Directional permeability

For direct permeability methods, infonnation supporting the suitability of a selected method that encompasses a description of the study method, criteria for selection of human subjects, animals, or epithelial cell line, drug concentrations in the donor fluid, description of the analytical method, method used to calculate extent of absorption or permeability, and where appropriate, infonnation on efflux potential (e.g., bidirectional transport data)... 

The situation, is more complex if S and/or DT are also functions of C or a. Eq. (52) is still valid but, if P(a, X) is not separable into a product of functions of a and X, Pe cannot, in general, be expressed analytically, Under these conditions, the value of Pe will, in general, also differ according to whether flow is in the +X or -X direction. This directional permeability property has attracted considerable interest, as indicated in a previous review 135). 

In applying equations 4-6, the directional permeabilities are treated as point functions, that is, as a property of a point in the medium. The point value of the directional permeability can be visualized as a statistical average of the fluid conductance in the given direction of all pores contained in a small volume surrounding the point in question. This small volume must be... 

Comstock G.L. (1970), Directional Permeability ofSoftwoods. iVood and Fiber, 1,283-289. 

Figure 2. Boundary condition for examination of average directional permeability...

The third mechanism can be seen as a combination of first and second basic mechanisms (Figure 1(c)). In a fractured rock with multiple fractures, anisotropy in fluid permeability may be significant due to the different orientations of fractures and anisotropic stresses. Each fracture is under different contact normal or shear stresses mobilized through deformations and this make the directional permeability anisotropic. 

A series of numerical experiments are conducted to calculate the equivalent permeability of the model under various stress conditions. The flow through fractures is calculated by the Cubic law and blocks are treated as impermeable medium. Mass conservation is assured at each fracture intersection and in domains between them, through an iterative process. Lateral sides of the model are set impermeable and x- and y-directional permeability with the specified hydraulic pressure boundary conditions are calculated by the following equations. 

Both pure elastic and elastoplastic models show similar response until the k value reaches approximately 2.5. With the increase of horizontal stress, the anisotropy in the permeability becomes significant. This is because the sub-vertical fractures are more vulnerable to the horizontal stress and its effect on y-directional permeability is larger. The difference between x- and y-directional permeability is about a factor of 2 for k ratios of 0.5 and 2. 

Magnetic properties of electrical steels are greatly improved by preferential orientation. Since the easy direction in Si-Fe is <100>, oriented sheets are extremely soft in the rolling direction permeability... 

Silva et al. (1981) reported results of low-gradienf permeability testing of fine-grained marine sediments using a modified back-pressured consolidation system for direct permeability measurements. They ran their experiments by first consolidating a sample under a... 

Table 40.7 summarizes some values of directional permeability available in the literature for different species. Depending on the experimental apparatus and the protocol nsed by the authors, some data are missing in the papers. For example, it is not always easy to calculate the permeability ratios from permeability value, or vice versa. Choong et al. (1974), for example, have reported the permeability values for sapwood and heartwood for the longitudinal direction, but not for the transverse directions. Only the mean anisotropy ratio is available in this paper. Perre (1992) and Perre et al. (2002) have used an experimental procedure to determine the longitudinal permeability and the anisotropy ratio on the same sample. In these instances, they just obtained the ratios and decided not to calculate the transverse permeability accordingly. 

Directional properties also occur in coal and these properties can affect the direction of flow of gases. For a particular coal seam, analyses of natural fracture orientation, directional permeability, directional ultrasonic velocity, and directional tensile strength (Berenbaum and Brodie, 1959 Ingles, 1961) may disclose distinct coal structures that are important for gas flow through the coal (Skawinski et al., 1991 Puri and Seidle, 1992). 

Anonymous (1961). Wendell E. Johnson. Engineering News-Record 166(Mar-23) 155. P Anonymous (1974). Wendell Johnson. New Civil Engineer 3(Oct.3) 7. P Anonymous (1980). Wendell E. Johnson. Civil Engineering 50(11) 53. P Anonymous (1981). Johnson, Wendell E. Who s who in America 4l 1730. Marquis Chicago. Anonymous (1982). Wendell E. Johnson, dam expert, dies. Civil Engineering 52(6) 88. P Johnson, W.E., Breston, J.N. (1951). Directional permeability measurements on oil sandstones from various states. Producers Monthly 15(4) 10-19. 

A. Hammani, F. Trochu, R. Gauvin, and S. Wirth, Directional permeability measurement of deformed reinforcement. J. Reinf. Plast. Compos. 15, 552-562 (1996). 

Mao N and Russell S (2000a), Directional permeability in homogeneous nonwo-ven structures Part II Permeability in idealised structures , / Text Inst, 91(2), 244-258. 

K2yy y-direction (i.e., through-thickness direction) permeability of the fiber preform... 

The anisotropy of nonwoven structures can be characterised by using the anisotropy of FOD functions. It has been shown by many researchers that the anisotropy of nonwoven structures influences the anisotropy of mechanical and physical behaviour of the nonwoven fabrics, and FOD plays an important role among them. The anisotropies of these mechanical and physical properties include tensile properties, bending properties, anisotropy of thermal insulation properties, acoustic absorptions, dielectric properties, and directional permeabilities. 

Table 36.7 summarizes some values of directional permeability available in the literature for different species. Depending on the experimental apparatus and the protocol used by the authors, some data are missing in the papers. For example, it is not always... 

Permeability (as fiber direction) Permeability (transverse direction) Fiber diameter Maximum pore size... 

X 10 cm/s high permeability Papp Often, bi-directional permeability studies (apical to basolateral and basolateral to apical) are performed in Caco-2 cells to evaluate both passive diffusion and efflux potential. In this... 

Initial studies showed that directional permeability is independent of driving pressure, fluid velocity, fluid viscosity and fiber surface wetting properties [12-14] performed a series of constant flow rate experiments using a different flow rate for each set. They reported that... 

FIGURE 3.10 Optimization of the parameter C in the equation for permeability estimate from NMR measurements with results of direct permeability measurements. The left three plots show calculated curves with different parameters C and measured permeability data (dots). The graph in the centre presents a summation of absolute errors between predicted and measured data as function of the used value for C curve has a minimum error at C= 14.5 and gives the optimal input for final solution (right plot). Georgi et al. (1997) and Kasap et al. (1999). 

E25 had similar permeability in both cell types and 10-fold higher permeability in the basolateral to apical direction than in the apical to basolateral direction (see Table 1). In either direction, permeability across airway or alveolar epithelium to the antibody (E25) was low. Similar transport rates were obtained by Kim and Crandall (19) for an IgG antibody in rat alveolar epithelial cells, although directional preferences for transport were the opposite of those observed in Table 1. 

Water and limonene direct permeability were finally evaluated for the PET and for their nanocomposites and are summarized in Table 3. Films of PET with 1% Wt Nanoter show a limonene permeability decrease of 26% compared to the unfilled material, but the sample with 5% Wt Nanoter content have a reduction in limonene permeability of ca. 68%. A reduction in water permeability of ca. 43% is observed in the nanocomposite of PET with 1% wt Nanoter but films of PET with 5% Wt Nanoter have a reduction in water permeability of only 14%. The reason for the latter counterintuitive behaviour in the water permeability could be related to the inherent hygroscopicity of the MMT clay. Previous studies reported that the limonene permeability for PET is of ca. 0.0000048 10" Kg m / s m Pa when measured at 23°C... 

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