The local displacement field around Co and Nb solutes in ω-phase forming bcc-Zr at high temperatures

In order to determine the displacement field around Co and Nb solutes in high temperature bcc-Zr the diffuse scattering intensity was measured in Zr_0.985Co_0.015 and Zr_0.92Nb_0.08. Strong diffuse intensities were found in the (110) and in the (001) reciprocal planes. The comparison of these results with model calculations shows that Co as well as Nb atoms cause radial symmetric displacement fields in the high temperature bcc phase of Zr. -phase like displacements around these defects, on the other hand, can explain the measured diffuse intensities less well. It is concluded, that the resulting displacement field is a superposition of all displacements for which low energy phonons exist. These low energy phonons are related to the martensitic transitions of the bcc structure to the hcp and -structure.     

Mapping properties of generalized Fourier transforms and applications to Kirchhoff equations

We prove the differentiability of generalized Fourier transforms associated with a self-adjoint and strictly elliptic perturbation A of the Laplacian with variable coefficients in an exterior domain, using results on the spectral differentiability of the resolvent of A. Moreover we show that differentiable functions with bounded support and vanishing near the origin are mapped by the generalized Fourier transform into polynomially weighted L ²-spaces. As an application of the generalized Fourier transform and exploiting the previous results, we deal with equations of Kirchhoff type. We will not only show the global (in t) existence and uniqueness of solutions for a class of small data, but also an assertion on its time asymptotic behavior. In addition, we obtain amplified results for Schr?dinger operators . Received March 1999     

Neutron scattering study of intermolecular excitations in solid C60 and C70

The spectrum of intermolecular excitations in solid C₆₀ and C₇₀ is investigated by neutron time-of-flight spectroscopy. The quasielastic scattering above the ordering transition is studied in detail and compared to a rotational diffusion model. Below the transition the scattering spectra have essentially a three peak structure with a prominent libronic excitation near ±2 meV for both fullerenes. A detailed analysis gives evidence for a broader distribution of librational modes with an additional pronounced maximum near 5 meV.