Coeflicient selectivity

This step response is sketched in Fig. 6.7 for several values of the damping coefTi-cient. Note that the amount of overshoot of the final sleadystate value increases as the damping coeflicient decreases. The system also becomes more oscillatory. In Chap. 7 we will tune feedback controllers so that we get a reasonable amount of overshoot by selecting a damping coefficient in the 0.3 to 0.S range. 

An important aspect of coking is its influence on the selectivity. As the product distribution or the selectivity depends on the ratios of the various rate coeflicients it is evident that the selectivity may also be affected by changes in catalyst activity, when the different reactions are not influenced in the same way by the catalyst activity decline. Froment and Bischoff [37] worked out the theory for such a situation. Figure 11.5.f-9 shows the results for a complex reaction with parallel coking scheme. The variation of the selectivity for the isomerization of n-pentane... 

That different solvents, or mixtures of solvents, are critically associated with differences in selectivity coeflicients of calcium (or indeed all other types) of PVC ISEs based on organo-sensors is evident from Tables 3.2-3.10. It is highly desirable that the mediator should additionally function as a plasticizer for the PVC membrane. In view of the extensive use of PVC for fabricating the organic sensor type of ISEs, it is indeed fortunate that many of the necessary solvents fulfil this additional role. Thus di-octylphenyl phosphonate with, or without, a calcium salt is perfectly compatible with PVC. This requirement is rarely observed with alkan-l-ols which fail to plasticize the master membranes, and surface exudations are common (13). Despite this drawback, functional PVC ISEs can sometimes be fabricated (Tables 3.8,3.10) and extensive studies have been made on various solvents (Tables 3.2-3.10). 

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