Single-layer walls

CARBON NANOTUBES WITH SINGLE-LAYER WALLS... 

Carbon nanotubes with single-layer walls... 

Fig. 2. By rolling up a graphene sheet (a single layer of ear-bon atoms from a 3D graphite erystal) as a cylinder and capping each end of the eyiinder with half of a fullerene molecule, a fullerene-derived tubule, one layer in thickness, is formed. Shown here is a schematic theoretical model for a single-wall carbon tubule with the tubule axis OB (see Fig. 1) normal to (a) the 6 = 30° direction (an armchair tubule), (b) the 6 = 0° direction (a zigzag tubule), and (c) a general direction B with 0 < 6 < 30° (a chiral tubule). The actual tubules shown in the figure correspond to (n,m) values of (a) (5,5), (b) (9,0), and (c) (10,5).

This process of filament growth is closely related to the synthesis of single walled carbon nano-tubes. Here the aim is to selectively produce a single layer of carbon in a tube that is as long as possible. Owing to their extreme mechanical strength and interesting electronic behavior these materials have recently attracted substantial interest in materials science. 

Peritoneal dialysis (PD) utilizes similar principles as hemodialysis in that blood is exposed to a semipermeable membrane against which a physiologic solution is placed. In the case of PD, however, the semipermeable membrane is the peritoneal membrane, and a sterile dialysate is instilled into the peritoneal cavity. The peritoneal membrane is composed of a continuous single layer of mesothelial cells that covers the abdominal and pelvic walls on one side of the peritoneal cavity, and the visceral organs, including the GI tract, liver, spleen, and diaphragm on the other side. The mesothelial cells are covered by microvilli that increase the surface area of the peritoneal membrane to approximate body surface area (1 to 2 m2). 

The structure of the blood capillary wall is complex and varies in different organs and tissues. It consists of a single layer of endothelial cells joined together by intercellular junctions. Each endothelial cell, on an average, is 20-40 pm long, 10-15 pm wide, and 0.1-0.5 pm thick, and contains 10,000-15,000 uniform, spherical vesicles called plasmalemmal vesicles. These vesicles range in size between 60 and 80 nm in diameter. About 70% of these vesicles open on the luminal side of the endothelial surface, and the remaining open within the cytoplasm. Plasmalemmal vesicles are believed to be involved in the pinocytic transport of substances across the endothelium. The transition time of pinocytic vesicles across the cell is... 

The movement of substances between the blood and the extracellular fluid surrounding the cells in most tissues of the body occurs very readily. This exchange takes place at the level of the capillaries, the smallest blood vessels in the cardiovascular system whose walls are formed by a single layer of endothelial cells. Lipid-soluble substances are able to move across this layer of endothelial cells at any point because they can move directly through the plasma membrane by passing between the phospholipid molecules of the bilayer. The movement of water-soluble substances is limited to the multiple pores found between the cells however, it also takes place rapidly and efficiently. 

Thyroid hormones. Internally, the thyroid consists of follicles, which are spherical structures with walls formed by a single layer of epithelial cells called follicular cells. The center of each follicle contains a homogenous gel referred to as colloid. Thyroid hormones are stored here as a component of the larger molecule, thyroglobulin. The amount of thyroid hormones stored within the colloid is enough to supply the body for 2 to 3 months. 

More specifically, the blood-gas interface consists of the alveolar epithelium, capillary endothelium, and interstitium. The alveolar wall is made up of a single layer of flattened type I alveolar cells. The capillaries surrounding the alveoli also consist of a single layer of cells — endothelial cells. In between the alveolar epithelium and capillary endothelium is a very small amount of interstitium. Taken together, only 0.5 pm separates the air in the alveoli from the blood in the capillaries. The extreme thinness of the blood-gas interface further facilitates gas exchange by way of diffusion. 

Like the walls of other capillaries, the glomerular capillary wall consists of a single layer of endothelial cells. However, these cells are specialized in that they are fenestrated. The presence of large pores in these capillaries makes them 100 times more permeable than the typical capillary. These pores are too small, however, to permit the passage of blood cells through them. 

Bethune, D.S., Kiang, C.H., De Vries, M.S., Gorman, G., Savoy, R. et al. (1993) Cobalt catalysed growth of carbon nanotubes with single-atomic-layer walls. Nature 363, 605-607. 

The vent area ratio for a single layer structure is the vent area divided by the total area of the wall. The vent area ratio for a multi-layer structure is... 

D. S. Bethune, C. H. Kiang, M. S. DeVries, G. Gorman, R. Savoy, J. Vazquez, R. Beyers, Cobalt-catalyzed growth of carbon nanotubes with single-atomic-layer walls, Nature, vol. 363,... 

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