Features of microstructure and fracture in the transient liquid phase bonded aluminium-based metal matrix composite joints

Transient liquid phase (TLP) bonded aluminium based metal matrix composite (MMC) joints can be classified into three distinct regions, i.e. the particulate segregation region, the denuded particulate region and the base material region. The microstructure of the particulate segregation region consists of alumina particulate and Al alloy matrix with the Al 2Cu and MgAl 2O 4. It contains more and smaller alumina particulates compared with the base material region. The TLP bonded joints have the tensile strength of 150 MPa ～200 MPa and the shear strength of 70 MPa ～100 MPa . With increasing tensile stress, cracks initiate in the particulate segregation region, especially in the particulate/particulate interface and the particulate/matrix interface, and propagate along particulate/matrix interface, througth thin matrix metal and by linking up the close cracks. The particulate segregation region is the weakest during tensile testing and shear testing due to obviously increased proportion of weak bonds (particulate particulate bond and particulate matrix bond).

Application of matrix-based system reliability method in complex slopes

Complex slopes are characterized by large numbers of failure modes,cut sets or link sets,or by statistical dependence between the failure modes.For such slopes,a systematic quantitative method,or matrix-based system reliability method,was described and improved for their reliability analysis.A construction formula of event vector c E was suggested to solve the difficulty of identifying any component E in sample space,and event vector c of system events can be calculated based on it,then the bounds of system failure probability can be obtained with the given probability information.The improved method was illustrated for four copper mine slopes with multiple failure modes,and the bounds of system failure probabilities were calculated by self-compiling program on the platform of the software MATLAB.Comparison in results from matrix-based system reliability method and two generic system methods suggests that identical accuracy could be obtained by all methods if there are only a few failure modes in slope system.Otherwise,the bounds by the Ditlevsen method or Cornell method are expanded obviously with the increase of failure modes and their precision can hardly satisfy the requirement of practical engineering while the results from the proposed method are still accurate enough.

Free-matrix-based time-dependent discontinuous Lyapunov functional for synchronization of delayed neural networks with sampled-data control

This paper is concerned with the synchronization of delayed neural networks via sampled-data control. A new technique, namely, the free-matrix-based time-dependent discontinuous Lyapunov functional approach, is adopted in constructing the Lyapunov functional, which takes advantage of the sampling characteristic of sawtooth input delay. Based on this discontinuous Lyapunov functional, some less conservative synchronization criteria are established to ensure that the slave system is synchronous with the master system. The desired sampled-data controller can be obtained through the use of the linear matrix inequality(LMI) technique. Finally, two numerical examples are provided to demonstrate the effectiveness and the improvements of the proposed methods.

ATTACKS AND IMPROVEMENTS ON THE RFID AUTHENTICATION PROTOCOLS BASED ON MATRIX

Most of the Radio Frequency IDentification (RFID) authentication protocols, proposed to preserve security and privacy, are analysed to show that they can not provide security against some passive or active attacks. In this paper, the security of two matrix-based protocols, proposed by Karthikeyan and Nesterenko (KN protocol) and Ramachandra et al. (RRS protocol) that conform to Electronic Product Code Class-1 Generation-2 (EPC Class-1 Gen-2) standard, are investigated. Using the linear relationship of multiplication of matrix and vector, we point out that both protocols can not provide scalability, and they are vulnerable to passive impersonation attack. In addition, both protocols are totally insecure if the adversary can compromise one tag to extract the secrets. A modified lightweight matrix-based authentication protocol is presented, which can resist mainly common attacks on an RFID authentication system including eavesdropping, relay attack, desynchronization attack, impersonation attack and tag tracking attack. The new protocol also has the desirable scalability property and can keep secure under compromising attack.

Modulus-Based Matrix Splitting Iteration Methods for a Class of Stochastic Linear Complementarity Problem

For the expected value formulation of stochastic linear complementarity problem, we establish modulus-based matrix splitting iteration methods. The convergence of the new methods is discussed when the coefficient matrix is a positive definite matrix or a positive semi-definite matrix, respectively. The advantages of the new methods are that they can solve the large scale stochastic linear complementarity problem, and spend less computational time. Numerical results show that the new methods are efficient and suitable for solving the large scale problems.

