Research on the Control Strategy of Variable Nozzle Turbocharger for Natural Gas Engine

A variable nozzle turbocharger (VNT) was applied to a 2.2-liter L4 natural gas engine,and a VNT control system was designed to operate it.Based on VNT matching test results,a VNT control strategy was studied,in which VNT adjustment is carried out through pre-calibrated VNT handling rod position,combined with a closed-loop target boost pressure feedback using proportional-integral-derivative(PID) algorithm.Experimental results showed that the VNT control system presented in this thesis can lead to optimized ...     

语篇分析理论对大学英语阅读教学的指导

本篇文章通过对语篇分析理论的阐述,运用其中的基本内容——主述位结构分析来指导不同体裁篇章的理解。体现了主述位结构分析在解读语篇时的重要作用,并将其运用到大学英语教学当中。     

基于神经网络的数字验证码识别研究

验证码是网络上普遍采用的一种用于真人交互证明的有效方法.对验证码识别的研究有助于解决硬人工智能问题,促进人工智能领域的进步.现有的研究多是针对一种验证码,通过多种方法进行识别.这类方法对先验知识的依赖很大,识别方法对其他验证码不一定有效,或者需要大量调整来适应新的验证码.为了研究验证码识别算法的适应性问题,通过选取多个具有代表性的网站的验证码图像,基于分割法和Hopfield神经网络进行分析和试验,取得了较好的试验结果.试验结果表明:利用字符图像灰度信息和Hopfield网络可以有效的对可分割的验证码进行分类识别,算法有一定的适应性,并且仅需字符图像的灰度信息既可适应新的验证码,对先验知识的依赖少.     

XML强闭包依赖范式的研究

为了解决从数据库整体的角度来消除基于不完全信息的XML数据冗余问题,研究了在不完全信息环境下XML数据库的各个模式之间存在的XML强闭包依赖引起数据冗余的判定条件和规范化算法.首先,给出了XML强函数依赖和XML强闭包依赖两者互不影响的定义;其次,提出了XML强函数依赖和非循环XML强闭包依赖互不影响的判定定理,研究了XML强闭包依赖范式以及相应的判定定理;最后,提出了把XML数据库模式转化为XML强闭包依赖范式的规范化算法,对时间复杂度进行了分析.该算法消除了冗余路径,避免了更新异常,实现了整个XML数据库模式更合理的设计.     

电磁污染控制用S带吸波粉煤灰板材的制备

报道了根据λ/4型电磁波吸收原理,通过理论设计和模拟分析,以电厂废渣粉煤灰为介电材料,通过电阻膜复合,成功制备出新型粉煤灰吸波板材.实验表明,电阻膜的电阻为356Ω/□(方块电阻),厚度1.5 cm的粉煤灰板试样在S带(2~4 GHz),-10 dB吸收带宽达到60%以上,在2.9 GHz,最大吸收为-25 dB,新材料可用于室内电磁环境的改善和污染控制,并为粉煤灰的利用提供了新的高附加值途径.     

Explosion limits for combustible gases

Combustible gases in coal mines are composed of methane, hydrogen, some multi-carbon alkane gases and other gases. Based on a numerical calculation, the explosion limits of combustible gases were studied, showing that these limits are related to the concentrations of different components in the mixture. With an increase of C4H10 and C6H14, the Lower ExplosionLimit (LEL) and Upper Explosion-Limit (UEL) of a combustible gas mixture will decrease clearly. For every 0.1% increase in C4H10 and C6H14, the LEL decreases by about 0.19% and the UEL by about 0.3%. The results also prove that, by increasing the amount of H2, the UEL of a combustible gas mixture will increase considerably. If the level of H2 increases by 0.1%, the UEL will increase by about 0.3%. However, H2 has only a small effect on the LEL of the combustible gas mixture. Our study provides a theoretical foundation for judging the explosion risk of an explosive gas mixture in mines.     

高效产表面活性剂菌株（Lz2～1）的筛选及其特性研究

从24份含油土壤和水等样品中,经富集培养、摇瓶培养和排油活性测定等方法筛选出一株能以原油为碳源产生表面活性剂的菌株Lz2—1;该菌株可以将水的表面张力由72mN／m降到28mN／m,且发酵液具有较好的乳化活性;经生理生化16SrDNA及生理生化实验确定该菌株为铜绿假单胞菌;提取其代谢产物经薄层层析及红外色谱分析显示,主要的表面活性剂类物质为鼠李糖脂类,其临界胶束质量浓度为0．63047g／L。结果表明,表面活性物质是Lz2—1菌株在微生物采油过程中发挥作用的主要因素。     

Relationships between gas reservoir and the evolution of stope surrounding rock fracture at the process of mining the closed distance protection layer

Overburden rock movements and fracture developments occur during mining activities. Consequently, relief gas reservoirs and migration in coal seams being mined as well as in near distant coal seams appear. We considered a gas disaster management project and rules on stope relief of gas flows together and explored a gas reservoir and the evolution of stope surrounding rock fractures in the process of mining near distant protective layers by physical simulation, numerical simulation and field testing. Different techniques provide evidence of the rules of interaction of gas reservoirs and the evolution of surrounding rock fractures and are able to find accurately the gas-rich regions around the stope. Finally, we found that these rules can provide a basis for taking measures to prevent gas accidents in the protective layer of the coalface as well as for demonstrating and designing programs to drain high concentrations of gas from the gob.     

预应力混凝土斜拉桥施工抗风性能计算分析

根据某预应力混凝土斜拉桥的悬臂施工过程,运用桥梁设计专用软件Midas/civil计算分析了索塔浇筑完成以及最大悬臂状态两种情况下主梁及索塔的抗风性能,得出了一些有益的结论,为以后其他同类桥梁的设计和建设提供参考.