Unzipping transition

If we consider a pure problem, there will be an unzipping transition as described in Sec. 7 above. The transition is first order in nature. In this particular case there is no thermal unbinding in one dimension but if we forbid crossing of the polymers, then a... 

It has been argued that the unzipping transition for the quenched averaged RANI case is second order [41]. However for real DNA, it is not the quenched averages that matter. There is strong ensemble dependence and sample to sample variation. This has been exploited to identify point mutants by a comparison of the unzipping force in a fixed distance ensemble [42]. An experimental determination of the unzipping phase boundary for a real DNA has been reported in Ref. [43]... 

By varying the temperature or tuning the interaction the system can be transformed from one state to another. The point at which the zipped-unzipped transition takes place is a tricritical point and in its proximity a crossover is observed. In the asymptotic limit the mean number of monomers M in contact with each other at the tricritical point is assumed to behave as... 

Marenduzzo, D., Bhattacharjee, S. M., Maritan, A., Orlandini, E., Seno, F. (2001a). Dynamical scaling of the DNA unzipping transition. Physical Review Letters, 88, 028102. 

Thirdly, experiments concerned with the whole process of conformational change and the unzipping process (e.g., [49]) studied the mechanical stability of individual double-stranded DNA molecules. It was foimd that the B-S transition of A-DNA occurred at 65 pN, followed by a second conformational transition during which the DNA double helix melted into two... 

The RANI model remains less understood compared to the random medium problem. Exact renormalization analysis establish the marginal relevance of the disorder at d = 1, indicating a disorder dominated unbinding transition in d > 1. Several features including a generalization of the Harris criterion for this criticality via relevant disorder and aspects of unzipping have been discussed. 

In welded hoppers, failure is much less likely in the hopper itself. Most failures occur near the top of the hopper, and are either rupture (the hopper is torn off, with unzipping passing around the perimeter) or plastic deformations. Both situations arise from an excessive total load on the hopper or from unsymmetrical pressures, not from a high switch pressure at the transition. For design and evaluation advice, see Rotter (2001a) and EN 1993-4-1 (2007). 

The polyacrylates have one feature in common with the polymethacrylates, however, in giving alkene formation from the ester side group if jS hydrogens are available to form the transition state analogous to that illustrated in Scheme 6. This reaction is more important in polyacrylate degradation because of the absence of unzipping to monomer. 

Monomers of formaldehyde vapor that can be dissolved in an inert hydrocarbon such as heptane along with an initiator. Initiators include Lewis acids such as BFj (Table 17,2, LA) as well as amines, phosphines, arsines, stibenes, organometallic componnds, and transition metal carbonyls. The polymer is often referred to as acetal homopolymer, polyacetal, or poly(oxymethylene). All of these terms distinguish the useful, stable polymer from polyformaldehyde, the thermally unstable, waxy material that forms easily from the pure monomer. Because of the instability of the chain structure and its tendency to unzip, esterification of the end-group hydroxyls or end blocking with acetic acid is one answer (Table 17.2, LA). Another is the copolymerization of formaldehyde with monomers that will interrupt the chain sequence. Ethylene oxide is one such monomer. 

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