Ring dynamics

Melt dynamics of rings are characterized directly by rheological and diffusion measurements. Early studies seem to have been motivated primarily by the notion that rings cannot 

PS was roughly double that determined for linear PS (in contrast to their earlier finding that linear c,ring) nd that the cyclic-PS plateau modulus is half that of linear PS (consistent with Roovers findings (Roovers, 1985)). 

It was clear that low concentrations of hnear contaminants had a large influence on the melt rheology of rings. The extent to which this is tme was revealed in a recent report on the stress-relaxation behavior of PS rings (161 and 198 kg/mol) that were purified by LCCC (Section 26.1) and characterized as pure as currently possible (Kapnistos et al, 2008). Kapnistos et al conducted small-amphtude oscillatory shear measurements at different 

Assuming the Dbiend reduction is related to the existence of threaded conformations, the fraction of threaded species across the entire CPOE concentration for the 1.5-kg/mol blend can be estimated from the magnitude of the deviation from the binary-mixing-rule prediction. For this analysis, a three-term mixing law was assumed for the average diffusion coefficient  

In a recently published single-molecule study (Habuchi etal, 2010), fluorophore-labeled cyclic poly(tetrahydrofuran) (3.8kg/mol) was mixed with unlabeled linear poly(THF) (3kg/mol) and examined at a semidilute concentration in toluene. Single-molecule trajectories were measured and diffusion coefficient distributions were constructed. Analysis of the distributions yielded two diffusion coefficients for cyclic poly(THF), 1.1 and 4.9 X 10 m /s, which were attributed to threaded and unthreaded rings, respectively. Comparison with the study discussed above using PFG NMR (Nam et al, 2009) reveals intriguing similarities low molecular weight cyclic poly ethers, diffusion coefficients of 10 m /s, ratio of threaded to unthreaded diffusion coefficients from 3 (NMR) to 4.5 

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Grinstein, F. F. 1995. Self-induced vortex ring dynamics in subsonic rectangular jets. J. Physics Fluids 7 2519-21. 

Metal migrations, around rings, dynamic NMR studies, 1, 411 Metal nitrides, synthesis, 12, 53... 

Maciejewska et a/.87 have published 13C CP/MAS NMR spectra of nine 4 -substituted-4-dimethylamino-tra/Ji-azobenzenes 27 (Table 13). The nonequivalence of C2/C6 and of C2 /C6 was observed and the difference in 13C chemical shifts was 14.0-22.0 ppm for C2/C6 and 12.2-22.5 for C2 /C6. The 13C CP/MAS NMR spectra of the compound with 4 -CHO substituent were measured in the temperature range 298-373 K but the spectra did not exhibit any substantial changes except for a small high-frequency shift of all resonances. These results confirm the lack of ring dynamics in the above-mentioned temperature range. 

Second, the positions and llneshapes of resonances arising from potentially mobile parts of the peptide (e,g, side chains) have revealed dynamical aspects of the solid-state structures of peptides. The analysis of molecular motions is simplified In the solid state by the absence of overall molecular tumbling, which modulates spin interactions and leads to complex frequency -dependent spectral responses. In particular, signals arising from aromatic ring side chains are well separated from other resonances, and may be interpreted in terms of reorientation models of these side chains. Such ring dynamics are of great importance in protein structures, and studies with model peptides can help elucidate fundamental aspects of these processes. 

The combined use of the utility of solid-state NMR analysis of ring dynamics. 

The ring dynamics of the two phenylalanine containing cyclic peptides have been studied in solution, both of these peptides show H and NMR spectra consistent with... 

Hiraoki et al. investigated the phenyl ring dynamics of poly(L-phenylalanine) using H-NMR, showing that it is characterized by a fairly broad distribution of correlation times. The mean correlation time of this distribution was 1.2 x 10 Hz at 25°C, which is close to that of the fast motional component of the B. mori and S.c. ricini silk fibroins. The Tyr ring flip in the pentapeptide [Leu ] enkephalin was reported to be 5.6 x 10 Hz at 25°C, which is close to that of the slow motional component observed here for silk fibroin. On the other hand, the ring motion in crystalline N-acetyl-L-Asp-L-Pro-L-Tyr-N -methylamide was found to be 1.1 X 10 Hz at 27°C, close to that of the fast motional component of the silk fibroins. 

