Handling degenerate cases in exact geodesic computation on triangle meshes

The computation of exact geodesics on triangle meshes is a widely used operation in computer-aided design and computer graphics. Practical algorithms for computing such exact geodesics have been recently proposed by Surazhsky et al. [5]. By applying these geometric algorithms to real-world data, degenerate cases frequently appear. In this paper we classify and enumerate all the degenerate cases in a systematic way. Based on the classification, we present solutions to handle all the degenerate cases consistently and correctly. The common users may find the present techniques useful when they implement a robust code of computing exact geodesic paths on meshes.     

The Transformation of Carbides during Austenization and Its Effect on the Wear Resistance of High Speed Steel Rolls

The transformation of carbides with austenization time of a high speed steel (HSS) roll material, manufactured by a centrifugal casting method, has been studied. The correlation between wear resistance and the type, morphology, volume fraction, and distribution of the carbides has also been investigated. Microstructural observations, X-ray diffraction (XRD) analysis, hardness measurements, and energy dispersive spectroscopy (EDS) have been used to characterize the carbides. The type and volume fraction of carbides were found to change with austenizing time. During austenization, the transformation of the M₃C carbides can be postulated as M₃C + γ-Fe → M₂C, with much finer nodular and rodlike MC carbides also forming through a solid-state transformation. The M₂C carbide decomposes as M₂C + γ-Fe → MC + M₇C₃ + M₆C. The decomposed carbide substantially maintains a platelike shape until the end of decomposition. The most important finding of this study is that austenization results in changes in the type, morphology, volume fraction, and distribution of carbides and that it can be controlled to produced a homogeneous distribution of hard carbides, resulting in an improvement in the wear resistance of HSS rolls. This finding may be of great use for the industrial production of HSS rolls.     

Numerical study of fluid flow and heat transfer in microchannel cooling passages

Numerical investigation was conducted for fluid flow and heat transfer in microchannel cooling passages. Effects of viscosity and thermal conductivity variations on characteristics of fluid flow and heat transfer were taken into account in theoretical modeling. Two-dimensional simulation was performed for low Reynolds number flow of liquid water in a 100 μm single channel subjected to localized heat flux boundary conditions. The velocity field was highly coupled with temperature distribution and distorted through the variations of viscosity and thermal conductivity. The induced cross-flow velocity had a marked contribution to the convection. The heat transfer enhancement due to viscosity-variation was pronounced, though the axial conduction introduced by thermal-conductivity-variation was insignificant unless for the cases with very low Reynolds numbers.     

提高E^2PROM中NMOS管源漏穿通电压的实验研究

为了提高Ｅ＾２ＰＲＯＭ中Ｎ管源漏穿通电压，用实验的方法对制造工艺进行了研究。结果表明，高能量注入是提高ＶＰＴ的有效手段，但受到ｐｎ结击穿的限制，只适用于低区短沟Ｎ管；ＤＤＤ工艺大幅度高ＶＰＴ，但ｐｎ结击穿电压低于２０Ｖ，不能应用于高压ＭＯＳ管；采用适量的防穿通注入和适当增大沟道长度为最理想的工艺途径。     

柴达木盆地北缘侏罗系烃源岩干酪根13C核磁共振研究

柴达木盆地北缘是柴达木盆地三大油气区之一,其源岩为早、中侏罗世煤系地层.烃源岩有机质类型以Ⅲ₁型和Ⅱ型干酪根为主,Ⅰ₂型干酪根仅在局部地区有分布.通过对柴达木盆地北缘侏罗系烃源岩中不同类型干酪根的¹³C核磁共振研究,指出了研究区Ⅰ₂、Ⅱ、Ⅲ₁型干酪根的化学结构特征以及化学结构中“芳构碳”、“油潜力碳”与“气潜力碳”的相对含量,据此从定量分析的角度对不同类型干酪根的生油气贡献作了评价.Ⅰ₂、Ⅱ、Ⅲ₁型干酪根的生烃能力依次减弱,对生油的贡献也依次减弱,且生成油气的比例不同,Ⅰ₂、Ⅱ型干酪根以生油为主,Ⅲ₁型干酪根则以生气为主.     

电镀锡机组软熔导电辊脱锡技术研究

粘锡是电镀锡机组软熔导电辊失效的主要原因,应用化学方法脱锡是延长导电辊寿命的重要途径.开发了氢氧化钠(钾)为主要组成,并加入适量亚铅酸钠(钾)和硝酸(亚硝酸)钠配制而成脱锡剂,当脱锡剂温度为40～80℃,导电辊表面温度为40～70℃时,对粘锡导电辊具有很好的脱锡效果.粘锡导电辊脱锡后的表面粗糙度可以恢复到4.0μm以上,导电辊使用寿命提高80%,降低导电辊修复成本90%,并大幅度减少导电辊更换时间,提高电镀锡机组生产作业率.     

Study on Numerical Simulation of Mold Filling and Solidification Processes under Pressure Conditions

The mold filling and solidification simulation for the high pressure die casting (HPDC) and low pressure die casting (LPDC) processes were studied.A mathematical model considering the turbulent flow and heat transfer phenomenon during the HPDC process has been established and paralled computation technique was used for the mold filling simulation of the process.The laminar flow characteristics of the LPDC process were studied and a simplified model for the mold filling process of wheel castings has been developed.For the solidification simulation under pressure conditions,the cyclic characteristics and the complicated boundary conditions were considered and techniques to improve the computational efficiency are discussed.A new criterion for predicting shrinkage porosity of Al alloy under low pressure condition has been developed in the solidification simulation process.     

Synthesis and Properties of the Bi-Based Superconducting Powder Prepared by the Pechini Process

Bi-based superconductors are of great interest in high-temperature superconductors. We describe what is believed to be the first synthesis of these materials using the Pechini process, a low-temperature synthetic method that often yields inorganic oxide of excellent phase purity and well-controlled stoichiometry. Using this process, it has been possible to synthesize phase-pure Bi-2223 phase by calcining the appropriate polymeric precursors in air at 800°C for several hours. The superconductivity studies show that the Pechini-synthesized materials appear to offer high-quality performance.     

固体理论进展——半世纪回顾

本文回顾了自1964年密度泛函理论(DFT)提出而引入了被称为第一原理计算电子学近半个世纪以来,固体物理在理论、材料与实验上的进展.所选的关注点是那些和微纳电子学与集成电路技术有关的重大进展.内容分为固体理论与计算电子学、低维与超导材料两个部分.硅基CMOS集成电路在经历了本文涵盖的同一历史时期中令人瞠目的高速发展后,无论在研究与产业上都处于一个新发展阶段的十字路口.通过回顾作为现代信息工程基石的固体器件与理论的进展,可以对今后集成电路的发展趋向提供一个分析参考.