幂格

本文引入了幂格的概念并讨论了其相关性质。     

On the power graph and the reduced power graph of a finite group

In this paper, for a finite group, we investigate to what extent its directed (resp. undirected) reduced power graph determines its directed power graph (resp. reduced power graph). Moreover, we investigate the determination of the orders of the elements of a finite group from its directed (resp. undirected) reduced power graph. Consequently, we show that some classes of finite groups are recognizable from their undirected reduced power graphs. Also, we study the relationship between the isomorphism classes of groups corresponding to the equivalence relations induced by the isomorphism of each of these graphs on the set of all finite groups.     

超导故障限流器的研究现状及其应用

超导故障限流器(Superconducting Fault Current Limiter,SFCL)是利用超导体的基本特性,有效限制电力系统故障短路电流,提高电网安全性和稳定性的一种新型电力设备。文中在综合大量文献的基础上,对超导故障限流器进行了一种较为系统的分类。基于该种分类,结合目前国内外的研究现状,就电阻型、磁屏蔽型、饱和铁芯电抗器型、桥路型SFCL的工作原理作了详细的分析介绍,还给出了它们在电力系统中的安装位置。最后,对超导故障限流器的研究中存在的问题及其发展趋势做了说明。     

50W功率放大器的研制

介绍了一种L波段50W功率放大器的研制情况,采用功率合成技术获得了61W的输出功率,放大器增益大于40dB。给出了1W功放、10W功放和八路功率分配器的设计分析过程。     

Ku波段微波小功率放大器的设计

文中论述了利用修正的S参数法,设计了Ku波段微波小功率放大器,具有功率增益高和可靠性高的优点。利用这种设计方法,设计并制作了两个实验的功率放大器,并且它们的性能与设计数据很接近     

中低速磁浮列车悬浮供电系统测试与分析

作为中低速磁浮列车的关键设备,悬浮供电系统是决定悬浮控制系统能否稳定可靠工作的前提。通过介绍电磁型中低速磁浮列车的悬浮供电系统基本结构和工作原理,以某型样车为研究对象,制定了多工况测试方案,对悬浮供电系统的主电源、蓄电池和超级电容组等的性能开展了详细测试。为进一步开展中低速磁浮列车各主要功能模组的多工况性能测试提供了参...     

低功耗高性能限流比较器的设计与仿真

为了进一步改善DC-DC开关电源的效率、功耗和精度,以其中最关键的电路:限流电路为突破口,对传统CPM控制结构进行了改进,并引入了动态偏置的思想,采用0.6μmBICMOS工艺模型,设计了一种高性能、低功耗的限流比较器.分析了电路的设计原理和过程,并给出了仿真结果.     

Butterworth Window for Power Spectral Density Estimation

The power spectral density of a signal can be estimated most accurately by using a window with a narrow bandwidth and large sidelobe attenuation. Conventional windows generally control these characteristics by only one parameter, so there is a trade-off problem: if the bandwidth is reduced, the sidelobe attenuation is also reduced. To overcome this problem, we propose using a Butterworth window with two control parameters for power spectral density estimation and analyze its characteristics. Simulation results demonstrate that the sidelobe attenuation and the 3 dB bandwidth can be controlled independently. Thus, the trade-off problem between resolution and spectral leakage in the estimated power spectral density can be overcome.     

Development of superconducting power devices in Europe

Europe celebrated last year (2008) the 100-year anniversary of the first liquefaction of helium by H. Kammerling Onnes in Leiden. It led to the discovery of superconductivity in 1911. Europe is still active in the development of superconducting (SC) devices. The discovery of high critical temperature materials in 1986, again in Europe, has opened a lot of opportunities for SC devices by broking the 4 K cryogenic bottleneck.     

Effect of dimethylamino substituent on tetraphenylethylene-based hole transport material in perovskite solar cells

A N,N-dimethylamino substituted tetraphenylethylene derivative (TPE-NMe) was synthesized and characterized, and was successfully applied as hole transport material (HTM) in perovskite solar cells. The methoxy-substituted analogue TPE-4DPA was also studied for comparison. The effect of replacing the para-methoxy substituent with N,N-dimethylamino on photophysical properties, energy levels, and hole transport properties is investigated. Photovoltaic performances of the corresponding devices using the two HTMs are studied. Compared to the methoxy substituent, the N,N-dimethylamino groups in TPE-NMe generates a lower V_oc (0.87 V), yet it provides higher J_sc (21.69 mA/cm²) and FF (0.73) values, resulting in an overall power conversion efficiency of 13.78%.