Stability improvement of selective oxidation during the fabrication of InGaAs/GaAs vertical cavity surface emitting laser

The effects of the carrier gas flow and water temperature on the oxidation rate for different reaction temperatures were investigated. The optimum conditions for stable oxidation were obtained. Two mechanisms of the oxidation process are revealed. One is the flow-controlling process, which is unstable. The other is the temperature-controlling process, which is stable. The stable region decreases for higher reaction temperatures. The simulation results for the stable oxidation region are also given. With optimum oxidation conditions, the stability and precision of the oxidation can be dramatically improved.

A 10-bit 2GHz current-steering CMOS D/A converter

This paper presents a 2GS/s 10-bit CMOS digital-to-analog converter (DAC). This DAC consists of a unit current-cell matrix for 6MSBs and another unit current-cell matrix for 4LSBs, trading off between the precision and size of the chip. The Current Mode Logic (CML) is used to ensure high speed, and a double Centro-symmetric current matrix is designed by the Q(2) random walk strategy in order to ensure the linearity of the DAC. The DAC occupies 2.2 x 2.2 mm2 of die area, and consumes 790mw at a single 3.3V power supply.

Fast Discrimination of Commerical Corn Varieties Based on Near Infrared Spectra

The existing methods for the discrimination of varieties of commodity corn seed are unable to process batch data and speed up identification, and very time consuming and costly. The present paper developed a new approach to the fast discrimination of varieties of commodity corn by means of near infrared spectral data. Firstly, the experiment obtained spectral data of 37 varieties of commodity corn seed with the Fourier transform near infrared spectrometer in the wavenurnber range from 4 000 to 12 000 cm (1). Secondly, the original data were pretreated using statistics method of normalization in order to eliminate noise and improve the efficiency of models. Thirdly, a new way based on sample standard deviation was used to select the characteristic spectral regions, and it can search very different wavenumbers among all wavenumbers and reduce the amount of data in part. Fourthly, principal component analysis (PCA) was used to compress spectral data into several variables, and the cumulate reliabilities of the first ten components were more than 99.98%. Finally, according to the first ten components, recognition models were established based on BPR. For every 25 samples in each variety, 15 samples were randomly selected as the training set. The remaining 10 samples of the same variety were used as the first testing set, and all the 900 samples of the other varieties were used as the second testing set. Calculation results showed that the average correctness recognition rate of the 37 varieties of corn seed was 94.3%. Testing results indicate that the discrimination method had higher precision than the discrimination of various kinds of commodity corn seed. In short, it is feasible to discriminate various varieties of commodity corn seed based on near infrared spectroscopy and BPR.

Influence of band bending and polarization on the valence band offset measured by x-ray photoelectron spectroscopy

The influence of band bending and polarization on the valence band offset measured by x-ray photoelectron spectroscopy (XPS) is discussed, and a modification method based on a modified self-consistent calculation is proposed to eliminate the influence and thus increasing the precision of XPS. Considering the spontaneous polarization at the surfaces and interfaces and the different positions of Fermi levels at the surfaces, we compare the energy band structures of Al/Ga-polar AlN/GaN and N-polar GaN/AlN heterojunctions, and give corrections to the XPS-measured valence band offsets. Other AlN/GaN heterojunctions and the piezoelectric polarization are also introduced and discussed in this paper.

An Enhanced Particle Swarm Optimization Algorithm

Particle Swarm Optimization (PSO) algorithm is often used for finding optimal solution, but it easily entraps into the local extremum in later evolution period. Based on improved chaos searching strategy, an enhanced particle swarm optimization algorithm is proposed in this study. When particles get into the local extremum, they are activated by chaos search strategy, where the chaos search area is controlled in the neighborhood of current optimal solution by reducing search area of variables. The new algorithm not only gets rid of the local extremum effectively but also enhances the precision of convergence significantly. Experiment results show that the proposed algorithm is better than standard PSO algorithm in both precision and stability.

