高加载率条件下LY12铝合金损伤断裂现象的研究

 本文以球形实体中含有一球形空穴为基本单元，通过分析单元的受力状态，推导出了一个韧性介质空穴增长模型。模型中考虑了介质的硬化，应变率效应，同时还考虑了惯性效应。在考虑空穴成核效应时，采用了热激活成核机制。对LY12铝合金进行了二维层裂实验，采用本文提出的动态损伤模型，借助于二维Lagrange弹塑性流动有限差分程序对二维层裂实验进行了数值模拟，计算结果与实验吻合较好。     

The mechanical anisotropy of stratified polyvinyl chloride

The mechanical anisotropy of a material obtained by stratification of oriented polyvinyl chloride (PVC) layers in different ways has been studied. PVC layers, uniaxially oriented by drawing each with a different draw ratio, were stratified in such a way that their draw axes were either parallel or perpendicular. The propagation velocities of ultrasonic pulses were measured in three principal planes defined by draw axes of the stratified material. With an immersion technique, measurements were performed at 2 MHz and 22°C. Experimentally, it was shown that while stratification of layers with draw axes parallel preserves hexagonal symmetry, the stratified material with layers' draw axes perpendicular possesses orthorhombic symmetry. © 1994 John Wiley & Sons, Inc.     

Future Direction for a Diffusion Barrier in Future High-Density Volatile and Nonvolatile Memory Devices

This article reviews the current status of high-density capacitor for volatile memory devices. The dielectric properties for both the Ta₂O₅ film and the (Ba, Sr)TiO₃ (BST) dielectric materials using either the metal organic chemical vapor deposition (MOCVD) or the atomic layer deposition (ALD) are reviewed briefly. New challenges of dielectric material for the next generation, and serious problems emerged during integration to date using Ta₂O₅ and BST. The material characteristics of many electrode materials for the high dielectric materials are introduced. We present the basic properties and integration issued for MOCVD-ruthenium (Ru). The second part of this review summarized the failure mechanisms from barrier properties of previously reported diffusion barriers and emphasizes new design concepts of diffusion barrier for high-density memory devices. Finally, the future direction for a diffusion barrier to advance high-density memory capacitors is suggested.     

Micro-scale mechanics of the surface- nanocrystalline Al-alloy material

Recentresearchesshowthatthehighstrengthnano-structuredmaterialscanbefabricatedbyusingsomeadvancedtechniques,andthemechanicalbehavioroftheconventionalmaterialscanbeimprovedbyusingasurface-nanocrystallinetechnique.Forexample,byusingthesevereplasticdeformation(SPD)method,onecanfabricatethenanocrystallinematerials[15].TheadoptedSPDmethodsmainlyincludethelargetorsionmethod[1],thelargepressingmethod[4]andtheultrasonicshotpeening(USP)method[5],etc.Theconstructionfeaturesofboththenano-structuredbl…     

Theoretical and numerical analysis for the quasi-continuum approximation of a material particle model

In many applications materials are modeled by a large number of particles (or atoms) where any one of particles interacts with all others. Near or nearest neighbor interaction is expected to be a good simplification of the full interaction in the engineering community. In this paper we shall analyze the approximate error between the solution of the simplified problem and that of the full-interaction problem so as to answer the question mathematically for a one-dimensional model. A few numerical methods have been designed in the engineering literature for the simplified model. Recently much attention has been paid to a finite-element-like quasicontinuum (QC) method which utilizes a mixed atomistic/continuum approximation model. No numerical analysis has been done yet. In the paper we shall estimate the error of the QC method for this one-dimensional model. Possible ill-posedness of the method and its modification are discussed as well.

     

三维有序二氧化锰大孔材料的模板技术合成及表征

以单分散SiO2 胶态晶体球形成的三维有序结构为模板 ,利用胶体晶模板技术合成了三维长程有序的二氧化锰大孔材料 .通过X射线粉末衍射 (XRD)和扫描电子显微镜 (SEM)对产物进行了表征 .其中XRD数据显示所得产物为纯四方相二氧化锰 .SEM结果表明 ,所合成的二氧化锰大孔材料孔大小均匀 ,空间排列高度有序 ,很好地复制了SiO2 胶态晶体球的自组装方式 .此外 ,对三维有序二氧化锰大孔材料的合成过程进行了分析 ,研究了前体填充次数对产物孔结构的完整性和有序性的影响 ,还发现产物孔径的收缩存在异常现象 .     

Domain sensitivity for singular elliptic problems: Harmonic transformation approach

A method for computing the sensitivities of functionals depending on the solutions of elliptic equations defined over variable domains is presented. It is based on the material derivative approach and allows the uniform treatment of both singular and nonsingular cases. The novelty consists in defining the vector field connected with the domain transformation as the solution of an auxiliary elliptic equation. Such a choice does not restrict the range of admissible goal functionals and has many advantages from the numerical point of view. It allows one also to consider singular domain variations.     

电动力学教学改革与实践

文章结合“电动力学”课程内容的特点，采用课内内容与课外内容相结合，理论与实践相结合，吸引学生对自己感兴趣的内容作深入的了解与研究，并写出一份研究性论文或理论性较强的综述性的报告，从而使学生具有初步的分析问题和解决问题的科研能力．这一教学尝试，不仅提高了学生独立从事研究能力，而且也提高了教师的业务水平．     

Advanced muon radiography with compact accelerator system

By using a well-defined mono-energetic, pencil-like, high-energy and intense muon beam, one can realize, via simultaneous measurements of energy-loss and multiple-scattering, a quick and element-selective radiography to detect e.g. a few kg of U which is shielded in a thick Fe container or hidden within 2–3 m of low-Z material. A source of such an ideal beam of muons can be realized in transportable form via truck trailers, by combining a compact 400 MeV electron accelerator for photo π/μ production, a superconducting solenoid for full-solid-angle π/μ capture and transport, a stopping in hot tungsten metal for cooling of energetic μ⁺ to sub-eV μ⁺, and finally a compact linear accelerator for rapid acceleration to 600 MeV. Principle and some details are described.     

Measurement of dynamic properties of dilute polymer solutions with a Laser-Doppler velocimeter

The complex velocity field of an oscillating Couette flow is measured with a Laser-Doppler velocimeter. Different evaluation methods are used for the determination of material functions such as relaxation times and the dynamic complex viscosity.