A spatiotemporal evolution model of a short-circuit arc to a secondary arc based on the improved charge simulation method

The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.

Optimization of short-circuit transition parameters of Q235B steel GMAW based on orthogonal gray relational analysis

In gas metal arc welding(GMAW)process,the short-circuit transition was the most typical transition observed in molten metal droplets.This paper used orthogonal tests to explore the coupling effect law of welding process parameters on the quality of weld forming under short-circuit transition,the design of 3 factors and 3 levels of a total of 9 groups of orthogonal tests,welding current,welding voltage,welding speed as input parameters:effective area ratio,humps,actual linear power density,aspect ratio,Vickers hardness as output paramet-ers(response targets).Using range analysis and trend charts,we can visually depict the relationship between input parameters and a single output parameter,ultimately determining the optimal process parameters that impact the single output index.Then combined with gray the-ory to transform the three response targets into a single gray relational grade(GRG)for analysis,the optimal combination of the weld mor-phology parameters as follows:welding current 100 A,welding voltage 25 V,welding speed 30 cm/min.Finally,validation experiments were conducted,and the results showed that the error between the gray relational grade and the predicted value was 2.74%.It was observed that the effective area ratio of the response target significantly improved,validating the reliability of the orthogonal gray relational method.

Partitioning Calculation Method of Short-Circuit Current for High Proportion DG Access to Distribution Network

Aiming at the problemthat the traditional short-circuit current calculationmethod is not applicable to Distributed Generation(DG)accessing the distribution network,the paper proposes a short-circuit current partitioning calculation method considering the degree of voltage drop at the grid-connected point of DG.Firstly,the output characteristics of DG in the process of low voltage ride through are analyzed,and the equivalent output model of DG in the fault state is obtained.Secondly,by studying the network voltage distribution law after fault in distribution networks under different DG penetration rates,the degree of voltage drop at the grid-connected point of DG is used as a partition index to partition the distribution network.Then,iterative computation is performed within each partition,and data are transferred between partitions through split nodes to realize the fast partition calculation of short-circuit current for high proportion DG access to distribution network,which solves the problems of long iteration time and large calculation error of traditional short-circuit current.Finally,a 62-node real distribution network model containing a high proportion of DG access is constructed onMATLAB/Simulink,and the simulation verifies the effectiveness of the short-circuit current partitioning calculation method proposed in the paper,and its calculation speed is improved by 48.35%compared with the global iteration method.

Stability analysis of CO_(2)gas shielded welding short-circuit transition process based on GMAW dynamic model

Base on the arc phase and short-circuit phase and their relationship, the paper considers the changes of the extension of wire, the arc length, liquid bridge resistance and mass of liquid bridge, combines the improved “mass-spring” model with the loop model of welding power system, puts forward the critical judgment condition of droplet transition, and establishes a more accurate dynamic model for describing the short-circuit transition process. The dynamic changes of short-circuit transfer frequency, welding current and voltage, contact droplet and residual droplet equivalent radius and droplet equivalent radius at different wire feeding speeds were calculated and analyzed, and compared with the experimental results. It shows that the fluctuation of droplet displacement, velocity and wire extension length at the optimal arc starting point is the smallest. The smaller the initial liquid bridge curvature radius is, the better the stability of short-circuit transfer is.

Evaluation of Protector 700 Wd in Controlling Tobacco Pests in Tanzania

In Tanzania, tobacco is an important cash crop benefiting most farmers and stakeholders. However, the crop is characterized by a low yield per unit area. Several factors are responsible for the low yield and quality of tobacco, among which are damages caused by the insects and other pests. Major insect pests of tobacco are cutworms (Agrotis spp), budworms (Heliothis virescens (F.)), (Lepidoptera Noctuidae) and aphids (Myzus persicae, Aphis tabaci) (Homoptera: Aphididae). These pests adversely affect crop growth, yield and leaf quality. In order to reduce insect attack in tobacco, applying pesticides is a critical management practices. In Tanzania, various pesticides have been approved for use in controlling the pests. Currently, farmers are using Bamethrine 2.5 EC to control the pests. The Pesticide named Protector 700 WG with an active ingredient imidacloprid 700 g/kg is a new product introduced in Tanzania during the 2021/22 crop season. Research trials were conducted in three research sites, namely Ulowa-Kahama, Tumbi-Tabora and Mtanila-Chunya, on Protector 700 WG efficacy in different rates, 15 g, 20 g, and 25 g each dissolved in 20 litres of water. The Protector 700 Wg was compared with the standard pesticide (Bamethrin 2.5 EC). Absolute control was also inclusive where the plot had no application of pesticides. The results showed that Protector 700 WG at all rates outweigh the commonly used pesticide. The difference in the number of pests between Protector 700 WG and Bamethrin 2.5 EC was significantly at P < 0.005 also, in dry and green weights, the yield was significantly different at P < 0.005. However, when yield and number of insects were compared among the rates of protector, there was no significant difference. From these results, farmers are advised applying Protector 700 WG at the rate of 0.15 kg/ha by dissolving it in 200 litres of water.

