Dispersion anomalous

Fig. 1. (a) Phase matched second harmonic generation (2cJ = 0.49 fiTo) at cj = 0.98 where = refractive index by ordinary rays and = by extraordinary rays, (b) Hypothetical anomalous dispersion phase matching at 850 nm in similar a crystal having a Lorent2ian absorption centered at 650... 

Most glasses have dispersions which follow a standard relation with change of wavelength. Some glasses have anomalous dispersion, and these are useful for the design of highly colour-corrcctcd lens sets, so-called apochromatic objectives. 

The parameters were then further refined by four successive least-squares procedures, as described by Hughes (1941). Only hk() data were used. The form factor for zinc was taken to be 2-4 times the average of the form factors for magnesium and aluminum. The values of the form factor for zinc used in making the average was corrected for the anomalous dispersion expected for copper Kot radiation. The customary Lorentz, polarization, temperature, and absorption factors were used. A preliminary combined scale, temperature, and absorption factor was evaluated graph-... 

X-Ray diffraction from single crystals is the most direct and powerful experimental tool available to determine molecular structures and intermolecular interactions at atomic resolution. Monochromatic CuKa radiation of wavelength (X) 1.5418 A is commonly used to collect the X-ray intensities diffracted by the electrons in the crystal. The structure amplitudes, whose squares are the intensities of the reflections, coupled with their appropriate phases, are the basic ingredients to locate atomic positions. Because phases cannot be experimentally recorded, the phase problem has to be resolved by one of the well-known techniques the heavy-atom method, the direct method, anomalous dispersion, and isomorphous replacement.1 Once approximate phases of some strong reflections are obtained, the electron-density maps computed by Fourier summation, which requires both amplitudes and phases, lead to a partial solution of the crystal structure. Phases based on this initial structure can be used to include previously omitted reflections so that in a couple of trials, the entire structure is traced at a high resolution. Difference Fourier maps at this stage are helpful to locate ions and solvent molecules. Subsequent refinement of the crystal structure by well-known least-squares methods ensures reliable atomic coordinates and thermal parameters. 

MAD multiwavelength anomalous dispersion MAD -nine-substituted protein. 

Several structurally different types of HNLs occur in nature, which likely originated hy convergent evolution from different ancestral proteins. The enzyme from almond (PaHNL) was first crystallized in 1994 and the structure was solved by multiple wavelength anomalous dispersion of a mercury derivative. The first 3D structure analysis of PaHNL was performed in 2001. ° (7 )-PaHNL from almond uses FAD as cofactor and is related to oxidoreductases it exhibits HNL activity only in the oxidized form of FAD." ... 

From this equation it can be seen that the depth of penetration depends on the angle of incidence of the infrared radiation, the refractive indices of the ATR element and the sample, and the wavelength of the radiation. As a consequence of lower penetration at higher wavenumber (shorter wavelength), bands are relatively weaker compared to a transmission spectrum, but surface specificity is higher. It has to be kept in mind that the refractive index of a medium may change in the vicinity of an absorption band. This is especially the case for strong bands for which this variation (anomalous dispersion) can distort the band shape and shift the peak maxima, but mathematical models can be applied that correct for this effect, and these are made available as software commands by some instrument manufacturers. 

Knight, J. C., Arriaga, J., Birks, T. A., Ortigosa-Blanch, A., Wadsworth, W. J. and Russell, P. S. (2000). Anomalous dispersion in photonic crystal fiber. IEEE. Photon. Technol. Lett. 12, 807-9. 

Ranka, J. K., Windeler, R. S. and Stentz, A. J. (2000). Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm. Opt. Lett. 25, 25-7. 

Figure 13. Absolute configuration of benzo[a]pyrene metabolites determined by anomalous dispersion (X-ray diffraction) studies of a bromoderivative.

Form I is the dilute solution form while Form II will predominate in concentrated solutions. In order to account for anomalous dispersion, we postulate that the two forms have different rotatory dispersion. There is, of course, no way of distinguishing between Form II and the Lowry type, because the two are merely different ways of saying the same thing. 

The changes in optical rotation and the anomalous dispersion of solutions of /-malic acid in solution are due to the presence of two tautomeric forms in dynamic equilibrium. 

The abnormal rotation and the anomalous dispersion cannot be accounted for satisfactorily on the basis of polymerization, electrolytic dissociation hydrates, lactones of the ordinary type, or of a structural reversal of the asymmetric carbon atom. 

Single crystals of ferroelectric TGS grown from solution generally contain domains of the two enantiomorphous phases (110). This juxtaposition of enantiomorphous domains may be explained in terms of the minor deviations of the crystal structure from a centrosymmetric arrangement. The relative concentrations of the two enantiomorphous phases in a single crystal may be determined by means of anomalous dispersion of X-rays (111,112). 

An unusual absorption of a lone Fe atom, not belonging to the Fe-S clusters, was detected in the reduced enzyme from A. vinosum (Fig. 7.12). The nature of this Fe atom was a mystery, however. It was only when X-ray anomalous dispersion... 

This is very crude measurement. Nevertheless, it is sufficient to discriminate against some of the dispersion formulae that have been proposed. This matter is considered in the next paper where it is shown that the formulae which are satisfactory in that they put the anomalous dispersion at the observed frequencies yield values for (jun 1) which differ from that given by experiment, by several times the margin indicated in (8). 

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