Sandwich 180° pulse

There are many tricks to get around the problem, such as sandwich 180° pulses (e.g., 90 -180 -90 ) and broadband shaped pulses. Figure 8.4 (top) shows the inversion profile for a simple 180° pulse at the highest available power (fp = 28.4 p,s, yB l2it — 17.6 kHz). The profile is obtained using an inversion-recovery sequence (180°x — r — 90° ) with recovery time r = 0. The final 90° pulse frequency and the 13C peak (13CH3l) are both at the center of the spectral window, but the frequency of the 180° pulse is moved in 10 ppm (1500 Hz)... 

A more robust way to invert the sample magnetization is the sequence 90°-180°-90°, with no space in between the pulses. This is called a composite pulse or sandwich pulse because a number of pulses are lined up right next to each other, like slices of cheese and meat in a sandwich. Suppose that what we think is a 90° pulse is really an 85° pulse due to miscalibration. The first 90° pulse on yf rotates the sample magnetization ccw by only 85°, leaving it in the x -z plane just 5° short of the x axis (Fig. 8.5). 

A. A. Nevzorov and S. J. Opella, A "Magic Sandwich" pulse sequence with reduced offset dependence for high-resolution separated local field spectroscopy, J. Magn. Reson. 164 182-186 (2003). 

Fig. 4.43. Depth profile of a triple Cu-Ag sandwich (the laser fluence is about 1 ) cm" 10 pulses accumulation. The dashed lines indicate different layers [4.245].

Composite pulse A composite sandwich of pulses that replaces a single pulse employed to compensate for B] field inhomogeneities, phase errors, or offset effects. 

In the laser flash method, a melt of interest is placed between two parallel plates. The upper plate is heated stepwise and the thermal diffusiv-ity is measured from the rise in temperature. The specific design for molten materials and especially slags employed by Ohta et al. is based on the differential three-layer technique utihzing a special cell that can be accommodated in the system. A schematic diagram of the principle of the measurement section is shown in Fig. 31. A laser pulse irradiates the upper (platinum) crucible and the temperature response of the surface of the lower platinum crucible is observed, a liquid specimen being sandwiched between the two. 

Fig. 2.3.8 Lower GARField profiles of a human skin sample sandwiched between two glass slides, recorded immediately after the sample was floated onto the first slide and again approximately 90 min later. Upper increasing the pulse gap T from 150 to 500 ps increases mobility contrast and allows discrimination between the stratum comeum (right) and viable epidermis (left). Again two profiles are shown, recorded approximately 90 min apart.

The electrolyte was a solution of ammonium chloride that bathed the electrodes. Like Plante s electrochemistry of the lead-acid battery, Leclanche s electrochemistry survives until now in the form of zinc-carbon dry cells and the use of gelled electrolyte.12 In their original wet form, the Leclanche electrochemistry was neither portable nor practicable to the extent that several modifications were needed to make it practicable. This was achieved by an innovation made by J. A. Thiebaut in 1881, who through encapsulating both zinc cathode and electrolyte in a sealed cup avoided the leakage of the liquid electrolyte. Modern plastics, however, have made Leclanche s chemistry not only usable but also invaluable in some applications. For example, Polaroid s Polar Pulse disposable batteries used in instant film packs use Leclanche chemistry, albeit in a plastic sandwich instead of soup bowls.1... 

The fluorescence spectra measured just upon ablation are given in Figure 2A as a function of laser fluence. The contribution below 370 nm was suppressed, as a Hoya L37 filter was used in order to cut off the laser pulse. Fluorescence spectra of this polymer film consist of sandwich (max. 420 nm, lifetime 35 ns) and partial overlap (max. 370 nm, lifetime 16 ns) excimers (20). The latter excimer is produced from the initially excited monomer state, while the sandwich excimer from the partial overlap excimer and the monomer excited states. Since these processes compete with efficient interactions between identical and different excimers (Si - Si annihilation) (12), the sandwich excimer is quenched to a greater extent compared to the partial overlap one under a high excitation. Actually the fluence-dependent spectral change around the threshold can be interpreted in terms of Si - Si annihilation. 

D NOE-pumping experiment. E Reverse NOE pumping experiment (bottom) and reference experiment (top). F e-PHOGSY NOESY sequence. The water-selective 180° pulse sandwiched by the first two gradients has a gaussian shape and a duration of 40-50 ms. The mixing time is approx. 2 s. For further details, see Refs. [29, 30]. 

Fig. 7. Frequency distribution of plasma Lp(a) concentrations (a) and apo(a) alleles (b) in three populations. Plasma Lp(a) levels were measured in 381 subjects by the sandwich ELISA technique apo(a) allele size (number of K-4 repeats) was estimated using pulsed-field gel electrophoresis and genomic blotting. [With permission of Gaw et at. (G11).]...

The polymerization of ethylene was also qualitahvely inveshgated by pulse injec-hons of ethylene into helium flowing over thorium (67) and uranium (86) metallocene hydrocarbyl complexes supported on 7-AI2O3.950 at 25 °C, both revealing similar achvihes [171, 173]. Supported thorium half-sandwich complexes 65 exhibited higher achvity than surface species, resulhng from coordinatively more saturated tris(cyclopentadienyl) and metallocene U/Th-alkyl/hydride complexes, that is, 77, 79, 82, 90 and 91 [171]. C CP MAS NMR spectra revealed no clear evidence of ethylene insertion into [Th-CHs] or [AL5-CH3] moiehes of material... 

A BIRD pulse sandwich [33] followed by a delay can be used to suppress the magnetization from C-bound protons [34]. The BIRD pulse sequence is 90° (i7)-r-180°(i7, C )-r-90° (if). With the delay r set to 1/(2J), where J is the one-bond coupling constant, the effect of the sequence is... 

Electrodes are made using heavy duty foil affixed to both ends of a microscope slide with a small (5 mm) gap in between. Wire loops are sandwiched between layers of each foil electrode. The wire loops can then be connected to the pulse generator. 

Similarly, fluorescence detected magnetic resonance effects observed during the pulse radiolysis of anthracene-dio in the presence of 2,3-dimethyl-l-butene support the presence of 8 equivalent methyl groups. Because the splitting, Odi = 0.82 mT, was approximately one-half that of the monomer splitting, Omon =1.71 mT, the sandwich dimer 91 + was invoked. ... 

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