Two-port calibration of test fixtures with different test ports

The open-short-load (OSL) method is very simple and widely used for one-port test fixture calibration. In this paper, this method is extended, for the first time, to the two-port calibration of test fixtures with different test ports. The problem of phase uncertainty arising in this application has been solved. The comparison between our results and those obtained with the SOLT method shows that the method established is accurate for practical applications. (C) 2002 Wiley Periodicals, Inc.

Scattering-parameter measurements of laser diodes

An accurate and simple technique for measuring the input reflection coefficient and the frequency response of semiconductor laser diode chips is proposed and demonstrated. All the packaging parasitics could be obtained accurately using a calibrated probe, and the impedance of the intrinsic diode chip is deduced from the directly measured reflection coefficient. The directly measured impedance of a laser diode is affected strongly by the short bond wire. In the frequency response (S(2)1) measurements of semiconductor laser diode chips, the test fixture consists of a microwave probe, a submount, and a bond wire. The S-parameters of the probe could be determined using the short-open-match (SOM) method. Both the attenuation and the reflection of the test fixture have a strong influence on the directly measured frequency response, and in our proposed technique, the effect of test fixture is completely removed.

New algorithms of the TSM and TOM methods for calibrating microwave test fixtures

Based on the conventional through-short-match (TSM) method, an improved TSM method has been proposed in this Letter. This method gives an analytical solution and has almost all the advantages of conventional TSM methods. For example, it has no phase uncertainty and no bandwidth limitation. The experimental results show that the accuracy can be significantly improved with this method. The proposed theory can be applied to the through-open-match (TOM) method. (C) 2002 Wiley Periodicals. Inc.

Phase uncertainty in calibrating microwave test fixtures

The problem of phase uncertainty arising in calibration of the test fixtures is investigated in this paper, It is shown that the problem exists no matter what kinds of calibration standards are used. It is also found that there is no need to determine the individual S-parameters of the test fixtures. In order to eliminate the problem of phase uncertainty, three different precise (known) reflection standards or one known reflection standard plus one known transmission standard should be used to calibrate symmetrical test fixtures. For the asymmetrical cases, three known standards, including at least one transmission standard, should be used. The thru-open-match (TOM) and thru-short-match (TSM) techniques are the simplest methods, and they have no bandwidth limitation. When the standards are imprecise (unknown), it is recommended to use any suitable technique, such as the thru-reflect-line, line-reflect-line, thru-short-delay, thru-open-delay,line-reflect-match, line-reflect-reflect-match, or multiline methods, to accurately determine the values of the required calibration terms and, in addition, to use the TOM or TSM method with the same imprecise standards to resolve the phase uncertainty.

Correlation of calibration equations for test fixtures

This paper begins from the thru-short-open (TSO) and thru-line-match (TLM) methods to investigate the correlation of the calibration equations of these two methods, The relations among the measurements with the corresponding standards are obtained. It is found that the line standard with zero length can be used instead of ideal open and short, in case that two test fixtures are symmetrical. For asymmetrical fixtures, the measurements with the standards line, open and short are related at certain frequencies, and the matched load can be replaced by the line standards. The relations established are used to test short and match standards and analyze the freqPuency limits of the TSO method, Good agreement between theory and experiment is obtained, It is found that the TSO method becomes very poor when the insertion phase of the thru standard is near n pi/4, and this method has a lower frequency limit. The TLM method is found unsuitable for calibrating asymmetrical fixtures.

Characterization of high-speed optoelectronics devices based optical and electrical spectra analyses - art. no. 68380Q

In this paper, we presents the characterization technique of high-speed optoelectronics devices based electrical and optical spectra, which is as important access to the devices performance as the prevalent vector network analyzer (VNA) sweeping method. The measurement of additional modulation of laser and frequency response of photodetector from electrical spectra, and the estimation of the modulation indexes and the chirp parameters of directly modulated lasers based on optical spectra analysis, are given as examples.

