Pulse-shaping modification

A simple pulse-shaping modification can be added to the Bessel-Thompson delay filter by using an additional operational amplifier. Resistors are used to divide down the supply voltage to half the output voltage of the delay filter, and its response is then compared with the delay filter s response, which results in a time-delayed square wave. The schematic of this circuit is shown in Fig. 3.31. This simulation also allows us to compare the operational amplifier models that came with each software package. The response of this circuit is driven from rail to rail, providing the saturation voltages of the models. Also, the slew rate of the output should be consistent with the measured and... 

R. D. Klafter and L. Hrebien. An in vivo study of cardiac pacemaker optimization by pulse shape modification. IEEE Trans Biomed Eng, 23(3) 233-239, May 1976. 

Both the pulsed and cw lasers were used for photodissociation of gaseous ions produced by laser desorption. The cw laser had a maximum output power of 50 watts at 10.61 micrometers and a beam diameter of 6 mm. The pulsed laser produced 2.6 joules in a pulse of 1 microsecond duration at 10.61 micrometers and had a 2 x 3 cm rectangular beam shape. Modifications of the FTICR vacuum chamber that facilitate ion irradiation have been reported previously (13). 

More elaborate pulse shapes have been developed over the years which aim to produce a near top-hat profile yet retain uniform phase for all excited resonances within a predefined frequency window. These operate without the need for purging pulses or further modifications, allowing them to be used directly in place of hard pulses. They are typically generated by computerised procedures which result in more exotic pulse envelopes (and acronyms Fig. 9.11) that drive magnetisation vectors along rather more tortuous trajectories than the simpler Gaussian-shap>ed cousins. Trajectories are shown in Fig. 9.15... 

For fibers with parameters of practical interest, the dominant effect of material absorption is the attenuation of total pulse power, together with a slight modification of pulse shape. The change in pulse shape is due to the fact that rays with larger inclinations to the fiber axis on step-profile fibers or with turning points closer to the interface of graded-profile fibers lose relatively more of their power to the cladding. 

In this chapter, the discussion will be focused on the ID TOCSY (TO-tal Correlation SpectroscopY) [2] experiment, which, together with ID NOESY, is probably the most frequently and routinely used selective ID experiment for elucidating the spin-spin coupling network, and obtaining homonuclear coupling constants. We will first review the development of this technique and the essential features of the pulse sequence. In the second section, we will discuss the practical aspects of this experiment, including the choice of the selective (shaped) pulse, the phase difference of the hard and soft pulses, and the use of the z-filter. The application of the ID TOCSY pulse sequence will be illustrated by examples in oligosaccharides, peptides and mixtures in Section 3. Finally, modifications and extensions of the basic ID TOCSY experiment and their applications will be reviewed briefly in Section 4. 

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