Wide-angle diffraction pattern

Other information that can be obtained from a wide-angle diffraction pattern includes the detection of stacking faults and microstrains, the lattice parameters, and the mean-square amplitude of vibratioiu... 

In situ X-ray examination of crystallizing polyethylene, at high temperature and pressure, then confirmed this proposal in detail, showing that the wide-angle diffraction pattern changed abruptly with the optical texture [ 10]. That corresponding to the spherulitic texture was of the usual orthorhombic form while the new intermediate phase had two-dimensional hexagonal symmetry, with an increased cross-sectional area per chain, but without... 

Extraction of the lipids with organic solvents resulted in the disappearance of the 4.2- and 3.7-A reflections, confirming that these reflections were from lipids. The 3.7-A reflection disappeared at 40°C, and the 4.2-A reflection disappeared at approximately 70°C, corresponding to thermal transitions detected calorimetrically at similar temperatures. The two protein reflections were not affected by temperature. Recrystallization of the lipids in the stratum comeum result in the same wide-angle diffraction pattern as untreated stratum comeum. The recrystallization was not affected by the water content in the stratum comeum. 

Figure 6 Wide-angle diffraction pattern from human SC oriented (a) parallel and (b) perpendicular to the plane of the SC. (From Garson et al., 1991.)...

Figure 10 Wide-angle diffraction patterns from human SC oriented parallel to the incident beam at a temperature of 75 C. (a) A 4.17-A reflection due to hexagonal lipid packing is seen (labeled I) along with reflections at 3.6, 4.6, and 7.16 A. The ring marked II has not been observed in any other donor, (b) Diffraction pattern obtained after recrystallization of the lipids from 120°C. The 4.17-A reflection has disappeared. (Data from Bouwstra et al., 1992b.)...

In most cases, the wide-angle diffraction pattern of membranes or phospholipid model systems shows more or less well-defined peaks which relate to the mutual packing... 

Fig. 24. Change of the wide-angle diffraction pattern of cw-polyacetylene during heating from room temperature with 11 °C/min. The disappearance of the (201) reflection at 150 °C indicates the cis/ trans isomerization, the broad peak above 290 °C indicates thermal degradation...

The diffraction maxima in the wide-angle diffraction pattern derive from the periodicity of the crystal lattice (Cullity and Stock 2001). Their angular pattern is characteristic of the crystal lattice, so is ideal for identification and detection purposes. For monochromatic radiation (X-rays, neutrons or electrons) of wavelength X, Bragg s Law gives... 

Figs. 3 THROUGH 8. Wide-angle diffraction patterns of collagens. All are at the same magnification, which is about three quarters of the original size as obtained at a specimen-to-film distance of 5 cm. (cf. Fig. 2). Individual patterns were obtained from the following specimens ... 

The absorption factor exp(-pt) (equal to for a normally incident beam) was measured as 76.4J. The wide-angle diffraction pattern is shown in Figure 1. 

Fig. 13. Wide angle diffraction patterns taken on a sample of low density polyethylene that had been cold rolled along Z to an extension ratio of 4 and then annealed without restraint. X-ray beam was directed along the respective axis indicated...

According to Raman spectroscopy the chains in the hexagonal form are confor-mationally disordered with an appreciable concentration of gauche bonds.(276,277) These results are consistent with the interpretation of the wide-angle diffraction pattern of this phase which requires an element of conformational disorder.(278,279) The gauche content of the pure melt of low molecular weight alkanes is known to increase with increasing applied hydrostatic pressure. 

Figure 12. Long-range lattice orientational order with (a) long-range positional order, and (b) short-range positional order. The corresponding wide angle diffraction patterns are shown to the right (From [14]).

The two most characteristic features of the ride-angle diffraction pattern of native collagen are a principal axial repeat of 2.9 A, and an equatorial periodicity of 11 A which varies somewhat with the degree of hydration of the specimen (Fig. 1). The wide-angle diffraction pattern is believed to derive from the triple helical structure made possible by the presence of glycine in every third position along the chains. The 2.9 A X-ray reflection represents the distance of one amino acid residue along the helical axis direction, and is a measure of the inclination of that residue with respect to the helical axis. The 11-A line is related to the distance betw een two laterally adjacent molecules. 

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