Quenching techniques

Figure 19.16(a) An SFg circuit breaker 123-145 kV, 31.5 kA. It can also be pneumatic or spring operated, depending upon the arc quenching technique adopted and energy required to extinguish 2 the arc (Courtesy BHEL) 3... 

Several determinations of the number of propagation centers by the quenching technique have been carried out (98, 111). As a quenching agent methanol, labeled C14 in the alkoxyl group, proved to be suitable in this case. The number of active centers determined by this technique at relatively low polymerization rates (up to 5 X 102 g C2H4/mmole Cr hr at 75° and about 16 kg/cm2) (98, 111, 168) in catalysts on silica was about... 

The number of active centers determined by the quenching technique was dependent on the polymerization temperature (98) that was the reason for the difference between the overall activation energy and the activation energy of the propagation step. 

Experimental data measured by the radio tracer quenching technique at 75°C. 

Each of these compounds, 53-56, was shown to be a very effective competitive inhibitor of the enzyme with respect to the fructose 1,6-diphosphate, whereas several other analogs, including acyclic structures, had no effect. These and other results suggest that the furanose form of the sugar diphosphate is the active form in the enzymatic reaction (105). More recent studies using rapid quenching techniques and C-nmr measurements have confirmed this hypothesis and indicate that the enzyme uses the a anomer 52 much more rapidly than the 3 anomer 50 and probably uses the a anomer exclusively (106). 

OV-absorbing compounds can be measured by fluorescence quenching as well as by reflectance. The fluorescence quenching technique provides a means of visualizing spots absorbing UV-light... 

Vo-Dinh T, Pal, T. 1992. Development of a fluorescence quenching technique to detect permeation of chemical agent simulants through protective clothing materials. Appl Spectrosc 46(4) 677-681. 

The location of a compound within a lipid bilayer can be studied using X-ray diffraction [167], neutron diffraction [164], fluorescence quenching techniques [163], differential scanning microcalorimetry [164], or NMR techniques [168,169],... 

In our previous paper (H), we introduced a novel experimental method to study the mechanistic details of solvent permeation into thin polymer films. This method incorporates a fluorescence quenching technique (19-20) and laser interferometry ( ). The former, in effect, monitors the movement of vanguard solvent molecules the latter monitors the dissolution process. We took the time differences between these two techniques to estimate both the nascent and the steady-state transition layer thicknesses of PMMA film undergoing dissolution in 1 1 MEK-isoproanol solution. The steady-state thickness was in good agreement with the estimate of Krasicky et al. (IS.). ... 

M. H. Winkler, A fluorescence quenching technique for the investigation of the configurations of binding sites for small molecules, Biochemistry 8, 2586-2590 (1969). 

R. Homan and M. Eisenberg, A fluorescence quenching technique for the measurement of paramagnetic ion concentrations at the membrane/water interface. Intrinsic and X537A-mediated cobalt fluxes across lipid bilayer membranes, Biochim. Biophys. Acta 812, 485—4-92 (1985). 

A dipping technique was proposed by Dickermann etal. in 1976 for the study of single-crystal electrodes, in which only the surface of a well-defined single-crystal is in contact with an electrolyte solution, and without any other pretreatment, the other portion of the crystal metal is not exposed to the solution. In the case of Pt, an annealing-quenching technique was developed by Clavilier etal in 1980. This technique has... 

Withers A.G., Zhang Y., and Behrens H. (1999) Reconciliation of experimental results on H2O speciation in rhyolitic glass using in situ and quenching techniques. Earth Planet. Sci. Lett. 173, 343-349. 

Let us recall the micellar aqueous system, as this procedure is actually the basic one. The chemistry is based on fatty acids, that build micelles in higher pH ranges and vesicles at pH c. 8.0-8.5 (Hargreaves and Deamer, 1978a). The interest in fatty acids lies also in the fact that they are considered possible candidates for the first prebiotic membranes, as will be seen later on. The experimental apparatus is particularly simple, also a reminder of a possible prebiotic situation the water-insoluble ethyl caprylate is overlaid on an aqueous alkaline solution, so that at the macroscopic interphase there is an hydrolysis reaction that produces caprylate ions. The reaction is very slow, as shown in Figure 7.15, but eventually the critical micelle concentration (cmc) is reached in solution, and thus the first caprylate micelles are formed. Aqueous micelles can actually be seen as lipophylic spherical surfaces, to which the lipophylic ethyl caprylate (EC) avidly binds. The efficient molecular dispersion of EC on the micellar surface speeds up its hydrolysis, (a kind of physical micellar catalysis) and caprylate ions are rapidly formed. This results in the formation of more micelles. However, more micelles determine more binding of the water-insoluble EC, with the formation of more and more micelles a typical autocatalytic behavior. The increase in micelle population was directly monitored by fluorescence quenching techniques, as already used in the case of the... 

Substituted cyclohexanones, bearing a methyl, isopropyl, tert-butyl or phenyl group, give, on deprotonation with various chiral lithium amides in the presence of chlorotrimethylsilane (internal quench), the corresponding chiral enol ethers with moderate to apparently high enantioselec-tivity and in good yield (see Table 2)13,14,24> 29 36,37,55. Similar enantioselectivities are obtained with the external quench " technique when deprotonation is carried out in the presence of added lithium chloride (see Table 2, entries 5, 10, and 30)593. 

Samples investigated were 0.3-3.0 o,m amorphous Sb Sei (0 < x < 0.05) films. These were preferentially prepared by conventional vacuum evaporation onto room-temperature sihca-glass substrates (plates). The a-Sb Sei source material was made by the usual melt-quenching technique. Coohng rate was estimated to be 100-200 K/s. Prior to measurements, the films prepared were aged at laboratory conditions (natural aging) for several weeks to allow their structure to equilibrate. 

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