Peak, asymmetrical shape, calculated

Table 2 shows that the size of microcrystalls is higher for precipitated fullerene than for C6o. The diffraction peak (111) has a shoulder at a lower angle, which is more pronounced for precipitated fullerene. According to [21] the asymmetric shape of (111) peak and the appearance of small peak marked by asterisk on the Fig. 2 could be associated with the distortion caused by the formation of two layer extrinsic hexagonal lattice in terchanged with normal fee lattice of C6o. The lattice parameter of precipitated fullerene calculated from the X-ray diffraction pattern a0 = 14.19 A is distinctly larger than that for pure C60 (a0 = 14.15 A). Most probably the gas atoms occupied octahedral lattice sites during crystallization and caused the lattice parameter increase observed in Ar, O2 or N2 fullerenes in comparison with pure C6o-... 

The observed cross sections for the 18s (0,0) collisional resonance with v E and v 1 E are shown in Fig. 14.12. The approximately Lorentzian shape for v 1 E and the double peaked shape for v E are quite evident. Given the existence of two experimental effects, field inhomogeneties and collision velocities not parallel to the field, both of which obscure the predicted zero in the v E cross section, the observation of a clear dip in the center of the observed v E cross section supports the theoretical description of intracollisional interference given earlier. It is also interesting to note that the observed v E cross section of Fig. 14.12(a) is clearly asymmetric, in agreement with the transition probability calculated with the permanent electric dipole moments taken into account, as shown by Fig. 14.6. 

Fig. 10.7 compares the calculations of Brauner et a/, with the distorted-wave Born approximation and the approximation to (10.13) of Curran and Walters (1987) for a coplanar-asymmetric experiment on hydrogen at Eo = 150 eV. No calculation yields fully-quantitative agreement with experiment in the peak for small values of p, but all describe the relative shape. The cross section that is observed at much larger p is not well described by the distorted-wave Born approximation, but the other two calculations predict the trends better. 

Asymmetry factor, Ai The plate number, N, assumes that the peak shape is Gaussian, but in practice this is rare. It is more hkely that the peak is asymmetrical, i.e. it tails . This is quantified using the asymmetry factor. As, calculated as shown in Fig. 31.7. 

The retention time is determined from the peak maximum in the case of symmetrical peak shapes. For well-packed columns symmetrical peaks should be achieved as long as the amount injected into the column is in the linear concentration range of the adsorption isotherm. If increased amounts of substances in the nonlinear concentration range of the adsorption isotherm are injected the peak is often heavily distorted and asymmetric. In that case the retention time has to be calculated from the centroid following the momentum method (Eq. 2.27). 

Barnett, D.A., Guevremont, R., Purves, R.W., Determination of parts-per-trillion levels of chlorate, hromate, and iodate hy electrospray ionization/high-field asymmetric waveform ion mohility spectrometry/mass spectrometry. Appl. Spectrosc. 1999, 53, 1367. Guevremont, R., Purves, R.W., Comparison of experimental and calculated peak shapes for three cylindrical geometry FAIMS prototypes of differing electrode diameters. J. Am. Soc. Mass Spectrom. 2005, 16, 349. 

If the peak of a test sample is not close to Gaussian shape, errors in the calculation may result. A column that gives an asymmetrical band sometimes has a high value of N in spite of peak tailing. To account for unrealistically high plate numbers for the asymmetrical band, the next equation has been proposed [ref. 10]... 

The diffusion coefficient of n-tetradecane on polystyrene in a fluid-viscous state calculated from free volume shows a sudden increase near Tg this behaviour was marked by its temperature dependence [219]. The introduction of diffusion coefficients into kinetic theory (which governs the shape of peaks [218]) yields very broad and asymmetric peaks above T,. This simplified model ignores adsorption and therefore fails to explain the behaviour of the retention volume at and below Tg. 

A presence of aluminium affects the position of the first peak, and changes its shape. Compared with the DSC profile of pepsin for all Ah+ concentrations (1, 5, 10 mM) the first peak becomes more broadened and asymmetric. Van t Hoff enthalpies calculated for the first transition temperature are more than twice larger than calorimetric enthalpies observed for the same transition temperatures. For these transitions calorimetric and van t Hoff enthalpies are calculated and are presented in Table 1. 

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