Research on Inter-turn Short-circuit Fault Diagnosis Method Based on High Frequency Voltage Residual for PMSM

Inter-turn fault is a serious stator winding short-circuit fault of permanent magnet synchronous machine(PMSM). Once it occurs, it produces a huge short-circuit current that poses a great risk to the safe operation of PMSM. Thus, an inter-turn short-circuit fault(ITSCF) diagnosis method based on high frequency(HF) voltage residual is proposed in this paper with proper HF signal injection. First, the analytical models of PMSM after the ITSCF are deduced. Based on the model, the voltage residual at low frequency(LF) and HF can be obtained. It is revealed that the HF voltage residual has a stronger ITSCF detection capability compared to the LF voltage residual. To obtain optimal fault signature, a 3-phase symmetrical HF voltage is injected into the machine drive system, and the HF voltage residuals are extracted. The fault indicator is defined as the standard deviation of the 3-phase HF voltage residuals. The effectiveness of the proposed ITSCF diagnosis method is verified by experiments on a triple 3-phase PMSM. It is worth noting that no extra hardware equipment is required to implement the proposed method.

基于拉格朗日功能平衡法的单轨吊失速保护器触发理论分析

通过假设分步法从机器人学的角度对单轨吊机车失速保护器触发装置进行运动学分析,并对点位进行了详细描述。采用拉格朗日功能平衡法对失速保护器触发机构中的滑动轴位移状况建立了完整的动力学数学模型,通过该模型可以描述在运动过程中的滑动轴位移与运行速度、各部件参数之间的关系。借助Adams软件构建虚拟样机模型进行动力学仿真分析,得出所需的速度-位移仿真结果图。分析结果表明,滑动轴的位移与运行速度有关,当运行速度到达所设定临界值2 m/s时,滑动轴能够伸出足够长度以满足失速保护工作要求,符合数学模型的预期计算。

19世纪中叶法国公使对巴黎外方西藏传教会进藏活动态度之嬗变

1848至1866年间,因进藏活动屡屡受阻,巴黎外方西藏传教会多次求助法国驻华公使,后者的态度由之前的“竭力”支持、“鼎力”相助逐渐转变为后来的“尽力”劝退,甚至可以说是“抛弃”。法国公使们对西藏传教会进藏活动态度之嬗变,一方面源于当时清朝中央同西藏地方两级政府通力协作坚决抵制法国传教士进藏;另一方面则是因为新形势下法国政府基于对华“合作”政策选择放弃其“保教”立场。清朝中央同西藏地方通力协作成功阻断西藏传教会进藏活动,既反映出当时西藏地方基于国家安全大局的深思熟虑,又反映出清朝中央对西藏地方的重视和体恤,同时彰显出中国中央政府一直以来严密的治藏方略及其不容西方擅入藏地、染指西藏的坚定外交立场。

防雷插座电压保护水平试验方法解析

本文解析了防雷插座电压保护水平的试验方法。首先,介绍了用于测试防雷插座电压保护水平两个常用标准IEC61643-11和UL1449的不同要求。其次,基于IEC61643-11和UL1449标准对防雷插座电压保护水平进行试验及分析。最后,总结了两种测试方法的优缺点,并指出在实际应用中应根据具体需求选择适合的测试方法,以确保防雷插座的性能和质量。

