Relaxation associated with

The ultrasonic relaxation loss may involve a thermally activated stmctural relaxation associated with a shifting of bridging oxygen atoms between two equihbrium positions (169). The velocity, O, of ultrasonic waves in an infinite medium is given by the following equation, where M is the appropriate elastic modulus, and density, d, is 2.20 g/cm. ... 

It appears that the observed breakdown must be explained in terms of the transient behavior of stress-induced defects even though the stresses are well within the nominal elastic range. In lithium niobate [77G06] and aluminum oxide [68G05] the extent of the breakdown appears to be strongly influenced by residual strains. In the vicinity of the threshold stress, dielectric relaxation associated with defects may have a significant effect on current observed in the short interval preceding breakdown. 

The y relaxation takes place at the lowest temperature, overlaps with the )3 relaxation (Fig. 15), and coincides in location and activation energy with the typical y relaxation of polyethylene [35,36], and also of polyethers [37], and polyesters [38] with three or more consecutive methylene units. It appears, for 3 Hz and tan6 basis, at - 120°C (P7MB) and - 126°C (P8MB), and its location and activation energy (35-45 kJ mol ) agree with the values of a similar relaxation associated with kink motions of polymethylenic sequences. 

The quantum alternative for the description of the vibrational degrees of freedom has been commented by Westlund et al. (85). The comments indicate that, to get a reasonable description of the field-dependent electron spin relaxation caused by the quantum vibrations, one needs to consider the first as well as the second order coupling between the spin and the vibrational modes in the ZFS interaction, and to take into account the lifetime of a vibrational state, Tw, as well as the time constant,T2V, associated with a width of vibrational transitions. A model of nuclear spin relaxation, including the electron spin subsystem coupled to a quantum vibrational bath, has been proposed (7d5). The contributions of the T2V and Tw vibrational relaxation (associated with the linear and the quadratic term in the Taylor expansion of the ZFS tensor, respectively) to the electron spin relaxation was considered. The description of the electron spin dynamics was included in the calculations of the PRE by the SBM approach, as well as in the framework of the general slow-motion theory, with appropriate modifications. The theoretical predictions were compared once again with the experimental PRE values for the Ni(H20)g complex in aqueous solution. This work can be treated as a quantum-mechanical counterpart of the classical approach presented in the paper by Kruk and Kowalewski (161). 

The y Relaxation. In common with many other polymers (8) both PPO and PS display significant loss maxima below room temperature at the frequencies under consideration. Whereas the process responsible for the a loss is at least qualitatively understood in terms of a main chain relaxation associated with the glass transition, y losses can often only tentatively be attributed to specific mechanisms. In PPO, for example, it does not seem unreasonable to propose that the y loss is associated with librations in the two pendant methyl groups this view is somewhat reinforced by the observation that in the dielectric measurements the relaxational strengths of the y and a loss processes are comparable. As the latter can be well interpreted (6) in terms of a dipolar relaxation of the main chain in which the entire dipolar contributions arise from the methyl groupings, it seems plausible to assume that the same dipoles are responsible for the y loss mechanism. In polystyrene there is a similar... 

Therefore, the free energy change against the number of carbon atoms in the side chain is in excellent agreement with the experimental data which means that the number of carbon atoms of the spacer group has an influence on the y relaxation associated with the chair-to-chair conformational change in the cyclohexyl... 

Figures 2.37 and 2.38, show the isochronal curves of the permittivity and loss factor for P2NBM and P3M2NBM as a function of temperature at fixed frequencies. A prominent relaxation associated with the dynamic glass transition is observed in both polymers. Clearly the effect of the methyl substitution in position 3 of the norbornyl group is to decrease the temperature of this relaxational process.

Only the 2,6-T-2P polyurethanes exhibited a relaxation associated with crystallization and later melting of the soft segments. The position of the crystallization maximum was estimated from the location of tan(8)m lx and was somewhat difficult to characterize accurately because of extreme overlapping of the a9 and ac relaxations, as evident in Figure 10. Melting occurred over the region 2°-7°C in all samples. Phase segregation in 2,6-T-2P samples was well developed to the point that the... 

The full extent of relaxation in the P+Qa- state spans about 120 meV over the time range from 100 ps to about 1 ms at room temperature (McMahon et al., 1998). Of this, as much as 80% is achieved prior to 1 ps. Thus, relaxations associated with diffusion-controlled net H+ uptake do not contribute more than 20-30 meV. However, proton rearrangements (intraprotein H+ transfer) can certainly be a significant part of the overall response of the protein at much shorter times. 

The energy relaxation associated with each of the regions can also be predicted, and the results are displayed in Fig. 13 in a comparison with numerical experiments. Again, there is impressive agreement between the numerical results and the theoretical calculations. 

Block copolymers sometimes yield two a relaxations (associated with the a relaxations of the two homopolymers) and sometimes a single a relaxations (as would a random copolymer). This behaviour can be understood as being related to the mutual solubility of the two constituent homopolymers. If the homopolymers have a certain grade of solubility, there is only one a peak, which is broader than the a peak of a random copolymer with the same... 

Similar anomalous kinetic behavior in alcohols was observed for other systems as well [148, 173]. Weaver and coworkers [3] discussed this behavior, considering the influence of high-frequency dielectric relaxation associated with rotation of solvent monomers and with translational motion of solvent dipoles. 

The properties of the JG relaxation discussed in Sections V.A-V.E call to mind the properties of the structural a-relaxation associated with vitrification. The properties discussed in Sections V.A, V.C, V.D, and V.E indicate that pressure P,... 

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