Incidence and Factors Associated with the Switch to the Second Line Antiretroviral Treatment at the Ambulatory Treatment Center (CTA) in Dakar

Introduction: Over the past years, efforts have been made to expand access to antiretroviral combinations (cART) in low-income countries. However, major concerns are noted with drug resistance emergence, as treatment failure result and need to introduce a second line treatment, more expensive and difficult to implement. The objective was to study the incidence of switch to second line, reasons for switch and risk factors using a cohort of people living with HIV in an Ambulatory Treatment Center in Dakar. Methodology: This was a cohort study of people living with HIV under cART from January 2004 to December 2013. Naive patients monitored for at least six months, regardless of their profile and regimen with baseline CD4 counts Results: The median age of the 827 patients included was 44 [IQR = 18 - 78]. The switch to second-line treatment was observed in 72 patients (8.7%) after an average of 38.5 months of follow-up. The overall incidence rate of switch to second line of antiretroviral treatment was 1.59 per 100 persons-years. Most of changes in first-line treatment were motivated by virological failures (n = 60, 83.3%) under treatment with AZT/3TC/NVP (n = 25, 34.7%) or AZT/3TC/EFV21 (29.2%). 9.7% of switch occurred after immunological failure, 1.4% after clinical failure, 4.2% after severe toxicity and 1.4% was not documented. Predictive factors identifying failures at the end of the multivariate analysis were age Conclusions: In total, CTA identified a low incidence rate of treatment failure of the first line of treatment. Associated risk factors were age < 44 years, CD4 counts below 100 cells/mm3 and high viral load at treatment initiation.

Real-time Performance Evaluation of Line Topology Switched Ethernet

Recently,switched Ethernet has become an active area of research because of its wide uses in industry.However,its uses have various real-time constraints on data communications.This paper analyzes the performance of the line topology switched Ethernet as a data acquisition network.Network calculus theory,which has been successfully applied to assess the real-time performance of packet-switched networks,is used to analyze the networks.To properly describe the activity of switches,a novel approach of modeling data flows into or out of switches is addressed.Based on our model,a concisely analytical expression of the maximal end-to-end delay in line topology switched Ethernet is derived.Finally,the relative simulation results are demonstrated.These results agree well with the analytical results,and thus they validate the data flow modeling techniques.

Modeling Methods for the Main Switch of High Pulsed-Power Facilities Based on Transmission Line Code

Based on the transmission line code （TLCODE）, a circuit model is developed here for analyses of main switches in the high pulsed-power facilities. With the structure of the ZR main switch as an example, a circuit model topology of the switch is proposed, and in particular, calculation methods of the dynamic inductance and resistance of the switching arc are described. Moreover, a set of closed equations used for calculations of various node voltages are theoretically derived and numericMly discretized. Based on these discrete equations and the Matlab program, a simulation procedure is established for analyses of the ZR main switch. Voltages and currents at different key points are obtained, and comparisons are made with those of a PSpice L-C model. The comparison results show that these two models are perfectly in accord with each other with discrepancy less than 0.1%, which verifies the effectiveness of the TLCODE model to a certain extent.

Tests on the First 500 kV Compact Transmission Line in China

The paper deals with the tests on the first 500 kV compact transmission line. The transmission line stretches from Fangshan Substation to Changping Substation nearby Beijing with a length of 83 km. In order to investigate the characteristics of the transmission line, many tests were performed on the line before and after its operation. The results indicate that all electrical parameters are perfectly identical to the design.

Real-time State Monitoring During Switching Mode Transitions in High Power Three-level Inverters

大功率多电平逆变器近年来在实际工业生产中得到越来越广泛的应用。多电平逆变器由于结构复杂,采用元器件较多,因此在设计和实验中,实现各个工作状态下运行参数的同步监测和分析较为困难。本文针对大功率三电平逆变器,实现开关动态特性的在线测试,在此基础上,进一步研究三电平逆变器在开关状态变化时理论与实际负载运行工况下电路拓扑的转换变化规律。通过全电路电气参数和元器件状态的实时监测,发现在三电平逆变器非正常运行状态下开关转换时额外电应力,同时,深入研究在实际工况运行条件非正常状态下该额外电应力出现的机理和原因,为三电平逆变器的故障诊断提供了参考,对于设计高可靠性的多电平逆变器系统有一定的理论和现实意义。

TinySwitch-Ⅱ系列第二代微型单片开关电源的原理

TinySwitch-Ⅱ系列为国际上最新开发的第二代微型单片开关电源集成电路,它适合制作高效率、低成本、23W 以下的微型化开关电源,本文介绍其性能特点与工作原理。

Aspects of High Voltage Cable Sections in Modern Overhead Line Transmission Systems

