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截止日期问题是重复性项目调度中研究最为广泛的问题之一,其旨在满足项目截止日期前提下求得一个工作队雇佣总量最小的调度方案。由于重复性项目往往为大型工程建设项目,一个准确的最优进度计划对于节约项目的资源和成本具有重要意义。在平衡线法(LOB)框架下,本文从控制工序的性质出发,研究并分析了控制工序工作队分配与项目总工期之间的关联,给出了截止日期问题的一些特殊性质。基于这些性质,一方面能够帮助项目管理人员判断一个调度方案是否可行且经济,另一方面能够得到一些有效的剪枝策略,从而设计出具有针对性的分支限界算法。最后,通过案例计算和仿真实验验证了本文提出的算法在计算效果和计算效率上的有效性。 相似文献
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Improvement of laser damage thresholds of fused silica by ultrasonic-assisted hydrofluoric acid etching 下载免费PDF全文
Polished fused silica samples were etched for different durations by using hydrofluoric(HF) acid solution with HF concentrations in an ultrasonic field. Surface and subsurface polishing residues and molecular structure parameters before and after the etching process were characterized by using a fluorescence microscope and infrared(IR) spectrometer, respectively. The laser induced damage thresholds(LIDTs) of the samples were measured by using pulsed nanosecond laser with wavelength of 355 nm. The results showed that surface and subsurface polishing residues can be effectively reduced by the acid etching process, and the LIDTs of fused silica are significantly improved. The etching effects increased with the increase of the HF concentration from 5 wt.% to 40 wt.%. The amount of polishing residues decreased with the increase of the etching duration and then kept stable. Simultaneously, with the increase of the etching time, the mechanical strength and molecular structure were improved. 相似文献
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对制冷剂二氟乙烷(HFC-152a)在内径为8mm的水平管内进行了两相流动沸腾摩擦压降的实验测量.实验测量的压力范围为0.19—0.41MPa,热流密度范围为14—62kW/m2,流量范围为128—200kg/m2s.实验测量表明:HFC-152a的两相摩擦压降随质量流量、质量含气率的增大而增大;热流密度则对摩擦压降的直接影响很小,但通过影响两相流流型间接影响了摩擦压降;当流型由分层流动转变为半环状流或环状流时,总压降中加速压降所占比例有所减小,而摩擦压降所占比例则有所增大;摩擦压降随饱和压力的增大而减小.使用两个应用广泛的压降计算式进行了计算.实验测试结果与计算结果对比后发现,Friedel模型与实验结果偏差较大,而Müller-Steinhagen-Heck模型则与实验结果符合较好. 相似文献
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