Structure characterization within the vicinity of the fine granular area by synchrotron radiation nano‐CT

The three‐dimensional (3D) microstructures within the vicinity of the fine granular area (FGA) were investigated with synchrotron radiation nano‐computed tomography (CT). In this investigation, the very high cycle fatigue test of a high‐strength steel was carried out with an ultrasonic fatigue testing machine. Then, focused ion beam cutting was used to cut a part near the surface of the FGA. Finally, the 3D structure of the sample was obtained with the nano‐CT imaging. The results indicated that the base material was composed of various subgrains that are tens to hundreds nanometres in size. Through analysis of the slices, small granular areas consist of several subgrains. The statistical analysis of the subgrain size indicated that the subgrain size near the surface of the FGA is similar to that far from the surface of the FGA and near the fracture surface except the FGA. It indicated that the refinement has not been found by nano‐CT.     

Investigation of fatigue crack initiation facets in Ti‐6Al‐4V using focused ion beam milling and electron backscatter diffraction

In the very high cycle fatigue regime, internal crack initiation can occur in Ti‐6Al‐4V because of the formation of facets, which are α grains that have fractured in a transcrystalline and planar manner. Because this crack initiation phase occupies most of the fatigue life, it is essential to understand which mechanisms lead to facet formation. Fatigue tests have been performed on drawn and heat‐treated Ti‐6Al‐4V wires, and the facets at internal crack initiation sites have been analysed in detail in terms of their appearance, their spatial orientation and their crystallographic orientation. The facets were not smooth, but showed surface markings at the nanoscale. In nearly all cases, these markings followed a linear pattern. One anomalous facet, in a sample with the largest grain size, contained a fan‐shaped pattern. The facets were at relatively steep angles, mostly between 50° and 70°. Cross‐sections of the fracture surfaces have been made by focused ion beam milling and were used to measure the crystallographic orientation of facets by electron backscatter diffraction. Most facet planes coincided with a prismatic lattice plane, and the linear markings were parallel to the prismatic slip direction, which is a strong indication that prismatic slip and slip band formation led to crack initiation. However, the anomalous facet had a near‐basal orientation, which points to a possible cleavage mechanism. The cross‐sections also exposed secondary cracks, which had formed on prismatic lattice planes, and in some cases early stage facet formation and short crack growth phenomena. The latter observations show that facets can extend through more than one grain, and that there is crack coalescence between facets. The fact that drawn wires have a specific crystallographic texture has led to a different facet formation behaviour compared to what has been suggested in the literature.     

甚低频矢量水听器水池校准方法研究

为研究水池条件下甚低频矢量水听器的校准方法,利用水池声场理论建模仿真的方法研究了声源位置、水池尺寸等因素改变时近源声场的变化规律.研究表明:在连续信号激励条件下,近源声场分布呈准球面波扩展规律,满足甚低频矢量水听器的校准需求.进而详细阐述了校准方法并仿真评估了标准水听器和待测甚低频矢量水听器所在位置的声场对校准结果的影...     

750kV GIS用变压器端部的快速暂态过电压的研究

GIS内开关操作产生的快速暂态过电压(VFTO)对系统的变压器构成了很大的威胁,对于超高压GIS更是如此。参考多个GIS变电站,建立了750kVGIS系统,并确定了断路器、隔离开关、接地开关及电抗器的计算模型可简化为等值对地电容或入口电容,其参数分别为276pF、240pF、240pF和5000pF。利用EMTP计算了不同操作过程在变压器端部出现的VFTO。分析了系统运行方式、开关操作顺序、变压器入口电容以及变压器与GIS的连接方式对变压器端部VFTO的影响。研究了断路器、隔离开关的并联电阻以及MOA对变压器的保护效果。     

面向密集部署的超高吞吐率Wi-Fi融合应用技术

为了降低网络密集部署对超高吞吐率( VHT) Wi-Fi性能的影响,提出了VHT Wi-Fi基于软件定义网络( SDN)的网络架构、无线网络侧虚拟化和增强型认证与快速切换技术,以提高系统的共存性、抗干扰性和安全性。实验结果表明,VHT Wi-Fi与SDN、网络功能虚拟化、伽罗瓦/计数模式协议结合,吞吐率性能获得约10%的提升,在保证安全性同时平均切换时延降低至40 ms,可保障VHT Wi-Fi在密集部署网络中发挥重要作用。     

矿山特大型采空区全尾砂充填封闭工程实践

为了解决采空区安全隐患，同时为矿山生产中大量的尾砂寻找堆存场地，经充分论证，利用全尾砂对采空区进行充填处理.井下采空区的封闭是实施全尾砂充填的必要条件之一，本文简述了井下采空区全尾砂充填封闭工程封闭墙位置的选择、墙体结构型式与厚度的确定及施工过程和实施效果等。     

数据采掘技术的研究

本文首先论述知识发现和数据采掘的概念,然后介绍数据采掘所采用的方法及数据采掘的应用领域,最后指出数据采掘是一种新型的、有着广泛应用背景的数据库技术。     

主成分分析同时单点pH滴定法研究

将主成分分析用于多组分同时单点ｐＨ滴定法中,讨论了方法原理,建立了主成分分析常数矩阵,对８ 个三组分极弱酸和１２ 个四组分极弱碱混合样进行了测定,相对误差和相对标准偏差约０．２％ ,结果令人满意．     

一种实用高效的高纯氮气制备装置的介绍

着重介绍了用催化剂制备高纯氮气的新型装置,该装置可使普通氮气中氧的含量降到 ５×１０－ ６ 以下,并对其经济性作了对比