广州地铁集中冷站的自动控制

本文介绍广州地铁二号线集中冷站的空调制冷自动控制系统的设计，对其控制原理与节能优化进行分析。     

光纤喇曼放大器的功率转换效率分析

在定义光纤喇曼放大器(FRA)功率转换效率(PCE)的基础上,考察了不同工作条件下光纤喇曼放大器的功率转换效率,分析PCE与光纤喇曼放大器的输入信号功率、输入泵浦功率和光纤长度的关系,比较了分布式与集总式FRA的功率转换效率,给出提高FRA功率转换效率的途径。     

乙苯/苯乙烯塔分离效率问题的技术分析及整改措施

分析了齐鲁分公司200kt/a乙苯/苯乙烯装置乙苯/苯乙烯塔(T-401)分离效率低的原因,即降液管设计偏小,液体在降液管内流速过快,引起液体飞溅;安装分布器使用的石棉垫片溶胀而粉碎后堵塞了分布槽;分布器上使用的垫片脱落形成缝隙而漏液;填料装得不密实,留有缝隙;二级分布槽变形等.针对存在问题提出了相应的整改措施,并考察了整改措施实施效果.结果表明,整改后该塔的分离能力满足了工艺要求,并有一定的操作弹性.     

Forming the optimal union of multiple databases

Many organizations, best illustrated by libraries, have access to hundreds of databases possessing varying degrees of complimentary and overlapping records. While users may receive positive marginal benefits from data duplications, all databases and their services cannot be supported because of resource limitations. This paper attempts to conceptualize the problem of database collection in an environment of multiple databases, with differential content and performance characteristics, diverse users, and limited resources. It defines the database collection problem as a constrained zero-one integer programming problem and solves for the optimal combination or union of databases. Several extensions are shown, where special conditions are imposed on the relationships between databases and/or their availability.     

Two- or three-stage least squares?

Two elements enter the choice between 2 and 3SLS for full-system estimation: statistical efficiency and computational cost. 2SLS always has the computational edge, but 3SLS can be more efficient, a relative advantage that increases with the strength of the interrelations among the error terms. A measure of these interrelations is thus helpful in making the choice, and, when there are only two equations, this has suggested using a high pairwise error correlation as an indicator of when to use 3SLS. In larger systems of equations, however, these pairwise correlations can remain small even though more general interrelations give 3SLS the relative advantage. More general indicators are therefore needed, and this paper suggests three such and demonstrates their efficacy.Professor of Economics, Boston College, and Principal Research Associate, Center for Computational Research in Economics and Management Science, MIT. All computation was done on the TROLL system at MIT. My thanks go to Josh Charap for his able research assistance. This research was sponsored in part by the National Science Foundation under grant #IST-8420614.     

一种新型悬臂棒条筛的设计与应用

介绍了一种新型悬臂棒条筛分机械,论述了其结构、工作原理和技术特性。从理论和实践两方面论证了它的结构、处理能力、筛分效率、返矿率都明显优于普通悬臂棒条筛分机械,可广泛应用于高炉槽下烧结矿的筛分作业。     

DC-DC电荷泵的研究与设计

以Dickson电荷泵的基本原理为出发点，研究了一种将正电压输入转为负电压输出的开关电容电路。由于开关电容的充放电特点，为确定电容时间常数，采用非交叠时钟控制信号避免了由于时钟交叠而造成的当电容充电还未完成即对下一级电容进行放电的现象。同时，参考功率MOS-FET的电容模型通过增大驱动电路的电流减小了开关管的上升延时，提高了开关动作的速度，使转换效率得到明显提高。此电路结构简单，性能优良，易于集成，可广泛应用于输出负电压的电源产品中。     

Delphi开发环境下的实时数据采集程序设计

本文介绍了利用Delphi开发平台开发数据采集程序的两种方法，并结合某测深仪给出了一个编程的例子.