义齿CAD/CAM系统中标准牙冠数据库的建立

CAD／CAM技术应用广泛，将其应用于口腔修复学中则是一个全新的课题。文章结合标准牙冠数据库的建库实践，从设计与制造技术层面上阐述了义齿CAD／CAM系统中标准牙冠数据库建立的过程，主要包括：利用三维机械式扫描仪扫描全口牙列28颗标准牙冠模型、利用图形处理软件对获得的数据进行处理、重建牙冠三维曲面模型，并根据国人恒牙统计数据调整模型。从而建立了具有标准解剖形态的牙冠图形数据库(动态)，并可以通过调整模型，使模型在任意方向产生位移，旋转和形变。文章最后指出数据库的建立为后阶段义齿的计算机辅助设计和制造(CAD／CAM)打下了基础。     

脉冲进气旋转喷吹技术的水力模拟

在铝合金熔体净化旋转喷吹技术的基础上 ,采用水力模拟实验研究了脉冲进气方式对气泡大小的影响。实验结果表明 :脉冲进气方式有利于产生射流 ,使气泡变小 ,并增加了气泡与熔体接触的比表面积 ,从而改善了除氢的动力学条件 ,有利于提高除氢效果。     

Sensing, modeling and control for laser-based additive manufacturing

Laser-Based Additive Manufacturing (LBAM) is a promising manufacturing technology that can be widely applied to part preparation, surface modification, and Solid Freeform Fabrication (SFF). A large number of parameters govern the LBAM process. These parameters are sensitive to the environmental variations, and they also influence each other. This paper introduces the research work in RCAM on improving the performance of the LBAM process. Metal powder delivery real-time sensing and control is studied to achieve a controllable powder delivery for fabrication of functionally graded material. A closed-loop control system based on infrared image sensing is built for control of the heat input and size of the molten pool in the LBAM process. The closed-loop control results show a great improvement in the geometrical accuracy of the built features. A three-dimensional finite element model is also established to explore the thermal behavior of the molten pool in the closed-loop controlled LBAM process.     

面向网络化定制的产品族复合建模技术

在分析了网络化定制关键技术的基础上，针对性地对信息映射方法和产品族建进行了研究。提出了多层结构信息映射模型，以及综合类元件和参数化特征建模的双层复合产品族模型。结合本方法和以往网络化制造领域中所取得的成果，实现了较完整的基于Web的个性化定制过程。     

Some new operational modes and parameters of stress relaxation for the viscoelastic characterization of solid polymers. III. The area ratio mode and the intrinsic “strain–clock” function

The introduced area ratio mode of operation with its corresponding parameters seems to have a fairly high sensitivity to the viscoelastic response of the solid polymer. This appeared from the fact that a good distinction among the linear viscoelastic, the nonlinear viscoelastic, and the viscoplastic ranges of behavior can be made. By using a relevant rheological modeling and its corresponding algorithmical approach, in the case of isotactic polypropylene, this material can be characterized as a morphological three‐phase material consisting of an intraspherulitic crystalline, an amorphous phase, and a interspherulitic para‐crystalline phase. In this sense, the material was simulated using two models: the Poynting–Thomson and the Maxwell–Wierchert, from where a good response of the material to the first model appeared. The so‐called intrinsic “strain–clock” function and its corresponding coefficient of strength of nonlinear viscoelastic behavior, which were relieved by the experimental data, seem to be some powerful and very practical “tools” that can give a proven suplementary characterization of the material. Finally, by this intrinsic function, the existence of permanent internal stresses, was confirmed, in an indirect way, which was mentioned in part II of this study. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 149–158, 2003     

Simulation studies on the fuel electrode of a H2---O2 polymer electrolyte fuel cell

The macro-homogeneous porous electrode theory is used to develop a model which describes the catalyst layer of the hydrogen electrode formed by catalyst particles that are bonded to the membrane. The water transport in the catalyst layer and polymer electrolyte membrane is considered. The effects of catalyst layer structure parameters such as polymer volume fraction, catalyst layer thickness, platinum loading and reactant gas humidity as well as CO poison on the hydrogen electrode behavior are examined. The results show that the catalyst layer thickness has a significant effect on the electrode performance. A thicker catalyst layer will result in a larger ohmic voltage loss and higher catalyst cost. The optimal polymer volume fraction and catalyst layer thickness are 0.5 and 1.5–4 μm, respectively, for this electrode. An optimal platinum surface coverage on carbon need not exceed 20% (20 wt% Pt/C). Larger platinum coverage will increase the cost, but only slightly enhance the electrode performance.     

Theoretical Models for Binder Burnout

The kinetics of binder burnout, from a ceramic green body, are considered for the case of an "unzipping" binder which decomposes to produce a volatile monomer. The process is considered to fail if the concentration of monomer in the green body exceeds that in equilibrium with vapor at 1 atm (≅10⁵ Pa), when an internal bubble would be expected to form. Steady-state diffusional calculations and computer simulations explore the size and temperature dependence of the process and are in agreement. The model suggests that it is not feasible to burn out a large flat piece greater than about 3 mm thick, without going to very long times of burnout. The kinetics are significantly improved if porosity develops in the piece during the early stages of decomposition, as opposed to the retreat of the binder into the piece on a uniform front.     

分子蒸馏过程模型化研究进展

介绍了分子蒸馏基本原理和常用分子蒸馏设备 ,系统地对分子蒸馏过程模型化的研究进展情况进行了叙述 ,重点介绍了蒸发系数法、液体内部传质传热和蒸馏区惰性气体压力对分子蒸馏的影响等方面的研究结果 ,并对其进行了评述 ,同时对分子蒸馏过程研究的进一步发展提出了一些展望。     

Transitions of saturated monoacid triglycerides: Modeling conformational change at glycerol during α→β′→β transformation

The glycerol region geometry of modeled saturated monoacid triglycerides was altered by bond rotations and minor angle distortions to convert theoretical α-forms into bent β′- and β-forms. Direct α to β conversion involves lateral disruption of fatty chain packing to generate side-chain character typical of the β-form. Such disruption, which could contribute to fat bloom, allows additional molecular movement and shifts in molecular mechanics energy (MME) that may approximate thermal changes observed by differential scanning calorimetry during α to β transformations. Energy calculations at 100 points throughout each transformation identified plausible conversion routes. A two-stage conversion, α to either of two stereospecific β′-forms bent at glycerol followed by subsequent conversion to β, showed less chain movement and more favorable MME than direct α to β conversion. The preferred path, based on energy profiles of each conversion, involves a β′-D form and rotation of carbonyl to α-carbon bonds in chain #2 and a side chain (chain #3).