Analysing Shaped Pulses

In the literature hard pulses and shaped pulses are usually treated as different entities such that any phase or amplitude modulation of hard pulses is neglected or assumed to be negligible whereas the phase and amplitude variation of a shaped pulse is always emphasized. The truth is that even hard pulses can have a significant phase and amplitude variation particularly at the extremes of their excitation bandwidth. For a comprehensive discussion the reader is referred to section 5.3.1. 

The following Check its will use the Bloch simulator module of NMR-SIM to study and analyse a number of different shaped pulses. Time Evolution, the Excitation Profile and the Rf field profile simulation are illustrated using a 90° Gaussian pulse while an adiabatic CHIRP pulse is used for the Waveform analysis. 

Check it 4.3.3.1 calculates the Time Evolution representation of a 90° GAUSSIAN pulse for a number of different rf offsets and displays the results as a set of lines on the surface of a sphere. 

Repeat Check it 4.3.3.1 and after the spherical representation is generated click on the XY View button in the option bar. Click the X button in the new option bar to display the x-component of the magnetization for the individual offsets as a 3D graph. Now click the Projections button to simplify the display further to a 2D graph. The 3D and 2D representations should be similar to graphs in result.pdf tWe. 

The Excitation Profile calculation displays information similar to the time evolution calculation but the units for the x-axis is now the rf offset instead of time. It also shows the phase modulation of the magnetization vectors derived from the projection of the 3D spherical representation into the x,y-plane. With the exception of the Phase and Phase range display options, the y-axis is scaled in relative units. 

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The entrance optics to the analyser is usually chosen so that it can be tuned to nearly constant transmission over a large energy range. The gun optics is also usually chosen so that the beam can be focussed at the same position with the same image size over a wide energy range. This is necessary in order to avoid distortion of peak shapes and resonance features and inaccuracies in the cross-section measurements. After transmission through the analyser a simple lens transfers the electrons to the surface of an electron multiplier, usually a channeltron, which is operated in the pulse count mode. 

Using this pulse-shape spectrum, the cross-over point between the two detectors was set at a rise-time of 3/ s, shown by the dotted line in the figure. Events with faster rise-times were analysed as coming from the photodiode and were essentially all due to 60 keV events all others were assumed to come from the caesium iodide scintillator. The two types of event were analysed individually in order to obtain raw energy spectra from each detector (also shown in Figure 2). The peaks in the energy spectra were then used to calibrate the energy scales for the two systems. 

Aerosols can be analysed using techniques that are based on the interactions between particles and light The examination of a scattered beam of light by a detector after hitting a particle is the basis for many optical instruments. For example, the number of scattered light pulses is a measure of particle number. Furthermore, the intensity and spatial scattering pattern can also be used for determination of particle size and particle shape, respectively. Optical methods are sensitive and easy to use. These methods are classified into four categories (1) optical particle counter, (2) laser diffractometer, (3) phase Doppler system and (4) intensity deconvolution system. 

Finally, it is of vital importance to analyse the shape and duration of single pulse profiles and this requires a streak camera. Comparative pulse diagnostics studies on our laser oscillator amplifier system have been reported in detail elsewhere (22) and illustrate the need to maintain excellent cavity control (to within y precision) to generate single laser pulses, rather than multiple pulse bursts, whose presence is often masked in the broadened wings n ensemble correlation function... 

The basis for the resistive pulse technique is the resistance pulses which are detected every time a particle passes through the pore. The principal theoretical problem is to determine the increase in resistance of a conducting circular cylinder when an insulating particle is inserted far from the ends. MaxwelP obtained an expression for the effective resistivity of a dilute suspension of small insulating spheres in a solution of known resistivity. Smythe analysed the problem of flow around a spheroid in a circular tube considering also large particle sizes. In the limit of small spheres, Smythe s numerical results confirm the derivation by Maxwell. Golibersuch introduced a shape factor which is a function of particle shape and orientation. 

The TOP mass spectrometer is well suited to the mass analysis of ions produced from a pulsed source. In contrast to scanning mass analysers, the TOP detects all ions sampled from the ion source. Por this reason it is widely used for coincidence PPPICO measurements and various laser ionization experiments. The pulsed nature of synchrotron radiation also lends itself to TOP photoionization studies. Peak shapes for different ions in a TOP mass spectrum can provide valuable information about their kinetic energy distributions. 

Short pulses ( 15 ns) create a plasma of positive and negative ions which are mass analysed by a time-of-flight (TOF) mass spectrometer. Although the mechanism of laser-induced ionization and volatilization of solids is not well known, it is established that the duration and shape of the laser pulse affect... 

Unless it is possible to impose a fixed dead-time on each pulse, which is greater than the maximum analyser conversion time for the particular spectrum, then it is far simpler to use a correction pulser. Electronic pulses, arranged to be as identical as possible to detector pulses in shape (although of constant height) are ipjected into the amplification system at the preamplifier where they become indistinguishable from detector pulses. During their detection and an ysis by the electronic system the injected pulses suffer the same probability of distortion and loss as do detector pulses, and consequently the area of the injected pulse peak in the spectrum will be decreased by the same proportion as a y-ray peak. Thus ... 

The typical sample consists in a 1 cm fluorimetric cell, filled with 3-4 ml solution of the compound under study, on which the laser pulse incides after being focused and shaped to have a rectangular section with a cylindrical lens. The analysed volume is a front cyhndrical portion of the excited solution placed at right angle geometry, as represented in Fig. 8.5. 

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