对Al-Cu合金中α-Al及Al2Cu生长行为的探讨

研究了Al-Cu合金中α-Al和Al2Cu的生长行为,分析了初生α-Al及初生Al2Cu作为共晶核心形核的能力.结果发现,在过共晶组织中,初生相Al2Cu形貌大部分有明显的拐角,观察其平面有的呈矩形,呈现小面生长特性.而α-Al与Al2Cu共晶生长时,Al2Cu择优生长特征削弱,与α-Al耦合生长呈现非小面-非小面生长,表明Al2Cu在不同的生长阶段表现出的生长行为不同.在亚共晶组织中,初生相α-Al周围形成离异共晶的Al2Cu,而过共晶组织中初生相Al2Cu周围没有离异共晶的α-Al,表明初生相Al2Cu作为共晶层片核心的能力比初生相α-Al作为共晶层片核心的能力强.     

An analysis of the internal oxidation of binary M-Nb alloys under low oxygen pressures at 600–800°C

The corrosion of M–Nb alloys based on iron, cobalt, and nickel and containing 15 and 30 wt% Nb has been studied at 600–800°C under low oxygen pressures (10^–24 atm at 600°C and 10^–20 atm at 700–800°C). Except for the Co–Nb and Ni–Nb alloys corroded at 800°C, which formed external scales of niobium oxides, corrosion under low O₂ pressures produced an internal oxidation of niobium. This attack was much faster than expected on the basis of the classical theory. Furthermore, the distribution of the internal oxide in the alloys containing two metal phases was very close to that of the Nb-rich phase in the original alloys. These kinetic, microstructural, and thermodynamic aspects are examined by taking into account the effects of the limited solubility of niobium in the various base metals and of the two-phase nature of the alloys.     

Fe—Cr—Ni—Mo—C阀座材料的时效硬化及时效过程中的相转变

Fe-18.2Cr-6.9Ni-2.5Mo-1.5C材料铸态组成相为奥氏体和M7C_3型碳化物,在随后加热时可产生时效硬化现象,最佳时效温度为650℃。时效过程中可产生α-铁索体和M_23C_6型碳化物两个新相。     

金刚石修整滚轮CAD/CAPP集成技术研究

金刚石修整滚轮是目前最为有效的高效、高精砂轮成形修整工具，迎合了磨削技术高精、高速和高效发展趋势，内电镀高精度修整滚轮制造工艺复杂、工序多，影响制造精度因素较多，修整参数选择、滚轮图纸设计和工艺编制是生产中的关键环节。本文从分析金刚石修整滚轮设计制造的特点人手，应用CAD／CAPP集成技术实现了金刚石修整滚轮设计、工艺规程编制和技术文件管理的自动化，提高了滚轮制造工艺水平和对产品质量的控制能力，较好地解决了一些设计和工艺过程相对简单、变化较小的定型产品的CAD／CAPP集成化的问题。     

用胶粘代替点焊工艺

采用点焊工艺生产拖拉机机罩，点焊压痕影响了外观质量，通过对几种方案的探讨和大量的胶粘试验，确定了一种用结构胶粘结代替点焊的工艺，该工艺使制件的外观质量得以大幅度提高，而生产成本则明显降低。     

基于B/S架构的嵌入式网络视频监控系统

根据目前视频监控需求,采用ARM11处理器与Linux操作系统相结合的方式,提出了一种基于B/S架构的远程网络视频监控方案。使用V4L2进行视频图像采集,选择H.264压缩标准,通过硬件多格式编码器MFC完成视频硬件压缩。运用RTP流媒体传输技术实现视频数据的打包传输,客户端通过安装Active X控件完成视频图像的显示,最终实现网络视频监控功能。     

PCET based copy-move forgery detection in images under geometric transforms

With the advent of the powerful editing software and sophisticated digital cameras, it is now possible to manipulate images. Copy-move is one of the most common methods for image manipulation. Several methods have been proposed to detect and locate the tampered regions, while many methods failed when the copied region undergone some geometric transformations before being pasted, because of the de-synchronization in the searching procedure. This paper presents an efficient technique for detecting the copy-move forgery under geometric transforms. Firstly, the forged image is divided into overlapping circular blocks, and Polar Complex Exponential Transform (PCET) is employed to each block to extract the invariant features, thus, the PCET kernels represent each block. Secondly, the Approximate Nearest Neighbor (ANN) Searching Problem is used for identifying the potential similar blocks by means of locality sensitive hashing (LSH). In order to make the algorithm more robust, morphological operations are applied to remove the wrong similar blocks. Experimental results show that our proposed technique is robust to geometric transformations with low computational complexity.     

Study on the security of the authentication scheme with key recycling in QKD

In quantum key distribution (QKD), the information theoretically secure authentication is necessary to guarantee the integrity and authenticity of the exchanged information over the classical channel. In order to reduce the key consumption, the authentication scheme with key recycling (KR), in which a secret but fixed hash function is used for multiple messages while each tag is encrypted with a one-time pad (OTP), is preferred in QKD. Based on the assumption that the OTP key is perfect, the security of the authentication scheme has be proved. However, the OTP key of authentication in a practical QKD system is not perfect. How the imperfect OTP affects the security of authentication scheme with KR is analyzed thoroughly in this paper. In a practical QKD, the information of the OTP key resulting from QKD is partially leaked to the adversary. Although the information leakage is usually so little to be neglected, it will lead to the increasing degraded security of the authentication scheme as the system runs continuously. Both our theoretical analysis and simulation results demonstrate that the security level of authentication scheme with KR, mainly indicated by its substitution probability, degrades exponentially in the number of rounds and gradually diminishes to zero.     

Recover Fault Services via Complex Service-to-Node Mappings in Wireless Sensor Networks

With the motivation of seamlessly extending wireless sensor networks to the external environment, service-oriented architecture comes up as a promising solution. However, as sensor nodes are failure prone, this consequently renders the whole wireless sensor network to seriously faulty. When a particular node is faulty, the service on it should be migrated into those substitute sensor nodes that are in a normal status. Currently, two kinds of approaches exist to identify the substitute sensor nodes: the most common approach is to prepare redundancy nodes, though the involved tasks such as maintaining redundancy nodes, i.e., relocating the new node, lead to an extra burden on the wireless sensor networks. More recently, other approaches without using redundancy nodes are emerging, and they merely select the substitute nodes in a sensor node’s perspective i.e., migrating the service of faulty node to it’s nearest sensor node, though usually neglecting the requirements of the application level. Even a few work consider the need of the application level, they perform at packets granularity and don’t fit well at service granularity. In this paper, we aim to remove these limitations in the wireless sensor network with the service-oriented architecture. Instead of deploying redundancy nodes, the proposed mechanism replaces the faulty sensor node with consideration of the similarity on the application level, as well as on the sensor level. On the application level, we apply the Bloom Filter for its high efficiency and low space costs. While on the sensor level, we design an objective solution via the coefficient of a variation as an evaluation for choosing the substitute on the sensor level.     

基于变周期技术的自适应数据采集算法

在数据采集系统中,按需采集是平衡数据数量、提高数据质量的有效手段。本文所提出的自适应数据采集算法是基于有限采样点的一元线性回归拟合,通过实时地对采集到的数据进行分析,不断修正采样周期,使得采样周期能够快速、准确地适应被测对象的动态变化。MATLAB软件仿真表明,本方法对于被测量加速变化具有较强的动态捕捉能力,能够在降低平均采样频率的前提下减小采样失真度,且与同类方法相比失真度低,稳定性高,是测控系统中实时数据采集的一种较好的代替方案。