Specificity mechanisms

The metal substrate evidently affords a huge ( 10 and even as high as 10 [84, 85]) increase in the cross-section for Raman scattering of the adsorbate. There are two broad classes of mechanisms which are said to contribute to this enhancenient [, and Ml- The first is based on electromagnetic effects and the second on cheniicaT effects. Of these two classes the fomier is better understood and, for the most part, the specific mechanisms are agreed upon the latter is more complicated and is less well understood. SERS enhancenient can take place in either physisorbed or chemisorbed situations, with the chemisorbed case typically characterized by larger Raman frequency shifts from the bulk phase. 

A rather more specific mechanism of microbial immobilization of metal ions is represented by the accumulation of uranium as an extracellular precipitate of hydrogen uranyl phosphate by a Citrobacter species (83). Staggering amounts of uranium can be precipitated more than 900% of the bacterial dry weight Recent work has shown that even elements that do not readily form insoluble phosphates, such as nickel and neptunium, may be incorporated into the uranyl phosphate crystallites (84). The precipitation is driven by the production of phosphate ions at the cell surface by an external phosphatase. 

Catalysis (qv) refers to a process by which a substance (the catalyst) accelerates an otherwise thermodynamically favored but kiaeticahy slow reaction and the catalyst is fully regenerated at the end of each catalytic cycle (1). When photons are also impHcated in the process, photocatalysis is defined without the implication of some special or specific mechanism as the acceleration of the prate of a photoreaction by the presence of a catalyst. The catalyst may accelerate the photoreaction by interaction with a substrate either in its ground state or in its excited state and/or with the primary photoproduct, depending on the mechanism of the photoreaction (2). Therefore, the nondescriptive term photocatalysis is a general label to indicate that light and some substance, the catalyst or the initiator, are necessary entities to influence a reaction (3,4). The process must be shown to be truly catalytic by some acceptable and attainable parameter. Reaction 1, in which the titanium dioxide serves as a catalyst, may be taken as both a photocatalytic oxidation and a photocatalytic dehydrogenation (5). 

These compounds vary in their specific mechanism of action and often have different effects on the individual patients. Thus, they are generally used in combinations, eg, corticosteroids with an alkylating agent, or an antimetaboUte with a plant alkaloid in a rotating schedule. 

Expectorants enhance the production of respiratory tract fluid and thus faciUtate the mobilisation and discharge of bronchial secretions. Historically, expectorants have been divided iato two classes based on specific mechanisms of action. Stimulant expectorants iacrease respiratory tract secretion by a direct effect on the bronchial secretory cells. Sedative expectorants act by gastric reflex stimulation. Many compounds classed as expectorants have been iaadequately studied and the mechanisms of action are not known with certainty. 

There is considerable literature on material imperfections and their relation to the failure process. Typically, these theories are material dependent flaws are idealized as penny-shaped cracks, spherical pores, or other regular geometries, and their distribution in size, orientation, and spatial extent is specified. The tensile stress at which fracture initiates at a flaw depends on material properties and geometry of the flaw, and scales with the size of the flaw (Carroll and Holt, 1972a, b Curran et al., 1977 Davison et al., 1977). In thermally activated fracture processes, one or more specific mechanisms are considered, and the fracture activation rate at a specified tensile-stress level follows from the stress dependence of the Boltzmann factor (Zlatin and Ioffe, 1973). 

What was the specific mechanical and/or weld repair process each piece was to undergo ... 

There is much evidence that weak links are present in the chains of most polymer species. These weak points may be at a terminal position and arise from the specific mechanism of chain termination or may be non-terminal and arise from a momentary aberration in the modus operandi of the polymerisation reaction. Because of these weak points it is found that polyethylene, polytetrafluoroethylene and poly(vinyl chloride), to take just three well-known examples, have a much lower resistance to thermal degradation than low molecular weight analogues. For similar reasons polyacrylonitrile and natural rubber may degrade whilst being dissolved in suitable solvents. 

Since the locus of failure can clearly distinguish between adhesive and cohesive failures, the following discussion separates loss of adherence into loss of adhesion and loss of cohesion. In the loss of cohesion it is the polysiloxane network that degrades, which can be dealt with independently of the substrate. The loss of adhesion, however, is dependent on the cure chemistry of the silicone, the chemical and physical properties of the substrates, and the specific mechanisms of adhesion involved. 

Filtration operations are capable of handling suspensions of varying characteristics ranging from granular, incompressible, free-filtering materials to slime-like compositions, as well as finely divided colloidal suspensions in which the cakes are incompressible. These latter materials tend to contaminate or foul the filter medium. The interaction between the particles in suspension and the filter medium determines to a large extent the specific mechanisms responsible for filtration. 

Cleaning mechanism The specific mechanical or pneumatic system used to clean the fabric. 

