X波段功率放大器设计

简要介绍了X波段100W固态功率放大器的设计过程,包括整机的设计框图、关键电路的设计仿真等,从功率管功耗的角度就设计过程中功率管的选择方法进行了详细探讨,并简要介绍了无过冲功率控制技术。     

突然开孔结构风致瞬态内压极值研究

基于经典内压控制方程,对特定开孔时刻下的瞬态内压峰值响应进行了详细研究,分析孔口开启时间对结构瞬态内压峰值的影响。提出突然开孔结构瞬态内压极值的估算方法,并与精确算法进行对比。结果表明:门窗开启时刻的外压值越大,瞬态内压峰值越大,但两者最大值之间存在着一定的时差;瞬态内压极值与外压达极值时的瞬态内压峰值之间的比值可用放大因子G=1.17来描述;提出的极值计算方法能有效地估算突然开孔结构瞬态内压极值。     

Non-overshooting and Non-undershooting Cubic Spline Interpolation for Empirical Mode Decomposition

To suppress the overshoots and undershoots in the envelope fitting for empirical mode decomposition (EMD), an alternative cubic spline interpolation method without overshooting and undershooting is proposed. On the basis of the derived slope constraints of knots of a non-overshooting and non-undershooting cubic interpolant, together with "not-a-knot" conditions the cubic spline interpolants are constructed by replacing the requirement for equal second order derivatives at every knot with Brodlie's derivative formula. Analysis and simulation experiments show that this approach can effectively avoid generating new extrema, shifting or exaggerating the existing ones in a signal, and thus significantly improve the decomposition performance of EMD.     

基于ADS2009的特性阻抗测试仪高速脉冲源的设计

简要阐述了特性阻抗测试技术的基本原理,主要分析了阻抗测试系统的主要组成部分即脉冲源的设计.文中根据阶跃恢复二极管的整形特性设计了一款上升时间达到99.61ps的脉冲源,利用安捷伦的软件ADS2009对设计的脉冲源电路和电路中的关键元器件SRD的动态性能进行了仿真,仿真所得的结果符合IPC-TM-650规范对特性阻抗测试仪脉冲过冲与振铃的要求.     

利率平价的人民币汇率与利率关系的实证研究

在评述利率平价及汇率超调理论模型的基础上，对我国1994年外汇体制改革后，人民币汇率波动及其与利率的关系进行实证分析．并针对利率平价理论在我国现阶段适用程度的差异，引入交易成本对利率平价模型进行修正，力求使其在我国金融市场进一步开放的条件，更好地解释人民币汇率、利率、资本流动之间的关系．     

pH–thermoreversible hydrogels. II. Synthesis and swelling behaviors of N-isopropylacrylamide-co-acrylic acid-co-sodium acrylate hydrogels

A series of pH–thermoreversible hydrogels are prepared from the three molar ratios of N-isopropylacrylamide (NIPAAm) and acrylic acid neutralized 50 mol % by sodium hydroxide (SA50) and N,N′-methylene bisacrylamide (NMBA). The influence of the environmental conditions, such as temperature and pH values, on the swelling behavior of these copolymeric gels is also investigated in this article. Results show that the hydrogels bearing negative charges exhibit different equilibrium swelling ratios under various pH media. The pH sensitivities of these gels also strongly depend on the molar ratio of SA50 in the copolymeric gels; thus, the more the SA50 content, the higher the gel pH sensitivity. These hydrogels exhibited thermosensitivity demonstrating a larger change of the equilibrium swelling ratio in aqueous media under temperature changes. An overshooting phenomenon is observed from the gel swelling kinetics under high-temperature conditions. The said hydrogels are also used to investigate the release of model drugs in this study. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1955–1967, 1999     

无线自组织网络TCP容量优化

为了计算无线自组织网络中准确的TCP容量,并利用其进行有效的窗口控制,以避免拥塞窗口增长过速的问题,提出一种适用于无线自组织网络TCP容量的优化计算。此方法基于时延和空间复用率,考虑网络中竞争干扰,解决了以往的计算方法对拓扑不能广泛适用的问题。模拟结果显示,基于文章的TCP容量进行拥塞窗口调节,能有效地提高网络的吞吐量。     

Preparation of Li-Mg-N-H hydrogen storage materials for an auxiliary power unit

Solid hydrogen storage materials as H₂ supply for PEM fuel cells have been attempted over the past decades because of their high efficiencies in H₂ storage. However, most investigations were focused on the stage of tank design for the storage materials. The Li-Mg-N-H hydrogen storage system was for the first time integrated into a HT-PEM fuel cell stack for a prototype auxiliary power unit, the maximum working temperature being 200 °C. With a designed output of 1 kW, a few kilograms of storage materials are needed. By using commercially available raw materials, an up-scaled preparation of the storage material was performed using laboratory facilities. Preparation conditions were established with the aid of FTIR, TG-DSC and x-ray diffraction to ensure the desired quality of materials. Prior to power the fuel cell stack, the storage materials need to go through an exothermic metathesis, and severe temperature overshooting is expected, which may cause deterioration in material performance and safety issue. Operation conditions were tested and the temperature overshooting could be effectively prevented under adequate conditions.     

低矮房屋瞬态内压的风洞试验研究

设计一种新的试验方法模拟低矮房屋模型的门窗突然开启过程,在边界层风洞中采用高速同步压力扫描系统对模型开孔的瞬态内压响应进行了试验研究,发现了有别于已有试验研究结论的结果并由内压传播理论所定性验证。试验考虑了开孔率和背景孔隙率对风致瞬态峰值内压的影响,结果表明:门窗突然开启的过冲比(定义为瞬态峰值内压系数和稳态峰值内压系数之比)随开孔率的增大而增加,对于气密性较好的房屋由试验得到的过冲比在1.17～1.34之间,而理论计算的过冲比则更大,相应稳态峰值内压随开孔率的变化相对较小。过冲比随背景孔隙的增大而下降,当背景孔隙率达到0.2%时,瞬时过冲现象消失。     

Overshooting Phenomenon in the Hyperbolic Microscopic Heat Conduction Model

The overshooting phenomenon under the effect of the microscopic hyperbolic heat conduction model is investigated. A map tracing the region within which the overshooting phenomenon occurs is presented. The two most important parameters which control the overshooting phenomenon are found to be the first and second time-derivatives of the temperature at t=0. However, in order for the overshooting to appear, a higher initial value of the second time-derivative of the temperature change is required than the initial value of the first time-derivative of the temperature. Overshooting is more likely to appear in the parabolic, rather than in the hyperbolic, microscopic heat conduction model.