Electrical properties and positron annihilation study of (Ba<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ho<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)TiO<Subscript>3</Subscript> ceramics

DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba_1−x Ho _x )TiO₃ ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba_1−x Ho _x )TiO₃ is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO₃ by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The local electron density and defect concentration estimated using positron annihilation technique conforms well to the features found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model.     

中压变频器在宣钢炼钢厂除尘风机中的应用

本文介绍了SIMOVERT MV中压变频器在宣钢炼钢厂一次除尘风机中的应用情况。变频器现场运行表明，采用中压变频器对转炉除尘风机进行调速节能获得了成功，节能效果明显。     

Anomalous splitting in microwave mode-beating spectra of semiconductor ring lasers

Mode-beating spectra are investigated in long-perimeter (1.028 cm) monolithically integrated multiple-quantum-well semiconductor ring lasers. The beating line near 8 GHz is found to be split into two components. With increasing pumping current, a normal component shifts to lower frequencies, while an anomalous higher-frequency component shifts in the opposite direction. It is suggested the anomalous blue-shifting line results from power-induced perturbation of the refractive index in the vicinity of a strong mode.     

室外LED显示及其在交通领域的应用

介绍了室外LED显示技术及其在道路交通信息显示领域中的应用,指出目前国内室外LED显示屏普遍存在的主要问题.结合应用于高速公路收费站的LED显示屏的设计,给出解决或者克服这些问题的方法.介绍了室外LED显示的现状,预测了其发展趋势.     

Transformations for nonideal uniform circular arrays operating in correlated signal environments

The Davies transformation is a method to transform the steering vector of a uniform circular array (UCA) to one with Vandermonde form. As such, it allows techniques such as spatial smoothing for direction-of-arrival (DOA) estimation in a correlated signal environment, developed originally for uniform linear arrays, to be applied to UCAs. However, the Davies transformation can be highly sensitive to perturbations of the underlying array model. This paper presents a method for deriving a more robust transformation using optimization techniques. The effectiveness of the method is illustrated through a number of DOA estimation examples.     

基于预前控制异步电机直接转矩控制方案的研究

在传统异步电动机直接转矩控制方案中，由于负载的变化规律不可预测，因此其常会带来较大的开关频率的变化，为此提出了一种基于预前控制的异步电动机直接转矩控制的方法。该方法依据前一个周期的磁链和转矩误差，对下一个开关周期所应施加到异步电动机的定子电压矢量进行预测，然后借助空间矢量PWM的方法，合成此开关电压矢量。样机实验结果表明，该方案不但能维持逆变器的开关频率基本恒定，而且还具有比传统直接转矩控制更为优良的动静态特性。     

新疆重质混合原油研制高等级道路沥青

对利用新疆重质混合原油生产的减压渣油作为基质沥青制备高等级道路沥青进行了研究。考察了低硫石蜡基原油（A）和含硫环烷-中间基原油（B）的掺炼比对基质沥青四组分组成的影响，减压渣油软化点与基质沥青四组分组成的关系，以及添加剂对改进沥青性质的作用。由此得出原油（B）的合适掺炼量，减压渣油软化点的控制范围和优化的生产工艺条件，调合出了符合GB／T18150—2000和JTGF40—2004要求的高等级道路沥青。     

Characterization of ultrashort optical pulses with third-harmonic-generation based triple autocorrelation

We present a method to obtain complete information of femtosecond pulses. By measuring triple-optical autocorrelation directly with third-harmonic generation, without spectral information, a temporal pulse shape can be obtained by analytical calculation without direction-of-time ambiguity. Combining the resulting optical pulse shape with its corresponding optical spectrum, the exact phase and color variations in time can all be recovered with a Gerchberg-Saxton algorithm through an iterative calculation with an O(n) complexity.     

Impact of temperature cycle profile on fatigue life of solder joints

In this paper the influence of the temperature cycle time history profile on the fatigue life of ball grid array (BGA) solder joints is studied. Temperature time history in a Pentium processor laptop computer was measured for a three-month period by means of thermocouples placed inside the computer. In addition, Pentium BGA packages were subjected to industry standard temperature cycles and also to in-situ measured temperature cycle profiles. Inelastic strain accumulation in each solder joint during thermal cycling was measured by high sensitivity Moire interferometry technique. Results indicate that fatigue life of the solder joint is not independent of the temperature cycle profile used. Industry standard temperature cycle profile leads to conservative fatigue life observations by underestimating the actual number of cycles to failure.