As normally polymerized, PVF melts between IH5 and 210 °C and contains 12 18% inverted monomer units ft is normally considered a thermoplastic, but because of its instability above its melting point, it cannot be processed by conventional thermoplastic techniques Instead it is generally extruded into films in a solvent swollen (organosol) form and the solvent is subsequently evaporated and recovered Such films can be onented further to achieve specific mechanical properties PVF films are exceptionally weather and radiabon resistant considenng their modest fluonne content PVF is insoluble below 100 °C but, at higher temperatures, it dissolves in polar solvents like amides, ketones, tetramethylene sulfone, and tetramethylurea Resistance to acids and bases at room temperature IS good [1, 29 ... 

Care should also be taken in the use of recovery factors, because these can exert a significant effect. In general, recovery paths are appropriate where there is a specific mechanism to aid error recovery, that is an alarm, a supervising check, or a routine walk round inspection. 

In the preparation and processing of ionomers, plasticizers may be added to reduce viscosity at elevated temperatures and to permit easier processing. These plasticizers have an effect, as well, on the mechanical properties, both in the rubbery state and in the glassy state these effects depend on the composition of the ionomer, the polar or nonpolar nature of the plasticizer and on the concentration. Many studies have been carried out on plasticized ionomers and on the influence of plasticizer on viscoelastic and relaxation behavior and a review of this subject has been given 119]. However, there is still relatively little information on effects of plasticizer type and concentration on specific mechanical properties of ionomers in the glassy state or solid state. 

Note, however, that the frequency/malfunction relationship is not mutually exclusive and a specific mechanical problem cannot definitely be attributed to a unique frequency. While frequency is a very important piece of information with regard to isolating machinery malfunctions, it is only one part of the total picture. It is necessary to evaluate all data before arriving at a conclusion. 

It is commonly found that polymers are less stable particularly to molecular breakdown at elevated temperatures than low molecular weight materials containing similar groupings. In part this may be due to the constant repetition of groups along a chain as discussed above, but more frequently it is due to the presence of weak links along the chain. These may be at the end of the chain (terminal) arising from specific mechanisms of chain initiation and/or termination, or non-terminal and due to such factors as impurities which becomes built into the chain, a momentary aberration in the modus operandi of the polymerisation process, or perhaps, to branch points. 

The balance of the DO is not readily released to the steam and is removed by a second stage in the DA. This stage is a gas scrubbing stage, and the specific mechanics vary with each of the different types of pressure DA. 

Many anodic oxidations involve an ECE pathway. For example, the neurotransmitter epinephrine can be oxidized to its quinone, which proceeds via cyclization to leukoadrenochrome. The latter can rapidly undergo electron transfer to form adrenochrome (5). The electrochemical oxidation of aniline is another classical example of an ECE pathway (6). The cation radical thus formed rapidly undergoes a dimerization reaction to yield an easily oxidized p-aminodiphenylamine product. Another example (of industrial relevance) is the reductive coupling of activated olefins to yield a radical anion, which reacts with the parent olefin to give a reducible dimer (7). If the chemical step is very fast (in comparison to the electron-transfer process), the system will behave as an EE mechanism (of two successive charge-transfer steps). Table 2-1 summarizes common electrochemical mechanisms involving coupled chemical reactions. Powerful cyclic voltammetric computational simulators, exploring the behavior of virtually any user-specific mechanism, have... 

When the polymeric material is compressed the local deformation beneath the indenter will consist of a complex combination of effects. The specific mechanism prevailing will depend on the strain field depth round the indenter and on the morphology of the polymer. According to the various mechanisms of the plastic deformation for semicrystalline polymers 40 the following effects may be anticipated ... 

The physical forms indicated are those which, for each specific type of product, assure product flowability within the reported range of residual moisture they can be achieved by specific mechanical devices operating at the outlet of the evaporator and cooler. 

Mitochondria have their own DNA (mtDNA) and genetic continuity. This DNA only encodes 13 peptide subunits synthesized in the matrix that are components of complexes I, III, IV, and V of the respiratory chain. Most mitochondrial proteins are synthesized on cytoplasmic ribosomes and imported by specific mechanisms to their specific locations in the mitochondrion (see below). 

Cosma MP (2002) Ordered recruitment gene-specific mechanism of transcription activation. Mol Cell 10(2) 227-236... 

Before eonsidering specific mechanisms of resistance for particular classes of antibiotic it is worth considering potential mechanisms of resistance in bacterial cells. These are summarized in Fig. 9.1 and specific examples are listed in Table 9.3. 

Group Specific mechanism Examples Additional notable actions... 

Anthocyanins are poorly absorbed from the gastrointestinal tract and the mechanisms involved remain unclear. These compounds are usually recovered in very small amounts in human serum after oral ingestion (less than 1% of the dose) or in the IN fraction after in vitro digestion (about 5%). ° Unlike other polyphenols, anthocyanins constitute an exception because intact glycosides are recovered in the body (without deglycosylation prior to absorption). - This may be explained by either the instability of the free aglycone form or by a specific mechanism of absorption for anthocyanins. 

Figure 1 Influence of the specific mechanical energy on the water-solubility (corrected from the blank values) of some raw materials...

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