Major mechanisms

Two major mechanisms for thermal degradation and one minor mechanism are shown in Fig. 9. The first mechanism is the reverse of urethane formation. The second mechanism, which was proposed by Fabris, forms a primary amine and an olefin. It involves a six-member intermediate, as shown in Fig. 10. A thermal... 

The major mechanism of a vapor cloud explosion, the feedback in the interaction of combustion, flow, and turbulence, can be readily found in this mathematical model. The combustion rate, which is primarily determined by the turbulence properties, is a source term in the conservation equation for the fuel-mass fraction. The attendant energy release results in a distribution of internal energy which is described by the equation for conservation of energy. This internal energy distribution is translated into a pressure field which drives the flow field through momentum equations. The flow field acts as source term in the turbulence model, which results in a turbulent-flow structure. Finally, the turbulence properties, together with the composition, determine the rate of combustion. This completes the circle, the feedback in the process of turbulent, premixed combustion in gas explosions. The set of equations has been solved with various numerical methods e.g., SIMPLE (Patankar 1980) SOLA-ICE (Cloutman et al. 1976). 

The major mechanism of resistance to chloramphenicol is mediated by the chloramphenicol acetyltransferases (CAT enzymes) which transfer one or two acetyl groups to one molecule of chloramphenicol. While the CAT enzymes share a common mechanism, different molecular classes can be discriminated. The corresponding genes are frequently located on integron-like structures and are widely distributed among Gramnegative and - positive bacteria. 

Due to the side-effect problems seen with high doses of inhaled glucocorticoids resulting from systemic absorption and the use of oral glucocorticoids in severely affected patients, there has been a search for safer glucocorticoids for inhalation and even for oral administration. As discussed above, a major mechanism... 

Protein Kinase Inhibitors. Figure 1 Major mechanism by which inhibitors can prevent the activity of protein kinases. 

Smooth Muscle Tone Regulation. Figure 3 Major mechanisms leading to relaxation of smooth muscle. See text for the abbreviations. 

Ear from being just the processing of water on Earth, this cycle is the basis for a wide range of meteorologic, geochemical, and biological systems. Water is the transport medium for all nutrients in the biosphere. Water vapor condensed into clouds is the chief control on planetary albedo. The cycling of water is also one of the major mechanisms for the transportation of sensible heat (e.g. in oceanic circulation) and latent heat that is released when water falls from the air. 

Transport in solution or aqueous suspension is the major mechanism for metal movement from the land to the oceans and ultimately to burial in ocean sediments. In solution, the hydrated metal ion and inorganic and organic complexes can all account for major portions of the total metal load. Relatively pure metal ores exist in many places, and metals from these ores may enter an aquatic system as a result of weathering. For most metals a more common sequence is for a small amount of the ore to dissolve, for the metal ions to adsorb onto other particulate matter suspended in flowing water, and for the metal to be carried as part of the particulate load of a stream in this fashion. The very insoluble oxides of Fe, Si, and A1 (including clays), and particulate organic matter, are the most important solid adsorbents on which metals are "carried."... 

For aliphatic electrophilic substitution, we can distinguish at least four possible major mechanisms, which we call Sgl, 8 2 (Iront), Se2 (back), and Sgi. The Sgl is unimolecular the other three are bimolecular. 

Ethanol is oxidized by alcohol dehydrogenase (in the presence of nicotinamide adenine dinucleotide [NAD]) or the microsomal ethanol oxidizing system (MEOS) (in the presence of reduced nicotinamide adenine dinucleotide phosphate [NADPH]). Acetaldehyde, the first product in ethanol oxidation, is metabolized to acetic acid by aldehyde dehydrogenase in the presence of NAD. Acetic acid is broken down through the citric acid cycle to carbon dioxide (CO2) and water (H2O). Impairment of the metabolism of acetaldehyde to acetic acid is the major mechanism of action of disulfiram for the treatment of alcoholism. 