Duraphat与Fluor Protector抑制固定正畸矫治中牙釉质脱矿的比较研究

目的使用激光龋齿探测仪,比较两种含氟物Duraphat与Fluor Protector抑制固定正畸矫治中牙釉质脱矿的临床效果。方法选取接受直丝弓固定矫治的12~18岁青少年患者60例,采用自身对照法,试验组A右上前牙及前磨牙涂布Fluor Protector,试验组B左下前牙及前磨牙涂布Duraphat,对照组A左上前牙及前磨牙不使用任何药物,对照组B右下前牙及前磨牙仅涂布0.9%的氯化钠水溶液。分别于患者粘接正畸托槽前、粘接托槽后1个月、3个月使用激光龋齿检测仪测试受试牙牙面并记录荧光值(DD),应用单因素方差分析比较各组数值是否有统计学差异。结果①正畸托槽粘接后1个月、3个月时,2组涂布氟漆试验组的DD值均低于2组未涂布氟漆的对照组(P<0.05),说明Duraphat与Fluor Protector两种氟漆均显示了明显抑制釉质脱矿的能力。②正畸托槽粘接后1个月、3个月时,涂布Flour Protector的试验组A与涂布Duraphat的试验组B的DD值间比较差异无统计学意义(P>0.05),说明两种不同浓度的氟保护漆在抑制牙釉质脱矿的能力方面没有明显优劣。结论①接受固定矫治的患者存在釉质脱矿的易感性。②Duraphat与Fluor Protector两种不同浓度的氟化物对正畸过程中牙釉质的脱矿均有抑制作用,二者抑制脱矿的能力没有明显差异。③DIAGNOdent激光龋齿检测仪适合临床探查釉质的脱矿及龋损,对釉质表面的改变感应相当敏锐,帮助医师对龋病做出早期诊断,及早监控并采取合适的措施。

有源降噪入耳式耳机声衰减实验测量及对比研究

针对有源降噪入耳式耳机声衰减测量,对比研究了4种典型的测量方法,包括真耳听阈衰减法(REAT)、等响法(LB)、真耳内置传声器法(MIRE)和专用声学测试装置法(ATF)。依据该类耳机的特点设计了测量装置、实验环境和实验方案,开展了3款耳机的测量研究。结果表明,对于无源声衰减测量, MIRE方法与作为护听器“黄金”标准的REAT方法相比,中高频差异在±3 dB范围内,而MIRE方法在低频更准确;对于有源声衰减测量, MIRE方法与LB方法的结果接近,差异在±2 dB范围内,且MIRE方法更易于操作。MIRE方法有较高的测试效率和准确性,是测量有源降噪入耳式耳机声衰减的一种有效方法。

A Novel Multi-Functional Leakage Current Protector IC Design

A novel type of leakage current protector chip,implemented in the mixed-signal 0.6μm CMOS process,is presented. This chip has the advantages of low power dissipation （10mW）, accurate protection control based on digital response delay time and integration of multi-functions such as leakage current/over-voltage/over-load detection and protection,auto switch-on and so forth. Additionally, the chip is programmable to suit different three-level protection applications with a high anti-interference ability.

基于AHP-熵值法的板式定制家具护角设计评价

针对板式定制家具包装内护角进行需求分析,并在此基础上,采用层次分析法(AHP法)及熵值法建立板式定制家具护角设计评价指标体系。确定了护角设计评价指标的综合权重,利用模糊综合评价法建立板式定制家具护角设计评价模型,并对3种典型板式定制家具护角进行了实例研究,实现了护角设计的定量评价。其中的模型与方法对优化板式定制家具护角设计及护角方案决策具有较大的参考价值。

Thermal runaway evolution of a 280 Ah lithium-ion battery with LiFePO_(4) as the cathode for different heat transfer modes constructed by mechanical abuse

Lithium iron phosphate batteries have been increasingly utilized in recent years because their higher safety performance can improve the increasing trend of recurring thermal runaway accidents.However,the safety performance and mechanism of high-capacity lithium iron phosphate batteries under internal short-circuit challenges remain to be explored.This work analyzes the thermal runaway evolution of high-capacity LiFePO_(4) batteries under different internal heat transfer modes,which are controlled by different penetration modes.Two penetration cases involving complete penetration and incomplete penetration were detected during the test,and two modes were performed incorporating nails that either remained or were removed after penetration to comprehensively reveal the thermal runaway mechanism.A theoretical model of microcircuits and internal heat conduction is also established.The results indicated three thermal runaway evolution processes for high-capacity batteries,which corresponded to the experimental results of thermal equilibrium,single thermal runaway,and two thermal runaway events.The difference in heat distribution in the three phenomena is determined based on the microstructure and material structure near the pinhole.By controlling the heat dissipation conditions,the time interval between two thermal runaway events can be delayed from 558 to 1417 s,accompanied by a decrease in the concentration of in-situ gas production during the second thermal runaway event.

