Low-resolution reflections

Incorrectly measured low-resolution reflections (e.g. overloaded reflections or reflections behind the beam-stop ) can seriously impede refinement at all stages. Care must be taken to assess the correctness of these reflections. If there are any doubts, a low-resolution cut-off can be applied using the SHEL keyword. 

As the elemental analysis of Form II crystals indicated 1/1 (Host)-/(guest) ratio, we have to look for three more barbital and 36 more water molecules. However, at the present stage, we can not assign these molecules because the separation of the peaks on Fourier maps are not good owing to the use of low resolution reflection data and/or the existence of the notable disorder at these areas. The R factor is 21.9 % for all available reflections using isotropic thermal parameters. 

The two limitations of optical interferometry, the one-quarter wavelength of light limit and the low resolution, have been addressed by using a combination of a fixedthickness spacer layer and spectral analysis of the reflected beam. The first of these overcomes the minimum film thickness that can normally be measured and the second addresses the limited resolution of conventional chromatic interferometry. 

The width of the 0-0 line in single-tryptophan proteins at 77 K has been interpreted to reflect inhomogeneous broadening arising because the protein exists as a distribution of conformations. 30 34 The width of the 0-0 band of liver alcohol dehydrogenase is 500 cm-1 at 22°C.(10 31 35) The widths of the 0-0 transition for other proteins are somewhat greater. In many cases for the spectra taken at room temperature, low-resolution optics were used (as in Figure 3.2), and hence the published spectra may overestimate the width of the emission band. 

The XRD patterns of as-synthesized and calcined samples show the typical reflections of MCM-41 molecular sieves. Four low angle reflections are observed. One main peak arises at 20 = 2 deg. which is assigned to the 100 reflection. The 110, 200 and 210 reflections are of lower and very weak intensity. The patterns could be indexed on a hexagonal lattice due to the hexagonal arrangement of pores. The appearance of the XRD pattern is maintained with the increasing aluminum content up to a total Si/Al ratio of 6.8 (9.8 gel). Only the resolution... 

McCaffery etal. discuss the use of a low-resolution Raman spectrometer to directly monitor a batch mini-emulsion polymerization.41 While this kind of equipment is unlikely to be installed in an industrial facility, the article raises several important points. In order to compensate for laser-power fluctuations, a functional group present in both the reactants and the product, the phenyl ring in styrene, was used as an internal standard. Since internal standards cannot be added to industrial reactions, this approach can be quite helpful. However, scientists must be certain that the internal standard will remain unchanged by the reaction and that changes in its signal only reflect laser-power fluctuations. 

Being able to record only low resolution data also implies that these are relatively few in number. Here some relief is provided by the high symmetry of regular helical molecules. Many helical polyncleotides, for example, provide 100-200 independent X-ray reflections that can be used to determine the molecular geometry of the one nucleotide residue from which all the others can be generated by symmetry operations. A comparable data set... 

Note that in the tubulin diffraction pattern shown in Fig. 1 alternate rows of diffraction spots are significantly weaker. The strong spots, on even-numbered rows, arise from the monomer-monomer spacing of about 40 A. The weaker spots on odd-numbered rows arise from the dimer spacing, and thus reflect differences between the monomers. These differences are rather small at the low resolution range that corresponds to the secondary structure, so these spots are weak. At higher resolution where differences between side chains in the two monomers become significant the odd and even rows show more similar intensities. 

In general, unlike for the perfect epitaxial structures of fully strained materials, for nitride heteroepitaxial layers it is essential to perform not a single scan for a symmetrical reflection, but a set of two- or even three-dimensional maps of symmetrical and asymmetrical reflections. Additionally, for some applications, an intense beam is needed and therefore low-resolution X-ray diffractometry can be sometimes a preferable technique to the commonly used high-resolution XRD. For example, if we examine a heterostructural nitride superlattice, low resolution diffractometry will give us a broader zeroth-order peak (information on the whole layer) but more satellite peaks (information on the sublayers). Therefore, multipurpose diffractometers with variable configurations are the most desirable in nitride research. 

The Absorption Cross Section (Abs. XS or XS or a(E)) of molecules in the visible and or UV range is due to (at least one) electronic transition. At low resolution, each Abs.XS has a bell shape which can be described with very few (3 or 4, see below) parameters. This bell shape can be understood as the "reflection" of the ground state vibrational wavefunction (which can be approximated as a onedimensional or multidimensional Gaussian) on the potential energy surface (PES)... 

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