Physicochemical gradients

Metal transport and deposition capacities of mineral systems are closely linked to propagation of redox and related physicochemical gradients (pH, aH2, aHCI, aH2S, aS02, aC02, aCH4, aH20, etc) within mineral systems. For metals transported in solution, the rate of mineralization is a product of 3 factors (see Fig. 2) ... 

The objectives of this study were (1) to assess the effect of colloid mineralogical composition on colloid-mediated transport of metals in subsurface soil environments, and (2) to establish physicochemical gradients and conditions enhancing or inhibiting colloid-mediated transport. The following case studies were used to demonstrate the effects of mineralogy on colloid-mediated transport of metals. 

Because protein samples are actually ampholytes, when samples are loaded onto the gel and a current is appHed, the compounds migrate through the gel until they come to their isoelectric point where they reach a steady state. This technique measures an intrinsic physicochemical parameter of the protein, the pi, and therefore does not depend on the mode of sample appHcation. The highest sample load of any electrophoretic technique may be used, however, sample load affects the final position of a component band if the load is extremely high, ie, high enough to titrate the gradient ampholytes or distort the local electric field. 

A surface whose physicochemical properties gradually change as a function of the position is called a gradient surface. While the gradient surface has potential applications as a substrate for combinatorial studies [29-31], the gradient of surface wetting is of particular interest because spontaneous motions of a droplet are induced on the surface [32]. 

Some Guidelines for a Typical Application of Gradient RPLC in Physicochemical Profiling... 

The rate of separation of the fragments depends on the functions A r), C(r), Fc> and the fragmentation number, while the rate of rotation depends only on the function B(r). Further, it is apparent that the separation between the fragments increases only when the hydrodynamic force exceeds the binding physicochemical force. The pair of fragments rotates as a material element in an apparent flow with an effective velocity gradient tensor... 

A thorough discussion of the mechanisms of absorption is provided in Chapter 4. Water-soluble vitamins (B2, B12, and C) and other nutrients (e.g., monosaccharides, amino acids) are absorbed by specialized mechanisms. With the exception of a number of antimetabolites used in cancer chemotherapy, L-dopa, and certain antibiotics (e.g., aminopenicillins, aminoceph-alosporins), virtually all drugs are absorbed in humans by a passive diffusion mechanism. Passive diffusion indicates that the transfer of a compound from an aqueous phase through a membrane may be described by physicochemical laws and by the properties of the membrane. The membrane itself is passive in that it does not partake in the transfer process but acts as a simple barrier to diffusion. The driving force for diffusion across the membrane is the concentration gradient (more correctly, the activity gradient) of the compound across that membrane. This mechanism of... 

Doi R, Sakurai K (2004) Principal components derived from soil physicochemical data explained a land degradation gradient, and suggested the applicability of new indexes for estimation of soil productivity in the Sakaerat Environmental Research Station, Thailand. Int J Sustain Dev World Ecol... 

In Mitchell s earliest physicochemical formulations of the chemiosmotic theory, any involvement of the membrane across which the proton gradient was established received little attention. Between 1961... 

Gibbs adsorption equation is an expression of the natural phenomenon that surface forces can give rise to concentration gradients at Interfaces. Such concentration gradient at a membrane-solution Interface constitutes preferential sorption of one of the constituents of the solution at the interface. By letting the preferentially sorbed Interfacial fluid under the Influence of surface forces, flow out under pressure through suitably created pores in an appropriate membrane material, a new and versatile physicochemical separation process unfolds itself. That was how "reverse osmosis" was conceived in 1956. 

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