Secondary relaxations

Short range rotations a-relaxation Secondary relaxations... 

Keywords glass Uansition, pressure, stmctural relaxation, secondary relaxation, inter-molecular relaxation, binary mixtures... 

Intermediate - Temperature Relaxations. Secondary relaxations in the glassy state at temperatures intermediate between those of the a- and P- relaxations have been reported, but workers disagree as to their nature, location and origin. Confusion arises in part from a failure to recognize the existence of two separate processes. Krum and MUller [19] observed an intermediate relaxation only for injection-moulded or cold-drawn polycarbonate samples. Since the magnitude was diminished by annealing and the loss was not detected in fully annealed samples, they concluded that the intermediate process is a non-equilibrium effect associated with residual stresses. 

Graphite will creep imder neutron irradiation and stress at temperatures where thermal creep is normally negligible. The phenomenon of irradiation creep has been widely studied because of its significance to the operation of graphite moderated fission reactors. Indeed, if irradiation induced stresses in graphite moderators could not relax via radiation creep, rapid core disintegration would result. The observed creep strain has traditionally been separated into a primary reversible component ( ,) and a secondary irreversible component (Ej), both proportional to stress and to the appropriate unirradiated elastic compliance (inverse modulus) [69]. The total irradiation-induced creep strain (ej is thus ... 

By changing from the simplest to larger aliphatic and cyclic ketones, structural factors may be introduced which favor alternative unimolecular primary photoprocesses or provide pathways to products not available to the simple model compound. In addition, both the increase in molecular size and irradiation in solution facilitate rapid vibrational relaxation of the electronically excited reactant as well as the primary products to thermally equilibrated species. In this way the course of primary and secondary reactions will also become increasingly structure-selective. In a,a -unsym-metrically substituted ketones, the more substituted bond undergoes a-cleavage preferentially. 

However, the relaxation process is rather slow whereas thermoplast processing calls for almost instantaneous cooling of the melt after molding and due to this fact the chain structure is not restored. From this it follows that in molding a conducting polymer composite the cooling of the melt should have a speed comparable to the speed of restoration of the filler secondary structure, otherwise the conductivity of the polymer composite will be reduced. 

Kolarik, J. Secondary Relaxations in Glassy Polymers Hydrophilic Polymethacrylates and Polyacrylates Vol. 46, pp. 119—161. 

These results indicate clearly the usefulness of the CP/MAS NMR method in analysing the structure of secondary valence bonds in polymers by using relaxation T1 data. Similarly useful data may be obtained by the Tip parameter. 

X-ray scattering studies at a renewed pc-Ag/electrolyte interface366,823 provide evidence for assuming that fast relaxation and diffu-sional processes are probable at a renewed Sn + Pb alloy surface. Investigations by secondary-ion mass spectroscopy (SIMS) of the Pb concentration profile in a thin Sn + Pb alloy surface layer show that the concentration penetration depth in the solid phase is on the order of 0.2 pm, which leads to an estimate of a surface diffusion coefficient for Pb atoms in the Sn + Pb alloy surface layer on the order of 10"13 to lCT12 cm2 s i 820 ( p,emicai analysis by electron spectroscopy for chemical analysis (ESCA) and Auger ofjust-renewed Sn + Pb alloy surfaces in a vacuum confirms that enrichment with Pb of the surface layer is probable.810... 

Last but not least, two epoch-marking technologies have been successfully implemented in 1989 and 1994 active optics, with the 3.5 m ESO New Technology Telescope (NTT), and segmentation, with the 10 m Keck. In the former, real-time adjustments of the primary mirror support forces and of the alignment of the secondary mirror guarantee consistent, optimal performance, and allow relaxation of opto-mechanical fabrication tolerances. These adjustments being derived from wavefront analysis of off-axis stellar sources located outside the scientihc held of view, imply minimal operational overheads at the beneht of reliable, substantial performance improvement... 

In summary, all the experiments expressly selected to check the theoretical description provided fairly clear evidence in favour of both the basic electronic model proposed for the BMPC photoisomerization (involving a TICT-like state) and the essential characteristics of the intramolecular S and S, potential surfaces as derived from CS INDO Cl calculations. Now, combining the results of the present investigation with those of previous studies [24,25] we are in a position to fix the following points about the mechanism and dynamics of BMPC excited-state relaxation l)photoexcitation (So-Si)of the stable (trans) form results in the formation of the 3-4 cis planar isomer, as well as recovery of the trans one, through a perpendicular CT-like S] minimum of intramolecular origin, 2) a small intramolecular barrier (1.-1.2 kcal mol ) is interposed between the secondary trans and the absolute perp minima, 3) the thermal back 3-4 cis trans isomerization requires travelling over a substantial intramolecular barrier (=18 kcal moM) at the perp conformation, 4) solvent polarity effects come into play primarily around the perp conformation, due to localization of the... 

Tessari, M., Vis, H., Boelens, R., Kaptein, R., Vuister, G. W. Quantitative measurement of relaxation interference effects between Hn CSA and H- N dipolar interaction correlation with secondary structure. J. Am. Chem. Soc. 1997, 119, 8985-8990. 

---