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Distributions membrane surface

The flow along the membranes also improves the mass transport there, and the separators between the membranes are constmcted to provide good flow distribution and mixing on the membrane surfaces. Membrane sizes are often about 0.5 x 1 m, spaced about 1 mm apart. Many types of polymers are used to manufacture these ion-exchange-selective membranes, which are often reiaforced by strong fabrics made of other polymers or glass fibers. [Pg.251]

At each phase boundary there exists a thermodynamic equilibrium between the membrane surface and the respective adjacent solution. The resulting thermodynamic equilibrium potential can then be treated like a Donnan-potential if interfering ions are excluded from the membrane phase59 6,). This means that the ion distributions and the potential difference across each interface can be expressed in thermodynamic terms. [Pg.226]

Membranes with a relatively uniform pore size distribution throughout the thickness of the membrane are referred to as symmetric or homogeneous membranes. Others may be formed with tight skin layers on the top or on both the top and bottom of the membrane surfaces. These are referred to as asymmetric or nonhomogeneous membranes. In addition, membranes can be cast on top of each other to form a composite membrane. [Pg.38]

The determination of the number of the SHG active complex cations from the corresponding SHG intensity and thus the surface charge density, a°, is not possible because the values of the molecular second-order nonlinear electrical polarizability, a , and molecular orientation, T), of the SHG active complex cation and its distribution at the membrane surface are not known [see Eq. (3)]. Although the formation of an SHG active monolayer seems not to be the only possible explanation, we used the following method to estimate the surface charge density from the SHG results since the square root of the SHG intensity, is proportional to the number of SHG active cation com-... [Pg.452]

In addition to fluorescence methods, another study [27] developed a method to permit electron microscopic localization of Ras anchor domains on cytoplasmic membrane surfaces by immunogold labeling. The particle neighbor distances can be analyzed to obtain information about possible domain structure. Expressing H-Ras and K-Ras in baby hamster kidney cells, a nonrandom particle distribution was obtained from which the estimated mean raft size was 7.5-22 nm and about 35% of the membrane area consists of rafts. The same technique applied to cells that had been incubated with [3-cydodextrin to reduce cholesterol produced completely random distributions of H-Ras. This cholesterol dependence suggests some type of coupling of rafts across the inner and outer membrane leaflets. [Pg.29]

Needless to say, uniform concentration distribution of an electrolyte over a membrane surface is the most important factor to maintain good membrane performance. Sufficient internal circulation results in good electrolyte mixing inside the chamber. As shown in Fig. 19.2,12 ribs installed in both anode and cathode chambers work as downcomers in the same manner as in B-l. The horizontal cross-sectional area of the downcomer in the Improved B-l has been approximately doubled. All electrolyte concentrations measured at various points over the whole electrolysis area are maintained at specification, even at 6 kA m-2 through to 8 kA m-2, as is shown in Fig. 19.3 (with the relevant data at the downcomer positions 1-4 given in Table 19.1). [Pg.253]

Under fuel cell operation, a finite proton current density, 0, and the associated electro-osmotic drag effect will further affect the distribution and fluxes of water in the PEM. After relaxation to steady-state operation, mechanical equilibrium prevails locally to fix the water distribution, while chemical equilibrium is rescinded by the finite flux of water across the membrane surfaces. External conditions defined by temperature, vapor pressures, total gas pressures, and proton current density are sufficient to determine the stationary distribution and the flux of water. [Pg.373]

For bilayer membrane problems it may be a mistake to treat permeation through the membrane as a single diffusion process. In the first place it is extremely unlikely that the distribution of permeant molecules across the membrane is described by the diffusion equation. Second, the permeation may be related to lateral density fluctuations in the membrane, giving a quite nonuniform lateral distribution of the permeant molecules near the membrane surface at any instant. [Pg.238]

In fact, due to an inevitable nonuniformity of the distribution of conductive spots over the membrane surface, a whole hierarchy of circulation on different length scales sets in the diffusion layer. Namely, this complex multiscale convection is expected to cause the mixing of the entire diffusion layer and the resulting overlimiting CP behaviour of the C-membranes. [Pg.157]

