Effects on the evolution of microstructure and properties of low-silicon cast aluminum alloys in service

ABSTRACT

The microstructure evolution and property change of four kinds of low silicon cast aluminum alloy exposed to heat for 0–50?h at 200°C were studied by means of Brinell hardness test, tensile property test, friction and wear property test and XRD analysis. The results show that with increasing thermal exposure time, the tensile strength of each group of samples decreased and the amount of wear increased. The tensile strength of samples with more Si content decreased slowly. When the time increased to 50?h, the increase of wear loss was the largest. The hardness of samples after thermal exposure increases compared with that before thermal exposure. The residual stress of (311) diffraction crystal surface of AlSi3.5Mg0.66 under different thermal exposure time was measured. The type of residual stress changed from residual tensile stress to residual compressive stress after thermal exposure. There is an abnormal phenomenon that the hardness of the sample increased and the amount of wear increased, and it is evident that the distribution of residual stress was inhomogeneous after thermal exposure. It is found that with increasing thermal exposure time to 50?h, the average lattice distortion ε of the low-index crystal plane and the high-index crystal plane in the aluminum alloys gradually increased.     

纳米CaCO3微晶的晶格畸变和反常红外特性

利用TEM、SEM、X射线衍射(XRD)和Voigt函数单峰分析法讨论了纳米CaCO₃微晶结构,解释了纳米CaCO₃微晶的反常红外吸收特性,并认为微结构中的尺寸效应使得纳米CaCO₃晶格中存在较大的畸变应力,从而引起了碳酸钙微晶的红外ν₃吸收峰有约40 cm^-1的蓝移和明显窄化。     

基于能量变分法的钢底板波形钢腹板组合箱梁畸变效应分析

为合理分析钢底板波形钢腹板梯形箱梁的畸变效应,按各板件面内外抗弯刚度不变的原则将全截面等效为钢材,利用圣维南原理考虑顶底板对波形钢腹板的约束作用,修正畸变扇性坐标分布模式,基于能量变分法建立畸变控制微分方程。与已有文献及有限元进行对比分析,并研究腹板俯角和波形钢腹板厚度变化对畸变翘曲正应力的影响。结果表明,本文解析解与文献解及ANSYS解均吻合较好;基于圣维南原理修正后的扇形坐标分布模式更合理;利用本文等效方法亦可分析传统波形钢腹板组合箱梁的畸变效应;腹板俯角的设置有利于减小畸变翘曲正应力;波形钢腹板厚度变化对腹板与底板交接处的畸变翘曲正应力影响显著。     

碲锌镉晶体晶格畸变的测定与分析

在高分辨X射线衍射仪上,利用不对称布拉格衍射STD技术与单晶摇摆曲线技术相结合的方法,对碲锌镉单晶材料的晶格畸变进行了分析测定.此方法实现了一次装样,多角度、多次测定晶体的摇摆曲线,从而利用多组实验数据完成多元线性回归方程组的求解,避开了一般应变测定方法中难以确定无应力状态下衍射角的问题.所测定的生长态碲锌镉晶片晶格畸变量为10-3～10-2数量级,该畸变量是碲锌镉晶片存在成份偏析、位错和空位等缺陷以及晶片受到的应力综合作用的结果.     

掺锗提高VO2薄膜的相变温度机理研究

二氧化钒(VO₂)作为一种长久以来备受关注的新型可逆相变材料,发展潜力巨大,其相变温度(T_MIT)的调控一直是研究热点。本文主要利用锗离子作为掺杂离子探索其对VO₂薄膜T_MIT的影响,并尝试解释其内部作用机理。在约1 cm²大小抛光的氧化铝薄片上沉积了一系列含不同比例锗离子VO₂薄膜。研究发现锗离子作为掺杂离子确实有利于T_MIT的提高(本课题T_MIT最大可达84.7 ℃)。T_MIT提高的主要原因是锗离子的引入能够强化单斜态V-V二聚体的稳定性,进而增强单斜态的稳定性,使得低温单斜态向四方金红石态转变更加困难。     

GDP vs. LDP: A Survey from the Perspective of Information-Theoretic Channel

The existing work has conducted in-depth research and analysis on global differential privacy (GDP) and local differential privacy (LDP) based on information theory. However, the data privacy preserving community does not systematically review and analyze GDP and LDP based on the information-theoretic channel model. To this end, we systematically reviewed GDP and LDP from the perspective of the information-theoretic channel in this survey. First, we presented the privacy threat model under information-theoretic channel. Second, we described and compared the information-theoretic channel models of GDP and LDP. Third, we summarized and analyzed definitions, privacy-utility metrics, properties, and mechanisms of GDP and LDP under their channel models. Finally, we discussed the open problems of GDP and LDP based on different types of information-theoretic channel models according to the above systematic review. Our main contribution provides a systematic survey of channel models, definitions, privacy-utility metrics, properties, and mechanisms for GDP and LDP from the perspective of information-theoretic channel and surveys the differential privacy synthetic data generation application using generative adversarial network and federated learning, respectively. Our work is helpful for systematically understanding the privacy threat model, definitions, privacy-utility metrics, properties, and mechanisms of GDP and LDP from the perspective of information-theoretic channel and promotes in-depth research and analysis of GDP and LDP based on different types of information-theoretic channel models.     

Flow dynamics analyses of pathophysiological liver lobules using porous media theory

Blood flow inside the liver plays a key role in hepatic functions, and abnormal hemodynamics are highly correlated with liver diseases. To date, the flow field in an elementary building block of the organ, the liver lobule, is difficult to determine experimentally in humans due to its complicated structure, with radially branched microvas-culature and the technical difficulties that derive from its geometric constraints. Here we established a set of 3D com-putational models for a liver lobule using porous media theory and analyzed its flow dynamics in normal, fibrotic, and cirrhotic lobules. Our simulations indicated that those approximations of ordinary flow in portal tracts (PTs) and the central vein, and of porous media flow in the sinusoidal network, were reasonable only for normal or fibrotic lobules. Models modified with high resistance in PTs and collateral vessels inside sinusoids were able to describe the flow fea-tures in cirrhotic lobules. Pressures, average velocities, and volume flow rates were profiled and the predictions compared well with experimental data. This study furthered our under-standing of the flow dynamics features of liver lobules and the differences among normal, fibrotic, and cirrhotic lobules.     

光学系统时间畸变和色时间滞后的研究

本文对皮秒和飞秒技术中瞬态现象测量系统所用的特殊光学系统校正时间畸变和压缩色时间滞后的问题进行了讨论。实验证明用该方法设计研制的光学系统校正效果显着。