Droplet dynamics in a proton exchange membrane fuel cell flow field design with 3D geometry

Water management is crucial to achieve both high-performance and durability of proton exchange membrane fuel cell (PEMFC). Therefore, it is necessary to investigate the dynamic behavior of droplets in PEMFC channel for water management. In this paper, we explore the kinetics of droplets in a 3D flow field by experimental and theoretical analysis. More specifically, we examine the following four perspectives: 1) the movement and falling of droplets, and their force and deformation, 2) the superiority of 3D flow field drainage, 3) the pressure and viscous force under different scenarios including varying droplet sizes and velocities, and 4) the expression describing the shape change of droplets. The results show that the 3D flow field has a greater driving force on droplets and that their deformation affects the discharge of liquid water. Throughout the study, we provide better understanding of droplet dynamic in PEMFC gas channels. It enables to optimize the design and working conditions of these channels.     

新2级能效低噪音节能环保变压器的研发设计

随着电力变压器新版能效标准于2021年6月1日起正式实施,如何降低变压器的损耗成为各生产厂家面临的主要课题.研发中首次使用宝武钢铁公司生产的低损耗B20R065硅钢片,通过电磁计算、结构设计、工艺制造等一系列的保障措施,试制出SB20-M-2500/10.5新2级能效低噪音节能环保叠铁心变压器,并通过型式试验验证了技术方案的可行性.     

Activated PPARβ/δ Protects Pancreatic β Cells in Type 2 Diabetic Goto–Kakizaki Rats from Lipoapoptosis via GPR40

GW501516-activated peroxisome proliferator-activated receptor (PPAR) β/δ and G-protein-coupled receptor (GPR) 40 were shown to protect pancreatic β cells against lipoapoptosis. Therefore, this study aimed to investigate whether activated PPARβ/δ could protect type 2 diabetic rats from lipoapoptosis through regulation of GPR40 and to compare the protective effects of activated PPARβ/δ and PPARγ. We made an animal model of type 2 diabetic lipoapoptosis by feeding spontaneously type 2 diabetic Goto–Kakizaki (GK) rats with a high-fat diet (HFD) to evaluate the effects of PPARβ/δ on islet β cell apoptosis. And, treated INS-1 cells with 0.5 mM palmitate (PAM) in the absence/presence of GW501516 (a specific agonist of PPAR β/δ) and with/without transfection of GPR40 siRNA to explore the underlying molecular mechanism. HFD aggravated GK rats' poorer INSR30, lower mass, greater apoptosis of β cells, lower mass, and lower expression of GPR40, which were similarly improved by GW501516 at 3 or 6 mg/kg day and pioglitazone. Compared with pioglitazone, GW501516 caused more weight loss and had no effect on insulin resistance. GW501516 protected INS-1 cells from PAM-induced apoptosis by upregulating GPR40 and activating Akt/Bcl-2/caspase-3. Activated extracellular regulated protein kinases (ERK) was relevant to the lipoapoptosis in INS-1 cells, but was not involved in the antilipoapoptotic effect of GW501516. These results showed that the PPARβ/δ agonist GW501516 protected β cells from lipoapoptosis and improved β cell mass by upregulating GPR40 and activating the Akt/Bcl-2/caspase-3 pathway, but not the ERK-signaling pathway.     

Experimental and computational study on the separation performance of an electrostatic precipitator with curved transvers collecting plates

Aiming at the problems of low collection efficiency of fine particulate matter and large area occupied by existing electrostatic precipitators (ESP), a new type of horizontal electrode ESP is proposed. It has the advantages of accelerating turbulent coalescence, increasing the effective dust collecting area and increasing the particle driving speed. The performance of the new type of ESP is systematic studied through simulation and experiment at the same time, and the results matches well. By comparing the dust removal effect of the horizontal electrode ESP and the conventional ESP, it can be concluded that the horizontal electrode ESP has a better dust removal efficiency, and can still maintain a better dust removal effect under high air velocity. The dust removal efficiency of new ESP can reach above 98% under the experimental conditions.     

一种基于重叠网格的反应堆控制棒落棒行为分流域耦合仿真方法

本文提出了一种基于重叠网格的反应堆控制棒落棒行为分流域耦合仿真方法,该方法分别建立了控制棒单棒和驱动杆的二维轴对称重叠网格模型,保证控制棒和驱动杆的部件网格和背景网格能够根据落棒运动规律自适应地变化。两个流域在每个时间步长内交换流体阻力计算结果,并根据运动方程求解得到的速度来更新控制棒和驱动杆的运动状态,实现分流域耦合。本方法建模简单,通用性好,计算中考虑了驱动线流道形状的影响,且在计算时间和求解精度之间取得了良好的折中,此外,本方法在计算条件允许的情况下,还能较容易地扩展到三维模型。本文采用该方法对某反应堆控制棒驱动线的落棒行为进行了仿真,结果表明:计算结果可信。     

基于机器学习的用户实体行为分析技术在账号异常检测中的应用

伴随企业业务的不断扩增和电子化发展,企业自身数据和负载数据都开始暴增。然而,作为企业核心资产之一的内部数据,却面临着日益严峻的安全威胁。越来越多以周期长、频率低、隐蔽强为典型特征的非明显攻击绕过传统安全检测方法,对大量数据造成损毁。当前,用户实体行为分析(User and Entity Behavior Analytics,UEBA)系统正作为一种新兴的异常用户检测体系在逐步颠覆传统防御手段,开启网络安全保卫从“被动防御”到“主动出击”的新篇章。因此,将主要介绍UEBA在企业异常用户检测中的应用情况。首先,通过用户、实体、行为三要素的关联,整合可以反映用户行为基线的各类数据;其次,定义4类特征提取维度,有效提取几十种最能反映用户异常的基础特征;再次,将3种异常检测算法通过集成学习方法用于异常用户建模;最后,通过异常打分,定位异常风险最大的一批用户。在实践中,对排名前10的异常用户进行排查,证明安恒信息的UEBA落地方式在异常用户检测中极其高效。     

Robustness analysis and distributed control of a networked system with time-varying delays

This paper is concerned with the robustness analysis and distributed output feedback control of a networked system with uncertain time-varying communication delays. This system consists of a collection of linear time-invariant subsystems that are spatially interconnected via an arbitrary directed network. Using a dissipation inequality that incorporates dynamic hard IQCs (integral quadratic constraints) for the delay uncertainties, we derive some sufficient robustness conditions in the form of coupled linear matrix inequalities, in which the coupled parts reflect the interconnection structure of the system. We then provide a procedure to construct a distributed controller to ensure the robust stability of the closed-loop system and to achieve a prescribed $\ell_2$-gain performance. The effectiveness of the proposed approach is demonstrated by some numerical examples.     

轿车后轿横梁焊缝纵向开裂的原因分析

针对某轿车后梁焊缝纵向开裂情况，采用宏观观察、金相检验和扫描电镜分析等方法，对材质为CP-800高强钢，厚度为2 mm焊缝开裂原因进行了分析。扫描电镜发现裂纹起源于Cr的氧化物，以及其与Al、Si、Ca和Mn的复合氧化物处，且有疲劳辉纹形成，说明开裂是疲劳裂纹扩展到临界尺寸时在外载荷作用下发生快速扩展造成的。