Optical and electrical characteristics of GaN vertical light emitting diode with current block layer

A GaN vertical light emitting diode(LED)with a current block layer(CBL)was investigated.Vertical LEDs without a CBL,with a non-ohmic contact CBL and with a silicon dioxide CBL were fabricated.Optical and electrical tests were carried out.The results show that the light output power of vertical LEDs with a non-ohmic contact CBL and with a silicon dioxide CBL are 40.6%and 60.7%higher than that of vertical LEDs without a CBL at 350 mA,respectively.The efficiencies of vertical LEDs without a CBL,with a non-ohmic contact CBL and with a silicon dioxide CBL drop to 72%,78%and 85.5%of their maximum efficiency at 350 mA,respectively. Moreover,vertical LEDs with a non-ohmic contact CBL have relatively superior anti-electrostatic ability.     

浅谈SDH系统故障定位及排除方法

根据多年SDH系统的调试及维护经验,概括了SDH系统故障定位的基本思路及常用排除方法,并结合案例分析介绍了SDH系统故障定位最常用的环回法。     

Solvent‐Induced Morphology in Polymer‐Based Systems for Organic Photovoltaics

Studies on the influence of four different solvents on the morphology and photovoltaic performance of bulk‐heterojunction films made of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM) via spin‐coating for photovoltaic applications are reported. Solvent‐dependent PCBM cluster formation and P3HT crystallization during thermal annealing are investigated with optical microscopy and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) and are found to be insufficient to explain the differences in device performance. A combination of atomic force microscopy (AFM), X‐ray reflectivity (XRR), and grazing‐incidence small‐angle X‐ray scattering (GISAXS) investigations results in detailed knowledge of the inner film morphology of P3HT:PCBM films. Vertical and lateral phase separation occurs during spin‐coating and annealing, depending on the solvent used. The findings are summarized in schematics and compared with the IV characteristics. The main influence on the photovoltaic performance arises from the vertical material composition and the existence of lateral phase separation fitting to the exciton diffusion length. Absorption and photoluminescence measurements complement the structural analysis.     

A Micromachined Reconfigurable Metamaterial via Reconfiguration of Asymmetric Split‐Ring Resonators

A micromachined reconfigurable metamaterial is presented, whose unit cell consists of a pair of asymmetric split‐ring resonators (ASRRs); one is fixed to the substrate while the other is patterned on a movable frame. The reconfigurable metamaterial and the supporting structures (e.g., microactuators, anchors, supporting frames, etc.) are fabricated on a silicon‐on‐insulator wafer using deep reactive‐ion etching (DRIE). By adjusting the distance between the two ASRRs, the strength of dipole–dipole coupling can be tuned continuously using the micromachined actuators and this enables tailoring of the electromagnetic response. The reconfiguration of unit cells endows the micromachined reconfigurable metamaterials with unique merits such as electromagnetic response under normal incidence and wide tuning of resonant frequency (measured as 31% and 22% for transverse electric polarization and transverse magnetic polarization, respectively). The reconfiguration could also allow switching between the polarization‐dependent and polarization‐independent states. With these features, the micromachined reconfigurable metamaterials may find potential applications in transformation optics devices, sensors, intelligent detectors, tunable frequency‐selective surfaces, and spectral filters.     

第一代机顶盒的电子节目指南

电子节目指南是由业务商为用户提供的一项重要的服务,它负责电视节目和各种增值业务的导航.讨论了电子节目指南的生成、系统构成及其实现.     

国产pnp双极晶体管在宽总剂量范围辐照下的ELDRS

研究了不同偏置条件下国产商用pnp型双极晶体管在宽总剂量范围内的辐射损伤特性和变化规律.实验结果表明,在100 rad(Si)/s和0.01 rad(Si)/s剂量率辐照下,总累计剂量达到200 krad (Si)时,这一宽总剂量范围内辐射损伤趋势均随着总剂量值不断累积而增大,且并未出现饱和.相同剂量率辐照下,发射结施加反偏状态时国产商用pnp双极晶体管的过剩基极电流变化最大,正偏下最小,零偏介于二者之间.两款晶体管均表现出明显的低剂量率损伤增强效应(ELDRS),且在反偏下ELDRS更显著.并对出现这一实验结果的损伤机理进行了探讨.     

