AlxGa1−xN Ultraviolet Avalanche Photodiodes Grown on GaN Substrates

Al_xGa_1-xN (x=0.05) ultraviolet (UV) avalanche photodiodes grown on a GaN substrate are reported. The epitaxial structure was grown by metal-organic chemical vapor deposition on a free-standing bulk GaN substrate having low dislocation density. The growth conditions for Al_xGa_1-xN epitaxial layers on GaN substrates were optimized to achieve improved crystalline and structural quality. With UV illumination at lambda~250 nm, devices with mesa diameters of ~30 mum achieve stable maximum optical gains of ~50 at a reverse bias voltage of ~87 V.     

USB端口找到新居,落户嵌入式系统

安装过PC的人员都知道,通用串行接口(USB)具有与即插即用相似的性能.因而,将USB端口移植到嵌入式系统是一种方便的控制外部设备的办法.毕竟USB只有两条信号线和两条电源连接线,设计一个USB端口不会有什么困难吧.这一任务说起来简单,对设计者却有不少困难.不过,供应商可以提供从板卡到软件的一切帮助.     

Modeling and simulation of mixed traffic on a prioritized shared medium

Network access systems (NAS) such as digital loop carriers (DLC) are increasingly utilizing a shared medium, such as Hybrid Fiber Coax (HFC) to provide point‐to‐multi‐point access from the public switched telephone network (PSTN) to the end user (consumer). New services, such as direct access to the packet switched network (PSN, WWW) have been added to DLC equipment in such a way as to provide for a prioritized set of services over a shared medium in an effort to take advantage of otherwise unused bandwidth. The introduction of such services requires the modeling and analysis of these network access systems. This becomes complex when considering the variability in different service type traffic characteristics. This work identifies a traffic engineering problem of prioritized circuit switched and packet switched (PSTN/PSN) traffic over the same shared medium as it may relate to “perceived” quality of service (QoS). Copyright © 2002 John Wiley & Sons, Ltd.     

The effects of sulphur fertilisers on the content of sulpho-amino acids in seeds of cowpea (Vigna unguiculata)

Seed meals of three cowpea (Vigna unguiculata) cultivars, grown in pots containing sulphur-deficient soil supplemented with 0, 0.2, 0.6, 1.8, 5, 15 and 45 parts/10⁶ sulphate-S levels in the soil solution, were examined for total nitrogen, total sulphur and sulpho-amino acid contents. The sulphur content and the ratio of sulphur to nitrogen were found to increase with the increasing level of sulphate-S fertilisation up to ca 5 parts/10⁶. Compared with the control the sulpho-amino acid content in seeds of cowpea TVu 76 increased with S-supplementation up to 5 parts/10⁶ and that of cowpea Sitao Pole increased with S up to 1.8 parts/10⁶. Similar levels (7 and 2 parts/10⁶ respectively) of sulphate-S were required in the soil solution to obtain 95% of the maximum yields of cowpea seeds. The content of sulpho-amino acids in the seeds from 5 parts/10⁶ treatments were similar to those reported for cowpeas grown under field conditions at IITA and elsewhere with adequate levels of soil sulphur for maximum yield.     

Automatic detection of conduction block based on time-frequencyanalysis of unipolar electrograms

It is commonly thought that lethal tachyarrhythmias, such as ventricular fibrillation (VF), are perpetuated by functional reentry, which occurs when an activation wave blocks and rotates around tissue that is excitable (i.e., functional block). Electrograms recorded near these regions typically contain two sequential deflections representing activation on either side of the block. By detecting these "double potentials," we hypothesize that functional block can be detected by a single electrode. METHODS: Unipolar electrograms were recorded from a 24 x 21 mapping array on the intact ventricular epicardium of five pigs during electrically-induced VF. The short time Fourier Transform (STFT) of each electrogram was analyzed to identify double potentials. To evaluate the performance of the STFT algorithm, conduction block was located in activation maps using a minimum conduction velocity criterion (10 cm/s) and then compared to the results of the STFT algorithm. RESULTS: The STFT algorithm detected conduction block with a sensitivity of 0.74 +/- 0.12 and a specificity of 0.99 +/- 0.00. CONCLUSION: We have developed an automated algorithm that can detect functional block during VF from a single electrode recording. Possible applications include fast, objective identification of block in mapping data and realtime localization of reentrant substrates using mapping catheters.     

Satellite UMTS/IMT2000 W-CDMA air interfaces

The third-generation IMT-2000 initiative of the International Telecommunication Union is aiming at the provision of a limited family of global standards providing worldwide multimedia wireless services in a host of environments encompassing indoor picocells to satellite megacells. The ITU IMT-2000 initiative has been supported by several regional standardization bodies such as the European Telecommunication Standard Institute with its Universal Mobile Telecommunication System. In this article a few air interface proposals for the satellite component of UMTS/IMT-2000 based on adaptation of the emerging terrestrial wideband CDMA standards are reviewed. In particular, S-UMTS requirements are examined together with W-CDMA applicability to the satellite environment. It is shown that with minor adaptations, the terrestrial W-CDMA air interface provides an efficient solution for the satellite UMTS component. This commonality will certainly help in the realization of low-cost low-size dual-mode user terminals encompassing both terrestrial and satellite components     

Organizational Media Affordances: Operationalization and Associations with Media Use

The concept of affordances has been increasingly applied to the study of information and communication technologies (ICTs) in organizational contexts. However, almost no research operationalizes affordances, limiting comparisons and programmatic research. This article briefly reviews conceptualizations and possibilities of affordances in general and for media, then introduces the concept of organizational media affordances as organizational resources. Analysis of survey data from a large Nordic media organization identified six reliable and valid organizational media affordances: pervasiveness, editability, self-presentation, searchability, visibility, and awareness. Eight media scales based on frequency of use of 10 media within each of three organization levels were differentially associated with these affordances. The conceptualization, measurement approach, and results from this study provide the foundation for considerable future organizational communication and ICT research.     

打破硬件至上的观念

正产品的硬件开发在今天尽管依然重要,但是它对于产品与众不同的帮助是微乎其微。目前设计价值以及设计的主要工作侧重在可决定竞争优势的软设计上,这也正是当今产品的真正IP——"器件智能性"。然而在传统的设计流程中,设计初始阶段的目标是创建可支持这些软件设计的硬件原型机。在硬件原型机没有制造出来之前我们不能进行任何有意义的软件开发。因此我们必须先做出一系列决定来确定所     

Effect of Raman amplification on stimulated Brillouin scatteringthreshold in dispersion compensating fibres

An investigation of how the stimulated Brillouin scattering threshold of dispersion compensating fibres is affected by Raman amplification is presented. Experimental data is in good agreement with the threshold values predicted by the theoretical approach     

User mobility profile prediction: An adaptive fuzzy inference approach

Predicting the probabilities that a mobile user will be active in other cells at future moments poses a significant technical challenge to network resource management in multimedia wireless communications. The probability information can be used to assist base stations to maintain a balance between guaranteeing quality of service (QoS) to mobile users and achieving maximum resource utilization. This paper proposes a novel adaptive fuzzy logic inference system to estimate and predict the probability information for direct sequence code division multiple access (DS/CDMA) wireless communications networks. The estimation is based on measured pilot signal strengths at the mobile user from a number of nearby base stations, and the prediction is obtained using the recursive least square (RLS) algorithm. Numerical results are presented to demonstrate the performance of the proposed technique under various path loss and channel shadowing conditions. This revised version was published online in July 2006 with corrections to the Cover Date.