Temperature field around a spherical, cylindrical, and needle-shaped crystal, growing in a pre-cooled melt

The growth of a single crystal in a precooled melt was examined. The conditions under which this occurs are described. It is found that the movement of the crystallization front is proportional to the root of time. The problem is solved based on the presented considerations

Velocity selection problem for combined motion of melting and solidification fronts

We discuss a free boundary problem for two moving solid-liquid interfaces that strongly interact via the diffusion field in the liquid layer between them. This problem arises in the context of liquid film migration (LFM) during the partial melting of solid alloys. In the LFM mechanism the system chooses a more efficient kinetic path which is controlled by diffusion in the liquid film, whereas the process with only one melting front would be controlled by the very slow diffusion in the mother solid phase. The relatively weak coherency strain energy is the effective driving force for LFM. As in the classical dendritic growth problems, also in this case an exact family of steady-state solutions with two parabolic fronts and an arbitrary velocity exists if capillary effects are neglected. We develop a velocity selection theory for this problem, including anisotropic surface tension effects. The strong diffusion interaction and coherency strain effects in the solid near the melting front lead to substantial changes compared to classical dendritic growth.Comment: submitted to PR

Astrometrical Observations of the Near-Earth Asteroid 308635 (2005 YU55) in Nikolaev

International audienceA near-Earth asteroid 308635 (2005 YU55) was discovered by Spacewatch group at Kitt Peak Observatory (691) on Decembre 28, 2005. The asteroid belongs to the Apollo group, moreover it is a potentially hazardous asteroid presented in the critical list of the Minor Planet Center, the minimum orbit intersection distance of the asteroid with the Earth is 0.000454 a.u. As to the radar observations in 2010, the diameter of the asteroid is 0.4 km. Due to the high eccentricity of its orbit, the asteroid has close encounters not only with the Earth and the Moon, but also with Venus and Mars, so the orbit of this asteroid can be a subject of special interest for studying different gravitational perturbations