Electrical power transmission is dominated by overhead line systems at present.This is mainly based on more than hundred years of experience of utilities in running overhead lines.Furthermore,overhead lines have proven their operational reliability and functional assurance.In the past,cables were used in distribution networks in urban areas for the most part with the exception of direct current submarine cables.New developments of high voltage XLPE cables make it possible to use this technology for EHV level applications in transmission networks.Within this paper,mixed network configurations,consisting of overhead lines and high voltage cables,are investigated.An exemplary EHV transmission line with a total length of about 100 km,which is quite typical for Central Europe,has been studied.Several different line combinations are discussed with varied rates between overhead line sections and cable sections length in practice.The length of the cable sections are ranging from several kilometers up to lengths of 100 km.In this paper the work focuses on the transient behavior of combined 400 kV overhead and cable lines during switching processes and lightning impacts.A number of calculations were carried out to get an overview of the transient stress in numerous network nodes along the transmission system.Numerical programs like ATP/EMTP have been used for these simulations.Peak values and wave shapes of the transient voltage stress have been evaluated,based on different systems and within possible combinations.In respect of the insulation coordination and transient stress at network nodes,the voltage-time trends are also analyzed.The combination of high voltage overhead and cable transmission systems,especially such with lengths of more than about 50 km,are making tightened and extended demands to the network design,to the operational management and of course to the network protection also.As an output of this investigations,the results might influence the strategy in running this new type of combined transmission systems.

A Novel Approach in RF-MEMS Switch Analysis Using Time Domain TLM Method

In this paper the transmission line matrix (TLM) method is exploited to evaluate the electromagnetic field distribution over a new radio frequency micro electromechanical system (RF-MEMS). A hybrid symmetrical condensed node is used to analyze S-parameters of the switch in on and off states. Furthermore, the effects of spring zigzag cuts over the bridge are analyzed. Results have authorized that TLM method offers a much faster and more reliable results compare to other numerical methods because of its time domain behavior and transmission line basis.

基于TinySwitch-Ⅲ开关电源外置保护电路设计

随着电力电子技术的发展,电力电子设备与人们的工作、生活关系日益密切,而任何电子设备都离不开可靠的电源。当今开关电源正向着集成化、智能化的方向发展,高度集成、功能强大的单片开关电源代表着当今开关电源发展的主流方向。Tiny Switch-Ⅲ芯片集成多种保护机制,如输入欠压,输出过压,热关断保护等,能够有效地使芯片在各种不同的环境下都能有很高的可靠性。但是此系列芯片没有输入过压保护。本论文首先介绍Tiny Switch-Ⅲ的内部结构和工作原理,然后介绍基于Tiny Switch-Ⅲ外置保护电路设计。

考虑柔性负荷整形的含源配电线路升级与开关配置综合优化

针对高比例分布式光伏接入造成配电线路重过载的问题,提出一种基于时序互补线路互联和柔性负荷整形的配电线路升级与开关配置综合优化方法。考虑柔性负荷功率调节意愿、线路负载率与功率反送约束,提出柔性负荷整形潜力和线路分段整形需求计算方法。以此为基础,建立了考虑柔性负荷整形的含源配电线路升级与开关配置综合优化双层模型。其中,上层模型以配电线路年规划成本最低、线路段净负荷功率和柔性资源均衡为目标进行线路选型和开关配置,下层模型以线路年运行成本最低为目标进行网络重构和负荷曲线整形,通过上、下层模型交互迭代获得互联线路改造优化方案。上、下层模型分别采用非支配排序遗传算法、二阶锥与大M法进行求解。算例仿真结果表明,所提方法可以提高互联线路资产利用率、规划方案的经济性和可靠性,对互联线路进行柔性负荷整形有利于突破线路负载率50%的限制。

A Novel Packet Switch Node Architecture for Contention Resolution in Synchronous Optical Packet Switched Networks

Packet contention is a key issue in optical packet switch (OPS) networks and finds a viable solution by including optical buffering techniques incorporating fiber delay lines (FDLs) in the switch architecture. The present paper proposes a novel switch architecture for packet contention resolution in synchronous OPS network employing the packet circulation in FDLs in a synchronized manner. A mathematical model for the proposed switch architecture is developed employing packet queuing control to estimate the blocking probability for the incoming traffic. The switch performance is analyzed with a suitable contention resolution al-gorithm through the computer simulation. The simulation results substantiate the proposed model for the switch architecture.

