Constraining spacetime torsion with LAGEOS

We compute the corrections to the orbital Lense-Thirring effect (or frame-dragging) in the presence of spacetime torsion. We derive the equations of motion of a test body in the gravitational field of a rotating axisymmetric massive body, using the parametrized framework of Mao, Tegmark, Guth and Cabi. We calculate the secular variations of the longitudes of the node and of the pericenter. We also show how the LAser GEOdynamics Satellites (LAGEOS) can be used to constrain torsion parameters. We report the experimental constraints obtained using both the nodes and perigee measurements of the orbital Lense-Thirring effect. This makes LAGEOS and Gravity Probe B (GPB) complementary frame-dragging and torsion experiments, since they constrain three different combinations of torsion parameters

Numerical simulation of the horizontal Bridgman growth of a gallium arsenide crystal

Two-dimensional numerical simulations have been developed which represent the thermomechanical behavior of semiconductor melts in horizontal crucibles. These computer models are based on time-dependent finite-difference and finite-element codes, capable of simulating steady and transient melt convection. At moderate Rayleigh numbers, one finds time-invariant solutions which typically involve several primary and secondary vortices, depending on aspect ratio. Above a critical Rayleigh number, these steady solutions are replaced by oscillatory melt convection, as suggested by earlier experimental and analytic studies. The finite element code was extended to include a solid-liquid interface, which permits the study of actual crystal growth processes.Anglai