Effect of thermal-cooling cycle treatment on thermal expansion behavior of particulate reinforced aluminum matrix composites

Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology. Microstructures and effect of thermal-cooling cycle treatment （TCCT） on the thermal expansion behaviors of three composites were investigated. The results show that the composites are free of porosity and SiC/Al2O3 particles are distributed uniformly. Inflections at about 300℃ are observed in coefficient of thermal expansion （CTE） versus temperature curves of two SiCp/Al composites, and this characteristic is not affected by TCCT. The TCCT has significant effect on thermal expansion behavior of SiCp/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles. However, no inflection is observed in Al2O3p/Al composite, while TCCT has effect on CTE of Al2O3p/Al composite. These results should be due to different relaxation behavior of internal stress in three composites.

Effect of Reinforcement Clustering on Crack Initiation Mechanism in a Cast Hybrid Metal Matrix Composite during Low Cycle Fatigue

The reinforcement distribution of metal matrix composites (MMCs) plays an important role in low cycle fatigue. Thus, it is essential to study the effect of reinforcement clustering on the crack initiation mechanism of MMCs. In this study, the effect of reinforcement clustering on the microcrack initiation mechanism in a cast hybrid MMC reinforced with SiC particles and Al2O3 whiskers was investigated experimentally and numerically. Experimental results showed that microcracks always initiated in the particle-matrix interface, located in the cluster of the reinforcements. The interface debonding occurred in the fracture which created additional secondary microcracks due to continued fatigue cycling. The microcrack coalesced with other nearby microcracks caused the final fracture. To validate the experimental results on the microcrack initiation, three dimensional unit cell models using finite element method (FEM) were developed. The stress distribution in both the reinforcement clustering and non-clustering regions was analyzed. The numerical analysis showed that high stresses were developed on the reinforcements located in the clustering region and stress concentration occurred on the particle-matrix interface. The high volume fraction reinforced hybrid clustering region experienced greater stresses than that of the SiC particulate reinforced clustering region and low volume fraction reinforced hybrid clustering region. Besides, the stresses developed on the non-clustering region with particle-whisker series orientation were reasonably higher than that of the non-clustering region with particle-whisker parallel orientation. The high volume fraction reinforced hybrid clustering region is found to be highly vulnerable to initiate crack in cast hybrid MMC during low cycle fatigue.

Minimum Cycle of Row Vector of a Generalized Circulant Fuzzy Matrix

In this paper,we intreduce the concept and discuss the properties of minimum cycle of row vector in a generalized circulant Fuzzy matrix. We present a new expression for circulant Fuzzy matrix,and discuss some properties of the idempotent elements of the semigroup of generalized circulant Fuzzy matrixes in connection with minimum cycle of row vector.

Effect of nano-sized Al2O3 reinforcing particles on uniaxial and high cycle fatigue behaviors of hot-forged AZ31B magnesium alloy

The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.

Limit Cycle Identification in Nonlinear Polynomial Systems

We present a novel formulation, based on the latest advancement in polynomial system solving via linear algebra, for identifying limit cycles in general n-dimensional autonomous nonlinear polynomial systems. The condition for the existence of an algebraic limit cycle is first set up and cast into a Macaulay matrix format whereby polynomials are regarded as coefficient vectors of monomials. This results in a system of polynomial equations whose roots are solved through the null space of another Macaulay matrix. This two-level Macaulay matrix approach relies solely on linear algebra and eigenvalue computation with robust numerical implementation. Furthermore, a state immersion technique further enlarges the scope to cover also non-polynomial (including exponential and logarithmic) limit cycles. Application examples are given to demonstrate the efficacy of the proposed framework.

On the Number of Cycles in a Graph

In this paper, we obtain explicit formulae for the number of 7-cycles and the total number of cycles of lengths 6 and 7 which contain a specific vertex vi in a simple graph G, in terms of the adjacency matrix and with the help of combinatorics.