Measurement and analysis of microwave frequency response of semiconductor optical amplifiers - art. no. 682406

The measurement and analysis of the microwave frequency response of semiconductor optical amplifiers (SOAs) are proposed in this paper. The response is measured using a vector network analyzer. Then with the direct-subtracting method, which is based on the definition of scattering parameters of optoelectronic devices, the responses of both the optical signal source and the photodetector are eliminated, and the response of only the SOA is extracted. Some characteristics of the responses can be observed: the responses are quasi-highpass; the gain increases with the bias current; and the response becomes more gradient while the bias current is increasing. The multisectional model of an SOA is then used to analyze the response theoretically. By deducing from the carrier rate equation of one section under the steady state and the small-signal state, the expression of the frequency response is obtained. Then by iterating the expression, the response of the whole SOA is simulated. The simulated results are in good agreement with the measured on the three main characteristics, which are also explained by the deduced results. This proves the validity of the theoretical analysis.

基于质谱的高性能蛋白质非标记定量软件设计与性能优化

本文介绍了定量蛋白质组学中一个较为年轻和重要的新课题：基于质谱的非标记定量。基于质谱的非标记定量技术不使用同位素标记等化学手段，而是通过对质谱原始数据的分析和处理来进行蛋白质定量。 本文对基于质谱的非标记定量技术做了概要性的调研，阐述了此技术中存在的大规模数据处理性能瓶颈问题，并进一步指出了高性能计算尤其是并行计算技术在非标记定量中应用的迫切性和必要性。 针对当前质谱数据可视化辅助分析工具共同存在的一个缺陷，即质谱数据需要全部导入内存，本文设计并实现了质谱可视化辅助分析工具MZ-Analyzer。与其它可视化分析工具不一样的是，MZ-Analyzer没有将质谱数据全部导入主存，而是通过构建外存索引提高质谱数据可视化辅助分析的性能。因此，尽管随着质谱数据量的指数性增长，MZ-Analyzer的性能仍然具有良好的可扩展性。 本文设计并实现了基于质谱的非标记定量软件QuantWiz，通过改变肽段定量的顺序，提高了定量软件的时间局部性和质谱数据缓存的命中次数。分析了QuantWiz的多种数据并行策略，设计并实现了按保留时间划分的并行QuantWiz。通过实验验证并行QuantWiz具有良好的并行效率，当进程数为32时，并行效率为63%。

