Supercritical regimes of liquid-metal fluid motions in electromagnetic fields: wall-bounded flows

An instability analysis of two-dimensional liquid-metal flows in a straight duct with free-slip boundary condition applied on the walls y = 0 and y = 2~ is conducted. The basic flow under examination is a Kolmogorov flow and it is driven by a transverse magnetic field interacting with an electric current supplied by lines of electrodes positioned in the bottom of the duct. It is proved by a rigorous theoretical analysis that all the secondary flows transitional from the basic flow are self-oscillations and that some secondary flows only arise when the Reynolds number R passes through a critical value Rc. That is, the instabilities are analytically proved to be supercritical Hopf bifurcations. Simple numerical predictions confirm the theoretical analysis

Archaeometallurgical Investigations in Nakhchivan, Azerbaijan: What Does the Evidence from Late Chalcolithic Ovçular Tepesi Tell Us about the Beginning of Extractive Metallurgy?

International audienceThe Late Chalcolithic (4400–3950 b.c.) occupation levels from Ovçular Tepesi have yielded a significant assemblage of copper objects and remains of copper production. Together with ore finds, two fragments of nozzle, crucible remains, and a number of small metal artifacts, this assemblage includes the unexpected discovery of three copper axes in an infant burial jar. These axes are the earliest examples of large copper tools known to date in southwestern Asia, whether it is in the Caucasus, Iran, or the Anatolian highlands. More importantly, the fact that these objects were locally produced suggests that significant metallurgical activities were being carried out at Ovçular as early as the second half of the 5th millennium b.c. After presenting the evidence from Ovçular Tepesi, this paper will proceed to a reassessment of the available archaeological and geochemical data concerning the emergence of extractive metallurgy in the southern Caucasus. © 2017, © Trustees of Boston University 2017