GM130通过14-3-3ζ对卵巢癌细胞增殖的影响及机制研究

目的探讨高尔基体基质蛋白130(GM130)通过14-3-3ζ对卵巢癌细胞增殖的影响及可能机制。方法采用免疫组化法检测在20例正常卵巢上皮组织和42例卵巢上皮恶性肿瘤中GM130和14-3-3ζ的表达,分析二者相关性。采用Western blot和RT-PCR法检测卵巢癌SKOV3/A2780细胞株GM130和14-3-3ζ蛋白及其mRNA表达情况,筛选出高表达细胞株。采用免疫荧光染色法检测GM130与14-3-3ζ在卵巢癌细胞中的共表达情况。将设计好的重组表达质粒shRNA-GM130片段稳转进入卵巢癌细胞中,采用Western blot和RT-PCR筛选出降低GM130的最佳片段。细胞分为三组:空白组(WT)、对照组(NC)、低表达组(313),采用CCK法和流式细胞术分别检测各组卵巢癌细胞生殖情况及周期变化情况,采用Western blot法检测各组14-3-3ζ、GRASP65、P115及增殖相关蛋白表达水平。结果GM130和14-3-3ζ在卵巢恶性肿瘤组织中的表达水平高于正常卵巢组织(P<0.001)。在卵巢恶性肿瘤组织中,GM130和14-3-3ζ呈正相关关系(r=0.873,P<0.001)。GM130蛋白及其mRNA在SKOV3细胞中的表达量高于A2780细胞(P<0.05),14-3-3ζ蛋白及其mRNA在SKOV3细胞和A2780细胞中比较差异无统计学意义(P>0.05)。后续实验选用SKOV3细胞。免疫荧光共定位染色显示,GM130与14-3-3ζ主要在胞质表达,前者近核膜部分呈堆叠样表达量较高,后者胞核中表达较少,二者可能存在共定位关系。转染313组片段后,对GM130的抑制效果最好。转染质粒313组细胞增殖能力降低,细胞在G1期阻滞的数量增多,G2期阻滞数量减少,S期阻滞的细胞数量稍减少,GM130、14-3-3ζ、P115、Cyclin A、Cdc25A蛋白相对表达水平降低,P21蛋白相对表达水平升高(P<0.05)。结论抑制GM130可抑制卵巢癌细胞增殖,其机制可能与抑制14-3-3ζ表达,影响卵巢癌细胞周期有关。

基于BIM技术的绿色建筑设计研究与应用——重庆市广阳岛项目

建设领域如何引入数字化手段,形成量化评估优化机制推进绿色建筑发展,减少碳排放,提升建筑工程品质,推动建筑业高质量发展迫在眉睫。本文以重庆市广阳岛绿色建筑全生命周期评估研究为例,搭建BIM模型底座,基于绿色建筑最新国标体系,提出了“BIM评估矩阵法”。结合标准中的各项评判控制因子,对项目BIM模型的专项模拟论证指标进行预评估。经过对控制因子不同阶段的持续优化、再论证,最终达到绿色建筑三星的要求,通过数字化手段实现绿色建筑的评判。“BIM评估矩阵法”的应用提高了建筑的整体性能,提供了更舒适的环境,对生态环境的影响更轻,实现了节地、节材、节能、节水和可持续发展的目标。

干湿循环中膨胀土吸力和膨胀力变化规律研究

以江苏省宿迁市某膨胀土航道整治工程为例,通过室内试验,研究膨胀力与基质吸力随含水率与干湿循环次数的变化规律。结果表明,膨胀力随含水率增加而降低,干湿循环后膨胀力整体下降,其中吸湿过程膨胀力大于干燥过程,在一定次数的循环后逐渐稳定;基质吸力随体积含水率增大而减小,干湿循环次数的增加使得基质吸力下降,含水率越大降幅越小,滞回曲线不明显。试验数据拟合发现,膨胀力与含水率关系式用指数函数拟合、土水特征曲线用Gardner模型拟合效果最好。结合相应的非饱和土抗剪强度公式,能用于非饱和膨胀土边坡的相关研究。

源于钛基铅酸电池的再生钛基体作为板栅集电体的研究

钛基铅酸电池能够大幅度提高铅酸电池的能量密度,并且解决了传统铅酸电池正极板易腐蚀和软化的问题,商业化潜力巨大.然而,相比于传统铅酸电池成熟的回收工艺和再生铅的利用,钛基铅酸电池的回收方法以及回收材料的应用途径是未来钛基铅酸电池应用和发展的关键.本文制备了源于钛基铅酸电池的再生钛基的正负极板栅,将正极板栅组成为再生钛基体/锡锑中间层/铅,将负极板栅组成为再生钛基体/铜/铅.通过研究源于钛基铅酸电池的再生钛基体用于板栅集电体的电化学性能,讨论了循环应用的可能性.结果表明,基于再生钛基正极板的活性物质放电比容量为72.4mA·h/g,相应电池在0.5C100%DoD(放电深度)下的循环寿命为180次;基于再生钛基负极板的活性物质放电比容量为98mA·h/g,相应电池在0.5C100%DoD下的循环寿命达到332次,用再生钛基体制备的板栅及电池的性能与纯钛基体相同.

