Membrane shape

White SH et al How membranes shape protein structure. J Biol Chem 2001 276 32395. 

Further progress in understanding membrane instability and nonlocality requires development of microscopic theory and modeling. Analysis of membrane thickness fluctuations derived from molecular dynamics simulations can serve such a purpose. A possible difficulty with such analysis must be mentioned. In a natural environment isolated membranes assume a stressless state. However, MD modeling requires imposition of special boundary conditions corresponding to a stressed state of the membrane (see Refs. 84,87,112). This stress can interfere with the fluctuations of membrane shape and thickness, an effect that must be accounted for in analyzing data extracted from computer experiments. 

Membrane shape Symmetrical and asymmetrical Asymmetrical Asymmetrical Asymmetrical... 

The extent and speed of this agglutination depends on the hapten concentration in the plane of the membrane and on the lateral mobility of the hapten (G. K. H. Humphries, P. Brulet, H. McConnell, unpublished). It is extremely probable that this simple agglutination reaction leads to a change in the membrane shape. 

Allowance for High Elux Membrane Shape of Colonizing Surface Attachment of Ligands Cell Adhesion... 

Caused membrane shape change without altering K+ efflux in human erythrocytes 410... 

Figure 2.1 Polymeric membrane shapes and cross-sectional structures. Tubular membranes are similar to flat sheet membranes because they are cast on a macroporous tube as support. Capillary membranes are hollow fibers with larger diameter, that is, >0.5 mm.

Different membrane shapes are used, such as plates, foils, spirals, hollow fibers, tubes, and even monilithic multichannel elements have been mentioned in the context of membrane reactors. In the following section, a general survey will be given indicating the main characteristics of the different types of inorganic membranes used in CMRs. More details can be found elsewhere [13-15]. 

Depending on the membrane shape (plate or tube) the reactor is different, but it is generally made of two chambers separated by the membrane. Figure 6 shows a reactor made of a tubular membrane and a conventional fixed-bed catalyst filling the inner part of the tube. In this example the reactant(s) is introduced into... 

There is some indication that a high "packing density" membrane shape may result in a greater conversion than, for example, membrane tubes. In a study of using an a-alumina hollow fiber (1.6 mm in diameter) coated with an y-alumina membrane as a membrane reactor for dehydrogenation of cyclohexane, Okubo et al. [1991] found that a given... 

For the identical experimental conditions, electroporation efficiency depends on the type of cells the composition of the membrane, shape, and size of cells strongly influences the electroporation efficiency [40-42]. In electroporation of bacteria, the growth phase of cell has significant influence on transformation efficiency, which is higher for cells harvested and electroporated from mid-log phase. However, cells from stationary phase can also be transected with reasonably good efficiency. Mammalian cell can be electroporated at relatively lower fields but pulse length controls the entry of external molecules into cells. 

Activation of lipases generates free fatty acids and lysolecithins. Lysolecithins are adsorbed within one minute by the cell wall [129], causing a reorganization of cell membrane constituents [130], recognizable by a change of the cell membrane shape [131]. Lysolecithines are reported to activate (at least in mammalian tissue) kinases [132]. 

In fact, F is also required to be at a minimum with respect to all possible membrane deformations, and this minimization with respect to membrane shape must be carried out self-consistently together with the electrostatic and lipid mixing contributions [27,36]. This presents a challenge, since in principle one has to consider all possible variations in membrane geometry, and these multiple shape deformations generally couple to other degrees of freedom. 

Figure 5.16 shows the principal steps for isos-tatically molding a simple solid cylinder. The mold cavity is formed inside an elastomeric membrane shaped like a hollow cylinder. In this case, it does not include any mandrels and is completely filled with the powder. The elastomeric bag is closed, sealed and placed inside a pressure vessel. The vessel containing a fluid is sealed, pressurized and held for a dwell period during which the powder is compacted by the action of a pressurized fluid. At the end of the dwell time, the vessel is depressurized and the mold is removed and disassembled for the removal of the preform. 

The membrane shapes described are usually incorporated into compact commercial modules and cartridges. The four more common types of modules are (1) plate-and-frame, (2) spiral-wound, (3) tubular, and (4) hollow-fiber. Table 9.2 is a comparison of the characteristics of these four types of modules. The packing density refers to the surface area per unit volume of module, for which the hollow-fiber modules are clearly superior. However, hollow-fiber modules are highly susceptible to fouling and very difficult to clean. The spiral-wound module is very popular for most applications because of its low cost and reasonable resistance to fouling. 

The next level up from the basic membrane architecture is the selection of membrane shape. The main two architectures studied have used tubular geometries and a modified planar geometry. Both have their advantages and disadvantages for oxygen separation. 

---