一般Lurie型控制系统的鲁棒绝对稳定性

本文得到一般的Ｌｕｒｉｅ类型非线性控制系统的鲁棒绝对稳定性的充分条件;同时,给出一些例子说明本文结果的有效性．     

The distribution pattern of squares on the stability of F4F6-(BN)n (n = 10–22) polyhedrons

To gain an insight into the structures and stability of F₄F₆-(BN)_n polyhedrons with alternation of B and N atoms, a density functional theory study was performed on all isomers of F₄F₆-(BN)_n polyhedrons with n between 10 and 22. The calculation results demonstrate that the lowest energy isomers do not contain B₄₄ bonds (the bonds shared by two squares) and the energies of those isomers containing B₄₄ bonds increase with the number of B₄₄ bonds linearly, indicating that the energetically favored structures of F₄F₆-(BN)_n polyhedrons satisfy the isolated square rule and square adjacency penalty rule. The structural analysis reveals that the stability is determined by the pyramidalization of B and N atoms at the square–square fusion. The binding energy is fitted to the numbers of edges and a model is proposed for predicting the relative stability of these B–N polyhedral molecules.     

Insights into Aptamer–Drug Delivery Systems against Prostate Cancer

Prostate cancer is a common cancer in elderly males. Significant progress has been made in the drug therapies for prostate cancer in recent years. However, side effects are still problems that have not been overcome by the currently used anti-prostate cancer drugs. Novel technologies can be applied to reduce or even eliminate the side effects of drugs. An aptamer may be a sequence of nucleic acids or peptides that can specifically recognize proteins or cells. Taking advantage of this feature, scientists have designed aptamer–drug delivery systems for the development of anti-prostate cancer agents. Theoretically, these aptamer–drug delivery systems can specifically recognize prostate cancer cells and then induce cell death without attacking normal cells. We collected the relevant literature in this field and found that at least nine compounds have been prepared as aptamer–drug delivery systems to evaluate their precise anti-prostate cancer effects. However, the currently studied aptamer–drug delivery systems have not yet entered the market due to defects. Here, we analyze the published data, summarize the characteristics of these delivery systems, and propose ways to promote their application, thus promoting the development of the aptamer–drug delivery systems against prostate cancer.     

Experimental Study of the Thermal Decomposition Properties of Binary Imidazole Ionic Liquid Mixtures

Ionic liquids (ILs) have a wide range of applications, owing to their negligible vapor pressure, high electrical conductivity, and low melting point. However, the thermal hazards of ILs and their mixtures are also non-negligible. In this study, the thermal hazards of various binary imidazolium ionic liquids (BIIL) mixtures were investigated. The effects of parent salt components and molar ratios on the thermal decomposition temperature (T_d) and flashpoint temperature (T_f) are investigated. It is found that both T_d and T_f increase as the proportion of highly thermally stable components in BIIL mixtures increases. Furthermore, the decomposition process of BIIL mixtures can be divided into two stages. For most molar ratios, the T_f of the BIIL mixtures is in the first stage of thermal decomposition. When the proportion of highly thermally stable components is relatively high, T_f is in the second stage of thermal decomposition. The flammability is attributed to the produced combustible gases during the thermal decomposition process. This work would be reasonably expected to provide some guidance for the safety design and application of IL mixtures for engineering.     

二次有限体积法定价美式期权

本文考虑二次有限体积法定价美式期权.构造了隐式欧拉和Crank-Nicolson两种全离散二次有限体积格式,并得到相应的线性互补问题.采用基于超松弛迭代的模方法求解线性互补问题,并与投影超松弛迭代法作数值比较.数值实验结果表明Crank-Nicolson二次有限体积格式的求解效率高于隐式欧拉格式,模方法的求解速度较快,二次有限体积法的求解精度较高.     

一类带有比例相关捕获函数的时滞微分代数经济系统的Hopf分支分析

本文研究了一类用更为合理的无选择性捕获函数来代替普通的单位捕捞鱼获量函数的微分代数经济系统. 利用范式定理和中心流形定理, 获得了生物经济系统内平衡点局部稳定和Hopf分支的稳定性,改进和推广了已有的结果. 最后, 用数值模拟来证明分析结果的有效性.     

Research on air tightness of image intensifier tube during laser sealing北大核心CSCD

采用高功率YAG激光焊接机对高性能三代像管管壳后端(4J34可伐合金)与荧光屏屏环(4J49可伐合金)进行封接试验。研究了激光功率、脉冲宽度对焊接接头成型及表面热扩散的影响规律。研究表明:4J34合金与4J49合金表面成型质量在设备最大工作电流100 A,激光功率195 W及脉宽1.7 ms时最好,相对于激光功率,脉冲宽度对焊缝熔宽和熔深的影响更加显著,接头焊接中心区硬化最为严重,其硬度最大,热影响区次之。     

陶瓷纤维基硅胶/分子筛复合吸附剂的实验研究

采用浸渍法在基材上原位反应生成硅胶,以硅溶胶作为分子筛的分散剂、黏合剂制备出陶瓷纤维基硅胶/分子筛复合吸附剂,采用静态法测定了吸附剂纸片和块体的吸附量,并利用静态吸附床结构来模拟转轮的工作状态,结果表明:在不同湿度条件下,复合吸附剂具有较高的静态和动态吸附量。     

反射式光纤共焦扫描成像的研究

建立了反射式光纤共焦扫描成像系统,分析了光纤－集光透镜参数Ａ及物透镜有效数值孔径等对系统成像分辨率的影响。并在此基础上选择了合适参数的透镜,获得了优化的反射式光纤共焦扫描成像系统,测试结果表明,该系统具有亚微米级横向成像能力,微米级向层析能力,成像稳定性那,它将应用于材料及生物组织三维成像检测中。     

The use of broadband acoustic transducers and pulse-compression techniques for air-coupled ultrasonic imaging

A pulse-compression technique has been applied to air-coupled testing of solid materials. Capacitance transducers were used to generate wide bandwidth swept-frequency (chirp) signals in air, which were then used to measure and image solid samples in through transmission. The results demonstrate that such signal processing techniques lead to an improvement in the signal to noise ratio and timing accuracy for air-coupled testing. Measurements of thickness and spectroscopic experiments are presented. Images of defects in a wide range of materials, including metals and carbon-fibre composites have also been obtained. This combination of capacitive transducers with pulse-compression techniques is shown to be a powerful tool for non-contact air-coupled ultrasonic measurements.