一种图像增强新方法

提出了一种四树复小波包变换域层内层间系数相关性图像增强新方法。该方法利用四树复小波包变换具有移不变性、良好方向选择性和对高频信号的细致分析能力,把含噪图像分解成低频逼近子图和若干高频方向子图;在保留低频逼近子图复系数不变的同时,充分利用变换域信号复系数层间相关性强和噪声复系数层间相关性弱的特点,采用非高斯双变量模型对每一个方向子图复系数进行降噪处理。同时考虑图像的弱边缘在变换域某些方向子图内复系数值较大,而在其他方向子带内其值较小的特点,甄别出弱边缘点对应的复系数并进行增强处理。实验结果表明,无论是PSNR指标,还是在视觉效果上,该方法的增强性能均好于传统的双树复小波变换去噪、四树复小波包变换去噪和小波域高斯尺度混合模型去噪,在有效抑制噪声的同时,具有很好的图像弱边缘增强和细节保护能力。     

核空间结合样本中心角度的大规模支持向量机

为了提高支持向量机在大规模数据集处理时的精度,提出了基于核空间和样本中心角度的支持向量机算法.在核特征空间下,求得原训练集的两类中心点和两个中心点的超法平面,并获取原训练集样本到超法平面距离和到两中心点中点的比值,用比值最小的n个样本点替代训练集.给出的数学模型显示,该算法不需要计算核空间,比现有的同类缩减策略保留了更多的支持向量数目.结合实例对算法进行了仿真实验,实验结果表明,与同类算法相比,该算法在基本没有降低训练速度的情况下获得了更准确的训练精度.     

基于时空注意力的社交网络信息级联预测模型

针对目前信息级联预测模型的构建多基于级联的时序信息或者空间拓扑结构、极少考虑两者的结合问题,该文提出一种面向社交网络的基于深度学习方法的信息级联预测(Information Cascade Prediction, ICP)模型。首先,使用拉普拉斯矩阵对级联节点采样,生成空间序列;然后,通过结合了图卷积网络的双向循环神经网络学习节点的时序信息和空间结构信息;最后,通过注意力机制对信息级联的时序信息和空间信息进行联合建模并在真实数据集上进行实验。实验结果表明: 与现有研究相比该文提出的ICP模型具有较高的预测精度,预测精度损失降低约为1%～8%,表明ICP模型是合理、有效的。     

A coupling dynamics and thermodynamics study of diesel pilot-ignition injection effect on hydrogen combustion of a linear engine

Linear hydrogen engine is a new type of energy conversion device to supports variable compression ratio operation for clean emission. However, the new hydrogen engine using conventional spark ignition shows slow combustion speed and low thermal efficiency. This study makes a preliminary assessment to discuss the application of diesel pilot-ignition technology in linear hydrogen engine aiming to accelerate combustion and improve efficiency. A new coupling model between dynamics and thermodynamics is proposed and then iteratively calculated to give insight the interrelationship of combustion and motion in a diesel pilot-ignited linear hydrogen engine, while the effect of injection position on the hydrogen engine combustion is also investigated to make clear the feasibility of combustion optimization. The results indicate that the linear hydrogen engine is speeded by properly advancing the injection to promote combustion, and it has a positive effect on in-cylinder gas temperature, pressure and pressure rise rate, unless the injection is too early which results in higher NO emissions and aggravate the working intensity of the engine. In addition, the closer the fuel injection is to the top dead center, the incomplete combustion of hydrogen and diesel in the cylinder, the decrease of engine fuel economy and the increase of soot emissions. There is an optimal thermal efficiency of 40.7% for the LHE when it operates in the 0.8 mm injection position condition.     

A comprehensive review of energy management optimization strategies for fuel cell passenger vehicle

With the gradual maturity of fuel cell vehicle technology, it gives a better opportunity for the application of passenger vehicles. In this paper, the energy management optimization strategies of fuel cell passenger vehicle (FCPV) are summarized for the first time. Initially, in this review, the topological configurations of FCPV are classified systematically. The optimization objectives, energy consumption and fuel cell life, are proposed for FCPV. Then the energy management strategies (EMSs) are illustrated and analysed based on the optimization objectives above. In terms of the complex and changeable characteristics of FCPV driving conditions, the latest FCPV EMSs which depend on driving information prediction technologies are discussed and summarized. The purpose of this paper is providing references for the development of new generation FCPV energy management optimization strategies.     

