Distribution passive

K+ ions in the presence of valinomycin do not distribute passively at electrochemical equilibrium rather, this represents a nonequilibrium state in which creates a diffusion potential following which protons move. 

It is well known that the behavior of electrical transmission lines can be represented in terms of distributed passive elements. As we mentioned at the beginning of this chapter, there exists an analogy between the electrical and mechanical behavior of the systems. Returning to the Maxwell model, one has... 

To achieve a pressure-sensitive fabric, Sergio et al. (2002) suggested a system composed of distributed passive arrays (in a grid pattern of rows and columns) of capacitors whose capacitance varies according to pressure exerted on the fabric surface. Each capacitor is made with two conductive strips separated by an elastic and dielectric material. The conductive grid can be produced by weaving or embroidering electroconductive yams in or onto a fabric. 

Infrared thermal sensing and imaging instruments make it possible to measme and map surface temperature and thermal distribution passively and nonintrusively. In addition to the passive measurement of temperature distribution, thermographers have learned to use active or thermal injection techniques to study and evaluate the structural integrity of materials and fabricated bonds. 

From polarization curves the protectiveness of a passive film in a certain environment can be estimated from the passive current density in figure C2.8.4 which reflects the layer s resistance to ion transport tlirough the film, and chemical dissolution of the film. It is clear that a variety of factors can influence ion transport tlirough the film, such as the film s chemical composition, stmcture, number of grain boundaries and the extent of flaws and pores. The protectiveness and stability of passive films has, for instance, been based on percolation arguments [67, 681, stmctural arguments [69], ion/defect mobility [56, 57] and charge distribution [70, 71]. 

Active Transport. Maintenance of the appropriate concentrations of K" and Na" in the intra- and extracellular fluids involves active transport, ie, a process requiring energy (53). Sodium ion in the extracellular fluid (0.136—0.145 AfNa" ) diffuses passively and continuously into the intracellular fluid (<0.01 M Na" ) and must be removed. This sodium ion is pumped from the intracellular to the extracellular fluid, while K" is pumped from the extracellular (ca 0.004 M K" ) to the intracellular fluid (ca 0.14 M K" ) (53—55). The energy for these processes is provided by hydrolysis of adenosine triphosphate (ATP) and requires the enzyme Na" -K" ATPase, a membrane-bound enzyme which is widely distributed in the body. In some cells, eg, brain and kidney, 60—70 wt % of the ATP is used to maintain the required Na" -K" distribution. 

Sweating, the other powerful heat loss mechanism actively regulated by the thermoregulatory center, is most developed in humans. With about 2,6 million sweat glands distributed over the skin and neurally controlled, sweat secretion can vary from 0 to 1 I7(h m ). The other, lesser, passive evaporative process of the skin is from the diffusion of water. The primary resistance to this flow is the stratum corneum or outermost 15 pm of the skin. The diffusion resistance of the skin is high in comparison to that of clothing and the boundary layer resistance and as a result makes water loss by diffusion fairly stable at about 500 grams/day. 

As a solution of molecules is passed through the column, the molecules passively distribute between and VJ, depending on their ability to enter the pores (that is, their size). If a molecule is too large to enter at all, it is totally excluded from and emerges first from the column at an elution volume, V, equal to (Figure 5A.1). If a particular molecule can enter the pores in the gel, its distribution is given by the distribution coefficient ... 

Proteins that can flip phospholipids from one side of a bilayer to the other have also been identified in several tissues (Figure 9.11). Called flippases, these proteins reduce the half-time for phospholipid movement across a membrane from 10 days or more to a few minutes or less. Some of these systems may operate passively, with no required input of energy, but passive transport alone cannot establish or maintain asymmetric transverse lipid distributions. However, rapid phospholipid movement from one monolayer to the other occurs in an ATP-dependent manner in erythrocytes. Energy-dependent lipid flippase activity may be responsible for the creation and maintenance of transverse lipid asymmetries. 

In general, a uniform distribution of potential over a regular-shaped passivated surface can be readily obtained by anodic protection. It is much more difficult to protect surface irregularities, such as the recessions around sharp slots, grooves or crevices since the required current density will not be... 

