Significant structures approach

Another attempt to understand glass transition phenomenon from the theory of viscosity was made by Eyring and co-workers (1962, 1970). In their significant structures approach, the total partition function of the liquid was expressed as a product of solid-like and gas-like contributions. Then the viscosity is obtained from the activated complex theory after ignoring the contribution from gas-like part to viscosity. The final working expression for the viscosity of a system of rigid spheres was obtained as. 

Considering that is initially used to evaluate Vg and the volume of the gas-like part, and the fact that this theory involves several other assumptions, significant structures approach is inherently weak. Further, the approach inherits all the limitations of free-volume theory in so far as it relates the viscosity to an essentially free volume term, (V- Vg). 

---

Although experimental studies of DNA and RNA structure have revealed the significant structural diversity of oligonucleotides, there are limitations to these approaches. X-ray crystallographic structures are limited to relatively small DNA duplexes, and the crystal lattice can impact the three-dimensional conformation [4]. NMR-based structural studies allow for the determination of structures in solution however, the limited amount of nuclear overhauser effect (NOE) data between nonadjacent stacked basepairs makes the determination of the overall structure of DNA difficult [5]. In addition, nanotechnology-based experiments, such as the use of optical tweezers and atomic force microscopy [6], have revealed that the forces required to distort DNA are relatively small, consistent with the structural heterogeneity observed in both DNA and RNA. 

A plot of wfPp(z) for rs = 3.24 employing the orbitals of the finite-linear-potential moder is given in Fig. 6. The corresponding local density approximation (LDA) potential is also plotted. In the interior and about the surface of the metal the two potentials are equivalent. But outside the surface vxapp(z) improves upon the LDA significantly and approaches the exact structure asymptotically. We thus expect that properties such as the surface energy and work function obtained with Eapp[p] and v pp(r) to be superior to those of the LDA. Such self-consistent calculations are in progress. 

Additional refinements showed that the quality of fit is only weakly sensitive to the Ceo orientation, and that the TDAE occupancy is 100 10%. Other TDAE molecular orientations differing by 45° and 90° rotations are clearly excluded. Difference Fourier maps do not show any significant structure. The nearest Qo-TDAE approach is 2.58 A, a reasonable distance for a nonbonding C-H distance. Similar refinements in C2/m, with the molecules disordered in two sets of mirror-related sites, gave equivalent results. 

---