Control active

Gordon R J and Rice S A 1997 Active control of the dynamics of atoms and molecules Annu. Rev. Phys. Chem. 48 601... 

A) ACTIVATION CONTROL (SEE ALSO SECTION C2.11 OF THIS BOOK)... 

In tlie polarization curve of figure C2.8.4 (solid line), tlie two regimes, activation control and diffusion control, are schematically shown. The anodic and catliodic plateau regions at high anodic and catliodic voltages, respectively, indicate diffusion control tlie current is independent of tlie applied voltage and7 is reached. 

Figure C2.8.4. The solid line shows a typical semilogaritlimic polarization curve (logy against U) for an active electrode. Different stages of reaction control are shown in tlie anodic and catliodic regimes tlie linear slope according to an exponential law indicates activation control at high anodic and catliodic potentials tlie current becomes independent of applied voltage, indicating diffusion control.

It is wortli noting tliat under activation control tlie reaction rate depends on crystal orientation as tlie strengtli of tlie... 

Conventional method to activate controls has been through... 

Although many engineers provide only the minimum adequate vessel design to minimize costs, it is inherently safer to minimize the use of safety interlocks and administrative controls by designing robust equipment. Passive hardware devices can be substituted for active control systems. For example, if the design pressure of the vessel system is higher than the maximum expected pressure, an interlock to trip the system on high pressure or temperatures may be unnecessary. 

The skin receives heat from the core by passive conduction and active skin blood flow (Table 5.3). It transfers this heat to the surroundings by convection, radiation, and evaporative (perspiration and diffusion) mechanisms. All of these mechanisms are unregulated or passive except evaporation from sweating. The sweating process is actively controlled by the humarrs thermoregulatory center where the rate of sweat secretion is proportional to eleva tions in core and skin temperature from respective set point temperatures (Table 5.3). 

Figure 4-418. Hydrogen-reduction reaction under activation control (simplified). (From Ref. [183].)...

Over the years the original Evans diagrams have been modified by various workers who have replaced the linear E-I curves by curves that provide a more fundamental representation of the electrode kinetics of the anodic and cathodic processes constituting a corrosion reaction (see Fig. 1.26). This has been possible partly by the application of electrochemical theory and partly by the development of newer experimental techniques. Thus the cathodic curve is plotted so that it shows whether activation-controlled charge transfer (equation 1.70) or mass transfer (equation 1.74) is rate determining. In addition, the potentiostat (see Section 20.2) has provided... 

Figure 1.30 gives examples of single metals corroding in a highly conducting acid in which both the anodic and cathodic reactions are assumed to be under activation control, and it can be seen that at... 

Fig. 1.30 Corrosion of a metal in an acid in which both metal dissolution and hydrogen evolution are under activation control so that the .log i curves are linear, (a) Effect of pH on and I o Hi increase in pH (decrease in an + ) lowers E and decreases / o (b) Effect of...

This is commonly known as the high field equation. It is of similar form to the Tafel equation for activation controlled electrochemical reactions with... 

A number of workers have suggested that there are situations in which two processes in series control the erosion corrosion rate, for example diflfusion plus partial activation control, leading to a lower dependency on mass transfer than expected. 

Thus the rate of change of ip under activation control is much faster than / i, which is under diffusion control, and for the same condition of solution velocity the two rates could become equal at some common temperature, i.e. = ip, and there is no active-passive transition. For many of the systems given in the table this temperature is about 100°C. Above this temperature the measured activation energy is lower and diffusion control is established. 

Active-passive transition It has been shown that /p, the current required to maintain a passive film, increases with temperature at a much greater rate than the critical current for passivation as a result of an activation-controlled process. At some temperature /p will exceed /pri,. and no active-passive transition will be observed, and more important no protection by a passive film is possible because of the high rate of dissolution. At this stage the slow process becomes the diffusion of reactants and control of the rate is... 

When film-forming reactions occur and activation control is the ratedetermining factor then the interfacial temperature again will determine the extent of corrosion. 

Slower ones are said to be activation-controlled or chemically controlled. 

Sec. 5.1, and Safety active-controlled oral, every 8 h drug, 148 primary Pull... 

The major issues associated with polishing segments will be dealt with in this presentation. The methods for providing adequate active control are described in the literature (Mast and Nelson, 1982a Mast and Nelson, 1982b Nelson et al., 1982 Chanan et a., 2004). The impact of segment edges is discussed in this presentation. 

Linearly polarized, near-diffraction-hmited, mode-locked 1319 and 1064 nm pulse trains are generated in separate dual-head, diode-pumped resonators. Each 2-rod resonator incorporates fiber-coupled diode lasers to end-pump the rods, and features intracavity birefringence compensation. The pulses are stabilized to a 1 GHz bandwidth. Timing jitter is actively controlled to < 150 ps. Models indicate that for the mode-locked pulses, relative timing jitter of 200 ps between the lasers causes <5% reduction in SFG conversion efficiency. 

The no marketing proviso for seriously underfilled units forces the filler to either systematically overfill as foreseen in the regulations or to install check-balances or other devices to actively control a high percentage (ideally 100%) of the containers and either discard or recycle under-filled ones. 

S. Candel. Combustion instabilities coupled by pressure waves and their active control. Proc. Combust. Inst., 24 1277-1296,1992. 

K. McManus, T. Poinsot, and S. Candel. A review of active control of combustion instabilities. Prog. Energ. Combust. Sci., 19 1-29,1993. 

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