Junction Passivity

Let / denote the finite-precision version of /. Then a sufficient condition for junction passivity is... 

A typical 7R-FR characteristic of a-Si H passivated junction (/a.Si) is shown in Fig. 5 together with that of a similar junction passivated with thermal oxide (Iox). The effect of BT stress at 5 V and 200°C is shown by curve (1) in Fig. 5. Then the specimen was subjected to annealing treatments for 30 min each at successively higher temperatures up to 650°C as also shown in Fig. 5. 

There are two cellular barriers that separate the brain extracellular fluid from the blood (see Figure 3.1). The first and largest interface is the brain capillary endothelial cells that form the BBB. The brain capillaries are a continuous layer of endothelial cells connected by well-developed tight junctional complexes.2 As a result of the tight junctions, passive diffusion of dmgs and solutes between the endothelial cells is restricted. In addition, brain capillary endothelial cells lack fenestrations (water-filled pores or channels within the plasma membrane) and have reduced pinocytic activity. These characteristics further restrict the movement of compounds from the blood into the extracellular environment of the brain.3-5... 

When cells lie adjacent to each other in animal tissues, they are often connected by gap junction structures, which permit the passive flow of small molecules from one cell to the other. Such junctions essentially connect the cells metabolically, providing a means of chemical transfer and communication. In certain tissues, such as heart muscle that is not innervated, gap junctions permit very large numbers of cells to act synchronously. Gap junctions also provide a means for transport of nutrients to cells disconnected from the circulatory system, such as the lens cells of the eye. 

NOTE Probably the most important junction of oxygen scavengers is, in reality, the ability to passivate boiler steel. In recognition of this, today most novel oxygen scavenger trials try to identify, not merely comparative oxygen reaction rates, but more importantly, the reduction in iron and copper transport rates through the boiler system. In other words, they seek to optimize the passivation of boiler surfaces and other system components. 

Josephson junctions for passive microwave devices, satellite-communication systems, and computer logic gates. 

In cancer treatment, passive targeting of macromolecular carriers to tumors is a commonly used approach. This passive targeting is based on the enhanced permeability and retention (EPR) effect, which leads to an accumulation of the high molecular weight carrier in the tumor tissue. The EPR effect arises from the different physiology of tumor vasculature, where the vessel walls are highly porous and lack the tight junctions that are present in healthy tissue. As a result, macromolecular carriers extravasate and accumulate preferentially in tumor tissue relative to normal tissues [63, 64]. 

The optical properties of electrodeposited, polycrystalline CdTe have been found to be similar to those of single-crystal CdTe [257]. In 1982, Fulop et al. [258] reported the development of metal junction solar cells of high efficiency using thin film (4 p,m) n-type CdTe as absorber, electrodeposited from a typical acidic aqueous solution on metallic substrate (Cu, steel, Ni) and annealed in air at 300 °C. The cells were constructed using a Schottky barrier rectifying junction at the front surface (vacuum-deposited Au, Ni) and a (electrodeposited) Cd ohmic contact at the back. Passivation of the top surface (treatment with KOH and hydrazine) was seen to improve the photovoltaic properties of the rectifying junction. The best fabricated cell comprised an efficiency of 8.6% (AMI), open-circuit voltage of 0.723 V, short-circuit current of 18.7 mA cm, and a fill factor of 0.64. 

Figure 2.7 Schematic of the apical phospholipid hilayer surface of the epithelial cells, indicating three types of passive diffusion transcellular (la > 1 b 1 c), paracellular (2a >2b 2c), and the hypothesized lateral, under the skin of the tight junction (3a—> 3b—> 3c) modes. Tight-junction matrix of proteins highly stylized, based on Ref. 75. [Avdeef, A., Curr. Topics Med. Chem., 1, 277-351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]...

Two principal routes of passive diffusion are recognized transcellular (la —> lb —> lc in Fig. 2.7) and paracellular (2a > 2b > 2c). Lateral exchange of phospholipid components of the inner leaflet of the epithelial bilayer seems possible, mixing simple lipids between the apical and basolateral side. However, whether the membrane lipids in the outer leaflet can diffuse across the tight junction is a point of controversy, and there may be some evidence in favor of it (for some lipids) [63]. In this book, a third passive mechanism, based on lateral diffusion of drug molecules in the outer leaflet of the bilayer (3a > 3b > 3c), wih be hypothesized as a possible mode of transport for polar or charged amphiphilic molecules. 

Brayden, D. J. Creed, E. Meehan, E. O Malley, K. E., Passive transepithelial diltiazem absorption across intestinal tissue leading to tight junction openings, J. Control. Rel. 38, 193-203 (1996). 

While both paracellular and passive transcellular pathways are available to a solute, the relative contribution of each to the observed transport will depend on the properties of the solute and the membrane in question. Generally, polar membrane-impermeant molecules diffuse through the paracellular route, which is dominated by tight junctions (Section III.A). Exceptions include molecules that are actively transported across one or both membrane domains of a polarized cell (Fig. 2). The tight junction provides a rate-limiting barrier for many ions, small molecules, and macromolecules depending on the shape, size, and charge of the solute and the selectivity and dimensions of the pathway. 

Water and electrolytes. Each day in an average adult, about 5.51 of food and fluids move from the stomach to the small intestine as chyme. An additional 3.5 1 of pancreatic and intestinal secretions produce a total of 9 1 of material in the lumen. Most of this (>7.5 1) is absorbed from the small intestine. The absorption of nutrient molecules, which takes place primarily in the duodenum and jejunum, creates an osmotic gradient for the passive absorption of water. Sodium may be absorbed passively or actively. Passive absorption occurs when the electrochemical gradient favors the movement of Na+ between the absorptive cells through "leaky" tight junctions. Sodium is actively absorbed by way of transporters in the absorptive cell membrane. One type of transporter carries a Na+ ion and a Cl ion into the cell. Another carries a Na+ ion, a K+ ion, and two Cl ions into the cell. 

There are two pathways by which a drug molecule can cross the epithelial cell the transcellular pathway, which requires the drug to permeate the cell membranes, and the paracellular pathway, in which diffusion occurs through water-filled pores of the tight junctions between the cells. Both the passive and the active transport processes may contribute to the permeability of drugs via the transcellular pathway. These transport pathways are distinctly different, and the molecular properties that influence drug transport by these routes are also different (Fig. 

Recently, Melosh has obtained electrically stable LAJs as large as 9 mm2 by atomic deposition of a nanometer-thick passivating layer of aluminium oxide on top of self-assembled organic monolayers with hydrophilic terminal groups [158,159]. Obviously, interlayers based junctions limit electrical measurements only to organic SAMs less conductive than the protecting layer. 

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