Nucleation-propagation mechanism

It is worthwhile to ask how the different pieces of the puzzle are relevant to a particular model The nucleation-propagation mechanism (which requires a single-search nucleation process followed by a rapid propagation) is the only which can be discarded, even if the process occurs within each domain for large proteins. This model certainly accounts, with a good... 

S-187) jjjg stabilization of the nucleation centers formed in the initial stage is achieved by interactions arising in the course of the subsequrait step of selforganization. In this context, a propagation mechanism and/or diffiis-... 

The second implication of the mechanism involving crack nucleation and propagation, as so far outlined, is that the presence of any cracks associated with an indent means a lowered hardness value for the material. Furthermore, increased iTO radial cracking that occurs with increased load must mean a bigger error in hardness values as indentation pressure is deflected into the crack nucleation and propagation mechanisms. This supports the intuitive position stated at the opening of this section. 

Emulsion Polymerization. Emulsion SBR was commercialised and produced in quantity while the theory of the mechanism was being debated. Harkins was among the earliest researchers to describe the mechanism (16) others were Mark (17) and Elory (18). The theory of emulsion polymerisation kinetics by Smith and Ewart is still vaUd, for the most part, within the framework of monomers of limited solubiUty (19). There is general agreement in the modem theory of emulsion polymerisation that the process proceeds in three distinct phases, as elucidated by Harkins (20) nucleation (initiation), growth (propagation), and completion (termination). 

Fig. 38 General mechanism of the nucleation and elongation stages of polymerization generating a helical structure (the arrows represent the interactions among repeating units). Secondary interactions light arrows), absent in the first turn of the helix, are the molecular origins of a less favorable nucleation event (i.e.,the critical chain length) beyond which propagation becomes more favorable...

Damjanovic et al. (13) treated the optical determination of mechanisms of lateral and vertical step propagation. Dickson et al. (12) studied the nucleation and growth of electrodeposited gold on surfaces of silver by means of electron microscopy. 

The admittance response at 1 kHz has also been interpreted in terms of the behavior at residual defects in anodic films. This interpretation is based on electron optical characterization, which shows that anodic films contain a distribution of preexisting defects associated with substrate inclusions and mechanical flaws (96,102). In aggressive environments, pits nucleate from these defects and propagate into the metal substrate. In this model, pits are distinct from anodic film flaws, and both can contribute to the measured admittance. Measurements of anodic films exposed to chloride solutions showed that the dissipation factor increased with time, but the capacitance remained nearly constant. Under these conditions, pit propagation at a flaw led to a pit area increase, which increased the resistive component of the admittance, resulting in an increased dissipation factor, but no increase in the capacitance. Measurements at 100 kHz were reflective of the electric double layer and not the components of the oxide film. 

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