Diffraction patterns Information

The determination of the double-helical structure was based primarily on model building and X-ray diffraction patterns. Information from X-ray patterns was added to information from chemical analyses that showed that the amount of A was always the same as the amount of T, and that the amount of G always equaled the amount of G. Both of these lines of evidence were used to conclude that DNA consists of two polynucleotide chains wrapped around each other to form a heUx. Hydrogen bonds between bases on opposite chains determine the alignment of the heUx, with the paired bases lying in planes perpendicular to the helix axis. The sugar-phosphate backbone is the outer part of the helix (Figure 9.7). The chains run in antiparallel directions, one 3 to 5 and the other 5 to 3. ... 

A TEM provides the means to obtain a diffraction pattern from a small specimen area. This diffraction pattern is obtained in diffraction mode, where the post-specimen lenses are set to examine the information in the transmitted signal at the back focal plane of the objective lens. 

The most direct information obtained from LEED is the periodicity and intermediate range order within the transfer width of the surface under investigation. This can be gathered by visual inspection of the diffraction pattern and/or by relatively simple mathematical transformations of the spot profiles. 

The task of predicting a reasonable structure for this alloy was carried out with no information about the powder X-ray diffraction pattern except that one group of investigators had said that it could not be indexed by any Bravais lattice. The prediction of the structure was made entirely on the basis of knowledge of the effective radii of metal atoms and the principles determining the structure of metals and intermetallic compounds. 

I thank Dr D. Schechtman for cooperation in providing me with the X-ray diffraction pattern and for other information, and Professor Barclay Kamb for pointing out to me that an icosahedron becomes chiral when it shares its faces. This investigation was supported in part by a grant from the Japan Shipbuilding Industry Foundation. 

Figure 1 is a TEM photograph of the Cu (10wt%)/Al2O3 catalyst prepared by water-alcohol method, showing the dispersed state of copper and was confirmed the particle sizes from XRD data. Figure 2 is X-ray diffraction patterns of above-mention catalysts, was used to obtain information about phases and the particle size of prepared catalysts. Metal oxide is the active species in this reaction. Particle sizes were determined fix)m the width of the XRD peaks by the Debye-Scherrer equation. 

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... 

To answer this question we need to consider the kind of physical techniques that are used to study the solid state. The main ones are based on diffraction, which may be of electrons, neutrons or X-rays (Moore, 1972 Franks, 1983). In all cases exposure of a crystalline solid to a beam of the particular type gives rise to a well-defined diffraction pattern, which by appropriate mathematical techniques can be interpreted to give information about the structure of the solid. When a liquid such as water is exposed to X-rays, electrons or neutrons, diffraction patterns are produced, though they have much less regularity and detail it is also more difficult to interpret them than for solids. Such results are taken to show that liquids do, in fact, have some kind of long-range order which can justifiably be referred to as a structure . 

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