extent of the Hquid/ceUular interfacial resistance. 

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