0.5T小型关节MRI仪器中低噪声前置放大器的设计

设计了一个可用于0.5T 小型关节MRI仪器中的低噪声前置放大器,给出了一种低场MRI仪器中LNA制作的可行方案。放大器采用两级级联的形式,第1级采用高电子迁移率晶体管ATF 54143,第2级采用双极型达林顿管ADA 4743。经过测试,所制作放大器的性能指标达到了预定要求,性能良好。放大器的工作频段为18~23 MHz,中心频率处噪声系数NF≈0.6 dB,增益G≈40 dB,带内波动小于1 dB,输入驻波比VSWR≤1.5,输出驻波比VSWR≤1.5。     

车用润滑剂的发展历程

简述了２０世纪以来车用润滑剂分类规格变化的发展历程,车用润滑剂包括发动机油、传动液、齿轮油以及润滑脂,其质量分类规格涉及很多领域。     

数字摄像机的使用与维护

介绍数字摄像机的特点及使用中应注意的事项,主要介绍在日常使用中如何进行维护以及一般故障的排除方法,有一定的实用价值。     

Wet Clutch Friction Interfaces under Water-Contaminated Lubricant Conditions

The performance of wet clutches used for automatic transmissions or other applications usually includes the desired positive friction characteristics and a shudder-free torque generation. Changes in the operating variables such as the lubricant conditions influence the formation of a tribofilm, and friction characteristics and can alter the degradation of the friction interfaces. In this work, the friction characteristics and degradation of the paper–steel friction interfaces were monitored when a commercial fully formulated automatic transmission fluid (ATF) was contaminated with water. It was found that water in ATF influenced the clutch stability by increasing the mean coefficient of friction (µ) and the negative friction–velocity slope. Surface studies of the posttest friction interfaces clearly indicated reduced surface porosity and permeability, increased wettability, and changed elemental composition on the contacting surfaces after tested with water-contaminated ATF. Moreover, water-contaminated paper liners' thermal decomposition shifted to a lower temperature compared to an uncontaminated liner during thermal analyses. These results displayed faster degradation and reduced service life of the clutch friction interfaces due to water contamination. The resultant surface condition can be associated with the observed unstable friction and negative friction–velocity slopes.     

锆合金表面CrAl基耐高温涂层及氧化行为研究

目的了解锆合金和涂层的高温氧化行为,通过表面涂层提升锆合金的耐高温氧化性能。方法采用多弧离子镀技术在锆合金基体上制备了CrAlN、CrTiAlN涂层,模拟反应堆失水(LOCA)事故时的高温氧化行为,在360～1160℃下进行1 h氧化测试,对原始锆合金和带涂层样品的氧化增重行为进行了研究。通过X射线衍射和扫描电子显微镜对氧化前后样品的物相结构和形貌进行系统表征分析。结果锆合金在760℃及以下形成深色的混合型锆氧化膜,在860℃以上呈现龟裂和局部剥落。两种涂层氧化时,通过形成致密的Cr_2O_3和Al_2O_3混合氧化层,显著降低了氧化增重。CrAlN涂层在760℃时具有较好的抗氧化性,1060℃时开裂而失去保护作用。CrTiAlN涂层在860℃时能保护基体不受氧化,1060℃时局部开裂,基体开始出现氧化层。结论利用多弧离子镀技术制备的锆合金表面CrAlN和CrTiAlN涂层,在模拟反应堆LOCA事故下具有良好的耐高温氧化性,显示出这两种涂层有潜力发展成为核用事故容错燃料(ATF)包壳涂层。     

Comparative analyses of coated and composite UN fuel – Monte Carlo based full core LWR study

Longer continuous operation of a nuclear reactor leads to higher availability of nuclear power plant, entailing economic gain. In this context the option being explored, recently, is the use of higher density fuels as compared to current fuels i.e. UO₂. Uranium mono nitride (UN) fuel is one of the options being explored in this regard. UN fuel has been used in nuclear industry for a long time with fast reactor option. More recently, studies have targeted its use in Light Water Reactor (LWR) environment. The main problem with using UN fuel in LWR is its potential reaction with water which produces hydrogen. Researchers have proposed different approaches to overcome this problem.One option is the use of coatings around UN fuel pellet to avoid the direct contact of water with fuel. The second option is use of a secondary phase (10 vol. percent) like ZrO₂ which can make an oxide layer in case of contact with water and protect the main phase, Uranium mono nitride (80 vol. percent). Remaining 10 vol. percent is considered to be consumed by porosity. This study aims at comparison of neutron physics behavior of both these options in LWR environment. The upshot of the study is to quantify the impact of adding layers or secondary phase with respect to pure/complete UN fuel. To study these effects, two theoretical densities i.e. 95% and 80% for UN fuel are chosen for analyses. To avoid the problem of C-14 production from N-14, fuels studied are considered to be having 100% N-15.A validated model of Benchmark for Evaluation and Validation of Reactor Studies (BEAVRS) is used to perform all the analyses. Integral neutron physics parameters like neutron energy spectra, Radial Peaking Factors, Axial Peaking Factor, Doppler coefficient of reactivity, Isothermal Coefficient of reactivity and Temperature defect, Control Rod worth and excess reactivity for whole core are compared at Beginning of Cycle (BoC). Burnup obtained by different fuel option is also compared. Consistent with pin-cell based earlier findings, this full 3D analyses with UN based fuel shows noticeable spectral hardening leading to decrease in the value of control rod worth and less negative Doppler coefficient of reactivity while power peaking factors remain mostly unchanged. The economic advantage of switching to UN based fuels is expected when UN fuel above 80% TD is used. Approximately 19% increase in Equivalent Full Power Days (EFPDs) is witnessed by using 95% TD UN based fuels.     

ATF三功能粘度指数改进剂的研制及性能评定

汽车自动传动液用三功能粘度指数改进剂是以甲基丙烯酸酯类为主体的包括含氮组分的高分子聚合物。它具有增粘、降凝及分散三种功能。简述了该剂的合成工艺，并着重介绍了它在自动传动液研制中的作用及效果     

浅谈自动变速器液压系统的维护

针对汽车自动变速器液压系统使用与维护中容易忽略的问题,根据汽车自动变速器液压系统的内在结构与工作特点,以丰田A341E自动变速器为例,提出在自动变速器维护与检修过程中如何采取有效措施,规范使用ATF(自动变速器油Automatic Transmission Fluid),有效控制人为污染,以及ATF使用中的相关问题解决办法等.这对正确维护和检修自动变速器,达到控制检修质量,减少故障率,延长自动档车辆的使用寿命具有现实的参照意义.