A myriad of pulses

F nre 10.5. The 90,90, composite 90° pulse compensates for B inhomogeneity by placing the vector closer to the transverse plane. 

Composite pulse Duration Bandwidth Properties References 

15 l247342ig2l8032o342ig2l51247 6.5 2.0 Phase stOTtionless spin-echoes, requires small rf phase shifts [7,8] 

Only a selection of available pulses is presented with the emphasis on compensation for resonance offset effects and on sequences of short total duration. Individual pulses are presented in the form XXyy, where XX represents the nominal pulse flip angle and yy its relative phase, either in units of 90° (x, y, X, —y) or directly in degrees where appropriate. Sequences are split into those suitable for (A) population inversion (act on M ) or (B) spin-echo generation (act on M,y). 

The moral of all this is that considerable care must be taken when composite pulses are introduced into pulse sequences. It is wise to test the compensated pulse sequences vs the original uncompensated sequences on a known sample to see if improvements are achieved in reality. This offers a check on whether the composite elements have been correctly introduced and on whether the spectrometer is capable of correctly executing the desired sequences, many of which demand accurate control of rf amplitudes and phases for extended periods. The experimental performance of the composite pulse itself is best tested with a simple experiment, such as an inversion sequence (180 t, y -90 r-FIDA ) or a spin-echo sequence (90 180 c,y, c, y—FID with 

One complicating factor associated with the implementation of composite pulses arises from the fact that many composite sequences have been designed with a particular initial magnetisation state in mind and may not perform well, or give the expected result, when the pulses act on other states. The two principal applications are the use of composite 180° pulses for population inversion, for example in the inversion-recovery experiment, or in the ubiquitous spin-echo for refocusing, in which they act on longitudinal and transverse 

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Although a series of standard referencing compounds has not been established for solid-state NMR as opposed to solution-phase studies (24), a number of unofficial standard samples are currently being used (25). Table 2 lists a series of compounds, their intended use, and appropriate references further detailing their intended uses and limitations. Additionally, like solution-phase NMR, a myriad of solid-state NMR pulse sequences exist that selectively investigate the sample of interest. A number of these pulse sequences are described within this Experimental section with further discussion outlined in the Applications section of this work. 

Metal nanoparticles can be prepared in a myriad of ways, e.g., by pulse radiolysis [110], vapor synthesis techniques [111], thermal decomposition of organometallic compounds [112], sonochemical techniques [113,114], electrochemical reduction [115,116], and various chemical reduction techniques. Some of the most frequently used reducing agents include alcohols [117,118], citrate [119,120], H2 [121], borohydrides [122], and, more recently, superhydride [123]. The chosen experimental conditions determine the size, size distribution, shape, and stability of the particles. Because naked metal particles tend to aggregate readily in solution, stabilizing the nanoparticles is the key factor for a successful synthesis. Sometimes the solvent can act as a stabilizer, but usually polymers and surfac-... 

What neither they nor Dariat quite appreciated were the myriad number of physical interfaces between the neural strata and Valisk s communications net. The tube trains and the starscraper lifts were the most obvious examples, but every mechanical and electronic utility system had a similar junction, a small processor nodule which converted fibre optic pulses to nerve impulses and vice versa. And Magellanic Itg not only built Valisk s communications net, it also supplied ninety per cent of the counterrotating spaceport s electronics. A fact which even fewer people were aware of was that every company processor had a back-door access function hardwired in, to which Rubra alone had the key. 

We have recently developed a small amplitude current-pulse method which is uniquely suited for solving the myriad problems associated with electrochemical analyses of electronically conductive polymers (30, 31). 

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