Numerical Simulation of the laser welding
The model takes into consideration thermophysical and metallurgical properties of theremelting steel, laser beam parameters and boundary conditions of the process. As a resultof heating the material, in the area of laser beam operation a weld pool is being created,whose shape and size depends on convection caused by the Marangoni force. The directionof the liquid stream depends on the temperature gradient on the surface and on the chemicalcomposition as well. The model created allows to predict the weld pool shape depending onmaterial properties, beam parameters, and boundary conditions of the sample.
Langmuir adsorption, the Gibbs adsorption isotherm, and interfacial kinetics in liquid metal systems
The adsorption of strongly surface active solutes is considered in terms of the ideal site-fillage or Langmuir isotherm. The resulting equation for the depression of surface tension of a liquid metal by such a solute isσP- σ = RTΓio ln (1 +Kai where σP- σ is the depression of surface tension of the pure liquid metal, Γio is the satura-tion coverage by the solute, ai is the bulk activity of the solute, andK is a coverage inde-pendent adsorption coefficient. The isotherm is found to give a very good description of the available data for Group VI solutes on several metals. The derived values of the adsorp-tion coefficient are applied to several kinetic studies and they are found to give good rela-tive and possibly absolute measures of the interference by such solutes on interfacial re-action rates. The iron-sulfur system appears to differ, but only by a factor of two. The application of these adsorption coefficients in aiding the interpretation of kinetic studies is considered.
Effect of a new inhibitor of cholesterol biosynthesis (AY 9944) on serum and tissue sterols in the rat.
AY 9944 is a novel inhibitor of cholesterol biosynthesis which appears to act on the Delta 7-reductase enzyme, interfering with the conversion of 7-dehydrocholesterol to cholesterol. In all tissues studied, with the exception of the lens, there was a reduction in cholesterol and a marked accumulation of 7-dehydrocholesterol. Isotope studies showed a reduced uptake of acetate into cholesterol, and an increased uptake into 7-dehydrocholesterol, in various tissues in vivo and by skin samples in vitro. There was no apparent accumulation of lanosterol or of the methostenols in the rat skin.