Transport carriers, natural

Waterborne Transport. Despite natural limitations, the transportation of chemicals by water has enjoyed substantial growth, especially siace the ead of World War 11. Assisted by governmental developmeat of the inland waterways system, including locks and other navigational aids, water carriers transport large quantities of bulk chemicals in barges between inland ports or between such ports and coastal ports. In addition, bulk chemicals ate transported by self-propelled tank vessels between U.S. coastal points, and between U.S. ports and overseas destinations. In 1989, 56.1 million metric tons (61.9 million short tons) of chemicals were transported in the U.S. domestic waterborne commerce (16). 

Ota, S. Uetani, H. Kawano, H. (2002). Use of hydrate pellets for transportation of natural gas - III - safety measures and conceptual design of natural gas hydrate pellet carrier. Proc. Fourth Int. Con. Gas Hydrate, Yokohama, Japan, Vol. I 991-996. 

On the one hand, such anisotropic stmcture of the membranes allows one to protect its internal part from unwanted external action and, on the other hand, the liquidity of such stmcture provides the high transport carriers properties of the cell - permeability, ions transportation, and so on. Most important proteins, such as receptors, enzymes, dmg, and hormone molecules, are freely floating inside double lipid layers maintaining the vitally important cell functions. Thus, the LC nature of the cells provides the unique combination of solid and liquid properties of many biological stmctures in living organisms. 

Slurry is essentially a mixture of solids and liquids. Its physical characteristics are dependent on many factors such as size and distribution of particles, concentration of solids in the liquid phase, size of the conduit, level of turbulence, temperature, and absolute (or dynamic) viscosity of the carrier. Nature offers examples of slurry flows such as seasonal floods that carry sUt and gravel. Every year during the flood season, the Nile transports massive amounts of silt over thousands of miles to the Saharan desert. To rephrase Herodotus, who once said Egypt is the gift of the NUe, one may consider that one of the most ancient civilizations was dependent on natural slurry flows for its survival. 

Cell membranes are lipophilic and designed to be barriers against large anionic molecules, although there is a natural mechanism for intercellular transport of anionic oligonucleotides. In order to enhance membrane transport, antisense oligonucleotides are frequentiy modified by covalent attachment of carrier molecules or lipophilic groups. 

A second source of inspiration for studying the open-chained equivalents of crown ethers was the observation that a number of naturally occurring antibiotics enhance cation transport and bear a structural similarity to open-chained crown ethers. A number of groups have examined neutral synthetic ionophores and a variety of novel cation carriers is now available. This is discussed in Sect. 7.4, below. 

Natural colloid particles in aqueous systems, such as clay particles, silica, etc. may serve as carriers of ionic species that are being sorbed on the particulates (pseudocolloids). It seems evident that the formation and transport properties of plutonium pseudocolloids can not yet be described in quantitative terms or be well predicted. This is an important area for further studies, since the pseudocolloidal transport might be the dominating plutonium migration mechanism in many environmental waters. 

Solid mixed ionic-electronic conductors (MIECs) exhibit both ionic and electronic (electron-hole) conductivity. Naturally, in any material there are in principle nonzero electronic and ionic conductivities (a i, a,). It is customary to limit the use of the term MIEC to those materials in which a, and 0, 1 do not differ by more than two orders of magnitude. It is also customary to use the term MIEC if a, and Ogi are not too low (o, a i 10 S/cm). Obviously, there are no strict rules. There are processes where the minority carriers play an important role despite the fact that 0,70 1 exceeds those limits and a, aj,i< 10 S/cm. In MIECs, ion transport normally occurs via interstitial sites or by hopping into a vacant site or a more complex combination based on interstitial and vacant sites, and electronic (electron/hole) conductivity occurs via delocalized states in the conduction/valence band or via localized states by a thermally assisted hopping mechanism. With respect to their properties, MIECs have found wide applications in solid oxide fuel cells, batteries, smart windows, selective membranes, sensors, catalysis, and so on. 

The most important application recently developed for synthetic liposomes is as potential drug carriers for controlled release, especially for cancer chemotherapy (7). In general, the success of liposomes as vehicles for the transport of specific drugs will largely depend on their stability under physiological conditions. Unlike the naturally occurring membranes, the synthetic vesicles have very limited stability, and this is a... 

Soluble macromolecules of both natural and synthetic origin have been used as drug carriers. When compared with the particulate carriers, soluble macromolecules (a) encounter fewer barriers to their movement around the body and can enter into many organs by transport across capillary endothelium or in... 

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