Ring electrodes during

Figure 55. SP microscope images of a potential wave on an Ag ring electrode during the reduction of eroxodisulfate (elapsed time between the images, 4.5 s). (After Flatgen etal. ) A color representation of this figure can be found following page 112.

FIGURE 8.4. Space-time plots of the potential distributions on a Pt ring electrode during passive-active transitions. The ring position refers to Fig. 8.3 [44]. (a) Local triggering, (b) Remote triggering. (See color insert.)... 

It is to be noted that activation by resonance resembles axial modulation (see Chapter 4) because both require the application of a radiofrequency of type Vcostot between the endcap electrodes. There are nevertheless two important differences between the two concepts. First, the value of V is around 3 to 4 volts in axial modulation and 0.2 to 1.5 V in MS/MS where the point is not to eject the precursor ions. The second difference is the value of the radiofrequency trapping amplitude applied to the ring electrode during the application of the radiofrequency of resonance. This value is high in axial modulation and low in MS/MS where the point is to trap the daughter ions formed by collision. 

The experimental setup of a rotating hemispherical electrode (RHSE) is similar to that of a rotating disk electrode [50]. The basic system consists of a removable hemispherical electrode, and a variable speed rotator equipped with a provision, such as the slip-ring contact, to make electric connection to the hemispherical electrode during the experiments. 

By applying the supplementary RF voltage during injection (without scanning the RF voltage on the ring electrode) it is possible to prevent certain ions from being trapped. 

To appreciate that during RRDE analyses, one reagent is in the solution while the other is electrogenerated at the disc electrode, and that the proportion of the electro generated reagent that remains after reaction is monitored at the ring electrode, and is a function of w and kj. 

The acute recording of evoked potentials and the stimulation at the spinal cord has been a well-established method for more than 20 years. The procedures require electrodes that are similar to pacemaker electrodes. Applications can be found in the field of skoliosis correction [38, 39] and the repair of aorta aneurysms [40]. An intraoperative stimulation of fibers of the sacral spinal cord was performed during dissection of unilateral testicle tumors to preserve ejaculation [41]. The main application of implants for chronic stimulation of the spinal cord is the handling of chronic pain [42]. There are two types of electrodes the percutaneous electrodes resemble the pacemaker electrodes. They consist of a mandrel with up to four ring electrodes of a platinum iridium alloy (Fig. 6). They have a length of 3 mm with an interelectrode distance of 6 mm or a length of 6 mm with an interelectrode distance of 12 mm. 

Fig. 20. Experimental I/U curve obtained during the H2 electrooxidation on Pt in H2-saturated 0.1 M H2SC>4 electrolyte solution in the presence of 10-3 M HC1 (curve a) and after addition of 10-4 M CUSO4 (curves b and c). The Pt ring-electrode (area 0.911 cm2) was rotated (rotation rate 20Hz). Curves a and b were obtained during a potential sweep (sweep rate lOmV s-1), curve c during a current scan with 7 pA s-1.

Fig. 31. Experimental potential fronts (a) during the corrosion of gold in a concentrated HCl/NaCl solution (after Ref. [85]) (b) during the potentiostatic reduction of SgOg2 on a silver ring electrode in dilute electrolyte [166], On the left are the corresponding set-ups.

Fig. 45. (a) Cyclic voltammogram and (b) stationary potential domains during the reduction of S20g2 on a Ag ring electrode at fixed outer potential (t/ = —1.13V) [42], The end of a Haber-Luggin capillary was positioned on the axis of the ring and close to the WE. 

Grauel and Krischer also detected similar stationary domains during the oxidation of H2 on a Pt ring electrode in sulfuric acid [182]. As can be seen in the cyclic voltammogram in Fig. 46a, in this case the homogeneous active branch coexisted with the oxide covered passive branch, and thus the homogeneous dynamics were bistable. The stationary structure displayed in Fig. 46b spontaneously formed when a... 