Although DNMR provides information on the site exchange information and some aspects of the mechanism, one must often rely on theory to provide details of the path. Fortunately, modem DFT methods are now available to provide the details with some confidence. In the case of inter-ring dynamics, there are questions regarding whether... 

Measurements of coupling constants and C spin lattice times for C-enriched tetroses and tetrofuranosides have enabled conformational changes and ring dynamics to be determined a thorough... 

Roy, A. K., Jones, A. A., and Inglefield, P. T. (1986) Phenylene ring dynamics in solid polycarbonate an extensive probe by carbon-13 solid state NMR line-shape studies at... 

Tetrafluoroethylene/propylene copolymer o-rings, chemical-resistant Chlorotrifluoroethylene polymer o-rings, dynamic aerospace Polyfluoroalkoxyphosphazene o-rings, dynamic industrial Polyfluoroalkoxyphosphazene o-rings, dynamic military Polyfluoroalkoxyphosphazene ornament mfg. 

M. Kamihira, A. Naito, S. Tuzi, H. Saito, Phenyl ring dynamics of enkephalin molecules and behavior of bound solvents in the crystalline state by H NMR spectroscopy,. Phys. Chem. A 103 (1999) 3356-3363. 

Barrio RA, Galeener FL, Martinez E, Elliot RJ (1993) Regular ring dynamics in AX2 tetrahedral glasses. Phys Rev B 48 15672-15689... 

Additional studies are underway to assess the ability of the RdPCA model to represent conformational space among different species. The perspectives opened by this preliminary research are to incorporate exocyclic dihedral angles into the RdPCA analysis, in order to probe the effects of exocyclic substituents on ring dynamics and eventually to analyse correlated motions within oligosaccharide structures, as well as to generalize this RdPCA analysis to other cyclic structures, such as not only furanosides, but also pyranose rings and even cyclodextrins. 

The solvent bath is stirred continuously by means of a tantalum paddle attached to a Pyrex tube, the latter being inserted into the calorimeter through a double 0-ring dynamic seal. Evacuation of the calorimeter and introduction of the specimens into the solvent bath are both effected through the Pyrex tube. 

Fluoroelastomers are presently widely used in the industry as 0-rings, V-rings, gaskets and other types of static and dynamic seals, as diaphragms, valve seals, hoses, coated clothes, shaft seals quick connector o-rings, dynamic sealing applications, membranes, [185], expansion joints, etc. [186]. They are also used in cars as O-rings for fuel, shaft seals and other components of fuel and transmission systems [35,58,62-65]. 

Figure 7.15 Plots of tan 8 versus temperature for DMA scans of extruded soy protein sheets at different moisture contents (reprinted from Polymer, 42(6), J. Zhang, P. Mungara and J. Jane, Mechanical and thermal properties of extruded soy protein sheets, 2569-2578. Copyright (2001), with permission from Elsevier) and amylose films plasticized with different glycerol contents (reprinted from Carbohydrate Polymers, 22(3), G. K. Moates, T. R. Noel, R. Parker and S, G. Ring, Dynamic mechanical and dielectric characterisation of amylose-glycerol films, 247-253. Copyright (2001), with permission from Elsevier.)...

E. Dornberger, 1997, Prediction of OFS ring dynamics and grown-in voids in Czochralshi silicon crystals, Thesis, Universite Catholique de Louvain, Louvain-la-Neuve. 

Figure 5 Consideration of axial ring dynamics in piston ring performance, after Mierbach et a/ [21]...

Tian, T., "Dynamic Behaviours of Piston Rings and their Practical Impact. Part 2 Oil Transport, Friction and Wear of Ring/Liner Interface and the Effects of Piston Ring Dynamics", Jour. Engineering Tribology, Proc. Instn. Mech. Engrs., Part J, 216, J4,2002, pp.229-247... 

The first detailed examination of ring dynamics was accomplished by James Clerk Maxwell in his 1857 Smith Prize essay, a study that still repays reading. He dealt with the question of the composition and stability of Saturn s rings, demonstrating that they must consist of a swarm of small particles trapped in planar orbits. The demonstration of differential rotation in the Saturn rings by the observation of Doppler shifts in a reflected solar spectrum was first performed by Keeler about 30 years later. 

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