Removing prior particle boundaries in a powder superalloy based on the interaction between pulsed electric current and chain-like structure

The chain-like prior particle boundaries (PPBs) as a kind of stubborn harmful precipitate will hinder atomic diffusion and particle connection.They can only be broken into nanoscale through thermal defor-mation (1160-1200 ℃).Here,treated by the pulsed electric current at 800 ℃,PPBs were dissolved quickly as a result of the interaction between the pulsed electric current and the chain-like structure.According to the electromigration theory and the calculation results,the high current density regions will be mainly produced at the gaps due to the conductivity difference between the precipitates and the matrix.The atomic diffusion flux caused by the pulsed electric current is proportional to the current density.There-fore,the existence of a large number of gaps in the chain-like PPBs will make the high current density regions play a more positive role in fast-dissolution.     

Characterization of the prior particle boundaries in a powder metallurgy Ti_2AlNb alloy

Ti_2 AlNb-based alloy powder metallurgy(PM) compacts were prepared via hot isostatic pressing(HIP)under relatively low temperature(920 and 980℃) and at certain pressure(130 MPa).The microstructure,composition and orientation of B2,α_2 and O phases in the compacts were characterized and analyzed with an aim to investigate the effect of unsuitable HIPping parameters on the appearance of prior particle boundary(PPB),which seriously affects the mechanical properties of the alloy.The results show that more α_2 phase is the characteristics of the PPB in Ti_2AlNb-based alloy when HIPped at relatively low temperature.Increasing HIPping temperature to the upper part of the two-phase region can effectively inhibit the formation of PPB.Electron backscatter diffraction measurements show the specific orientation relationship between phases,which helps us understand the origin of a2 and O phase and the corresponding transformation path.The HIPping at a higher temperature can weaken the micro-texture intensity of the α_2 and O phase due to the increase of misorientation in B2 phase.The α_2 phase at cell wall keeps the Burgers orientation relationship(BOR) with the grain on one side,and does not satisfy the BOR with the other.It is found that some O phase variants inside the cell HIPped at 980℃ can only maintain α_2-O OR with α_2 owing to the α_2→O phase transformation forming the O phase,while these O variants deviate from B2-O OR with B2 phase.     

Transfer estimation of evolving class priors in data stream classification

Data stream classification is a hot topic in data mining research. The great challenge is that the class priors may evolve along the data sequence. Algorithms have been proposed to estimate the dynamic class priors and adjust the classifier accordingly. However, the existing algorithms do not perform well on prior estimation due to the lack of samples from the target distribution. Sample size has great effects in parameter estimation and small-sample effects greatly contaminate the estimation performance. In this paper, we propose a novel parameter estimation method called transfer estimation. Transfer estimation makes use of samples not only from the target distribution but also from similar distributions. We apply this new estimation method to the existing algorithms and obtain an improved algorithm. Experiments on both synthetic and real data sets show that the improved algorithm outperforms the existing algorithms on both class prior estimation and classification.     

Wide-baseline view synthesis for light-field display based on plane-depth-fused sweep volume

The advancements in three-dimensional (3D) display technology have led to a wide interest in light-field display. However, the need to simultaneously capture a large number of object views made content generation for light-field displays still a bottleneck. In this paper, we propose a method for light-field content generation based on plane-depth-fused sweep volume (PDFSV), focusing on handling wide-baseline views and exhibiting scene generalization when the camera array remains unchanged. Specifically, the proposed PDFSV exploits the prior depth of the images captured by a 4 × 4 spherical camera array to represent 3D information of scenes. Then two optimized sequential convolutional neural networks (CNN) are employed for implicit depth modeling and final color calculation, respectively. By doing these, the prior depth facilitates the synthesis of regions with complex textures in the target view. We produce a Wide-baseline Multi-view Image Set (WMIS) which has a field of view (FOV) angle reaching 54°and could be publicly available for access. In our experiments, we use only the 4 vertex views as input. Results demonstrate that the proposed approach can synthesize high-quality views at arbitrary positions between sparse views, outperforming existing neural-radiance-fields-based (NeRF-based) methods. Finally, we conduct autostereoscopic display experiments, achieving satisfactory results.     