Fig. 49. (a) Local potential drop across the double layer as a function of position and time during a remotely induced transition in the bistable regime of the oxidation of formic acid on a Pt ring electrode. The RE was positioned close to the WE. At the position marked by the arrows the potential was disturbed locally toward positive values. The ring position gives the electrode number of (b). (b) Set-up for measurements used to obtain the data of (a). The outside potential probes serve to measure the local potential the central one serves as the reference electrode. At position 12 is a trigger electrode. (This figure was provided by courtesy of P. Strasser and M. Eiswirth see also Ref. [36].)... 

Fig. 52. Standing wave observed during the potentiostatic oxidation of formic acid on a Pt ring electrode. The RE was located on the axis of and close to the WE. See Fig. 51(B) for the experimental set-up. (Courtesy of P. Strasser and M. Eiswirth, for details see [184].)...

Fig. 53. (a) Cyclic voltammogram during the formic acid oxidation on a Bi-modified Pt ring electrode scan rate 5mV s-1. The change in the oscillation form close to t = 73.7 s (i.e. U = 0.16 V) indicates a qualitative change in the dynamics, (b) Spatio-temporal profile of the interfacial potential in the transition region of the oscillation form in (a). For the experimental set-up, see Fig. 49b. (Reproduced from J. Lee, J. Christoph, P. Strasser, M. Eiswrith and G. Ertl, J. Chem. Phys. (2001) 115, 1485 by permission of the American Institute of Physics.)...

Fig. 56. Position-time plots of the local double layer potential and corresponding time series of the global current during the oxidation of H2 on a Pt ring electrode for 6 different values of the external potential [173], The RE was on the axis of the ring in an intermediate distance between the WE and the RE. (Electrolyte 0.5 mM H2SO4, 0.1 mM HC1, and 0.025 mM Q1SO4 saturated with H2.)...

In an N-NDR model Christoph et al. [35, 37] found stable target patterns coexisting with the pulse solution for values of the external voltage for which the stationary state is also unstable with respect to homogeneous perturbations. In contrast, the asymmetric target patterns and the more complex motions observed during H2 oxidation on Pt ring electrodes (cf. Fig. 56) have not yet been reproduced in simulations. 

Fig. 61. Cluster pattern observed during the electrodissolution of a Fe ring electrode in the active/passive transition region under potentiostatic conditions. The RE was located in the plane of the WE. (a) and (b) Snapshots taken during two successive oscillations of the total current, (c) Spatiotemporal plot of the azimuthal intensity. (Reproduced with permission from B. J. Green and J. L. Hudson, Phys. Rev. E 63 (2001) 026214, (2001) by the American Physical Society).

Fig. 63. Cluster-type patterns observed during the electrooxidation of H2 on Pt ring electrodes. (Electrolyte 1 mM H2SO4, 10-6 mM CuSC>4, 10 5 mM HC1.) (a) Period 2 two-phase clusters and (b) three-phase clusters. (Shown is only the spatially varying part of the data.)...

The quadrupole ion trap (QJT) is about the size of a small fist and consists of a ring electrode and two hyperbolic end electrodes (see March and Todd68 for a detailed theory of operation and history of development). Like the linear ion trap (LIT, see below), the QJT operates at relatively high pressure (10 3 torr) with a helium buffer gas that assists the ions to maintain a stable orbital frequency. The buffer gas also serves as the collision gas for collision-induced dissociation (CID) during MS/MS experiments. 

A typical transition from the passive to the active state, as measured with a potential probe and a rotating Ag ring electrode, is reproduced in Fig. 53. The accelerated motion of the interface immediately leaps to the eye. It is, according to the explanation given in Section III.l, a consequence of nonlocal coupling. Accelerated fronts were found to be the characteristic feature in aU passive to active transitions. By contrast, during the much slower transitions from the active to the passive state, often only faint spatial variations were observed, but no sharp interfaces between... 

Figure 71. Differences of successive snapshots of the surface during passivation phases of two successive current oscillations of a period-2 state of the potentiostatic dissolution of an iron ring electrode. (Reprinted with permission from J. C. Sayer and J. L. Hudson, Ind. Eng. Chem. Res. 34, 3246, 1995. Copyright 1995, American Chemical Society.)...

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