Depolarization, concentration

Smooth Muscle Tone Regulation. Figure 2 Membrane mechanisms leading to an increases in cytosolic calcium concentration, depolar, depolarisation of the membrane see text for abbreviations. 

Figure 4.18 Concentration depolarization by dipole-dipole mechanism. Arrows indicate the vector directions.

Fredrickson3 has formulated expressions for the concentration depolarization of fluorescence in the presence of molecular rotation. A theoretical examination of diffusion influenced fluorescence quenching by nearest possible quenching neighbours in liquids has been made35. A modified version of Smoluchowski - Collins - Kimball formulation of the Stern - Volmer equations has been matched with experimental data for quenching of anthraquinone derivatives by N,N-dimethyl- -toluidine. Another paper discusses this work on the basis of the kinetics of partly diffusion controlled reactions3 . 

Electronic excitations in molecular aggregates have received considerable attention from theoretists and experimentalists in recent years. Much of the work has focused on excitonic transport in molecular crystals (J.), in sub s t i t u 11 o na 11 y disordered mixed crystals (2.) and in amorphous structures (3.). Furthermore, excitation energy transfer (EET) has been studied in fluorescence concentration depolarization of donor molecules in solution (4.) as well as in excited-state energy transfer of donor -acceptor dyes in condensed phase systems (5.). 

Both absorption and emissirm processes may be intramolecular, localized in a single molecule. On the other hand, they can also involve whole crystals that may act as absorbers and emitters. Such energy transfers can manifest themselves in different ways that include sensitized fluorescence or phosphorescence, concentration depolarization of fluorescence, photo-conduction, and formation of triplet acceptor molecules. 

Detection of Bromine Vapor. Bromine vapor in air can be monitored by using an oxidant monitor instmment that sounds an alarm when a certain level is reached. An oxidant monitor operates on an amperometric principle. The bromine oxidizes potassium iodide in solution, producing an electrical output by depolarizing one sensor electrode. Detector tubes, usefiil for determining the level of respiratory protection required, contain (9-toluidine that produces a yellow-orange stain when reacted with bromine. These tubes and sample pumps are available through safety supply companies (54). The usefiil concentration range is 0.2—30 ppm. 

The corrosion rate is controlled mainly hy cathodic reaction rates. Cathodic Reactions 5.2 and 5.3 are usually much slower than anodic Reaction 5.1. The slower reaction controls the corrosion rate. If water pH is depressed. Reaction 5.3 is favored, speeding attack. If oxygen concentration is high. Reaction 5.2 is aided, also increasing wastage hy a process called depolarization. Depolarization is simply hydrogen-ion removal from solution near the cathode. 

Crevices, deposits on metal surface or any geometrical configuration which results in differences in the concentration of oxygen or other cathodic depolarizers (e.g., Cu ). Metal in contact with the lower concentration—this follows from considerations of an equivalent reversible cell, although the situation is more complex in practice. 

Environment Differences in aeration or concentration of cathodic depolarizers. Metal in contact with lower concentration. 

Oxygen dissolved in aqueous solutions, even in very low concentrations, is a leading cause of corrosion problems (i.e., pitting) in drilling. Its presence also accelerates the corrosion rate of other corrodents such as hydrogen sulfide and carbon dioxide. Oxygen plays a dual role both as a cathodic depolarizer and an anodic polarizer or passivator. Within a certain range of concentration the... 

Generally, the corrosivity of water containing dissolved salts increases at low-salt concentrations, until some maximum is reached, and beyond this maximum the corrosion rate decreases. Corrosion rate throughout the salt concentration range is under the influence of oxygen s ability to depolarize. It is believed that... 

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