固载AlCl_3催化甲基三氯硅烷/三甲基氯硅烷再分配反应实验研究

针对有机硅单体二甲基二氯硅烷生产中的副产物—甲基三氯硅烷(—甲)和三甲基氯硅烷(三甲),采用固载 AlCl_3催化剂,在800mm×20mm(内径)的固定床反应器中进行一甲和三甲的再分配反应,制得二甲基二氯硅烷。通过催化剂筛选试验,结果表明以活性炭为载体的固载 AlCl_3催化剂为佳。通过工艺条件实验,确定了在活性炭固载 AlCl_3催化剂上一甲和三甲再分配反应的适宜工艺条件为:反应物摩尔比为1.0.液时空速 LHSV 为0.66 mL/(h·g-cat),反应温度为320℃,得到二甲收率70%左右。该催化剂还表现出一定的催化稳定性。     

一种基于族相合性的文本增量聚类箅法

传统文本聚类方法只适合处理静态样本,且时间复杂度较高。针对该问题,提出一种基于簇相合性的文本增量聚类算法。采用基于词项语义相似度的文本表示模型,利用词项之间的语义信息,通过计算新增文本与已有簇之间的相合性实现对文本的增量聚类。增量处理完部分文本后,对其中错分可能性较大的文本重新指派类别,以进一步提高聚类性能。该算法可在对象数据不断增长或更新的情况下,避免大量重复计算,提高聚类性能。在20 Newsgroups数据集上进行实验,结果表明,与k-means算法和SHC算法相比,该算法可减少聚类时间,提高聚类性能。     

Correlation between chemical and electrical profiles in Si+, Se+ and S+ implanted bulk and epitaxial GaAs

We compare the chemical profiles of Cr, Mn, Si and Se with the electron concentration profiles in Si, Se and S implanted semi-insulating Cr-O doped bulk GaAs substrates and undoped VPE buffer layers annealed with and without a SiO₂ encapsulant in a H₂-As₄ atmosphere. A higher activation efficiency in the net electron concentration and the gateless saturated channel current is measured for SiO₂ encapsulated wafers annealed under arsine overpressure than for capless annealed ones using Cr-O doped bulk GaAs substrates. On the other hand, the net donor concentration peak is higher for implanted buffer epi layers capless annealed under arsine overpressure than for SiO₂ encapsulated ones. Secondary ion mass spectrometry (SIMS) studies of the Cr decoration of the implant damage indicate that the damage from the 100 keV Si implant anneals out at 840°C while a temperature of 900°C is required to anneal out the 260 keV Se implant damage. An explanation of these differences is provided using an impurity redistribution model and charge neutrality considerations. Excellent Hall electron mobilities at liquid nitrogen temperature of 5400–9200 cm²/V-sec are measured for Si-implanted buffer epi substrates.     

糊状区变形及浓度再分布的模拟实验

用丁二腈－丙酮合金实验研究试样变形开始时间、初始厚度及变形量对枝晶变形及溶质再分布的影响。结果表明，枝晶变形满足幂次大于1的能量函数关系；枝晶变形能力主要与变形时糊状区固相分数有关；从糊状区挤出的液相相对浓度与固相分数、变形比率成线性关系。实验结果对建立糊状区变形与宏观偏析数学模型及优化连铸液芯压下工艺有意义。     

