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针对大规模动态图流三角形计数的边哈希分布式抽样算法
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作者 何玉林 吴波 +2 位作者 吴定明 黄哲学 菲律普弗尼尔-维格 《计算机研究与发展》 EI CSCD 北大核心 2024年第8期1882-1903,共22页
三角形计数是大图分析的一个经典问题,近年的研究工作主要集中在针对静态流式图的三角形数量估计上,相关流式图抽样算法只能处理边的插入操作,无法处理边的删除操作;而现有的动态流式图抽样算法估计准确性又偏低.针对上述问题,提出了基... 三角形计数是大图分析的一个经典问题,近年的研究工作主要集中在针对静态流式图的三角形数量估计上,相关流式图抽样算法只能处理边的插入操作,无法处理边的删除操作;而现有的动态流式图抽样算法估计准确性又偏低.针对上述问题,提出了基于边哈希分配的分布式抽样(edge hashing assignmentbased distributed sampling,EHADS)算法,它是一个用于估计动态流式图中三角形数量的分布式流算法,可以快速准确地估计动态流式图中的全局三角形数量以及每个顶点的局部三角形数量.EHADS算法只对输入的图流进行1次处理,并在多台机器上对边进行抽样.与先进的单机流算法相比,EHADS算法具有2点优势:1)在相同样本容量的情况下,EHADS算法以更短的运行时间获得了更小的估计误差,估计全局三角形数量的误差平均降低了31.79%,估计局部三角形数量的误差平均降低了23.35%;2)EHADS算法能够提供流式图中三角形数量的无偏估计,并且严格的数学证明显示该无偏估计具有更小的方差. 展开更多
关键词 三角形计数 动态 边抽样 分布式算法 边哈希分配
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超超临界汽轮机保护系统软件安全分析技术研究
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作者 夏冰 巩琦 +1 位作者 胡立生 包锦华 《热力透平》 2016年第2期138-143,共6页
目前人们已经认识到传统的安全性方法难以体现保护软件安全性与工艺系统动态之间存在的耦合性。以超超临界汽轮机超高压缸排汽温度保护为对象,利用动态流图模型,对其保护定值进行安全分析,最终得出该保护定值是安全可靠的。这种安全分... 目前人们已经认识到传统的安全性方法难以体现保护软件安全性与工艺系统动态之间存在的耦合性。以超超临界汽轮机超高压缸排汽温度保护为对象,利用动态流图模型,对其保护定值进行安全分析,最终得出该保护定值是安全可靠的。这种安全分析方法对于提高产品的质量等级具有重要的现实意义。 展开更多
关键词 超超临界 安全分析 动态流图模型 保护定值
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基于DFM的AP1000壳内压力超限ESF驱动可靠性分析
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作者 王志超 王豪 周赟 《仪器仪表用户》 2016年第8期1-6,41,共7页
本文运用美国核管会(NRC)报告NUREG/CR-6465提出的动态流图(DFM)可靠性分析方法,以AP1000核电站安全壳压力超限专设安全设施(ESF)驱动系统为对象进行可靠性分析。该方法体现过变量输入输出的因果关系、动态特性、部件状态变化和软件逻... 本文运用美国核管会(NRC)报告NUREG/CR-6465提出的动态流图(DFM)可靠性分析方法,以AP1000核电站安全壳压力超限专设安全设施(ESF)驱动系统为对象进行可靠性分析。该方法体现过变量输入输出的因果关系、动态特性、部件状态变化和软件逻辑对系统可靠性的影响,将数字化保护系统与工艺系统有机结合。其分析结果是带时间标签的质蕴含(PI)集合,对进一步地定量分析以及提高系统的可靠性具有很重要的指导意义。 展开更多
关键词 AP1000 非能动安全壳冷却系统 专设安全设施 动态流图
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Hot deformation behavior and processing maps of as-cast Mg-8Zn-1Al-0.5Cu-0.5Mn alloy 被引量:6
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作者 朱绍珍 罗天骄 +1 位作者 张廷安 杨院生 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2015年第10期3232-3239,共8页
The hot deformation behavior of as-cast Mg-8Zn-1Al-0.5Cu-0.5Mn alloy was studied by hot compression tests at temperatures of 200-350 °C and strain rates of 0.001-1 s-1.The results show that the flow stress increa... The hot deformation behavior of as-cast Mg-8Zn-1Al-0.5Cu-0.5Mn alloy was studied by hot compression tests at temperatures of 200-350 °C and strain rates of 0.001-1 s-1.The results show that the flow stress increases significantly with increasing strain rate,and decreases as the temperature increases.The flow stress model based on the regression analysis was developed to predict the flow behavior of Mg-8Zn-1Al-0.5Cu-0.5Mn alloy during the hot compression,and the model shows a good agreement with experimental results.Meanwhile,the processing maps were established according to the dynamic materials model.The processing maps show that the increase of strain enlarges the instability domains,and the alloy shows good hot workability at high temperatures and low strain rates. 展开更多
关键词 magnesium alloy hot deformation flow stress processing map dynamic recrystallization
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Processing map and hot deformation behavior of Ta-particle reinforced TiAl composite 被引量:6
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作者 Cheng-hao YUAN Bin LIU +1 位作者 Yu-xi LIU Yong LIU 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2020年第3期657-667,共11页
