Barrier leakage

Zisper, B.D., Johanson, C.E., Gonzalez, L., et al., 2007. Microvascular injury and blood-T rain barrier leakage in Alzheimer s disease. Neurobiol. Aging 28, 977-986. 

The mechanical seal is a device that forms a barrier benvecn rotary and stationary parts in the pump. The seal must block leakage at three points (Figure 13-4) ... 

A packing is required on double-acting cylinders to provide a barrier to leakage past the rod where it passes through the crank end cylinder closure. The same arrangement is needed at the head end if a tail rod or tan-... 

Tubesheets form the end barriers to separate the shell-side and tube-side fluids. Most exchangers use single plates for tubesheets. However, for hazardous or corrosive materials such as chlorine, hydrogen chloride, sulfur dioxide, etc., where the intermixing due to leakage from shell- to tube-... 

In principle, reaction schemes similar to that given in the preceding paragraph may be developed for other comparable rate processes, for example spinel formation. However, Stone [27] has pointed out that, where the barrier phase is not an efficient ionic conductor, the overall reaction may be controlled by the movement of a single cation and anion. In addition, there is the probability that lattice imperfections (internal surfaces, cracks, leakage paths [1172], etc.) may provide the most efficient route to product formation.]... 

The tube sheet forms the barrier between the shell and tube fluids, and where it is essential for safety or process reasons to prevent any possibility of intermixing due to leakage at the tube sheet joint, double tube-sheets can be used, with the space between the sheets vented Figure 12.16c. 

Satisfactory agreement of experiments with kinetic laws, described by Eqs. (44) and (45), are observed only for tantalum and niobium, when the current efficiency approaches 100%. Even for these metals, certain deviations occur which could be attributed to space charge effects,82 electronic leakage currents,83 or other factors. In the case of aluminum, these deviations are relatively large, as, even in barrier-forming electrolytes, some oxide dissolution takes place from the very beginning of voltage supply to an anodized sample.32... 

The Schottky barriers were excellent diodes for films annealed at 600 °C, with turn on voltages of 0.6-0.8V and minimal reverse bias leakage.48 However, many of the contacts on the as-deposited films gave large reverse bias currents and nearly ohmic responses. This behavior is indicative of degeneracy of the semiconductor because of a high carrier density resulting from native defects. The improvement in the diode behavior of the annealed films is attributed to enhanced crystallinity and reduction of defects. 

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