干湿循环作用下岩桥破裂演化及前兆异常定量识别研究

为探究干湿循环作用下锁固段型岩质边坡内部岩桥的破裂演化及前兆异常,对岩桥试件开展不同干湿循环次数下的单轴压缩试验。基于数字图像相关(DIC)技术,实现加载过程中试件全场变形的实时测量,通过求解位移矢量识别裂纹扩展类型。引入协方差矩阵,定量描述应变场多元分量的离散程度,提出一种识别岩桥应变场前兆异常的方法,并分析干湿循环作用的影响规律。研究结果表明:随着干湿循环次数的增加,岩桥的起裂应力和抗压强度均逐渐劣化。岩桥中裂纹发展时,周围岩石的位移矢量会发生明显的差异,共识别出两种基本裂纹,即张拉裂纹和剪切裂纹。裂纹起裂和贯通所需的轴向应力随着干湿循环次数的增加而逐渐减小。应变场有效方差的演化过程可划分为初始分异、稳定分异和加速分异3个阶段;当剪切裂纹起裂时,干燥状态下的试件有效方差突增,而干湿循环作用后的试件有效方差出现加速增长的态势,均可识别为前兆点。经过干湿循环作用的试件前兆应力水平和时间水平均小于干燥状态下的试件,这是因为干湿循环作用对岩样产生了软化作用。

生命周期管理视角下高校个人信息保护探索

高校个人信息保护对于保障师生权益、促进个人信息价值转化、平衡信息安全与利用之间的矛盾、深化高校信息化建设具有极其重要的现实意义。按照生命周期管理理论,高校个人信息的形成演变过程可划分为创建、采集、组织、存储、使用、归档六个阶段,通过建立各阶段管理指标和模型,创建“一数一源”管理矩阵,指出采集、使用阶段中个人信息的交互关系,厘清信息“源—终”端的保护、共享、质量提升等方面的具体职责。在此基础上,基于个人信息“可识别性”“重要性”“敏感性”,将高校个人信息划分为不同的类别,并建立分类目录;对于不同类别的个人信息,通过加密、脱敏,设置粒度适当的管理权限,明确各级别使用规则和责任权限,建立相应的应急响应制度,最终实现个人信息的分级保护。据此提出,高校个人信息生命周期管理是一项复杂、动态的过程,需要业务部门及信息主体全时、全员参与,在领导支持、部门配合、师生认可之后,才能找到个人信息保护和价值使用之间适当的平衡点;高校还应当在组织保障、信息主体信息安全素养提升、应急响应机制等方面,建立较为完善的配套机制。

Study on the Thermal Expansion and Thermal Cycling of AlNp/Al Composites

The AIN particle reinforced aluminum matrix composites with 50% volume fraction were fabricated by squeeze-casting technology. The thermal expansion behavior and its response to thermal cycling were studied between 20℃ and 400℃. Compared with four theoretical models, the measured CTEs of the composite lie within the elastic bounds derived by Schapery’s analysis. Schapery’s model and Kerner’s model agree well with the CTEs of the composites at lower temperature and elevated temperature, respectively. Strain hysteresis was observed between heating and cooling curves during cycling. This was attributed primarily to the anelastic behavior of the matrix induced by matrix residual stresses.

A Matrix-Based Approach for Sustainability in Product Design

The paper proposes a matrix-based approach that a designer can use to evaluate the sustainability of one or more design solutions in the conceptual phase of a product development process. The methodology is structured in two main phases. In the first one, a data structure, called Augmented-DSM （Design Structure Matrix）, has to be drawn in order to collect design information such as functional links among product components, indicators that provide information about the life cycle of each element, connections with the environment and toward other systems. The matrix is based on a DSM format, where new records were introduced to store and organize different types of data and an editing protocol was formalized. In the second stage, a set of procedures have to be applied in order to evaluate sustainability of a design solution and compare it with the others. The presented procedures, in fact, allow designers to assess a product in its proper characteristics, evaluate a device during its use stage and verify the coherence of links present in the functional model. This new approach is conceived to manage different performance indicators and, as a support tool, it is an attempt to aid designers in a quantitative evaluation.