软件属性保障中的源代码静态分析技术研究

随着硬件性能的不断提升，计算机正在被赋予越来越艰巨的任务，运行其上的软件作为沟通人类思维和底层硬件的桥梁，其重要性日益增加。与此同时，软件系统的规模也在不断变大，所涉及的逻辑也更为复杂，这导致开发人员难免会由于疏漏在软件设计实现的过程中引入缺陷、埋下隐患。所以,如何检验、确保软件的属性就成为时下一个亟待解决的热点问题。而在此背景下，源代码静态分析技术由于恰好可以弥补现有测试方法的不足，已经开始在这一研究领域崭露头角。有鉴于此，本文为了推进安全信息系统的研发，分别围绕源代码静态分析技术在软件属性保障中两个最主要的应用场景展开研究，涉及高等级安全操作系统开发过程中的源代码自动化审计，以及分布式信息系统中平台间互信建立时针对软件属性所进行的远程验证，其中，前者是为从深度上将现有安全操作系统向更高等级推进提供助力，而后者是为了从广度上将信息安全领域现有的围绕单机平台的研究成果向分布式架构推广建立基础。具体来说，本文选择针对编程接口规范的一致性检验和应用静态分析的软件属性远程验证作为研究的切入点，探讨了应用源代码静态分析技术检验、确保软件属性的方法和用途，主要取得以下几个方面的成果： 第一，本文给出了一个基于值等价类的别名分析方法。该方法依据相关的传值操作维护一个值等价类空间，可以在编程接口规范一致性检验的过程中按需推导变量符号间的等值关系，不仅有能力支持上下文相关、路径相关的全局分析，还可以有效应对C代码中因结构、指针等构件所衍生出来的大量变量符号。 第二，针对大部分现有代码静态分析工具分析规模受限的问题，本文围绕编程接口规范的一致性检验给出了可以与别名分析有效结合的性能优化方案。该方案不仅能通过剔除与分析无关的执行分支和引入缓存机制提高分析效率，还可以尽量确保分析的准确性少受影响。 第三，我们设计、实现了一个C代码静态分析工具ABAZER（A Bug AnalyZER）。该工具可以依据用户使用有限自动机模型描述的编程接口规范，对操作系统内核级别的软件进行全局分析，指出代码中可能有悖于规范的部分。我们使用ABAZER实际考查了FreeBSD内核中锁机制以及GCC 4.x中库GNU Libiberty的使用情况，从中发现了若干真实的缺陷。 第四，本文针对现有应用可信计算技术、基于完整性信息进行远程验证的方案在灵活性和实用性上所存在的不足，给出一个扩展方案。该方案通过引入虚拟机技术，在软件构建过程中收集举证信息，应用静态分析方法分析软件功能模块间的相关性，划分出与验证相关的模块，有效控制用户定制软件验证时所要依赖的可信列表的规模，使其有能力适应当今网络环境中的大量异质平台和各种安全需求。此外，它还可以为自身所依赖的可信计算基的替换和更新提供支持。 第五，本文针对Flask架构的特点，给出了一个既能检验强制访问控制实现正确性，又能最大限度保留软件灵活性、使得用户可以在一定程度上对软件进行定制的远程验证方案。该方案依赖源代码静态分析技术界定软件中无需基于完整性进行验证的模块，在进一步缩减可信列表规模的同时，使用代码改写技术在这些模块中自动化地插入监控代码约束软件的动态行为，以达到确保强制访问控制实现正确性的目的。该方案初步展现了源代码静态分析技术在远程验证中广阔的应用前景。

基于规则推导的特权隐式授权分析

介绍了一种研究系统特权安全问题的方法．由于其特有的迁移系统安全状态的能力，使得分析及保护系统特权都很困难，因此，传统访问控制研究中所采用的技术无法复制到该领域．在访问控制空间理论下，检查了系统特权的来源问题及其特点，从而将系统规则划分为约束规则与执行规则两类，分别描述授权的限制与效果．进一步对规则逻辑形式进行推导，发现特权操作间的特殊授权关系以及相关属性，并设计了一种快速构造授权推导图的算法．在此基础上，分析隐式授权安全问题可能存在的滥用特权威胁．最后对POSIX(portable operating system interface)标准的权能机制进行形式化描述，计算并构造其授权推导图．对标准设计中存在的滥用威胁提供了对策，有效地实现了与最小特权原则的一致性．

一种静态最少优先级分配算法

随着实时系统越来越多地应用于各种快速更新系统,尤其是各种片上系统,如PDA(personal digital assistant),PSP(play station portable)等,性价比已成为系统设计者的主要关注点.实际应用中,实时系统通常仅支持较少的优先级,常出现系统优先级数小于任务数的情况(称为有限优先级),此时,需将多个任务分配到同一系统优先级,RM(rate monotonic),DM(deadline monotonic)等静态优先级分配算法不再适用.为此,静态有限优先级分配是研究在任务集合静态优先级可调度的情况下,可否以及如何用较少或最少的系统优先级保持任务集合可调度.已有静态有限优先级分配可分为两类:固定数目优先级分配和最少优先级分配.给出了任意截止期模型下任务静态有限优先级可调度的充要条件以及不同静态有限优先级分配间转换时的几个重要性质,指出了系统优先级从低到高分配策略的优越性,定义了饱和任务组与饱和分配的概念,证明了在任务集合静态优先级可调度的情况下,最少优先级分配比固定数目优先级分配更具一般性.最后提出一种最少优先级分配算法LNPA(least-number priority assignment).与现有算法相比,LNPA适用范围更广,且复杂度较低.

