特高压气体绝缘输电设备载流连接结构过热腐蚀特性

在特高压气体绝缘输电设备运行过程中,触指载流连接结构处容易因安装不当、载流不均而产生过热温度,加剧接触劣化,引发过热性故障。以气体绝缘设备中表带触指为研究对象,通过电热计算及红外温谱,确定触指过热范围,开展触指在SF_(6)、N_(2)、氮氧混合3种气氛下的过热腐蚀实验。利用扫描电镜、能谱分析对触指的接触形貌、腐蚀产物进行分析。结果表明,短时和长时大电流条件对接触电阻的影响相反。在铝电极组合和加速腐蚀48h内,3种气氛差异明显,纯氮气下接触电阻最低。在掺杂氧气、纯SF_(6)下接触电阻呈现波动、增长、稳定3个阶段,电阻最大值比氮气条件增长约14%。触指过热劣化机制主要为镀层高温剥落,基体暴露生成腐蚀产物。其表面氧、氟元素占比高,集中于触点。纯SF_(6)下触点及边缘腐蚀严重,铜银分界区存在明显的CuF、CuF_(2),与故障套管中触指表面形貌及产物较为相似,表明模拟实验的有效性。该研究可为气体绝缘输电设备中触指结构过热劣化分析提供依据。

基于流连接信息熵的DDoS攻击检测算法

分析了分布式拒绝服务(DDoS)攻击的特点,提出了流连接信息熵的定义,并通过对流连接信息熵时间序列的分析,采用非参数CUSUM算法进行DDoS攻击检测。该检测方法对固定IP、端口号随机变化的DDOS攻击有比较好的检测效果。实验结果证明,该方法能够以较高的精确度及时地检测出DDoS攻击行为。

电力设备载流连接板温升研究

针对电力设备载流故障与接触电阻、设备载流、外部环境温度及其结构尺寸之间的关系,研究建立了高压电气设备载流连接板温升故障的有限元计算方法,借助传热学理论,建立温升模型。并针对一起35 k V电流互感器载流连接板仿真发热故障进行了ANSYS计算分析,重点研究了载流连接板通过的电流大小、外部环境温度及连接板尺寸对其温度升高的影响。该分析结果可以用于对红外测温过程中电气设备电流型致热故障进行参考分析,并对实际设计中生产厂家选用高压电气设备一次电流连接板尺寸大小有一定的指导意义。

换流变阀侧套管表带触指接触电阻数值计算

换流变阀侧套管的载流连接结构由中心导杆、载流端子以及表带触指组成。为了研究单片表带触指接触电阻与其所受压力的关系,基于Greenwood和Williamson接触模型(G–W模型)推导出单片表带触指接触电阻与压力的关系式,引入表带触指受力偏转修正和接触区域表面轮廓修正,得到3种不同电极组合(紫铜–紫铜、紫铜镀银–紫铜镀银、铝合金镀银–铝合金镀银)下单片触指接触电阻与压力的关系。同时,开展试验验证触指的受力偏转现象,测量了不同电极组合下单片触指随压力变化的接触电阻。研究结果表明:接触电阻随压力增大而减小,当单片触指压力为5~9 N时,修正后计算值与试验值的相对误差在10%以内,验证了修正的准确性。该研究可为提高套管电连接可靠性提供参考。

