Web搜索引擎评估技术研究

搜索引擎是Web信息检索的有力工具，科学地评估搜索引擎不仅能够激励和推动搜索引擎技术提供者提供更好的技术支持，并且对搜索引擎技术的发展有很好的引导作用。本文简要介绍了搜索引擎评估技术发展状况，针对评估任务、评估指标等方面进行了具体分析，并对搜索引擎评估的发展方向和评估重点提出了建议。     

涡扇发动机组合变几何调节优化方法研究

基于单纯形及惩罚函数法，建立了涡扇发动机扩稳和改善性能的多变量变几何组合优化方法。在给定的喷管面积、风扇导叶、压气机导叶及静叶变几何规律下，应用该方法对某型涡扇发动机巡航状态性能和稳定工作范围进行了多变量变几何优化分析。结果表明，在保持推力一定的条件下，实施多变量变几何优化调节不仅可显著提高发动机压缩系统稳定裕度，而且还能明显改善发动机性能。     

岩土本构关系的特殊性和统一性

在阐明岩土塑性变形的基本特殊性,特别是应力应变关系与应力路径相关性,产生机理的基础上,明确指出了导致这些特性的内在的共同的根源是,岩土塑性变形中存在两个相对独立的变形,即体积应变和剪切应变,两者之间存在着强烈的非线性的相互作用.这种耦合作用造成岩土的力学响应不仅具有多样性和复杂性,而且也具有内在的统一性.     

室温氯铝酸离子液体络合吸附噻吩类硫化物的研究

以室温氯铝酸离子液体作为催化剂 ,将石油一厂的直馏柴油进行预先精制 ,并且在其中加入一定量的噻吩为原料 ,在室温和氮气保护的条件下 ,考察了室温氯铝酸离子液体催化剂脱除噻吩的效果。实验结果表明 :在n(AlCl3 ) /n(BMIMCl)为 2∶1、剂油比为 0 .15、反应时间为 4 0min的条件下 ,氯铝酸离子液体对精制柴油中的噻吩脱除率可达到 4 6 % ,从而说明氯铝酸离子液体具有很好的吸附噻吩类杂环化合物的能力。虽然氯铝酸离子液体对水和空气敏感、不稳定 ,但是可以再生重复循环使用     

电控汽油机怠速模糊RBF神经网络控制

针对电控汽油机怠速控制要求,提出了一种模糊径向基函数(RBF)神经网络控制方案,在MATLAB环境下进行了控制仿真,获得了比PID、模糊、模糊BP神经网络更好的控制性能。     

Effect of EGR on the exhaust gas temperature and exhaust opacity in compression ignition engines

In diesel engines, NOx formation is a highly temperature-dependent phenomenon and takes place when the temperature in the combustion chamber exceeds 2000 K. Therefore, in order to reduce NOx emissions in the exhaust, it is necessary to keep peak combustion temperatures under control. One simple way of reducing the NOx emission of a diesel engine is by late injection of fuel into the combustion chamber. This technique is effective but increases fuel consumption by 10–15%, which necessitates the use of more effective NOx reduction techniques like exhaust gas recirculation (EGR). Re-circulating part of the exhaust gas helps in reducing NOx, but appreciable paniculate emissions are observed at high loads, hence there is a trade-off between NOx and smoke emission. To get maximum benefit from this trade-off, a paniculate trap may be used to reduce the amount of unburnt particulates in EGR, which in turn reduce the paniculate emission also. An experimental investigation was conducted to observe the effect of exhaust gas re-circulation on the exhaust gas temperatures and exhaust opacity. The experimental setup for the proposed experiments was developed on a two-cylinder, direct injection, air-cooled, compression ignition engine. A matrix of experiments was conducted for observing the effect of different quantities of EGR on exhaust gas temperatures and opacity     

Thermomechanical design in the automotive industry

In this paper thermomechanical fatigue assessment in the automotive industry is discussed. The design strategy is based upon a consistent approach of the thermomechanical loading, the mechanical constitutive law of the material, the damage parameters and the fatigue strength criteria. The good understanding of these different steps allows one to perform predictive calculations of automotive parts subjected to thermomechanical loading. The main hypotheses and modelling choices are presented and results are illustrated by a series of computations on real 3D structures. Cracked area and lifetime prediction are described in the case of aluminium alloy cylinder heads subjected to transient thermal loadings.     

Nonlinear capillary free-surface flows

Capillary free-surface flows are considered. The fluid is taken to be inviscid and incompressible and the flow to be irrotational. Particular attention is devoted to two-dimensional flows for which the free surfaces intersect rigid walls. These include cavitating flows and local flows at the front of a small object (probe or insect) moving at the surface of a fluid. A general study of the effect of surface tension on the possible singularities which can occur at the separation points is presented. The results confirm and generalise previous findings on the subject.     

一种新型选相方案

针对目前微机保护中选相元件的不足,提出了几种新型的数字式选相元件,重点探讨了基于模故障分量的选相元件,基于电压序分量的选相元件和弱电源侧电压选相元件,由此构成了一套完整的微机线路保护选相方案。针对这几种选相元件作了比较详尽的分析,进行了横向和纵向的比较。最后,利用ATP与MAT LAB仿真运算验证了新方案的有效性和可靠性。     

基于单端电流量的同杆双回线故障定位方法

提出了一种基于同杆双回线单端电流量的故障测距方法。在故障状态下,双回线可以分解成同向网和环流网,其中环流网只与双回线有关,且两端电压为零。根据双回线环流网的特点,只需电流量就可求取环流网中的电压分布。因为双回线环流网中的行波具有两端母线处反射强、故障点反射弱的特点,所以可以根据环流网中行波首次到达测点的时刻为起点,由前行波和反行波电压的最强叠加点所处的时刻和位置进行故障定位。仿真验证表明该方法定位精度高,不受过渡电阻影响。