Dense and core-rim structured B4C-TiB2 ceramics with Mo-Co-WC additive

B₄C-TiB₂ ceramics (TiB₂ ranging 5~70 vol%) with Mo-Co-WC as the sintering additive were prepared by spark plasma sintering. In comparison with B₄C-TiB₂ without additive, the enhanced densification was evident in the sintered specimen with Mo-Co-WC additive. Core-rim structured grain was observed around TiB₂ grains. The interface of the rim between TiB₂ and B₄C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B₄C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B₂ rim around the TiB₂ core may occur as a result of the solid solution and dissolution-precipitation between TiB₂ phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB₂ content increased, alongside the decreased hardness. B₄C-30 vol% TiB₂ specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m^1/2.     

受限波兹曼机联合稀疏近似的脑功能检测模型

人脑功能连通性检测是神经科学研究的重要技术．使用受限制波兹曼机（RestrictedBoltzmannMachine,RBM）对大量多被试功能磁共振（functionalMagneticResonanceImaging,fMRI）数据进行建模可以检测人脑功能连接,但是不能有效检测单被试数据的功能连接．本文研究一种新颖的融合了稀疏近似与RBM技术的脑功能连通性检测模型,该模型充分利用fMRI数据的稀疏性,采用稀疏近似理论对fMRI数据进行空间域稀疏近似压缩,然后使用RBM建立模型,以检测脑功能连通性．实验结果表明,该融合模型可以有效地提取单被试数据的脑功能时间域混合模型及其相应的脑功能图谱,解决了RBM在单被试数据分析上的瓶颈．     

Analysis and Implementation of an Open Programmable Router Based on Forwarding and Control Element Separation

A router architecture based upon ForCES (Forwarding and Control Element Separation), which is being standardized by IETF ForCES working group, gains its competitive advantage over traditional router architectures in flexibility, programmability, and cost-effectiveness. In this paper, design and implementation of a ForCES-based router (ForTER) is illustrated. Firstly, the implementation architecture of ForTER is discussed. Then, a layered software model, which well illustrates ForCES features, is proposed. Based on the model, design and implementation of Control Element (CE) and Forwarding Element (FE) in ForTER are introduced in detail. Moreover, security for ForTER is considered and an algorithm to prevent DoS attacks is presented. Lastly, experiments of ForTER are illustrated for routing and running routing protocols, network management, DoS attack prevention, etc. The experimental results show the feasibility of the ForTER design. Consequently, the ForTER implementation basically testifies the feasibility of ForCES architecture and some IETF ForCES specifications.     

大幅面地图的快速自动地形晕渲

在提出一个建立三维规则数据场的新算法的基础上,提出了一个可用于大幅度地图的快速实用的地形自动晕渲算法,与传统数据网格化的方法不同,本算法采用了用网格点相邻等高线的高程值插值计算出网格点高程值的新思想,并且提出了相应的网格点相邻等高线的识别方法,该方法充分利用等高线所具有的先验知识,得到的网格点高程值质量很高,另外,该规则数据场的建立方法经改进后,其时间复杂性与数据点数（ｍ）和网格点数（ｎ）成线性关     

Synthesis and characterization of a new Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> pillared triple-layered perovskite KSr<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>10</Subscript>

A n-Hexyl NH₃Sr₂Nb₃O₁₀ is obtained by the stepwise ion-exchange reaction, then is dispersed in aqueous solution of trinuclear acetato-hydroxo iron (III) nitrate, [Fe₃(OCOCH₃)₇OH·2H₂O]NO₃, and the interlayer potassium cations of the perovskite niobate are exchanged with the partially hydrolyzed trinuclear acetato complex ions. On heating, the exchanged complex ions are converted into iron oxide pillars which keep the perovskite sheets apart. The product is characterized by XRD, SEM, EDAX and surface area measurement respectively. Zhang Hui: Born in 1970 Funded by the National Natural Science Foundation of China (No. 50002007), Major Program of Ministry of Education (No. 0201) and Open Foundation of State Key Lab of Advanced Tech. for Materials Synthesis and Processing.     

信息系统安全需求分析方法研究

1 引言在人类社会的发展和生存越来越依赖于信息的今天,信息系统已成为人们用于产生、传送、使用、管理信息的主要工具和手段。然而,随着计算机和通信网络技术的飞速发展,信息系统的安全保密问题也日益突出和复杂化。怎么才能确保信息系统的有效性和安全性,已经成为社会普遍关注的重点问题。为此,在新信息系统的构建以及旧信息系统的维护和扩     

基于模式映射的查询计划生成算法

因特网的迅速发展使得多数据源综合集成日益重要.但是,不同数据源之间数据结构和语义的异构性导致数据集成是相当困难的.本文提出了一种基于模式映射的查询计划生成算法.该算法在正确定义映射规则的前提下,根据不同的查询条件和不同的数据源模式,自动构造查询计划,并保证结果数据满足目标模式结构与引用完整性要求.     

对DCT域连续LSB隐写术的提取攻击

基于JPEG图像的空域特征,针对DCT域连续LSB隐写术提出一种唯载密提取攻击方法。根据JPEG图像编码块在空域的块不连续性,将嵌入消息起止点估计问题转化为序列突变点的估计问题,建立逼近理想序列模型估计序列突变点。新模型不仅适用于对连续JSteg算法的提取攻击,对一类可抵抗χ²检验攻击的连续JSteg改进算法同样有效。实验结果表明,对消息嵌入起止点的平均估计误差约为260个系数。     

对空域图像LSB隐写术的提取攻击

隐写分析的研究一直集中于检测隐藏信息的存在性,而关于如何提取隐藏信息(即对隐写术的提取攻击)的研究还非常少.对于使用密钥的隐写术,提取攻击等价于恢复隐写密钥.文中结合隐写分析中的检测技术和密码分析中的相关攻击技术,对空域图像LSB隐写术提出了一种隐写密钥恢复方法.理论分析说明:此攻击方法的计算复杂度主要由所需的样本量决定,并且当嵌入率r接近0或1时攻击将失败.作者通过混合高斯模型给出了一个估计最小样本量的方法.针对隐写软件"Hide and Seek 4.1"的实验表明:此攻击方法可以成功恢复隐写密钥,从而提取隐藏的消息.如果消息长度L未知,当嵌入率5.3%＜r＜94.7%时攻击可以成功;如果L已知,当1.1%＜r＜98.4%时攻击可以成功,并且当11%＜r＜50%时,使用估计的最小样本量可以将攻击速度提高10%～45%.