Dielectric and thermal properties of GFs/PTFE composites with hybrid fillers of Al2O3 and hBN for microwave substrate applications

The alumina/hexagonal boron nitride/glass fibers cloth/Polytetrafluoroethylene (Al₂O₃–hBN/GFs/PTFE) composites were prepared by blending-impregnation followed by hot compression method, and the dielectric, thermal properties of the composites with various hBN fillers content (0–20 wt.%) were investigated. The results show that the thermal conductivity of the composites increase significantly, while the coefficient of thermal expansion (CTE) decrease gradually, with the hBN content increasing. Composite substrates with 20 wt.% hBN exhibited high thermal conductivity as 1.05 W m^?1 K^?1, which is 5.3 times that of pure PTFE. Such compositions may be a promising material in high thermal conductivity copper clad laminate.

     

Systematic generation of manufacturing changes for safety-critical components

Every time a component’s design is changed, the corresponding manufacturing has to be changed as well. Due to several recent developments such as increasing market dynamics or ever-shorter product life cycles, the amount of component changes is rising sharply. Therefore, the number of manufacturing changes is increasing at a fast pace. Particularly for safety-critical components, the implementation of component changes within manufacturing poses a significant challenge. The reason for this is the high planning reliability required to implement a component change via a manufacturing change. This implementation has to be performed without endangering the component’s functionality, by causing any other change than the intended one. An approach for the systematic generation of manufacturing changes was developed as a contribution to increasing planning reliability and efficiency. The approach systematically enables technology planners to identify alternative manufacturing changes, to analyze the propagation of these changes, and to evaluate the alternatives to form a basis for decision-making. Its practical applicability is validated using a case study from medical technology.     

高频Buck变换器稳定运行的参数域分析

高频条件下的Buck变换器具有体积小、效率高等特点而备受关注,其同时更易因参数选择不当而带来严重的非线性行为影响系统稳定性。对高频条件下的Buck变换器的非线性行为进行了分析,研究了电压控制方式下的高频Buck变换器,从其状态方程出发,建立了该变换器在连续运行模式下的精确离散迭代映射模型。通过Jacobian矩阵判断系统稳定性随输入电压和电路中电感电容等不同参数变化规律,并确定系统的稳定运行区域。最后通过实验验证了理论分析的正确性。本结论不但能够为高频Buck变换器的稳定运行提供参考,也为系统参数的优化及控制性能的提升提供理论依据。     

Performance of surface chromizing layer on 316L stainless steel for proton exchange membrane fuel cell bipolar plates

Stainless steels as proton exchange membrane fuel cell bipolar plates have received extensive attention in recent years. The pack chromizing layer was fabricated on 316L stainless steel to improve the corrosion resistance and electrical conductivity. The corrosion properties were investigated in 0.5 M H₂SO₄ + 2 ppm HF solution at 70 °C purged with hydrogen gas and air. Higher electrochemical impedance and more stable passive film were obtained by chromizing the 316L stainless steel. Potentiodynamic polarization results showed the corrosion current densities were reduced to 0.264  μA cm⁻² and 0.222  μA cm⁻² in two simulated operating environments. In addition, the interfacial contact resistance was decreased to 1.4 mΩ⋅cm² under the compaction force of 140 N⋅cm⁻² and maintained at low values after potentiostatic polarization for 4 h. The excellent corrosion and conductive performances could be attributed to the chromium carbides and high alloying element content in chromizing layer.     

TGP-PCQA: Texture and geometry projection based quality assessment for colored point clouds

Colored point cloud (PC) will inevitably encounter distortion during its acquisition, processing, coding and transmission, which may affect the visual quality of the colored PC. Therefore, it is necessary to design an effective tool for colored PC quality assessment (PCQA). In this paper, considering the mapping relationship of perception between the colored PC and its corresponding projection images, we propose a novel PCQA method based on texture and geometry projection (denoted as TGP-PCQA). The main idea of the proposed TGP-PCQA method is to obtain texture and geometry projection maps from different perspectives for evaluating the colored PC. Specifically, 4D tensor decomposition is used to obtain the combination and difference information between the reference and distorted texture projection maps for mainly characterizing texture distortion of colored PC. Meanwhile, the edge features of the geometry projection map are calculated to measure the global or local geometry distortion. All of the extracted features are combined to predict an overall quality of colored PC. In addition, this paper establishes a multi-distorted colored PC database named CPCD2.0 with compression distortions and Gaussian noise, which orients to the influence of both geometry and texture components in distortion. Experimental results on two open subjective evaluation databases (IRPC and SJTU-PCQA) and the self-built CPCD2.0 database show that the proposed TGP-PCQA method outperforms the state-of-the-art PCQA methods. We are also providing the self-built CPCD2.0 database free of charge at https://github.com/cherry0415/CPCD2.0.