Incremental maintenance of aggregate and outerjoin expressions

Views stored in a data warehouse need to be kept current. As recomputing the views is very expensive, incremental maintenance algorithms are required. Over recent years, several incremental maintenance algorithms have been proposed. None of the proposed algorithms handle the general case of relational expressions involving aggregate and outerjoin operators efficiently.     

Treatment of Humic Waters By Ozone

Two different generators for ozone were tested, a traditional electrical discharge generator and a generator based upon UV–irradiation of air at 150–180 nm. It was demonstrated that the traditional generator gave slightly higher reductions in levels of color for equivalent ozone dosages. Both gases affected the molecular weight distribution in the way that the bigger molecules were broken down to smaller ones. No significant difference between the molecular weight reduction efficiency of the gases was found.     

糠醛装置腐蚀机理分析及防护

重质糠醛精制装置设备腐蚀严重与糠醛氧化变质有关,通过分析装置设备腐蚀机理和糠醛氧化、变质的原因,提出了用N_2汽提回收和原料脱水等改进措施。     

1000m~3/h空分设备板翅式换热器带水冻堵故障处理

介绍 10 0 0m3 /h空分设备板翅式换热器循环水加杀菌剂产生泡沫 ,引起空冷塔雾沫夹带而严重带水冻堵的故障现象、原因及处理措施 ,并指出运行中的不足。     

罗茨真空泵的溢流阀与旁通阀的组合

在简要地介绍了罗茨泵功能的基础上，通过溢流阀的改进设计，使溢流阀成为既能旁通又能溢流的组合阀，罗茨泵的功能将更加完备。     

喷墨打印机的使用与维护

介绍使用喷墨打印机应注意的事项，探讨打印机墨水消耗过快的问题。     

80年代黄河中游来沙减少的原因分析

80年代黄河中游来沙量减少,主要原因是降雨量减少和降雨强度减小,流域综合治理也起到了减沙作用。据分析,降雨因素减沙约占总减沙量的70％,流域综合治理减沙约占30％。     

铜街子工程坝基预裂控制爆破

本文介绍了在复杂地质条件下,通过反复试验、采用预裂爆破技术在玄武岩坝基进行各种坡面角度的全方位、大面积的生产性实践,并对预裂控制爆破提出了一些意见和具体施工方法.     

Facilities management, building maintenance and modernization link

The widening of interest and scope of property management and maintenance has attracted a greater diversity of professional disciplines into facilities management. Dr Quah, coordinator of CIB W70 on Management, Maintenance and Modernization of Building facilities, expresses her personal views on the current fascination with the subject.     

GaAs器件工艺中等离子刻蚀及计算机辅助监控技术研究

用Ｎ２气和ＮＦ３反应气体，在较低的刻蚀功率下实现了用薄正性光刻胶ＡＺ１５１８作掩模，均匀、快速刻蚀ＳｉＯ２，ＳｉＯＮ，Ｓｉ３Ｎ４，ＷＮ，Ｗ等材料的等离子刻蚀技术。利用到蚀过程中射频参数的变化和计算机技术，将射频参数的变化在计算机屏幕上实时显示，实现了计算机辅助监控和终点检测技术。