The adaptive boundary approach for exposure assessment in a broadband EMF monitoring

The boundary approach for the assessment of daily exposure to electromagnetic fields (EMF) has been recently proposed for the continuous and broadband EMF monitoring of the Serbian Electromagnetic Field Monitoring Network – SEMONT. This approach is based on the determination of the daily upper and lower exposure boundaries, combining data of the continuous in situ EMF monitoring in a broadband frequency range and the minimal and maximal prescribed reference levels. The real exposure is positioned between these boundaries. In this paper, the enhancement of the boundary approach is presented. By adjusting the existing boundaries and reducing the difference between them, the precision of the daily exposure assessment in the SEMONT system has been improved. The frequency selective measurement has been used to determine the frequencies on which EMF sources radiate over a particular area and in situ location. Consequently, the new minimal and maximal reference levels can be selected; these are suitable for a particular in situ location and should be used for the calculation of exposure boundaries on that location. A simple in situ test measurement of the high-frequency electric field strength was performed, in order to verify the proposed adaptive boundary approach. The analysis shows that this approach attained reduction in boundaries difference of 36.25%, regarding the Serbian legislation, resulting with the increased precision of the daily exposure assessment for the broadband EMF monitoring.     

煤炭称重销售系统中射频卡的应用与研究

以煤炭称重销售系统中的射频卡开发与应用为基础,探讨煤炭称重销售系统中射频卡的应用原理、射频卡的选用、读写、防冲撞、初始化以及中文字符存储、内容读写及编程的实现方法。     

Experimental investigation on workers’ exposure to electromagnetic fields in proximity of magnetic resonance imaging systems

The paper presents the results of an experimental activity focused on the measurement of electromagnetic fields generated by magnetic resonance imaging systems, carried out with the purpose of assessing exposure of workers to static, low frequency and radio-frequency electromagnetic fields , as required by the EU Directive 2004/40/EC. The main contribution of the paper is that it presents a comparative study of exposure carried out during operation of the MRI system and close to the sources, with different scanning sequences and RF coils. Results show that the static magnetic field follows the theoretical values only close to the magnet due to the effect of the walls, with a few percent variation due to the operating conditions; exposure to the magnetic field in the low frequency band is mainly determined by emissions generated by the power grid at 50 Hz and by the pulses driving the gradient coils; and finally the radio-frequency band only shows contributions by the diagnostic pulses at the resonance frequency, with exposure levels usually below the limits contained in the Directive.     

射频导纳技术在蒸发器液位测量中的应用

针对海水淡化蒸发器运行工况复杂、结构设计紧凑、液位测量范围小、常规差压法安装困难等问题,提出了一种利用射频导纳技术测量蒸发器液位的方法。重点对射频导纳液位计的工作原理、主要特点、电极选型、安装注意事项以及标定方法进行了阐述和探讨,并在30t/d LT-MED中试装置中成功应用。结果表明:该仪表安装简单、测量准确、维护方便且适用范围较广,具有很好的应用前景。     

井温测试中由时间响应常数引起的深度误差

井温测井资料在石油开发中的应用日渐广泛，根据我国目前测井设备的情况，本文讨论了测井速度和时间响应常数在井温测试时对深度数据的影响，分析了由时间响应常数所造成的深度误差，提出了深度误差不容忽视的见解。     

射频识别技术在离散生产车间中的应用综述

回顾和总结了近年来射频识别技术(RFID)在离散生产车间中的应用。首先简要分析了离散生产车间应用RFID的主要需求;然后总结了RFID在物料跟踪、质量控制与质量追溯、设备资产管理、在制品管理、生产过程控制与调度等方面的具体应用模式及其案例;最后讨论了当前应用RFID的主要障碍,以及离散生产车间应用过程中需要解决的若干关键科学和技术问题。     

振镜二维扫描的图形畸变校正和曝光量补偿

主要讨论了物镜前振镜二维扫描光学系统中图形畸变的产生原因,分析比较了图形畸变与振镜布放、像面坐标系方位及fθ特性误差等的关系,并结合视场大小为75×75的实际物镜fθ特性误差的最小二乘拟合,给出了校正图形畸变的准确关系式.另外,在矢量扫描方式中光斑移动速度的非线性会导致扫描图形各部分曝光不均匀,文中也给出了对扫描图形曝光量加以补偿的方法和公式.     

