Permeation effect

Most gene therapy applications require extravasation of the DNA carriers so that only relative small DNA complexes can pass through the blood vessels and interact directly with parenchymal cells after vascular administration [2]. Under pathophysiological conditions, the structure of the vasculature can change. This phenomenon - termed the enhanced permeation effect - has been utilized to passively target macromolecules to tumors, since blood vessels in tumors are relatively more leaky. 

The permeation effect is also shown by the suited reduction of the reaction volume (or catalyst amount) (Figure 13.11) in fact, the MR reaction volume is significantly lower than that of a TR. 

Other gas permeation effects. It should be noted that all plastics are to some degree permeable to gases. This means that even when the closure is highly effective, permeation into the pack can give rise to physical or chemical changes. Examples of these are as follows. 

The force g normal to the layers will be associated with permeation effects. The idea of permeation was put forward originally by Helfrich to explain the very high viscosity coefficients of cholesteric and smectic liquid crystals at low shear rates (see figs. 4.5.1 and 5.3.7). In cholesterics, permeation falls conceptually within the framework of the Ericksen-Leslie theory > (see 4.5.1), but in the case of smectics, it invokes an entirely new mechanism reminiscent of the drift of charge carriers in the hopping model for electrical conduction (fig. 5.3.8). 

In the right part of the figure, the direction of the flow coincides with the helical axis. This case is especially interesting because it results in the so-called permeation effect. 

The explanation of these observations has been given in terms of the so-called permeation effect [16]. Helfrich assumed that the helical structure with wavevector qo is fixed by the boundary conditions at the walls of a cylindrical capillary of radius R. Schematically it is shown by fixation points at each period of the helix in Fig. 9.10a. The liquid crystal flows out of the capillary with a constant velocity vllq . Therefore, the mass of the liquid of density p escaping the capillary in a time unit is given by Q = nR pv. The flow velocity is considered to be uniform along the capillary radius (except the boundary layer / < R). At the same time molecules... 

Fig. 9.10 Poiseuille flow in a cylindrical capillary with permeation effect in the cholesteric (a) and smectic A (b) phases...

For the smectic A phase the permeation effect is even more important [16]. In fact, with the layers fixed at the walls of a capillary, a smectic may flow only as a whole, like a plug, without velocity gradients. Fig. 9.10b. The velocity is again given by equation Vp = kpV, where kp is the permeation coefficient depending on the smectic characteristic length given by Eq. (8.46), cmiventional nematic viscosity q and temperature ... 

If both the compressibility and the permeation effect are disregarded, the structure of the viscous stress tensor CTy is identical for the SmA and nematic phases... 

Fig. 9.11 Two geometries for easy flow in Smectic A flow velocity in both cases is in the layer plane but shear is either perpendicular to layers (a) or parallel to them (b). For the flow velocity along the layer normal the permeation effect is observed, see Fig. 9.10b...

Recently, the interest in gel pore volume effects has been applied to the so called "inverse permeation" effect, where porosities of rigid gel materials are found from chromatographic results (refs. 48-50). 

Approximately 200 ppm residual methanol leaves the scmbber and enters the separator train. As indicated in Fig. 20.2-3, the major feed components consist of H2, CO2, CO, CH4, and N2 with a saturated vapor pressure of water pesent from the scmbbing operation. The stream is preheated prior to entering the separator train to prevent depression of the product gas permeation rate. This preheating prevents complications arising from water condensation and other more subtle permeation effects discussed later in the fundamentals section. Then the feed is split and fed in parallel to the series of separators shown in Fig. 20.2-3. 

One phase is called the permeate V, the other phase the reject L. The designators also refer to the (molar) flow rate of each of the phases, which varies with position. The reject is the continuation of the feed-stream. Its inlet rate and composition are those of the feed, its final or exit rate and composition depend on the permeation effected. 

In this case, the anisotropy parameter does not contain the viscosity coefficients due to the permeation effect... 

Up to now the influence of the permeation effect has been neglected and the Eqs. (123-126) give only meaningful results if the flow velocity component perpendicular to the layers can be neglected. 

In the other case the permeation effect, that is, an energy dissipation for a flow perpendicular to the layers, has to be taken into account. For this purpose the layer normal is assumed to be parallel to the z axis (Fig. 20) and the stress tensor becomes... 

The elastic behaviour of the smectic layers, the permeation effect and the viscous flow lead to a great variety of phenomena in SmA phases effects due to the compression of the layers [70,71], flow behind obstacles [69, 72], and instabilities [73, 74],... 

For a net drag coefficient of 4.0, no hydraulic permeation effects, and an electro-osmotic drag coefficient of 3.0, calculate the water crossover and equivalent f)ower lost per day for a 10 M methanol solution at idle in the anode of a 10-cell, 10-cm /cell DMFC stack. 

---