Discriminator, pulses processed

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. 

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

The digital form of the signal facilitates its further processing. The discriminator pulses can be directly fed into a computer that analyzes the data and may control the experiment [4.146]. 

FIGURE 4.5 Pulses processed by (a) a low-level discriminator, and (b) a constant-fraction discriminator. 

Figure Bl.10.2. Schematic diagram of a counting experiment. The detector intercepts signals from the source. The output of the detector is amplified by a preamplifier and then shaped and amplified friitlier by an amplifier. The discriminator has variable lower and upper level tliresholds. If a signal from the amplifier exceeds tlie lower tlireshold while remaming below the upper tlireshold, a pulse is produced that can be registered by a preprogrammed counter. The contents of the counter can be periodically transferred to an online storage device for fiirther processing and analysis. The pulse shapes produced by each of the devices are shown schematically above tlieni.

Discrimination in radiation detection circuits refers to the process of distinguishing between different types of radiation on the basis of pulse height. A discriminator circuit selects the minimum or maximum pulse height that is to be counted. 

The nonresonant background in CARS spectroscopy originates from instantaneous four-mixing processes, while the resonant contribution involves real vibrational states. This provides a basis for possible discrimination against the nonresonant background. To do so, one has to come up with a pair of pulses that excite the vibrational state, and the third, time-delayed pulse will only contribute to the resonant part of the CARS signal. However, to make this scheme work efficiently, one has to overcome certain obstacles. To achieve high spectral resolution, the bandwidth of the third pulse should... 

The 5 ns pulses of about 10 electrons released at the anode by a photon absorbed by the photocathode of a PM tube can be used to count photons. In such instruments the intensity of light is displayed as a count per second which varies between about 15 (dark count) and 105. A photon-counting detector system is of course much more complex than the simple PM/ampli-fier used in conventional spectrofluorimeters. Figure 7.27(a) is a block diagram of such a photon counter (b) gives a simple illustration of the important process of pulse selection through a discriminator. The output of... 

The diffracted X-radiation is detected by Geiger, proportional, or semiproporhonal detectors. See Fig. 10. The detector of each monochromator generates pulses, which are a measure of the intensity of radiation of each wavelength. The pulses are filtered through a discriminator in order to avoid undesired interferences. Pulses shrinking due to an increase of frequency of pulses is automatically compensated. Collected pulses are transferred to a computer for processing and output. See Fig. 11. 

All the experiments reported here are on vibrations with near-zero depolarization ratios (Table 1). In this case, the excitation pulse pairs must have the same polarization, but the relative polarization of different interactions is unimportant. In practice, we take all excitation polarizations perpendicular to the plane of the excitation beams and the Lm polarization parallel. In this configuration, the signals with parallel polarization are only generated by scattering from Lm. A polarizer is placed in the signal beam to provide additional discrimination against competing nonlinear processes. 

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