Kink diffusion

The yield stress for both basal and prism plane slip as a function of temperature have been determined over a vide temperature range (Figure 9.4). The Castaing Law - In(CRSS) decreasing linearly with temperature - has been explained by Mitchell et al. [22] in terms of conventional kink pair nucleation and kink diffusion (as discussed in Section 9.2). 

Water weakening can occur in olivine, as in quartz [167-170]. It has been suggested by Mackwell et al. [171] that water enhances dtmb mobility, although more detailed explanations are still lacking. Another possibility is that the point defects associated with the addition of water cause enhanced kink nucleation and/or kink diffusion (as described in Section 9.2.3). 

Attempts to determine experimentally the values of and Wm were carried out using various techniques internal friction [36,37], deformation under load pulse sequence [38], and TEM. There are very few internal friction experiments on semiconductors. The reason is the brittleness of these materials and the need to work at very low frequencies in order to get a relaxation peak at moderate temperatures. The direct observation of kink motion was realized by TEM, either by studying the relaxation of out-of-equilibrium dissociated dislocations [39], by in situ deformation [40], or by using forbidden reflections in the high-resolution mode [41,42]. These various experiments were analyzed within the framework of the kink-diffusion model of Hirth and Lothe [12], which does not take into account... 

One of the most striking higher-level behaviors observed in CMLs is the diffusion of the kinks/anti-kinks that separate the different domains, a behavior that should remind the reader of our earlier discussion of the diffusion of local kinks induced by the deterministic elementary CA rule R18 (grass84a] (see section 3.1.2). Before looking at some examples, let us see how this comes about. 

Localized Kink Regime when the diffusive coupling is too small for kinks to move, the initial kinks separating domains remain locked in position. The behavior is analogous to that of class c2 elementary CA. 

Studies of the effect of permeant s size on the translational diffusion in membranes suggest that a free-volume model is appropriate for the description of diffusion processes in the bilayers [93]. The dynamic motion of the chains of the membrane lipids and proteins may result in the formation of transient pockets of free volume or cavities into which a permeant molecule can enter. Diffusion occurs when a permeant jumps from a donor to an acceptor cavity. Results from recent molecular dynamics simulations suggest that the free volume transport mechanism is more likely to be operative in the core of the bilayer [84]. In the more ordered region of the bilayer, a kink shift diffusion mechanism is more likely to occur [84,94]. Kinks may be pictured as dynamic structural defects representing small, mobile free volumes in the hydrocarbon phase of the membrane, i.e., conformational kink g tg ) isomers of the hydrocarbon chains resulting from thermal motion [52] (Fig. 8). Small molecules can enter the small free volumes of the kinks and migrate across the membrane together with the kinks. 

Fig. 5.3. Log-log plot of the self-diffusion constant D of polymer melts vs. chain length N. D is normalized by the diffusion constant of the Rouse limit, DRoUse> which is reached for short chain lengths. N is normalized by Ne, which is estimated from the kink in the log-log plot of the mean-square displacement of inner monomers vs. time [gi (t) vs. t]. Molecular dynamics results [177] and experimental data on PE [178] are compared with the MC results [40] for the athermal bond fluctuation model. From [40]...

Fig. 19 Our hybrid microrelaxation model. The solid circles are occupied by a polymer chain. The dashed lines show the new bond positions produced by a move consisting of kink generation and partial sliding diffusion along the chain. The arrows indicate the directions of monomer jumping [134]... 

Since the evaporation of a solid would occur at the kink sites because the bonding is weaker, atoms would diffuse also to these sites before evaporation. A demonstration of this is to be found on the morphologies of single crystals after a period of heating in vacuum to cause substantial evaporation. The resultant surface shows an increase in the number of ledges and kinks relative to the area of the terraces. It is also to be expected that dislocations emerging at the surface of catalysts, either as edge or screw dislocations, would play a... 

Along the step a kink site is shown. Adsorbed ions diffuse along the surface and become preferentially incorporated into the crystal lattice at kink sites. As growth proceeds, the surface step winds up in a surface spiral. Often the growth reaction observed occurs in the sequence c, a, b. 

It is conceivable that diffusion of kinks, or overdamped solitons, along the DNA could act to relax the FPA with a time dependence similar to that predicted for torsional deformation/31 32) High levels of intercalated dyes would be expected to alter both the equilibrium population of kinks and their mobility along the DNA. Hence, this question is addressed by examining the effect of intercalating dyes on the torsional dynamics. 

Figure 6.15. Ion transfer to the terrace site, surface diffusion, and incorporation at kink site.

Terrace Ion-Transfer Mechanism, In the terrace siteion-transfer mechanism a metal ion is transferred from the solution (OHP) to the flat face of the terrace region (Fig. 6.15). At this position the metal ion is in the adion (adsorbed-like) state, having most of its water of hydration. It is weakly bound to the crystal lattice. From this position it diffuses on the surface, seeking a position of lower energy. The final position is a kink site. 

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