Spatial Period-Doubling Instability of Dendritic Arrays in Directional Solidification.
A directional solidification study of succinonitrile doped with coumarin 152 was performed in which the pulling speed {ital V}{sub {ital P}} was gradually reduced in small steps. A spatial period-doubling instability was observed when {ital V}{sub {ital P}} reached 17.4 {mu}m/s, in good quantitative agreement with the prediction of Warren and Langer [Phys. Rev. A {bold 42}, 3518 (1990)]. This experiment, in conjunction with two previous studies, conclusively demonstrates the absence of a dynamical selection mechanism for the interdendritic spacing {lambda}{sub 1}. {copyright} {ital 1996 The American Physical Society.}
Abstract Techniques for recording and analysing fibre diffraction data from DNA using the instrument D19 at the Institut Laue-Langevin Reactor Source and the instrument SXD at the Rutherford Appleton Laboratory ISIS Spallation Source are described and compared. Data recorded from a specially prepared sample of deuterated DNA in the A conformation using SXD are compared with previously analysed data from a normally hydrogenated DNA in the same conformation recorded on D19. A preliminary Fourier difference analysis of these two datasets has allowed their consistency to be established.