Site of Formation

Radiochemical studies indicate that the pore base is the actual site of formation of aluminium oxide, presumably by transport of aluminium ions across the barrier-layer, although transport of oxygen ions in the opposite direction has been postulated by some authorities. The downward extension of the pore takes place by chemical solution, which may be enhanced by the heating effect of the current and the greater solution rate of the freshly formed oxide, but will also be limited by diffusion. It has been shown that the freshly formed oxide, y -AljOj, is amorphous and becomes slowly converted into a more nearly crystalline modifipation of y-AljO . 

While steroids generated in the brain have been referred to as neurosteroids , another useful term is neuroactive steroids to refer to all steroids that affect brain function via any mechanism and irrespective of site of formation. The term neuroactive steroid also has been used to describe neuroactive steroid drugs. 

In the open ocean, the major advective water motion is associated with the surfece-water geostrophic currents and meridional overturning circulation. These flow paths are shown in Figures 4.4b and 4.6. Advection is much fester than molecular diffusion and turbulence. This enables water masses to retain their original temperatures and salinities as they are advected away from their sites of formation. Slow turbulent mixing with adjacent water masses eventually alters this temperatme and salinity signal beyond... 

NADW flows south from its site of formation until it reaches the Southern Ocean where it joins up with AABW The water masses then flow eastward under the influence of the Westerlies. A branch heads off into the Indian Ocean and the rest enters the South Pacific. All along these flow paths, upward advection and turbulent mixing slowly return the water to the surface where the geostrophic currents eventually carry it back to the Atlantic Ocean. Because a major feature of the flow paths is transport across latitudes. 

Plankton produce biogenic particles in the surfece waters of all the ocean basins. Most of these particles sink into the deep sea and are then remineralized. The rain of biogenic particles causes the nutrient concentration of the deep-water masses to increase as they move through the ocean basins for two reasons. First, the further a deep-water mass has traveled from its site of formation, the greater the amount of particles it will... 

Phosphorite deposits are currently forming in areas of high organic productivity and low detrital input. These are typically coastal upwelling zones adjacent to arid continental lands. Phosphorites form at slow rates, so low detrital input is important to prevent dilution or burial. As shown in Figure 18.10, sites of formation include the continental margins of Peru, Chile, and southwest Africa. 

Similar trends are seen in the C/N ratio of DOM. The C/N ratio of bulk deepwater DOM (18 1) is higher than bulk surface-water DOM (14 1), which is in turn higher than plankton (6.6 1). The radiocarbon and C/N observations gave rise to the two-pool model presented in Figure 23.8 in which surface-water DOM is viewed as an admixture of relatively young labile DOM and a much older refractory pool. The labile pool is effectively restricted to its site of formation in the surfece waters, whereas the refractory pool is persistent enough to spread via advective currents throughout the surface and deep ocean. 

The flow of cerebrospinal fluid is essentially unidirectional that is, it flows from its site of formation in the choroid plexus through the ventricles to its site of exit at the arachnoid villi. Drugs in this fluid can either enter the brain tissue or be returned to the venous circulation in the bulk flow of cerebrospinal fluid carried through the arachnoid villi. Some drugs, such as penicillin, wUl not leave the cerebrospinal fluid compartment by bulk flow but will be actively transported by the choroid plexus out of the fluid and back into the blood. Finally, drugs may diffuse from brain tissue directly into blood capUlaries. 

The sites of formation of hot spots may be provided in both liquid and solid expls not only by bubbles of gas but also by bubbles of vapor, if the expl is more or less volatile. The importance of some heterogeneous initiation mechanism is shown by the failure of deton to propagate, in at least some expls, when the density of material exceeds a certain value [See under "Detonation (and Explosion), Resistance to ]. For the type of expls referred to by D. Price as Group 2 (Ref 33), see under "Detonation (and Explosion), Critical or Limiting Charge Densities. Price noted that in other expls, however, the homogeneous process plays the major part in the transmission, if not the initiation, of detonation (Ref 34)... 

On the basis of the likely assumption that the sites of formation of nitriles are different from those reponsible of degradation of the aromatic hydrocarbon (sites of deep oxidation), the evolution of activity and selectivity seems to indicate a change in the same proportion of the two types of sites when the... 

As distinct from the purple bacteria, plants, when photosynthesizing carbohydrates from C02, use water rather than H2S as an oxidized substrate. The oxidation of water requires far more energy than that of hydrogen sulphide. This circumstance plus the necessity for the sites of formation of oxidized and reduced particles to be spatially separated (in order to avoid their rapid recombination) seems to be the reason for the formation in plants... 

The site of formation of renin is not known, although the indirect and circumstantial evidence favors slightly the juxtaglomerular apparatus rather than the tubules as a source (18). Crude renin, however, is extracted readily from renal cortex by saline extraction, acidification, and precipitation with ammonium sulfate and sodium chloride. Other active protein substances are likewise extracted, and their separation from renin is often a matter of considerable difficulty. The renin substrate, an arglobulin, is found in blood serum and is probably formed by the liver. It can be easily salted out of beef serum as a crude preparation. 

The activation of pulmonary toxicants falls into three main categories or mechanisms, depending either on the site of formation of the activated compound or on the nature of the reactive intermediate. 

Figure 23 Possible Se-cys assisted oxidation of formate by the (MPTpG)2Mo(Se-cys)(OH) site of formate dehydrogenase.

Fig. 3. Conserved sequences for RNA splicing. The residue marked as A in the branchpoint sequence is the site of formation of the 2 5 branch.

Thromboembolism Obstruction of a blood vessel by a broken thrombus (blood clot) that was transported to the occluded vessel from another site of formation. 

The actual site of formation of oxytocin and vasopressin is in the hypothalamus, from which the two peptides are carried to the posterior pituitary bound to neuro-physins (transport proteins) and stored. The structure and synthesis of oxytocin 44 and vasopressin 45 were worked out by du Vigneaud et al. 91... 

The sites of formation of the various clotting factors, and the metabolic requirements involved are still matters of conjecture. It has long been supposed that the liver is concerned with the production of fibrinogen, but the evidence is not con-... 

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