Transient of current

Fig. 8.29 Transients of current (a, open circles) and the sulfate band intensity (b) for a potential step from 0.1 to 0.3 V (vs SCE). The solid curve in (a) represents a numerical fit with Langmuir kinetics and spontaneous nucleation-and-growth kinetics. The contributions of the first and second kinetics...

Fig. 24. Transient of current (solid line) with fit (dotted line) and of optical transmittance (normalized) for Y film after a potential step of 0.2 V to —0.95 V was applied (Di Vece and Kelly, 2003a Di Vece et al., 2003b, 2003c).

The scheme is termed a closed transient switching. A comparison of the two methods in terms of voltage transients and current overshoots is given in Table 4.1. In an AIT starter The same logic can be applied as discussed above. The star point of the AIT is opened and connected through the main contactor C3 to provide a near replica to a Y A switching. Figure 4.7 illustrates the revised scheme. 

The instant (sub-transient) fault current, /jjgf, through a generator in a symmetrical three-phase system, irrespective of the condition of neutral as defined in Table 13.9 will be... 

Another major second messenger in cells is calcium ion. Virtually any mammalian cell line can be used to measure transient calcium currents in fluorescence assays when cells are preloaded with an indicator dye that allows monitoring of changes in cytosolic calcium concentration. These responses can be observed in real time, but a characteristic of these responses is that they are transient. This may lead to problems with hemi-equilibria in antagonist studies whereby the maximal responses to agonists may be depressed in the presence of antagonists. These effects are discussed more fully in Chapter 6. 

The first indication that NEMCA is due to electrochemically induced ion backspillover from solid electrolytes to catalyst surfaces came together with the very first reports of NEMCA Upon constant current application, i.e. during a galvanostatic transient, e.g. Fig. 5.2, the catalytic rate does not reach instantaneously its new electrochemically promoted value, but increases slowly and approaches asymptotically this new value over a time period which can vary from many seconds to a few hours, but is typically on the order of several minutes (Figure 5.2, galvanostatic transients of Chapters 4 and 8.)... 

In Figure 4.14 we have seen a typical galvanostatic transient of this system. Positive current application (1=400 pA) causes a 88-fold increase in catalytic rate (p=88). The rate increase is 770 times larger than the rate I/2F ofO2 supply to the catalyst(A=770). The NEMCA time constantt is 40s in good qualitative agreement with the parameter 2FNG/I=18s. 

Figure 8.27. Transient effect of current on the rate of CO oxidation on Pt (solid lines) and on catalyst potential (broken lines) inlet compositions and temperatures (a) pco=0.47 kPa, po2-10 kPa, T=412°C (b) pco=2.9 kPa, po2=0.40 kPa, T=555°C.33 Reprinted with permission from Academic Press.

As already shown in Figure 6.3b the system exhibits remarkable electrophilic promotional behaviour with p values up to 20.64 This is also shown in Fig. 8.60 which depicts a galvanostatic transient. Application of a negative current between the Pt catalyst-working electrode and the Au counter electrode causes a sharp increase in all reaction rates. In the new steady state of the catalyst (achieved within lhr of current application) the catalytic rate increase of C02 and N2 production is about 700%, while lesser enhancement (250-400%) is observed in the rates of CO and N20 production. The appearance of rate maxima immediately after current application can be attributed to the reaction of NO with previously deposited carbon.64... 

Figure 8.17. Potentiostatic transient of C2H4 oxidation on Pt/Ce02. Rate and current responses to step changes in catalyst potential, UWR) are plotted against time. T = 500°C, p02 = 5.5 kPa, PC2H4= 1 5 kPa.71 Reproduced by permission of The Electrochemical Society.

Figure 2.4 Noradrenergic inhibition of Ca " currents and transmitter release in sympathetic neurons and their processes, (a) Inhibition of currents through N-type Ca " channels by external application of noradrenaline (NA) or by over-expression of G-protein P y2 subunits, recorded from the soma and dendrite of a dissociated rat superior cervical sympathetic neuron. Currents were evoked by two successive 10 ms steps from —70 mV to OmV, separated by a prepulse to -1-90 mV. Note that the transient inhibition produced by NA (mediated by the G-protein Go) and the tonic inhibition produced by the G-protein Piy2 subunits were temporarily reversed by the -1-90 mV depolarisation. (Adapted from Fig. 4 in Delmas, P et al. (2000) Nat. Neurosci. 3 670-678. Reproduced with permission), (b) Inhibition of noradrenaline release from neurites of rat superior cervical sympathetic neurons by the 2-adrenoceptor stimulant UK-14,304, recorded amperometrically. Note that pretreatment with Pertussis toxin (PTX), which prevents coupling of the adrenoceptor to Gq, abolished inhibition. (Adapted from Fig. 3 in Koh, D-S and Hille, B (1997) Proc. Natl. Acad. Sci. USA 1506-1511. Reproduced with permission)...

The further fate of the solvated electrons depends on solution composition. When the solution contains no substances with which the solvated electrons could react quickly, they diffuse back and are recaptured by the electrode, since the electrochemical potenhal of electrons in the metal is markedly lower than that of solvated electrons in the solution. A steady state is attained after about 1 ns) at this time the rate of oxidahon has become equal to the rate of emission, and the original, transient photoemission current (the electric current in the galvaihc cell in which the illuminated electrode is the cathode) has fallen to zero. Also, in the case when solvated electrons react in the solution yielding oxidizable species (e.g., Zn " + Zn" ),... 

Benndorf, K., Friedrich, M. and Hirche, H. (1991). Reoxygenation-induced arrhythmogenic transient inward currents in isolated cells of the guinea-pig heart. Pflugers Arch. 418, 248-260. 

Karagueuzian, H.S. and Katzung, B.G. (1982). Voltage-clamp studies of transient inward current and mechanical oscillations induced by ouabain in ferret papillary muscle. J. Physiol, 327, 255-271. 

Kass, R.S., Tsien, R.W. and Weingart, R. (1978). Ionic basis of transient inward current induced by strophanthidin in cardiac Purkinje fibres. J. Physiol. 281, 209-226. 

Lue, W.M. and Boyden, P.A. (1992). Abnormal electrical properties of myocytes from chronically infarcted canine heart - alterations in V and the transient outward current. Circulation 85, 1175-1188. 

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