Permeability characterization

The action of Bcl-2-related proteins constitutes a major life-or-death decision of the mitochondria that depends on the ratio of the antiapoptotic and proapoptotic proteins (Fig. 1). It has been shown that mitochondria undergo a transition of permeability characterized by a breakdown of membrane potential followed by an outflow of AIF and cytochrome C into the cytoplasm. It seems that Bcl-2 and Bc1-Xl act against this permeability transition, whereas Bax and Bak suppress this antiapoptotic activity of Bcl-2 and Bc1-Xl (T6). 

K. Seto, Miscible displacement simulation and permeability characterization in porous media. PhD thesis, Texas A M University, 1999. 

Kuentzer, N., Simacek, P, Advani, S. G. and Walsh, S., Permeability characterization of dual scale fibrous porous media . Composites Part A Applied Science and Manufacturing, 37, 2057-2068, 2006. 

Parnas, R.S. Luce, T. Advani, S.G. Howard, G. Permeability characterization, Part 1 A proposed standard reference material. Polym. Compos. 1995, 16, 430-446. 

Let us consider a domain U e R, representing the three-dimensional flaw imbedded in a homogeneous conductive media, with electric conductivity uo and permeability The flawed region D is assumed to be inhomogeneous, and characterized by the relative real conductivity ... 

Membrane Characterization The two important characteristics of a UF membrane are its permeability and its retention characteristics. Ultrafiltration membranes contain pores too small to be tested by bubble point. Direc t microscopic observation of the surface is difficult and unreliable. The pores, especially the smaller ones, usually close when samples are dried for the electron microscope. Critical-point drying of a membrane (replacing the water with a flmd which can be removed at its critical point) is utihzed even though this procedure has complications of its own it has been used to produce a Few good pictures. 

There are essentially four important physical parameters that characterize a filter media and are used as a basis for relating the characteristics of the material to the system flow dynamics. These are porosity, permeability, tortuosity and connectivity. 

A microscopic description characterizes the structure of the pores. The objective of a pore-structure analysis is to provide a description that relates to the macroscopic or bulk flow properties. The major bulk properties that need to be correlated with pore description or characterization are the four basic parameters porosity, permeability, tortuosity and connectivity. In studying different samples of the same medium, it becomes apparent that the number of pore sizes, shapes, orientations and interconnections are enormous. Due to this complexity, pore-structure description is most often a statistical distribution of apparent pore sizes. This distribution is apparent because to convert measurements to pore sizes one must resort to models that provide average or model pore sizes. A common approach to defining a characteristic pore size distribution is to model the porous medium as a bundle of straight cylindrical or rectangular capillaries (refer to Figure 2). The diameters of the model capillaries are defined on the basis of a convenient distribution function. 

Ideally, separators would present no resistance to ion transport. In practice, some resistance must be tolerated. Still, the resistance of the separator is usually insignificant relative to the transport limitations in the electrodes. Separator permeability is typically characterized by air permeability. The Gurley number expresses the time required for a specific amount of air to pass through a specific area of separator under a specific pressure (e.g., 10 mL through 1 in2 (6.45 cm2) at 2.3 cm Hg). This measurement depends on porosity, pore size, thickness, and tortuosity according to Eq. (1) [17] ... 

The open channel has in most cases a selective permeability, allowing a restricted class of ions to flow,for example Na+, K+, Ca++ or Cl- and, accordingly, these channels are called Na+-channels, K+-channels, Ca -channels and Cr-channels. In contrast, cation-permeable channels with little selectivity reject all anions but discriminate little among small cations. Little is known about the structures and functions of these non-selective cation channels [1], and so far only one of them, the nicotinic acetylcholine receptor (nAChR, see Nicotinic Receptors), has been characterized in depth [2, 3]. The nAChR is a ligand-gated channel (see below) that does not select well among cations the channel is even permeable to choline, glycine ethylester and tris buffer cations. A number of other plasma... 

For heterogeneous media composed of solvent and fibers, it was proposed to treat the fiber array as an effective medium, where the hydrodynamic drag is characterized by only one parameter, i.e., Darcy s permeability. This hydrodynamic parameter can be experimentally determined or estimated based upon the structural details of the network [297]. Using Brinkman s equation [49] to compute the drag on a sphere, and combining it with Einstein s equation relating the diffusion and friction coefficients, the following expression was obtained ... 

Mitochondria have an outer membrane that is permeable to most metabohtes, an inner membrane that is selectively permeable, and a matrix within (Figure 12-1). The outer membrane is characterized by the presence of various enzymes, including acyl-CoA synthetase and glycerolphosphate acyltransferase. Adenylyl kinase and creatine kinase are found in the intermembrane space. The phospholipid cardiolipin is concentrated in the inner membrane together with the enzymes of the respiratory chain. 

As observed by Celus, a Roman physician during the first century A.D., the four cardinal signs characterize inflammation swelling, redness, heat, and pain. Swelling/edema occurs in response to the accumulation of fluids from damaged capillaries following injury. Increased fluid accumulation leads to increase capillary permeability. Histamine, produced and released by resident mast cells, also... 

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