Uniform crossover

The generation of heat always accompanies the operation of a fuel cell. The heat is due to inefficiencies in the basic fuel-cell electrochemical reaction, crossover (residual diffusion through the fuel-cell solid-electrolyte membrane) of fuel, and electrical heating of interconnection resistances. Spatial temperature variation can occur if any of these heat-generating processes occur preferentially in different parts of the fuel cell stack. For example, non-uniform distribution of fuel across the surfaces of electrodes, different resistances between the interconnections in a stack, and variations among... 

Selecting the points for crossover and mutation according to a probability distribution, either uniform or skewed towards points at which the optimized function takes high values (the latter being a probabilistic expression of the survival-of-the-fittest principle). 

Fig. 9. The types of recombination most commonly utilized in genetic algorithms for (a) one parent and (b) multiple parents. In the cases of 1-point and n-point crossover, the cut points do not have to be evenly distributed over the sequence. Uniform crossover gives the offspring the amino acid of either parent with equal probability and can be extended to multiple parents.

To determine the optimal number of cut points, it is necessary to return to the balance of exploration and exploitation. Uniform crossover is more exploratory than single-point crossover because the number of schema that can be sampled increases (Spears, 1993). However, the exploration comes at the cost of exploitation because more of the schema are disrupted (Eschelman et al., 1989). The specific balance between these effects will depend on the sampling ability of the library, the structure of the schema, and the ruggedness of the fitness landscape. 

Fig. 10. The probability of disrupting a schema versus the defining length for a sequence of length N. The lines are for n-point crossover and the flat line is for uniform crossover. Note that for large defining lengths, uniform crossover is less likely to be disruptive. Reprinted from De Jong and Spears (1990) with permission, 1990 by Springer-Verlag.

In a four-way crossover study in 16 healthy men a mod-ified-release formulation of metoclopramide (30 mg) administered fasting and after a high-fat meal, an immediate-release formulation (30 mg) and a short intravenous infusion of 30 mg have been compared (16). The absolute systemic availability of the modified-release formulation was about 17% lower than that of the immediate-release formulation. Food had no significant effect on absorption. Uniform absorption of the drug from modified-release formulations supports their use in long-term treatment. 

The use and possible mechanism of amphetamines to counteract opioid-induced sedation has been reviewed (18). Most studies had methodological problems, including small numbers of patients completing short-term trials (under 1 week) and the small number of randomized, placebo-controlled, crossover trials. The quantitative measure of sedation was highly subjective and no uniform cognitive tests were performed to help compare the... 

Only a very low concentration of TPP in PFO is needed to entirely quench PFO fluorescence. Figure 10.31 show the fluorescence quantum yields for TPP and PFO emission components of the spectra as a function of TPP concentration in the blend film. The effective distance between TPP molecules is given on the upper horizontal axis, assuming a uniform dispersion of TPP in the film (1/n = r3). The crossover point from PFO to TPP occurs at 5.4 nm separation, in rough agreement with the calculated Forster-transfer radius. 

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