A note on power-law devices and their effect on signal-to-noise ratio

The effect of power-law devices, used as either band-pass nonlinear amplifiers or envelope detectors, on the signal-to-noise ratio is determined for both limiting cases of very large and very small input signal-to-noise ratio. Expressions are derived for the degradation in signal-to-noise ratio in terms of the envelopes and phases of the signal and noise. The results are general, applying to Gaussian and non-Gaussian noises and modulated and unmodulated signals, and allow important conclusions to be reached concerning the value of power-law devices in communications systems in various signal and noise environments. It is found that band-pass nonlinear amplifiers can generally be chosen to improve the signal-to-noise ratio if the input signal-to-noise ratio is small and the noise is non-Gaussian. Envelope detectors usually degrade the signal-to-noise ratio since they exhibit a "small-signal suppression" effect in all noise environments except for the special case of unmodulated sine-wave interference.     

A note on utilizing far-field phase information

The far-field phase information available from an antenna pattern is discarded in most system applications. Making use of such information for an angle-of-arrival estimation application across a relatively wide region of space is discussed in this note. The far-field phase difference response from two simultaneous shaped beam receive patterns generated by a linear array antenna is shown to provide an appropriate relative phase property for making unambiguous angle determinations.     

A note on evaluation of matrix series

An improved method is presented for the numerical evaluation of a sequence of powers of a matrix, as used in series expansions.     

A note on expected Fisher information for the Burr XII distribution

We present a self-contained derivation of the expected Fisher information for the Burr XII distribution for the case of complete samples. We also indicate how results obtained for the basic two parameter case may be adapted to cover an extended parameterisation which includes a scale parameter.     

Babel in document design: the evaluation of multilingual texts

The aim of the study is to analyze the process of document design in a multilingual setting. In order to evaluate translation quality, a theoretical perspective is formulated as a basis for criteria for a good translation. In this perspective, the target text is considered an autonomous document. Two sets of criteria are distinguished: correctness errors and functional errors. The tools that were used to assess translation quality were expert analysis and reader focused evaluation. For both tools, a multilingual evaluation team was formed with the highest possible expertise in the target languages, in linguistics, and in usability. In this case study, the process of evaluation and the results are described     

Schottky diodes and other devices on thin silicon membranes

The fabrication of ultra-thin silicon membranes of micron or submicron sizes with thicker supporting frames makes possible improvements in several kinds of electronic devices. We show that the series resistances of some devices can be reduced significantly, thus effecting increases in the cutoff frequencies. The resistance swing of Schottky diodes can also be raised. Initial experimentation relating to some of these applications is presented.     

A note on the correct evaluation of junction capacitance of a solar cell

In the fabrication of low-cost solar cells one has often to contend with finite series and shunt resistances. These tend to give misleading values of the junction capacitance as measured with an ordinary bridge. The problem is discussed analytically and graphical plots are given for determination of the true values from the measured ones. Practical use of these plots is discussed and illustrated with the help of experiments on thin-film Cu₂S-CdS solar cells.     

A note on the evaluation of Schottky diode parameters in the presence of an interfacial layer

Metal-semiconductor barrier height and semiconductor doping concentration evaluated from room temperature current-voltage and capacitance-voltage data of Schottky barrier diodes exhibit significant error in the presence of an interfacial oxide layer of appreciable thickness (?50 ?). The effective Richardson constant obtained from an activation energy plot of saturation current is shown to provide a sensitive indication of the presence of the interfacial layer.     

Searching the Web: general and scientific information access

The World Wide Web has revolutionized the way people access information, and has opened up new possibilities in areas such as digital libraries, general and scientific information dissemination and retrieval, education, commerce, entertainment, government and health care. There are many avenues for improvement of the Web; for example, in the areas of locating and organizing information. Current techniques for access to both general and scientific information on the Web provide much room for improvement; search engines do not provide comprehensive indices of the Web and have difficulty in accurately ranking the relevance of results. Scientific information on the Web is very disorganized. We discuss the effectiveness of Web search engines, including results showing that the major Web search engines cover only a fraction of the “publicly indexable Web”. Current research into improved searching of the Web is discussed, including new techniques for ranking the relevance of results, and new techniques in metasearch that can improve the efficiency and effectiveness of Web search. The creation of digital libraries incorporating autonomous citation indexing is discussed for improved access to scientific information on the Web     

A note on feedback communication with noisy side information at the receiver (Corresp.)

A feedback communication system which has noisy side information at the receiver is considered. The estimation scheme is a simple extension of the conventional one without side information. The resulting mean-squared error is compared with the rate-distortion bound obtained recently by Wyner and Ziv.     

