Spatial pulse spread

Figure 6.4 displays the result of this statistical analysis for one single thunderstorm. At the location of the laser filaments (arrow head), 43% (3 out of 7) of the pulses are synchronized with the laser repetition rate, corresponding to a high statistical significance (1 — async = 0.987). The delay mismatch between the RF pulses detected on the different LMA detectors correspond to some tens of meters, typical of spatially spread events, such as a series of... 

Due to the distribution of translational directions and kinetic energies and the spatial spread of the ion pulses leaving the ion source, the mass resolution of a... 

Mazo (1998) studied Taylor dispersion in fractal media and found that the proportionality constant between the spatial spreading of a solute pulse and the time depended on both the fractal dimension of the medium and the dimension of the random walk through it. In normal diffusion the average particle position is directly proportional to the time. Diffusion in fractal media is anomalous with proportional to f2/dt, where dt is the random walk dimension. 

In most GC-TOF-MS instruments, an appropriate voltage pulse is applied to accelerate the ions in the direction orthogonal to their initial flight direction. In such oa-TOF-MS a nearly parallel ion beam ideally has no velocity spread, and the finite spatial spread is corrected with a linear or reflecting instrument geometry. Noise-free mass spectra are produced within a very short time (a few milliseconds). Only TOF-MS instruments have the capability required to detect peaks in GC GC since the half widths of the peaks eluting from the second column are of the order of 200 msec. Selecting the proper scan rate is essential since an increase in the acquisition speed... 

Time-of-flight (TOP) mass spectrometers are ideally suited for use with the MALDI technique because of their theoretically unlimited mass range, high ion transmission, and for the pulsed nature of the laser used in this method. Mass resolution is the ability of an instrument to separate the signals from ions of similar mass, expressed as the mass of a given ion divided by the full width at half maximum of the peak (fwhm). Resolution in MALDl-TOP MS is mainly restricted by the ionization process, rather than by instrumental limits, because the ions have a certain time-span of formation, a spatial distribution, and a kinetic energy spread. ... 

MALDI sources are typically used in combination with TOP mass analyzers as a consequence of the inherent pulsed nature of the process due to the short temporal spread (nanoseconds) of the laser sources. The small spatial distribution of desorbed ions further favors the use of TOP analyzers that exhibit both high mass resolution (M/AM == 10,000), mass accuracy (few parts per million), and also high sensitivity [33]. Recently, similar performances have also been obtained by using ion trap mass analyzers [34]. The latter offer an easier access to tandem mass spectrometry (MS/MS) analyses than TOP analyzers. 

In Refs. [466] and [221], the transient grating interferometry signal from the conical intersection dynamics in NO2 (see Sec. 5.4.1.2) was measured for a 401 nm (3.09 eV), FWHM 40 fs pump pulse. The left panel of Fig. 5.33 shows the time-dependence of Im= , t) for the 13th harmonic, which re-hects the time evolution of the diabatic excited state population (Fig. 5.33, right). In the case of ionization out of the same orbital and spatially spread vibrational waveftmction as in the present case, the dependence of di Q,t) on the molecular geometry (vibrational dynamics) was found to be small... 

The X dependence of this function has a form similar to g(x,w) shown in Fig. 6.2. In the present case the curves would be drawn for fixed values of time as a parameter. At small values of n(x,0 would show a sharply peaked form much like the shape of (x,mo). This curve would represent the spatial distribution of neutrons soon after their release from the source plane at x = 0. As t increases, the density function n(x,0 flattens much like the curves for Wi, U2, etc., of Fig. 6.2, indicating that as time progresses the neutrons wander farther from the source plane and tend to spread more evenly throughout the medium. One can also sketch from Eq. (6.32) a density-time function for given x analogous to the curve of Fig. 6.3. Such a curve would show how the density at a specified station would vary as the initial neutron burst passes by. In this case the interpretation of the curve would be as follows At short times after the burst, the neutrons have not yet had time to reach point x, and therefore the density would be low very long after the burst, the neutron density has fallen everywhere because of spreading out and absorption. Thus from the viewpoint of an observer at x, a pulse of neutrons passes sometime after the initial burst at the source. The time at which the maximum neutron density occurs at x is... 

---