Individual-based models disadvantages

Business valuation literature provides various other methods for estimating terminal values (for an overview see Koller et al. 2005, pp. 271-290). Unfortunately, as cash flows cannot be allocated to individual decisions in a network design model, a cash flow-based estimate is not possible. Instead, book value or liquidation value at the end of the planning horizon could be used. For example, Fong and Srinivasan (1981, p. 790) include a terminal value function in the unit capacity acquisition cost function. However, they do not specify how this function can be quantified in real-world applications. The major disadvantages are that it is difficult to justify the assumptions underling the terminal value estimate and that restructuring expenditures cannot be properly evaluated. 

Disadvantages arise mainly from the complexity of the statistical algorithms and the fact that fitting models to data is time consuming. The first-order (EO) method used in NONMEM also results in biased estimates of parameters, especially when the distribution of inter individual variability is specified incorrectly. The first-order conditional estimation (EOCE) procedure is more accurate but is even more time consuming. The objective function and adequacy of the model are based in part on the residuals, which for NONMEM are determined based on the predicted concentrations for the mean pharmacokinetic parameters rather than on the predicted concentrations for each individual. Therefore, the residuals are confounded by intraindividual, inter individual, and linearization errors. 

The kinetics for catalytic systems can be modeled by one of two general methods. The first is based on continuum concentrations and uses deterministic kinetics whereas the second approach follows the temporal fate of individual molecules over the smface via stochastic kinetics. Both approaches have known advantages and disadvantages, as will be discussed. B These methods provide the constructs for simulating the elementary kinetics. However, in order to do so, they require an accurate and comprehensive initial kinetic database that contains parameters for the full spectra of elementary surface processes that make up the catalytic cycle. The ultimate goal for both approaches would be to call upon quantum mechanics calculations in situ in order to establish the potential energy surface as the simulation proceeds. This, however, is still well beyond our computational capabilities. 

The fed-batch technique of cultivation is limited by fermenter volume because the volume of fermentation broth increases after each substrate addition. This disadvantage can be avoided by application a cyclic feeding strategy [9-11] which allows one to control the synchrony of individual cell development [9] by the limiting substrate concentration. The preliminary simulation results on a computer show that this type of environmental control of continuous production of exocellular hydrolytic enzymes based on our model is very promising. 

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