通过再燃降低炉膛NO_x技术中再燃燃料制备问题探讨

燃料再燃是降低NOx的一项新技术。其原理是炉膛内已经生成的NOx遇到CHi、未完全燃烧产物CO、C和未完全燃烧中间产物HCN、CNNHi基团时，会被还原为N2。再燃技术实施时，一般将炉膛分为3个燃烧区域：主燃烧区、再燃区和燃尽区。80％左右的燃料进入主燃烧区，在过量空气系数人于1条件下燃烧，生成一定量的NOx。其余20％左右的燃料作为再燃燃料送入再燃区。     

新型半导体断路开关及其脉冲功率发生器

基于半导体断路开关（SOS）的脉冲功率发生器是一种新型的全固态开关系统，具有输出脉冲电压高、使用寿命长、可靠性和重复率高的特点。本文详细介绍了SOS效应与断路开关的工作原理，研究了基于SOS的脉冲功率发生器电路结构并对开关电流进行仿真，仿真结果与国外器件的实测特性相近。     

Accelerometer-based position and speed sensing for manual pipe welding process

For manual pipe welding process, welding position and speed are two of the most important welding parameters. Highly skilled pipe welders can well adjust their operation to produce high-quality welds. However, even experienced welders may sometimes have defected welds due to improper welding speed. The weld quality will be better guaranteed if the welding position and speed can be measured and other welding parameters can be changed accordingly. This paper introduced the development and experiment results on a practical accelerometer-based torch sensor to measure torch position and speed. Based on the measured acceleration data, the two important welding parameters were calculated with moderate computing load by an embedded control system. For future work, the welding position and speed calculation with sufficient accuracy can help the design of advanced control algorithm to various pipe welding processes.     

An in-depth investigation into the relationships between structural metrics and unit testability in object-oriented systems

There is a common belief that structural properties of classes are important factors to determine their unit testability.However,few empirical studies have been conducted to examine the actual impact of structural properties of classes.In this paper,we employ multiple linear regression(MLR) and partial least square regression(PLSR) to investigate the relationships between the metrics measuring structural properties and unit testability of a class.The investigated structural metrics cover five property dimensions,including size,cohesion,coupling,inheritance,and complexity.Our results from open-source software systems show that:(1) most structural metrics are statistically related to unit testability in an expected direction,among which size,complexity,and coupling metrics are the most important predictors;that(2) multivariate regression models based on structural metrics cannot accurately predict unit testability of classes,although they are better able to rank unit testability of classes;that(3) the transition from MLR to PLSR could significantly improve the ability to rank unit testability of classes but cannot improve the ability to predict the unit testing effort of classes.     

Study on co-occurrence character networks from Chinese essays in different periods

Co-occurrence networks of Chinese characters are constructed from collections of essays in different periods of China:the ancient Chinese language,the Chinese language in Wei,Jin,and Southern-Northern Dynasties,the recent Chinese language,and the modern Chinese language,and their statistical parameters are studied.It has been found that 99.6% networks have the scale-free feature and 95.0% networks have the smallworld e?ect.This study reveals some commonalities and di?erences among articles in different periods of China from a complex network perspective.There has been a controversial question as to whether the literatures in Wei,Jin,and Southern-Northern Dynasties should belong to the ancient Chinese language or the recent Chinese language in the linguistic study.Our work shows that the statistical parameters of networks in Wei,Jin,and Southern-Northern Dynasties are clearly different from those of networks in the other periods of China,and it seems more reasonable that the literatures in Wei,Jin,and Southern-Northern Dynasties belong to the recent Chinese language.     

