A detailed comparison between molecular dynamics computer simulations and the experimental characterization of molecular motion through deuterium nuclear magnetic resonance (NMR) spectroscopic methods has been carried out for the crystalline phase of nylon 66 (polyhexamethyleneadipamide) at room temperature and just below the melting point. The computer simulations agree quantitatively with the experimental results at room temperature and qualitatively near the crystalline melting point. Both methods demonstrate that individual methylene groups within the crystals exhibit librational motion, which becomes very large in amplitude near the melting point, rather than undergoing discrete conformational jumps; furthermore, the hydrogen-bonded amides are relatively immobile at all temperatures below 230 degrees Celsius. The simulations are shown to be particularly useful for exaning the cooperativity of motion and for providing insight into structural-dynamical correlations. These aspects of the simulations are exemplified by the observation of concerted counterrotation of odd-numbered bonds within the methylene segments and the entropic stabilization of the crystal structure.
Background Electromyography (EMG) biofeedback (BF) training is potentially an effective cognitive‐behavioural approach to regulate bruxism. Objective This study examined sleep bruxism regulation by daytime clenching control using a single‐channel auditory EMG BF device. Methods Seventeen male subjects (mean age, 24.4 ± 3.1 years; mean ± SD) with self‐reported awake/sleep bruxism were recruited and divided into a BF (n = 10) and a control (CO) group (n = 7). All subjects underwent four EMG recording sessions during both daytime and sleep over 3 weeks. During the daytime, in week 2, the BF group received feedback alert signals when excessive EMG activity with certain burst duration was detected while the subjects performed regular daily activities. The CO group underwent EMG recording sessions without receiving any alerts of parafunctional activity. The number of phasic burst events during sleep was compared between the BF and CO groups. Results While the number of phasic EMG events was not significantly different between the BF and CO groups at baseline, significantly smaller phasic events were observed in the BF compared to the CO group at the follow‐up session (week 3) (P = .006, Tukey's HSD). Since daytime BF training is aimed at raising awareness of awake bruxism, it does not interrupt the sleep sequence or involve associated side effects. Conclusion The present results suggest that EMG BF targeting for tonic EMG events during the daytime can be an effective method to regulate phasic EMG events during sleep.
Solid-state deuterium NMR spectroscopy coupled with line shape simulations has been used to examine the segmental dynamics of individual methylene sites and N-D sites within the amorphous domains of selectively deuterated nylon 66 polymers over a wide temperature range. Magnetization only from amorphous domains may be isolated via spin-lattice relaxation time discrimination due to the presence of small-angle fluctuations (librations) a t all sites within the amorphous domains above -50 "C. The N-D sites exhibit very little motion below Tg, and above Tg a fraction of the sites undergo nearly isotropic motion. The C-D sites exist in two discrete environments below T, (not a continuous distribution): one of the populations exhibits only librational motion and the other exhibits both librational and internal rotation (7-relaxation) motions. Above Tg, a fraction of the C-D sites undergo nearly isotropic motion (essentially the same fraction as the N-D sites), and this behavior of the entire repeat unit is identified with the a relaxation. The addition of 2 f 0 . 3 wt % water has no apparent effect upon the y relaxation and depresses the a process by approximately 40 "C; additionally, T , relaxation data indicate that the p relaxation is a process which involves all C-D sites and is observed only in wet polymer.
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