Unwanted features

Unwanted stmctures in the film plane—often found within LB films fonned from simple rodlike molecules or from molecules polymerized after deposition—can be problematic, since many possible applications of such films require a unifonn stmcture within the plane. On the other hand, however, the production of a system in which the stmcture within the plane is so disordered that there exist no stmctural features large enough to cause problems would also render applications possible. In tliree-dimensional materials, for example, both inorganic glasses and many polymers are capable of transmitting light without any appreciable scattering for substantial distances. 

Table 12.5 summarizes the applieation of these prineiples (after Kletz - see Bibliography). Where this approaeh is not feasible, external features of plant must ensure the minimization of unwanted eonsequenees. 

One of the earliest steps in product design is to establish the configuration of the product that will form the basis on which a suitable material is selected to meet performance requirements. During this phase certain design features have to be kept in mind to avoid problems such as reduction of properties. Such features are called detractors or constraints. Most of them are responsible for the unwanted internal stresses that can reduce the available stress level for load bearing purposes. Other features may be classified as precautionary measures that may influence the favorable performance of a product if they are properly incorporated. 

Third, sinks are not only the result of the causes listed above but also can occur whenever supporting or reinforcing ribs, flanges, or similar features are used in an attempt to provide functional service without changing the basic wall thickness of a product. If the appearance of a sink on the surface is objectionable, the ribs and transition radius should be proportioned so that their contribution to the sink is minimal. Sinks can usually be eliminated by changing the process controls that usually results in the unwanted longer cycle times. 

Clinical features Priapism is defined as a painful and unwanted erection, which is classified as stuttering (less than 3 hours), often multiple prolonged (more than 3 hours). Up to 89% of males with SCD will have at least one episode by age 20. The mean age of the initial episode is 12 years of age. Repeated episodes can cause fibrosis and impotence. 

The synthesis of reaction-separation systems. The recycling of material is an essential feature of most chemical processes. The use of excess reactants, diluents, solvents or heat carriers in the reactor design has a significant effect on the flowsheet recycle structure. Sometimes, the recycling of unwanted byproduct to the reactor can inhibit its formation at the source. 

Sulfur dichloride is difficult to handle it disproportionates readily, has an unpleasant odor, and tends to introduce extra, unwanted chlorine atoms. Several reagents have been developed, especially by Harpp and co-workers, in which these undesirable features have been modified or eliminated. Succinimide-N-sulfenyl chloride (28) and phthalimide-N-sulfenyl chloride (29) are both stable crystalline compounds which undergo many of the reactions of the sulfur dichloride itself. They can, for example, be used in a facile, high yield synthesis of thiiranes from alkenes.33... 

In the contemporary production of enantiopure compounds this feature is highly appreciated. Currently, kinetic resolution of racemates is the most important method for the industrial production of enantiomerically pure compounds. This procedure is based on chiral catalysts or enzymes, which catalyze conversion of the enantiomers at different rates. The theoretical yield of this type of reaction is only 50%, because the unwanted enantiomer is discarded. This generates a huge waste stream, and is an undesirable situation from both environmental and economic points of view. Efficient racemization catalysts that enable recycling of the undesired enantiomer are, therefore, of great importance. 

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