FJoin:一种基于FPGA的流连接并行加速器

流连接广泛应用于提取多源流数据之间的关键信息,是大数据处理的重要支撑技术.但连接两条大数据流时大规模的连接谓词计算,使其易成为性能瓶颈.为提高处理性能,流连接系统常采用并行和分布式两种方式扩展.然而,采用多核并行的流连接系统的扩展性受到CPU核数限制,无法应对大规模数据流.采用分布式扩展的流连接系统由于引入分布式框架运行的开销,导致硬件处理效率严重下降.为实现高效大规模扩展,本文提出一种利用FPGA加速器外设向上扩展的流连接系统FJoin.加速器可进行高并行的流动连接,载入多个流元组后,连接窗口中的数据流经一次即可完成所有连接计算.对于逻辑容易在FPGA实现的连接谓词,通过大量基本连接单元串联构成深度连接流水线,实现大规模并行.通过主机CPU和FPGA设备协同进行连接控制,将连续的流连接计算划分为独立的小批量任务,高效地保证并行化流连接的完整性.在装备FPGA加速卡的平台实现了FJoin,基于大规模真实数据集的测试结果表明,对比部署在40个节点集群上的目前最好的分布式流连接系统,本文提出的流连接加速器FJoin可在单一FPGA加速卡上将连接计算速度提升16倍,达到5倍的系统吞吐,且时延满足实时流处理要求.

基于非参数CUSUM算法的DDoS攻击防御策略

分布式拒绝服务攻击(DDoS)具有突发性、攻击主机分布广等特点,对其防御尤显困难.从分析DDoS攻击原理及常见的防御策略入手,根据非参数CUSUM算法,给出了基于流连接密度时间序列分析的DDoS攻击防御策略及其模型,并进行了与理论值比较的实验取证.结果表明:该防御模型能够在很大程度上有效防御DDoS攻击.

检测DDos攻击的方法研究

DDos攻击已经严重影响网络的安全,文中对两种DDos检测方法进行了研究,包括基于流连接密度和流特征熵的方法。介绍了这两种方法的核心思想,给出了检测的过程,并分析了它们的应用范围。实验表明,这两种方法能够有效检测DDos攻击。

网络仿真环境下一种新的网络蠕虫检测方法

利用网络连接图刻画网络流的连接关系,提出了级联模体发现算法以挖掘网络蠕虫的连接模式;仿真实验表明,该方法无论是面对已知蠕虫还是新型蠕虫,都具有较高检测率和低误检率,能够较好地应用于网络蠕虫检测。

基于马尔科夫聚类的通信网络敏感信息监测

通信网络敏感信息自动监测是识别网络异常行为的关键所在。针对目前方法难以有效区分通信网络异常行为与正常行为之间关系的问题,提出了一种基于马尔科夫聚类的网络敏感信息自动监测方法。该方法首先基于网络流信息构建邻接矩阵,然后利用马尔科夫聚类。利用聚类前后簇数和核心结构节点数目的变化特征,自动监测通信网络的敏感信息。实验结果表明,该方法能够有效监测出通信网络的敏感信息,且具有较高的识别准确率。

对家电产品中灼热丝试验的几点探讨

本文通过对GB 4706.1中“支撑载流连接件的绝缘材料,以及这些连接件3 mm距离内的绝缘材料部件”这句话进行分析解读。结合IEC 60335-1:2020标准和两个具体案例,着重探讨了以下问题:标准意义的绝缘材料部件该如何判定?在何种情况下即要对部件进行灼热丝试验(GB/T 5169.11)又要对部件的材料进行灼热丝试验(GB/T 5169.12)?当“3 mm距离”内有多种绝缘材料时,该如何进行灼热丝试验?

Development of aluminum rheo-extrusion process using semi-solid slurry at low solid fraction

An aluminum extrusion process is mainly used to fabricate long tubes, beams and rods for various applications. However, this process has a high production cost due to the need for investment of high-pressure machinery. The objective of this work is to develop a new semi-solid extrusion process using semi-solid slurry at low solid fractions. A laboratory extrusion system was used to fabricate aluminum rods with the diameter of 12 ram. The semi-solid metal process used in this study was the gas induced semi-solid （GISS） technique. To study the feasibility of the GISS extrusion process, the effects of extrusion parameters such as plunger speed and solid fi-action on the extrudability, microstructure, and mechanical properties of extruded samples were investigated. The results show that the plunger speed and solid fraction of the semi-solid metal need to be carefully controlled to produce complete extruded parts.