动态需求跟踪方法及跟踪精度问题研究

在对动态需求跟踪现有研究综述的基础上,详细分析了动态需求跟踪面临的精度问题,并提出了解决方案——动态需求跟踪框架.该框架以自动化的需求跟踪为核心,组合了变更请求、影响分析、变更控制等活动,利用工作产品的特点和迭代过程中累积的变更信息来辅助建立需求跟踪关系,提高了需求跟踪关系的精度.

measuring acoustic wave transit time in furnace based on active acoustic source signal

Accurate measurement of transit time for acoustic wave between two sensors installed on two sides of a furnace is a key to implementing the temperature field measurement technique based on acoustical method. A new method for measuring transit time of acoustic wave based on active acoustic source signal is proposed in this paper, which includes the followings: the time when the acoustic source signal arrives at the two sensors is measured first; then, the difference of two arriving time arguments is computed, thereby we get the transit time of the acoustic wave between two sensors installed on the two sides of the furnace. Avoiding the restriction on acoustic source signal and background noise, the new method can get the transit time of acoustic wave with higher precision and stronger ability of resisting noise interference.

需求变更影响分析模型及相关技术研究

需求是后续开发活动的基准，早期的一些研究者认为应该在需求完全确定之后再进行后续开发，Royce所提出的瀑布模型就是这种思想的一个体现。但是，实践经验告诉我们，不管前期的需求分析做的多么完美，需求还是会发生变更。一方面是因为需求本身很复杂，对它的分析、理解和描述是一个循序渐进的过程，不可能一蹴而就；另一方面由于用户期望和偏好的改变、市场环境的转变、使用环境的日益复杂、技术的革新等都会使得原有的软件系统无法满足各涉众的利益。因此，需求变更是软件开发中固有的规律，是不可避免和普遍存在的。 需求变更通常会导致需求间及需求与后续工作产品间的不一致。因此，频繁的需求变更会造成产品质量下降、进度延期、成本超支等问题。变更影响分析(Change Impact Analysis)通过分析变更对象及其相关工作产品间的关系来评估变更造成的影响，从而控制变更。现有方法多数是从软件维护的角度，对代码的变更影响进行分析，过于细节和技术化，不能对需求变更影响分析提供有力支持。即使针对需求变更的影响分析方法也只是基于形式化需求规约，通过分析需求间的关系来识别影响范围，并未考虑需求变更对后续工作产品造成的影响，同时形式化需求规约的应用困难也限制了该方法的实用性。此外，随着需求和工作产品的规模与复杂性日益增加，使得手工建立和维护需求间及需求与工作产品间关系面临着不小的难度。 基于以上分析，本文提出了针对自然语言需求规约的需求变更影响分析模型RCIAM (Requirement Change Impact Analysis Model)，围绕着如何自动识别和筛选需求间的关系——横向需求跟踪关系(Horizontal Requirement Traceability)、如何自动识别和筛选需求与工作产品间的关系——纵向需求跟踪关系(Vertical Requirement Traceability)、如何较全面的进行需求变更影响计算和决策三个问题展开了研究。 本文的主要贡献有： (1) 提出了需求变更影响分析模型RCIAM 本文对RCIAM进行了形式化定义。该模型不但提供了需求变更影响分析算法和对决策的支持，还提供了自动识别横向和纵向需求跟踪关系的方法。RCIAM主要包含数据处理和数据分析两个层次。数据处理层采用了文本处理(Text Processing)技术实现了横向和纵向需求跟踪关系的自动识别，为数据分析层提供需求跟踪关系数据；数据分析层基于需求跟踪关系数据，在产生需求变更申请(Change Request)时，进行量化影响计算，并提供决策支持。 (2) 提出了横向需求跟踪关系的识别与筛选方法 在对自然语言需求规约文档进行深入分析后，我们发现了两种与需求变更影响密切相关的关系类型，并从文本相似性的角度将它们定义为相似跟踪关系和引用跟踪关系。在将需求项拆分为需求片段的基础上，利用信息检索技术(Information Retrieval，IR)计算需求片段间的文本相似度，并设计了相应的算法对相似跟踪关系和引用跟踪关系进行自动识别。最后，提出了“变更影响跟踪”的规则来辅助对候选跟踪关系的人工筛选。 (3) 提出了纵向需求跟踪关系的识别与筛选方法 已有的研究多采用IR技术来自动建立需求与工作产品之间的跟踪关系，但是却存在着精度不理想的问题。我们从查全率(Recall)和查准率(Precision)的角度，分析了应用IR技术自动建立需求与代码跟踪关系的方法中产生的错误关系，发现了造成精度问题的根源所在。依据这一发现，基于现有方法，本文方法加入了相关反馈(Relvant Feedback)辅助识别和代码注释信息辅助识别等改进措施，并提供了人工筛选策略。 (4) 提出了需求变更影响分析计算与决策方法 本文通过矩阵运算说明了需求变更影响通过需求跟踪关系传播到其它需求和工作产品的过程，并设计了相应的需求变更影响分析算法。该算法考虑变更发生在不同阶段时对不同类型工作产品的影响，采用变更类型和关系强度两个因子加权计算影响值，并提出了根据影响值来进行变更决策的方法。 (5) 应用研究 结合中科方德公司Qone平台的开发，对以上工作进行了应用研究和性能分析。在Qone平台的需求管理工具版本1.0的开发中，首先采用本文方法对横向和纵向需求跟踪关系进行了自动识别，然后对开发期间发生的十次需求变更申请进行了影响分析和决策。在项目完成后，设计了实验对横向和纵向需求跟踪关系的识别进行了性能分析。结果表明，本文方法能够有效辅助进行需求变更影响分析。

