Reverse component

For a given amplitude of the quasi-elastic release wave, the more the release wave approaches the ideal elastic-plastic response the greater the strength at pressure of the material. The lack of an ideally elastic-plastic release wave in copper appears to suggest a limited reversal component, however, this is much less than in the silicon bronze. Collectively, the differences in wave profiles between these two materials are consistent with a micro-structurally controlled Bauschinger component as supported by the shock-recovery results. Further study is required to quantify these findings and... 

Graphite will creep imder neutron irradiation and stress at temperatures where thermal creep is normally negligible. The phenomenon of irradiation creep has been widely studied because of its significance to the operation of graphite moderated fission reactors. Indeed, if irradiation induced stresses in graphite moderators could not relax via radiation creep, rapid core disintegration would result. The observed creep strain has traditionally been separated into a primary reversible component ( ,) and a secondary irreversible component (Ej), both proportional to stress and to the appropriate unirradiated elastic compliance (inverse modulus) [69]. The total irradiation-induced creep strain (ej is thus ... 

The unsymmetrical shapes of the forward and reverse components of an SW voltammogram have similar origins as those of the CV. However, unlike the reverse scan wave in CV, the reverse SWV wave is measured almost simultaneously with the forward component. Therefore, there is much less accumulation of the reaction product at the electrode surface during the potential scan. This feature of SWV makes it very useful for understanding... 

Particnlarly interesting is the case when the second electrode reaction reqnires lower energy than the first one, i.e., R2 is more easily oxidized than Ri. In this case the total response consists of a single peak. The exact shape and position of this peak and its forward and reverse components reflect the relative contribntions of the redox conples Ri/Oi and R2/O2 over a narrow range of potentials dictated by the oxidation of Ri. As a conseqnence, the response due to Ri/Oi masks the response... 

For the catalytic electrode mechanism, the total surface concentration of R plus O is conserved throughout the voltammetric experiment. As a consequence, the position and width of the net response are constant over entire range of values of the parameter e. Figure 2.35 shows that the net peak current increases without limit with e. This means that the maximal catalytic effect in particular experiment is obtained at lowest frequencies. Figure 2.36 illustrates the effect of the chemical reaction on the shape of the response. For log(e) < -3, the response is identical as for the simple reversible reaction (curves 1 in Fig. 2.36). Due to the effect of the chemical reaction which consumes the O species and produces the R form, the reverse component decreases and the forward component enhances correspondingly (curves 2 in Fig. 2.36). When the response is controlled exclusively by the rate of the chemical reaction, both components of the response are sigmoidal curves separated by 2i sw on the potential axes. As shown by the inset of Fig. 2.36, it is important to note that the net currents are bell-shaped curves for any observed kinetics of the chemical reaction, with readily measurable peak current and potentials, which is of practical importance in electroanalytical methods based on this electrode mecharusm. 

Fig. 2.36 Reversible electrode reaction. The forward and reverse components of the theoretical voltammograms simulated for log(e) = —3 (i) —0.5 (2) and 0.1 (i). The inset shows the corresponding net voltammograms. The other conditions are the same as for Fig. 2.35...

Kv = j reflecting the influence of the kinetics of the surface and volume follow-up chemical reaction, respectively. Figure 2.78 depicts the variation of the dimensionless net peak current with kv, for a variety of adsorption strengths of the redox couple, obtained by simulations of the mechanism (2.177). Instead of decreasing, the enlarges by accelerating the volume chemical reaction. The increase of AWp is a consequence of the enhancement of the reverse component of the response. Beside the pecuhar variation of A Fp, the peak potential shifts in a positive direction with a slope of = 2.303. Accordingly, the overall voltammetric behavior is... 

A reaction in a metabolic pathway is likely to be nonequilibrium if the maximum catalytic activity of the enzyme that catalyses the reaction is low in comparison with those of other enzymes in the pathway. In consequence, the concentration of substrate of this reaction is likely to be high whereas that of the product is likely to be low, since the next enzyme in the sequence readily catalyses its removal. Because the concentration of this product is low, the rate of the reverse component of the reaction is very much less than the rate of the forward component. This situation characterises a non-equilibrium process. Conversely, a reaction is near-equiUbrium if the maximum catalytic activity of the enzyme is high in relation to those of other enzymes in the pathway in this case, the rates of the forward and the reverse components of the reaction are similar and both are much greater than the overall flux... 

The principal use of theophylline is in the management of asthma. It is also used to treat the reversible component of airway obstruction associated with chronic obstructive pulmonary disease and to relieve dyspnea associated with pulmonary edema that develops from congestive heart failure. 

Figure 7.36a-c shows the forward and reverse components of the square wave current. When the chemical kinetics is fast enough to achieve kinetic steady-state conditions (xsw > 1.5 and i + k2 > (D/rf), see [58,59]), the forward and reverse responses at discs are sigmoidal in shape and are separated by 2 sw. This behavior is independent of the electrode geometry and can also be found for spheres and even for planar electrodes. It is likewise observed for a reversible single charge transfer at microdiscs and microspheres, or for the catalytic mechanism when rci -C JDf(k + k2) (microgeometrical steady state) [59, 60]. 

Ipratropium appears to be at least as effective in patients with chronic obstructive pulmonary disease that includes a partially reversible component. A longer-acting, selective antimuscarinic agent, tiotropium, is in clinical trials as treatment for COPD. This drug s 24-hour duration of action is a potentially important advantage. 

Renal damage is the most significant toxic reaction. Renal impairment occurs in nearly all patients treated with clinically significant doses of amphotericin. The degree of azotemia is variable and often stabilizes during therapy, but can be serious enough to necessitate dialysis. A reversible component is associated with decreased renal perfusion and represents a form of prerenal renal failure. An irreversible component results from renal tubular injury and subsequent dysfunction. 

It can be shown that in a well-mixed closed vessel, under conditions in which the ratio of the concentration of enzyme (E0) to substrate (S) is very small, the enzyme remains fully active, and the forward and reverse components of the first reaction are in steady state, the rate of change of substrate and product concentrations (P) can be written as [4] ... 

The second aspect of this problem is that the area densities may be different on the two sides of a given barrier. This difference in the area densities would lead to a difference in the forward and reverse components of the hopping current, even if the height of the barrier were the same as viewed from the forward and reverse directions. For example, if the barrier heights are W(f) and W(r) as viewed from the two directions, respectively, and the area density for forward hopping is denoted by nif) and the area density for reverse hopping is denoted by n(r), then the net current density over the barrier would be given by... 

It is informative to examine the limiting cases of the above expressions for the current over a specific local barrier. The thermal equilibrium limit is reached whenever the current J is chosen to be zero. We note that this requires forward and reverse components of the hopping current to be equal in magnitude. From eqn. (74), we obtain... 

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