Some Important Relationships Based on Theory

Let us now briefly outline the structure of this review. The next section contains information concerning the fundamentals of the electrochemistry of semiconductors. Part III considers the theory of processes based on the effect of photoexcitation of the electron ensemble in a semiconductor, and Parts IV and V deal with the phenomena of photocorrosion and light-sensitive etching caused by those processes. Photoexcitation of reactants in a solution and the related photosensitization of semiconductors are the subjects of Part VI. Finally, Part VII considers in brief some important photoelectrochemical phenomena, such as photoelectron emission, electrogenerated luminescence, and electroreflection. Thus, our main objective is to reveal various photo-electrochemical effects occurring in semiconductors and to establish relationships among them. 

The Eulerian continuum approach, based on a continuum assumption of phases, provides a field description of the dynamics of each phase. The Lagrangian trajectory approach, from the study of motions of individual particles, is able to yield historical trajectories of the particles. The kinetic theory modeling for interparticle collisions, extended from the kinetic theory of gases, can be applied to dense suspension systems where the transport in the particle phase is dominated by interparticle collisions. The Ergun equation provides important flow relationships, which are useful not only for packed bed systems, but also for some situations in fluidized bed systems. 

The second classification is the physical model. Examples are the rigorous modules found in chemical-process simulators. In sequential modular simulators, distillation and kinetic reactors are two important examples. Compared to relational models, physical models purport to represent the actual material, energy, equilibrium, and rate processes present in the unit. They rarely, however, include any equipment constraints as part of the model. Despite their complexity, adjustable parameters bearing some relation to theory (e.g., tray efficiency) are required such that the output is properly related to the input and specifications. These models provide more accurate predictions of output based on input and specifications. However, the interactions between the model parameters and database parameters compromise the relationships between input and output. The nonlinearities of equipment performance are not included and, consequently, significant extrapolations result in large errors. Despite their greater complexity, they should be considered to be approximate as well. 

QSAR are useful In the design of pesticides and medicinal drugs, and In environmental problems such as the prediction of toxicity and blodegradablllty. An empirical relationship can be properly used only for Interpolation whereas one based solidly on well-established theory can be used at least to some extent for extrapolation as well. It seems of real Importance, then, to determine the nature and slgmiflcance of steric and bulk parameters In QSAR. 

A aubstantial amount of recent experimental data demonstrate that the model of styrene emulsion polymerization (1.2) on which the quantitative theory is based (, is not capable of adeqiiate interpretation of polymerization in many real systems. An attempt to use the theoretical relationships to describe polymerization of such industrially important monomers as vluyl acetate, vinyl chloride, alkylacrylates, as well as copolymerization of common monomers with functionally substituted ones, leads to a conclusion that the theory disregards some of the essential factors of the process. Therefore, this theory cannot be a foimdatlon for polymerization technology of the above monomers to be modernized and automatized. 

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