Channel efficiency

M. L. Booy, The Influence of Non-Newtonian Flow on Effective Viscosity and Channel Efficiency in Screw Pumps, Polym. Eng. Sci., 21, 93 (1981). 

Plant sterols are products of primary metabolism, but they may also be regarded as direct precursors of many secondary plant metabolites, such as the cardiac glycosides, saponins and steroid alkaloids. All of the compounds mentioned share the same basic skeleton therefore, the accumulation of a particular compound can only be achieved if (1) enzymes with a high degree of substrate specificity are involved in their biosynthesis, (2) metabolites can be channelled efficiently to the respective pathways and (3) products can be transported, sequestered and/or stored in specific compartments. 

Three features of the reaction kinetics are essential to ensure that indole is channeled efficiently (1) the reaction of serine at the f3 site modulates the formation of indole at the a site such that indole is not produced until serine has reacted to form E AA (2) the rate of reaction of indole and E AA is fast and largely irreversible and (3) the rate of indole diffusion from the a site to the f3 site is very fast (>1000 s ). ° This mechanism accounts for the fact that indole does not accumulate during a single turnover of conversion of IGP into tryptophan (the af3 reaction). This model makes several predictions, which have been tested by kinetic and structural analysis of mutants and alternate substrates ° using single enzyme turnover experiments. 

In this chapter, we explore a modelling paradigm for supply chain coordination using the notion of supply chain intermediary. Our goal is to complement the view offered by the supply chain contracting literature that uses long-term coordination contracts as a primary mechanism to achieve channel efficiency. We propose to look at the problem of supply chain coordination... 

McGuire, T.W. and R. Staelin, Channel Efficiency, Incentive Compatibility, Transfer Pricing, And Market Structure An Equilibrium Analysis Of Channel Relationships, Research in Marketing, 8 (1986), 181-223. 

The equations above are based on the assumption that the flow is laminar, which will generally be the case for polymer melts due to their high viscosity. If, however, turbulent flow takes place, then even in a simple circular channel efficient mixing can occur. When two fluids of equal density are introduced side by side into an empty pipe with diameter D, then the degree of mixing after length L can be expressed as [260] ... 

Since these neurotoxins target channels with similar shapes, the neurotoxins themselves look similar. Animals like amphibians defend themselves from predators with tetrodotoxin, a small molecule that blocks predator s sodium channels, leaving them with quite a bad taste in their mouths. Then the snakes that eat amphibians remolded their sodium channels so the tetrodotoxin can t fit snugly. Six species of snakes at three places around the world all reshaped their sodium channels in the exact same way, making them worse at moving sodium but better at resisting the toxin (they sacrificed sodium channel efficiency so they could eat toxic amphibians). The shape that resists the channel-blocking toxin is as predictable as the shape that channels the sodium. 

The rate coefficient for the overall reaction (R3.1) (= (R3.1a) + (R3.1b)) is ki, which is equal to the sum of the rate coefficients for the two reaction channels, so ki = ki + ib. The branching ratio for the two channels is the ratio of their rate coefficients, so that in the example above the branching ratio is kiJki, while the channel efficiency for channel (R3.1a) is kiJki The determination of branching ratios is as important as the determination of overall rate coefficients but presents greater challenges. 

These definitions of branching ratio and channel efficiency are not universally agreed. For example, the KIDA data base uses branching ration for the ratio of the rate coefficient for a particular channel to that fra- the overall reaction, so that the branching ratios sum to unity. 

The next chapter discusses, inter alia, chemical networks and the context in which research on the kinetics of elementary reactions is applied in the ISM. In particular it provides a rationale for the provision of rate coefficients, channel efficiencies and uncertainties in rate parameters. It provides the justification for many of the topics discussed in Chap. 3. 

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