Crystallization of Hexagonal BaNb2O6

Pure hexagonal BaNb₂O₆ crystallizes at 640° to 700°C from an amorphous material prepared by simultaneous hydrolysis of barium and niobium alkoxides. The structure is characterized by layer networks of NbO₆ octahedra. Crystallization isotherms are described by the Avrami equation In (1—f) = -ktⁿ with n=2; the activation energy is 268 kJ-mol-'. Hexagonal BaNb₂O₆ transforms to the ortho-rhombic modification one at 12.50° to 1310°C.     

Effect of aging treatment on irradiation-induced segregation of high Mn-Cr steel

To investigate the effect of aging treatment on irradiation-induced segregation of high Mn-Cr steel, specimens for electron-beam irradiation were prepared from the high Mn-Cr austenitic steel which was solution treated at 1 373 K for 1 h and aging treated at 573 K for 1 000 h, respectively. The electron-beam irradiation was performed at 573 K up to doses of 5.4 dpa in a 1 250 kV HVEM and irradiation-induced segregation analyses were carried out by an EDX in a 200 kV FE-TEM. The results show that void formation is not observed in both solution treated and aging treated ones. The amount of Cr segregation at the grain boundary decreases in the aged one; however, that of Mn is not changed in solution treated one.     

基于辐射压力控制的微型元件的加工与检测

We have been developing new fabrication tools based on optical radiation pressur e and related phenomena to develop aflexible and accurate microfabrication tec hnology. In this paper, the laser trapping probe for the nano-CMM for assessment, in addition to micromachining technique using a small particle controlled by optical radiation pressure and laser aggregation technique are discussed. As the positional detection probe for the nano-CMM, an optically trapped silica particle with 8 mm diameter in forced oscillation state is used. A probe sphere retains a stable position when applied with trapping force by Nd:YAG laser light formed an nu lar and is forced to oscillate by the driving force changed by modulating the in tensity of LD emission. Experintal results show that this vibrational microprobe h as the possibility to achieve positional sensing accuracy of less than 25 nm. As a new micromachining technique, nano-removal process using an optically trapped micro-grain is proposed. The laser trapping force enables not only to stably trap the diamond grain with asymmetrical shape but also to freely control the positi on with spinning. Using this micro machining tool, the machining experiments of h ydrocarbon film are performed. AFM observation confirmed that the fine groove wi th depths of about 3～4 nm can be fabricated. As an additive process based on ra diation pressure, a laser microstructure fabrication using laser agglomeration p h enomena of colloidal particles aided by radiation pressure is investigated. By c ontrolling laser beam scanning in slurry containing KOH solution and SiO₂ par ticles with a diameter of 140 nm, colloidal particles are aggregated and adhered firmly to a silicon wafer substrate. Using this laser agglomerating process, two-dimensional grid microstructures at the pitch of 5 mm can be fabricated.     

Ultrasonic echo signal fetures of dissimilar material bonding joints

An ultrasonic evaluation method of echo feature of diffusion bond joint between two dissimilar materials is presented. The echo signal was acquired by an automatic ultrasonic C-scan test system. It is found that the intensity of echo and its phase can he used to evaluate the joint quality, and interface products of dissimilar materials bonding can be evaluated by ultrasonic method.     

列车动力学模型时变环境参数自适应辨识

考虑列车制动性能与制动距离对列车安全的重要影响,分析了列车运行的动力学特性,构建了列车离散化制动模型,并针对影响列车制动性能的关键参数—钢轨粘着系数难以直接观测、随钢轨环境变化的特点,提出基于滑动窗口与最大期望理论的轮轨粘着系数在线辨识算法.首先,依据数据特征确定滑动窗口位置与窗口尺寸;然后,构造列车动力学模型参数的条件数学期望,并结合粒子滤波与粒子平滑算法以及贝叶斯理论,估计预设模型参数下的列车运行状态;在此基础上,分析粘着系数的后验概率,并极大化条件数学期望对模型参数预设进行优化更新,进而实现模型真实参数的逐步逼近.最后,考虑雪地、隧道等场景下的粘着系数变化,对本文方法进行了仿真验证,并数值分析了粘着系数对制动距离的影响.仿真结果表明本文算法可快速、准确地对粘着系数进行实时辨识,掌握轮轨间实时粘着状态.     

12Cr-ODS钢中氧化物强化相（Y2O3）辐照损伤行为研究

本文采用电子束（e^－） 氦离子（He⁺）、氢离子（H⁺）束同时复合辐照方式研究12Cr-ODS铁素体钢中氧化物弥散强化相（Y₂O₃）辐照损伤行为,对不同辐照方式下辐照区内的氧化物形貌变化进行原位观察。研究结果表明,15dpa辐照后,氧化物周围出现微小高密度空洞,相界面变得不规则,氧化物在此特定条件下发生体积收缩或长大,尺寸有少量变化,但无明显溶解现象,对钢的性能不会产生影响。     

强磁场对不同磁化率非磁性金属凝固组织的影响

根据热力学分析,强磁场对晶体凝固过程均质形核的影响是通过改变熔点、系统Gibbs自由能,从而促进或抑制形核过程来实现的．实验研究表明,相同的磁场条件对不同磁性金属凝固组织的细化作用、取向作用效果是不同的,从磁能、Lorentz力和磁化力效果等热力学和动力学角度探讨了相关规律．强磁场可以改变金属材料的凝固组织,从而进一步改善材料的质量和性能．     

Crack-healing and mechanical behaviour of Al2O3/SiC composites at elevated temperature

Alumina/silicon carbide (Al₂O₃/SiC) composite ceramics with large self‐crack‐healing ability, high strength and high heat‐resistance limit temperature for strength were developed and subjected to three‐point bending. A semicircular surface crack 100 μm in diameter was made on each sample. Crack‐healing behaviour was systematically studied, as functions of crack‐healing temperature and healing time, and the fatigue strengths of the crack‐healed sample at room temperature and 1373 K were investigated. Four main conclusions were drawn from the present study. (1) Al₂O₃/SiC composite ceramics have the ability to heal after cracking from 1273to 1673 K in air. (2) The heat‐resistance limit temperature for strength of the crack‐healed sample is ?1573 K, and ?68% of the samples fractured from outside the crack‐healed zone in the testing‐temperature range 873–1573 K. (3) The crack‐healed sample exhibited very high fatigue limit at room temperature and also 1373 K. (4) The large self‐crack‐healing ability is a desirable technique for the high structural integrity of ceramic component.     

Aflatoxin Contamination in Nutmeg: Analysis of Interfering TLC Spots

When a mixture of ground nutmeg and ground cinnamon leaves was subjected to thin layer chromatography (TLC), spots that hampered detection of aflatoxins appeared on the TLC plate. These spots represented oxidation or heat-induced degeneration products of the cinnamon leaves. Between 1986 and 1991, 67 samples of nutmeg, that were commercially available in Japan, were examined for aflatoxin contamination. Aflatoxins were detected in 29 (43%) of the 67 samples.     

Flexibility of production ordering systems

The flexibility of production ordering systems as medium range production control systems are studied. The changes affecting flexibility, production ordering systems as responses to changes, and the performance measures of flexibility are clarified. On the basis of this framework, mathematical models of production system and production ordering systems are developed to evaluate their flexibility. Two types of changes are considered: demand fluctuation and downtime fluctuation due to machine breakdown, and two models for ‘push-type’ and ‘pull-type’ production ordering systems are investigated. By simulating the models, the amplifications of production quantities and inventory levels as flexibility measures for each type of production ordering system are analysed and the flexibility compared.