Potential Probes

Depolarization times greater than 48 hours should be allowed when applying the 100-mV criterion. Comparison of measured potentials is only possible where conditions of temperature and moisture are similar. Figure 19-8 shows the dependence on season and temperature which can probably be ascribed to different aeration. In repair work, potential probes should be provided at different places on the object to reduce IR errors in off potential measurements arising from equalizing currents. 

Measurement of space potential in a large container using the field meter head as a potential probe (3-5.3.4). 

Lloyd-Jones G, PCK Lau (1997) Glutathione 5-transferase-encoding gene as a potential probe for environmental bacterial isolates capable of degrading polycyclic aromatic hydrocarbons. Appl Environ Microbiol 63 3286-3290. 

In addition to their use as reference electrodes in routine potentiometric measurements, electrodes of the second kind with a saturated KC1 (or, in some cases, with sodium chloride or, preferentially, formate) solution as electrolyte have important applications as potential probes. If an electric current passes through the electrolyte solution or the two electrolyte solutions are separated by an electrochemical membrane (see Section 6.1), then it becomes important to determine the electrical potential difference between two points in the solution (e.g. between the solution on both sides of the membrane). Two silver chloride or saturated calomel electrodes are placed in the test system so that the tips of the liquid bridges lie at the required points in the system. The value of the electrical potential difference between the two points is equal to that between the two probes. Similar potential probes on a microscale are used in electrophysiology (the tips of the salt bridges are usually several micrometres in size). They are termed micropipettes (Fig. 3.8D.)... 

Fig. 6.18 Experimental arrangement for measurement of the membrane potential of a nerve fibre (axon) excited by means of current pulses (1) excitation electrodes, (2) potential probes. (According to B. 

A comprehensive series of mono- and dinuclear iodoplatinum(II) complexes [Ptl(dien)]+ and [ PtI(dien) 2(/r-CH2) ] (42) (dien = parent or substituted diethylenetriamine n = 2-9), respectively, have been synthesized as potential probes of nucleic acid structure.158 Both chiral and achiral species were prepared. In general, the complexes are synthesized by the reaction of trans-[PtI2(DMSO)2] with the dien ligand in DMF solution. 

C. J. Drummond and F. Grieser, Absorption spectra and acid-base dissociation of the 4-alkyl derivatives of 7-hydtoxycoumarin in self-assembled surfactant solution Comments on their use as electrostatic surface potential probes, Photochem. Photobiol. 45, 19-34 (1987). 

Figure 6. A modern automatic film balance. The ionizing source for the surface potential probe is shown on its swinging arm, out of the way at the rear of the trough. Readout equipment is at the far left.

R. F. G. Frohlich, R. H. Fumeaux, D. J. Mahuran, R. Saf, A. E. Stiitz, M. B. Tropak, J. Wicki, S. G. Withers, and T. M. Wrodnigg, 1-Deoxy-D-galactonojirimycins with dansyl capped N-substitu-ents as P-galactosidase inhibitors and potential probes for GMi gangliosidosis affected cell lines, Carbohydr. Res., 346 (2011) 1592-1598. 

The styryl dye Di-4-ANEPPS (3.69) is a fast-responding membrane potential probe, particnlarly nsefnl for the studies of neuronal membrane potentials. 

The experimental determination of a potential change across a solid/solid interface is a most difficult task since it means that potential probes have to be placed very near the interface. Electrochemists face a similar problem when they study electrode kinetics, but the handling of fluids in this respect is much easier. Nevertheless, we will exploit their concepts and methods to some extent in what follows. 

Fig. 6. Conductivity methods, a) guard ring techniques, b) potential probe technique...

There are a number of empirical tests for the near ideality of potential probes. Ideal probes should exhibit a solvent dependence of the fluorescence Stokes-shift (hvabs - hvn) that is in account with the Lippert-Mataga equation [9,10]. 

The excited molecule is a unique surface probe. The decay time provides a clock which can be used to study such dynamics. Since both singlets and triplets are potential probes, the time scale extends from seconds to picoseconds. In addition, the nature of any photo-... 

Mutations of the human APC gene are associated with both sporadic and familial forms of colon cancer. The APC protein is a large, multi-domain protein that has a 55-residue, N-terminal dimeric coiled coil (APC-55). Alber and colleagues used rules of thumb and those derived from an analysis of the covariation of a d and d d pairs in the cytokeratins (which form obligate heterodimers) to create a mutant of APC-55, anti-APCpl, as a potential probe for the APC protein (Sharma et al, 1998). 

AgBr by the aid of thermal treatment [312, 313], These wires can, for example, be used as local potential probes. Moreover, very fine metal wires have been welded on oxide surface [314, 315],... 

Fig. 40. Activation of a ribbon electrode with modulation and reflection at the end of the ribbon during Co dissolution in buffered phosphoric acid. The patterns were measured with 16 potential probes. White denotes total passivity black, highest activity. (Reproduced with permission from R. D. Otterstedt, N. I. Jaeger, P. J. Plath and J. L. Hudson, Phys. Rev. E 58 (1998) 6810, (1998) by the American Physical Society).

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].)... 

A series of 3-(alkylamino)-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1 -dioxides (168a-j) that are related to diazoxide (396) (a compound which induces hyperglycemia in vivo through decreased insulin secretion and is a potent pancreatic KATP channel opener) and pinacidil (397) were prepared and tested as inhibitors of insulin release from rat pancreatic islets. Of the compounds tested, BPDZ 44 (168g) was chosen for further study as a potential probe for KATP channels. The compounds tested were the most powerful inhibitors of insulin release reported at that time <93JMC32li>. 

Both alternating and direct current techniques can be used (see also impedance spectroscopy), but the electrode polarization effects should be minimized or taken into account in all cases. For this goal, a four-electrode method where the potential probes are placed between current probes, is often used. 

In this method, two saturated calomel reference electrodes (SCEs) are used as the potential probes, Pt gauze is used for both current probes, and 1 M H2S04 is the electrolyte. Figure 5.14 shows the schematic of the hardware and instruments in this method. 

Resistivity Measurements. The measurements by the Cornell group have all been made on single crystals by a potential-probe method, the details of which have been reported (32). Typical results are presented graphically in Figure 3. 

Electrical resistivity was measured by a d.c. method using four-probe techniques to avoid problems arising from contact resistance. Pressure contacts were used for both current and potential probes. At low temperatures, the current contacts could be improved by ultrasonically tinning the ends of the samples. 

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