Ultraviolet detectors based on epitaxial ZnO films grown by MOCVD

High-quality zinc oxide (ZnO) films were epitaxially grown on R-plane sapphire substrates by metalorganic chemical vapor deposition at temperatures in the range of 350°C to 600°C. In-situ nitrogen compensation doping was performed using NH₃. Microstructural and optical properties of the films, as well as the N-doping effects, were studied. The metal-semiconductor-metal ultraviolet sensitive photodetectors were fabricated on N-doped epitaxial ZnO films. The detector showed fast photoresponse, with a rise time of 1 μs and a fall time of 1.5 μs. Low-frequency photoresponsivity, on the order of 400 A/W at 5 V bias, was obtained.     

Technology trends toward a system-in-a-module in power electronics

Currently, assemblies of power semiconductor switches and their associated drive circuitry are available in modules. From a few 100 watts downward, one finds silicon monolithic technology as the integration vehicle, while upward into the multi-kilowatt range, mixed mode module construction is used. This incorporates monolithic, hybrid, surface mount and wirebond technology. However, a close examination of the applications in motor drives and power supplies indicates that there has been no dramatic volume reduction of the subsystem. The power semiconductor modules have shrunk the power switching part of the converter, but the bulk of the subsystem volume still comprises the associated control, sensing, electromagnetic power passives and interconnect structures. The paper addresses the improvement of power processing technology through advanced integration of power electronics. The goal of a subsystem in a module necessitates this advanced integration. The central philosophy of this technology development research is to advance the state of the art by providing the concept of integrated power electronics modules (IPEMs). The technology underpinning such an IPEM approach is discussed. The fundamental functions in electronic power processing, the materials, processes and integration approaches and future concepts are explained.     

下一代移动通信系统中的信道分配策略

下一代移动通信系统是一个由微蜂窝、宏蜂窝和卫星小区构成的多层覆盖体系结构,在该体系结构中,多媒体业务将占有很大的比重。基于这一特点,建立新的通信系统模型, 并通过将软-通信质量概念与统计复用技术相结合,获得了一种较好的信道分配方法。通过对算法进行系统仿真,比较了它与传统信道分配算法的优劣。仿真结果表明:新的信道分配方法会增加系统容量,减少通信业务阻塞概率,极大的提高整个系统的性能。     

均匀会聚菲涅尔透镜设计及性能研究

提出了一种均匀会聚菲涅尔透镜设计方案,透镜基于离轴聚焦设计,采用方形非旋转对称结构,利用光强叠加实现均匀会聚.文章基于该方法建立了几何聚光比分别为56、100、400和900倍,焦距分别为300 mm、400 mm、500和600 mm的透镜模型,并利用光学仿真软件对其聚光性能进行分析.研究结果表明:基于该方法设计的透镜能够较好地实现均匀会聚,且聚光效率和聚光分布均匀度均超过80％,可以满足聚光光伏需要.     

基于动态逆与QFT 的鲁棒飞行控制器

针对保证无人战斗机控制器的解耦性能和鲁棒性能问题,设计一个某无人战斗机的姿态控制器。将动态逆(DI)和定量反馈理论(QFT)相结合,用动态逆实现无人战斗机控制的动态解耦,用定量反馈理论保证控制器的鲁棒性能,并以实例进行仿真结果分析。仿真结果表明:在气动数据变化±30%的范围内,DI与QFT控制器可以实现对飞机姿态的精确控制,能很好地解决飞机的姿态控制问题,有较好的工程应用价值。     

HYBRID INTERNET TRAFFIC CLASSIFICATION TECHNIQUE1

Accurate and real-time classification of network traffic is significant to network operation and management such as QoS differentiation, traffic shaping and security surveillance. However, with many newly emerged P2P applications using dynamic port numbers, masquerading techniques, and payload encryption to avoid detection, traditional classification approaches turn to be ineffective. In this paper, we present a layered hybrid system to classify current Internet traffic, motivated by variety of network activities and their requirements of traffic classification. The proposed method could achieve fast and accurate traffic classification with low overheads and robustness to accommodate both known and unknown/encrypted applications. Furthermore, it is feasible to be used in the context of real-time traffic classification. Our experimental results show the distinct advantages of the proposed classification system, compared with the one-step Machine Learning (ML) approach.     

风冷压缩单元式空调器节能探讨

从分析风冷压缩单元式空调器的制冷原理入手,提出了两种空气源热泵热水模块＋空气源压缩制冷模块机,为提高能源综合利用效率、节约建筑能耗提供了一定的实践思路。     

铝丝阵Z箍缩电子温度径向轮廓研究

利用均匀色散云母弯晶分析器,在"阳"加速器上测量了铝丝阵Z箍缩等离子体的时间积分X射线光谱。采用碰撞辐射模型,通过测量Al的Ly-α/He-α以及Ly-β/He-ε的强度比推断出平均电子温度,分别为512eV和489eV。针对记录的连续辐射,由连续谱斜率拟合得到了等离子体核心电子温度为1215eV。对圆柱箍缩温度径向轮廓的研究表明,此次聚爆实验的电子温度从箍缩轴心向外缘近似线性降低。谱线强度比法是诊断平均电子温度的有效手段,而连续谱拟合法为诊断铝丝阵箍缩核心区的等离子体电子温度提供了重要信息。     

Fluorescence enhancement of single-phase red-blue emitting Ba3MgSi2O8:Eu2+,Mn2+ phosphors via Dy3+ addition for plant cultivation

Fluorescence enhancement of red and blue concurrently emitting Ba₃MgSi₂O₈:Eu²⁺,Mn²⁺ phosphors for plant cultivation has been investigated by Dy³⁺ addition. The Ba₃MgSi₂O₈:Eu²⁺,Mn²⁺,Dy³⁺(BMS-EMD) phosphors have two-color emissions at the wavelength peak values of 437 nm and 620 nm at the excitation of 350 nm. The two emission bands are coincident with the absorption spectrum for photosynthesis of plants. An obvious enhancement effect has been observed upon addition of Dy³⁺ with amount of 0.03 mol%, in which the intensities of both blue and red bands reach a maximum. The origin of red and blue emission bands is analysed. The photochromic parameters of the samples at the nearly UV excitation are tested. This fluoresence enhancement is of great significance for special solid state lighting equipment used in plant cultivation. This work has been supported by National Natural Science Foundation of China (Grant No 50872091) and the Natural Science Foundation of Tianjin, China (06YFJMJC02300, 06TXTJJC14602).     

An inchworm mobile robot using electromagnetic linear actuator

The capability of motion is one of the important aspects for a micro-robot to fulfill its given tasks. Micro-autonomous systems usually require large force, large displacement and less power consumption. Among different actuation schemes, electromagnetic actuator shows the benefit in a combination of force, displacement and cost effective control. A bristle-based inchworm mobile robot using a short stroke electromagnetic linear actuator is described in the paper. The main body and movable unit of the robot are joined by using a sealed bellows and the bristle legs are designed so that it can operate both on plane surfaces and in liquid. The actuator designed for the robot is a tubular type linear machine with an overall size of Φ7 × 10 mm. The key dimensions of the actuator were determined through magnetic field analysis to achieve optimum force output and necessary travel stroke within the limited space. The predicted actuation force of the actuator is 20 mN and the stroke length is 1.2 mm. Two working prototypes of the actuator were constructed and the performance tests show the effectiveness of the design. A sensorless control scheme with a novel start-up strategy for the designed actuator was developed based on the robotic system modeling and the analyzed results show the satisfactory performance of the system.