Model and simulation of a new ultra-narrow trigger frequency alterable pulse generator

Two new kinds of ultra-narrow trigger frequency alterable picosecond pulse generator are presented. One can produce positive pulses and the other can produce negative pulses. The two pulse generators are subdivided into three parts: signal driving circuit, differentiator network and pulse shaping circuit. The pulse shaping circuit is made of step recovery diode (SRD) and short-circuit microstrip line. A positive pulse with width of 54 ps (50%–50%), rising time of 30 ps (10%–90%) and falling time of 32 ps (90%–10%), and a negative pulse with width of 54 ps (50%–50%), rising time of 30 ps (90%–10%) and falling time of 30 ps (10%–90%) are achieved in simulation. All of the components are ready-made and inexpensive. They can be applied in ultra-wideband (UWB) communication system, such as transmitters and receivers.     

旧路平面线形测量及计算机辅助拟合

为实现旧路改造时旧路平面及纵断面线形的拟合,在完成旧路路面分中点、一元线性回归穿线交点以及曲线参数初步配置的基础上,计算路面分中点至初步拟合平面线形的法线偏差,并依据法线偏差分布特征与圆曲线半径偏差及缓和曲线长度偏差的相关关系,调整旧路路面各段平曲线的圆曲线半径及缓和曲线长度,从而提高拟合精确度.     

发动机冷却风扇的降噪研究与优化

介绍了汽车发动机冷却风扇噪声的产生机理,简述了影响冷却风扇噪声的风扇性能参数、结构参数、安装条件等因素。结合新技术的发展对发动机风扇的降噪策略进行了研究,并在此基础上对原风扇进行了优化设计。优化前、后风扇性能参数的对比结果表明,优化后风扇风量和静压略有增加,消耗功率和噪声均有所降低,达到了降低风扇噪声的效果。     

基于多体动力学的钢板弹簧建模方法研究

简述了钢板弹簧的3种建模方法.分别运用ADAMS/Car的非线性梁建模方法和ADAMS/Chassis的专业板簧模块leafspring,建立了某轻型货车钢板弹簧多体动力学模型,并将两模型集成到同一前悬架中进行了静力学和动力学仿真和试验对比.结果表明,采用两模型所得到的仿真结果具有较高的一致性,且仿真结果与试验结果吻合...     

增程式电动汽车动力系统设计与仿真研究

针对电动汽车续驶里程短的问题,为开发的增程式电动汽车动力系统进行了结构分析和主要参数匹配。基于AVL-Cruise/Simulink联合仿真平台,采用定点能量管理策略,对设计的动力系统进行了仿真验证。结果表明,整车动力系统的设计和参数匹配比较合理,能实现增程器的高效工作和有效延长电动汽车的续驶里程。     

Nonlinear analysis of short concrete-filled double skin tube columns subjected to axial compressive forces

Proper material constitutive models for concrete-filled double skin tube (CFDST) columns with circular cross-section and subjected to axial compressive forces are proposed and verified against experiment data using the nonlinear finite element program Abaqus. It is shown that CFDST columns can provide a good confining effect for concrete core, especially when the diameter-to-thickness ratios of both the outer and the inner tubes are small. In addition, empirical equations are proposed to predict the lateral confining pressure of the concrete core for CFDST columns. Finally, the axial strengths of the CFDST columns calculated by the proposed formulations are compared with AISC formulations against the experimental data. It has been shown that the proposed formulations are better than the AISC formulations.     

Discriminant analysis in the study of Alzheimer’s disease using feature extractions and support vector machines in positron emission tomography with 18F-FDG

With more successful applications of advanced medical imaging technologies in clinical diagnosis,various analytic discriminant approaches, by seeking the imaging based characteristics of a given disease to achieve automatic diagnosis, gain greater attention in the medical community. However the existing computer-aided discriminant procedures for Alzheimer's disease(AD) are yet to be improved for better identifying patients with mild cognitive impairment(MCI) from those with AD and those who are cognitively normal. In this work we present a computer assisted diagnosis approach by first statistically extracting characteristics from whole brain2-deoxy-2-(18F)fluoro-D-glucose positron emission tomography(18F-FDG PET) images, and then using support vector machines for classification. Evaluations of the proposed procedure with patient data exhibit satisfactory accuracies in distinguishing AD from its early stage MCI, and normal controls.     

乳化沥青冷再生试验方法改进及性能研究

对《公路沥青路面再生技术规范》（JTG F41-2008）中乳化沥青冷再生混合料试验规程中的最佳含水率OWC的确定方法以及试件成型的养生温度等进行改进,以完善和简化规范要求的试验方法,并通过室内试验对改进后的试验方法进行验证和对比研究。研究表明,使用最佳流体含量OFC作为乳化冷再生混合料外加水的控制指标优于规范要求的最佳含水量OWC指标;提高试验养生温度至110℃,可以获得与规范60℃养生温度相似的结果,并能够缩短试验所需时间,提高工作效率;乳化沥青冷再生混合料具有较好的水稳定性能及高温稳定性能,能满足或高于热拌沥青混合料的技术要求。     

室内停车场防撞带设计的碰撞仿真分析

针对室内停车场碰撞事故的伤害问题,提出了停车场防撞带的设计,建立有无防撞带的车辆碰撞模型,并对长方体防撞带与波浪形防撞带进行性能分析比较,运用LS-DYNA软件对车辆、防撞带以及墙体碰撞进行仿真模拟。得到防撞带和车辆翼子板的等效应力分布和能量转化情况,证实了防撞带能有效减少车辆的损害程度,且长方体防撞带效果更好。     

Study on horizontal and vertical temperature gradient of ballastless track on curve lineEI北大核心

Research purposes: In order to get the time-varying rules of temperature field distribution in the track structure with superelevation and build the horizontal and vertical temperature gradient of ballastless track, a continuous observation of CRTS II; by using temperature sensors on curve segment of a passenger dedicated line was held. Research conclusions: (1) The temperature change of ballastless track between daytime and nighttime is big, the temperature changing value of surface was 24.7℃ in maximum, 19℃ in average. (2) The temperature changing value became small and the time of maximum temperature come late with the increase of distance to surface. (3) At the bottom of the track structure, the temperature changing value was 6.1℃ in maximum, 5.0℃ in average. (4) Fitting curve of vertical temperature gradient of longitudinally connected ballastless track on curve line can be exponential curve, and the curve sharp can match the distribution about the vertical temperature gradient of the code for design of bridge and culvert in China. (5) The horizontal temperature gradient of the CRTS II; longitudinally connected ballastless track included the track slab and support layer, temperature gradient of track slab could be fitted by using quadratic function, temperature gradient of support layer could be fitted by using piecewise linear function. (6) This study can provide guidance for the temperature load model in the design of high speed railway in central China.