Shifts with temperature

Time-temperature superposition [10] increases the accessible frequency window of the linear viscoelastic experiments. It applies to stable material states where the extent of reaction is fixed ( stopped samples ). Winter and Chambon [6] and Izuka et al. [121] showed that the relaxation exponent n is independent of temperature and that the front factor (gel stiffness) shifts with temperature... 

Leite, R. C. C. DiGiovanni, A. E. 1967. Frequency shift with temperature as evidence for donor-acceptor pair recombination in relatively pure n-type gallium arsenide. Phys. Rev. 153 841-843. 

It should be noted that the unfolding kinetics can sometimes involve quite complex unfolding schemes of different substates in equilibrium with the native state. Staphylococcal nuclease is an example of such behavior, known to unfold with three different substates that exhibit an equilibrium that does not appear to shift with temperature.49 Irreversible aggregation processes of proteins have been known to involve first- or second-order reactions.132141 The mechanism of recombinant human interferon-y aggregation is an example where thermodynamic and kinetic aspects of the reaction provided a powerful tool for understanding the pathway of instability and permitted a rationale for screening excipients that inhibited the process.141... 

Some of the complexes were found to exhibit redox potentials that shifted with temperature (230-300 K). The complexes with Cys-Gly-Ala and Cys-Gly-Ala-Cys sequences were found to be particularly susceptible to temperature variations in CH2CI2 (13,14) with positive shifts at (ca. 0.10 V). These shifts were rationalized by the formation of NH—S hydrogen-bonded conformers (see Fig. 5), which are expected to stabilize the reduced forms of the complexes Such a hydrogen-bonded structure has been deduced from the X-ray analysis of several bacterial Fds (26). 

In some species, male variation in response to component ratio offset from the natural blend is somewhat modulated by ambient temperature (Linn et al, 1988). The response specificity of G. molesta and P. gossypiella to off-ratios of pheromone acetate components in a wind tunnel assay was narrower at 20 °C than at 26 °C. In the field, sexual activity in both species occurs at both of these temperatures, depending on time of year. Some field evidence of this phenomenon with P gossypiella appears in the distribution of catch in traps baited with a range of ratios measured at various times of the flight season. Flint et al. (1977) found an evidently narrower response breadth early in the season (when temperatures were cool) compared with late-season responses. In the omnivorous leafroller Platynota stultana, the optimum ratio of its two components for attraction seems to shift with temperature in the... 

Typical aw shifts with temperature are shown in Figure A2.3.4. The aw shift by temperature is mainly due to the change in the excess enthalpy of water binding, dissociation... 

Their u9Sn NMR spectroscopy has been used to study autoassociation in methyl- and butyl-tin trialkoxides (64, 68, 72). Figure 7 illustrates the variation of chemical shift with temperature for the neat liquid butyltin trialkoxides, BuSn(OR)3. (72)... 

It has been reported (72) that three unassociated methyltin compounds with highly shielded tin nuclei show linear increases in chemical shift with temperature Me2Sn(OlBu)2 + 0-06 ppm K-1 MeSn(OlBu)3 + 0-11 ppm K-1 MeSnI3 + 0-26 ppm K-1. 

Some of the polycrystalline spin crossover systems of iron(II) described above retain their spin equilibrium property upon dissolution in appropriate solvents. The Evans NMR method of measuring the change of the paramagnetic shift with temperature is the most common technique to study the magnetic behaviour of such systems. The spin transition characteristics has been observed to depend on various chemical modi-... 

The sensitivity of the phonon frequencies to temperature shows quite clearly the importance of their anharmonicity.42 The width of the Raman peaks, very small at low temperature ( 1cm-1), evolves in parallel with the frequency shift with temperature, which is still a consequence of the phonon-phonon interactions due to the anharmonicity. The fundamental reason for this strong anharmonicity, as well as the importance of the equilibrium-position shifts between 4 and 300 K,45 resides in the weakness of the van der Waals cohesive forces in the molecular crystal. 

