One- and two-region homogeneous

Parametric cost studies at ORNL. The homogeneous reactor systems considered include one- and two-region reactors, breeders, converters, and burners. Although no one fuel or type of reactor shows a marked advantage in power cost over all the others, the superior fuel utilization of a thorium breeder system suggests that it is potentially the most economical one for power production. Much effort has been devoted... 

If mechanisms one and two do not act, then under stress, a two-dimensional homogeneous nucleation would be needed. Just as with three-dimensional nucleation of phase change (e.g., condensation or crystallization) homogeneous nucleation of bare regions can be expected to be a slow, and hence rate-limiting, process. If the solid surface is rough, then stress concentrations around asperities might accelerate this nucleation process. 

Temperature quench is not always a viable route to form structures since this approach requires the blend components to be thermally stable in the one- and two-phase region for a sufficiently long time. In effect, thermal stability is required in order to both ensure complete mixing in the homogeneous state and permit the formation of an equilibrium structure in the demixed state [14]. In addition to the thermal stability, the wetting properties of the polymers employed for the blend plays a key role. The coated polymers do not always wet the substrate and therefore dewetting competes with phase separation [71]. In those blends having components with a limited stability in relation to tanperature, the use of solvent to improve the phase separation can, at least to some extent, overcome these limitations. 

The effects due to the finite size of crystallites (in both lateral directions) and the resulting effects due to boundary fields have been studied by Patrykiejew [57], with help of Monte Carlo simulation. A solid surface has been modeled as a collection of finite, two-dimensional, homogeneous regions and each region has been assumed to be a square lattice of the size Lx L (measured in lattice constants). Patches of different size contribute to the total surface with different weights described by a certain size distribution function C L). Following the basic assumption of the patchwise model of surface heterogeneity [6], the patches have been assumed to be independent one of another. 

In contrast, a heterogeneous solution of noncritical composition (e.g., v < xc, as shown by the arrow and dashed line in Fig. 7.11) shows a qualitatively different behavior as it is rises through the coexistence boundary and into the homogeneous region near and above Tc. For each increase in temperature along the dashed line in Fig. 7.11, a horizontal tie-line yields both the compositions of the A-rich and B-rich liquids (from the two ends of the tie-line), as well as the relative amounts of each phase (from the lever rule). Clearly, the critical composition xc remains near the middle of the tie-line as T increases toward Tc, whereas a noncritical composition x xc moves toward one or other terminus of the tie-line as the temperature is raised. 

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