Characterization of indoor wireless channel at 5 GHz U-NII bands

The paper reports on the experiments undertaken at the University of Wollongong to characterise fading profiles and delay parameters of an indoor wireless channels at 5 GHz U-NII bands. The measurements were undertaken at different locations around the campus with results recorded for a post-processing to calculate the Rician K-factor, the level crossing rate and the average fade duration as well as mean excess delay, rms delay spread, and the coherence bandwidth of the channel. The presented measurement results can be useful in developing a Markov chain based model of the transport channel for IEEE802.11a or HYPRLAN-2 networks. The results also indicate scenarios where the coherence bandwidth of the channel is smaller than the width of the sub-carrier OFDM channels in either of the mentioned systems.     

非匹配不确定系统的模糊滑模控制

研究多输入不确定系统的模糊滑模控制问题，利用动态补偿器和不等式技巧设计了滑动模态，解决了非匹配不确定性的抑制问题，并给出了保守性较小的滑模稳定性条件．为克服滑模的抖振，提出了用模糊数模型和双二次函数插值构造模糊滑模控制律的方法．仿真结果表明，该方法对于参数摄动和外部扰动具有良好的鲁棒性．     

介质周期结构色散特性的严格分析：一种三维边值问题的求解方法

本文以耦合模理论和Ｆｌｏｑｕｅｔ理论为基础，把本征模展开与空间谐波展开巧妙地结合起来，严格分析了斜入射情况下介质周期结构的色散特性－三维边值问题。这种新方法既避免了通常耦合模方法分析此类问题所引入的微扰近似，又比Ｆｌｏｑｕｅｔ方法简单方便。通过对斜入射情况下一些介质结构滤波特性的数值分析，证实了本文方法的有效性，精确性和实用性。     

负色散镜的设计、制备及在掺钛蓝宝石激光谐振腔内的使用

根据钛宝石激光器的要求设计了性能优良的两种负色散镜(NDM1和NDM2)。NDM1同时引入啁啾效应和G-T效应产生大的群延迟色散量以减少光在负色散镜上的反射次数。NDM2仅引入G-T效应产生较小的群延迟色散以补偿腔内自相位调制带来的部分啁啾。选用离子束溅射法制备了这两种负色散镜。用分光光度计测试了它们的透射率。结果表明,所制备的负色散镜的性能与设计性能非常接近。使用这两种负色散镜进行掺钛蓝宝石激光谐振腔内色散补偿实现了飞秒脉冲锁模,获得了15 fs的超短脉冲。     

色散补偿技术在通信传输系统中的应用

本文介绍了色散补偿现象对光信号在传输过程中的影响,并结合中国网通长途传输网工程,提出了解决色散问题的具体措施及建议.     

用单端矢量网络分析仪测试手机RF电路的差分散射参数

本文以声表的测试为例,说明了采用单端矢量网络分析仪测试手机射频(RF)电路的差分散射参数的原理及方法,其中包含物理三端口的散射参数和模式三端口网络散射参数。     

天然橡胶-氢化丁腈橡胶的共硫化及性能研究

天然橡胶(NR)和氢化丁腈橡胶(HNBR)因不饱和度和极性的差异,存在硫化速度不匹配、填料分散等问题,难以实现两胶的并用。本文通过先制备不同硫黄/促进剂比例的NR和HNBR母炼胶,再将母炼胶并用制备NR/HNBR复合材料,解决了NR和HNBR共硫化的问题。研究了NR/HNBR的相态结构和填料在NR和HNBR两相的分散状态,结合相态结构和填料分散分析了NR/HNBR并用比对复合材料硫化特性、动静态力学性能、耐磨性和压缩温升的影响。结果表明:并用HNBR的复合材料混炼胶的门尼黏度增大,焦烧时间和正硫化时间缩短;随着HNBR含量增加,HNBR相的尺寸增大,硫化胶的硬度及100%和300%定伸应力增加,拉伸强度、撕裂强度、断裂伸长率和拉断永久变形减小,耐磨性和抗湿滑性提高,压缩疲劳温升增大。     

A fault analysis of DC electric arc furnaces with SVC harmonic filters in a mini-mill plant

This paper proposes the most feasible solution to overcome the failure of the 2nd harmonic filter in the static VAR compensator (SVC) which operates with the DC electric arc furnace (EAF) at Gwangyang Steel Mill in Korea. In order to investigate the causes of this failure, various measurements were carried out on the DC EAF and the main transformer at the PCC (point of common connection). It was concluded that the two causes for the failure are; the inrush current in the main transformer, and the parallel resonance between the system impedance and the harmonic filter. Three solutions to suppress the transformer inrush current and another three solutions to avoid the parallel resonance are suggested. The feasibility of these solutions was verified through the computer simulation with PSCAD/EMTDC. The most feasible solution to avoid further failures of the 2nd harmonic filter was selected, based on the estimated result for the six optional solutions in the point of performance and cost.     

直接电流控制的配电网静止无功补偿器研制

研制了±50kV.A的配电网静止同步补偿器(Distribution Static Synchronous Compensator,简称DSTATCOM)。其硬件主电路以IGBT功率模块为开关器件,采用PWM整流器结构。通过检测电路采集电流电压信号,利用TMS320F2812型DSP处理器进行算法处理和PWM脉冲输出。为提高系统的动态性能,采用直接电流控制策略,通过矢量变换消除静态误差,提高PWM开关频率等措施来减少输出谐波。实验结果验证了该方案的正确性。     

低渗透污染土水动力弥散参数试验研究

污染土的治理中通常采用降低渗透性的措施来控制其二次污染。通过获得其水动力弥散参数可以对其二次污染进行评价和预测,但是现有的土柱试验以及求解方法不适用于低渗透污染土水动力弥散参数的测定和求解。针对低渗透污染土水动力弥散参数试验和求解的问题,提出采用改进的柔性壁渗透仪测定其污染物的穿透曲线,根据所获得的穿透曲线,采用数值反演的方法计算污染土的水动力弥散参数。结果表明,采用柔性壁渗透仪和数值反演的方法,能够满足低渗透污染土水动力弥散参数测定的需要。