Ag-Au-Cu合金表面张力的理论计算

表面张力对于材料而言是一种关键性的性质,该性能在液态金属和合金的成分设计领域有着十分重要的地位,其对铸造以及键合丝键合时金属凝固过程中表面是否开裂、焊接后焊接处的微观形貌有着决定性的影响。使用Butler模型和Toop模型分别计算金银铜及其对应二元合金在熔融状态下的表面张力并与实验值进行对比,从而为金银键合丝的成分设计起到一定的指导作用。结果表明:采用Butler模型和Toop模型计算出二元以及三元合金的表面张力与实验值相差较小。在1381K下,Ag-Au-Cu三元合金表面张力随Au和Cu含量变化介于0.89392~1.32471 N/m之间,表面张力随Ag或者Cu含量增加呈现单调减小或单调增大的趋势。     

累积叠轧焊温度对AZ31镁合金板材组织与性能的影响

目的研究叠轧温度对AZ31镁合金板材组织与性能的影响。方法在450℃和550℃下,对AZ31镁合金板材进行2道次叠轧,研究不同温度下板材界面裂纹的金相组织、RD-ND面晶体取向、力学性能以及断面形貌的异同。结果 450℃累积叠轧制备的ARB2镁合金板材室温断裂伸长率为2.3%,550℃累积叠轧制备的ARB2镁合金板材室温断裂伸长率为8%;450℃叠轧板材中动态再结晶晶粒大多数尺寸约为1～3μm左右,550℃叠轧板材中动态再结晶晶粒大多数尺寸约为600 nm～2μm。结论通过提高温度,可改善界面结合性能,促进基面晶粒往非基面取向偏转,提升了叠轧板材的力学性能,使叠轧板材由较低温度下的脆性断裂向韧性断裂转变。     

某SUV内外场气动噪声数值分析

运用分离涡模拟(DES),以商用软件Star CCM+为研究工具对某SUV在车窗封闭状态下,对汽车后视镜区域进行了外流场稳态和瞬态的计算分析,获得车身表面和周围的压力脉动,以此作为激励计算车内噪声。应用声学软件对后视镜以及周围进行流场到声场的耦合分析,得到声压级的频谱图。通过分析基础模型和改进模型内、外场气动声学特性表明:后视镜柄的长度,镜柄与镜罩的夹角以及镜罩形状对后视镜下游流场和声压级影响较大。改进模型相比基础模型前侧窗玻璃外表面总声压级得以降低,驾驶员左耳处内场总声压级降低了6.41%,语音清晰度提高了33.89%,取得很好的改进效果。     

基于智能算法的轴对称锻件预成形优化设计

为提高轴对称锻件预成形优化设计的效率,提出了一种基于遗传算法和数值模拟相结合的轴对称锻件自动优化方法。在这种自动优化方法中,CATIA和DEFORM-2D协同工作,从而实现锻造工艺的参数化数值仿真;MATLAB优化工具箱对参数化数值仿真进行智能化控制,实现实时协调通信;此外,在该优化算法中,将锻件中零件本体内等效应变在给定范围[0. 5,1. 0]外单元体积的百分比作为优化目标,将预锻模的尺寸数据作为优化设计变量。最后,使用某轴对称锻件作为样件,并设计了两种方案进行优化测试。优化结果表明,该优化方法能够将锻件内等效应变在[0. 5,1. 0]范围内的单元体积百分比从85%提高到95%,并且没有折叠等缺陷。     

改进YOLOv3的无人机拍摄图玻璃绝缘子检测

绝缘子作为电力巡检中的重要目标,对其检测受到高度重视.针对传统无人机拍摄图像绝缘子检测算法需要通过人工提取特征进行检测,效率低且鲁棒性差等问题,通过对绝缘子图像数据集进行分析,结合YOLOv3目标检测算法与Inception-Resnet-v2分类算法,提出一种改进的YOLOv3绝缘子检测算法,该方法分别从增加Ince...     

