Time-suspension sequence

In order to preserve the effect of the gradients on the evolution of magnetization in a time-suspension sequence, the gradient pulses must be applied with alternating polarity in successive free-evolution windows of the magic-echo sequence. In this case, the evolution of the density operator can be expressed similar to (8.8.2),... 

In combination with multi-pulse excitation, rotating-frame imaging can also be used for imaging of solids [Choi]. A time-suspension multi-pulse sequence (cf. Table 3.1) is applied to the sample by use of an rf coil with a homogeneous B field so that both... 

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. 

Fig. 8.7.3 Proton images (bottom) of a phantom made from poly (acetal) (Delrin) acquired with the time-suspension pulse sequence of Fig. 8.6.2, The field of view is (5.9 mm). The sample (top) has been imaged in three dimensions at 400 MHz with a voxel size of 92 x 92 x 625(pLtti). Adapted from [Corl2] with permission from Flsevier Science.

The purpose of this section is to describe recent achievements in time-resolved X-ray diffraction from liquids. Keeping the scope of the present chapter in mind, neither X-ray diffraction from solids nor X-ray absorption will be discussed. The majority of experiments realized up to now were performed using optical excitation, although some recent attempts using infrared excitation were also reported. The main topics that have been studied are (1) visualization of atomic motions during a chemical reaction, (2) structure of reaction intermediates in a complex reaction sequence, (3) heat propagation in impulsively heated liquids, and (4) chemical hydrodynamics of nanoparticle suspensions. We hope that the actual state-of-the-art will be illustrated in this way. 

Fig. 7. 300 MHz H HRMAS NMR spectra of a resin suspension swollen with DMF-dq from a reaction mixture and spun at 4 kHz. The spectrum (A) was obtained with a single-pulse sequence. The spectra in (B), liberated from the reaction vessel at the times indicated, were obtained using a diffusion filter to reduce the signals from non-bound species. Note the excellent suppression of the solvent DMF peak at 8 ppm. Reproduced with permission from Ref. 75. Copyright 2000 American Chemical Society.

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