交流传动试验系统方案综述

随着电力电子器件、数字信号处理、数据采集、实时仿真和控制等技术的发展,交流传动必将取代直流传动占据传动领域的主导地位。各国都在极力开拓和发展交流传动,并研制相应的试验系统以更加方便、快捷、经济地实现对交流传动系统的功能、性能测试。结合交流传动的发展历程,论述了交流传动试验系统的原理,综合比较了各种交流传动试验系统方案并归纳总结了交流传动试验系统的要求,最后提出了今后的发展趋势。     

采用三电平电压型PWM整流器的地铁牵引供电系统

提出了一种基于三电平电压型PWM整流器的新型地铁牵引供电系统(1500VDC),具有节能效果好、功率因数高、谐波含量小等优点,且易于采用模块化和冗余设计.论文重点介绍了变流系统的主电路拓扑、并联控制策略和三电平整流器控制策略,最后给出仿真及实验结果.     

基于专家控制器的水厂加氯串级控制系统

水厂加氯消毒是保证自来水品质的关键环节之一。由于加氯系统具有大时延和时变性的特点,加之系统的干扰因素较多,常规的PID控制器往往难以胜任。采用专家控制与传统串级控制相结合的加氯系统自动控制方案,能有效地解决上述问题。在工程上,通过将该方案与PLC和组态软件技术相结合,成功实现了对南京市某水厂加氯工艺的自动控制,并取得了良好的控制效果。     

Interactive Depth-of-Field Rendering with Secondary Rays

This paper presents an efficient method to trace secondary rays in depth-of-field (DOF) rendering, which significantly enhances realism. Till now, the effects by secondary rays have been little addressed in real-time/interactive DOF rendering, because secondary rays have less coherence than primary rays, making them very difficult to handle. We propose novel measures to cluster secondary rays, and take a virtual viewpoint to construct a layered image-based representation for the objects that would be intersected by a cluster of secondary rays respectively. Therefore, we can exploit coherence of secondary rays in the clusters to speed up tracing secondary rays in DOF rendering. Results show that we can interactively achieve DOF rendering effects with reflections or refractions on a commodity graphics card.     

滑板磨制粉泥在滑板中的利用研究

为了研究滑板磨制粉泥利用的可行性,将经过干燥和碎化处理的滑板磨制粉少量取代或全部取代常用铝锆碳滑板生产配方中的预混粉,成型后的样块经200℃24 h干燥后,分别在电炉中裸烧(500℃3 h、1 000℃3 h)和在滑板生产线的匣钵中埋炭烧成(1 300～1 450℃)。通过检测不同条件热处理后试样的显气孔率、体积密度、质量变化率、线变化率、常温耐压强度、高温抗折强度及抗水化性能发现:用少量(质量分数1.9%～5.5%)的滑板磨制干粉泥部分取代滑板生产配方中的预混粉时,对滑板的性能影响较小;用其全部取代预混粉且加入铝粉和增强抗水化剂进行基质调节时,试样的各项性能接近甚至超过滑板生产试样的。可见,滑板磨制粉泥经干燥和碎化处理后,可作为优质微细粉原料应用于滑板生产中。     

Thermal insulation of muscovite/glass ceramic foam for solid oxide fuel cell

A direct foaming method of dispersed suspensions containing muscovite particulates and a glass powder (47BaO-21B₂O₃-27SiO₂-5Al₂O₃, in mol%) is used to prepare porous ceramic structures. The sintered foams exhibit extremely low thermal conductivity and slight expansion during the thermal treatment at 1000 °C. Both the foam stability and its thermal conductivity are investigated by considering foaming agents, muscovite/glass ratios, solid contents, microwave drying, wetting behaviors, and foam consolidation. One of the muscovite/glass ceramic foam, thermally treated at 950 °C for 1 h, showed the lowest thermal conductivity of 0.18 W m⁻¹ K⁻¹ at 800 °C among all of the prepared samples. Its gas permeability and compressive strength are 0.1 × 10⁻⁷ cm² and 440 kPa, respectively.     

Bubble growth and ink ejection process of a thermal ink jet printhead

The present study investigated bubble growth and the ink ejection process of a thermal ink jet (TIJ) printhead with a thin-film heater on the bottom-wall of the ink nozzle. Numerical predictions are presented for bubble volume, temperature, and pressure, and ink jet ejection length under various heating conditions. An inexpensive optical system was set up to visualize the transient ink ejection process. Experimental results to show the effect of the heating pulse conditions on the ejected droplet volume and ejected ink length are also presented. The experimental and numerical results agree well on both the ejected ink length for shorter time history (< 6 μs) and the threshold operating voltage for the ink ejection.     

广义倍数原理及其应用

本文提出了广义倍数原理,大家熟知的“柯氏倍数原理”只是它的一个特例。用它可使更多的受侧力多跨多层刚架简化为单跨多层刚架来计算,大大地扩大了倍数原理的应用范围。     

低功率激光对大白兔血清LDL含量影响的实验研究

目的探索低功率氦氖激光对大白兔血液LDL含量的影响。方法大白兔分实验组与对照组,以波长为632.8nm,功率密度为5.4mw/cm2氦氖激光照射实验组大白兔,每天20分钟,连续照射10天。用血清脂蛋白琼脂糖凝胶电泳法测定实验组与对照组HDL、LDL、VLDL的含量。结果两组大白兔LDL水平有明显差异。结论低功率氦氖激光能明显降低大白兔血清LDL的水平。     

De-Agglomeration Kinetics of Feedstocks with Granule Tetragonal Zirconia Polycrystalline Powder

This study establishes the relationship between homogeneity of tetragonal zirconia polycrystalline (TZP) feedstocks and the kneading time in order to understand the kneading energy adsorption during the de-agglomeration period of pre-existing ceramic granules. Two spray-dried Y-TZP powders with different compress strengths were investigated using torque rheometer and transmission optical microscopy. Several properties, kneading torque ( T ), Casson viscosity (μ), Reynolds number ( Re ), and dispersive index ( D _s) of the feedstocks were introduced, and monitored as a function of kneading time. Optimal processing windows were identified from the dependence of dispersive index with a power number ( N _p). The best shear-kneading procedure was proposed in consideration of best feedstock homogeneity and shortest kneading time. One homogenous feedstock and two comparable cases were prepared for subsequent injection molding, debinding, sintering, and mechanical testing. The fracture strength of sintering parts by a partially homogeneous feedstock can be improved from 520 to 680 MPa by a homogeneous feedstock.