基于差模开关振荡的变频电机绕组相端绝缘状态特征提取与解耦

变频电机相端绝缘受脉冲宽度调制高频开关暂态过电压冲击易发生劣化。利用开关振荡谐振效应可望灵敏感知相端绝缘状态的微弱变化,但绝缘状态特征存在多因素高频耦合的问题。为此,该文提出一种基于差模开关振荡的相端绝缘状态特征提取与解耦方法。首先,通过分析变频电机系统开关振荡主导模态,选择高频差模开关振荡作为敏感模态,解耦逆变器功率器件分布电容的影响;然后,通过变分模态分解算法提取多模态开关振荡中的差模频率特征,解耦暂态运行工况下功率器件动态开关时间的影响。最后,利用逆变器侧和电机侧差模开关振荡电流幅值比特征,解耦电缆高频分布参数的影响。在380V/3kW永磁电机变频驱动系统中验证所提方法的有效性,结果表明,所提方法能够灵敏反映电机相端绝缘状态的微弱变化,可以有效解耦逆变器、电缆、运行工况等因素的影响。

考虑最少线路切换数量的电压稳定性增强优化方法

为提升电力系统的电压稳定性,提出一种基于输电线路切换的电压稳定性增强控制模型,该模型以最少的切换输电线路数量为目标来满足电力系统负荷裕度的提升需求。为灵活构建线路切换数学模型,提出基于支路追加法将线路切换融入原问题模型中。为降低模型求解难度,提出一种阶段式求解策略:基于负荷裕度对线路参数的灵敏度快速预筛选出可以提高系统负荷裕度的候选切换集,降低0-1整数变量的搜索范围;基于外逼近和松弛策略将原问题分解为2个子问题进行迭代求解,进一步提高模型的求解速度和精度。IEEE118节点和IEEE662节点系统仿真结果验证了所提模型与方法的有效性。

10kV线路带电断和接电缆引线消弧开关绝缘引流线电流异常情况分析

随着城市建设发展和电网建设发展的需要,10 kV配电网电缆与架空线路混合的情况越来越普遍,通过配电网不停电作业方式对架空线路和电缆线路实施不停电作业在技术上已经成为主流作业方式。带电断、接电缆引线的情况也比较常见,分析了作业中存在的问题和现象。

新线建设道岔联合整治前置法的分析与运用

道岔是铁路行车的主要设备,是实现改变列车运行方向的重要基础装备,其设备运用质量对后续的线路稳定运营至关重要。阐述新线建设过程中道岔工电联合整治流程的既有现状,分析并指出关键环节面临的实际问题,并提出相应的建议及针对性的解决措施,以降低对新线建设工程总体速度的影响,同时提升道岔设备施工质量,提高后续线路运营期间的设备运用质量,为铁路安全运输打下坚实基础。

关于取消新疆电网750 kV断路器合闸电阻可行性的仿真研究

目前,超、特高压输电线路常用合闸电阻吸收能量,并将其作为限制合闸过电压的主要手段,但是带有合闸电阻的断路器不仅造价昂贵,而且还存在运行可靠性差、故障率高等缺点,如果能利用低残压、保护性能优异的金属氧化物避雷器替代合闸电阻来限制操作过电压,不仅可以降低成本,还能简化断路器操纵机构以提高电力系统运行的可靠性。文中以新疆电网最长距离的750 kV线路为研究对象,通过沿线安装多组避雷器的方式,将沿线最大2%合闸过电压限制到规程规定的1.8 p.u.以内,为新疆电网所有750 kV长距离线路取消断路器合闸电阻的可行性提供了理论依据。

基于无功补偿技术的电气设备通信线路自动化切换

常规的电气设备通信线路自动化切换方法主要使用功能扩展板调整连接切换指令,易受操作单元参数设定的影响,导致通信线路切换成功率较低,因此文章提出一种基于无功补偿技术的电气设备通信线路自动化切换方法。利用无功补偿技术确定通信线路自动化切换的位置,设计电气设备通信线路自动化越区切换算法,从而完成电气设备通信线路的自动化切换。实验结果表明,文章设计的电气设备通信线路自动化切换方法在不同切换触发条件下的通信线路切换成功率较高,切换效果较好。

一种L~U波段RF MEMS单刀十掷开关的设计

论文提出了一种适用于1GHz~60GHz频段的RF MEMS单刀十掷开关。该开关采用三角形上电极结构,以减小悬臂梁等效弹性系数和闭合接触面积,达到低驱动电压、高隔离度的目的。通过渐进传输线结构,改善阶跃补偿引起的信号损耗问题。仿真结果显示:该单刀十掷开关的驱动电压为13V,在1GHz~60GHz频段范围内,输入端两侧输出端口的插入损耗<2dB,其余八个端口插入损耗≤0.59dB,所有端口隔离度均>30dB。此开关可适用于无线通信系统、雷达系统和仪器测量系统等对射频性能要求高的领域内。

适用于开关特性试验的端子灵活切换装置设计

开关特性试验接线复杂,往往需要多人配合调整接线端子,因其安全风险高、操作难度大、工作效率低,亟待优化和调整。研究设计一种适用于开关特性试验的端子灵活切换装置,针对开关分合闸试验中的测试内容及操作流程,设置合闸、第一组分闸、第二组分闸共六条控制电压输出线,通过内置刀闸快速切换二次回路,同时配合弹性形变自动收线,大大提高了测试效率,保障了操作安全,值得深入研究和拓展应用。