10 Gbit/s伪随机序列光纤通信系统PMD补偿

光纤通信线路检测到的电功率随差分群延迟变化,可作为PMD补偿的反馈控制信号。给出了这一变化关系的理论计算和曲线并通过实验验证这一关系,确定电压信号与DGD的变化关系。建立了一套完整的实验系统,并考虑了影响反馈电压信号的多种因素以及减小这些影响的措施。通过眼图给出的实验结果说明了补偿的效果,还通过误码测试仪测量了补偿前后的接收灵敏度的改变以定量说明补偿的效果,最后比较了不同情况下的补偿结果。     

空气中微细电火花沉积铜合金工艺方法

提出了一种在空气中将工具电极丝黄铜材料沉积到工件上的新工艺方法。实现该方法的基本条件为:(1)工具电极接脉冲电源正极;(2)在空气中放电;(3)窄脉宽配合宽脉间。通过大量实验对微细电火花沉积加工的工艺规律进行了系统深入的研究,得出各主要工艺参数对沉积工艺效果的影响规律。最终以黄铜电极丝为工具电极,在高速钢工件表面上沉积出直径为0.19 mm、高度为7.35 mm的微小圆柱体。利用SEM、能谱分析和X射线衍射及显微硬度测试等方法对沉积物进行分析,得出该沉积物的组织结构、化学成分和硬度等方面的基本性质,为进一步研究三维沉积加工奠定了基础。     

典型电离层多普勒记录及其讨论

由于地面电离层多普勒频率偏移测量具有时间连续、设备相对简便等固有特征，它特别适合于扰监测。本文在整理北京大学电离层高频多普勒台站观测资料的基础上，给出了一些典型电离层多普勒效应观测现象，这些现象反映了多普勒的细致分析对电离层形态学研究有其特殊意义。利用IRI模型，对多普勒频移的太阳耀斑效应及电离层不规则结构对多普勒频移的影响进行了模拟计算，理论结果与观测基本一致，从而大体上解释了这些响应的物理机制。论文最后对观测到的一种特殊的记录类型－－S型描迹的具体成因作了详细的分析和讨论，指出在一定条件下，以一定相位速度水平传播的声重波可以产生这类记录，给出了相位速度和振幅等声重波参数与记录描迹形状的关系，这对从多普勒频移记录推演电离层中的波动特征有一定的帮助。     

大型转动机械碰摩故障分析的声发射检测系统

汽轮发电机、空气压缩机等采用油膜支撑的大型转动机械,由于安装或运行中的原因,在转子旋转过程中,可能和器壁发生轻微的摩擦和碰击,简称碰摩.声发射技术在碰摩发生特别是故障早期诊断上有优越性.本系统的特点是没有沿用传统的计数、幅度、能量和持续时间等声发射特性参数,而是在声发射包络信号的频率分析中进行特征提取.声发射发生的过程分析和现场试验都表明这种方法对碰摩检测很敏感,在碰摩发生的起始阶段,包络谱中与转速同步的周期性分量显著增加.根据这种新的设计思想自行研制了BUAA碰摩声发射检测仪并对此作了介绍.     

MONITORING OF ENERGETIC PARTICLE ENVIRONMENT INSIDE THE CHINA-BRAZIL EARTH RESOURCE SATELLITE

On 14 October 1999, the Chinese-Brazil earth resource satellite (CBERS-1) was launched in China. On board of the satellite there was an instrument designed at Peking University to detect the energetic particle radiation inside the satellite so the radiation fluxes of energetic particles in the cabin can be monitored continuously. Inside a satellite cabin, radiation environment consists of ether penetrated energetic particles or secondary radiation from satellite materials due to the interactions with primary cosmic rays.Purpose of the detectors are twofold, to monitor the particle radiation in the cabin and also to study the space radiation environment The data can be used to study the radiation environment and their effects on the electronics inside the satelhte cabin. On the other hand, the data are useful in study of geo-space energetic particle events such as solar proton events, particle precipitation and variations of the radiation belt since there should be some correlation between the radiation situation inside and outside the satellite.The instrument consists of two semi-conductor detectors for protons and electrons respectively. Each detector has two channels of energy ranges. They are 0.5-2MeV and ≥2MeV for electrons and 5-30MeV and 30-60MeV for protons. Counting rate for all channels are up to 104/(cm2@s)and power consumption is about 2.5 W. There are also the additional functions of CMOS TID (total integrated dose) effect and direct SEU monitoring. The data of CBMC was first sent back on Oct. 17 1999 and it's almost three years from then on. The detector has been working normally and the quality of data is good.The preliminary results of data analysis of CBMC not only reveal the effects of polar particle precipitation and radiation belt on radiation environment inside a satellite, but also show some important features of the geo-space energetic particle radiation.As one of the most important parameters of space weather, the energetic charged particles have great influences on space activities and ground tech nology. CBMC is perhaps the first long-term on-board special equipment to monitor the energetic particle radiation environment inside the satellite and the data it accnmulated are very useful in both satellite designing and space research.     

基于FPGA的高准确度数字频率信号源设计

介绍了直接数字频率合成技术的实现方法,分析了其优越的技术特性。根据其特性,利用FPGA设计了高准确度的数字频率信号源。仿真结果表明,与传统的信号源相比,使用该方法实现的信号源,其信号种类多,准确度高,满足测试设备数字化、软件化的趋势。     

利用MF雷达对耀斑期间电离层D区电子密度的观测研究

利用MF雷达观测资料对X级别耀斑爆发期间在66-80km高度之间的电子密度进行了研究，观测到了耀斑爆发期间电子密度的突然增加，在较低高度上的电子密度的时间变化趋势与耀斑的软X射线辐射通量相关．电子密度的变化强度依赖于具体的耀斑参数，有些耀斑引起的电子密度增加高达400cm^-3，有些仅为100cm^-3左右．但耀斑期间在这一高度区间增加的总电子含量增量仅占耀斑辐射引起的整个电离层总电子含量增量的千分之一左右．最后，利用恢复阶段电子密度的时间变化过程估算了1997年11月4日耀斑期间部分高度上的有效复合系数．     

Evaluation and improvement of coastal GNSS reflectometry sea level variations from existing GNSS stations in Taiwan

Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1?m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10?cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7?cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used.     

新一代战斗机非定常流动数值研究综述

新一代战斗机强调超机动能力和强隐身性，其中大攻角下的静态失速、动态失速及内埋弹仓绕流是与高机动和强隐身密切相关的、极具挑战的几类典型的非定常流动，它们对数值方法提出了极高的要求。为了高精度地仿真流场、清楚地揭示流动机理，有效地控制非定常流动，非常有必要发展高精度且高效率的RANS-LES混合方法体系，包含RANS-LES混合方法本身、与RANS-LES混合方法匹配的高精度自适应耗散格式、基准湍流模式、高质量计算网格、高精度时间推进方法、非定常量的统计方法等，具有极强的紧迫性。提出、发展、验证并应用该类方法数值仿真新一代战斗机（包括单独部件、组合体、甚至全机）的非定常流动，数值预测结果与风洞实验数据吻合良好；此类方法可为新型战斗机设计提供理论依据和分析手段。