Transport processes discriminate

The presence of -S02(OH) groups reduced the carbon dioxide permeability by a factor of three. This can be explained (15) by the decrease in local segmental mobility of the polymer chains due to the interactions arising from hydrogen bonding. However, the overall transport process for this polymer membrane is more complicated and involves a more pronounced discrimination against methane molecules due to the highly polar nature of the polymer. 

Understanding the adsorption, diffusivities and transport limitations of hydrocarbons inside zeolites is important for tailoring zeolites for desired applications. Knowledge about diffusion coefficients of hydrocarbons inside the micropores of zeolites is important in discriminating whether the transport process is micropore or macropore controlled. For example, if the diffusion rate is slow inside zeolite micropores, one can modify the post-synthesis treatment of zeolites such as calcination, steaming or acid leaching to create mesopores to enhance intracrystalline diffusion rates [223]. The connectivity of micro- and mesopores then becomes an... 

We are often concerned with the dispersion of pollutants and other chemicals in the environment. Advection and mass flux are indiscriminate transport processes. In the water column of a lake, for example, these processes transport dissolved and particle-bound chemicals equally across the boundaries of the test volume. Settling of particles, in contrast, causes a downward flux of particle-bound chemicals while leaving dissolved chemicals in place. Similarly, surfactants or gases that join rising air bubbles are carried to the surface. These discriminate transport processes are very important in a variety of environmental situations ... 

One of the main functions of the plasma membranes of living cells is to control the transport processes into and out of the cells of many substances and thus to regulate the composition of the intracellular fluid. The fluid usually contains solutes at concentrations which are quite different from their corresponding values in the bathing medium. This is achieved by the ability of the membrane to discriminate among various solutes so that some are allowed through, others are kept inside or outside the cell, and still others are carried actively. In addition, important processes such as oxidative metabolism, protein synthesis and several other synthetic processes are intimately connected with and dependent on membrane processes. In fact, continued existence of the cell is critically dependent on its having a functional plasma membrane. 

As well known, 18-crown-6 type carriers transported NH cation but could not discriminate NH cation from K cation in the transport process. Furan-bearing double armed crown ether 4 also showed high transport efficiencies for both cations and seemed to be non-selective carrier in some sense. 

The objective of kinetic measurements is to discriminate between micro- and macrokinetics. As microldnetics we consider the kinetics of the chemical reaction, that is, the measured rate is not affected by transport processes (intrinsic kinetics), if the intrinsic kinetics cannot be separated from transport processes at the conditions reievant for technicai operation we speak of macro-kinetics or effective apparent kinetics. 

The transport processes and biological response involved in quinone-stimulated human epithelial cells were further studied by Rotenberg and Mirkin. They demonstrated that quinone-based mediators rapidly cross the cell wall to electrochemically react in the intracellular lumen. These events are reported to occur on a microsecond timescale. The apparent electron transfer rates measured for nonmetastatic and metastatic cells demonstrate the modulation effects of protein kinase Ca. Such studies establish the potential for SECM to evolve in an analytical tool capable of discriminating between cancerous and healthy cells. As such, the judicious choice of redox mediator couple will be key in achieving the desired electrochemical contrast. ... 

The ability of varying the rate of the mass transport by agitating the solution (or the working electrode) constitutes the basis of hydrodynamic methods (hydrodynamics = liquids in motion), which are a further support to the study of electrode kinetics. Nevertheless we wish to cite them here simply to cover a drawback of cyclic voltammetry. In fact, cyclic voltammetry is unable to discriminate between oxidation and reduction processes, and vice-versa. 

Although confocal microscopic imaging of cells incubated with labeled targeted systems allow a rather clear decision about cytoinvasion, the quantification of cellular uptake is rather challenging, due to coincidence of cytoadhesion with cytoinvasion. The discrimination between both processes, however, is possible by taking into account some distinctive features of certain transport mechanisms. 

Comprehensive monographs are also available detailing the analysis of mass transfer though porous and dense membranes. Standard textbooks [e.g., Refs. 26, 27] provide the basis for discriminating between various possible transport mechanisms and the selection of models capable of describing the processes in quantitatively. 

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