Time and frequency characterization of radiated disturbance in telecommunication bands due to pantograph arcing

Radiated emissions from arcing between pantograph and overhead wire in electrical transportation systems extend up to the frequency bands currently used for telecommunications and may therefore affect quality of telecommunication systems. The paper investigates on the time and frequency characteristics of the disturbances. Transient amplitude, rise time and pulse duration were measured in the time domain to obtain the associated empirical distributions; the power spectrum and the frequency content were calculated in the bands of interest; finally a time–frequency representation has been used to observe the evolution of the power spectrum over time and determine the location of the main contributions. Measurement of the channel power has also been carried out to investigate on the relevance of the disturbance power for some bands of interest for telecommunication services.     

射频技术在电子秤上的研究应用

本文就射频技术在电子秤上的应用进行研究与探讨。     

基于CPLD与51单片机的数字频率计的设计与应用

分析了数字式频率计测量的原理,在需求分析的基础上设计了频率计的硬件电路。用C语言及Verilog HDL硬件设计语言分别编制了单片机及CPLD上的人机交互、测量运算、数据处理等各个功能模块,实现了数字式频率测量的功能。实际应用表明,该数字频率计达到了预期的目标,能满足应用的要求。     

冷镱原子光钟绝对频率测量及相关跃迁研究的进展

光学原子钟的稳定度和不确定度都已全面进入小数 10 -18 量级,是目前最精密的时间频率测量工具之一。 光学原子钟 已在精密测量和基础物理研究等尖端科研领域展现出潜力,并有望重新定义时间单位“秒”。 镱原子光钟因其独特的能级优势 而成为了目前世界上发展最成熟、研究最广泛的光钟之一。 镱原子钟跃迁的绝对频率测量和镱原子相关跃迁光谱的精密测量 具有重要意义。 综述了冷镱原子光钟的钟跃迁 6s 21 S0 -6s6p 3 P0 能级绝对频率测量的国内外进展,并介绍以 7. 3×10 -16 的不确定 度测量镱原子钟跃迁绝对频率的实验,测量值为 518 295 836 590 863. 30±0. 38 Hz。 综述了利用已完成绝对频率测量的镱原子 光钟为基准,对镱原子的 649,770 和 1 389 nm 抽运光的对应跃迁绝对频率进行精密测量的结果。     

外差干涉仪光路调节方法及对拍频的理解

外差激光干涉仪由于测量精度高,环境适应能力强和实时动态高速测量等特点而广泛应用于机床误差的实时监测中。外差激光干涉仪中,使用平面镜作为转向装置时,接收器上的两束光有可能只是相交而不是重合,这给光路的调节增加了很大的难度。针对这一问题,提出一种辅助光路调节方法,先将光路切换到单频干涉仪,调好光路,再切换到外差干涉仪,利用单频干涉条纹的直观性能可看出外差干涉仪光路调节的好坏。理论分析和实验结果表明,提出的调节方案具有可行性,效果良好,同时通过从单频切换到双频能更深入地理解拍频。     

A few remarks about assessment methods of electric power quality on ships – Present state and further development

This paper concerns the problem of reliable assessment of a power quality in naval networks. Two aspects of the problem were discussed. Firstly, the parameters for electric power quality assessment and their permissible levels were presented. Further, the methods of their measurement were analyzed. Especially the critical analysis of relevant IEC standards was presented and proposals for their amendment were laid. These considerations were based on the results of the original author’s research carried out in ship electrical power systems for a few years. Finally, the original and complete methods of signal processing and basic features of newly constructed instrumentation for power quality assessment were shown. Presented paper is a continuation and in some respect the synthesis of the earlier works prepared by the same author completed by new contribution.     

