Solid-Echo Based Sequences

The total Hamiltonian of a dipolar coupled spin system may be written as 

Sequence a (0) DD DD Tj(d) DDxCS DD DDxCS Scale Factor Tilt Angle 

Terms such as and T-L dd- cs vanish for all sequences in Table 1, since all of them except MREV8 possess internal reflection symmetry [26]. The scale factors of these sequences decrease with increasing number of pulses. Thus, line narrowing must compensate for the scaling of the spectral width in order to increase the resolution on a corrected ppm scale. 

A combination of the sequences in Table 1 with MAS is also necessary to average out the CSA interaction. Such a combination is not straightforward, given the possible interference effects from the simultaneous presence of both RF and MAS. Such problems forced the above sequences to be applied in the quasi-static limit, where the MAS period Tj. is much longer than the cycle time of the sequence 

The scale factors and tilt angles were evaluated assuming the pulse parameters given in Section 7.3. 

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Figures 3 and 6 show representative spectra with the application of TREV8 and MSHOT3 sequences, some of which are compared with solid-echo based sequences such as MREV8 and BR24.

Table 1. Properties of solid-echo based pulse sequences ...

Multiple-pulse sequences based on magic echoes -are very similar to the solid echo-based methods, but have the advantage of longer windows for the gradients. 

Multi-pulse sequences for line narrowing based on magic echoes represent another possibility to realize time-suspension. Such sequences are less difficult to implement than pulse sequences based on solid echoes and consequently, appear to be more popular for use in imaging. Therefore, they are treated separately in Section 8.8. 

The bipolar pulsed pair stimulated echo (BPPSTE) pulse sequence was used to measure the water self-diffusion coefficients these were used as indicator of the Ostwald ripening extent in precursor emulsions leading to poly(divinyl-benzene) emulsion-derived solid foams based on a three component amphiphile system. 

Multiple-pulse sequences based on solid echoes -which are very efficient at refocusing all internal... 

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