In-situ monitoring the setting behavior of foamed concrete using ultrasonic pulse velocity method

The applicability of ultrasonic pulse velocity （UPV） method to in-situ monitor setting and hardening process of foamed concrete （FC） was systematically investigated. The UPVs of various FC pastes were automatically and continuously measured by a specially designed ultrasonic monitoring apparatus （UMA）. Ultrasonic tests were performed on FC mixtures with different density （300, 500, 800 and 1 000 kg/m3）, and different fly ash contents （0%, 20%, 40% and 60%）. The influence of curing temperatures （20, 40, 60 and 80~C） was also studied. The experimental results show that three characteristic stages can be clearly identified during the setting process of an arbitrary FC paste： dormant stage, acceleration stage, and deceleration stage. Wet density, fly ash content, and curing temperature have great impact on setting behavior. A stepwise increase of the wet density results in shorter dormant stage and larger final UPV. Hydration reaction rate is obviously promoted with an increase in curing temperature. However, the addition fly ash retards the microstn,lcture formation. To aid in comparing with the ultrasonic results, the consistence spread test and Vicat needle test （VNT） were also conducted. A correlation between ultrasonic and VNT results was also established to evaluate the initial and final setting time of the FC mixtures. Finally, certain ranges of UPV with reasonable widths were suggested for the initial and final setting time, respectively.     

基于PIC单片机的焊接工艺参数设定与显示系统

数字化焊接系统需要数字化的过程参数输入/输出接口设备。以高性价比的PIC单片机为控制核心,通过单旋钮式旋转编码数字调节电路和数码动态显示方法,设计了一种多焊接参数的数字化分时设定与显示系统。试验结果表明,该系统外围硬件配置简单、抗干扰能力强、参数调节方便、可扩展性好,具有工程实用价值。     

半导体温控系统的自抗扰控制器设计

针对半导体温控系统大时间常数、时滞较大且易受参数扰动影响的问题,提出了自抗扰控制(ADRC)技术。针对自抗扰控制器待调节参数多、参数整定较为困难的问题,从fal函数特性及扩展状态观测器(ESO)设计出发,确定了自抗扰控制器的参数,并探讨了如何准确估计建模误差与外扰。仿真试验表明,系统在半导体致冷器件优值系数、冷热端温差发生变化及受到电压纹波干扰时均具有良好的鲁棒性能和动态性能。     

基于磁链与负载观测器的异步电机反步滑模控制

针对参数摄动及负载转矩未知且变化会影响异步电机速度控制的问题,设计了一种改进型指数趋近律的滑模转子磁链观测器,用于估算电机转子磁通值,同时将磁通观测值用于负载转矩的估计。引入磁链误差、转速误差,通过反步滑模控制算法,将转子磁通与负载转矩的观测值用于异步电机控制。在转子电阻摄动与负载转矩未知且变化的情况下,将该控制策略与自适应反步控制方法进行实验结果对比。实验结果表明,该控制策略的响应速度快且跟踪精度高,提高了异步电机速度控制系统的抗干扰性能。最后,提出一种转速软给定方法,实验表明该方法能有效抑制转速变化时刻定子电流与电磁转矩的急剧增加,进一步改善了电机系统的性能。     

基于5G通信的配电网区域保护应用及整定分析

5G网络为配电网各断路器保护装置之间的信息交互提供了通信平台。为解决配电网传统过流保护定值因整定失配造成的越级风险,文中提出一种基于5G通信的配电网区域保护方案,通过在成都配电网开展的实际应用,验证了该方案的可行性。首先,给出了配电网5G区域保护的架构;其次,分析了配电网5G区域保护的动作逻辑,该方案依据区域内断路器的过流及方向标志的组合信号进行故障定位;最后,给出了配电网5G区域保护的整定计算原则。     

同塔双回线接地距离保护应对事故过负荷的改进整定方法

对于同塔双回线的距离保护,目前有应对事故过负荷情况的2类通用整定方法:一类是躲过系统静稳极限运行下发生邻线断线故障时的过负荷入侵;另一类是躲过线路热稳极限运行下发生邻线跳闸故障时的过负荷入侵,这2类通用整定方法均存在不能相互覆盖彼此盲区的缺陷.为此,首先计算出上述2种事故过负荷情况下健全线路的测量阻抗的变化量,比较了其负荷入侵的严重程度,在此基础上提出了一种兼顾2种过负荷情况的过负荷入侵阻抗定值的改进整定方法,并基于PSCAD/EMTDC仿真测试对比了3类整定方法的优劣.算例分析结果表明,与已有的2类整定方法相比,所提改进方法能在保证事故过负荷不误动的情况下兼顾较强的抗过渡电阻能力,更具合理性.     

Work Setting and Burnout Among Professional Psychologists.

How does work setting relate to burnout among professional psychologists? Five hundred and seventy-one doctoral psychologists responded to a survey about professional activities, work environment, and burnout. Solo and group independent practitioners reported a greater sense of personal accomplishment than agency respondents. However, women experienced higher levels of emotional exhaustion in agency settings than in either solo or group independent practice, whereas men experienced higher exhaustion in group independent practice. Overall, greater emotional exhaustion was associated with less control over work activities, working more hours, spending more time on administrative tasks and paperwork, seeing more managed care clients and fewer direct pay clients, and having to deal with more negative client behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

变压器外部相间短路时继电保护配置方案研究

就变压器外部相间短路时变压器保护的配置方案进行了研究,认为必须通过继电保护整定计算分析,才能科学地确定保护配置方式,并列出了各种保护方式在工程实际中的一些简化整定计算方法。     

连续热镀锌生产线的张力控制

针对鞍钢新建的连续热镀锌生产线,论述了带钢张力的主要作用、张力的设定原则和设定方法以及连续生产线上张力控制方式,并且根据已有的生产经验,对该生产线的张力控制方式提出了改进意见.     

实用的发电厂继电保护定值计算及设备管理软件

结合目前发电厂的实际情况，提出了一种实用的发电厂继电保护定值计算和设备管理软件设计方案。该方案采用直接面向具体的继电保护装置进行整定的设计思想，按照保护装置的不同分别建立设备信息库。整定过程中减少人员参与，同时提供自定义保护整定模式，从而更好地贴近实际生产应用。