Spectral efficiency

The photoionization efficiency is defined as the number of ions, produced by one incident photon on unit path length at unit gas pressure. The curves in Figures 3-6 represent spectral efficiency curves. On them the ratio of the measured photocurrent to the number of incident monochromatic photons is plotted as function of the photon energy (in e.v.). At the low pressure used in the mass spectrometer (< 10 3 torr) the efficiency curves are proportional to the photoionization cross-section curves.3... 

In addition to the positively charged parent molecules, there appear under the action of the same photon energies, but in a much smaller proportion (0.5 to 1%) than the former, positively charged fragments, in which the parent molecule has additionally lost a hydrogen atom. Their spectral efficiency curves, magnified 10- to 75-fold are shown below that of the simple photoionization. 

Fig. 6. Spectral efficiency of the photoionization processes in benzylamine vapor...

The kinetic spectrum reveals more peculiar details than the usual spectral efficiency curve of the external photoeffect. For example, the kinetic spectra for pinakryptol and pinacyanol are quite different, whereas the efficiency curves are much alike.45... 

Lyons and Morris,42 working with hydrocarbon monocrystals, obtained on the spectral efficiency curves two thresholds at 6.4 and 7.7 ev, for anthracene and at 6.0 and 7.3 e.v. for tetracene. Their difference, equal to 1.3 e.v., is in good agreement with the first energy loss, obtained from the kinetic spectra. 

Obtaining product energy distributions from the intensities of chemiluminescence spectra is relatively straightforward, requiring a knowledge of the appropriate transition probabilities and the spectral efficiency of the detector. One complication that can arise in the analysis of chemiluminescence data is the possibility of cascading an emitting state... 

This type of echelle grating and order separation gives rise to the most sensitive analytical line(s) that can be chosen for any element. High spectral efficiencies can be obtained across the entire wavelength due to the use of multiple orders. 

The surface coverage in both experiments was less than monomolecu-lar. Such photodissociation experiments with the sensitive EPR method have to be substantially improved by spectral efficiency measurements. 

In this case the geometry is quite poor and it is preferable to measure the relative spectral efficiency function by making use of chemiluminescent reactions whose emission spectra are known precisely, i.e. the Luminol chemiluminescence and the firefly bioluminescence. 

Bandwidth is defined as the range of positive frequencies occupied by a signal. Thus, for the baseband signal shown in Fig. 12.9(b), the bandwidth equals the highest frequency present, B Hz. By comparison, the modulated signal shown in Fig. 12.9(c) has a bandwidth of 2B Hz, which occupies double the bandwidth of the baseband signal and, therefore, represents poor spectral efficiency. 

Spectral efficiency is a function of the modulation system used. Among the modulation formats that have been evaluated for DAB transmission are QPSK, M-ary QAM, and MSK (Springer, 1992). Using these and other formats, digital transmission systems that use no more spectrum than their analog counterparts have been designed. 

The spectral efficiency of a flare composition is closely related to the combustion enthalpy of the flare composition, the plume temperature and the spectral emissivity of its combustion products as described in Eq. (10.18)... 

Table 10.1 Enthalpy of combustion, spectral efficiency and fraction of radiation in band of interest under static conditions [25, 26],...

Figure 10.18 Spectral efficiency of MTV in two bands as a function of Mg content [25).

Long-burning formulations for infrared tracking flares typically comprise burn rate modifiers that extend the burning time. For this purpose, barium stearate has been proposed. Figure 10.20 shows the effect of stearate content on both normalized burn rate and spectral efficiency. Whereas the burn rate drops to levels of 20% of the unaffected composition shown below, the spectral efficiency climbs up to levels of 140% [28]. 

Graphite is a good thermal conductor, with thermal diffusivities in the order of 0.6-0.9cm s K As such, it is useful to increase the thermal conductivity of a pyrolant grain [29]. At a 5% weight level, it causes an increase in burn rate but does not affect the spectral efficiency (Table 10.3). 

Figure 10.20 Normalized spectral efficiency and burn rate of MT-based formulation modified with barium stearate [28],...

Even though burn rate is increased, this occurs at the expense of spectral efficiency, as is depicted in Figure 10.22. 

Table 10.6 Spectral efficiency and radiance in two band pass ranges.

The radiant intensity profile for equal amounts of standard MTV decoy flare mix with the above composition is depicted in Figure 10.23. The spectral efficiency for the latter is about twice ( 2.03) in the 2-2.6 pm band. This is due to the much higher Mg content in MTTP formulation (66 vs 54wt% Mg). However, despite the high Mg content, the latter formulation shows a very slow rise in intensity, indicating a slower burn rate. Thus this material would require a different grain geometry to meet with operational rise time specifications. 

Binder (vrt%) Softening agent (wt%) PTFE (wt%) Mg (wt%) Modifier (wt%) Normalized burn rate (mm ) Radiant intensity (Wsr- ) Spectral efficiency Og- sr-i)... 

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