Multilevel Solvers for Unstructured Surface Meshes

Parameterization of unstructured surface meshes is of fundamental importance in many applications of digital geometry processing. Such parameterization approaches give rise to large and exceedingly ill-conditioned systems which are difficult or impossible to solve without the use of sophisticated multilevel preconditioning strategies. Since the underlying meshes are very fine to begin with, such multilevel preconditioners require mesh coarsening to build an appropriate hierarchy. In this paper we consider several strategies for the construction of hierarchies using ideas from mesh simplification algorithms used in the computer graphics literature. We introduce two novel hierarchy construction schemes and demonstrate their superior performance when used in conjunction with a multigrid preconditioner

Polyassociative thermodynamic model of A²B⁶ semiconductor meltand phase equilibria in Cd-Hg-Te system. 4. p-T-x diagram of Cd-Hg-Te system

p −T− x diagram of Cd-Hg-Te system is analyzed in the framework of the polyassociative solution model. The temperature dependence of the dissociation constant for ternary complexes, which describes the mixing effects, was determined using the low temperature data on phase equilibrium in the system. A satisfactory agreement between calculated and experimental data of various works about phase equilibrium was attained

Isothermal growth kinetics of CdxHg₁₋xTe LPE layers

Within the diffusion-limited growth model, the kinetic analysis of the LPE process for CdxHg₁₋xTe solid solutions is carried out. It is assumed that a phase equilibrium exists on the interface, and the concentrations of components are connected by the equations of phase equilibria in the frame of the model of polyassociated solutions. These equations serve as the boundary conditions in solving the diffusion mass transfer problem. The developed thermodynamic model of growth allowed us to achieve the precision description of solid solutions, in particular to predict the regimes of the growth of layers with a given composition in the Cd-Hg-Te system

Influence of elastic strains on LPE growth kinetics in the Cd-Hg-Te System

By comparing the results of calculations concerning the dependence of the parameters of a layer on the growth conditions with and without regard for mechanical strains in the growing system, we have analyzed the influence of the elastic energy of the strained solid phase on the phase formation in the Cd–Hg–Te system. It is shown that the occurrence of elastic strains in a layer results in an insignificant reduction of the growth rate and has almost no influence on the composition of a growing layer. The ideas of coherently matched phases in the presence of elastic deformations in the system, as well as the assumption about the existence of the chemical equilibrium of phases on the interface, give rather close results as for the crystallization of the material. Both approaches describe the experimental data on the growth of layers in various temperature-time regimes quite satisfactoril

Handover in Mobile WiMAX Networks: The State of Art and Research Issues

The next-generation Wireless Metropolitan Area Networks, using the Worldwide Interoperability for Microwave Access (WiMAX) as the core technology based on the IEEE 802.16 family of standards, is evolving as a Fourth-Generation (4G) technology. With the recent introduction of mobility management frameworks in the IEEE 802.16e standard, WiMAX is now placed in competition to the existing and forthcoming generations of wireless technologies for providing ubiquitous computing solutions. However, the success of a good mobility framework largely depends on the capability of performing fast and seamless handovers irrespective of the deployed architectural scenario. Now that the IEEE has defined the Mobile WiMAX (IEEE 802.16e) MAC-layer handover management framework, the Network Working Group (NWG) of the WiMAX Forum is working on the development of the upper layers. However, the path to commercialization of a full-fledged WiMAX mobility framework is full of research challenges. This article focuses on potential handover-related research issues in the existing and future WiMAX mobility framework. A survey of these issues in the MAC, Network and Cross-Layer scenarios is presented along with discussion of the different solutions to those challenges. A comparative study of the proposed solutions, coupled with some insights to the relevant issues, is also included

Non-Iterative, Feature-Preserving Mesh Smoothing

With the increasing use of geometry scanners to create 3D models, there is a rising need for fast and robust mesh smoothing to remove inevitable noise in the measurements. While most previous work has favored diffusion-based iterative techniques for feature-preserving smoothing, we propose a radically different approach, based on robust statistics and local first-order predictors of the surface. The robustness of our local estimates allows us to derive a non-iterative feature-preserving filtering technique applicable to arbitrary "triangle soups". We demonstrate its simplicity of implementation and its efficiency, which make it an excellent solution for smoothing large, noisy, and non-manifold meshes.Singapore-MIT Alliance (SMA

Piecewise Rational Manifold Surfaces with Sharp Features

We present a construction of a piecewise rational free-form surface of arbitrary topological genus which may contain sharp features: creases, corners or cusps. The surface is automatically generated from a given closed triangular mesh. Some of the edges are tagged as sharp ones, defining the features on the surface. The surface is C s smooth, for an arbitrary value of s, except for the sharp features defined by the user. Our method is based on the manifold construction and follows the blending approach