The numerical analysis of the rotational theory for the formation of lunar globules

The morphology of lunar globules is studied through the application of a numerical analysis of their rotation in space during cooling. It is assumed that molten rock is shot from the surface of the moon, solidifies in space above the moon and then falls back to the surface. The rotational theory studied makes the following assumptions: the volume of the molten rock does not change during cooling; the angular momentum is conserved; there are no internal motions because of the high viscosity of the molten rock, i.e., in equilibrium the globule is rotating as a rigid body; finally, the kinetic reaction of the globule to the forces is fast relative to the rate of cooling, i.e., the globule reaches equilibrium at constant energy. These assumptions are subjected to numerical analysis yielding good agreement between the actual globule shapes and the numerical results, but leaving some doubt as to the validity of the rotational theory due to the failure to establish the existence of true local minima and an incomplete understanding of the thermokentics

Periodic formation of FeSi bands in diffusion couples Fe (15 wt.% Si) - Zn

During the reaction in Fe(15 wt.% Si)-Zn diffusion couples at temperatures between 623 and 723 K thin regularly spaced parallel bands containing very small FeSi precipitates are observed throughout the 6 and ~ reaction layers. The periodic nature of this effect is strongly reminiscent of the well-known Liesegang phenomenon. A detailed analysis of our results with respect to the principles underlying the Liesegang mechanism, however, shows that such a mechanism cannot explain the observed phenomenon in our case. A more probable explanation is found in the action of shear and tenSile stresses in the diffusion couple which lead to a periodic release ofthe continuously formed FeSi precipitates from the Fe(15 wt.% Si) substrate. Preliminary results obtained with substrates of varying thicknesses are strongly in favour of the latter explanation

Investigations on the phase formations, properties and single crystal growth in the high-Tc superconducting Ca-Sr-Bi-Cu-O system

We have performed investigations on the Ca-Sr-Bi-Cu-O system with respect to high-Tc superconductivity and structural properties. It is shown that there are two high-Tc superconducting phases in the system, i.e. a 110 K and an 85 K phase. The 85 K phase has a body-centred tetragonal structure with a stoichiometry of CaSr2Bi2Cu2O8. The 110 K phase is closely related to the 85 K phase. It is formed only in a very narrow temperature range and easily deteriorates to the phase with the lower Tc by quenching. Although some samples show a large diamagnetic signal at 110 K in ac-susceptibility measurements, there is still evidence of the presence of the 85 K phase. X-ray diffraction studies, especially in the low-angle region, show a structural relation between these two superconducting phases. The procedures of the preparation and the characterization of the 85 K and 110 K polycrystalline superconducting phases as well as the single crystal growth of the 85 K superconducting phase are described

ISiS: A 4pi Detector System for Complex Fragments

This research was sponsored by the National Science Foundation Grant NSF PHY-931478