Profile asymmetry

Other kinds of defects could give rise to peak broadening, for example the staking faults. In this case, the equation taking into account this phenomenon depends on the peculiar structure of the crystals and the analysis can be more complex some defects, in fact, introduce profile asymmetry and a shift in the position of some selected peaks [26]. 

MAS 01] MASSON O., GUINEBRETIERE R., DAUGER A., Modelling of line profile asymmetry cause axial divergence in powder diffraction , J. Appl. Ciyst., vol. 34, p. 436-441,2001. 

FIGURE 5.7 Schematic illustration of excluded volume effect on movement of spherical antifoam entity in a draining plane-parallel foam film (of 100 microns radius) with immobile surfaces. Film would exhibit drainage according to Reynolds equation (Equation 5.20) with characteristic parabolic velocity profile. Asymmetry of shear forces means that particles will also rotate except when equidistant from each surface of film. 

Instrumentation for studies of this nature are usually variations of the normal powder X-ray diffractometer. Except for faulting and strain in single crystals, which are better treated as defects, the very nature of the material limits studies to powders or aggregates. X-ray powder patterns of simple metals can be analyzed to yield information on particle size, deformation fault probability, mean-square strain, and twinning. The theory and techniques used to study diffraction line broadening, peak shifts, and line profile asymmetry have been derived and applied by Warren, " and Warren and Averbach. To assess faulting probability, certain drastic assumptions are necessary, reducing the detectability limit to approximately one faulted layer in 200. 

Comparisons between Raman-measured and predicted transverse profiles of CsHg and H2O mole fractions, at four selected streamwise locations, are illustrated in Fig. 4.1 for Cases 1 for clarity, 27 of the total 63 measured points are provided. Modest profile asymmetries are evident due to small differences between the upper- and lower-wall temperatures (see the wall temperatures of Fig. 4.2). 

Part of a 15-nm long, 10 A tube, is given in Fig. 1. Its surface atomic structure is displayed[14], A periodic lattice is clearly seen. The cross-sectional profile was also taken, showing the atomically resolved curved surface of the tube (inset in Fig. 1). Asymmetry variations in the unit cell and other distortions in the image are attributed to electronic or mechanical tip-surface interactions[15,16]. From the helical arrangement of the tube, we find that it has zigzag configuration. 

Under circumstances where two solutes are incompletely resolved and one of the pair is present at a much lower concentration than the other, the profile of the pair often resembles a normal peak with slight asymmetry. Consider the combined elution profile of the two peaks shown in figure 3. 

The area of a peak is the integration of the peak height (concentration) with respect to time (volume flow of mobile phase) and thus is proportional to the total mass of solute eluted. Measurement of peak area accommodates peak asymmetry and even peak tailing without compromising the simple relationship between peak area and mass. Consequently, peak area measurements give more accurate results under conditions where the chromatography is not perfect and the peak profiles not truly Gaussian or Poisson. 

Yang, Y., Zhu, D., Piegat, T.J. and Hua, L. (2007) Enzymatic ketone reduction mapping the substrate profile of a short-chain alcohol dehydrogenase (YMR226c) from Saccharomyces cerevisiae. Tetrahedron Asymmetry, 18 (15), 1799-1803. 

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