Fine particle physics and technology; some results

The new techniques of fine particle synthesis are shown to lead to better ceramic materials such as yttrium iron garnet (YIG) and ferroelectric lead zirconate titanate (PZT). The densities are greater than 99% of the theoretical density and the grain size can be easily controlled from 2 microns upwards. For YIG this means higher values of the nonlinear spin-wave excitation thresholdh _c. For PZT the result is higher values of the tensor componentd ₃₃ and poling voltage. It is also shown that the fine particle systems and the fine-grain microstructure lead to interesting physics results. For PZT the lowering of the peak dielectric constant, the increasing transition temperatures and the decreasing values ofd ₃₃ with decreasing grain size can be understood in terms of the changing low-frequency cut-off of the soft lattice vibration mode. Another interesting result is that for 2000 Å size particles of α-Fe₂O₃ the anisotropy constant is found to be 1·38 × 10² ergs/cm³ from Mössbauer measurements.     

海外科研开发的几个重点项目

（1）论述勘探开发海天然气水合物矿藏,待解决的一些问题,试验室模拟它成长和溶解的实验,探索利用它的必要条件;（2）简要介绍美国,日本,欧洲几个国家和我国,研究纳米技术的安排;（3）可代替有机溶剂的人工合成离子液的应用开发情况;（4）欧美大,中,小企业都设有专为精细化学品的中间体,助剂以及其他的成品或半成品的委托制造服务部。既为客户生产小量或少量的产品,又提高技术开发能力,形成自己的专利,还是有偿服务,一举三得。     

2Gsps高速数据采集系统的设计与实现

本文介绍了一种基于交替采样技术的高速数据采集系统，该系统采用了两片采样率为1GSPS的A／D实现了2GSPS的采样率，并利用FPGA对A/D输出数据的进行转换和缓存。本文着重介绍了该数据采集系统设计和高速存储所涉及到的问题，并给出了仿真波形。     

某型数字射频存储器的设计研究

数字射频存储器(DRFM)采用高速采样和数字存储作为其技术基础,具有对射频和微波信号的存储和再现能力,可实现对雷达设备性能的无线检测。但DRFM系统设计中存在着高速高精度信号采集与回放、高速大容量数据实时存储等诸多设计难点。本文以实际工程项目为背景,论述了某型DRFM系统的技术要求、总体设计及系统的测试验证,并着重论述了在本项目中解决DRFM系统设计中诸多难题的方法。     

Sensitivity analysis of distributed parameter elements in high-speed circuit networks

This paper presents an analysis method, based on MacCormack's technique, for the evaluation of the time domain sensitivity of distributed parameter elements in high-speed circuit networks. Sensitivities can be calculated from electrical and physical parameters of the distributed parameter elements. The proposed method is a direct numerical method of time-space discretization and does not require complicated mathematical deductive process. Therefore, it is very convenient to program this method. It can be applied to sensitivity analysis of general transmission lines in linear or nonlinear circuit networks. The proposed method is second-order-accurate. Numerical experiment is presented to demonstrate its accuracy and efficiency.     

Effect of Media Grain Shape on Particle Straining during Filtration

This paper investigates how straining mechanisms of angular media (crushed limestone) provide improved filtration performance compared to rounded media (river stone). Columns of granular media were set in resin, sectioned, photographed, and digitized to produce a three-dimensional model of pore space geometry. This process was repeated for four filter media, each representing different grain shapes or packing densities. From measured pore throat distributions, a stepwise particle movement model was used to estimate the maximum volume of particles that could be stored in the bulk of the filter media. The results showed that the more angular the media, the wider the range of particle sizes that could be strained in the bulk of the filter. The stepwise model was applied only to individual particles; trapping of colloidal particles was not considered. However, when individual particles are too small to be strained, the same pore throat trapping contributes to the physical capture of avalanches and flocculates. Thus the findings of this work are relevant to deep bed filtration applications where headloss results from straining, such as storm-water best management practices or soil filters.     

Sensitivity analysis of distributed parameter elements in high-speed circuit networks

This paper presents an analysis method, based on MacCormack＇s technique, for the evaluation of the time domain sensitivity of distributed parameter elements in high-speed circuit networks. Sensitivities can be calculated from electrical and physical parameters of the distributed parameter elements. The proposed method is a direct numerical method of time-space discretization and does not require complicated mathematical deductive process. Therefore, it is very convenient to program this method. It can be applied to sensitivity analysis of general transmission lines in linear or nonlinear circuit networks. The proposed method is second-order-accurate. Numerical experiment is presented to demonstrate its accuracy and efficiency.     

FeCrAl和高镍铬合金涂层的抗高温腐蚀性能研究

根据火电厂锅炉的运行工况,采用高温涂盐试验对高速电弧喷涂技术制备的FeCrAl涂层和高镍铬合金涂层进行耐高温腐蚀性能试验,并通过金相显微镜、扫描电镜、X射线衍射、能谱分析等手段对涂层在熔盐环境下腐蚀前、后的性能和腐蚀机理进行细致研究。结果表明,FeCrAl和高镍铬合金涂层均具有良好的抗高温腐蚀性能,是一种经济有效的火电厂锅炉水冷壁防护涂层。     

高速PCB串扰分析及其最小化

技术进步带来设计的挑战,在高速、高密度PCB设计中,串扰问题日益突出。本文就串扰原理和对信号完整性影响进行分析,并在此基础上提出了高速PCB设计中串扰最小化的方法。