Relative change in concentration

SIMS intensities from the "clean" Cu/Ni surfaces cannot be used to determine Cu/Ni surface concentrations, or relative change in concentration from one surface to another. This is because trace impurities (of very low but unknown concentration) preferentially bond to Ni sites and therefore the Ni containing SIMS cluster ions are preferentially enhanced, leading to an erroneously high determination of Ni concentration. 

The relative change in concentration of hydrogen atoms in the volume of reaction vessel can be expressed through the stationary value of electric conductivity of adsorbent as follows ... 

The diffusion parameter calculated by the root time method is an average parameter, and is generally considered to be operative over the range of time from initial diffusion flux to near steady state flux conditions. The method is applicable for the situation where adsorption and desorption occur, and for various pH values of the influent. The closer (DE) is to (DB) in Fig. 5 d, the greater is the accuracy of the D coefficient. It is important to note that in the case of low pH values of the influent, desorption of cations from a clay soil could produce conditions where C2 > C1. Accordingly, the experimental values for relative change in concentration would then become negative. 

The concentration of a regulator (jc) changes by Ax, so that the relative change in concentration is Ax/x. This results in a change in flux, J, by AJ, so that the relative change in flux is AJ/J. The sensitivity of the flux to the change in concentration of x is given by the ratio... 

Figure 20.31 The principle of interconversion cycles in regulation of protein activity or changes in protein concentration as exemplified by translation/proteolysis or protein kinase/protein phosphatase. They result in very marked relative changes in regulator concentration or enzyme activity. The significance of the relative changes (or sensitivity in regulation) is discussed in Chapter 3. The principle of regulation by covalent modihcation is also described in Chapter 3. The modifications in cyclin concentration are achieved via translation and proteolysis, which, in effect, is an interconversion cycle. For the enzyme, they are achieved via phosphorylation and dephosphorylation reactions. In both cases, the relative change in concentration/activity by the covalent modification is enormous. This ensures, for example, that a sufficient increase in cyclin can occur so that an inactive cell cycle kinase can be converted to an active cell cycle kinase, or that a cell cycle kinase can be completely inactivated. Appreciation of the common principles in biochemistry helps in the understanding of what otherwise can appear to be complex phenomena.

The corrections Ah and dlnCJdlnQ, accounting for the relative change in concentration are usually small. If these are neglected, Eq. (7.12) can be expressed as [29]... 

Here R is the gas constant, T the absolute temperature, F the interfacial or surface concentration in moles per unit area, and c the concentration in arbitrary units (dine = dc/c is the relative change in concentration and hence dimensionless). 

The distribution of sulfur (originally added as CS2) in xanthated crumb can be determined by UV absorption spectrophotometry. Hovenkamp [154] and others have used this technique to follow the course of the xanthate reaction. Typical results are outlined in Figure 10.56, which summarizes the relative change in concentration of reactants and products. The CS2 concentration continually decreases and sulfide and by-products increase as the reaction proceeds. The xanthate concentration passes through a maximum and then begins to decrease, while the by-product (trithiocarbonate) continues to increase after the CS2 has been consumed. 

Fig. 6. Relative change in concentration of (O) inner membrane, ( ) phospholipid, and (O) cytochrome a -f- as in mitochondria from rat brown adipose tissue. Ordinate, percentage change from day before birth abscissa, days after birth (B). CA, cold acclimated rats. After Lindgren and Barnard (1972).

Nuclear characteristics refer to the conditions and material concentrations under which reactor systems will remain critical, the relative changes in concentration of materials within the system as a function of reactor operation, and the time behavior of variables in the reactor system which occur when deviations from criticality take place. The material concentrations are closely connected with fuel costs in power reactors, while reactor behavior under noncritical conditions is closely related to the safety and control of the reactor system. These nuclear characteristics are determined from the results obtained from so-called "reactor criticality and "reactor kinetic calculations. In such studies, certain parameter values pertaining to nuclei concentrations and reaction probabilities are used for convenience some of these are listed in Section 2-2. 

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