Effect of Electrical Conductivity

A theoretical consideration of the influence of the anisotropy of the electrical conductivity on a Prederiks transition was carried out independently by different groups [22-24]. The principal result is that the anisotropy of the electrical conductivity has no influence on the threshold voltage, but it does affect the above threshold variation of the director in the cell. The relationship of the angle of deviation 6m to the external voltage for small 6 z) is derived from (4.17) as follows  

The dependence of the normalized Prederiks threshold on the parameter A = irKii/Wd is shown in Fig. 4.5(a). 

It is easiest to examine the kinetics of the Frederiks effect for the experimental geometry shown in Fig. 4.4(c), since a pure twist or T deformation is not accompanied by a change in position of the centers of gravity of the molecules. In contrast, for S- and B-effects the rotation of the director is accompanied by such a change in position, i.e., by a movement of the liquid (back-flow). In order to allow for this back-flow the equation of motion of the director is coupled with that of the fluid. 

For a pure T deformation the equation of motion of the director expresses the balance between the torques due to the elastic and viscous forces and the external field (and does not contain the fluid velocity) [33] 

This equation describes the director rotation in a magnetic field H with the inertia term I d ipldt being disregarded, 71 = as — a2 is rotational viscosity, and ai are Leslie coefficients. Equation (4.28) in the limit of small ip angles, ip 1, transforms to 

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In paper [141] it was shown that the change in electric conductivity in case of chemisorption of various alkyl radicals on the same oxide is notably dependent on chemical nature of free radicals. In this case the arrangement of simplest radicals in the order of decreasing degree of effect of electric conductivity of ZnO given in [132, 186] will be the following ... 

Vastamaki, P. Jussila, M. Riekkola, M.-L. The effect of electrically-conductive wall coating on retention in ThFFF. 7th Int. Symp. on FFF, 1998. 

Yamauta M, Sato K, Iwata K (1992) Memory effect of electrical conductivity upon the coimter-anion exchange of polypyrrole films. Synth Met 48(3) 337-354 Yao Q, Alici G, Spinks GM (2008) Feedback control of tri-layer polymer actuators to improve their positioning ability and speed of response. Sens Actuators A 144(1) 176-184 Yoo DS et al (2011) Multiple time constant modelling of a printed conducting polymer electrode. Electrochim Acta 56(13) 4711-4716... 

Goldberg SN, Ahmed M, Gazelle GS, et al (2001a) Radio-frequency thermal ablation with NaCl solution injection effect of electrical conductivity on tissue heating and coagulation-phantom and porcine liver study. Radiology 219 157-165... 

Kabanov [351] has provided an excellent review of the application of measurements of electrophysical effects in studies of the thermal decomposition of solids, including surveys of electrical conductivity, photoconductivity, dielectric measurements and interface (contact), Hall and thermal (Seebeck) potentials. Care must be exercised in applying the results obtained in such studies to the interpretation of data for thermal decomposition in the absence of an applied electric field since many examples have been given [352] in which such a field markedly influences the course of decomposition. 

The dependence of the local Nusselt number on non-dimensional axial distance is shown in Fig. 4.3a. The dependence of the average Nusselt number on the Reynolds number is presented in Fig. 4.3b. The Nusselt number increased drastically with increasing Re at very low Reynolds numbers, 10 < Re < 100, but this increase became smaller for 100 < Re < 450. Such a behavior was attributed to the effect of axial heat conduction along the tube wall. Figure 4.3c shows the dependence of the relation N /N on the Peclet number Pe, where N- is the power conducted axially in the tube wall, and N is total electrical power supplied to the tube. Comparison between the results presented in Fig. 4.3b and those presented in Fig. 4.3c allows one to conclude that the effect of thermal conduction in the solid wall leads to a decrease in the Nusselt number. This effect decreases with an increase in the... 

Manheim (1970) presents a critical review of the confusing variety of data found in the literature, but according to Home et al. (1969), pressures up to several thousand atmospheres seem to have no significant effect on Dg. Values for Ds are sometimes not available or are difficult to estimate but can be obtained indirectly by means of electrical conductivity measurements (Klinkenberg, 1951). Table 8-7 provides a list of Ds values found in the literature for the most... 

Above a critical hller concentration, the percolation threshold, the properties of the reinforced rubber material change drastically, because a hller-hUer network is estabhshed. This results, for example, in an overproportional increase of electrical conductivity of a carbon black-hUed compound. The continuous disruption and restorahon of this hller network upon deformation is well visible in the so-called Payne effect [20,21], as represented in Figure 29.5. It illustrates the strain-dependence of the modulus and the strain-independent contributions to the complex shear or tensUe moduli for carbon black-hlled compounds and sUica-hUed compounds. 

Interpretation of this effect was considered to be a crucial key to a better understanding of the mechanism of electric conductance of molten... 

We outline experimental results and provide theoretical interpretation of effect of adsorption of molecular oxygen and alkyl radicals in condensed media (water, proton-donor and aproton solvents) having different values of dielectric constant on electric conductivity of sensors. We have established that above parameter substantially affects the reversible changes of electric conductivity of a sensor in above media which are rigorously dependent on concentration of dissolved oxygen. 

Above theoretical analysis of adsorption effects on electric conductivity and VAC profiles in polycrystalline semiconductor adsorbent with accounting for its barrier disorder indicate that the value and kinetics of change in o(t) and yS(t) during adsorption of both acceptors and donors sharply differ from those predicted by theory both for the case of ideal monocrystal and for polycrystal considered from the standpoint of bicrystal model. 

As it has been mention in preceding section, the vast effect of the mechanism of adsorption-caused change in electrophysical characteristics of adsorbent is provided by availability of defects [32]. However, various admixtures play similarly important role on effects of properties of oxides including the sensitivity of their electrophysical properties to adsorption [4, 5]. Small amounts of admixtures (of the order of 0.5 -1 mol.-%) can both increase the sensitivity of oxide for instance to oxygen (addition of Y2O3 to calcium oxide over pressure interval lO -10 Torr [189]) and decrease it (addition of Ga203 to ZnO [190]), or can result in insensitivity of electric conductivity on the pressure of the gas in question (as it is the case with respect to O2 while adding 0.5 -1 mol.-% of lithium to NiO [190]). 

The contacts of the third type (see Fig. 2.2, a) which are interfaces or contact areas separate microcrystals are equivalent (this has been shown in preceding Section) to the double Shottky barrier or, to put it more correctly, to the isotype heterotransitions [22, 29]. As it has been shown in Section 1.10 in detail, the energy of activation of electric conductivity of the material with dominant fraction of contacts of this type is dependent on the heights of intercrystalline barriers. The change in electric conductivity due to effects of various external effects (adsorption in particular) is related to the height of these barriers. 

The latter conclusion is reliably confirmed by experimental results [40] in which the studies of effect of the structure on the character of adsorption change in electric conductivity of monocrystal or partially reduced polycrystalline ZnO adsorbents were conducted. The comparative studies of the character and the value of response of electric conductivity in both types of adsorbents on adsorption of various atoms and molecular particles led the authors to conclusion on identical origin of both the mechanisms of electric conductivity and mechanisms of its adsorption induced change. 

We should note that this effect of the hydrogen on electric conductivity is related neither to reduction of oxide nor to the volume dissolution of hydrogen in oxide. The first option was ruled out due to initial heating of adsorbent in hydrogen atmosphere up to establishing the stationary value of electric conductivity at the temperature exceeding the maximum temperature of experiment (Theati 400 420 C). The con-... 

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