Virtual pulse generator

Figure 4.40 The function of the virtual pulse generator. Adapted by permission from a Canberra Nuclear Application Note...

VPG Virtual Pulse Generator A concept used in a version of loss free counting. 

The idea of using phase increment to achieve frequency-shifted excitation can be extended virtually to any sort of RF pulses, including the most complicated adiabatic inversion pulses where a non-linear phase increment has already been applied. Using the phase increment, double or multiple pulses can be constructed with only a single waveform generator in order to excite different regions of a NMR spectrum or to compensate the BSFS, BSPS, as well as BSOS. 

The use of variable spin system parameters and the visualization of magnetization vectors using the Bloch simulator module require additional commands to be implemented in the NMR-SIM pulse programs that do not appear in the standard BRUKER pulse programs. The increment or decrement of a spin system parameter is triggered by a command line in the pulse program. The Bloch simulator module uses the increment of the virtual chemical shift to generate the offset dependence of a pulse. 

In air-saturated seawater samples with small a terms (low pH or C02-free removal, hence giving the best constraints on the B term). fc(2)/c values are very similar to those for pure bromide solutions (stippled area in Fig. 2). This consistency strongly supports the identity of the major transient Br2. The close comparability between the Icinetic parameters fit to the data by the flash photolysis of aerated seawater (no OH generated) and those fit to transients initiated by pulse radiolysis (no direct Br oxidation, OH the initiating radical) strongly buttresses this conclusion. Finally, the a values obtained in flash experiments using air or nitrous oxide at constant pH near 8 are virtually identical to each other and to those from pulse radiolysis. 

Recently, the superoxide dismutase activity of low molecular mass copper chelates in the indirect coupled assay systems has been dispute It was demonstrated that copper in CuSO and Cu(II)(gly)2 prevents the ferricytochrome c and nitroblue tetrazolium reduction. This is not virtually new, as it is a well known phenomenon that Cu(II)-salts lead to a reoxidation of ferrocytochrome c and that they are potent inhibitors of xanthine oxidase which is often used as Oj" -generator in indirect SOD assay systems Although the indirect assays may be sometimes inadequate for the measurement of the SOD-activity, there are no doubts that low molecular mass copper chelates have their superoxide dismutase during pulse radiolysis. 

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