Diffusion trapping

Gingell, D., Owens, N. (1992). How do cells sense and respond to adhesive contacts Diffusion-trapping of laterally mobile membrane proteins at maturating adhesions may initiate signals leading to local cytoskeletal assembly response and lamella formation. J. Cell Sci. 101, 255-266. 

Table 10.4 lists the values of trap density and binding energy obtained in the quasi-ballistic model for different hydrocarbon liquids by matching the calculated mobility with experimental determination at one temperature. The experimental data have been taken from Allen (1976) and Tabata et ah, (1991). In all cases, the computed activation energy slightly exceeds the experimental value, and typically for n-hexane, 0/Eac = 0.89. Some other details of calculation will be found in Mozumder (1995a). It is noteworthy that in low-mobility liquids ballistic motion predominates. Its effect on the mobility in n-hexane is 1.74 times greater than that of diffusive trap-controlled motion. As yet, there has been no calculation of the field dependence of electron mobility in the quasi-ballistic model. 

Koehler, M. Biaggio, I. Influence of diffusion, trapping, and state filling on charge injection and transport in organic insulators. Phys. Rev. B Condens. Matter 68, 075205/1-075205/8 (2003). 

Several solvent induced relaxation processes are involved in this process Diffusion, trapping, geminate recombination, and vibrational relaxation. In addition, the A X transition represents the important class of nonadiabatic reactions, here induced by the solute-solvent interaction. Furthermore, the interaction between the molecular species and the radiation field, used to initiate and to monitor the process, is modified by the solvent environment. Other important solvent induced processes Diffusion controlled reactions, charge (electron, proton)... 

Thomann and co-workers have reported that all of the spins are localized in 99% C enriched trans- and cis-(accurate composition is cisIQ. -tmnslO.l) polyacetylene, studied by the multiple quantum NMR (MQNMR) detected by the ESE-technique [165,186]. This is, however, clear experimental evidence demonstrating the validity of the difFuse/trap model [6,82]. 

It is important to know that tlie result firom proton NMR is consistent with that from ESR. If we lake into account a quantitative large ambiguity induced Irom the diffuse/trap model (especially in proton NMR, almost the entire temperatuve dependence is governed by the trapping effect), this consistency is satisfactory and suggests that both methods delected the same phenomenon, in spite of the criticism that l/ /oJ dependence observed by proton NMR could come from a relaxation... 

The topic of neutral soliton dynamics has been controversial for many years. The reasons have been due to a lack of definite data and a lot of different interpretations from a variety of bases for many experimental data. In this review, we tried to explain most of the important experimental results in terms of a diffuse/trap model based on observations of the ESR linewidth as functions of temperature and frequency. Anomalous broadening observed only in (CH) but not in (CD), at frequencies lower than 6 MHz was explained in a clear-cut way by this model, giving a consistent value of the maximum spin density of the neutral soliton, 0.15-0.17 in comparison with 0.17 determined by the ENDOR technique. These successes represented in the finally obtained diffusion rates which are found to be consistent between NMR and ESR seem to settle the controversy. 

Current theories suggest that carbon dioxide potentiates the action of local anesthetics by initial indirect depression of the axon, followed by diffusion trapping of the active form of the local anesthetic within the nerve. Use of the carbonate salt appears to be one pharmaceutical modification of the classic local anesthetic agents that may result in significant clinical advantages. 

Fig. 7.39 The temperature (T) dependence of the diffusion rate along the chain (D//) for the trans-PA together with that obtained by H-NMR. The thick solid curve indicates the variation of D// for the trans-PA without the diffuse-trap modei correction. The figure is adapted from [41] with permission from the American Physical Society...

In the time interval between t = 0 and t = T, the current is no longer constant but decays exponentially in time. The effects of diffusion, trapping, and recombination of charge carriers is illustrated in Figure 4.3.33. 

Figure 4.333. Effects of diffusion, trapping, and recombination of charge carriers on the TOP response.

However, the nuclear relaxation rate T decreases at low temperature, while it is scarcely affected in the presence of oxygen. The latter result shows that the data could not all be accounted for just by introducing a diffusion coefficient dependent on both temperature and oxygen content. A comprehensive explanation of the data has been proposed in terms of a two-spin species model [56], also called the diffusive-trap model," as follows. In a pure ideal (CH)v chain we would be dealing with diffusive solitons with a diffusion coefficient D( T) that will be discussed later. In the presence of impurities such as adsorbed oxygen, traps are created in which the solitons can be temporarily pinned and thus localized. The total number of solitons, n, is thus = + /Ji., where... 

Using the previous equations we can derive the microscopic structure (/. e., the kinds of defects and their concentrations) from the experimentally determined lifetimes and intensities if the problem is homogeneous. This premise, however, does not hold for RPV steels completely. In inhomogeneous problems, the diffusion of positrons from the various implantation sites to the trapping centres must also be considered [125,130]. However, the mathematical difficulties associated with the corresponding diffusion-trapping model (DTM) [73] have so far prevented exact solutions from being obtained for all but the simplest problems [116,117], Thus, it is impossible to qualitatively analyse the very detailed experimental results obtained with a pulsed positron beam. 

B. G. Pound, Evaluation of a Diffusion/Trapping Model for Hydrogen Ingress in High-Strength Alloys, Final Report to the Office of Naval Research, Contract N00014-86-C-0233, 1990. 

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