Fluid-structure coupled analysis of underwater cylindrical shells

Underwater cylindrical shell structures have been found a wide of application in many engineering fields, such as the element of marine, oil platforms, etc. The coupled vibration analysis is a hot issue for these underwater structures. The vibration characteristics of underwater structures are influenced not only by hydrodynamic pressure but also by hydrostatic pressure corresponding to different water depths. In this study, an acoustic finite element method was used to evaluate the underwater structures. Taken the hydrostatic pressure into account in terms of initial stress stiffness, an acoustical fluid-structure coupled analysis of underwater cylindrical shells has been made to study the effect of hydrodynamic pressures on natural frequency and sound radiation. By comparing with the frequencies obtained by the acoustic finite element method and by the added mass method based on the Bessel function, the validity of present analysis was checked. Finally, test samples of the sound radiation of stiffened cylindrical shells were acquired by a harmonic acoustic analysis. The results showed that hydrostatic pressure plays an important role in determining a large submerged body motion, and the characteristics of sound radiation change with water depth. Furthermore, the analysis methods and the results are of significant reference value for studies of other complicated submarine structures.

Failure analysis of a kind of low power connector

A kind of low power connector used e.g. in household appliances was partly burned in routine experiment. The heat sources were four paralleled contacts constructed by springs (Sn/CuSn-alloy) in socket and a plug sheet (Ni/Steel) while mating. The contact interfaces were detected by scanning electronic microscope (SEM) and X-ray energy dispersive spectros- copy (XEDS), obvious wear tracks and various contaminants, including element Si, Al, Na, K, S, Cl, O, etc., were found. The contamination degrees on the four paralleled contacts were different, so that the ratio of average contact resistance on the four contacts was about 5:8:3:1. The maximum contact resistance on contacts of the plug sheet reached 28 ?. The main failure rea- sons were fretting and contamination between the contact interfaces. Fretting simulation showed that connection resistance of connectors was raised up, even to ohms level. When the current increased to 5 A, the socket housing was heated and decom- posed. By the thermal analysis, it was estimated that the connector would be burned under the lower current if the current was not evenly distributed on the four paralleled contacts caused by uneven contamination. Improvement methods for connector failure are also discussed.

Potential Connection between the Australian Summer Monsoon Circulation and Summer Precipitation over Central China

This study investigated the connection between the Australian summer monsoon(ASM) and summer precipitation over central China. It was found that,following a weaker-than-normal ASM, the East Asian summer monsoon and western North Pacific subtropical high tend to be stronger, yielding anomalous northward moisture to be transported from the western Pacific to central China. Besides, anomalous upwelling motion emerges over 30–37.5°N, along 110°E. Consequently,significant positive summer precipitation anomalies are located over central China. Further analysis indicated that the boreal winter sea surface temperature(SST) in the Indian Ocean and South China Sea shows positive anomalies in association with a weaker-than-normal ASM. The Indian Ocean warming in boreal winter could persist into the following summer because of its own long memory, emanating a baroclinic Kelvin wave into the Pacific that triggers suppressed convection and an anomalous anticyclone. Besides, the abnormal SST signal in the South China Sea develops eastward with time because of local air-sea interaction, causing summer SST warming in the western Pacific. The SST warming can further affect East Asian atmospheric circulation and precipitation through its impact on convection.

