Influence of base resistance on extracting thermal resistance for SiGe HBTs

In this article, the influence of base resistance on extracting thermal resistance for SiGe heterojunction bipolar transistors is studied and an improved approach for determining the junction temperature and thermal resistance is presented. The proposed method for extracting thermal resistance is based on the temperature sensitivity of the base–emitter (B–E) voltage when the device is biased with a fixed emitter current density. This approach not only takes into account the self‐heating during the different ambient temperature measurement but also revises the empirical equation of B–E voltage due to the influence of base resistance during the power dissipation increment measurement. Results are obtained for devices with different emitter lengths and fingers. Compared with the conventional method, the thermal resistance is about up to 15% improvement for the device with 0.3 × 1.9 μm² emitter area and 13.8% for the device with 0.3 × 13.9 μm² emitter area. The accurate thermal resistance implemented in HICUM model has resulted in better fit for transistor output characteristics. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Fuzzy local maximal marginal embedding for feature extraction

In graph-based linear dimensionality reduction algorithms, it is crucial to construct a neighbor graph that can correctly reflect the relationship between samples. This paper presents an improved algorithm called fuzzy local maximal marginal embedding (FLMME) for linear dimensionality reduction. Significantly differing from the existing graph-based algorithms is that two novel fuzzy gradual graphs are constructed in FLMME, which help to pull the near neighbor samples in same class nearer and nearer and repel the far neighbor samples of margin between different classes farther and farther when they are projected to feature subspace. Through the fuzzy gradual graphs, FLMME algorithm has lower sensitivities to the sample variations caused by varying illumination, expression, viewing conditions and shapes. The proposed FLMME algorithm is evaluated through experiments by using the WINE database, the Yale and ORL face image databases and the USPS handwriting digital databases. The results show that the FLMME outperforms PCA, LDA, LPP and local maximal marginal embedding.     

基于STM32的逆变弧焊电源控制器设计

数字化是弧焊电源的发展趋势,其关键在于控制器的数字化。目前市场上的大多数数字化产品价格相对高昂,采用STM32系列单片机进行经济型数字化弧焊电源控制器的设计和实现。该控制器采用数字式PI方法进行输出电流控制,并具有按键操作、液晶显示、过流保护、过热保护等功能。该控制器还具有良好的扩展I}生,可以通过修改程序增强系统功能。     

相对压强对白炭黑氮吸附表面积测试稳定性的影响

研究相对压强对白炭黑氮吸附表面积测试稳定性的影响。结果表明:在相同液氮纯度、脱气温度、脱气时间、氮吸附点数量条件下,与相对压强范围为0.05~0.1时相比,相对压强范围为0.05~0.2时白炭黑的氮吸附表面积测量值偏低,且差值随氮吸附表面积的增大呈增大趋势;相对压强范围较小时,氮吸附表面积测试结果的线性相关因数较大,再现性较好,测试结果较稳定。     

铝储液筒高频感应钎焊的应用研究

对铝储液筒和铝管之间焊接的难点和存在的问题进行了分析,选择高频感应焊接进行生产应用,对铝储液筒和铝管之间高频感应焊接的生产工艺过程,从接头的几何形状及尺寸等,到实际生产的工装使用,进行了生产实验并总结了生产工艺要点,这些方法的实施,较好解决了铝储液筒和铝管之间焊接的难点问题,取得了良好的焊接质量.通过在生产实际中的普及应用,收获了明显的经济效益.其中针对实际应用中的问题给出的解决办法,对于类似铝管类制品之间的焊接,具有重要的指导意义.     

B2O3含量对SiO2-Al2O3-B2O3-RO体系玻璃的性能和微观结构的影响

针对B2O3含量的变化对SiO2-Al2O3-B2O3-RO体系玻璃的介电性能、失透温度和微观结构的影响进行研究分析.研究发现:随着B2O3含量的提高,玻璃的介电常数和介电损耗逐步下降,玻璃的失透温度范围变的更大.而且,B2O3含量升高后玻璃更易于失透,导致玻璃失透的主要原因是玻璃分相;FTIR光谱分析显示,随着B2O3含量的升高,B2O3在玻璃中存在的结构发生了转变,[BO3]逐步向[BO4]进行转变.     

基于电力载波通信的道路照明智能控制系统设计

智能照明是未来道路照明的发展方向.基于电力载波通信技术,设计开发出一套道路照明智能控制系统.该系统无需额外敷设照明控制信号通信线缆,可实现路灯故障自动检测、远距离分组调光控制、单灯调光控制、整体调光控制等,从而实现道路按需照明,为城市道路照明节能化、舒适化、智慧化建设提供了一套系统解决方案.该系统在城市隧道照明节能改造工程试点运行,综合节能率达78.8％.     

一种恒压恒流开关电源设计

分析了开关电源容性负载对电源电路可靠性和环路稳定性的影响,对现有模拟控制方案和数字控制方案进行了对比,提出了基于数字双环控制的恒压恒流控制方式.基于以上分析,较全面评估了恒压恒流控制在超大容性负载电源中的应用.最后,设计了具有恒压恒流控制的模块和常规控制方案电源模块.仿真和试验电路测试结果表明,具有恒压恒流控制的电源模块具有可靠性高、浪涌电流小的优点.     

Nd：NaR（WO4）2晶体光谱性能研究（R=Bi，Y）

采用提拉法生长出了掺钕钨酸铋钠（分子式Nd：NaBi（WO4）2，简称Nd：NBW）和掺钕钨酸钇钠（分子式Nd：NaY（WO4）2，简称Nd：NYW）晶体。通过TG-DTA分析得到Nd：NBW的熔点为936．2℃，Nd：NYW的熔点为1209．07℃。由吸收光谱可以看出，Nd：NBW在802nm有较强的吸收峰，Nd：NYW在804nm，752nm，586nm附近有较强、较宽的吸收峰，二者均适合于LD泵浦；并计算了晶体中Nd^＋3＋的吸收截面积。通过比较Nd：NBW和Nd：NYW的红外光谱和拉曼光谱结果，认为二者结构基本相同，为四方晶系、白钨矿结构、141/a空间群。     

Thermal decomposition kinetics and lifetime of the complex of Tb2（BA）6（PHEN）2

The thermal behavior of Tb2(BA)6(PHEN)2 (BA: benzoate, and PHEN: 1,10-phenanthroline) in a static air atmospbere was investigated by TG-DTG, SEM and IR techniques. By the kinetic method of processing thermal analysis data put forward by Malek et al., it is defined that the kinetic model for the first-step thermal decomposition is SB(m, n). The activation energy E for this step reaction is 99.07 kJ/mol, the entropy of activation ΔS^≠ is -84.72 J/mol, the enthalpy of activation ΔH^≠ is 94.26 kJ/mol, the free energy of activation ΔG^≠ is 144.77 kJ/mol and the pre-exponential factor lnA is 20.93.The lifetime equation at mass-loss of 10% was deduced as lnτ = -29.0312 19760.83/T by isothermal thermogravimetric analysis.