Peak, asymmetrical symmetrical

Thus, for the second-order desorption kinetics and the hyperbolic heating schedule, the peaks are symmetric about Tm in the scale (1/T). The first-order peaks are asymmetric in this scale, exhibiting a steeper descent than ascent. These considerations suggest that the hyperbolic heating schedule is especially favorable for an analysis of the peak shapes and for the detection... 

The perpendicular drop should only be used if (1) the peaks are symmetrical and about the same height and width, (2) the valley between the peaks is no more than 5% of the peak height, (3) the baseline is flat, and (4) noise does not obscure the accurate placement of the baseline. If the peaks are asymmetrical, a perpendicular drop will overestimate the area of the smaller peak. Under those circumstances, a tangential skim may be a better approach. 

Not all experimental peaks are symmetrical around their center, and there are various schemes to generate skewed curves to fit such asymmetric experimental data. For example, Losev (Applied Spectrosc. 48 (1994) 1289) used a function of the form... 

The main spectral features that were identified for DIMP and DMMP were at 1000 and 1050 wavenumbers, respectively, assigned to the P=0 stretches. Other peaks such as the asymmetric/symmetric methyl C-H stretches at 2975 and 2950 cm could also be used to aid in the identification. The negative peaks between 1200-1300 wavenumbers correspond to the dominant C-F stretch from the HC polymer and are present as a result of the computer s overcompensation for these peaks when a new background was taken after the polymer was applied to the diamond window. 

Equation (4.10) applies only to symmetrical peaks. Asymmetrical peaks show that infinite dilution has not been attained and the more general eqn (4.8) should be used. The asymmetry originating in kinetic factors or those not depending on the column may not be api)lied in any theory and therefore it should be avoided, for instance by utilizing low flow rates. In the following is assumed that the asymmetry of peaks is not due to these factors. 

If the DSC peak is symmetric and the exotherms are uniformly spaced with heating rate, as in Fig. 2.77, it is reasonable to expect E to be constant to within 10%. An asymmetric peak, a peak with a shoulder, or two exothermic peaks indicate that E will most likely not be constant. 

The chemical structure of PI and silica/PI composite films was characterized with Fourier transform infrared (FTIR) spectroscopy, and the results are shown in Figure 13.5. The characteristic peaks of symmetric C—O stretching and asymmetric C-O stretching of the imide group are clearly visible near 1720 and 1780 cm , respectively. The assignment of stretching of the imide ring is at approximately... 

A current wave propagating symmetrically about its zero axis, i.e. when the envelopes of the peaks of the current wave are symmetrical about its zero axis, is termed symmetrical (Figure 13.24) and a wave unable to maintain this symmetry is termed asymmetrical (Figure 13.25). 

The order of the desorption process is estimated in the first place from the shape of the desorption peak, preferably in the l/T scale. The first-order peaks here are clearly asymmetric, the falling branch being steeper than the ascending one. The second-order peaks are near symmetric and are broader. The third-order peaks are even broader and are again asymmetric, but in this case the ascending branch is steeper than the falling one. 

We may contrast this behavior to that found for AOT. As shown in Figure 1, the chromatograms for AOT exhibit sharp fronts and somewhat diffuse tails, intermediate in shape between the symmetrical peaks typical of conventional solutes and the highly asymmetric chromatograms obtained for sodium dodecyl sulfate micelles in water (15). In addition, the concentration dependence of Mp" for AOT is gradual, not abrupt as for lecithin. These differences may be attributed to the lability of the AOT micelles which makes the observed retention time quite sensitive to the initial concentration (12) and leads to broadened chromatograms. 

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