Condensed Matter

1110 Submissions

[2] viXra:1110.0074 [pdf] submitted on 29 Oct 2011

Maximum Entropy Boundaries in Lattice Boltzmann Method

Authors: Vasili Baranau
Comments: 37 pages.

We propose a universal approach in the framework of the lattice Boltzmann method (LBM) to modeling constant velocity constraints and constant temperature constraints on curved walls, which doesn't depend on dimensionality, LBM scheme, boundary geometry; which is numerically stable, accurate and local and has a good physical background. This technique, called a maximum entropy method, utilizes the idea of recovering unknown populations on boundary nodes through minimizing node state deviation from equilibrium while assuring velocity or temperature restrictions. Also, theoretical justifications of a popular Zou-He boundaries technique and isothermal boundaries algorithm are provided on the basis of the method derived. Finally, while conducting numerical benchmarks, typical straight boundaries algorithm (Zou-He) was compared to a typical curved boundaries algorithm (Guo-Zheng).
Category: Condensed Matter

[1] viXra:1110.0053 [pdf] submitted on 17 Oct 2011

Tridimensional Morphology and Kinetics of Etch Pit on the {0001} Plane of Sapphire Crystal

Authors: Lunyong Zhang, Hongbo Zuo, Zhiyong Yuan, Ji Zhou, Jianfei Sun, Dawei Xing, Jiecai Han
Comments: 17 pages

The tridimensional morphology and etching kinetics of the etch pit on the C-{0001} plane of sapphire crystal (a-Al2O3) in KOH molten were studied experimentally. It was shown that the etch pit takes on tridimensional morphologies with triangular symmetry same as the symmetric property of the sapphire crystal. Pits like centric and eccentric triangular pyramid as well as hexagonal pyramid could be observed, but the latter is much less in density. Analyses show the side walls of the etch pits belong to the {1 0 } family, and the triangular pit contains edges full composed by Al3+ ions on the etching surface so it is more stable than the hexagonal pit since whose edges on the etch surface contains Al2+ ions. The etch pits developed in manner of kinematic wave by the step moving with constant speed controlled by the chemical reaction with activation energy of 96.6KJ/mol between Al2O3 and KOH.
Category: Condensed Matter