Data offloading and task allocation for cloudlet-assisted ad hoc mobile clouds

Nowadays, although the data processing capabilities of the modern mobile devices are developed in a fast speed, the resources are still limited in terms of processing capacity and battery lifetime. Some applications, in particular the computationally intensive ones, such as multimedia and gaming, often require more computational resources than a mobile device can afford. One way to address such a problem is that the mobile device can offload those tasks to the centralized cloud with data centers, the nearby cloudlet or ad hoc mobile cloud. In this paper, we propose a data offloading and task allocation scheme for a cloudlet-assisted ad hoc mobile cloud in which the master device (MD) who has computational tasks can access resources from nearby slave devices (SDs) or the cloudlet, instead of the centralized cloud, to share the workload, in order to reduce the energy consumption and computational cost. A two-stage Stackelberg game is then formulated where the SDs determine the amount of data execution units that they are willing to provide, while the MD who has the data and tasks to offload sets the price strategies for different SDs accordingly. By using the backward induction method, the Stackelberg equilibrium is derived. Extensive simulations are conducted to demonstrate the effectiveness of the proposed scheme.     

高斯光束经波长级圆孔衍射的轴上光强特性

基于横截面上精确表述的光强和精确的衍射场公式 ,对高斯光束经波长级圆孔衍射的轴上光强特性进行了研究。结果表明 ,高斯衍射光束的轴上光强特性取决于初始高斯半宽度w0 和波长级圆孔的孔径R。对于w0 /R≥ 1的高斯衍射光束 ,轴上光强存在的极值个数和出现的位置仅由比值m=2R/λ决定 ,最大的轴上光强均出现在N =R2 / (λz) =1的地方 ;至于轴上光强极值的峰和谷明显与否 ,取决于w0 /R的比值 ,比值越大 ,轴上光强极值的峰和谷就越明显。当w0 /R的比值足够大时 ,就趋向于平面波入射时的情形。而对于w0 /R<1的这一类高斯衍射光束 ,轴上光强存在特定的演化规律 :随着初始高斯半宽度的减小 ,轴上光强极值个数逐步减少直至全部消失。     

高Q值光学微球腔的温度系数研究

光学微球谐振腔由于其具有超高的Q值及极小的模式体积等优点,在高灵敏度传感和光通信等方面得到了广泛的研究。测试了未封装和封装后微球腔谐振波长随温度的变化,实验结果表明随温度增大,谐振波长线性红移,且线性度高。二者温度系数不同,未封装时为25.6 pm/℃,封装后为4.4 pm/℃,主要原因为紫外胶的负热光系数所致。理论分析了紫外胶的热光效应,通过控制紫外胶厚度可以改变光在紫外胶中的比例,从而调节温度系数。当光在紫外胶中比例为0.1135时,温度系数变为0,可以抑制温度漂移,实现了温度补偿;该比例继续增大,温度灵敏度提高。低温漂、高灵敏度、微型化拓宽了回音壁模式(WGM)传感器的应用潜力。     

软件定义FiWi网络中网络编码控制方法

针对传统FiWi(光纤无线混合接入)网络中网络编码控制过程中大量Gate、Report信息交换导致的网络信息复杂、编码时延增大等问题,设计了一种支持编码功能的软件定义FiWi网络架构和基于Openflow协议的网络编码控制方法。仿真结果表明,所提出的软件定义FiWi网络架构中的集中编码控制方法及其实现方案能够减少网络中控制信息数量,提高带宽利用率,有效降低数据传输时延并提高网络吞吐量。