Optical gain of strained wurtzite GaN quantum-well lasers

A theory for the electronic band structure and the free-carrier optical gain of wurtzite-strained quantum-well lasers is presented. We take into account the strain-induced band-edge shifts and the realistic band structures of the GaN wurtzite crystals. The effective-mass Hamiltonian, the basis functions, the valence band structures, the interband momentum matrix elements, and the optical gain are presented with analytical expressions and numerical results for GaN-AlGaN strained quantum-well lasers. This theoretical model provides a foundation for investigating the electronic and optical properties of wurtzite-strained quantum-well lasers.     

碳掺杂β-FeSi2薄膜的电子显微学研究

本文利用透射电子显微镜对离子注入合成的β-FeSi2和β-Fe(C,Si)2薄膜进行了对比研究.电镜观察结果表明,选择C作为掺杂元素,能够得到界面平直、厚度均一的高质量β相薄膜,晶粒得到细化,β-FeSi2层稳定性提高.尤其在60kV、4×1017ions/cm2条件下注入直接形成非晶,在退火后会晶化为界面平滑、厚度均匀的β-FeSi2薄膜.因此从微结构角度考虑,引入C离子有益于提高β-FeSi2薄膜的质量.     

一类可由基本模型嵌套组成的工作流系统的性能分析方法

工作流是近年来网络领域里研究的一个热点,对工作流模型的性能分析是工作流研究的一个重要内容.实际的模型往往规模大而复杂,这为分析其性能带来了很大的困难.但有一类模型可由工作流的四种基本模型(顺序、并行、选择、循环)嵌套组成,对于这类模型,本文给出了计算其性能乘积解的数学公式.文中给出了如何由这四种基本模型嵌套组成实际模型的方法,推导出了计算这四种基本模型的性能等价公式,并按建立实际模型相反的顺序,用由里到外逐层的分析方法,给出了计算实际模型的性能乘积解.     

A Study of AlN Films Prepared by Arc Ion Plating

Hexagonal AlN films have been obtained by arc ion plating at different negative biases ,X-ray diffraction and scanning electron microscopy results show that AlN films with smooth surfaces and (002) preferred orientation are obtained at low biases ,whereas those with coarse surfaces and (100) preferred orientation are obtained at high biases,The formation mechanism of AlN is analyzed and the experiment results are discussed,The effect of bias on adhesion strength has also been examined.     

Synthesis and characterization of a novel proton‐exchange membrane for fuel cells operating at high temperatures and low humidities

The synthesis of a p‐toluidine/formaldehyde (PTF) resin was performed, and the effects of the molar ratio of the individual monomers and the polymerization conditions on the structure of the PTF resin were studied. Fourier transform infrared and ¹³C‐NMR spectra were used to characterize the PTF. Wide‐angle X‐ray diffraction patterns revealed the crystalline structures of various PTFs. Polarized optical microscopy revealed that the molar ratio of the monomers had a strong effect on the crystalline morphologies. A longer polymerization time turned out a polymer with a higher intrinsic viscosity and molecular weight, which led to differences in the proton conductivity. All of the PTFs showed a higher proton conductivity than a commercial Nafion membrane at 90–100°C and 0% relative humidity. The proton conductivity of the PTF series could be improved by sulfonation with sulfuric acid and could be maintained after blending with polyurethane. Pure methanol could be used as a fuel source because of the insolubility and nonwetting properties of PTF in methanol to increase the output current density for a PTF membrane electrode assembly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Toward a scalable, silicon-based quantum computing architecture

Advances in quantum devices have brought scalable quantum computation closer to reality. We focus on the system-level issues of how quantum devices can be brought together to form a scalable architecture. In particular, we examine promising silicon-based proposals. We discover that communication of quantum data is a critical resource in such proposals. We find that traditional techniques using quantum SWAP gates are exponentially expensive as distances increase and propose quantum teleportation as a means to communicate data over longer distances on a chip. Furthermore, we find that realistic quantum error-correction circuits use a recursive structure that benefits from using teleportation for long-distance communication. We identify a set of important architectural building blocks necessary for constructing scalable communication and computation. Finally, we explore an actual layout scheme for recursive error correction, and demonstrate the exponential growth in communication costs with levels of recursion, and that teleportation limits those costs.     

Tunneling injection quantum-dot lasers with polarization-dependent photon-mediated carrier redistribution and gain narrowing

A theoretical and experimental study of a particular transverse-electric (TE) mode lasing mechanism of a tunneling injection InP quantum-dot (QD) laser is reported. In the experiment, the TE mode lasing action takes place at the first excited state of InP biaxially compressively strained QDs. This QD state is coupled to the ground state of two tensile-strained InGaP quantum wells (QWs) although the tensile-strained QW structure favors the transverse-magnetic (TM) polarization light emission. The measured TE and TM modal gain spectra show a typical QW gain evolution behavior at low injection currents, which can be theoretically modeled by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier redistribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier redistribution, which depends on the optical transition energy and polarization. This concept of the polarization-dependent photon-mediated carrier redistribution explains the TE gain narrowing and TM gain pinning behavior. In addition, a coupled rate equation model is established, and the calculated polarization power ratio based on the coupled rate equations explains the experimental observation.     

一种使用开路并联线的改进型螺旋微带谐振单元

提出了一种改进型螺旋微带谐振单元(SCMRC)的结构.该改进型螺旋微带谐振单元具有微带并联开路线,在低频通带内通过设计达到50Ω的端口阻抗.同时,并联的微带开路线在SCMRC结构的禁带中谐振,来实现更强的慢波效应和更宽的禁带.实际设计、制作和测试了该改进型螺旋微带谐振单元,该滤波器在低频通带内具有低插入损耗、改善的回波损耗,以及在较小面积下的宽禁带.     

Dyspnea resulting from phrenic nerve paralysis after interscalene brachial plexus block in an obese male--a case report

While current psychiatric taxonomies recognise a classification of amphetamine dependence, derived from the notion of an alcohol dependence syndrome, little research has validated that such a condition exists for this drug. Current amphetamine users (N = 331), were interviewed using the World Health Organization operationalisation of DSM-III-R substance dependence criteria, and a measure of the psychological components of dependence. Structural analyses indicated that a unidimensional dependence syndrome as assessed by DSM-III-R and DSM-IV criteria exists for amphetamine, and that physiological, psychological and behavioural indicators were all important in accounting for the variance in responses. It was demonstrated that the concept of a dependence syndrome is applicable to amphetamine, and that the inclusion of the amphetamine dependence syndrome in DSM-III-R and DSM-IV is valid.