Phase-alternating composite pulse

NOESY) sequence (see Fig. 26D, Table 3), which was computer-optimized by Kadkhodaei et al. (1993), is based on the MLEV-16 expanded composite pulse R = 15° 75°, 279°45°. In the TOWNY sequence, a 2 1 ratio of and is achieved by the created trajectory of z magnetization during the course of the optimized phase-alternated composite pulse R, without the need for additional delays or modulation of the rf amplitude. Clean Hartmann-Hahn mixing sequences based on shaped pulses were developed by Mayr et al. (1993). The parameters of the shaped MW-1 sequence (Mayr and Warren, 1995) are given in Table 3. 

Only recently, new multiple-pulse sequences that were developed specifically for broadband heteronuclear Hartmann-Hahn experiments in liquids were reported. The SHR-1 sequence developed by Sunitha Bai et al. (1994) consists of a windowless phase-alternated composite pulse R, which is expanded according to the MLEV-8 supercycle. R was optimized based on a phase-distortionless single-spin 180° composite pulse and is related to the composite pulses used in DIPSI-1 (Shaka et al., 1988) and the composite pulses in the homonuclear IICT-1 sequence (Sunitha Bai and Ramachandran, 1993). The bandwidth of the SHR-1 sequence is comparable to the bandwidth of DIPSI-3, albeit with a slightly reduced transfer efficiency (Sunitha Bai et al., 1994 Fig. 33F). 

Structure of Solids - A H- H dipolar coupling NMR study of the water molecule in magnetically H dilute crystalline hydrates has been reported. High resolution F MAS and F- Cd REDOR NMR spectroscopy has been used to study oxygen/fluorine ordering in oxyfluorides. Solid-state N NMR spectroscopy has been used to investigate nitrosoarene-metal interactions in model systems and in haem proteins. Phase-alternated composite pulses have... 

In addition to multiple-pulse sequences that were derived from heteronuclear decoupling experiments, a number of rf sequences have been specifically developed for homonuclear Hartmann-Hahn transfer. A systematic search for phase-alternated composite 180° pulses R expanded in an MLEV-16 supercycle was reported by Glaser and Drobny (1990). Several clusters of good sequences were found for the transfer of magnetization in the offset range of 0.Av. However, substantially improved Hartmann-Hahn sequences were found after the condition that restricted R to be an exact composite 180° pulse on-resonance was lifted. For example, the GD-2 sequence is based on R = 290° 390° 290°, which is a composite 190° pulse on-resonance and is one of the best sequences based on composite pulses of the form R = (Glaser and Drobny, 1990). 

Fig. 22. Maps of global quality factors (2 for multiple-pulse sequences based on phase-alternated, symmetric composite pulses R = SS with 5 = and A...

For this reason, a perspective alternative may be a photonic crystal based on opal-vanadium dioxide (VO2) composite, with a semiconductor- metal phase transition in VO2. Experiments on pump-probe measurements of the VO2 phase transition, which use pulses from mode-locked lasers, have shown that this transition occurs for a period of several hundreds of femtoseconds [6]. 

The important question as to whether the chemical steps involved in the transient oxygen storage and release processes previously described (Sections 3.3.1 and 3.3.2) should be considered as equilibrium controlled processes (reversible elementary steps) has recently been addressed. It was found that reduction of ceria by CO or Hg to form COg or HgO, respectively, is very important, and if not included in proposed reaction schemes, a number of effects experimentally observed under the dynamic conditions of OSC measurement cannot be understood. For example (i) the observed OSC is lower in the presence of HgO and COg in the CO/He and Og/He alternate pulse or step-change gas compositions (ii) the observed OSC depends on the CO/Hg concentration (iii) when the catalyst is exposed to a rich-lean step, the outlet gas composition remains rich for some time after the inlet has switched to lean (iv) when a previously oxidized catalyst is subjected to a short rich pulse followed by stoichiometric operation, the catalyst emits a delayed pulse of CO/ Hg during the stoichiometric phase (v) when a catalyst is operated with an oscillating air/fuel ratio at slightly rich conditions, the... 

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