Voltage gradient

Electrical trees consist of visible permanent hoUow channels, resulting from decomposition of the material, and show up clearly in polyethylene and other translucent soHd dielectrics when examined with an optical microscope. Eresh, unstained water trees appear diffuse and temporary. Water trees consist of very fine paths along which moisture has penetrated under the action of a voltage gradient. Considerable force is required to effect this... 

The disadvantages appear to be that the bipolar membranes are comparatively expensive, and the economic life is limited to about one year. Such short lifetime appears to result from the very high (- 10 V/cm) voltage gradients at the interface between the AX and CX regions. Additionally, practical current densities are limited to about 1000 A/m available area. 

The electrical-resistance method involves passing an electric current through the structure and exploring the surface with voltage probes. Flaws, cracks, or inclusions will cause a disturbance in the voltage gradient on the surface. Railroads have used this method for many years to locate transverse cracks in rails. 

Density gradients to stabilize flow have been employed by Philpot IT> Yin.s. Faraday Soc., 36, 38 (1940)] and Mel [ j. Phys. Chem., 31,559 (1959)]. Mel s Staflo apparatus [J. Phys. Chem., 31, 559 (1959)] has liquid flow in the horizontal direction, with layers of increasing density downward produced by sucrose concentrations increasing to 7.5 percent. The solute mixture to be separated is introduced in one such layer. Operation at low electrolyte concentrations, low voltage gradients, and low flow rates presents no cooling problem. 

Figure 22.9 Likely positions in which a human body may come in contact with phase and the ground conductors and the corresponding voltage gradients (illustrated through the layout of Figure 13.21)...

FIGURE 10.31 The umbrella model of membrane chamiel protein insertion. Hydrophobic helices insert directly into the core of the membrane, with amphipathic helices arrayed on the surface like an open umbrella. A trigger signal (low pH or a voltage gradient) draws some of the amphipathic helices into and across the membrane, causing the pore to open. 

Electrical supply systems and equipment are grounded in order to maintain the voltage at any part of the system at a known potential relative to true earth and to provide a path for current flow under earth fault conditions so that protective devices operate correctly. The connection to earth should be such that the flow of fault current to earth does not cause voltages or voltage gradients to be of sufficient magnitude or duration likely to cause danger. 

D Limited by local or environmental safety requirements regarding apparatus and/or earth voltage gradient regulations E Minimum current density to ensure passivation SO Am ... 

Application of charges and filtration may separate protein very efficiently. Electro-kinetic deposition uses voltage gradients of 1050V/cm to produce solid biomass with densities of up to 40% w/v. 

Countercurrent electrophoresis can be nsed to split a mixtnre of mobile species into two fractions by the electrical analog of elntria-tion. In such countercurrent electrophoresis, sometimes termed an ion still, a flow of the suspending flnid is maintained parallel to the direction of the voltage gradient. Species which do not migrate fast enough in the applied electric field will be physically swept out of the apparatus. An apparatus based mainly on this principle bnt nsing also natural convection currents has been developed (Bier, Electrophoresis, vol. II, Academic, New York, 1967). 

The technique described above measures only light-induced potential changes from a whole population of organisms. Therefore, it had to be verified that these changes are based on a light-induced voltage gradient between the two ends of the... 

The rate of movement of a charged particle is also related to the voltage gradient applied across the supporting medium, which is quoted in volts per centimetre (i.e. the distance between electrodes). The current generates heat,... 

Figure 3.30 Isotachophoresis. The spontaneous development of different voltage gradients across the two electrolyte solutions has the effect that both types of anion migrate at the same velocity.

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