Synthesis Gas Generation by Chemical-Looping Reforming Using Ce-Based Oxygen Carriers Modified with Fe, Cu, and Mn Oxides

Chemical-looping reforming (CLR) is a technology that can be used for partial oxidation and steam reforming of hydrocarbon fuels. It involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from combustion air to the fuel. Composite oxygen carriers of cerium oxide added with Fe, Cu, and Mn oxides were prepared by co-precipitation and investigated in a thermogravimetric analyzer and a fixed-bed reactor using methane as fuel and air as oxidizing gas. It was revealed that the addition of transition-metal oxides into cerium oxide can improve the reactivity of the Ce-based oxygen carrier. The three kinds of mixed oxides showed high CO and H-2 selectivity at above 800 degrees C. As for the Ce-Fe-O oxygen carrier, methane was converted to synthesis gas at a H-2/CO molar ratio close to 2:1 at a temperature of 800-900 degrees C; however, the methane thermolysis reaction was found on Ce-Cu-O and Ce-Mn-O oxygen carriers at 850-900 degrees C. Among the three kinds of oxygen carriers, Ce-Fe-O presented the best performance for methane CLR. On Ce-Fe-O oxygen carriers, the CO and H-2 selectivity decreased as the Fe content increased in the carrier particles. An optimal range of the Ce/Fe molar ratio is Ce/Fe > 1 for Ce-Fe-O oxygen carriers. Scanning electron microscopy (SEM) analysis revealed that the microstructure of the Ce-Fe-O oxides was not dramatically changed before and after 20 cyclic reactions. A small amount of Fe3C was found in the reacted Ce-Fe-O oxides by X-ray diffraction (XRD) analysis.

SOA-based actively mode-locked fiber ring laser by forward injecting an external pulse train

An actively mode-locked fiber ring laser based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is demonstrated to operate stably with a simple configuration. By forward injecting an easily-generated external pulse train, the mode-locked fiber laser can generate an optical-pulse sequence with pulsewidth about 6 ps and average output power about 7.9 mW. The output pulses show an ultra-low RMS jitter about 70.7 fs measured by a RF spectrum analyzer. The use of the proposed forward-injection configuration can realize the repetition-rate tunability from I to 15 GHz for the generated optical-pulse sequences. By employing a wavelength-tunable optical band-pass filter in the laser cavity, the operation wavelength of the designed SOA-based actively mode-locked fiber laser can be tuned continuously in a wide span between 1528 and 1565 nm. The parameters of external-injection optical pulses are studied experimentally to optimize the mode-locked fiber laser. (C) 2009 Elsevier B.V. All rights reserved.

Kinetics of photoinduced anisotropy in bacteriorhodopsin film under two pumping beams

Photoinduced anisotropy in bacteriorhodopsin (BR) film arises from the selective bleaching of BR molecules to linearly polarized light. The kinetics of photoinduced anisotropy excited by single and two pumping beams are investigated theoretically and experimentally. Compared with a single pumping beam (650 nm), which produces comparatively small photoinduced anisotropy, dual-wavelength linearly polarized pumping beams (650 and 405 nm) can obviously change the photoinduced anisotropy. When the polarization orientation of the 405 ran pumping beam is perpendicular to that of the 650 nm pumping beam, the peak and steady values of the photoinduced anisotropy kinetic curves are remarkably enhanced. But when the two pumping beams have parallel polarization orientation, the peak and steady values are restrained. At a fixed intensity of the 650 nm pumping beam, there exists an optimal intensity for the 405 nm pumping beam to maximize the value of the photoinduced anisotropy. The photoinduced transmittance of the polarizer-BR-analyzer system is modulated by the polarization angle of the 405 nm pumping beam in an approximate-cosine form. (C) 2008 Optical Society of America.