基于轻量化YOLOv7的井下高压场景安全识别研究

为了使杨柳煤矿安全监测平台精准快速地识别机电人员高压作业场景中存在的不安全行为,以井下中央变电所为例,聚焦绝缘护具佩戴情况设计安全识别框架。基于YOLOv7目标检测算法引用部分卷积(PConv),提高模型在处理遮挡或缺失画面的鲁棒性和泛化能力;融合快速神经网络结构(FasterNet),降低计算冗余优化检测性能;最后融合时间空间注意力模块(CBAM),提高算法的特征提取能力。实验结果表明:轻量化处理后较原模型体积缩小30.5%,计算量减少23.7%,识别平均精度可达97.3%,单张图片检测速度提升38.1%。在复杂背景下小目标检测任务中有效地解决了漏检问题。

大豆预处理车间刮板输送机断链保护器的应用

为及时监测大豆预处理车间刮板输送机在生产中出现的断链、脱链等故障问题,保障刮板输送机的设备安全,分析了刮板输送机断链、脱链的故障原因,并提出了将刮板断链保护器应用于刮板输送机中。刮板断链保护器由速度传感器与信号处理器组成,当刮板输送机出现断链、脱链故障时,速度传感器所传输的脉冲信号频率会下降,信号处理器通过检测脉冲信号频率快速有效地作出反应,快速停机并发出声光报警,保障设备和生产安全。断链保护器结构简单,安装方便,并且不影响刮板输送机的正常运行,适合应用于一些传统企业中。

慢性心力衰竭急性加重患者血清保护素D1的表达及其与预后的关系研究

目的:分析慢性心力衰竭急性加重患者血清保护素D1的表达情况,及其与患者预后的关系。方法:连续纳入我院2018年3月至2021年12月收治的476例慢性心力衰竭患者,并根据是否急性加重将患者分为非急性加重组(n=322)和急性加重组(n=154)。收集所有患者的临床资料,测量两组患者血清保护素D1的含量,并分析保护素D1的含量对慢性心力衰竭急性加重患者预后的评估作用。结果:与非急性加重组患者比较,急性加重组患者血清保护素D1的含量显著降低[(488.6±172.9)vs.(146.3±71.8)μg/L,P<0.05];保护素D1低表达组患者的年龄、NYHA分级、FBG、NT-proBNP、全因死亡和复合事件发生率,均显著高于保护素D1高表达组(P<0.05),而LVEF明显低于保护素D1高表达组(P<0.05);Kaplan-Meier分析显示,保护素D1低表达组患者全因死亡和复合终点事件的发生率明显高于保护素D1高表达组(P<0.05);Cox回归分析显示,血清保护素D1含量、NYHA分级、NT-proBNP和LVEF是慢性心力衰竭急性加重患者发生复合终点事件的危险因素(P<0.05);ROC曲线结果表明,血清保护素D1含量对慢性心力衰竭急性加重患者复合终点事件具有预测价值(曲线下面积为0.882,P<0.05)。结论:慢性心力衰竭急性加重患者血清保护素D1的含量显著降低,且保护素D1的含量与慢性心力衰竭急性加重患者的预后有关。

马来亚华人族群对华民护卫司署的因应探析(1877-1934)

论文梳理了马来亚华民护卫司署的设立过程与主要职能,分析探讨了马来亚各阶层华人对设置华民护卫司署的不同态度。19世纪60年代起,英国对马来亚的殖民统治从间接治理转向直接治理,华人族群作为移入型群体却在诸多地方占据较大比例乃至第一大族群的事实,促使英国在马来亚设置治理华人族群的专门机构——华民护卫司署,规定凡涉及华人事务均归其负责。面对这一新设机构华人族群反应各异,以绅商阶层为代表的华人领导层通常配合华民护卫司署,并以多种形式表达对护卫司署的支持与感谢;大部分底层华人如妇女、劳工等,对华民护卫司署则经历从疑虑到认可的转变;少数个人利益受到冲击的华人,以及政治上不认同华民护卫司署的政治活动者等华人群体,抵制或激烈对抗华民护卫司署。华人社会在被纳入英国直接殖民治理体系时的复杂心态,反映了马来亚华人族群在地化进程的曲折与分歧。

一种C波段雷达接收机防护技术研究

随着战场环境日益复杂,尤其是高对抗环境下,对现有各类装备均产生了极大威胁。设计了一款C波段雷达接收机保护器,采用充气微波开关管+波导同轴转换的结构设计,创新性地提出将固态限幅器芯片融合在波导同轴转换内部,限幅芯片采用级联的形式,提高了微带限幅器的承受功率。实现接收机保护器耐受功率10 MW以上,响应时间5 ns以内,不仅可用于雷达发射期间接收机防护,还可应对外部电磁干扰、高功率微波攻击。