Front mixed order

This diffusive instability mechanism has only recently been examined in reaction-diffusion systems. Continuing with the analogy between isothermal fronts and nonisothermal flames, we pursue the case where > 1 in Equations (4). Thus, the front is destabilized when the diffusivity of the reactant A becomes sufficiently larger than that of the autocatalyst B. We consider systems with pure cubic autocatalysis here in a detailed study [12], pure quadratic and mixed-order fronts are also considered and found to have different sensitivities to the destabilizing effects of diffusion. 

All chemical waves reflect the features of their fronts. We have described in this chapter how the most basic fronts are related and how they may give rise to differences in behavior - differences that are important in certain instances. The mixed-order description provides insights into the quadratic form, often employed as the prototype for propagating fronts, as well as the cubic form, which has features related to reaction-conduction flames. Diffusion-induced instabilities in 2-D and 3-D fronts offer interesting experimental and theoretical challenges for studies of dynamical complexity. 

New units can be ordered having dry, low NO burners that can reduce NO emissions below 25 ppm on gaseous fuels in many cases, without back-end flue-gas cleanup or front-end controls, such as steam or water injection which can reduce efficiency. Similar in concept to low NO burners used in boilers, dry low NO gas turbine burners aim to reduce peak combustion temperatures through staged combustion and/or improved fuel—air mixing. 

FIGURE 11.14 Concept of EMDC. Panel A, in conventional displacement, separation times are long (on the order of honrs) and components form highly concentrated zones near the displacer front, some mixed with the displacer. Panel B, in elntion modified displacement, acetonitrile is added to the carrier and to the displacer solution in a targeted way to effect elntion of some components and displacement of others. Other components are mixed with the displacer. Rnn times are <1 h. (Reprinted with permission from Elsevier from Kalghatgi, K. et al., J. Chromatogr., 604,47, 1992. Copyright.)... 

EXAMPLE 5.4 The mixing of two Streams (concentration front withmoving coordinates and first order and zero-order source terms)... 

On the basis of this finding, a two-step (stepwise) development technique12 was applied to separations of possible three binary mixtures of polybutadienes with different chain microstructure, namely, those of cis-1,4 + tram-1,4, tram-1,4+1,2-1,2-vinyl, and 1,2-vinyl + cis-1,4. The principle consisted of a utilization of the different development characteristics exhibited by carbon tetrachloride and amyl chloride. An example of this procedure applied by these authors83 will be described below. A mixture cis-1,4 + tram-1,4 was developed primarily with amyl chloride until the solvent front reached a distance, e.g., 10 cm from the starting point by this development only the cis-1,4 polymer should have migrated up to the solvent front (cf. Table 4). In order to identify the immobile component, the chromatogram was dried in vacuum at room temperature and treated with carbon tetrachloride until the solvent front reached an intermediate distance, e.g., 5 cm. It is obvious that this procedure can be alternatively used for identification of any unknown binary mix-... 

Mixed-Layer Minerals. In addition to polymorphism resulting front the disordering and proxying of one element for another, clay minerals exhibit ordered and random intercalation sandwiches with one another. 

The complete separation from I-carotene to violaxanthin requires 35 min. Figure F2.3.4 illustrates the separation of carotenoids in a mixed food extract using this LC system. The hydrocarbon carotenes ( -carotene, a-carotene, lycopene) elute together at the solvent front. The elution order is fi-cryptoxanthin, u-cryptoxanthin, lutein, cis-lutein, zeaxanthin, cis-zeaxanthin, neoxanthin, and violaxanthin. 

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