同步辐射高分辨率衍射光束线的设计

介绍了第三代同步辐射高分辨率X射线衍射光束线的总体设计。给出了高分辨率衍射的基本原理并描述了获得确定光子能量的近平行高强度X射线光束线所必需的光学元件。特别是用X射线动力学理论,解释了双晶及四次反射晶体单色器。作为一个实例,介绍了将于2009年开始在德国汉堡运行的一个新的同步辐射源PETRAⅢ的高分辨率衍射(HighRes)光束线的设置情况。通过优化光学部件,对微米尺寸光束,q空间的分辨减小到Δq=10^-5 nm^-1,光通量大于10¹¹ cts/s。     

超长混凝土结构的研究与应用

本文结合南京国际展览中心工程 ,对超长混凝土结构的设计、温度应力的有限元分析以及施工措施等进行了深入的探讨 ,并介绍了长期测试结果。     

Mechanisms of ion-induced GaN thin layer splitting

The underlying physics and the role of H-defect interaction in H ion-induced splitting of GaN were investigated by transmission electron microscopy, high resolution X-ray diffraction, positron annihilation spectroscopy, ion channeling, elastic recoil detection, and infrared spectroscopy. A high concentration of void-like nanoscopic structures, nanobubbles, is detected immediately after implantation. Positron annihilation measurements demonstrate that the detected structures are vacancy clusters. FTIR data show that H-defect vibrational spectrum peaks at 3141 cm^?1 mode attributed to V_Ga–H₄. A large fraction of H was found to be trapped in higher frequency modes which we associate tentatively to N–H stretch modes in the internal surfaces of nanobubbles. These nanobubbles persist during annealing up to 450 °C. An increase of the strain is observed in this temperature range. This strain relaxes partially above 450 °C following the formation of the platelets which are embryos of the microcracks.     

Neutronics design analyses of fusion power reactors based on a novel integral approach

A novel integral approach was applied for the nuclear design analyses performed for the European DEMO Conceptual Study including, for the first time, the automatic generation of analysis models for Monte Carlo calculations from available CAD geometry data by the new McCad conversion tool. Starting from neutronics pre-analyses to define the radial reactor build, a generic neutronics CAD model of the DEMO reactor was constructed serving as basis for the generation of DEMO reactor models employing the HCLL (Helium Cooled Lithium Lead) and HCPB (Helium Cooled Pebble Bed) blankets for the tritium breeding and the power production. The HCLL and HCPB DEMO reactor models were converted to the MCNP geometry representation by the newly developed McCad software tool. The nuclear analyses performed on the basis of MCNP Monte Carlo calculations using the converted models showed that both DEMO reactor variants could satisfy the requirements for a sufficient shielding and tritium breeding performance. As a major outcome of this work it is concluded that the newly established integral approach for neutronics analyses, including the automatic generation of analysis geometry models by McCad, is mature for applications to reactor design analyses and studies.     

Optimised plasma stabilisation at TEXTOR with an advanced, real-time digital control scheme

The tokamak TEXTOR at the Research Centre in Jülich is in operation since more than 25 years. The various control systems at the start, in 1982, were based on analogue techniques, a standard at the time, and were later partly replaced by specially developed digital systems. These systems proved their robustness over the years. As a replacement for the old system, off-the-shelf products were used to ensure continuity, reliability and to reduce the development cost. To provide advanced control scenarios, the new system allows the implementation of more sophisticated algorithms for magnetic and kinetic control. The LabVIEW Real-Time (RT) modules and real-time hardware from National Instruments satisfy these requirements to a large extent. The new system has already been successfully commissioned at TEXTOR and is used to calculate in real-time the plasma density profile (10 ms), the Shafranov shift (10 ms), the plasma vertical and horizontal position (20 $\mu$s) and to control the plasma shape (1 ms). TEXTOR has circular plasmas and has an iron core. Its central part is operated in saturation. During the saturation phase, stray fields change the plasma shape from nearly circular to slightly triangular. By using a shape-control coil set, we can control and adjust the plasma form. The new real-time system is presented as well as the implemented control applications.     

An X-ray absorption spectroscopy study of Mo oxidation in Pb at elevated temperatures

The corrosion of fuel cladding and structural materials by lead and lead-bismuth eutectic in the liquid state at elevated temperatures is an issue that must be considered when designing advanced nuclear systems and high-power spallation neutron targets. In this work, lead corrosion studies of molybdenum were performed to investigate the interaction layer as a function of temperature by X-ray absorption spectroscopy. In situ X-ray absorption measurements on a Mo substrate with a 3-6 μm layer of Pb deposited by thermal evaporation were performed at temperatures up to 900 °C and at a 15° angle to the incident X-rays. The changes in the local atomic structure of the corrosion layer are visible in the difference extended X-ray absorption fine structure and the linear combination fitting of the X-ray absorption near-edge structure to as-deposited molybdenum sample and molybdenum oxide (MoO₂ and MoO₃) standards. The data are consistent with the appearance of MoO₃ in an intermediate temperature range (650-800 °C) and the more stable MoO₂ phase dominating at high and low temperatures.     

一种改进的多跳分组无线网路由协议

对于多跳分组无线网来说,路由协议非常重要.而传统的主动式路由、按需路由和混合路由由于自身的缺陷,都不能保证多跳分组无线网传输的可靠性.为了适应网络拓扑不断变化的客观环境,提高数据通信的可靠性,提出了一种相邻矩阵路由协议,它克服了传统路由协议的缺点,大大提高了多跳分组无线网的链路性能.     

基于半控桥的三相接地系统短路限流器及其控制方法

提出了一种用于三相接地系统的基于半控桥的新型短路故障限流器拓扑结构。对新型限流器在单相对地短路、两相对地短路和三相短路状态下的控制方法和限流工作原理进行了详细介绍。该限流器中含有一对功率二极管组成的桥路,可以自动为直流电感提供续流通道,因此,在短路故障发生并被检测到之后,只需要控制关断与故障相相连接的桥臂上的开关管,则故障相即可退出系统,非故障相仍然正常供电。采用PSIM6软件,对各种短路模式下的限流方法及限流效果进行仿真研究。制作了小容量的半控桥式限流器实验装置,并进行了详细的实验研究,给出了3种短路模式下主要变量的实验波形。仿真和实验结果一致,验证了所提限流器及其控制策略的有效性和实用性。     

Effect of inductively coupled plasma surface treatment on silica gel and mesoporous MCM-41 particles

Silica gel and MCM-41 synthesized mesoporous materials were treated with either oxygen (O2),hexamethyldisiloxane (HMDSO) and organic vapors like ethanol (EtOH),and acrylonitrile (AN) inductive plasma.The radiofrequency power for the modification was fixed to 120 W and 30 min,assuring a high degree of organic ionization energy in the plasma.The surface properties were studied by infrared spectroscopy (FTIR),scanning electron microscopy,x-ray photoelectron spectroscopy and dynamic light scattering technique was used for characterizing size distributions.When the silica and MCM-41 particles were modified by AN and HMDSO plasma gases,the surface morphology of the particles was changed,presenting another color,size or shape.In contrast,the treatments of oxygen and EtOH did not affect the surface morphology of both particles,but increased the oxygen content at the surface bigger than the AN and HMDSO plasma treatments.In this study,we investigated the influence of different plasma treatments on changes in morphology and the chemical composition of the modified particles which render them a possible new adsorbent for utilization in sorptive extraction techniques for polar compounds.