MODELLING THE TENSILE FRACTURE BEHAVIOUR OF THE REINFORCING FIBRE YARNS IN CERAMIC MATRIX COMPOSITES

Abstract— Using experimentally determined data on fibre radius distributions, yarn geometry, matrix and fibre elastic moduli and frictional shear stress at the matrix/fibre interface (obtained by nano-indentation experiments), the failure probability of the composite fibre yarns (after matrix cracking) is estimated. Each fibre is divided into a fixed number of segments above and below the matrix crack. The failure probability on every segment of each fibre is computed using Weibull fibre strength statistics. A fibre is assumed to be broken when the cumulative failure probability for the complete yarn reaches a value of 0.5. The segment and fibre are then selected at "random", according to their individual failure probabilities. After fibre failure, the broken fibre can only carry the frictional load and the load drop is transferred to its neighbours according to their distances to the broken fibre. The remote stress is then modified to match again the cumulative failure probability of 0.5 and a new fibre is broken. This procedure is repeated until all the fibres are broken. In this way, it is possible to obtain the "characteristic" load carried by the yarn and its corresponding elongation. Fibre extraction and pull-out behaviour are also considered. The roles of different load-transfer laws (from global to highly localised) are examined. The model is applied to simulate the fracture tensile behaviour of individual yarns of SiC/SiC ceramic-matrix composites. The results are compared with those obtained from tensile experiments on SiC/SiC individual yarns. The computed fracture morphology, in terms of individual pull-out lengths, is also compared to the actual SEM fractography of a woven SiC/SiC composite.     

火灾下有支撑体系钢框架的倒塌特性

使用作者研发的静态-动态程序研究火灾下二维有支撑体系钢框架结构的连续倒塌机理。对20种不同火灾条件下不同支撑体系的钢框架进行综合分析,总结这些支撑体系的连续倒塌机理,并分析其刚度和强度。结果表明,柱的承载力丧失是连续倒塌的主要原因之一。尽管横向"帽桁架"支撑体系能够直接将屈曲柱的轴向荷载重新分配到邻近柱,它们支承高温楼板的能力仍然有限。另一方面,竖向支撑体系不仅加强了框架的侧向约束,也有效牵制了由局部到整体的倒塌进程。刚度较大的竖向支撑体系能够将屈曲柱的荷载重新分配到邻近柱。"帽桁架"和竖向支撑体系相结合能够尽可能提高框架性能,以防止高温柱屈曲时发生连续倒塌。     

钢筋混凝土框架节点破坏模式影响因素分析及分化参数研究

钢筋混凝土框架节点受力情况复杂,破坏形式多样,已有的节点抗震设计理论及规范中没有给出明确的节点破坏模式分化的界定方式。选取了典型的足尺框架节点,分析了不同弯矩调幅、混凝土抗压强度、轴压比及剪跨比影响下节点的抗震性能,并在此基础上提出了节点破坏模式分化参数的设计计算方法,进一步明确了节点破坏模式分化的影响因素,为实现节点基于性能的抗震设计提供了理论基础。     

A cascading failure model for interdomain routing system

There have been many researches on border gateway protocol (BGP) security, most of which mainly focused on how to enhance the security of the BGP protocol or the interdomain routing system. However, few works studied the vulnerabilities especially the production mechanism of security events in the interdomain routing system. It takes many obstacles to understand and improve the security of the interdomain routing system. This paper explores the cascading failure phenomenon of the interdomain routing system. First, we devise a state machine to describe the state transition of BGP nodes and then give a detailed analysis of the BGP failure. Second, on the basis of the preferential attachment characteristic, we propose a cascading failure model for the interdomain routing system, which depicts the production mechanism of cascading failure, and introduce two evaluating indicators, the proportion of failed nodes and the proportion of failed links, to assess the scale of cascading failure. Furthermore, we apply the cascading failure model to display two different cascading failure scenes. The experimental results show that random failure has less influence on the interdomain routing system, while its robustness against hostile attack is weak. Copyright ©2011 John Wiley & Sons, Ltd.     

基于比例冲突再分配规则的目标识别方法

高冲突证据下的目标识别方法研究一直是热点和难点问题。比例冲突再分配规则正是处理高冲突证据的一种有效方法。介绍并分析了比例冲突再分配系列规则,并通过具体的例子对不同方法进行了仿真验证,说明了比例冲突再分配规则能很好地处理目标识别问题中的高冲突证据。     

内力重分布对桥梁施工的影响研究

介绍了桥梁结构施工中,在施工荷载、温度、混凝土的收缩与徐变、支座、偶然荷载以及人为荷载等因素的作用下,使得结构的内力出现重分布的现象,提出了结构内力重分布现象对施工及桥梁结构的不利影响及可能的控制措施,对工程实践中认识和避免结构内力重分布具有一定的意义.