Presumably the hydrogen entering a reactor or charged into an autoclave could be relatively clean and dry, represented by a point in the lower lefthand comer of the reactor zone (or if accompanied by steam, somewhere on the left side of the square). As the reaction proceeded, the reactor gas would become relatively wet (from the balance of the coal reactions or from water in the coal) and loaded with H2S as the H2 was consumed, and would be represented by points near the upper righthand comer of the reactor zone. The area of the reactor zone would stay the same (6x6 log units) but the position of the reactor zone will shift with temperature since the two equilibrium constants are functions of temperature. Note that at 527°C (Figure 3), the reactor zone is almost entirely in the pyrrhotite FellS12 zone Note that at 427°C (Figure 4) the reactor zone is... 

Fig. 38.—The shift with temperature of the infrared absorption spectrum of the carbonyl group in acetic acid.

On other surfaces both the concentration and strength of bonding of the spiltover species will vary. The rate-controlling step may shift, and since the activation energies of the individual steps are not equal, the rate control can shift with temperature. For example, the diffusion coefficient may behave as T312 Ti/2 for two-dimensional diffusion as a surface gas. If a jump-like diffusion occurs from point to point, the dependence may contain an appropriate activation energy. 

The shape of adjacent curves must match exactly. That is, while the frequency of the curve will shift with temperature the shape must be frequency independent. 

As a second simple example, consider how the zero-shear viscosity t q shifts with temperature. Since tjo — limaj >.o G" jo), we have--------------------------------------... 

A fit of the data for anorthite to Equations 7 and 8 describes the change in chemical shift with temperature in the PI phase (Fig. 18) and yields a value for the critical exponent, P = 0.27( 0.04), that is consistent with measurements using techniques sensitive to muchjonger length scales, such as X-ray diffraction (Redfem et al. 1987), that indicate the PI -71 transition in Si,Al ordered anorthite is tricritical. 

The Si MAS-NMR spectra of the 3-phase contain a single peak near -69.4 ppm (Fig. 21). Upon transformation to the INC phase near 75°C, a shoulder develops near -68.3 ppm, the intensity of which increases with temperature. The chemical shift of the peak at -68.3 ppm does not change with temperature, because it corresponds to Si atoms with the local structure of the a-phase (Fig. 20b). The peak near -69.4 ppm moves to higher chemical shifts with temperature. This observation suggests that the amplitude of the modulation decreases with increasing temperature. Physically,... 

The equation describing the variation of centre shift with temperature (Eq. 1, this Chapter) contains two adjustable parameters, m and 5q. Using a non-linear least squares method, the values of these parameters which best fit the data were determined (Table A2). The centre shift data together with the Debye model calculations are plotted in Figure A3. 

Figure A3. Variation of centre shift with temperature based on spectral fits incorporating two quadrapole doublets. The solid line represents the Debye model fit (Eqns. 1 and 2, this Chapter) to the centre shifts (data taken from McConnell et al. 2000).

The observed XANES spectra over the temperature range from r.t. to 220 C are shown in Fig. 3. Despite the EXAFS result, the XANES spectra do show a systematic shift with temperature as directed by the arrows. 

D is correct. Equilibrium will probably shift with temperature. The direction is dictated by thermodynamics. We need more information. 

Small variations of 15N chemical shifts with temperature in amino azo dyes (Table 19) are hardly any indication of the presence of a significant amount of hydrazone forms. In compound 54, measured in acetone at 200 and 300 K, the differences in <5I5N are less than 3.8ppm, contrary to the values found in the hydroxy analogue 48, for which the difference for Na is 50.2 ppm within the same temperature interval (230 and 330 K in CDC13). 15N Chemical shifts lead to the conclusion that aminoazo compounds exist in azo forms in a broad temperature range, in agreement with the l3C NMR results.102... 

From a practical viewpoint, an increase of the absorption of CdTe near the RT band gap ( 1.5eV) has been correlated with 10.06 pm laser illumination [73]. It has been attributed to the temperature-induced shift of the band gap to lower energies generated by residual absorption of the crystal at 10.06 pm. The band-gap increase of silicon between RT and LHeT is 50 meV, and recent measurements at ultra-high resolution of the shift with temperature of the strongest B acceptor bound exciton line of qmi 28Si between 4.8 and 1.3 K show a band-gap increase of 1 GHz or 4 peV in this temperature domain [17]. 

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