Diffusion periphery

Water loss in operating an HDR faciUty may result from either increased storage within the body of the reservoir or diffusion into the rock body beyond the periphery of the reservoir (38). When a reservoir is created, the joints which are opened immediately fill with water. Micropores or microcracks may fill much more slowly, however. Figure 11 shows water consumption during an extended pressurization experiment at the HDR faciUty operated by the Los Alamos National Laboratory at Fenton Hill, New Mexico. As the microcracks within the reservoir become saturated, the water consumption at a set pressure declines. It does not go to zero because diffusion at the reservoir boundary can never be completely elirninated. Of course, if a reservoir joint should intersect a natural open fault, water losses may be high under any conditions. 

For turbines at Reynolds numbers less than 100, toroidal stagnant zones exist above and below the turbine periphery. Interchange of hq-uid between these regions and the rest of the vessel is principally by molecular diffusion. 

As well as electrodissolution and electrodeposition, periphery and surface diffusion play important roles. 

Diffuser vanes are used to decelerate a high velocity flow to create a pressure rise. They are usually at the periphery of each impeller. The variable diffuser vane system may be controlled manually by a handwheel or automatically by a hydraulic or air-operated positioner. See Figure 12-44B. 

In particular the use of solution of Eq. (2.37) or Eq. (2.39) allows one to calculate the moments in (2.35) preserving fast vanishing components with / < L. Consequently, the time-dependent diffusion coefficient D(t) makes it possible to recover information about the periphery of the spectrum... 

Dendrimer micelles of this type have been formulated as drug delivery vehicles. Dendrimers with a hydrophobic interior have been used to entrap a hydrophobic drug such as indomethacin. This is retained because of the hydrophilic periphery containing ethylene glycol functional groups, and is released slowly because of the collapsed configuration of the interior, through which molecular diffusion is obstructed. 

Although reaction-diffusion limitation and the presence of nutritionally restricted phenotypes are obviously important determinants of biofilm drug resistance, neither, either separately or in combination, provides a complete explanation of the phenomena. Cells on the periphery of the biofilm, subject to nutrient fluxes similar to planktonic organisms would succumb to antibacterial concentrations that are effective against the planktonic cells. Cell-death at the periphery would lead to increased nutrient availability for deeper-lying cells. These would, in turn, grow faster and adopt a more susceptible... 

The rate of a catalytic reaction depends on the rate of diffusion of both substrates and products to and from the catalytic sites. Therefore it is of outmost importance that the catalytically active sites are freely accessible for reactions. Only dendrimers of low generation number can possibly be expected to be suitable carriers for catalytically active sites, especially when these are located in the interior. In high-generation dendrimers with crowded surfaces catalytic activity of an internal site would be prevented. On the other hand, a crowded surface will not only hinder access to an interior ligand site but will also cause steric hindrance between groups attached to it and thus prevent high reactivity of sites at the periphery. 

The action of catecholamines released at the synapse is modulated by diffusion and reuptake into presynaptic nerve terminals. Catecholamines diffuse from the site of release, interact with receptors and are transported back into the nerve terminal. Some of the catecholamine molecules may be catabolized by MAO and COMT. The cate-cholamine-reuptake process was originally described by Axelrod [18]. He observed that, when radioactive norepinephrine was injected intravenously, it accumulated in tissues in direct proportion to the density of the sympathetic innervation in the tissue. The amine taken up into the tissues was protected from catabolic degradation, and studies of the subcellular distribution of catecholamines showed that they were localized to synaptic vesicles. Ablation of the sympathetic input to organs abolished the ability of vesicles to accumulate and store radioactive norepinephrine. Subsequent studies demonstrated that this Na+- and Cl -dependent uptake process is a characteristic feature of catecholamine-containing neurons in both the periphery and the brain (Table 12-2). 

The intracellular environment of eukaryote cells can be subdivided into many regions, including the organelles, nucleus, cytoplasm and the cell periphery. Thus solutes must be delivered to the right intracellular compartment at the correct time to efficiently serve cellular biochemistry. Uncharged solutes such as glucose presumably diffuse across the cell, and the traditional view held until recently was that the major electrolytes, such as Na+,K+,CF and Mg2+, also move around the cell by simple diffusion to eventually arrive at the relevant subcellular compartment by chance. 

Therefore, concentrations of the polyvinyl monomer, the branching and network formation proceeds as shown in Figure 12. Mlcrogel-llke species are formed first which are highly internally crossllnked. The pendant double bonds in the interior are very Immobile so that their reactivity is strongly diffusion controlled and they almost cannot react at all, even with the monomers. Only the more mobile pendant double bonds in the periphery of these species can enter into reactions with macroradicals and participate in Interbinding of the species together. 

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