复杂网络中节点重要性排序的研究进展

如何用定量分析的方法识别超大规模网络中哪些节点最重要, 或者评价某个节点相对于其他一个或多个节点的重要程度, 这是复杂网络研究中亟待解决的重要问题之一. 本文分别从网络结构和传播动力学的角度, 对现有的复杂网络中节点重要性排序方法进行了系统的回顾,总结了节点重要性排序方法的最新研究进展, 并对不同的节点重要性排序指标的优缺点以及适用环境进行了分析, 最后指出了这一领域中几个有待解决的问题及可能的发展方向. 关键词： 复杂网络 节点重要性 网络结构 传播动力学     

Imprints of molecular orbitals using photoelectron angular distribution by strong laser pulses of circular polarization

We theoretically investigate the strong-field ionization of H+2 molecules in four different electronic states by calculating photoelectron angular distributions in circularly polarized fields. We find that the structure of photoelectron angular distribution depends on the molecular orbital as well as the energy of the photoelectron. The location of main lobes changes with the symmetric property of the molecular orbital. Generally, for molecules with bonding electronic states, the photoelectron's angular distribution shows a rotation of π/2 with respect to the molecular axis, while for molecules with antibonding electronic states, no rotation occurs. We use an interference scenario to interpret these phenomena. We also find that, due to the interference effect, a new pair of jets appears in the waist of the main lobes, and the main lobes or jets of the photoelectron's angular distribution are split into two parts if the photoelectron energy is sufficiently high.     

高效率的蓝色磷光有机电致发光器件

制备了基于双母体结构的高效率蓝色磷光有机电致发光器件。通过与采用单母体结构和双发光层结构的器件性能进行对比,发现双母体结构的应用对蓝光器件的性能起到了明显的提升作用。双母体蓝光器件的最大效率为14.9 cd/A(13.3 lm/W),最大亮度达到10 440 cd/m~2,其开启电压仅为2.7 V。蓝光器件同时展示出低的效率滚降特性,在100~5 000 cd/m~2范围内,器件的效率滚降仅为35.3%。在3~8 V的电压变化内,器件的色坐标一直位于蓝光区域。     

Study on anti-emission materials for non-emitting grid applications in microwave power tubes

Hafnium and platinum were deposited onto molybdenum grids by ion-beam assisted deposition method. Electron-emission characteristics from molybdenum grids with Hf and Pt films, which were contaminated by active electron-emission substances (Ba, BaO) of the cathode, were measured using analogous diode method. The surfaces of grids were analyzed by X-ray diffraction. The results revealed that the reaction between BaO and Hf formed BaHfO₃ compound, which greatly reduced the accumulation of BaO on the surface and accordingly decreased grid emission. In contrast, Ba were formed by the decomposition of BaO on the surface of Pt film under high temperature and re-evaporated from its surface, which reduced the active electron-emission substances on the surface of the grid and effectively restrained grid emission. Their mechanisms for grid-emission suppression are discussed and a good method to develop new grid-coating materials is suggested.     

Annealing and measurement temperature dependence of W2B5-based rectifying contacts to n-GaN

The thermal stability and measurement temperature dependence of Schottky contact characteristics on n-GaN using a W₂B₅/Ti/Au metallization scheme was studied using current-voltage (I-V), scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) measurements. The elemental profile obtained from samples annealed at 350 °C showed some titanium diffusion into the gold layer but little other difference from the as-deposited wafer. Annealing at 700 °C produced significant diffusion of titanium. The Schottky barrier height increased with anneal temperature up to 200 °C, reaching a maximum value of 0.65 eV, but decreased at higher annealing temperatures. The reverse breakdown voltage from diodes fabricated using the W₂B₅-based contacts showed a similar dependence. The reverse current magnitude was larger than predicted by thermionic emission alone. The barrier height showed only minor changes with measurement temperature up to 150 °C.     

Cu、N空位对Cu_3N的电子结构、电学和光学性能影响的第一性原理研究

本文采用基于密度泛函理论的第一性原理计算方法,研究了立方相Cu_3N晶体中含Cu、N空位体系的稳定性、电学、光学性能.研究结果表明含Cu空位和N空位体系的结构比较稳定,Cu空位和N空位降低了体系的导电性,但增加了体系的透射率;含Cu空位和N空位体系的禁带宽度均大于Cu_3N体系,说明实验中制备的Cu_3N有时表现为绝缘体的可能原因为体系中存在Cu空位或N空位.     

CuCrZr合金质子辐照效应的模拟研究

基于Monte Carlo方法,跟踪一大批入射粒子的运动,模拟1~10 Me V质子辐照下质子与CuCrZr合金的相互作用,计算出合金的阻止本领、能量传递、能量损失、射程、空位分布情况以及合金的辐照损伤分别与辐照深度、质子能量的关系,通过模拟CuCrZr合金在聚变反应中的工作环境,分析热沉材料的失效机理.研究结果表明:质子能量在1~10 Me V时,质子与CuCrZr合金发生非弹性碰撞,能量损失以电离能损失为主,表现出很好的抗辐照性能;质子在合金中的峰值深度随质子能量增加而增加,且近似指数关系,峰值深度为2~250μm;入射质子能量达到Me V级别时,溅射产额为零,CuCrZr合金可以很好的避免器壁的侵蚀;合金中空位的个数与入射质子能量呈线性关系,合金中空位和质子在合金中的分布具有同步性;质子损伤效率在合金深度方向呈现高斯分布,损伤最大值位置与辐照深度接近,随着入射质子能量的增加损伤效率最大值不断减小.     

基于DSP的航天器压力变化检漏仪的设计

航天器的密封性能是极其重要的指标之一,利用压力变化方法进行舱体密封性检漏是保障其密封性的重要技术手段;设计研制小型压力变化检漏仪对满足航天器检漏设备小型集成化、高精度的迫切需求是十分重要的;以DSP为数据的核心处理器,分析绝压和差压具有温度补偿方法,设计基于485通信接口实现数字绝压传感器的数据采集,采用250Ω的高精度电阻接入电流环的方法实现差压传感器的信号调理,通过ADS1247高精度24位数模转换器实现差压信号的采集;并采用恒流供电和电阻比测量原理实现对两路热敏电阻温度传感器的测量;各信号经DSP中固化的压力变化检漏算法集中处理,得到被测物体的漏率值,检测结果通过LCD显示。所研制集绝压、差压和温度多参量监测于一体的检漏仪,经过温度、压力、检漏试验等测试,验证了其精度和检漏能力满足要求;研究结果表明：所研制的检漏仪小巧,精度高,可靠性高,可实现压力、温度、漏率等多参量的同时监测,漏率检测的最大相对误差为19.3%,相对不确定度小于2%,可有效地解决航天器泄漏检测的问题。     

考虑运动受限的履带式移动机器人轨迹跟踪控制

针对履带式移动机器人的轨迹跟踪控制问题进行研究,首先,建立了履带式移动机器人的运动学模型和跟踪误差模型;其次,设计了转速有限时间控制和线速度滑模控制的轨迹跟踪控制律,并给出了考虑运动受限作用下的控制律修正表达式;最后,基于MATLAB对所提控制律进行仿真,对比分析了不考虑运动受限情况下跟踪控制效果;结果表明,设计的跟踪控制律能够实现履带式移动机器人对圆轨迹的有效跟踪,且考虑运动受限作用的控制律更加符合实际;文章研究分析了运动受限作用对于移动机器人轨迹跟踪控制的影响,分析结果对其他移动机器人的运动控制研究具有参考价值。