FLOW STRUCTURE IN THE HORIZONTAL SLUG FLOW

Successions of long gas bubbles and liquid slugs form the so-called slug flow pattern in a gas-liquid flow. A unit cell encompassing one gas bubble and one liquid slug characterizes this alternating gas-liquid flow. The kinematic and dynamic flow mechanisms responsible for the interactions between the successive unit cells are still an open question. Inside this context, this work addresses specifically to the bubble velocity, the bubble to bubble interactions and the entrance mechanisms. Within an experimental framework the spatial evolution of each unit cell structure is individualized during the acquisition period. The experimental apparatus consisted of a 23.4 m long transparent Plexiglas pipe, 26mm ID, which means a total relative length of 900 free diameters. The air and water were mixed at the inlet of the test section and discharged into a collecting tank open to the atmosphere. The instantaneous measurements of the flow structure were made with double-wire conductive probes. The probes were installed in four measuring stations; each station had two probes slightly apart. The measuring stations were located at 127D, 273D, 506D e 777D from the mixer. The experimental database is further processed to give rise to histograms and correlations among flow variable

Photon Self-Induced Spin to Orbital Conversion in TGG crystal at high laser power

In this paper, we present experimental evidence of a newly discovered third-order nonlinear optical process Self-Induced Spin-to-Orbital Conversion (SISTOC) of the photon angular momentum. This effect is the physical mechanism at the origin of the depolarization of very intense laser beams propagating in isotropic materials. The SISTOC process, like self-focusing, is triggered by laser heating leading to a radial temperature gradient in the medium. In this work we tested the occurrence of SISTOC in a terbium gallium garnet (TGG) rod for an impinging laser power of about 100~W. To study the SISTOC process we used different techniques: polarization analysis, interferometry and tomography of the photon orbital angular momentum. Our results confirm, in particular, that the apparent depolarization of the beam is due to the occurrence of maximal entanglement between the spin and orbital angular momentum of the photons undergoing the SISTOC process. This explanation of the true nature of the depolarization mechanism could be of some help in finding novel methods to reduce or to compensate for this usually unwanted depolarization effect in all cases where very high laser power and good beam quality are required.Comment: 6 pages, 10 figures, submitte