Another major drawback of polysaccharides is their hydrophilic nature leading to low degrees of adhesion between fiber and matrix [11]. Moisture absorption takes place by three types of mechanisms namely diffusion, capillarity, and transport via micro cracks [2]. Among the three, diffusion is considered to be the major mechanism. Water absorption largely depends on the water-soluble or hygroscopic components embedded in the matrix, which acts as a semipermeable membrane. While, fiber/matrix adhesion and fiber architecture also affect the moisture absorption. The results of the water sorption experiment showed an interesting trend. The extent of water uptake was not very significant and also did not increase linearly with amount of filler (Table-2). 

The other major mechanism of pyrethroid resistance found in some field strains of Heliothis virescens was enhanced detoxication due to a high rate of oxidative detoxication, mediated by a form of cytochrome P450 (McCaffery 1998). Some strains, such as PEG 87, which was subjected to a high level of field and laboratory selection, possessed both mechanisms. Other example of pyrethroid resistance due to enhanced detoxication may be found in the literature on pesticides. 

If the plasma membrane is relatively impermeable, how do most molecules enter a cell How is selectivity of this movement established Answers to such questions are important in understanding how cells adjust to a constantly changing extracellular environment. Metazoan organisms also must have means of communicating between adjacent and distant cells, so that complex biologic processes can be coordinated. These signals must arrive at and be transmitted by the membrane, or they must be generated as a consequence of some interaction with the membrane. Some of the major mechanisms used to accomplish these different objectives are listed in Table 41-3. 

MTX caused a contraction of vascular smooth muscle and positive inotropic, positive chronotropic and arrhythmogenic effects on cardiac muscle. The effect of MTX was little affected by various receptor blockers, a Na channel blocker or a catecholamine depleting agent. Further, MTX had no effect on the enzymes which were related to Ca movements, such as Na , K -ATPase, cyclic AMP phosphodiesterase, and sarcoplasmic reticulum Ca -ATPase. These results would eliminate the possible involvement of an indirect action elicited by the release of chemical mediators and direct modifications of their receptors, Na channels, or various enzymes as a major mechanism of action of MTX. 

Having formally defined the branching structure, we must now make explicit the mechanisms by which we can eliminate subsets of the solution space from further consideration. Ibaraki (1978) has stated three major mechanisms for controlling the evolution of the branch-and-bound search algorithms, by eliminating potential solution through... 

We have indicated that flow of mass is important in sintering. There are several operative mechanisms which are determined by the type of material involved. Actually, the study of sintering deserves a separate chapter, but we wiU only summarize the major mechanisms that have been observed for the constants of 5.2.18. These are given in 5.2.19. on the next page. 

The following sections use selected examples to illustrate the major mechanisms by which phytochemicals influence some of the characteristics and functions of the GIT. Although much more is known about their influences on the processes associated with the digestion of feedstuflfs, there is increasing awareness of the impact on the other functions of the GIT. 

The beneficial effect of deprenyl in Parkinson s disease was su ested to be in part due to its effect on increasing the levels of SOD activity in several brain regions (Carrillo et al., 1993). Deprenyl is known to inhibit monoamine oxidase type B, which results in a reduction in hydrogen peroxide formation by blockade of the oxidative deamination of dopamine. That is believed to be the major mechanism of action of this drug in inhibiting the progression of Parkinson s disease. 

In reality, the adsorption of gas particles on a real surface can be simultaneously influenced by inhomogeneity of the surface and interaction between absorbed particles. Presumably, it is the nature of a specific absorbate-adsorbent pair that controls the major mechanism in each case. 

Cleavage of 8-0-4-ethers in alkaline pulping is also facilitated by HS as used in kraft pulping.98 The major mechanisms (Fig. 12.8b) are via addition to the quinone methide QM1 to give adduct 19, followed by anchimerically assisted fragmentation via a thioepoxide 20. 

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