六轴工业机器人先验引导RRT*避障轨迹算法研究

针对六轴工业机器人装配避障路径运动问题,研究了机器人整体避障运动路径规划方法,提出一种RRT*改进算法;算法以RRT*算法为基础,在障碍物建模中引入包围盒算法,加入对机器人各轴与障碍物的碰撞检测;在路径规划中加入对随机点生成方向与树枝生长方向的先验引导机制,优化了算法路径长度与路径搜寻效率;通过Matlab进行了试验验证,结果表明与标准RRT*算法相比,先验引导RRT*算法缩短路径长度14%左右,且满足机器人末端路径与手臂各轴的避障需求。     

Understanding information systems continuance: The case of Internet-based learning technologies

Our research model expanded the Bhattacherjee's IS continuance model by adding a moderating effect (IS habit) to IS continuance intention and IS continued usage, postulating direct links between satisfaction and IS continued usage, as well as between prior behavior and IS continued usage. The model was tested with an Internet-based learning technology in a longitudinal setting. Data collected from 505 students were examined using partial least squares analysis. The results presented strong support for the theoretical links of IS continuance model, and for the new moderating effect. Both satisfaction and prior behavior were found to have significant impact on IS continuance. In addition, our findings confirmed the theoretical argument that the strength of intention to predict continuance was weakened by a high level of IS habit.     

UAV侦察图像自适应预处理仿真研究

研究无人机(Unmanned Aerial Vehicle,UAV)侦察目标识别中的图像增强问题。针对UAV侦察活动中因云雾干扰和由于成像距离较远而造成的图像不清晰这两个常见的原因,提出一种自适应的预处理算法。首先判断侦察图像上是否存在云雾,若不存在,则采用指示滤波器(Guided filter)对图像进行增强,可以细化图像的边缘,增强图像的对比度,并能增加可用于识别的特征点;若存在云雾,则采用基于暗通道优先的图像去雾技术,对于侦察获取的薄雾图像可以较清晰的还原出图像的无雾场景,而在浓雾条件下,可以清楚的分辨出图像中的道路、村庄等有意义的目标。仿真结果证明,通过自适应预处理算法后的图像清晰度有所增强,可满足识别需求。     

软件可靠性估计的经验贝叶斯扩展

首先讨论理论模型参数的物理意义，使之与具体软件开发及测试过程建立联系，并以此为依据建立参数的经验估计公式，从而得到参数的先验值。一方面这些参数是软件及软件开发过程的度量值，可用于对软件开发过程的控制、优化和管理；另一方面，有了先验值后，就可对理论模型进行经验贝叶斯扩展，以使人们的软件实践经验融入到理论模型中。     

Can the Prior Cathodic Polarisation Treatment Remove the Air-Formed Surface Film and Is It Necessary for the Potentiodynamic Polarisation Test?

This paper clarifies two issues related to the prior cathodic polarisation treatment(PCPT) for the potentiodynamic polarisation test: whether PCPT can(1) remove the air-formed surface film and(2) affect the polarisation test results. X-ray photoelectron spectroscopy analyses of fluoride ion-labelled samples show that PCPT cannot remove the surface film completely due to the low reaction rate. Potentiodynamic polarisation tests demonstrate that PCPT with proper operating parameters,-1.0 V SCE for 5 min with subsequent open circuit potential(OCP) stabilisation in this study, is necessary because it can improve the test reproducibility without affecting the corrosion parameters by unifying the initial surface state. However, PCPT with lower potentials, longer time or no OCP stabilisation has significant effects on the electrochemical corrosion parameters due to the hydrogen absorption under the conditions of this study.     

基于支持向量机的捷联惯组历次测试数据建模预测

针对捷联惯组历次测试数据的小样本建模问题,在对测试数据进行了插值和相空间重构的基础上,提出了通过支持向量机建立测试数据的回归模型,用来预测捷联惯组历次测试数据的变化趋势.实例分析证明该方法能够准确反映捷联惯组历次测试数据的变化规律,具有一定的实际应用价值.