基于显式保积方法的电磁暂态初始化计算方法

交流–电网换相换流器型高压直流输电(AC-line commutated converter high voltage direct current,AC-(LCC)DC)混联系统的电磁暂态初始化在计算模型上可表述为一个扰动的可分无源动力系统。因此,将无源动力系统的显式保积算法应用于电磁暂态初始化计算。采用相空间分析方法,对基于逐次积分法的电磁暂态初始化方法的收敛条件以及收敛速率进行了定量分析。在上述基础上,提出了一类新的、系统化的初始化计算方法,该方法计算格式简单、易于编程,在计算效率上具有明显的优势。算例结果验证了所提方法的有效性。

基于循环对抗神经网络的快速最小二乘逆时偏移成像方法

最小二乘逆时偏移成像方法因计算量巨大,限制了其大规模的工业应用。基于此,建立循环对抗神经网络表征Hessian矩阵的逆,构建逆时偏移结果和反射系数之间的映射关系。通过建立的神经网络对逆时偏移成像结果进行去模糊化处理,提高成像质量,同时大幅减少计算时间。将训练好的网络应用于Marmousi模型和Sigsbee2A模型的逆时偏移结果。结果表明,本文方法在不显著增加计算量的情况下较好地提高了逆时偏移成像质量。

一种基于弱监督学习的图像镜面高光去除算法

高质量图像是计算机视觉任务的基础,但实际生活中高光的出现会覆盖物体表面的纹理和颜色信息,导致图像质量显著下降。目前用于高光去除的深度学习方法往往需要大量高光-无高光配对图像进行监督,而高光图像对应的无高光版本存在收集和处理困难的问题。本文提出一种基于弱监督学习的图像镜面高光去除算法,旨在仅使用高光图像完成训练且达到很好的高光去除效果。首先,利用稀疏非负矩阵分解(NMF)方法估计图像的高光区域,并从无高光区域裁剪出无高光的参考图像。然后,将两者输入到联合训练的高光生成、高光消除和图像重建模块,协同优化各模块功能。总体采用循环生成对抗网络(CycleGAN)架构训练网络并最终生成无高光图像。选取自然图像数据集SHIQ和LIME进行实验,实验结果表明,所提方法能够有效去除镜面高光,并且在性能上对比现有的弱监督学习方法有较大提升。

基于H∞回路成形的变循环发动机多变量控制

为了进一步提升变循环发动机的性能,针对3输入3输出变循环发动机模型,利用相对增益矩阵(RGA)分析了发动机内部的耦合性;采用基于目标函数的2自由度H∞回路成形法设计了多变量控制器,并与传统单变量PI方法做了对比。仿真结果表明:多变量控制系统具有良好的扰动抑制能力和跟踪性能,且能够顺利实现模态转换;与单变量方法相比,在同等的穿越频率及相位裕度约束下,n1回路阶跃响应的超调量减小了95.3%、调节时间缩短了51.5%;πe回路的最大偏移量减小了89.69%、调节时间缩短了27.4%。表明多变量方法可以对变循环发动机进行有效控制且在跟踪控制过程中的性能更优,可以显著提升变循环发动机的性能。

有向图的埃尔米特拉普拉斯矩阵研究

拉普拉斯矩阵对于无向图的研究具有重要意义,其特征值反映了图的部分结构与性质,据此可以设计有效的算法以解决图上一些相关的任务,如划分、聚类等。将拉普拉斯矩阵推广至有向图,一大难点是失去了对称性,特征值可能为复数。为了规避该问题,最近的研究引入了k次单位根作为边权,定义了复数域上的拉普拉斯矩阵,该矩阵是埃尔米特矩阵。文中提出了有向边的旋转角的概念,对该矩阵进行了推广,证明了其具有与无向图拉普拉斯矩阵类似的代数性质;给出了有向图的约束方程组和有向环路的定义,证明了拉普拉斯矩阵最小特征值为0、约束方程组有解以及图中任意有向环路旋转角为2lπ(l∈Z)这三者间的等价性。最后给出了一些相关推论及应用。