Secondary region

Secondary region with partly oriented water... 

The present reduced density operator treatment allows for a general description of fluctuation and dissipation phenomena in an extended atomic system displaying both fast and slow motions, for a general case where the medium is evolving over time. It involves transient time-correlation functions of an active medium where its density operator depends on time. The treatment is based on a partition of the total system into coupled primary and secondary regions each with both electronic and atomic degrees of freedom, and can therefore be applied to many-atom systems as they arise in adsorbates or biomolecular systems. 

In contrast, the secondary region, which stretches from the termination of the primary region to the resumption of the normal bulk structure, cannot be sharply defined the bulk properties and structure are asymptotically approached. 

These structural changes in the primary and secondary regions are generally referred to as solvation (or as hydration when, as is usual, water is the solvent). Since they result from interactions between the ion and the surrounding solvent, one often uses the term solvation and ion-solvent interactions synonymously the former is the structural result of the latter. 

Figure 3.2 A cation aquocomplex, showing the primary region with oriented water molecules in contact with the cation, typically in six- or fourfold coordination. The plot is schematic in that the water molecules in the primary region actually occur in a spherical envelope surrounding the cation. A secondary spherical envelope of partially oriented water molecules lies farther away from the cation. Water molecules in the bulk solution beyond this secondary region are unoriented. From J. O. Bockris and A. K. N. Reddy, 1973, Modern electrochemistry, vol. 1. 1973, Plenum Pub. Corp. Used by permission.

The adsorption and hydrogenation " of acetylene over supported metal catalysts have been extensively studied by Thomson, Webb, and coworkers. The adsorption of [14-C]acetylene at 298 K on all the metals studied, occurs in two distinct stages, a steep primary region, in which the species are predominantly dissociatively adsorbed, and a linear secondary region. A typical example is shown in Figure 3. Evidence was presented to... 

Figure 8.29 Typical creep curve of strain versus time at constant load and constant elevated temperature. The minimum creep rate Ae/Af is the slope of the linear segment in the secondary region. Rupture lifetime is the total time to rupture.

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