FIGURE 19-1 Biochemical anatomy of a mitochondrion. The convolutions (cristae) of the inner membrane provide a very large surface area. The inner membrane of a single liver mitochondrion may have more than 10,000 sets of electron-transfer systems (respiratory chains) and ATP synthase molecules, distributed over the membrane surface. Heart mitochondria, which have more profuse cristae and thus a much larger area of inner membrane, contain more than three times as many sets of electron-transfer systems as liver mitochondria. The mitochondrial pool of coenzymes and intermediates is functionally separate from the cytosolic pool. The mitochondria of invertebrates, plants, and microbial eukaryotes are similar to those shown here, but with much variation in size, shape, and degree of convolution of the inner membrane. [Pg.691]

Table 11. Average Pore Size and Pore Size Distribution on Membrane Surfaces... Table 11. Average Pore Size and Pore Size Distribution on Membrane Surfaces...
Cases in Which Two Normal Pore Size Distributions Are CONSIDERED. In two normal distributions, five parameters, namely Rb,i, pore size distribution on the membrane surface. Five or more reference solutes are necessary for obtaining such parameters. Let us use eight reference solutes. By setting eq 5 and eq 6 for each reference solute, we have eight eq 5 s and eight eq 6 s, corresponding to / — 1,2,3...8. [Pg.148]

Determination of Pore Size Distributions on the Surface of CA Membranes and Aromatic PAH Membranes. The organic solutes listed in Table IV were chosen as reference solutes, and then D and B values with respect to CA-398 and PAH materials were obtained by step 4. The results are listed in Table IV. Then, by using these B and D values, the average pore size and the pore size distribution on surfaces of membranes under study were calculated by following step 5. In these calculations, B and D values for CA-400 material were assumed to be equal to those of CA-398 material because of the closeness of acetyl content. The results are listed in Table II. [Pg.150]

This approach also enables the design of the pore size distribution that optimizes the fractionation of different solutes. Furthermore, the correlation of the process of the membrane formation to the average pore size and the pore size distribution produced on the membrane surface enables one to produce membranes that are most appropriate for the fractionation of a given set of solutes. Therefore, this approach contributes to the rational design of membranes for the concentration of water pollutants of particular interest. [Pg.164]

Many of the proteins of membranes are enzymes. For example, the entire electron transport system of mitochondria (Chapter 18) is embedded in membranes and a number of highly lipid-soluble enzymes have been isolated. Examples are phosphatidylseiine decarboxylase, which converts phosphatidylserine to phosphatidylethanolamine in biosynthesis of the latter, and isoprenoid alcohol phosphokinase, which participates in bacterial cell wall synthesis (Chapter 20). A number of ectoenzymes are present predominantly on the outsides of cell membranes.329 Enzymes such as phospholipases (Chapter 12), which are present on membrane surfaces, often are relatively inactive when removed from the lipid environment but are active in the presence of phospholipid bilay-ers.330 33 The distribution of lipid chain lengths as well as the cholesterol content of the membrane can affect enzymatic activities.332... [Pg.409]

The cell membranes are predominantly a lipid matrix or can be considered a lipid barrier with an average width of a membrane being approximately 75 A. The membrane is described as the fluid mosaic model (Figure 6.2) which consist of (1) a bilayer of phospholipids with hydrocarbons oriented inward (hydrophobic phase), (2) hydrophilic heads oriented outward (hydrophilic phase), and (3) associated intra- and extracellular proteins and transverse the membrane. The ratio of lipid to protein varies from 5 1 for the myelin membrane to 1 5 for the inner structure of the mitochondria. However, 100% of the myelin membrane surface is lipid bilayer, whereas the inner membrane of the mitochondria may have only 40% lipid bilayer surface. In this example the proportion of membrane surface that is lipid will clearly influence distribution of toxicants of varying lipophilicity. [Pg.79]

After the test pressure has been reached, a stabilization time of 10 minutes begins in order to saturate the water column, to distribute the water bubble-free over the entire membrane surface and to ensure complete compaction. [Pg.214]

The subsequent test time lasts 10 minutes. It is not advisable to shorten either the stabilization time or the test time because this could cause increased intrusion values due to insufficiently thorough water distribution on the membrane surface. [Pg.214]


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See also in sourсe #XX -- [ Pg.249 ]




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