Optima existence

One intriguing aspect of enzymatic catalysis in low water environments (this includes 85% dioxane where the water activity is substantially less than unity) is the effect of reaction pH. In aqueous solutions, the ionogenic functional groups of an enzyme respond to the pH of the solution. Definitive pH optima exist for all enzymes. In organic solvents, however, the lack of water as a bulk solvent makes pH an unmeasurable variable although there will be a small concentration of protons in the vicinity of... 

It is clear that for some heterogeneous food systems, at least two optima exist, as indicated in the uppermost curve shown in Fig. 5, which is taken from Rockland and Nishi (1980). This curve represents the relationship between a and the integrated resultant relative stability based on the summation of a series of independent and/or interdependent chemical reactions, which are characterized diagrammatically in the figure. This figure presents an updated diagrammatic summary of a and its major effects upon some chemical, enzymatic, and microbiological properties of foods. 

Movement to a local optimum may occur if numerous optima exist. 

The smallest size difference that can be resolved is related to the pore volume, the solute shape, and the efficiency of the column (see Fig. 2.6). However, this is at very low loadings. At higher loadings the sample volume will contribute to zone broadening and may, in some cases, be the dominating factor for resolution. Thus, for fractionation, an optimum exists with respect to column efficiency (represented by the flow rate as operational parameter) and sample volume for processing a particular volume of feed per unit time. As a rule of thumb this optimum can be found at a relative sample volume of 2-5% of the column volume (Hagel et al., 1989). 

In the geometric method1,11 experimental results are used to minimize the region in which the optimum exists. The response is obtained for a number of points that are located very near one another. The number of points should be one greater than the number of independent variables. From the results a surface (this is aline when there are two independent variables) representing a constant value of the response is constructed. This method hypothesizes that on one side of this surface will be all the pointsthatyieldabetterresponse,andthereforetheoptimummustlieonthatsideofthe surface. 

Of these, the feed mixture may or may not vary, but is generally taken as given. The column pressure and the degree of subcooling are normally fairly constant. The main operational variables are the reflux ratio R and the heat input to the reboiler QR and once these are set, the amount of product withdrawal at the bottom or at the top will also be given by the product specifications. An optimum exists for the reflux ratio in terms of operating costs, and normally a number of ratios are tested, and the economics of each scenario is investigated, before a decision is reached. 

Simulation results from Pope et al. (1979) showed that the best oil recovery for a given amount of injected surfactant occurred where a salinity higher than the optimum existed downstream of the slug and a salinity lower than the optimum existed upstream of the slug (in the polymer drive) and the slug itself traversed as much of the reservoir as possible in the low-tension type III environment. Generally, the chemical slug is small. Therefore, the initial and drive salinities matter most. Pope et al. observed that the low final salinity promoted low final retention of surfactant. 

Generally an optimum exists in the grafting effleiency as a function of amounts of grafting material and initiator. 

A report on the continuous flash pyrolysis of biomass at atmospheric pressure to produce Hquids iadicates that pyrolysis temperatures must be optimized to maximize Hquid yields (36). It has been found that a sharp maximum ia the Hquid yields vs temperature curves exist and that the yields drop off sharply on both sides of this maximum. Pure ceUulose has been found to have an optimum temperature for Hquids at 500°C, while the wheat straw and wood species tested have optimum temperatures at 600°C and 500°C, respectively. Organic Hquid yields were of the order of 65 wt % of the dry biomass fed, but contained relatively large quantities of organic acids. 

Fa.n Spra.ys, It was demonstrated around the 1950s that iastabiHty theory can be used to analyze the wave growth on a thin Hquid sheet (18). This analysis predicted the existence of an optimum wavelength at which a wave would grow rapidly. This optimum wavelength, X corresponds to a condition that leads to Hquid sheet disiategration. It can be expressed as ia equatioa 2 ... 

The viscosity of an adhesive directly influences its penetration into a substrate as the viscosity increases, the penetrating power decreases. It also determines the amount of mileage or spread that can be obtained. An optimum viscosity exists for each substrate and each set of machine conditions and must be achieved in order to manufacture an efficient adhesive. Poly(vinyl acetate) emulsions are frequently too low in viscosity to be metered efficiently or to perform well as adhesives by themselves. They must be bodied to working viscosities, eg, by adding thickeners. 

An optimum temperature exists at which the ethanol production rate is maximal. Ethylene conversion is limited by catalyst activity at lower temperatures and by equiUbrium considerations at higher temperatures. 

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