Parallel structures

Figure 3.4 Packing of amides in unit cell (a) a-parallel structure of even-even PA (b) /3-antiparallel structure of even-even PAs with equal methylene sequence length in amine and acid unit, as in PA-4,620 (c) antiparallel PA-6-type polymer.

Process components interact in two different fashions. In some cases a process failure requires the simultaneous failure of a number of components in parallel. This parallel structure is represented by the logical AND function. This means that the failure probabilities for the individual components must be multiplied ... 

We ll search for a solution of equation of motion in a stationary potential thermoelectric field with distributed potential. Such a field is generated in a plane-parallel structure (Fedulov, 2003) with distributed potential (fig. 1). The potential thermoelectric field in this structure can be described by the following independent expressions ... 

The Eqs. (10) and (11) functionally connect thep parameter, the initial electron s velocity Vo and velocity s constituents Vqx and Voy in plane-parallel structure with distributed potential with the coordinate of its entry s point xo, on the electrode with distributed potential. Let us analyze Eq. (10) Under pxo < B the electron will lose the initial kinetic energy completely with generation of electromagnetic radiation (the kinetic energy is absorbed completely). Under these conditions the electron doesn t leave the structure. There is the partial selection of energy under px0 > B and the electron comes beyond the limits of structure. If electron enters the structure normally (Voy = Vo, Vox = Vo) the boundary condition after that electron leaves the structure can be written as ... 

Figure 11.3d shows a process where the manipulated variable affects the two controlled variables and in parallel. An important example is in distilla tion column control where reflux flow aSecte both distillate composition and a tray temperature. The process has a parallel structure and this leads to a parallel cascade control system. 

In the second type of correlation (B) a search is made for relationships between two processes, one of them being under study and the other one being well known from the viewpoint of mechanism. The advantage of this approach lies in the clear kinship of the two processes when they show parallel structure effects on rate or equilibrium manifested by a good correlation. However, one must use the same derivatives in both series of compounds, and this may cause experimental problems. 

Pursuit of parallel structure is an important principle that is often ignored by the less experienced writer. For example, suppose the listing of topics for this section had been written as follows ... 

Figure 14. Motifs of double crossover molecules. The top row contains the three parallel isomers of double crossover (DX) molecules, DPE, DPOW and DPON P in their name indicates their parallel structure. Arrowheads indicate 3 ends of strands. Strands drawn with the same thickness are related by the vertical dyad axis indicated in the plane of the paper. DPE contains crossovers separated by an even number (two) of half-turns of DNA, DPOx by an odd number in DPOW, the extra half turn is a major groove spacing, in DPON, it is a minor groove spacing. The middle row illustrates two other DX isomers, DAE, and DAO. The symmetry axis of DAE is normal to the page (and broken by the nick in the central strand) the symmetry axis of DAO is horizontal within the page in DAO, strands of opposite thickness are related by symmetry. DAE+J, in the second row, is a DAE molecule, in which an extra junction replaces the nick shown in DAE.

The calculated phase behavior for asymmetric surface fields, where the interactions between the components and the top (cmi) and bottom (rM2) interface may vary freely, is even much richer (see Fig. 12 for two layers of structure) than for the symmetric case. A particular feature is the appearance of hybrid structures, which are either a coexistence of different surface reconstructions close to each of the interfaces or interconnected structures. Nevertheless, the general features of Fig. 12 can still be explained in terms of surface field and confinement effects, noting that each of the surface fields now supports its own surface reconstruction, which may interconnect for combinations of perpendicular and parallel structures. As in the symmetric case, this behavior is modulated by the film thickness via interference and confinement effects in a very complicated manner. 

Parallel structure involves pairs and lists of words and phrases. Both items in a pair, and all items in a list... 

---