Spin time duration

For the basic PFGE experiment a spin-echo experiment (either the two-pulse Hahn echo sequence, Fig. la, or the three-pulse stimulated echo sequence. Fig. lb) is combined with two magnetic field gradient pulses with duration 8 and separated by the time duration A. The gradient pulses generate a magnetic... 

A plot of the relative contributions against the spin-lock time tsL (Fig- 34) shows a distinctly bi-exponential decay of the QlO-protons, while the protons of the matrix exhibits a largely mono-exponential decay down to values scattered by the background noise. The initial slopes of both decays are identical within the given experimental error. However, for spin-lock durations of more than 2 ms, the QIO contribution shows a much smaller relaxation rate, being detectable even after tsL= 10 ms. 

Fig. 34. Relative signal contributions for QIO (squares) and for the lipid cetyl palmitate (diamonds) plotted logarithmically vs. the spin-lock duration %l. The grey lines indicate linear relaxation sections with relaxation times of 1.9 ms (lipid for the full duration as well as QIO for hi <2 ms) and 13 ms (QIO for sl>2 ms). The extrapolation of the latter curve toward sl —0 yields the relative amount of the separate fraction of QIO which amounts to approximately 40%.

Figure 7 Pulsed-gradient spin-echo (PGSE) electrophoretic NMR sequence. This ENMR pulse sequence is used to detect electrophoretic mobility during the gated electric field E, which is applied fora time duration 3 equal to the spacing between a pair of magnetic field gradient pulses. Reprinted with permission from Ref. [37], Copyright [2014], AlP Publishing LLC.

The time duration of the spin-off process to attain this thickness will be... 

Fig. 1.19 Spin-echo based pulse sequence to each gradient pulse, A the separation between encode velocity change. The gradients are each pair of bipolar gradient pulses and tm the stepped pair-wise independently (2D VEXSY) mixing time between the bipolar gradient pairs, or simultaneously (1 D VEXSY). For a VEXSY The opposite polarity of the bipolar gradient experiment, 7q to k4 are usually applied along pair is realized by an inversion 180° pulse, the same spatial direction. 8 is the duration of...

Fig. 2.7.2 Diffusion-relaxation correlation se- The detection (2nd) segment for both is a quences using pulsed field gradients, (a) The CPMG pulse train that is similar to that in first segment is a spin-echo with the echo Figure 2.7.1. The amplitude or the duration of appearing at a time 2tcpi after the first pulse, the gradient pairs in both sequences is (b) The first segment is a stimulated echo incremented to vary the diffusion effects, appearing at a time tcpi after the third pulse.

Fig. 14. SeqHNCA-TROSY experiment for establishing sequential 1HN(i), 15N(i), 13Ca(i— 1) correlations in 13C/15N/2H enriched proteins. Durations of transfer delays A = 1/(4/Hn) 2Ta = 20-27 ms, depending on rotational correlation time of protein 2Tc = 5-7 ms S = gradient + field recovery delay 0 < k < Ta/t2,max- Phase cycling i = y (j>2 = y, — y + States-TPPI 0 = x 0ret. = x, — x. Semi-selective decoupling of 13C spins is attained using a SEDUCE-1 decoupling sequence.95...

Fig. 14. Measured water spin-lattice relaxation rates of a hydrated mortar at w/c = 0.38 as a function of the proton Larmor frequency, for different duration of hydration Oh 34 min ( ), 7h 27 min (O), 8h 45 min ( ), and 9h 40 min ( x ), upwards. The insert represents the data obtained after a hydration time of lOh 32 (+), the labels for the two axis are equivalent to those of the main figure. The continuous lines correspond to the best fits to the theory.

This contribution will describe the manipulation of spin multiplets as a whole, and the word selective - or soft - will be used for multiplet-selective pulses, in contrast to band-selective, which refers to a broader bandwidth which may affect several spins, and to transition selective when only one line is affected. The discussion will be based on proton spectra, but all aspects are similar for other nuclei. Soft pulses use lower amplitudes and much longer irradiation times than non-selective hard pulses. Typical durations for soft pulses are of the order of 1 to 500 ms with a peak amplitude... 

---