Electrical coupling

In ion-exchange resins, diffusion is further complicated by electrical coupling effec ts. In a system with M counterions, diffusion rates are described by the Nernst-Planck equations (Helfferich, gen. refs.). Assuming complete Donnan exclusion, these equations canbe written... 

The windings should have tight electrical coupling. 

Till this point an electric coupling with the wall is assumed. More generally, we may assume the existence of a short-range potential located at the wall. The following form will be used ... 

Cathodic protection (CP) is an electrochemical technique of corrosion control in which the potential of a metal surface is moved in a cathodic direction to reduce the thermodynamic tendency for corrosion. CP requires that the item to be protected be in contact with an electrolyte. Only those parts of the item that are electrically coupled to the anode and to which the CP current can flow are protected. Thus, the inside of a buried pipe is not capable of cathodic protection unless a suitable anode is placed inside the pipe. The electrolyte through which the CP current flows is usually seawater or soil. Fresh waters generally have inadequate conductivity (but the interiors of galvanized hot water tanks are sometimes protected by a sacrificial magnesium anode) and the conductivity... 

Homo sapiens (compared to Drosophila melanogaster) Large-scale gene duplications with substantial expansion of genes involved in acquired immune response (B cells, T cells, major histocompatibility complex genes, cytokines, chemokines and their receptors), plasma proteases (complement and hemostatic proteins), proteins associated with apoptotic regulation and proteins related to neuronal network formation and electrical coupling... 

For mixtures of unlike ions (the usual case), the apparent diffusivity will be intermediate between these values because of the electrical coupling effect. For a system with two counterions A and B, with charge zA and zB, Eqs. (16-73) and (16-74) reduce to ... 

The communication between neurons in the CNS occurs through chemical synapses in the majority of cases. (A few instances of electrical coupling between neurons have been documented, and such coupling may play a role in synchronizing neuronal discharge. However, it is unlikely that these electrical synapses are an important site of drug action.) The events involved in synaptic transmission can be summarized as follows. 

Heart muscle fibers are coupled by gap junctions. These intercellular channels provide the exchange of small molecules (<1,000 D), like second messengers, between the cells and they allow electrical coupling. Thus, these cells connected to each other form a syncytium. However, from mapping studies it became evident that under certain conditions, e.g. regional ischemia, the ischemic region uncouples. In addition, mapping studies demonstrated that there is a special activation pattern which accounts for a directed activation of the whole heart. This activation pattern exhibits a considerable similarity from beat to beat. It is well known that the conduction velocity varies between... 

Furthermore, synchronization of contraction is facilitated by gap junctional communication as well as synchronization of electrical activation. The electrical coupling between cardiomyocytes mitigates differences in the membrane potential between these cells, for example in the course of an action potential if both cells repolarize at different timepoints. This results in smaller differences in the repolarization times thereby causing a reduction in the dispersion of the action potential duration. Since increased dispersion is known to make the heart more prone to reentrant arrhythmia, sufficient gap junctional communication can be considered as an endogenous arrhythmia-preventing mechanism. For a detailed discussion of the role of gap junctional communication in the biophysics of cardiac activation as related to anisotropy, nonuniformity and stochastic phenomena, see chapter 1 for a discussion of their role in arrhythmia, see chapter 6, and for a possible pharmacological intervention at the gap junctions for suppression of arrhythmia, refer to chapter 7. 

Dekker LRC, Fiolet JWT, VanBavel E, Coronel R, Opthof T, Spaan JAE, Janse MJ Intracellular Ca2+, intercellular electrical coupling and mechanical activity in ischemic rabbit papillary muscle. Effects of preconditioning and metabolic blockade. Circ Res 1996 79 237-246. 

De Mello WC Influence of the sodium pump on intercellular communication in heart fibers Effect of intracellular injection of sodium ion on electrical coupling. J Physiol (Lond) 1976 263 171-197. De Mello WC Effect of intracellular injection of cAMP on the electrical coupling of mammalian cardiac cells. Biochem Biophys Res Commun 1984 119 1001-1007. 

De Mello WC Interaction of cyclic AMP and Ca in the control of electrical coupling in heart fibers. Biochim Biophys Acta 1986a 888 71. 

Joyner RW Effects of the discrete pattern of electrical coupling on propagation through an electrical syncytium. Circ Res 1982 50 192-200. 

Kameyama M Electrical coupling between ventricular paired cells isolated from guinea pig heart. J Physiol (Lond) 1983 336 345-357. 

Gap junctions in synapses. Not all neurons communicate via chemical synapses. Gap junctions, which are found in both neurons, astrocytes, and other cells, serve as electrical synapses. Thus, heart cells are all electrically coupled together by gap junctions.606-608 Gap junctions are formed with the aid of hexameric connexons, which are present in each of the opposed membranes and are aligned one with the other (Fig. 1-15F,G).607 609 610 There may be thousands of connexons in a single gap junction, which resemble ion channels in appearance but contain pores 1.5 nm in diameter. They are formed from 26- to 43- kDa... 

As can be seen from Fig. 30-32, neurons send "trains" of spikes down their axons. These form synapses with dendrites, usually on dendritic spikes, of a postsynaptic cell.593,1007-1009 However, each such cell typically receives input from thousands of other neurons. At any moment most of these are probably "silent," but others are sending trains of impulses. Among the important questions are "How does the postsynaptic neuron know whether to fire or not " and "What kinds of information, if any, are encoded in the trains of impulses both in the presynaptic inputs and in the output of the postsynaptic neuron "10101011 Part of the answer to the first question is probably that firing occurs if two or more input impulses arrive synchronously,10101012-1014 and if there are not too many inhibitory impulses that damp the response. In the hippocampus a network of neurons electrically coupled via gap junctions may be synchronized to the theta and gamma brain rhythms by high-frequency (150-200 Hz) oscillations.988 See also Fig. 30-15. 

Figure 7.23. Performances of fans with several kinds of controls (American Standard Co. Inc.), (a) A damper in the duct with constant-speed fan drive, (b) two-speed fan driver, (c) inlet vanes or inlet louvers with a constant-speed fan drive, (d) multiple-step variable-speed fan drive, and (e) hydraulic or electric coupling with constant-speed driver giving wide control over fan speed.

HCl.Aq + Zn = ZnCl2.Aq + 2H the hydrogen ion unites with the arsenic, negatively charged in the electric couple, forming electrically neutral hydride of arsenic, which escapes... 

At a minimum, the working electrode must be electrically coupled to a second electrode that completes the circuit. The second electrode must allow a current to flow into or out of it that is directly opposite to the current flowing through the working electrode. A battery will not work if only one end of it is attached to the device that it is intended to power. Both ends of the battery are required to be attached so that a current can flow out from one end of the battery into the other end. The electrode that performs this function is called the counter electrode. The main requirement for the counter electrode is that it must always pass a current that is larger than the working electrode so that the current at the working electrode is not limited by the current output at the counter electrode. 

Schirrmacher, K., Brummer, F., et al. (1993) Dye and electric coupling between osteoblasts-like cells in culture. Calcified Tissue International 53 53-60... 

In 2001, the Netherlands Organization for Scientific Research (NWO) started a project called Chemically and electrically coupled transport in clayey soils and sediments to quantify the role of chemically and electrically coupled transport in clayey soils and to assess its relevance for the distribution and emission of contaminants and water. The project involves three Ph.D. students working on field and laboratory experiments and modelling of chemical-and electro-osmosis. 

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