Time signal equivalence

To unambiguously identify the presence of a peak and, in addition, be able to give some proximate estimation of its size for quantitative purposes, the peak height needs to be at least 5 times the noise level. The detector sensitivity, or the minimum detectable concentration, (Xd), is defined as that concentration of solute that will give a signal equivalent to twice the noise level and, consequently, the concentration of solute at the limiting (k ) value must be 2.5Xd. 

Although the boron atoms in B9CI9 are not equivalent (three B atoms are of connectivity four, and six atoms of connectivity five), the 11B NMR spectrum shows only one signal. This indicates that the compound is fluxional in solutions making all boron atoms on the NMR time scale equivalent [138]. 

Transient Time domain signal equivalent to the ion image... 

Figure 2. Neon spectra (hollow cathode emission) acquired with an SIT detector cooled to —50°C. (a) Real-time detection, 20 ms/scan, neutral density filter (ND) = 0 (b) Readout, after signal integration for 20 seconds (c) Integration equivalent to 10s scan periods. ND filter = 5 (0.001% transmission) was used to attenuate the signal. Equivalent dark spectra were subtracted from each neon...

The peak represented 3 pm of material and, taking the concentration at the peak maximum as twice the peak average concentration, the peak maximum concentration was about 8 pm/ml. The peak height appears to be about three times the noise and so the sensitivity (that concentration that will give a signal equivalent to twice the noise) is about 5.3 pm/ml or in more standard terms 5.3 x 10 g/ml. As the chiral detector is a bulk property detector, a sensitivity of 5.3 x 10 g/ml seems more realistic. Nevertheless, this sensitivity is a great improvement on many chiral detectors previously described. 

The silicon intensified target (SIT) vidicon has a number of unique properties which make it a valuable detector for atomic spectroscopy. The SIT vidicon provides two-dimensional photoelectric detection with high sensitivity and rapid signal readout. Time resolution can be obtained in a time-resolved (real time) mode on the millisecond scale and in a time-gated (equivalent time) mode on the submicrosecond scale. 

The long absorption cells naturally lend themselves to a hollow-cathode discharge configuration for the study of molecular ions. A preliminary experiment revealed the HCO line at 1 THz with a signal-to-noise ratio (100 1 with a 1 s time constant) equivalent to that obtained using the laser sideband technique (16). Possible transitions in H2D and OH have also been observed however they are weak and only tentatively identified, and further work is underway. 

The LPl characteristics of DSSS systems can be observed in the spectra of Fig. 12.76. Since the chip time of the PN generator is much less than the symbol time of the message source, the PN spectrum is much wider than the NB signal. From basic Fourier transform theory, we know that multiphcation in time is equivalent to convolution in the frequency domain. Since the NB signal spectra is narrow compared to the spreading code, it will act almost the same as an impulse function. The result of the convolution will essentially be the PN spectrum shifted to the carrier frequency. This very wide bandwidth signal will resemble thermal noise over than bandwidth of the receiver. 

The relative number of equivalent nuclei associated with each chemical shift is obtained from the integrated spectmm by normalizing the areas so that the area corresponding to the smallest peak in the spectmm is defined as 1. This relation may not be exactly correct in ft experiments where signals may be affected by significant differences in relaxation times for nuclei in different environments. 

Resonance theory can also account for the stability of the allyl radical. For example, to form an ethylene radical from ethylene requites a bond dissociation energy of 410 kj/mol (98 kcal/mol), whereas the bond dissociation energy to form an allyl radical from propylene requites 368 kj/mol (88 kcal/mol). This difference results entirely from resonance stabilization. The electron spin resonance spectmm of the allyl radical shows three, not four, types of hydrogen signals. The infrared spectmm shows one type, not two, of carbon—carbon bonds. These data imply the existence, at least on the time scale probed, of a symmetric molecule. The two equivalent resonance stmctures for the allyl radical are as follows ... 

Several types of analyzers exist today that allow a time-domain signal to be eonverted to a frequeney-domain speetrum. The resulting speetrum of all speetrum analyzers is equivalent to the amplitude/frequeney plot, whieh is obtained by passing the given signal aeross a set of eonstant bandwidth filters and noting the output of eaeh filter at its eenter frequeney. 

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