Analysis and optimization of high-power pulse transformer for SXFEL

Longitudinal injection is a promising on-axis injection scheme for diffraction-limited storage rings. In the latest version of the Hefei advanced light source(HALS), both the dynamic aperture and momentum aperture have been optimized. A longitudinal injection scheme was investigated on the HALS using a doublefrequency radio frequency system. To evaluate the injection performance, various errors were considered. A series of tracking simulations were conducted, and the injection efficiency was obtained under different error levels.     

非线性增益递归滑模动态面自适应NN控制

针对一类严反馈非线性不确定系统的跟踪控制问题,提出一种非线性增益递归滑模动态面 (Dynamic surface control, DSC)自适应控制方法. 通过设计一个新的非线性增益函数,并构造递归滑模动态面的控制策略和新的Lyapunov函数,同时利用神经网络在线逼近系统不确定项, 该方法有效解决了具有输入饱和约束条件下系统控制精度与动态品质间的矛盾,增强了控制器对其自身参数摄动的非脆弱性. 理论证明了闭环系统所有状态是半全局一致最终有界的,且跟踪误差可收敛至任意小.     

Ptolemy离散事件模型形式化验证方法

Ptolemy是一个广泛应用于信息物理融合系统的建模和仿真工具包,主要通过仿真的方式保证所建模型的正确性.形式化方法是保证系统正确性的重要方法之一.本文提出了一种基于形式模型转换的方法来验证离散事件模型的正确性.离散事件模型根据不同事件的时间戳触发组件,时间自动机模型能够表达这个特征,因此选用Uppaal作为验证工具.首先定义了离散事件模型的形式语义,其次设计了一组从离散事件模型到时间自动机的映射规则.然后在Ptolemy环境中实现了一个插件,可以自动将离散事件模型转换为时间自动机模型,并通过调用Uppaal验证内核完成验证.最后以一个交通信号灯控制系统为例进行了成功的转换和验证,实验结果证实了该方法能够验证Ptolemy离散事件模型的正确性.     

凝胶注模工艺制备高强度多孔氮化硅陶瓷

采用凝胶注模成型工艺,成功地制备了具有高强度、结构比较均匀并有较高气孔率的氮化硅多孔陶瓷。本文研究了制得的多孔氮化硅的力学性能和微观结构,并讨论了获得高性能的原因。结果表明,采用适当的成型条件可制备出结构均匀、强度高、加工性能优良的坯体,烧成的多孔氮化硅陶瓷强度均>150MPa,气孔率>50％。SEM照片显示气孔是由长柱状β-Si3N4晶搭接而成的。均匀的气孔分布和柱晶结构是获得高性能的主要原因。     

Mechanism of high-temperature oxidation effects in fatigue crack propagation and fracture mode for FGH97 superalloy

The high-temperature fatigue crack growth behaviors in powder metallurgy(P/M)Ni-based superalloy FGH97 for turbine disk application were investigated at different temperatures(650,700 and 800 ℃)in air using a combination a servohydraulic test system,fractographic and microanalytical investigations.It is found that there is a temperature-sensitive region in which the fatigue life of FGH97 alloy decreases sharply.To further evaluate the crack propagation mode and oxidation effects,interruption experiments were conducted at 700 and 300 ℃,respectively.The results indicate that the reduction of the fatigue lifetime for FGH97 takes place when the fracture mechanism transforms from a predominantly transgranular mode to an intergranular one as the temperature increases.Although the microstructures and mechanical properties may vary with the temperature,they are not the dominating factors contributing to the temperature sensitivity of fatigue property for FGH97.It is the oxidation that governs the fatigue crack growth behaviors in air at elevated temperature.The enhanced thermal activity of oxygen and certain active metal elements result in accelerated oxidation reaction.The brittle oxide intrusions formed at the crack tip and grain boundaries of crack frontier lead to grain boundary weakness,which is responsible for the transformation of crack growth mode and degradation of the fatigue property of FGH97 alloy.     

Fabrication of Densely Packed AlN Nanowires by a Chemical Conversion of Al2O3 Nanowires Based on Porous Anodic Alumina Film

Porous alumina film on aluminum with gel-like pore wall was prepared by a two-step anodization of aluminum, and the corresponding gel-like porous film was etched in diluted NaOH solution to produce alumina nanowires in the form of densely packed alignment. The resultant alumina nanowires were reacted with NH₃ and evaporated aluminum at an elevated temperature to be converted into densely packed aluminum nitride (AlN) nanowires. The AlN nanowires have a diameter of 15–20 nm larger than that of the alumina nanowires due to the supplement of the additional evaporated aluminum. The results suggest that it might be possible to prepare other aluminum compound nanowires through similar process.     

基于概念和关联扩充的文本标题分类机制

文本分类是处理电子可读文本的重要手段，本文提出了基于标题的文本分类机制．其基本思想是：鉴于文本标题的重要性和简洁性，利用汉语语义分类树寻求概念上的扩充，利用语料库的关联矩阵，进行关联扩充，以丰富标题的语义内涵，从而获取较高精度的文本分类结果．该方法不依赖于汉语分析器和相应的领域知识库，速度较快。应用面较广．     

基于UCON的无线阅读DRM系统

针对现有无线阅读DRM技术缺乏真正分布式网络环境下动态授权决策机制的问题,提出一套基于UCON的无线阅读DRM系统方案,阐述系统的模型及其关键技术。实验结果表明系统能有效进行阅读用户进行动态授权并具有良好的可用性。     

A New and Practical Synthetic Method for the Synthesis of 6-O-Methyl-scutellarein: One Metabolite of Scutellarin in Vivo

Scutellarin (1) has been used for the treatment of angina pectoris, cerebral infarction and coronary heart disease with a large market share in China. Pharmacokinetic studies on scutellarin showed that scutellarin (1) is readily converted into its metabolites in vivo. In this paper, a new and practical synthetic method for the synthesis of 6-O-methyl-scutellarein (3) (one metabolite of scutellarin in vivo) is reported. The benzyl bromide was firstly used to selectively replace the acetyl group at C-7 in 7, and was then used to protect the hydroxy groups at C-4'' in 10, 6-O-methyl-scutellarein (3) is obtained in high yield through these methods.     

Electrode wear-compensation of electric discharge scanning process using a robust gap-control

Robust gap-control is applied to compensate for electrode wear in an electric discharge scanning (ED-Scanning) process. This control compensates for the wear without reference to the wear ratio of the electrodes. An auxiliary gap-control loop in the vertical direction can compensate for the wear of the electrode, according to the discharge voltage when the electrode is driven along the two horizontal axes. A proportional controller for a gap-control system with maximal robustness is designed and robustly analyzed to override the non-linear and time-varying feedback. The simulated and practical responses of such a robust gap-control system yield favorable performances. The controller can maintain the location of the discharge on the vertical axis and fix the depth of the removal to that of a particular layer. The practical scanning process reveals that the dimension of a hole can be guaranteed only if the data concerning the depth of removal under specific discharge conditions and electrode diameters are applied.