Fast spinning

Nutation. The axis of a spin-stabilized projectile in flight is subject to spasmodic small conical vibrations, called nutation, which should not be confused with yaw (qv) or precession (qv). The instant a spinning projectile leaves a gun, the turbulence produced by the release of proplnt gases causes nutations to occur. Their amplitude is usually small, and, in the case of concentric fast spinning projectiles, they disappear due to the action of equal and opposite centrifugal forces. 

Since the magnetic moments are smaller, now we have a smaller susceptibility and therefore much smaller signal, requiring more sensitive detection systems. These are resonance or SQUID (see Section 14.5) techniques. Thermal response time are shorter, since pure metals can be used with good thermal conductivity and fast spin-lattice relaxation. The parameter to be measured is the nuclear susceptibility ... 

For the second-order term in the Hamiltonian, the rotation of the rotor implies similar transformations, which in the fast-spinning case yields an average operator... 

In the fast-spinning case Tics = resonance offset or the isotropic chemical shift and the quadrupolar terms are given by (16) and (18). Thus, we obtain... 

Most clinical examinations apply robust spin-echo or fast spin-echo sequences. These types of sequences provide tissue contrast changes by variation of the chosen repetition time TR (time interval between succeeding RF excitations) and echo time TE (time delay between RF excitation and signal acquisition). 

Fig. 5. Standard fast spin-echo imaging of the pelvis and the lower leg. Typical contrasts between musculature and other tissues are demonstrated. Bl = bladder, Fe = femur. Gluteus = gluteus muscle. Original recording parameters matrix 192 x 256, slice thickness 6 mm, a-c field of view (fov) = 380 mm, d-f fov = 180 mm. (a) and (d) Proton density weighting TR = 5000 ms, TE = 12 ms. (b) and (e) Ti-weighting TR = 500 ms, TE = 12 ms. (c) and (f) 7 2-weighting TR = 5000 ms, TE = 100 ms.

Figure 7.2 Fast spinning, high pressure NMR sapphire tube with safety and charging device (constructed at ICCOM-CNR, 2003).

The proposed ID TOCSY-NOESY experiment is illustrated by the assignment of NOEs from anomeric protons H-lc and H-ld of the polysaccharide 1. Because the resonances of H-lc and H-ld overlapped, this assignment was not possible from a ID NOESY spectrum as shown in fig. 3(b). Although these protons differed in their chemical shifts, it was not possible to separate them by chemical-shift-selective filtration because of the very fast spin-spin relaxation of backbone protons (20-50 ms) in this polysaccharide. Instead, a ID TOCSY-NOESY experiment was performed in which the initial TOCSY transfer from an isolated resonance of H-2c was followed by a selective NOESY transfer from H-lc. The ID TOCSY-NOESY spectrum (fig. 3(c)) clearly separated NOE signals of the H-lc proton from those originating from the H-ld proton and established the linkage Ic —> 6a. 

Photoinduced spin-related phenomena are a particularly important field of the solid-state photophysics, because fast spin switching is a prospective basis for applications in the field of spintronics. An illustrative example is the production of the metastable state of the iron propyltetrazole (ptz) complex [Fe(ptz)6](BF4)2 by laser light-induced excited spin-state trapping (LIESST) and the determination of the resulting structure by steady-state X-ray photodiffraction [68]. In another example, steady-state X-ray photodiffraction at cryogenic temperatures was successfully utilized to study photoinduced phase transition due to spin crossover in the tris(a-picolylamine)iron(II) complex [69]. The phase transition is accompanied by... 

Use of DPS, WURST and HS pulses (for 41 testing methods). Sample with fast spin relaxation. 

From numerical calculations using these equations, it can be shown that when the spin-diffusion rate is at least 10 times faster than the values, the apparent relaxation decays for both MA and MB become practically identical and can be expressed by a single exponential with a common relaxation rate. In this fast spin-diffusion case, the apparent relaxation rate... 

FIGURE 28. 39.758-MHz CPMAS 29Si NMR spectrum of solid 1,1,1-trimethyltriphenyldisilane. (a) Slow spinning (206 Hz), (b) Fast spinning (3.2 kHz). The two spinning sideband manifolds in (a) are indicated by different symbols. Experimental conditions contact time 8 ms, recycle time 10 s, number of transients 2090 (a) and 405 (b). Reproduced by permission of the Royal Society of Chemistry from Reference 140... 

---