Graph-theoretic algorithm for spectrum allocation in IEEE 802.22 wireless mesh network

The IEEE 802.22 standard based on wireless Cognitive Radio (CR) is an optimal solution to resolve the inefficient spectrum utility problem. In this paper, we focus on the spectrum allocation in IEEE 802.22 mesh networks and propose a new graph-theory algorithm. The algorithm aims at two objectives: one is the sum of the allocated channel bandwidth is maximum, and the other is the number of users can be active simultaneity is maximum. In this proposed algorithm, the topology of network was modeled as a general graph and could be transformed into a weighted complete bipartite-graph by three processes. The simulations show that the presented algorithm can improve the performance of spectrum allocation.     

Pulsed CH<Subscript>3</Subscript>OH Terahertz Laser Emission Pumped by a TEA CO<Subscript>2</Subscript> Laser

A simple terahertz (THz) cavity and a TEA CO₂ laser for the optically pumped THz emission is studied experimentally. To obtain high peak power of pump laser, pressure ratios of gas mixture in the cavity of the TEA CO₂ laser are discussed. When CH₃OH are pumped by the 9P(16) and 9P(36) CO₂ laser lines, the generation of terahertz radiation with energy as high as 353 μJ and 307 μJ are obtained, respectively. The corresponding photon conversion efficiencies are 0.705% and 0.29%. Meanwhile, higher peak power of pump laser effectively improves the photon conversion efficiency. And the optimum THz laser pressure increases with narrower pulse width of pump laser.     

计算全息双通道半色调编码技术的研究

本文在罗曼型编码的基础上,运用空间脉冲调制技术,提出了新型的编码技术——双通道半色调编码。双通道半色调型编码用两个圆形通光孔代替矩形孔,以两个圆孔面积及位置来记录两个物体的全息信息,加快了计算速度。记录的两个平面物体同时再现在同一衍射级的相同或不同方向上,在空间完全分离开来,从而实现了载波信息的通道变化。文中给出了相应的原理和实验结果。     

Epitaxial growth of ZnO on GaN/sapphire substrate by radio-frequency magnetron sputtering

Zinc oxide (ZnO) thin films were grown on n-GaN/sapphire substrates by radio-frequency (RF) magnetron sputtering. The films were grown at substrate temperatures ranging from 400 to 700 ℃ for 1 h at a RF power of 80 W in pure Ar gas ambient. The effect of the substrate temperature on the structural and optical properties of these films was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra. XRD results indicated that ZnO films exhibited wurtzite symmetry and c-axis orientation when grown epitaxially on n-GaN/sapphire. The best crystalline quality of the ZnO film is obtained at a growth temperature of 600 ℃. AFM results indicate that the growth mode and degree of epitaxy strongly depend on the substrate temperature. In PL measurement, the intensity of ultraviolet emission increased initially with the rise of the substrate temperature, and then decreased with the temperature. The highest UV intensity is obtained for the film grown at 600 ℃ with best crystallization.     

Ultra high-speed InP/InGaAs SHBTs with ft and fmax of 185 GHz

An InP/InGaAs single heterojunction bipolar transistor(SHBT) with high maximum oscillation frequency (f_(max)) and high cutoff frequency(f_t) is reported.Efforts have been made to maximize f_(max) and f_t simultaneously including optimizing the epitaxial structure,base-collector mesa over-etching and base surface preparation.The measured f_t and f_(max) both reached 185 GHz with an emitter size of 1×20μm~2,which is the highest f_(max) for SHBTs in mainland China.The device is suitable for ultra-high spee...     

单片开关电源TPS54350的失效分析

分析和解决了开关电源TPS54350在小负载应用电路下的失效问题.通过对失效器件进行外观镜检、I-V曲线测试、X线检查,对典型应用电路的分析和异常测试波形分析找到了器件失效的根本原因.TPS54350典型应用电路在下电时存在反灌电流,且外接欠压保护电阻,由此引起的输入电压波动对输出使能ENA端间接干扰,从而使器件误启动,造成输出端电流反灌入器件,导致器件内部电路出现闩锁失效.采用TPS54550替换TPS54350(ENA端抗干扰能力更强),并去除UVLO端欠压保护电阻,解决失效问题,稳定地实现12 V转5 V,电流约为100 mA的小负载应用.     

可扩展的箱体类零件工艺知识管理

箱体类零件工艺知识管理是基于工艺知识重用与共享的需要,但其复杂性致使难于统一管理.提出一种具有可扩展性的箱体类零件工艺知识管理系统设计,采用了分类的工艺编码系统,并将工艺知识划分为基本信息和辅助信息.利用SQL及ADOX技术实现了工艺信息和辅助信息的自定义.通过动态建立查询SQL语句,并使用ADO及DataGrid的自适应性来显示查询结果.系统满足了箱体类零件加工工艺知识管理与重用的需要.该方法为企业箱体类零件加工工艺知识的管理与重用提供了思路.     

MEMS金属微构件的激光微喷丸强化技术分析与展望

介绍了适用于金属微构件处理的激光微喷丸技术,通过控制工艺参量和合理的路径规划,在试件表面产生有益的残余压应力分布,能有效提高工件的抗疲劳和磨损性能。概述了微喷丸技术的研究现状,总结了激光微喷丸的机理、关键技术和影响因素,分析了激光微喷丸研究中存在的问题,为今后激光微喷丸技术的进一步研究提供指导。     

Pixel‐Structured Scintillator with Polymeric Microstructures for X‐Ray Image Sensors

We introduce a pixel‐structured scintillator realized on a flexible polymeric substrate and demonstrate its feasibility as an X‐ray converter when it is coupled to photosensitive elements. The sample was prepared by filling Gd₂O₂S:Tb scintillation material into a square‐pore‐shape cavity array fabricated with polyethylene. For comparison, a sample with the conventional continuous geometry was also prepared. Although the pixelated geometry showed X‐ray sensitivity of about 58% compared with the conventional geometry, the resolving power was improved by about 70% above a spatial frequency of 3 mm^?1. The spatial frequency at 10% of the modulation‐transfer function was about 6 mm^?1.     

光纤CAN总线网络设计与实现

从双绞线控制器局域网(Wire-CAN)总线网络的缺陷和光纤优良的抗电磁干扰、衰减小的特性出发,详细分析了双绞线CAN总线的接口协议,通过改造CAN总线的物理层,提出光纤媒介的CAN总线信号传输方案,并给出具体接口电路的设计,节点的逻辑控制由复杂可编程逻辑器件(CPLD)完成.