Improved empirical DC Ⅰ-Ⅴ model for 4H-SiC MESFETs

A novel empirical large signal direct current （DC）Ⅰ-Ⅴ model is presented considering the high saturation voltage, high pinch-off voltage, and wide operational range of drain voltage for 4H-SiC MESFETs. A comparison of the presented model with Statz, Materka, Curtice-Cubic, and recently reported 4H-SiC MESFET large signal Ⅰ-Ⅴ models is made through the Levenberg-Marquardt method for fitting in nonlinear regression. The results show that the new model has the advantages of high accuracy, easily making initial value and robustness over other models. The more accurate results are obtained by the improved channel modulation and saturation voltage coefficient when the device is operated in the sub-threshold and near pinch-off region. In addition the new model can be implemented to CAD tools directly, using for design of 4H-SiC MESFET based RF＆MW circuit, particularly MMIC （microwave monolithic integrate circuit）.     

泸州老窖国窖曲曲坯层次间微生物差异研究

系统地研究了泸州老窖国窖曲不同层次间微生物数量、种类和优势种群差异及规律。结果表明:国窖曲层次间微生物数量、种类和优势种群差异较大,其中曲侧表层和曲包表层微生物数量多,以霉菌为主,微生物种类少,优势菌是根霉;曲包心、曲心、曲底表层微生物数量少,以细菌为主,优势菌是芽孢细菌,微生物(主要是细菌)种类较多;青霉和犁头霉主要分布在曲底层;黄曲霉、红曲霉、酵母菌均匀分布在曲坯各层。     

Numerical and experimental analysis of the reusability of spring energized metal C rings

It is well known that static seals are usually designed to be used once.In this paper,we discuss the reusability of a type of static seal called the spring energized metal C ring,which is required to be reused 4–5 times without maintenance during the lifetime of the pump.A theoretical analysis based on the nonlinear finite element method and an experimental investigation of the reusability of the C ring are carried out.The effects of the elastic modulus of the ring material,the ring wall thickness,the amount of assembly interference between the spring and the C ring,the operating temperature and the compression ratio are discussed.The parameter S,which denotes the reaction force difference percentage,is determined to measure the reusability of the C ring.The results show that the ring wall thickness plays an important role in the reusability.Although the normal force of a thick wall decreases after the ring is reused eight times,the value is still higher than the first normal force of a thin wall.In contrast,the elastic modulus of the material has the lowest impact.Here,a pre-compression ratio of 18.2%not only produces a larger first normal force but also leads to a smaller reduction in the normal force when the ring is reused.A simulated experiment is carried out to investigate the influence of the coating of the C ring on its reusability.The results show that when plastic deformation occurs on the contact surface,the contact state of the C ring coating becomes a major factor that affects the seal performance.Aging treatment at high temperatures(250°C)reduces the binding force of the silver coating on the spring energized metal C ring,which leads to the deterioration in the reusability of the ring.     

Control of 3D weld pool surface

The 3D weld pool surface in gas tungsten arc welding (GTAW) is characterized by its width, length, convexity and measured in real-time using an innovative machine vision system. The dynamic response of these characteristic parameters to welding current and speed as control variables is modeled. Based on the identified dynamic model, a predictive control algorithm is developed to control these characteristic parameters. The proposed algorithm is given in a closed form and no online optimization is required. Welding experiments confirm that the developed control system is effective in achieving the desired 3D weld pool surface geometry despite various disturbances.     

Measurement of mirror surfaces using specular reflection and analytical computation

In many applications, it is desirable to know three-dimensional information of mirror surfaces. However, the reflective characteristic of mirror surfaces makes many traditional three-dimensional reconstruction methods, such as stereovision or structured light scanning, fail. In this paper, a novel method is proposed to measure mirror surfaces. It is implemented with practical hardware and software that directly obtain analytic solutions for three-dimensional points on a mirror surface. Experimental results verified the effectiveness of the proposed method. In particular, this proposed method aims at providing an effective method to reconstruct specular weld pool surfaces which typically are highly dynamic and irregular. The capability to directly obtain analytic solutions for a set of points from a mirror surface as proposed and developed in this paper is a key to effectively measuring such highly dynamic and irregular mirror surfaces.