Distribution depots

Oil of viscosity 10 mN s/m2 and density 950 kg/m3 is pumped 8 km from an oil refinery to a distribution depot through a 75 inm diameter pipeline and is then despatched to customers at a rale of 500 tonne/day. Allowance must be made for periods of maintenance which may interrupt the supply from the refinery for up to 72 hours. If the maximum permissible pressure drop over the pipeline is 3450 kN/m2, what is the shortest time in which the storage tanks can be completely recharged after a 72 hour shutdown Take the roughness of the pipe surface as 0.05 mm. 

Despatches by rail can be cheaper per tonne of product and more acceptable from an environmental viewpoint. They require suitable rail reception facilities and are particularly suitable for supplying distribution depots and large-offtake, long-term customers. In general, rail becomes more competitive relative to road transport as the distance from the quarry to the customer increases. 

Vehicle fires can also be a primary source for a secondary fire in a building, e.g. delivery/haulage vehicle within a distribution depot, or a forklift truck within a warehouse, where a fire starting from a vehicle quickly spreads within a building causing the whole building to be involved. 

Generally, vertical or horizontal coalescer-separator vessels for fuels are fabricated from carbon steel, coated internally with various linings such as epoxy resin. Applications include their use in refuelling facilities around the world, helicopter and VTOL support bases, with large capacity units used for bunkering or fuel distribution depots. 

Fats and oils may be synthesized in enantiomerically pure forms in the laboratory (30) or derived from vegetable sources (mainly from nuts, beans, and seeds), animal depot fats, fish, or marine mammals. Oils obtained from other sources differ markedly in their fatty acid distribution. Table 2 shows compositions for a wide variety of oils. One variation in composition is the chain length of the fatty acid. Butterfat, for example, has a fairly high concentration of short- and medium-chain saturated fatty acids. Oils derived from cuphea are also a rich source of capric acid which is considered to be medium in chain length (32). Palm kernel and coconut oils are known as lauric oils because of their high content of C-12 saturated fatty acid (lauric acid). Rapeseed oil, on the other hand, has a fairly high concentration of long-chain (C-20 and C-22) fatty acids. 

Specifications for gas turbine fuels prescribe test limits that must be met by the refiner who manufactures fuel however, it is customary for fuel users to define quality control limits for fuel at the point of delivery or of custody transfer. These limits must be met by third parties who distribute and handle fuels on or near the airport. Tests on receipt at airport depots include appearance, distfllation, flash point (or vapor pressure), density, freezing point, smoke point, corrosion, existing gum, water reaction, and water separation. Tests on delivery to the aircraft include appearance, particulates, membrane color, free water, and electrical conductivity. 

Certain small-volume injections are available where the dmg is dissolved in a viscous oil because it is insoluble in water non-aqueous solvent must be used, hi addition, drags in non-aqueous solvents provide a depot effect, for example for hormonal compounds. The intramuscular route of injection must be used. The vehicle may be a metabolizable fixed oil such as arachis or sesame oil (but not a mineral oil) or an ester such as ethyl oleate which is also metabolizable. The latter is less viscous and therefore easier to administer but the depot effect is of shorter duration. The dmg is normally dissolved in the oil, filtered under pressure and distributed into ampoules. After sealing, the ampoules are sterilized by dry heat, for example, at 160°C for 2 hours. A bactericide is probably ineffective in such a medium and therefore offers very httle protection against contamination in a multidose oily injection. 

There is no gold standard for measuring the content of the triacylglycerol store, since adipose tissue is distributed in many different depots (see Appendix 2.4 for some of the methods that are available). 

Restricted diffusion also limits tissue distribution after intraparenchymal drug administration, as shown in Figure 2.7c and d. Distribution has been measured in the rat brain after implantation of polymer discs containing NGF [66]. Drug concentrations decreased to less than 10% of the values measured on the disc surface within a distance of 2-3 mm, even after prolonged periods of several days. Therefore, applying this approach in the larger human brain would require the stereotaxic placement of multiple intraparenchymal depots, as has been evaluated in rat brain [67], on a repetitive schedule. 

Ethambutol is a synthetic agent and not related to any of the other tuberculostatics. Its mechanism of action is not well understood but in actively dividing mycobacteria it appears to be an inhibitor of mycobacterial RNA synthesis. It also has effects on bacterial phosphate metabolism and on polyamine synthesis. It is an bacteriostatic agent and its main function in combination therapy is to delay the occurrence of resistance, mainly against isoniazid and rifampicin. It is well absorbed after oral administration. It is widely distributed, except to the CNS. Protein binding is about 20-30%. It is mainly excreted unchanged in the bile and urine with an elimination half-life of 3 h. Ethambutol is concentrated in erythrocytes and thus provides a depot for continuous release. 

As emphasized earlier, the concentration gradient of the drug in Eq. (1) refers to that of the unbound drug and its ionic distribution, which depends upon its acid-base properties. This can be modified by appropriate choice of excipients to ionize the drug by salt formation, thereby affecting the distribution of ionic versus nonionic species by acid-base equilibrium, using the Henderson-Hasselbach equation. All of the drug will eventually leave the depot and enter the body, but the rate may be reduced if membrane transport is limited by solubility of the neutral species within the membrane. 

The body is composed of about 70% water by weight. The fluid portion of the blood (plasma) accounts for 6 liters or about 4% of that total. Intracellular water constitutes about 41 % while interstitial (between cells) fluid is 13%. The rest is extracellular. Therefore solubility in water will be an important factor in drug distribution. Fat depots within adipose and other fatty tissues are also important in that they can sequester lipophilic molecules and release them very slowly back into the general blood circulation. This is the case with tetrahydrocannabinol (THC), the psychoactive component of marijuana. It shows two periods of presence in the blood the first immediately after consumption and the second a more lingering presence for up to 27 days after use. 

Thus, a large dose may be ineffectively distributed and remain at the site of administration as a depot. A large dose of a compound given orally, for instance, may not be all absorbed, depending on the rates of absorption and transit time within the gut. Saturable active absorption processes would be particularly prone to dose effects, which could result in unexpected dose-response relationships. 

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