6R Robot Inverse Solution Algorithm Based on Quaternion Matrix and Groebner Base

This article proposes a new algorithm of quaternion and dual quaternion in matrix form. It applies quaternion in special cases of rotated plane, transforming the sine and cosine of the rotation angle into matrix form, then exporting flat quaternions base in two matrix form. It establishes serial 6R manipulator kinematic equations in the form of quaternion matrix. Then five variables are eliminated through linear elimination and application of lexicographic Groebner base. Thus, upper bound of the degree of the equation is determined, which is 16. In this way, a 16-degree equation with single variable is obtained without any extraneous root. This is the first time that quaternion matrix modeling has been used in 6R robot inverse kinematics analysis.

High Quality Audio Object Coding Framework Based on Non-Negative Matrix Factorization

Object-based audio coding is the main technique of audio scene coding. It can effectively reconstruct each object trajectory, besides provide sufficient flexibility for personalized audio scene reconstruction. So more and more attentions have been paid to the object-based audio coding. However, existing object-based techniques have poor sound quality because of low parameter frequency domain resolution. In order to achieve high quality audio object coding, we propose a new coding framework with introducing the non-negative matrix factorization(NMF) method. We extract object parameters with high resolution to improve sound quality, and apply NMF method to parameter coding to reduce the high bitrate caused by high resolution. And the experimental results have shown that the proposed framework can improve the coding quality by 25%, so it can provide a better solution to encode audio scene in a more flexible and higher quality way.

基于会话的独立邻域矩阵偏好交互推荐

通过合并输入和输出邻域矩阵可以使一些工作生成全局和局部偏好,并直接对这2个偏好建模来构建会话表示,从而实现改进。然而,一个会话的输入矩阵和输出矩阵并没有很强的相关性,它们的连接可能会为构建2个偏好引入噪声。其次,全局偏好和局部偏好可以相互促进,且邻域会话的协同信息可能有助于提高推荐性能。因此,一种基于会话的偏好交互推荐被提出,它来自独立的输入邻域矩阵和输出邻域矩阵框架,包括2个并行模块:输入会话表示编码器(ISE)和输出会话表示编码器(OSE)。ISE通过GNN和并行协同注意力机制对具有输入信息的会话表示进行建模。OSE通过GNN和并行协同注意力机制对具有输出信息的会话表示进行建模。最后,引入一种融合门控机制来平衡ISE和OSE产生的会话表示的重要性。结果表明,在Yoochoose和Diginetica数据集上,提出的模型明显优于其他先进的方法。

面向6G的QC-LDPC码

在各无线通信标准中,如Wi-Fi、WiMAX和5G标准等,都采用了QC-LDPC码作为数据信道的纠错编码方案。QCLDPC码的译码具有较高并行度,非常适合于高数据传输速率的通信系统。目前5G的QC-LDPC码虽然可以满足上行10 Gbps和下行20 Gbps的峰值速率需求。然而,面对未来6G无线移动通信系统对超过100 Gbps峰值速率的迫切需求,现有QC-LDPC编码正面临着前所未有的挑战。鉴于此,基于迭代阈值和距离上限等设计新QC-LDPC码,其最大提升值为1024,对应的基础矩阵兼容5G-BG1,可以兼容5G的译码方法。仿真结果表明,新LDPC码具有更高的译码吞吐量和更低的差错平层性能。

数字化γ能谱测井探管研制

针对铀钍混合型矿床上无法精确测量地层中铀、钍含量的问题,本文研制了一台基于溴化铈晶体的数字化γ能谱测井探管。该仪器采用直径38 mm×38 mm的溴化铈晶体,提高了铀灵敏度和在低铀、低钍含量矿层的探测效率。采用C8051单片机作为核心处理器,对溴化铈探测器原始信号进行了滤波成形处理,通过能谱采集器得到γ能谱数据。通过对γ能谱数据进行逆矩阵解谱,即可得到矿层中铀、钍的精确含量。通过RS-485总线将γ能谱数据传送至测井主机。测试结果表明:本仪器在标准铀钍混合模型上的测量准确度高,其示值误差小于6%,稳定性小于1.5%,重复性小于1%,钍系^(208)Tl的2.62 MeV能量峰漂移不超过±0.3道,检查测井异常相对误差小于4%,可应用于铀矿勘查测井工作。

