Waveform, broadband

The best empirical values for this spectral parameter vary somewhat due to experimental technique, particularly due to the solvent used. Although rounded due to the width of the spectral filter used, the values of Wald Brown are still the most widely quoted118. They are a = 447 nm, b = 502 nm, c = 549 nm. It would be easily to interpret the median of this waveform at the mean of the two half-amplitude points, 498 nm. It is common to find the waveform shifted slightly to a center wavelength at 495nm. However, the 502 nm wavelength is frequently reported in an attempt to relate it to the peak of the scotopic spectrum when that spectrum is measured with a broadband spectral filter. 

Stored waveform inverse Fourier transform (SWIFT) pulses [17] have been applied as a means of broadband ejection of matrix ions generated by Cs+ desorption [18]. These pulses are generated by taking the inverse Fourier transform of the desired frequency domain spectrum and applying the stored time domain waveform to the endcap electrodes via an arbitrary waveform generator. The magnitude of the SWIFT pulse determines the degree of excitation for ions of specific secular frequencies. 

Shaped pulses are created from text files that have a line-by-line description of the amplitude and phase of each of the component rectangular pulses. These files are created by software that calculates from a mathematical shape and a frequency shift (to create the phase ramp). There are hundreds of shapes available, with names like Wurst , Sneeze , Iburp , and so on, specialized for all sorts of applications (inversion, excitation, broadband, selective, decoupling, peak suppression, band selective, etc.). The software sets the maximum RF power level of the shape at the top of the curve, so that the area under the curve will correspond to the approximately correct pulse rotation desired (90°, 180°, etc.). When an experiment is started, this list is loaded into the memory of the waveform generator (Varian) or amplitude setting unit (Bruker), and when a shaped pulse is called for in the pulse sequence, the amplitudes and phases are set in real time as the individual rectangular pulses are executed. 

R.K. JULIAN and R.G. COOKS develop broadband excitation of ions using the stored-waveform inverse Fourier transform (SWIFT) [67],... 

This equation, demonstrated in [62], is indeed independent of the m/z ratio. Thus broadband excitation will bring all the ions onto the same radius, but at frequencies depending on their m/z ratio, provided that the voltage is the same at each frequency. This can be best performed by applying a waveform calculated by the inverse Fourier transform, namely SWIFT [63], As usual for a technique based on Fourier transform, the resolution depends on the observation time, which is linked with the disappearance of the detected signal (relaxation time). Here the disappearance of the signal mainly results from the ions being slowed by... 

Llewellyn, S. K., Broadband magnetic waveforms radiated from lightning, M. S. Thesis, Florida Institute of Technology, Melbourne, Florida, 1977. 

Tomographic results. Upper-mantle velocity structure (James et al. 20016) was determined by tomographic techniques based on the analysis of delay times from teleseismic broadband waveform data. Relative arrival times of phases P, PKPdf, S and SKS were retrieved via a multichannel cross-correlation procedure using all possible pairs of waveforms (VanDecar Crosson 1990). This procedure produces highly accurate delay times, with typical standard errors for the... 

Owens, T. J. 1987. Crustal structure of the Adirondacks determined from broadband teleseismic waveform modeling, Journal of Geophysical Research, 92, 6391-6401. 

To perform broadband FTMW spectroscopy we require a microwave source that can produce phase-locked linear frequency sweeps over an 11 GHz frequency range in times ranging from 100 ns to 1 ps (sweep rates of 10 ° - lO" MHz/s). The short sweep durations are required so that the sample is polarized on a time scale faster than the pure dephasing of the rotational free indnction decay (FID). Traditional microwave synthesized sweepers are typically limited to sweep rates of about 10 MHz/s. We have developed a microwave source based on a 4 Gs/s arbitrary waveform generator that can produce the required excitation pulses. A schematic of the microwave source is shown in Figure 1. 

Equipment modifications are needed for a white light bias (see optional equipment in Fig. 7.1). The experiment requires a low noise broadband DC illumination, while simultaneously illuminating the sample with chopped ( AC) monochromatic light. The waveform of the chopped monochromic light must be monitored to verify that the chopping speed is low enough for the sample response to reach steady state. The bias level should be set to 37 % of the expected j c [2-4]. 

Wells proposed an ion isolation method [33], which consisted of two steps for the isolation of precursor ions. The method employed a modified mass-selective instability technology (axial modulation technology) to ejea sequentially ions with m/z less than that of the molecular precursor ion, M+, for example. Combined with an empirical calibration procedure, ions with mass/charge ratio > M Th are ejected resonantly with a broadband waveform. Figure 15.17 shows the scan function of this isolation method. 

FIG U RE 15.17 The process of ion isolation is execnted seqnentiaUy. First, lower masses are ejected with a modified mass-selective axial instability scan that is, essentially, the same as normal analytical scanning. Second, higher masses are ejected resonantly with a broadband waveform. The ejection order may be reversed to avoid product ions of higher m/z-values. WFl is a notch waveform to eject unwanted ions during ionization and the post-ionization period WF2 is a broadband waveform to eject higher mass ions during higher mass isolation period. 

Usually, ions of tn/z 69 and 414 from the calibration chemical PFTBA are used to find the values for the two parameters, A and B. The trapping frequency calibration is carried out near = 0.845 at a fixed RF trapping field. A linear relation between q xm and RF c is true only under ideal conditions but, as a first-order approximation, it works well for this two-step isolation method in a non-ideal quadrupole ion trap. Typically, in an ion trap for which the oscillation frequency of the RF potential is 1 MHz, the frequency error of the calibration is less than 1 kHz, which corresponds to an error of < 1 Th in the high-mass isolation step. The amplitude of the broadband waveform is determined empirically by the manufacturer and can be accessed by users. 

FIGURE 15.19 The frequency spectrum of the broadband waveform used to eject higher mass ions. The expanded view of the spectrum (bottom right corner) showed clearly that the spectrum tailed into higher frequency area. 

Wang, M. Lee, D. Newton, K. Schachterle, S. High-Resolution Ion Isolation Utilizing Broadband Waveform Signals, US Patent 2008, 7,378,648. 

The detector D is often a broadband diode or photomultiplier tube, followed by waveform-shaping electronics and an amplifier, a signal-averager such as a boxcar integrator, and a chart recorder. Scattering from windows, lenses, etc. can lead to contamination of the spatially-filtered coherent antiStokes beam at O3 by components of the to, and to2, beams, which can be suppressed using a dispersive element such as a prism P or a spectrometer in front of the detector. 

If a signal-based approach is used, the waveforms recorded by the sensors (preferably broadband sensors) need to be analyzed. A suite of analysis procedures exists to evaluate fracture parameters. The first step in the analysis is usually the 3D localization of the rupture. More advanced analyses may then be applied, for instance, source mechanism calculations. 

In contrast, MFI involves the application of a resonant excitation waveform consisting of several frequency components while the value of is held constant. The frequency components of the waveform bracket the entire anticipated range of the secular frequency so as to compensate for frequency shifts. Other variants of multi-frequency irradiation (March 1998) include random noise, swept frequency and broadband excitation. A rather different ion activation method (Paradisi 1992, 1992a Curcuruto 1992) is accessible with ion trap instruments equipped with a DC power supply so that non-zero values of U and thus a are available. The method involves moving the working point of a given ion species to either the P,. or the p, boundary of the stability diagram... 

---