琴心三叠道初成——记联想研究院信息安全研究室主任韦卫

IT时代,拥有改造网络的知识意味着拥有世界。他们中许多人拥有辉煌的成就和低调的处事风格,这让他们的生活充满神秘。对于许多人来说,解读韦卫就是在解读一种生活和事业的态度。了解韦卫的人都知道,他是一个谦和写在脸上,自信揣在心里的人。这位1999年毕业于中国科学院计算     

高校科技文献信息管理系统的设计与实现

随着高校数字化建设的不断深入,科技文献管理系统是提高高校数字化水平的一个重要手段。该系统不但能提高管理部门的管理效率、减轻工作负担,而且为广大教师和科研工作者提供更多更快捷的服务。根据实际需求出发,提出了一个科技文献管理系统,并进行了系统功能和流程的设计与开发,阐述了部分功能特色的具体实现,并对系统实施后的运行情况进行了讨论。     

信息服务信息传递效能评估指标体系研究

通过研究指标体系的构建方法,根据需求分析,对影响信息服务信息传递效能的要素逐步分层、细化,从技术性能指标和战术性能指标两个方面构建指标体系。对指标的获取及量化进行研究,并对指标体系的完整性、合理性、有效性进行检验,为下一步的效能评估工作打好了基础。     

高校数字图书馆网络信息服务评估模式探究

伴随着网络技术的高速发展,数字图书馆发展成为图书馆建设的主要内容。以高校数字图书馆网络信息服务能力的角度,综合分析高校数字图书馆网络信息服务能力的构成要素,总结出高校数字图书馆信息服务的评价指标,通过调查问卷获悉高校数字图书馆的专家、馆员、用户对评价指标的重要性感知,遴选出关键评价指标,以层次分析法构建高校数字图书馆信息服务能力评估模式。     

高校数字图书馆网络信息服务评估模式探究

伴随着网络技术的高速发展,数字图书馆发展成为图书馆建设的主要内容。以高校数字图书馆网络信息服务能力的角度,综合分析高校数字图书馆网络信息服务能力的构成要素,总结出高校数字图书馆信息服务的评价指标,通过调查问卷获悉高校数字图书馆的专家、馆员、用户对评价指标的重要性感知,遴选出关键评价指标,以层次分析法构建高校数字图书馆信息服务能力评估模式。     

A note on the superposition principle

Two theorems concerning the superposition principle are stated and proved. These theorems are useful in the computation of total power dissipated in a network.     

COB封装LED器件寿命评价方法研究

COB封装的LED器件应用日趋广泛,但是其寿命评价方法仍限于做3000h或6000h的光通维持率试验,试验本身耗时较长,因此本文基于半导体器件的指数衰减规律和LED光通量的慢退化特性提出一种加速试验方法,对器件进行高温加速寿命试验,并对试验结果进行计算,得到了器件在加速试验温度下的L70寿命,然后利用相应水平的激活能,得到了在较低结温下的L70寿命。     

A note on the anatomy of federation

Federation can be perceived as a security foundation accommodating federated identity management solutions. In this paper we analyse the structure and function of federations with the aim of revealing the essential elements and architecture principles of federation models. Firstly, we identify some fundamental concepts that underpin the structure and operation of a trust realm. Then we analyse how these aggregate to provide for identity management and trust brokerage in a federation. We then explain various federation models in terms of these concepts. Finally, we examine the current state of Web-based federation standards and products, indicate specific research challenges for the next generation of federation-enabling technology. The paper targets an audience of research professionals and practitioners with some security and software engineering background who wish to find out more about federation models, and it can also be useful to (security) architects and consultants who are considering different federation architecture options for their projects.     

Detailed evaluation of in-operando potentials in OLED devices: A combined experimental and drift-diffusion study

We report on a technique to determine in-operando transport properties of Organic Light Emitting Diodes (OLEDs). Two types of OLEDs that solely differ in the emission layer but obviously exhibit a different potential distribution are investigated in this study. If the emission layer consists of the isomer TH-A a large shift in onset voltage can be observed in case of layer thickness variation of the emission layer. In case of the isomer TH-B a thickness variation has no impact on the onset voltage. Therefore the voltage developments per layer are determined with the help of IV measurements on a set of devices with varying layer thickness. From an empirical point of view the voltage behaviour in each layer follows a simple power law. A drift-diffusion model is developed that well describes the current density dependent evolution of coefficient and exponent of the power law. From the model we are able to derive the carrier injection mechanism into the respective layer as well as the injection barrier height. Also the carrier mobility is determined. Finally we are able to show that the existence of a large injection barrier can not explain the observed onset voltage shifts in case of TH-A. Instead an electric field at or close to the interface is necessary to describe the TH-A behaviour.