Rotor-synchronized exchange

Fig. 6 The RFDR-sequence with two 7x/2-pulses sandwiching the t evolution period. The mixing period is comprised of rotor-synchronized n-pulses. If these pulses are absent, the sequence is that for 2D-exchange spectroscopy. The third 7i/2-pulse produces transverse magnetisation...

Fig. 10. Rotor-synchronized C-2D MAS exchange spectrum of dimethylsulfone at a MAS rate v =1.5 kHz and a mixing time Tm = 20 ms. Top stack plot. Bottom contour plot. The marked cross-peaks denote negative intensity. (Adapted with permission from Ref. 155.)...

Fig. 11. Rotor-synchronized H-2D MAS exchange spectra of dimethylsulfone. (a), (b) and (c) are experimental and were recorded with z/r = 4.06 kHz at 30°C and nominal mixing times as indicated, (d), (e) and (f) are calculated using an axially symmetric quadrupole tensor with a jump angle of 108°. (Adapted with permission from Ref. 152.)...

Fig. 12. rotor-synchronized 2D-MAS exchange spectra of a tropolone sample enriched to... 

The use of orientational constraints represents only one solid-state NMR approach for polymer structural characterization. In the future, a combination of constraints will be used, no doubt, for such characterizations, in particular distance constraints from REDOR [45], or rotational resonance [46] will be helpful. Direct measurement of torsion angles using DRAWS [47], C7 [48] or rotor-synchronized 2D exchange [49] may also prove to be beneficial. 

Fig. 24. (a) Two-dimensional transverse-echo SEDRA with t-SEDRA in the mixing time. The phase of the ir/2 pulse is altered with x and y (reproduced from Weintraub et with permission), (b) Two-dimensional homonuclear correlation (RFDR). The Till pulses set up longitudinal exchange. Mixings accompanied by rotor-synchronized IT pulses. (Reproduced from Benett et al with permission.)... 

In recent years, it has evidenced a remarkable progress using solid-state MAS NMR to monitor the structure and dynamics, especially hydrogen bonding network and proton dynamics of polymer exchange membrane. Suarez and Greenbaum have reviewed the contribution of NMR spectroscopy to the development of the PEMFC, with particular emphasis on its use in the characterization of structure and transport in polymer electrolyte membranes [3]. Graf reviewed the application of 2D rotor-synchronized... 

A low speed synchronous motor consists mainly of a stator stack with stator winding supported by the stator frame, the rotor with exciter winding, a heat exchanger, stator end-shields and, depending upon the construction, rotor bearings and a rotor shaft. 

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