雷达目标电磁散射特性仿真与测量

首先,对雷达目标电磁散射特性的重要性做了简单介绍,对获取雷达目标电磁散射特性数据的方法进行了分类;然后,详细回顾了电磁仿真与测量的主要方法的基本原理、发展过程与适用范围;最后,阐述了国内在雷达目标电磁散射特性研究方面取得的进展与基本情况,对电磁仿真与测量的技术发展趋势进行了总结。     

深部软岩泵房硐室群集约化设计技术

为了研究深部软岩泵房硐室群空间布置对稳定性的影响,分析了采用常规设计的深部泵房硐室群系统变形破坏特点和原因,提出了深部软岩泵房硐室群集约化设计技术,分析了设计原理和特点,给出了组合吸水并的等效计算公式和硐室群最佳施工过程.结果表明:深部软岩泵房硐室群采用集约化设计减少了吸水井个数、减少或取消了配水巷,提高了整体稳定性,将研究成果应用于我国最深的第三系软岩矿井一柳海矿,效果良好.     

外壳为聚苯乙烯硬泡沫的角锥吸波材料

随着使用频率的降低,微波暗室角锥吸收体的高度也相应增加。传统的聚氨脂泡沫角锥吸收体由于在浸渍和烘干方面存在困难,因而不易制作。为避免聚氨脂泡沫角锥吸收体在大尺寸时浸渍和烘干的困难,以聚苯乙烯硬泡沫板为外壳,以聚苯乙烯泡沫小球和吸波材料混合体为充填物的新型角锥吸波材料已开发成功。聚苯乙烯泡沫具有低密度,高阻燃和低介电常数的特点,因而保证了吸收体的重量轻,阻燃好,吸收性能高的要求。而且吸收体表面平整,洁白,采光好。试验结构表明,500mm高度的吸收体,在2.6-18GHz频率范围内,反射率基本上都优于-50dB。     

GEMGrid: a wafer post-processed GEM-like radiation detector

This paper presents a new wafer post-processed micropatterned gaseous radiation detector called GEMGrid. The device consists of a GEM-like structure fabricated with SU-8 photoresist directly on top of a Timepix chip with zero gap distance. The detector characteristics have been studied in several gas mixtures. The device is capable of tracking minimum ionizing particles and exhibits good energy resolution on ⁵⁵Fe decays. We further show a strongly improved mechanical robustness of these GEM-like structures as compared to a pillar-supported integrated Micromegas.     

基于EMC屏蔽暗室的显示器的电磁泄漏测试

针对计算机系统中显示器电磁泄漏问题的重要性,该文分析了显示器电磁泄露的特性,提出了在EMC屏蔽暗室中测试显示器电磁泄露的方法并进行了实践。在实验中取得了比较具有针对性的数据,并对实验数据进行了初步的分析,得出了相应的结论。     

An analytical and experimental analysis of a very fast thermal transient

According to some international standards, some products, developed for use under heavy thermal conditions, have to be tested by subjecting them for a short time to a particular heating and cooling thermal stress to allow them an acceptable future operative life. It is possible to obtain these fast thermal gradients in confined environments, called climatic chambers where the air is heated by an electrical resistance and is cooled with a finned evaporator which is linked to a vapour compression system subjected to a particular control system of the refrigerating power. In particular, in this paper the air and object tested thermal transients are studied from an analytical and experimental point of view. The study of the mathematical model is realized assuming simplified hypotheses about the air, the object and the air cooled evaporator temperature. The most complex circumstances are related to a very fast temperature decrease because under this working condition the mathematical model is characterized by a nonlinear differential system. The nonlinear term is represented by the refrigerating power that varies in a definite range with the evaporator temperature according to a sinusoid trend. For this power a suitable analytical expression, derived by the control system performance and by the compressor characteristic, has been found. The analytical–experimental comparison during a cooling thermal stress of typical products subjected to international standard tests as the electronic boards, has been carried out showing acceptable results. The model presented is useful to foresee the climatic chamber performances in the presence of a specific refrigerating power trend; this is the start‐point for the design of the vapour compression plant and its control system. Copyright © 2001 John Wiley & Sons, Ltd.     

Effect of animal activity and air temperature on heat production,heart rate,and oxygen pulse in lactating Holstein cows

A linear relationship between heart rate (HR) and oxygen consumption (VO₂) has been reported in homeothermic animals, indicating that is possible to estimate heat production through HR measurements. This relationship may depend on the animal activity and environmental conditions. The main objective of the present study was to evaluate the effect of the air temperature and animal posture and activity on heat production and VO₂ in relation to HR. In addition, as a secondary objective, the energy cost of eating and ruminating versus idling and standing versus lying down was determined. Twelve Holstein lactating cows were housed inside climate-controlled respiration chambers for 8 d, where the air temperature was gradually increased from 7 to 21°C during the night and from 16 to 30°C during the day with daily increments of 2°C for both daytime and nighttime. During the 8-d data collection period, HR and gaseous exchange measurements were performed, and animal posture and activity were recorded continuously. The oxygen pulse (O₂P), which represents the amount of oxygen that is consumed by the cow per heartbeat, was calculated as the ratio between VO₂ and HR. Results showed that heat production and VO₂ were linearly and positively associated with HR, but this relationship largely varied between individual cows. Within the range tested, O₂P was unaffected by temperature, but we detected a tendency for an interaction of O₂P with the temperature range tested during the night versus during the day. This indicates that the effect of air temperature on O₂P is nonlinear. Standing and eating slightly increased O₂P (1.0 and 2.5%) compared with lying down and idling, respectively, whereas rumination increased O₂P by 5.1% compared with idling. It was concluded that the potential bias introduced by these effects on the O₂P for the application of the technique is limited. The energy cost of eating and ruminating over idling was 223 ± 11 and 45 ± 6 kJ/kg^0.75 per day, respectively, whereas the energy cost of standing over lying down was 53 ± 6 kJ/kg^0.75 per day. We concluded that O₂P in dairy cows was slightly affected by both animal posture and activity, but remained unaffected by air temperature within 8 to 32°C. Nonlinearity of the relationship between the O₂P and air temperature suggests that caution is required extrapolating O₂P beyond the temperature range evaluated in our experiment.     

直喷式柴油机活塞燃烧室结构设计与有限元分析评价

缩口型燃烧室能改善发动机的排放性能,正在引起人们的极大兴趣,但认为其可能不太可靠,对此进行了分析设计规则。分析时改变活塞燃烧室倾角的大小及坑底过渡半径,而使凹坑最大直径与唇口径保持不变,燃烧室容积保持不变,并进行温度场分析,从而得出最佳倾角的大小。     

移动通信天线远场三维测试系统集成技术

针对现有及未来5G移动通信天线空间辐射特性测试需求和特点,设计了一套分布式天线远场三维测试系统,集成于高性能微波暗室内。发射天线采用多工位设计,高效率地实现了远程无人值守测试。基于U型测试转台实现了待测天线的三维方向图一键测试,具备双测试通路多频点多端口测试功能,有效提高了天线测试效率。系统软件具有较强后处理能力,将测试理论知识有效地应用于工程实践,如软件时域门和远场修正技术等,可获取更为精确的测试结果。以运营商提供的定向基站天线作为系统性能验证鉴定天线,通过与其在其它优良测试远场获取的测试数据进行对比。结果表明,本系统能够较好地满足运营商对目前移动通信天线测试场地及设备的测试要求,具备一键测试、多功能、宽频带、高精度、高效率等特点,易于拓展具备5G移动通信天线空间辐射特性的测试功能。