Fig. 5. Tentative mixed potential model for the sodium-potassium pump in biological membranes the vertical lines symbolyze the surface of the ATP-ase and at the same time the ordinate of the virtual current-voltage curves on either side resulting in different Evans-diagrams. The scale of the absolute potential difference between the ATP-ase and the solution phase is indicated in the upper left comer of the figure. On each side of the enzyme a mixed potential (= circle) between Na+, K+ and also other ions (i.e. Ca2+ ) is established, resulting in a transmembrane potential of around — 60 mV. This number is not essential it is also possible that this value is established by a passive diffusion of mainly K+-ions out of the cell at a different location. This would mean that the electric field across the cell-membranes is not uniformly distributed.

Due to their physicochemical properties trace amines can pass the cell membrane to a limited extent by passive diffusion, with the more lipophilic PEA and TRP crossing membranes more readily than the more polar amines TYR. and OCT. In spite of these features, trace amines show a heterogeneous tissue distribution in the vertebrate brain, and for TYR. and OCT storage in synaptic vesicles as well as activity-dependent release have been demonstrated. So far, trace amines have always been found co-localized with monoamine neurotransmitters, and there is no evidence for neurons or synapses exclusively containing trace amines. 

DEHA is volatile and has a distribution ratio of approximately 1.3 1. Consequently, as a result of this volatility, it offers excellent oxygen-scavenging protection to the post-boiler section. In addition, it is a strong reducing agent, is an excellent passivator, and does not contribute to TDS. 

As mentioned, corrosion is complexly affected by the material itself and the environment, producing various kinds of surface films, e.g., oxide or hydroxide film. In the above reactions, both active sites for anodic and cathodic reactions are uniformly distributed over the metal surface, so that corrosion proceeds homogeneously on the surface. On the other hand, if those reaction sites are localized at particular places, metal dissolution does not take place uniformly, but develops only at specialized places. This is called local corrosion, pitting corrosion through passive-film breakdown on a metal surface is a typical example. 

As mentioned earlier, although we cannot directly observe the local breakdown process of passive film, according to Shibata and Takeyama,21,22 the stochastic breakdown of passive film follows Poisson s distribution. 

Figure 13 shows the relationship between the time interval At of passive film breakdown of stainless steel with chloride ions and the logarithms of cumulative probability P(Af) for breakdown at time intervals longer than At. From these results, it is clear that the logarithm of the probability is almost proportional to the time interval, and therefore the cumulative probability for film breakdown follows Poisson s distribution, i.e., the following equation is obtained,... 

Galvani, measurability of, 7 Potential distribution in passivation, 229 Potential formation as a variation of thickness with passive film, 225 Potential of zero charge, 1, 5-6, 189-192 accuracy of determination, 19 and the adsorption method, 39 at the air-solution interface (Nikitas), 30 and alloys, 142... 

CuNPs) in Fig. 7 shows the monodisperse and uniformly distributed spherical particles of 10+5 nm diameter. The solution containing nanoparticles of silver was found to be transparent and stable for 6 months with no significant change in the surface plasmon and average particle size. However, in the absence of starch, the nanoparticles formed were observed to be immediately aggregated into black precipitate. The hydroxyl groups of the starch polymer act as passivation contacts for the stabilization of the metallic nanoparticles in the aqueous solution. The method can be extended for synthesis of various other metallic and bimetallic particles as well. 

Numbering up microchannels to large-scale capacity reactors is driven by a rigorous understanding of pressure drop in every parallel circuit Passive flow distribution permits sufficient flow to each channel. No serious evaluation of microvalves or actuators has been undertaken for high-capacity systems with thousands to tens... 

Figure 11.19 Manufacturing scale-up device with submanifolds for passive flow distribution to feed thousands of parallel microchannels. Flow is mapped using ranges to show variations from a normalized value.

Via a passive scalar method [6] where or, denotes the volume fraction of the i-th phase, while T, represents the diffusivity coefiBcient of the tracer in the i-th phase. The transient form of the scalar transport equation was utilized to track the pulse of tracer through the computational domain. The exit age distribution was evaluated from the normalized concentration curve obtained via measurements at the reactor outlet at 1 second intervals. This was subsequently used to determine the mean residence time, tm and Peclet number, Pe [7]. 

Modern representations of the virtual heart, therefore, describe structural aspects like fibre orientation in cardiac muscle, together with the distribution of various cell types, active and passive electrical and mechanical properties, as well as the coupling between cells. This then allows accurate reproduction of the spread of the electrical wave, subsequent contraction of the heart, and effects on blood pressure, coronary perfusion, etc. It is important to point out, here, that all these parameters are closely interrelated, and changes in any one of them influence the behaviour of all others. This makes for an exceedingly complex system. 

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