Impedance locus

Keiser et al.164 first showed that the more occluded the shape of the pore, the more distorted the impedance locus from the ideal capacitive behavior. However, the pore shapes in real system turn out to be much complicated and thus a straightforward analytical calculation is not usually possible of the overall impedance for those complicated pores. In connection with this problem, the fractal geometry has given a powerful tool for the analysis of the CPE behavior of the porous electrode. A number of theoretical papers166,179 191 have devoted to investigate the relationship between the fractal geometry of the electrode and the CPE impedance on the basis of the electrolytic resistive distribution due to the surface irregularity. 

Some features of the impedance locus diagram depend on the gas composition in a characteristic manner. This impedance locus is described by... 

Figure 6. Effect of a switch from pure Nj to Nj with 10 ppm propane (all dry) on the impedance locus diagram (measurement day 1 6.5 h to 6.9 h, measurement period 2 minutes per curve).

Figure 9.12 The impedance locus (ZARC) of the Colez system.

He introduced a constant phase element (CPE), defined in the paper by the phase angle ( )3 = arccotan (m), and m = accordingly using m completely differently from Fricke ideal resistor has m = oo and < )3 = 0°, and found the impedance locus for such a system was a circular arc with the center below the real axis in the Wessel diagram. A plot of complex immittance or immittivity in the Wessel diagram with the purpose of searching for circular arcs, may according to this book, be called a Cole-plot. 

Eq. (74) is shown in Figure 4.4.18. As expected, the impedance locus is a straight line when... 

During the analysis of the impedance data for Alloy-22, it became evident that the impedance locus depended in a very sensitive manner on the magnitude of the rate constant for the film dissolution reaction at the barrier layer/solution interface. Using parameter values that are typical for Alloy-22 (Table 4.4.7), Nyquist plots of the impedance of Alloy-22 in 6.2 m NaCl + 0.001 m HCl (pH = 3) at 80°C, together with the experimental data for a voltage of 0.398 Vsbe, are shown in Figure 4.4.33. The data are plotted with equal scales on the two axes, which is the accepted convention for Nyquist plots. 

The impedance of small lithium-copper oxide primary cells has been investigated in a frequency range from 5 mHz to 10 kHz. The cells had been stored after assembly for from three weeks up to three years and their state of charge was from 100% down to 20%. After an initial period of electrochemical stabilization, the cells exhibited consistent results and the shape of the impedance locus was found to depend markedly on the state of charge of the cell. An interpretation of the results is given in terms of an analogue circuit which contains components to represent the contribution to the impedance of each electrode and of the electrolyte. 

Fig. 4. Impedance locus of a 1% discharged cell after 72 h at the 100 h rate (37.5 mA) (open-circuit voltage, 2.09 V).

This lecture is not aimed at presenting a comprehensive review of fluctuation studies of nerve membranes, but rather a digest of the experimental work which I consider to be most representative of the present state of knowledge in this field. Only measurements of current fluctuations in nerve membranes kept under voltage-clamp conditions will be considered, reminding that equivalent information can also be extracted.from voltage fluctuations measurements provided the membrane impedance locus is known (8). A brief review of the basic theoretical concepts of fluctuations analysis is first presented. 

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