Folded configurations

J-sheet configurations fold back on themselves. When an antiparallel /5-sheet doubles back on itself in a pattern that resembles a common Greek pottery design, the motif is called the Greek key. 

In another beam configuration (folded BOX CARS), the pump beam with co is split into two parallel beams, which are directed by the focusing lens in such a way that the wave vectors k2 and = ka are contained in a plane orthogonal to that of the two ki vectors (Fig. 3.22d). This has the advantage that neither of the two pump beams overlaps the signal beam at the detector [355]. If the Raman shifts are small, spectral filtering becomes difficult and the advantage of this folded BOX CAR technique is obvious. 

Aspects of the Jahn-Teller symmetry argument will be relevant in later sections. Suppose that the electronic states aie n-fold degenerate, with symmetry at some symmetiical nuclear configuration Qq. The fundamental question concerns the symmetry of the nuclear coordinates that can split the degeneracy linearly in Q — Qo, in other words those that appeal linearly in Taylor series for the matrix elements A H B). Since the bras (/1 and kets B) both transform as and H are totally symmetric, it would appear at first sight that the Jahn-Teller active modes must have symmetry Fg = F x F. There... 

An sp -sp2 or sp -sp - single bond where the sp atom is in Group VIA (for example, the C-0 bond of vinyl alcohol) has a two fold barrier with an optimal planar configuration described by V2=h-2.0 kcal/mol. 

If a molecule has a plane of symmetry, for which the symbol is a, reflection of all the nuclei through the plane to an equal distance on the opposite side produces a configuration indistinguishable from the initial one. Figure 4.3(a) shows the two planes of symmetry, (7 (xz) and (yfyz), of H2O using conventional axis notation. Just as theyz plane, the plane of the molecule, is a plane of symmetry so any planar molecule has at least one plane of symmetry. The subscript u stands for vertical and implies that the plane is vertical with respect to the highest-fold axis, C2 in this case, which defines the vertical direction. 

Fig. 4. Contact spring configurations for separable electronic connectors. Examples (a)—(g) ate engaged by sliding the spring contact and its mating member together (a)—(d) ate blade-fork contacts (e), folded cantilever contact for printed circuit boards (f), straight cantilever contact for printed circuit...

In judging hindrance, it is useful to view the molecule in its three-dimensional, folded configuration. For instance, 17 can be reduced without undue difficulty, whereas 18 requires extreme conditions (Raney Ni, 2(WC, 200 atm) (7), a difference not expected from planar representations of the molecule. Saturation of A -octalin (17) may largely go through a prior isomerization to A -octa in, despite an unfavorable equilibrium 121). 

Of interest is the detailed structural configurations that can form in sedimentary rock formations, because hydrocarbons are nearly always found in sedimentary rocks. The structural features of interest are faults and folds [26]. 

The composition of the copolymer determines its electroluminescence efficiency. Optimal efficiency (0.3%) was achieved in system 34 when the feed ratio of monomer 4 to monomer 34 was 9 1. This represents a 30-fold improvement in luminescence efficiency relative to PPV in the same device configuration (AlALOj/polymer/Al) 58, 62. Copolymer 33 has found uses as waveguides and... 

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