Cumulant-based deconvolutionand identification: several new families of linear equations

This paper presents several new families of cumulant-based linear equations with respect to the inverse filter coefficients for deconvolution (equalisation) and identification of nonminimum phase systems. Based on noncausal autoregressive (AR) modeling of the output signals and three theorems, these equations are derived for the cases of 2nd-, 3rd and 4th-order cumulants, respectively, and can be expressed as identical or similar forms. The algorithms constructed from these equations are simpler in form, but can offer more accurate results than the existing methods. Since the inverse filter coefficients are simply the solution of a set of linear equations, their uniqueness can normally be guaranteed. Simulations are presented for the cases of skewed series, unskewed continuous series and unskewed discrete series. The results of these simulations confirm the feasibility and efficiency of the algorithms.     

Effect of heat treatment on photoluminescence behavior of Zn2SiO4:Mn phosphors

The thermal treatment in reducing atmospheres gives rise to the increase both in emission intensity and 10% decay time in Zn₂SiO₄:Mn phosphors. The present investigation aims to take account of such changes in association with the structural change. For this sake, X-ray absorption spectroscopy techniques such as XANES and EXAFS were conducted to the Zn₂SiO₄:Mn phosphors. The Zn₂SiO₄:Mn phosphors were fired in the air and then thermally treated in two different reducing atmospheres (hydrogen or carbon). The photoluminescent (PL) behavior was closely related to the X-ray absorption data. The XANES and EXAFS prove that the oxidation state (+2) remains identical regardless of whether or not the samples are treated, but that the Mn–O distance was reduced by the heat treatment. In order to give a plausible interpretation to the change in PL results, two possible suggestions are presented. Firstly, it is conceivable that the thermally activated diffusion process of manganese ions splits Mn–Mn pair during the heat treatment. Another possibility is that the thermal treatment annealed out some quenching site, which is related with defects and impurities. Such hypotheses can be rationalized systematically by considering the results from lifetime measurement, Debye–Waller factor calculation, and XANES pre-edge peaks.     

Performance analysis of cell discarding techniques for best effort video communications over ATM networks

With increasing interest in the transmission of audio–visual applications over ATM best effort services, efficient video-oriented control mechanisms for improving the video quality in the presence of loss have to be designed. In this paper, we propose and evaluate two new slice-based discard schemes for use with available bit rate and guaranteed frame rate services (e.g. formerly UBR+). The schemes adaptively and selectively adjust the discard level to switch buffer occupancy and video cell payload types. To improve their performance, we also introduce a dynamic frame-level priority data partition technique based on MPEG data structure and feedback from the network. To support these mechanisms, enhancements to the ATM adaptation layer 5 and a new MPEG-2 encapsulation strategy are also proposed. The presented quality of picture (QoP) control framework is evaluated using simulation and actual MPEG video data. The overall aim of the framework is double. First, ensuring a graceful picture quality degradation by minimizing cell loss probability for critical video data, and second optimizing the network effective throughput by reducing transmission of non useful data. In comparison to previous approaches, the performance evaluation have shown a significant reduction of the bad throughput and minimization of losses of intra- and predictive-coded frames at both cell and slice layers.     

教室监控下学生异常行为检测系统

针对教室监控中学生异常行为无法实时检测并反馈的现状,设计了一套基于YOLO v3算法的教室监控学生异常行为检测系统,包括摄像头硬件采集、异常行为识别和响应三个模块.其中采用基于数据标签的随机擦除预处理方法模拟图像中的目标被遮挡的情形,提高网络的泛化能力,使得网络仅通过学习局部特征即可完成目标的检测和识别;其次改进了YO...     

基于小偏置碰的乘员二次碰撞分析及约束系统仿真优化

研究64 km/h小偏置碰的乘员动态响应及约束系统参数影响.通过建立50 km/h全正碰与64 km/h小偏置碰的约束系统模型,比对两种工况中的乘员二次碰撞运动姿态与损伤特点.仿真结果表明小偏置碰中乘员上躯干相对车体产生较大的横向加速度,导致头部和颈部等部位损伤加剧.基于上述损伤特点,导入侧气帘模块并分析其对乘员损伤的...