Kinetics of transport processes

Figure 9.24 b compares the isotope ion distribution of natural 40Ca+ and doped 44Ca+ in a cross section of a root of a Norway spruce. These measurements were carried out by SIMS using 69Ga+ primary ions (lOkeV, 0.1 nA, Ionoptika) with a lateral resolution < 0.1 pm.80 The investigations can be used to study the mechanism of mineral element uptake and kinetics of transport processes in plants as a function of time. About 20 min after the start of the tracer experiment a barrier was observed for the transport of enriched isotope 44Ca+ in the middle of the root.80... 

We have discussed point defects in elements (A) and in nearly stoichiometric compounds having narrow ranges of homogeneity. Let us extend this discussion to the point defect thermodynamics of alloys and nonmetallic solid solutions. This topic is of particular interest in view of the kinetics of transport processes in those solid solutions which predominate in metallurgy and ceramics. Diffusion processes are governed by the concentrations and mobilities of point defects and, although in inhomogeneous crystals the components may not be in equilibrium, point defects are normally very close to local equilibrium. 

The presence of water-filled pores that are interconnected with each other has a marked influence on the kinetics of transport processes. It hinders those processes that take place easily in the gaseous phase, such as oxygen and carbon dioxide diffusion. On the other hand, it facilitates those processes that occur in aqueous solution, like the diffusion of chlorides, or ions in general. 

Noise analysis, in particular the evaluation of experimental spectra, has been extensively used for interpreting the kinetics of transport processes in membranes. (See, for example Frehland (1982) and Section 5.5 of this book.) In Chapter 7 an example will be given of how to use stochastic kinetics to obtain stoichiometric and kinetic information referring to the transmitter-receptor interaction at the surface of the postsynaptic membrane of nerve and muscle cells. 

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See also in sourсe #XX -- [ , , , , ]

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