• Y T Thathachari

      Articles written in Proceedings – Section A

    • Theory of image formation in combinations of x-ray focussing mirrors

      Y T Thathachari

      More Details Abstract Fulltext PDF

      It is shown that ideally Bragg reflections can occur successively from two surfaces only if they form parts of the same sphere, a result shown to be sufficient (but not necessary) in an earlier publication. However, if the aperture radius and the size of the object are small compared to the radius of curvature of the reflecting surfaces (such that fourth and higher power of their ratios are less than (10−6), then the combination will work even with aspherical surfaces, provided the two reflectors are surfaces of revolution about a common axis and they are both concave reflectors having the same vertex radius of curvature and are separated by a distance equal to twice this radius. If a combination of two such mirrors are used, andN multiple reflections obtained with them, then the optical path is reduced appreciably (approximately as 1/N) and the spherical aberration is also decreased (being proportional to 1/N) for large magnifications. The resolving power of such a combination should be of the order of 50 °A. A combination of X-ray mirrors in the form of an X-ray microscope has, therefore, distinct advantages and it appears that the problem of realising such a unit in practice is worth investigating.

    • The crystal and molecular structure of 3, 4-dihydroxy L-phenyl-alanine

      Joseph W Becker Y T Thathachari Paul G Simpson

      More Details Abstract Fulltext PDF

      The molecule crystallizes in spacegroup P21 with two molecules per unit cell. The unit cell dimensions area = 6.044 Å,b = 13.607 Å,c = 5.311 Å,γ = 97.55°. The density was calculated to be 1.512 g.ml.−1 and found to be 1.51 g.ml.−1 The major atoms were located by the reliable image method and the hydrogen atoms were located from a difference electron density map. Full-matrix least squares refinement of the parameters yielded an unweighted residual indexR of 0.088.

      The bond lengths and angles of the amino acid grouping are consistent with values in other amino acids. The structural parameters of the aromatic system are very similar to those of noradrenaline and dopamine hydrochlorides. The crystal structure is dominated by a three-dimensional intermolecular hydrogen bonding system. The molecular conformation is different from that displayed by any other aromatic amino acid or peptide whose crystal structure is known.

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