The hot deformation behavior of a Ta-particle reinforced TiAl composite was studied.Ti-48Al-2Cr-2Nb-0.2 W(at.%)/20 vol.%Ta metal matrix composite was fabricated by spark plasma sintering.The deformation behavior was i... The hot deformation behavior of a Ta-particle reinforced TiAl composite was studied.Ti-48Al-2Cr-2Nb-0.2 W(at.%)/20 vol.%Ta metal matrix composite was fabricated by spark plasma sintering.The deformation behavior was investigated by hot compression tests at the temperature ranging from 1050 to 1200℃ and the strain rate ranging from 1×10-3 to 1 s-1.The constitutive equation containing true strain variables was established.The values of activation energy Q under different strain degrees are between 240 and 280 kJ/mol,which are lower than that of pure TiAl.Based on dynamic material modeling,the processing maps at various strain degrees were established,and the optimized parameters for hot working are 1050-1100℃ and 0.005-0.01 s-1.The microstructural evolution during deformation was characterized,which indicated that the dynamic recrystallization plays an important role in this process. 展开更多
关键词 TiAl-based composite flow behavior processing map dynamics recrystallization
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Processing map and microstructure evaluation of AA6061/Al_2O_3 nanocomposite at different temperatures 被引量:2
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作者 H.R.EZATPOUR S.A.SAJJADI +2 位作者 M.HADDAD SABZEVAR A.CHAICHI G.R.EBRAHIMI 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2017年第6期1248-1256,共9页
Hot compression behavior of Al6061/Al2O3nanocomposite was investigated in the temperature range of350-500°C andthe strain rate range of0.0005-0.5s-1,in order to determine the optimum conditions for the hot workab... Hot compression behavior of Al6061/Al2O3nanocomposite was investigated in the temperature range of350-500°C andthe strain rate range of0.0005-0.5s-1,in order to determine the optimum conditions for the hot workability of nanocomposite.Theactivation energy of285kJ/mol for the hot compression test is obtained by using hyperbolic sine function.By means of dynamicmaterial model(DMM)and the corresponding processing map,safe zone for the hot workability of AA6061/Al2O3is recognized attemperature of450°C and strain rate of0.0005s-1and at temperature of500°C and the strain rate range of0.0005-0.5s-1,with themaximum power dissipation efficiency of38%.Elongated and kinked grains are observed at400°C and strain rate of0.5s-1due tothe severe deformation. 展开更多
关键词 NANOCOMPOSITE hot compression test processing map dynamic recrystallization instability flow
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Hot deformation and processing maps of as-sintered CNT/Al-Cu composites fabricated by flake powder metallurgy 被引量:2
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作者 Chun-hong LI Ri-sheng QIU +2 位作者 Bai-feng LUAN Wei-jun HE Zhi-qiang LI 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2018年第9期1695-1704,共10页
The deformation behaviors of as-sintered CNT/Al-Cu composites were investigated by isothermal compression tests performed in the temperature range of 300-550°C and strain rate range of 0.001-10 s-1 with Gleeble 3... The deformation behaviors of as-sintered CNT/Al-Cu composites were investigated by isothermal compression tests performed in the temperature range of 300-550°C and strain rate range of 0.001-10 s-1 with Gleeble 3500 thermal simulator system.Processing maps based on dynamic material model(DMM)were established at strains of 0.1-0.6,and microstructures before and after hot deformation were characterized by scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)and high-resolution transmission electron microscopy(HRTEM).The results show that the strain has a significant influence on the processing maps,and the optimum processing domains are at temperatures of 375-425°C with strain rates of 0.4-10 s-1 and at 525-550°C with 0.02-10 s-1 when the strain is 0.6.An inhomogeneous distribution of large particles,as well as a high density of tangled dislocations,dislocation walls,and some sub-grains appears at low deformation temperatures and strain rates,which correspond to the instability domain.A homogeneous distribution of fine particles and dynamic recrystallization generates when the composites are deformed at 400 and 550°C under a strain rate of 10 s-1,which correspond to the stability domains. 展开更多
关键词 CNT/Al-Cu composites flow stress processing map dynamic recrystallization
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