采用局部子图嵌入的MOOCs知识概念推荐模型

大规模开放在线课程(MOOCs)在减少用户学习盲区和改善用户体验方面已经有大量的研究,尤其是基于图神经网络的个性化课程资源推荐,但现有工作主要集中在固定或同质图上,容易受到数据稀疏问题的影响且难以扩展。在局部子图上使用图卷积,并结合扩展的矩阵分解(MF)模型来解决这一问题。首先,将异构图分解为多个基于元路径的子图,结合随机游走采样方法实现在采样节点富有影响力邻域的同时捕获实体之间复杂的语义关系,并在局部邻域上进行图卷积平滑各节点表示,实现高可扩展性;然后,使用注意力机制适应性地融合不同子图的上下文信息,更全面地构建用户偏好;最后,通过扩展矩阵分解优化模型参数,获得推荐列表。为了验证提出模型的性能,在公开的MOOCs数据集上进行对比实验,相较于最优基线,性能提升了2%,内存计算需求降低了近500%,缓解数据稀疏问题的同时仍具有较强的可扩展性。

矩阵逆与行列式的新型求法

本文将根据线性空间基与基之间的过渡矩阵来求两类矩阵的逆,并且由此过程得到范德蒙矩阵的逆与行列式的具体值,也由此衍生出来关于复数的一些相关结论.

水泥基纤维复合材料与混凝土的黏结性能试验研究

为了实现对老旧混凝土结构快速修补的目的,以磷酸镁水泥代替普通硅酸盐水泥,制备了一种高性能水泥基纤维复合修补材料,并以黏结抗拉强度、抗折强度和抗剪强度为评价指标,考察了其与混凝土结构之间的黏结性能。试验结果表明:混凝土的界面粗糙度越大,水泥基纤维复合材料与混凝土之间的黏结抗拉强度、抗折强度和抗剪强度值均先增大后减小,当界面粗糙度为3.5 mm左右时,黏结性能可达到最佳;混凝土基体强度越大,水泥基纤维复合材料与混凝土之间的黏结抗拉强度、抗折强度和抗剪强度值就越大,黏结性能越好。试验制备的水泥基纤维复合材料与混凝土之间的黏结性能较好,能够满足老旧混凝土结构修补施工的需求。

Characterizations and mechanical properties of impregnated diamond segment using Cu-Fe-Co metal matrix

Diamond impregnated Cu-Fe-Co based saw-blade segments are directly processed by vacuum and pressure-assisted sintering at different temperature,with the purpose of reducing the cobalt content in diamond tools.Copper and iron are used as the bonding elements and co-balt-chrome pre-alloyed powder is used as the hardening phase.Effects of sintering temperature on microstructures and mechanical properties of the sintered matrix and diamond graphitization were investigated by X-ray diffraction analysis,electron probe micro-analyzer,universal testing machine,digital Rockwell hardness tester and Raman scattering analyzer.Results showed that microstructures of the sintered matrix were refined and porosities in the sintered matrix were closed to a more spherical-like shape with the increase of the sintering temperature.Densification,hardness and tensile strength of the matrix sintered at 820 ℃ were 12.75%,2.72% and 156.38% higher than that of the matrix sintered at 740 ℃,respectively.Diamond graphitization was not occurred at 820 ℃.The hardness and the tensile strength rose 32.8% and 13.5%,respectively,after 7.5 h ageing treatment.The matrix densification ascent and the dispersed distribution of Co-Cr pre-alloyed powders contributed a hardness improvement and a tensile strength improvement to the Cu-Fe based matrix.

