Pulsed process

Ultrasonic pulses are generated within the sample on the transducer s resonance frequency, pass through sample and are received by the wideband receiver. After received pulse processing in the computer, results analysis is carried out. 

The construction of a TXRF system, including X-ray source, energy-dispersive detector and pulse-processing electronics, is similar to that of conventional XRF. The geometrical arrangement must also enable total reflection of a monochromatic primary beam. The totally reflected beam interferes with the incident primary beam. This interference causes the formation of standing waves above the surface of a homogeneous sample, as depicted in Fig. 4.1, or within a multiple-layered sample. Part of the primary beam fades away in an evanescent wave field in the bulk or substrate [4.28],... 

Quantitative Analysis. The efficiency of the detector is such that almost 100% of the X-rays entering it will produce a pulse, but the pulse processing speed limits the rate at which X-rays can be counted. If the count rate is less than a few thousand counts per second, then most of the incoming pulses are processed, but as the count rate rises an increasing fraction of the pulses are rejected. The live time during an analysis when the detector was counting is thus less than the elapsed time, and the EDS system records both times in order that the true count rate may be measured. 

Analyze on a flow cytometer (see Notes 9 and 10). This type of staining can be analyzed on any of the modem flow cytometers with the proviso that the machine is equipped with a pulse processing facility to enable the discrimination of cell doublets. The most commonly used flow cytometer is the Becton Dickinson FACScan. In this machine, PI should be collected into FL3 rather than FL2 to overcome any crossover of the FITC into the FL2 channel The FL3 detector should be routinely set around 400, whereas FL1 is usually set at around 500 in linear amplification Controls, without either BrdU or the monoclonal antibody, should be included whenever possible to determine the lower limits of detection of the DNA precursor. At least 10,000 events should be analyzed, but more might be required in the case of slowly proliferating (low BrdU incorporation) tissues or tumors. 

TABLE 18.1 Summary of Common Pulse-Processing Modules... 

As well as software-based aggregate subtraction, so-called pulse processing (or, more recently, digital) electronics can give us help in this task. In general, particles (cells or nuclei) give out signals that... 

These assumptions facilitate use of the theory of linear transformation of determinate, fluctuating, and pulse processes both to ascertain function Tj(t) in (5.34) with U and r] given, and to identify field Uj from the results of radiometric measurements. 

Abstract Measurement of the effective acquisition time of a spectrum by the pulser method is described. The measurement results were verified up to count rates of 12000 s1 at various settings of the pulse processing electronics and spectral shapes. Systematic effects of up to 2% were observed. The clocks in the spectrometers were calibrated by counting pulses generated by the DCF 77... 

The counting conditions, such as the count rate, spectrum shape and settings of the pulse-processing electronics influence the shape of the pulser peak. In Fig. 1 various shapes of the pulser peak measured at low count rates are presented. The spectra A and B were measured with the channel width of 0.1 keV on a low-volume ger-... 

TOF analysers are directly compatible with pulsed ionization techniques such as plasma or laser desorption because they provide short, precisely defined ionization times and a small ionization region. However, to take advantage of TOF analysers, it is interesting to combine such powerful analysers with continuous ionization techniques. These ionization techniques can be compatible with TOF analysers but require some adaptations to pulse the source or to transform a continuous ion beam into a pulsed process. For instance, the coupling of an ESI (or any other API) source with a TOF mass spectrometer is difficult, because ESI yields a continuous ion beam, whereas the TOF system works on a pulsed process. 

In Sec. V we extend the treatment of Sec. IV to the purification of unpolarized racemic mixtures. We show that when the three laser polarization directions are mutually perpendicular (thus forming a system of axes with definite handedness) one can purify ordinary (unpolarized) racemic mixtures. In accordance with the general theorem of Sec. II, a change in the handedness of the three polarization vectors results in a change in the handedness of the enantiomer to which the racemic mixture is being converted. It then follows that, as discussed in Sec. VI, enantioselectivity can also be achieved by a two-pulse process performed on a sample in which the axis of the molecules (rather than their M projection) has been preoriented. 

Fig. 6 Schematic of a FTICR MS instrument. This type of MS consists of an ion cyclotron resonance (ICR) analyzer cell that is situated in the homogeneous region of a large magnet. The ions introduced into the ICR analyzer are constrained (trapped) by the magnetic field to move in circular orbits with a specific frequency that corresponds to a specific mass-to-charge ratio (m/z). Mass analysis occurs when radiofrequency (rf) potential is applied (pulsed) to the ICR analyzer so that all ions are accelerated to a larger orbit radius. After the pulse is turned off, the transient image current is acquired and a Fourier transform separates the individual cyclotron frequencies. Repeating this pulsing process to accumulate several transients is used to improve the signal-to-noise ratio. (Courtesy of Bruker Daltonics, Billerica, MA.)...

Zhang, Q.H., Qiu, X., and Sharma, S.K. 1997. Recent development in pulsed processing. Washington, DC National Food Processors Association. New Technologies Yearbook. 

Resolution in a semiconductor detector EDXRF system is a function of both the detector characteristics and the electronic pulse processing. The energy resolution of semiconductor detectors is much better than either proportional counters or scintillation counters. Their excellent resolution is what makes it possible to eliminate the physical dispersion of the X-ray beam without the energy resolution of semiconductor detectors, EDXRF would not be possible. 

Factor for pulse losses and discrimination in the pulse processing system p The radionuclide and the sample affect the following ... 

In addition, the pulsing process requires sophisticated electronics which must prove durable over many years. They are likely to be less reliable than transformer rectifier systems providing straight DC for impressed current cathodic protection. 

The Bosch process results in scalloping side-walls due to the pulsed process. This limits its applications in optics, and some fluidic devices are also sensitive to sidewall roughness. The amplitude of scalloping can be minimized by shortening the pulse lengths, and this minimizes the amplitude as well, and 20 nm can be obtained. However, etch rate will be sacrificed. Scallops can also be treated after etching by thermal oxidation or wet etch smoothing. 

The extreme action effects of structures are caused by service and chmate loads and may be modeled as intermittent rectangular renewal pulse processes. Therefore, it is e q)edient to treat the safety margin of particular members as a random sequence. The revised values of instantaneous survival probabihty of particular members may be analyzed by the concepts of truncated probabihty distribution and Bayes theorem. The presented new design methodology based on conventional resistances, rank sequences, correlation factors and transformed conditional probabihties may be successfully used in the prediction of long-term survival probabilities of members and their systems during residual service Ufe. 

Selection of a relatively long time constant for the integration of the detected signal in the main pulse processing amplifier. 

With these features, the overall resolution of a Si(Li) detector and pulse processing system used in XRF applications measured as the full-width at halfmaximum (FWHM) of the Mn K-L2,s (Ka) line at 5.9 keV is typically 140-155 eV (noting that < 120 eV FWHM is technically feasible). 

Spectral artifacts are peaks that are not present in the source fluorescence spectrum but result from idiosyncrasies in the response of the detector and pulse processing system (such as the sum peaks referred to above). Their presence can cause ambiguities in the... 

Figure 8.26 Schematic of the pulse processing of an MCA. (a) The coins (photons) are separated by denomination and binned, (b) second from the bottom The number of coins gives a stack height (counts). The typical EDXRF output is the lower-right plot of counts per second versus energy.

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