专业课教师讲授通识课存在的问题及改进策略——以《〈圣经〉文学选读》为例

专业课教师讲授通识课既存在教育理念方面的问题,也存在教学策略方面的问题。在教育理念方面,专业课教师往往用自己所熟悉的文化素质课、公共必修课、公共选修课的概念来理解通识课程,简单地将通识课理解为专业知识的普及课,没有在通识教育理念的指导下研究学生、教学目的、教学内容、教学形式和教学方法。在教学策略方面,大班上课,难以实行因材施教;以讲授法为主,难以激发学生的积极性、主动性和创造性;过分依赖多媒体,难以在课堂上开发新的课程内容;教学评价手段单一,难以实现教学评价的激励和调节功能。改变现状首先要改变文化素质教育的观点,树立起通识教育的理念,正确处理好通识课与专业课的关系。作为一种大学教育的理念,通识教育旨在通过对自由学术的探讨,培养理性完善、情感优美、行为优雅的＂完整的人＂,中国古代的＂大学之道＂就是一种通识教育的理念。其次要改进教学策略,选择经典名著作为教学内容;采用灵活多样的教学组织形式;更多地采用共同解决问题型的教学方法。     

镜面物体三维测量系统中两显示屏的平行正对校正

针对镜面物体三维测量系统中两显示屏无法精确平行正对的问题,提出了一种在镜面物体三维测量系统中通过软件产生变形条纹等效两显示屏精确平行正对的方法。该方法首先采用机器视觉技术标定两显示屏的外参。然后基于所标定的外参,利用软件编程产生等效两显示屏平行正对的变形条纹,变形条纹通过半透半反镜后所成的像在相机坐标系内呈现前后精确平行正对的关系。最后,利用对应两个显示屏上的变形条纹计算相应位置相位的差值,并通过均方根误差定量评定所提出的方法。实验结果表明,所提出的方法能将水平方向的均方根误差缩减为原来的24.21%,竖直方向的均方根误差缩减为原来的8.15%,从而提高三维测量系统的精度。     

高精度标准源中低频信号源的设计与分析

针对直接数字合成的高精度信号源在低频段容易产生杂波干扰,难以适应我国公共电网频率的问题,采用锁相合成频率技术来产生范围在40 Hz~65 Hz、分辨率为0.01 Hz的低频信号作为高分辨率信号源合成的时钟频率。采用数模转换器外接基准可调电压技术产生了调节细度优于满量程的0.000 1%的可调幅值;同时利用相位计数器区分相位,设计出了频率、幅值、相位都可调的正弦波信号;建立了信号源失真度与数模转换器位数的关系和取样点数的关系,找到了影响信号源输出稳定性的原因;在理论分析和实践的基础上提出了减小信号源失真度的方法。研究结果表明,该低频信号源可以在误差接受范围内减小差频影响和公共阻抗的影响,输出40 Hz~65 Hz频率范围内标准正弦波信号的失真度小于0.03%。     

Experimental characterization of low-frequency noise in power MOSFETs for defectiveness modelling and technology assessment

In this work we analyse the applicability of low-frequency (LF) noise measurement in order to study the defectiveness in the gate oxide of power MOSFETs (Metal–Oxide–Semiconductor Field-Effect Transistors). To this purpose, we implement a low-noise experimental set-up, which is able to measure, in particular, the flicker (“1/f”) contribution to the drain noise current of the device under test, with high accuracy in terms of noise floor and the adequate bias system flexibility required by the application. First, we show how these measurements can be used to empirically detect the physical model and related compact expressions, which best describe the source of 1/f-like fluctuations in this type of devices. Then, according to the selected physical model, the defect density in the gate oxide is extracted. In order to validate the proposed methodology, experimental data are reported and discussed in the case of power U-MOSFETs.