钢锭模设计的现状及研究趋势

综述了在设计钢锭模过程中所用材质、结构、工艺的最新研究现状以及数值模拟在钢锭模设计中的作用。认为：稀土蠕墨铸铁钢锭模具有很好的发展前景,设计合理的化学成分和生产工艺来铸造性能优良的锭模仍需探索;数值模拟可以为实际生产提供有力的指导,为提高铸锭的质量,有效改善钢锭模的使用寿命,降低生产成本提供可靠的技术支持。     

声频钻机的公理设计分析

应用公理设计理论对声频钻机的设计过程进行分析,检验其是否符合公理设计理论的要求,并对其核心部件--振动器的两种设计方案进行公理化分析比较,选出优化的设计方案,在一定程度上保证声频钻机设计的稳定性和可靠性。     

发电机组静止励磁系统励磁电流基值分析

针对励磁系统建模时由于励磁电流测量误差大,引起发电机空载特性测量稳定性差,励磁电流基值整定困难的问题,本文通过对励磁电流测量位置和测量方式的分析对比,结合建模时的现场条件,提出采用直流侧分流器法,采样频率30kHz以上,时间常数0.2~0.3s滤波的方法测量励磁电流。最后,将该方法应用于630MW机组励磁电流基值整定,并利用电力系统仿真软件验证。结果表明,该方法能满足工程化应用要求。     

对某增压柴油机润滑系统的一维流体动力学分析及设计改进

针对某国产增压柴油机的润滑系统存在的增压器轴承早期失效,活塞温度偏高等问题,应用一维流体动力学分析软件FLOWMASTER建立润滑系统仿真模型,对润滑系统旁通控制阀的开启参数设置的合理性进行了仿真分析。仿真分析表明:上述问题产生的根源是机滤总成旁通阀和活塞冷却喷嘴的开启压力设置不合理。据此进行了优化设计,优化后的润滑系统避免了上述问题,发动机工作可靠性得到提高。     

谷氨酸及其衍生物在304不锈钢表面的自组装膜

采用电化学阻抗谱、极化曲线、量子化学和分子动力学,研究了谷氨酸、焦谷氨酰胺、焦谷氨酸三种自组装膜在0.5 mol/L硫酸溶液中对304不锈钢的缓蚀性能.结果表明,三种缓蚀剂均为阴极型缓蚀剂,对不锈钢具有较好的缓蚀作用;在0.02 mol/L的浓度下,随着组装时间的延长,自组装膜对不锈钢的缓蚀效率也相应增强.它们的缓蚀能力与理论EHOMO越高、能量间隙△E越低.自组装分子成键能力越强、缓蚀效率越高相一致.三种缓蚀剂分子中的氮原子、氧原子可以与铁原子形成化学键,发生化学吸附.缓蚀能力依次为:焦谷氨酸＞焦谷氨酰胺＞谷氨酸.     

Microstructures and corrosion mechanism of AISI 304L stainless steel irradiated by high current pulsed electron beam

AISI 304L austenite stainless steel was irradiated by a high-current pulsed electron beam (HCPEB) source in different process. The microstructures were investigated in detail by electron microscopy. The relationship between corrosion resistance and the microstructures has been established. Our experimental results suggest that much abundant defect structures were formed within the irradiated surface which promoted the formation of a compact and thick passive layer during the process of corrosion experiment in simulated sea water. This passive layer effectively prevented corrosive anionic species from passing through the surface oxidation layer and delayed the corrosion process, leading to the improvement of irradiated materials’ corrosion performance. However, the craters on the treated surfaces may be turn into new active points on the metal surface which favored local pitting. Our experimental results demonstrate the potential of proper HCPEB processing for improving the corrosion resistance of metallic materials.     

快淬速度对Nd9.5Fe76Zr3Co5B6.5纳米晶复合永磁合金磁性能和微观结构的影响

以Nd9.5Fe76Zr3Co5B6.5合金为研究对象,研究了不同快淬速度(8~65 m/s)对合金的磁性能、交换耦合作用和微观结构的影响。结果表明,快淬速度对合金退火后的微观结构和磁性能具有显著地影响,适当的快淬速度将使合金退火后的晶粒细化、分布均匀,提高软、硬磁性相间的交换耦合作用,进而提高合金的磁性能。当淬速为15 m/s时,合金退火后具有最佳的综合磁性能:Br=0.976 T,Hcj=711.57 kA/m,(BH)max=150.61 kJ/m3。     

Insights into the reaction mechanisms of methanol decomposition,methanol oxidation and steam reforming of methanol on Cu(111): A density functional theory study

Cu-based catalysts have been widely used for hydrogen production from methanol decomposition, methanol oxidation and steam reforming of methanol (MSR). In this study, we have systematically identified possible reaction paths for the thermodynamics and dynamics involved in the three reactions on a Cu(111) surface at the molecular level. We find that the reaction paths of the three reactions are the same at the beginning, where methanol scission is favourable involving O–H bond scission followed by sequential dehydrogenation to formaldehyde. Formaldehyde is an important intermediate in the three reactions, where direct dehydrogenation of formaldehyde to CO is favourable for methanol decomposition; for methanol oxidation, formaldehyde tends to react with oxygen to form dioxymethylene through C–H bond breaking and finally the end products are mainly CO₂ and hydrogen; for MSR, formaldehyde tends to react with hydroxyl to form hydroxymethoxy through formic acid and formate formation, followed by dissociation to CO₂. CH₂O formation from methoxy dehydrogenation is considered to be the rate-limiting step for the three reactions. In general, the thermodynamic and kinetic preference of the three reactions shows the order methanol oxidation > MSR > methanol decomposition. Methanol oxidation and MSR are faster than methanol decomposition by about 500 and 85 times at typical catalytic conditions (e.g., 523 K), respectively. The result may be useful for computational design and optimization of Cu-based catalysts.     

SCC casting prediction for the realization of prototype VHPC-precambered composite beams

Casting simulations of self-compacting concrete are carried out in order to obtain a value of the minimum fluidity needed to cast a VHPC precambered composite beam. The mix proportioning of the concrete takes into account this minimum value. The numerical predictions are finally compared with the experimental observations during two casting tests and the real casting of the two 13 m beams. Although the simplifying assumptions needed to carry out the simulations are numerous, there is an agreement between the predictions and the real casting.     

Compression based clustering technique for enhancing accuracy in web scale videos

Multimedia Tools and Applications - Detection and clustering of commercial advertisements plays an important role in multimedia indexing also in the creation of personalized user content. In...