RESUMEN
Phonon dispersion curves were obtained from inelastic x-ray and neutron scattering measurements on alpha-uranium single crystals at temperatures from 298 to 573 K. Both measurements showed a softening and an abrupt loss of intensity in the longitudinal optic branch along [00zeta] above 450 K. Above the same temperature a new dynamical mode of comparable intensity emerges along the [01zeta] zone boundary with energy near the top of the phonon spectrum. The new mode forms without a structural transition but coincides with an anomaly in the mechanical deformation behavior. We argue that the mode is an intrinsically localized vibration and formed as a result of a strong electron-phonon interaction.
RESUMEN
High-resolution triple-axis X-ray diffraction techniques have been used to monitor the defect structure in hen egg-white lysozyme crystals. Analyses from the (440), (12;0) and (160) reflections showed significant differences in the intensity distribution around the respective reciprocal-lattice points. This work suggests that X-ray diffraction analytical methods developed primarily for relatively perfect inorganic crystals can be successfully applied to structurally defective macromolecular crystals. The analysis of defects at high angular resolution is complicated, however, by the observation that protein crystals lie at the convergence of the kinematic (ideally imperfect) and dynamic (ideally perfect) treatments of diffraction.