Scheduling algorithm based on prefetching in MapReduce clusters

Due to cluster resource competition and task scheduling policy, some map tasks are assigned to nodes without input data, which causes significant data access delay. Data locality is becoming one of the most critical factors to affect performance of MapReduce clusters. As machines in MapReduce clusters have large memory capacities, which are often underutilized, in-memory prefetching input data is an effective way to improve data locality. However, it is still posing serious challenges to cluster designers on what and when to prefetch. To effectively use prefetching, we have built HPSO (High Performance Scheduling Optimizer), a prefetching service based task scheduler to improve data locality for MapReduce jobs. The basic idea is to predict the most appropriate nodes for future map tasks based on current pending tasks and then preload the needed data to memory without any delaying on launching new tasks. To this end, we have implemented HPSO in Hadoop-1.1.2. The experiment results have shown that the method can reduce the map tasks causing remote data delay, and improves the performance of Hadoop clusters.     

无溶剂碱催化制备取代2-氨基-2-色烯

在氢氧化钠催化及无溶剂条件下,由芳亚甲基丙二腈与1-萘酚或2-萘酚发生加成、环化反应生成相应的取代2-氨基-2-色烯。     

Investigation of electroless plating of Ni–W–P alloy films

The electroless deposition of Ni–W–P alloy coatings onto metal substrates using H₂PO₂ ^– as reducing agent from solutions containing nickel sulfate, sodium tungstate, sodium citrate, ammonium sulfate and other additives was studied. At most temperatures (60–80 °C) and pHs (7–11) investigated, bright and coherent coatings uniform in appearance were produced. Phosphorous and tungsten contents ranging from 3.5 to 8 wt % and 0.5 to 6 wt %, respectively, were obtained depending upon solution temperature and pH. Trends such as the effects of pH and temperature on average metal deposition rate and the P content in the alloy are similar to that reported previously for the Ni–P system. Correlation of open-circuit potentials with events occurring at the electrode surface in different solutions and polarization curves provide strong evidence that Ni²⁺ ions participate in W and P deposition, H₂ evolution and H₂PO₂ ^– oxidation and that H₂PO₂ ^– ions participate in cathodic reduction. This indicates that the partial reactions for the Ni–W–P system do not occur independently of one another.     

Oxygen-ion diffusion and electrical conduction of La2Mo2?2 x Fe x O9?δ systems

Based on the novel oxygen ion conductor La₂Mo₂O₉, a series of Fe-doped samples of La₂Mo_2−x Fe _x O_9−δ (x = 0, 0.025, 0.05, 0.1) was prepared by conventional solid-state reaction method. The structure, phase transition, oxygen ion diffusion and electrical conductivity were studied with X-ray diffraction (XRD), differential scanning calorimeter (DSC), direct current (dc) resistivity, and dielectric relaxation (DR) measurements. One DR peak associated with the short-distance diffusion of oxygen vacancies was observed in both temperature and frequency spectra. The activation energy for oxygen ion diffusion in Fe-doped La₂Mo₂O₉ samples was smaller than that in un-doped samples. Fe doping can increase the ionic conductivity of La₂Mo_2−x Fe _x O_9−δ samples as well as the ionic transference number in the temperature range from 680°C to 400°C in comparison with the un-doped samples, although the electronic conductivity slightly increases. It is found that because of the small solubility of Fe₂O₃ in La₂Mo₂O₉ (<5%), Fe doping cannot suppress the phase transition that occurred around 570°C, but 2.5% K doping at La site at the same time (e.g. in sample La_1.95K_0.05Mo_1.95Fe_0.05O_9−δ ) can completely suppress this phase transition and increase conductivity at lower temperatures.     

Study on removal mechanism and removal characters for SiC and fused silica by fixed abrasive diamond pellets

Fixed abrasive is known as a high-efficient and stable technique for fabricating various materials. This work studies the removal mechanism and removal characters of fixed abrasive diamond pellets (FADPs) for lapping SiC and fused silica. The critical sizes of diamond particles changing brittle fracture to ductile removal (with better surface roughness and less damages) are figured out for SiC (9.56 μm) and fused silica (0.53 μm). Multi-distribution models are presented and a mathematical removal model is built based on Preston law. Then, removal characters of FADPs are investigated, including removal profile, removal rate, linear removal, removal stability, surface roughness, subsurface damage etc. Results show that (i) the removal shape is predictable and the removal rate is highly correlative with diamond size, velocity and pressure; (ii) the cumulative removal is temporally linear and removal stability is within ±10%; (iii) SiC can be ductilely lapped by 1.5, 3, 5 μm pellets, with best roughness Ra=4.8 nm and a specular surface for optical metrology; (iv) removal of fused silica is mostly brittle fracture and it can change as semi-ductile by 1.5 μm pellets, with a non-specular or semi-specular surface which is hard for optical metrology; (v) subsurface damage is highly dependent on diamond size, but free to pressure and velocity. Finally, two engineering applications validated its feasibility in uniform or deterministic lapping/polishing of optical mirrors.     

A unified point-by-point planning algorithm of machining fixture layout for complex workpiece

Workpiece-fixturing is necessary to achieve the correct position of the workpiece with respect to the cutting tool. Therefore, a unified point-by-point planning algorithm of fixture layout is systematically created for a complex workpiece based on the discretization thought. Firstly, based on the inclusion of the theoretical Degrees of Freedom (DOFs) within the practical DOFs and the relationship between the locator number and the rank of Jacobian matrix, two necessary and sufficient conditions are suggested for the judgment criterion of locating determination. According to the variation of locating reference and locator number, a planning algorithm of locating layout is further established by iteratively analysing the locating determination. Secondly, the combination of the virtual work principle with the linear programming technology is employed to formulate a judgment criterion for fixturing stability. Consequently, with the discretization of clamping surfaces, a deterministic algorithm of clamping force is suggested by evaluating the fixturing stability at every node. Three typical examples are finally used to demonstrate the design procedure of fixture layout.     

液压作动筒裂纹分析

某型发动机液压作动筒在打压和试车阶段发现泄漏,检查发现焊缝处存在裂纹。利用微距照相机和扫描电镜对液压作动筒裂纹外观、裂纹断口进行宏微观观察,并用能谱仪进行成分分析,利用金相显微镜和显微硬度计对作动筒进行了组织与硬度检测。结果表明：液压作动筒受到应力腐蚀作用,在打压试验或试车前期就萌生裂纹,造成早期失效;建议严格控制焊缝背面余高和尖角过渡,同时从作动筒清洗等工序查找腐蚀介质来源并加以控制。     

即插式家用电能测量仪的设计

本文阐述了家用电能测量仪的工作原理及设计过程,并列出了整体设计过程中需要注意的问题。     

高速CO2焊电流波形控制系统

针对高速CO2焊焊缝成形差、飞溅大的问题,提出了一种新型的焊接电流波形控制方法,在短路阶段控制短路电流和电流上升率,在燃弧阶段采用大恒流 小恒流的两段恒流法来控制燃弧能量.根据该控制原理,设计了基于单片机控制的高速焊系统和控制软件.探讨了波控参数对焊缝成形的影响,并通过大量试验对波控参数进行优化.试验结果表明,该系统采用两段恒流控制法对电流波形实时控制,可精确控制燃弧能量,有效地改善焊接工艺性能,满足了高速CO2焊的控制要求.