Interleukin-6, desmosome and tight junction protein expression levels in reflux esophagitis-affected mucosa

AIM： To investigate the correlation between the expression levels of interleukin （IL）-6 and proteins in tight junctions （TJs） in the esophageal mucosa of rats modeling different types of reflux esophagitis （RE）, and the ability of aluminum phosphate to protect against RE-induced mucosal damage via these proteins. METHODS： Male SPF Wistar rats aged 56 d were divided randomly into acid RE, alkaline RE, mixed RE, and control groups. Various surgical procedures were performed to establish rat models of acid RE. At 14 d after the procedure, some of the rats started aluminum phosphate treatment. Transmission electron microscopy （TEM） was used to observe the morphological features of TJs and desmosomes in the esophageal epithelium. Immunohistochemical methods and Western blotting were used to measure expression of claudin 1, occludin, ZO-1, JAM-l, DSG-1 and IL-6; reverse transcription polymerase chain reaction （RT- PCR） was used to measure expression of mRNA of claudin 1, occludin, ZO-1, JAM-1, DSG-1 and IL-6. RESULTS： At day 14 alter the procedures, an RE model was established in all subsequently sacrificed rats of groups A, B and C. By both gross and microscopic observation, the mucosa was damaged and thickened as the disease progressed. With TEM observation, a widened intercellular space was noticed, with significantly fewer desmosomes. Immunohistochemistry showed significantly higher levels of all proteins in all RE models compared to control rats at 3 d after operation （65.5% ± 25.6% vs 20.5% ± 2.1%, P 〈 0.05, respectively）. At 14 d after operation, along with continuing hyperplasia in the basal layer, the expression of TJ proteins in individual cells gradually decreased （12.4% ± 2.1% vs 20.5% ± 2.1%, P 〈 0.05, respectively）. Western blottings and RT-PCR showed a directly proportional increase in IL-6 levels in relation to TJ proteins, as compared to controls （0.878 ± 0.024 vs 0.205 ± 0.021 and 0.898±0.022 vs 0.205 ± 0.021, P 〈 0.05, respectively）. Upon treatment with aluminum phosphate, however, these protein levels were restored to normal gradually over 30-60 d in rats with acid RE （30.4% ± 2.1% vs 20.5% ± 2.1%, P 〉 0.05, treated vs untreated, respectively）. These levels increased in the rat with alkaline RE, and this increase was accompanied by continued hyperplasia in comparison with controls （85.5% ± 25.6% vs 20.5% ± 2.1%, P 〈 0.05, respectively）. Furthermore, the expression of TJ proteins was not correlated significantly with that of IL-6 in this group. CONCLUSION： These findings indicate that TJ proteins are highly expressed as an early molecular event involved in RE development, and that IL-6 is an inflammatory factor in this process,

A Parameter-Uniform Finite Difference Method for a Coupled System of Convection-Diffusion Two-Point Boundary Value Problems

A system of m (≥2) linear convection-diffusion two-point boundary value problems is examined,where the diffusion term in each equation is multiplied by a small parameterεand the equations are coupled through their convective and reactive terms via matrices B and A respectively.This system is in general singularly perturbed. Unlike the case of a single equation,it does not satisfy a conventional maximum princi- ple.Certain hypotheses are placed on the coupling matrices B and A that ensure exis- tence and uniqueness of a solution to the system and also permit boundary layers in the components of this solution at only one endpoint of the domain;these hypotheses can be regarded as a strong form of diagonal dominance of B.This solution is decomposed into a sum of regular and layer components.Bounds are established on these compo- nents and their derivatives to show explicitly their dependence on the small parameterε.Finally,numerical methods consisting of upwinding on piecewise-uniform Shishkin meshes are proved to yield numerical solutions that are essentially first-order conver- gent,uniformly inε,to the true solution in the discrete maximum norm.Numerical results on Shishkin meshes are presented to support these theoretical bounds.

