Sigmoidicity, measure

In case b) a potentiometrically measured calibration curve for ion M+ would show a sigmoidal form, starting with a sub-Nernstian slope leading to a super-Nemstian... 

K2C03 3 H202 contains hydrogen peroxide of crystallization and the solid phase decomposition involves the production of the free radicals OH and HOi, detected by EPR measurements [661]. a—Time curves were sigmoid and E = 138 kJ mole-1 for reactions in the range 333—348 K. The reaction rate was more rapid in vacuum than in nitrogen, possibly through an effect on rate of escape of product water, and was also determined by particle size. From microscopic observations, it was concluded that centres of decomposition were related to the distribution of dislocations in the reactant particles. 

Isothermal a—time curves were sigmoid [1024] for the anhydrous Ca and Ba salts and also for Sr formate, providing that nucleation during dehydration was prevented by refluxing in 100% formic acid. From the observed obedience to the Avrami—Erofe ev equation [eqn. (6), n = 4], the values of E calculated were 199, 228 and 270 kJ mole"1 for the Ca, Sr and Ba salts, respectively. The value for calcium formate is in good agreement with that obtained [292] for the decomposition of this solid dispersed in a pressed KBr disc. Under the latter conditions, concentrations of both reactant (HCOJ) and product (CO3") were determined by infrared measurements and their variation followed first-order kinetics. 

From comparable systems with a particle-size distribution width of 7%, experimental and computational results for temperature-dependent conductivity measurements were reported on by Remade et al. [57]. At low temperatures, the I(U) characteristics have a sigmoid shape and are non-linear (Figure 25). 

Because both Tg and water activity are functions of water content, the two parameters can be correlated to each other. This can be done in two main ways, as presented by Roos (1995). The first is to measure Tg of samples humidified to known water activity values (i.e., using saturated salt solutions) and then plot Tg values as a function of water activity (e.g., see Figure 6.2A in Roos, 1995). Over the entire nw range, a sigmoid-shaped curve was... 

S02 is a very stable oxide and its thermal decomposition is only measurable at the very high temperatures attained in a shock tube. A study357 of the time-dependence of light emission from shock-heated S02/Ar mixtures in the region of 3000 °K has shown that S02 is removed in accordance with a sigmoid-shaped concentration-time curve typical of a chain or autoaccelerated reaction. The induction period observed357 prior to the onset of detectable decomposition corresponded closely with the time for the formation of a fixed concentration of O (or SO) calculated from the rate expression (Table 24) for the unimolecular decomposition... 

In order to study the shape of a polymer-Cu complex, viscometric measurements of a homogeneous solution of QPVP were carried out (Fig. 1). At constant QPVP concentration, an increase in the added amount of Cu ions causes a decrease in viscosity, which reveals that the polymer-ligand chain is markedly contracted due to intra-polymer chelation. An intra-polymer chelate takes a very compact form and Cu ions are crowded within the contracted polymer chain (Scheme 2). The adsorption of Cu ions on the polymer ligand is sigmoidal, as can be seen in Fig. 1. At a low... 

Rush et al.51 first described the effect of thermally induced conformational changes on migration behavior of a-lactalbumin. A sigmoidal dependency of the viscosity-corrected mobility on temperature was observed. Transition temperature also agreed closely with that determined by intrinsic fluorescence measurements. 

For the catalytic electrode mechanism, the total surface concentration of R plus O is conserved throughout the voltammetric experiment. As a consequence, the position and width of the net response are constant over entire range of values of the parameter e. Figure 2.35 shows that the net peak current increases without limit with e. This means that the maximal catalytic effect in particular experiment is obtained at lowest frequencies. Figure 2.36 illustrates the effect of the chemical reaction on the shape of the response. For log(e) < -3, the response is identical as for the simple reversible reaction (curves 1 in Fig. 2.36). Due to the effect of the chemical reaction which consumes the O species and produces the R form, the reverse component decreases and the forward component enhances correspondingly (curves 2 in Fig. 2.36). When the response is controlled exclusively by the rate of the chemical reaction, both components of the response are sigmoidal curves separated by 2i sw on the potential axes. As shown by the inset of Fig. 2.36, it is important to note that the net currents are bell-shaped curves for any observed kinetics of the chemical reaction, with readily measurable peak current and potentials, which is of practical importance in electroanalytical methods based on this electrode mecharusm. 

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