Data Matrix二维条码在奥运会门票系统中的应用研究

运用Data Matrix二维条码的特点重新设计奥运体育场馆电子门票系统,并构建了一个完整的奥运电子门票Data Matrix二维条码自动识别系统。对Data Matrix二维条码系统进行详细地规划,并通过实际条码生成的例子,证明其可行性和可实践性。本文突破了Data Matrix二维条码本身的适用领域的限制,有一定新意和实践价值。

纤维复合材料剪滞理论的改进与参数分析

对于纤维复合材料,传统剪滞理论没有考虑基体轴向应变的影响,导致无法反映基体在应力传递中的作用。通过对剪滞理论的改进,解决了上述问题,推导了纤维轴向应力、纤维轴向变形、基体轴向应力、基体轴向变形、纤维/基体界面剪应力、纤维/基体相对滑移量的分布公式,分析了界面弹性模量对应力传递机制的影响,结果符合现有研究成果。经与有限元分析结果对比,验证了改进理论的合理性。

Structural Damage Detection in Framed Structures Under Foundation Settlement/Rotation of Bases

This paper describes the damage detection in framed structures due to thevertical support settlement and rotation of footing bases. The damage detection procedureproposed by Nobahari et al. [Nobahari and Seyedpoor (2013)] is used to detect thedamage in the members of the frame. In the present study, instead of using the flexibilitymatrix (referred here as original flexibility matrix) method, the generalized flexibilitymatrix is used in the same algorithm and the results are compared. The algorithm usesflexibility matrix and strain energy concept to detect the damage in the members. Thebehaviour of the frame is discussed through changes observed in flexibility in theassociated degree of freedom. Finally, the results indicate that, the damage indexdetermined by generalized flexibility matrix method is more reliable than using theoriginal flexibility matrix based method for the problem of settlement and rotation offooting base.

Study on iron-based diamond bit by DC-electroplating method

Iron-plating technology used for restoration of axis parts was applied to the manufacture of diamond bits in this paper.The technology for electroplating diamond bit of iron matrix was mastered through repeated experiments and research.The productive practice indicated that the DC-electroplated iron matrix of diamond bit has high hardness and good diamond exposure ability;the drilling rate of electroplated iron-based diamond bit was 2 m/h when drilling in grade 9 granite and bit life can reach 44 m,which can satisfy the drilling production requirements.

MoS2对热压Fe基金刚石钻头胎体性能的影响研究

金刚石钻头是勘探工作中的常见破岩工具,但金刚石热稳定性较差,在钻进过程中会不断产生热量,干旱缺水条件下钻头自冷却对钻进效率的提高具有非常重要的意义。为降低干钻条件下钻头胎体与岩石界面间的摩擦因数从而减少钻进过程中金刚石的热损伤,在热压Fe基金刚石钻头胎体中添加二硫化钼(MoS2),研究MoS2含量对Fe基钻头胎体相对密度、洛氏硬度、抗弯强度以及与白刚玉砂轮干磨时的磨损量和摩擦因数的影响,并用扫描电子显微镜(SEM)和能谱仪(EDS)等测试仪器分析了抗弯强度和摩擦磨损试验后的试样断口和表面的形貌及物相成分。试验结果表明,在试验范围内,Fe基胎体相对密度与MoS2含量关系不大,但是与未添加MoS2的Fe基胎体相比,其相对密度提高了约2.5%,达98%以上。Fe基胎体洛氏硬度随着MoS2含量的增加先增大后减小,在MoS2体积分数为8%时胎体硬度最大,洛氏硬度HRB值达101.3。Fe基胎体抗弯强度随着MoS2含量的增加先增大后减小,在MoS2体积分数为2%时胎体抗弯强度最大,达1140 MPa。Fe基胎体磨损量随着MoS2含量的增加先减小后增大,在MoS2体积分数为4%时磨损量最小,为0.376 g。Fe基胎体与岩石界面间的摩擦因数则随着MoS2含量的增加而逐渐下降,在MoS2体积分数为10%时摩擦因数最小,为0.325。抗弯强度断裂试样断口形貌和物相分析表明,MoS2的加入降低了Fe基胎体显微组织的连续性。摩擦磨损试验后试样形貌分析表明,MoS2的加入降低了摩擦磨损过程中的粘着磨损和塑性变形。研究成果为减少干钻条件下金刚石磨损和热损伤,提高胎体耐磨性,延长钻头寿命奠定了理论基础。

High Temperature Property Development of Bauxite Based Bricks

Physical properties and microstructural evolution on firing of 3 types of bauxite based refractory bricks were carried out using techniques such as porosimetry, XRD and SEM. The groups differed from each other by progressive refining of the matrix or bond phase. It is revealed that such a refinement of the matrix can improve the high temperature properties of the bricks made from poor grade materials.