Ultrafast sum-frequency polarization beats in twin Markovian stochastic correlation

An analytic closed form for the second- order or fourth- order Markovian stochastic correlation of attosecond sum- frequency polarization beat ( ASPB) can be obtained in the extremely Doppler- broadened limit. The homodyne detected ASPB signal is shown to be particularly sensitive to the statistical properties of the Markovian stochastic light. fields with arbitrary bandwidth. The physical explanation for this is that the Gaussian- amplitude. field undergoes stronger intensity. fluctuations than a chaotic. field. On the other hand, the intensity ( amplitude). fluctuations of the Gaussian- amplitude. field or the chaotic. field are always much larger than the pure phase. fluctuations of the phase-diffusion field. The field correlation has weakly influence on the ASPB signal when the laser has narrow bandwidth. In contrast, when the laser has broadband linewidth, the ASPB signal shows resonant- nonresonant cross correlation, and the sensitivities of ASPB signal to three Markovian stochastic models increase as time delay is increased. A Doppler- free precision in the measurement of the energy- level sum can be achieved with an arbitrary bandwidth. The advantage of ASPB is that the ultrafast modulation period 900as can still be improved, because the energy- level interval between ground state and excited state can be widely separated.

Twin Markovian field correlation on four-level attosecond polarization beats

Based on the phase-conjugate polarization interference between two two-photon processes, we obtained an analytic closed form for the second-order or fourth-order Markovian stochastic correlation of the four-level attosecond sum-frequency polarization beat (FASPB) in the extremely Doppler-broadened limit. The homodyne-detected FASPB signal is shown to be particularly sensitive to the statistical properties of the Markovian stochastic light fields with arbitrary bandwidth. The different roles of the amplitude fluctuations and the phase fluctuations can be understood physically in the time-domain picture. The field correlation has a weak influence on the FASPB signal when the laser has narrow bandwidth. In contrast, when the laser has broadband linewidth, the FASPB signal shows resonant-nonresonant cross-correlation, and drastic difference for three Markovian stochastic fields. The maxima of the two two-photon signals are shifted from zero time delay to the opposite direction, and the signal exhibits damping oscillation when the laser frequency is off-resonant from the two-photon transition. A Doppler-free precision in the measurement of the energy-level sum can be achieved with an arbitrary bandwidth. As an attosecond ultrafast modulation process, it can be extended intrinsically to any sum frequency of energy levels.