Investigation on a vertical radial flow adsorber designed by a novel parallel connection method

Due to the increasing global demand for industrial gas, the development of large-scale cryogenic air separation systems has attracted considerable attention in recent years. Increasing the height of the adsorption bed in a vertical radial flow adsorber used in cryogenic air separation systems may efficiently increase the treatment capacity of the air in the adsorber. However, uniformity of the flow distribution of the air inside the adsorber would be deteriorated using the height-increasing method. In order to reduce the non-uniformity of the flow distribution caused by the excessive height of adsorption bed in a vertical radial flow adsorber, a novel parallel connection method is proposed in the present work. The experimental apparatus is designed and constructed; the Computational Fluid Dynamics(CFD) technique is used to develop a CFD-based model, which is used to analyze the flow distribution, the static pressure drop and the radial velocity in the newly designed adsorber. In addition, the geometric parameters of annular flow channels and the adsorption bed thickness of the upper unit in the parallelconnected vertical radial flow adsorber are optimized, so that the upper and lower adsorption units could be penetrated by air simultaneously. Comparisons are made between the height-increasing method and the parallel connection method with the same adsorber height. It is shown that using the parallel connection method could reduce the difference between the maximum and minimum radial static pressure drop by 86.2% and improve the uniformity by 80% compared with those of using the height-increasing method. The optimal thickness ratio of the upper and lower adsorption units is obtained as 0.966, in which case the upper and lower adsorption units could be penetrated by air simultaneously, so that the adsorbents in adsorption space could be used more efficiently.

Norton equivalent circuit for current control loop of grid-connected system

Modeling method for the current control loop of a grid-connected PWM inverter with the LCL output filter was discussed.Firstly,the current control loop with the LCL inverter-side current as feedback was established.Then,parameters of PI controller were calculated on the basis of an equivalent controlled object.Finally,Norton equivalent circuit for the current control loop of grid-connected system was derived by integrating one control equation,which connected the PWM inverter output voltage and the LCL inverter-side current,with two circuit equations,separately using the LCL inverter-side current and the injected current as loop currents.With the induced Norton equivalent circuit,system-level resonant and unstable issues on real grid-connected system applied in weak distributed power systems can be easily analyzed.The validity of substituting Norton equivalent circuit for grid-connected system is verified by simulation and experiment.

Side-stream smoking reduces intestinal inflammation and increases expression of tight junction proteins

AIM:To investigate the effect of side-stream smoking on gut microflora composition,intestinal inflammation and expression of tight junction proteins.METHODS:C57BL/6 mice were exposed to side-stream cigarette smoking for one hour daily over eight weeks.Cecal contents were collected for microbial composition analysis.Large intestine was collected for immunoblotting and quantitative reverse transcriptase polymerase chain reaction analyses of the inflammatory pathway and tight junction proteins.RESULTS:Side-stream smoking induced significant changes in the gut microbiota with increased mouse intestinal bacteria,Clostridium but decreased Fermicutes(Lactoccoci and Ruminococcus),Enterobacteriaceae family and Segmented filamentous baceteria compared to the control mice.Meanwhile,side-stream smoking inhibited the nuclear factor-κB pathway with reduced phosphorylation of p65 and IκBα,accompanied with unchanged mRNA expression of tumor necrosis factor-α or interleukin-6.The contents of tight junction proteins,claudin3 and ZO2 were up-regulated in the large intestine of mice exposed side-stream smoking.In addition,side-stream smoking increased c-Jun N-terminal kinase and p38 MAPK kinase signaling,while inhibiting AMPactivated protein kinase in the large intestine.CONCLUSION:Side-stream smoking altered gut microflora composition and reduced the inflammatory response,which was associated with increased expression of tight junction proteins.

Similarity based mixed transaction concurrency control protocol

Due to the various performance requirements and data access restrictions of different types of real-time transactions, concurrency control protocols which had been designed for the systems with single type of transactions are not sufficient for mixed real-time database systems (MRTDBS), where different types of real-time transactions coexist in the systems concurrently. In this paper, a new concurrency control protocol MRTT_CC for mixed real-time transactions is proposed. The new strategy integrates with different concurrency control protocols to meet the deadline requirements of different types of real-time transactions. The data similarity concept is also explored in the new protocol to reduce the blocking time of soft real-time transactions, which increases their chances to meet the deadlines. Simulation experiments show that the new protocol has gained good performance.