Effect of V2O5 and CuO additives on sintering behavior and microwave dielectric properties of BiNbO4 ceramics

The influences of V₂O₅ and CuO additives on the sintering behavior and microwave dielectric properties of BiNbO₄ ceramics were investigated. The V₂O₅ and CuO additives lowered the sintering temperature of BiNbO₄ ceramics to the range 875 °C–935 °C. All BiNbO₄ compounds with additives had the orthorhombic structure. The dielectric constant _r was not significantly changed, while the unloaded Q value was affected with additives. The Qf value was found to be a function of the sintering temperatures and the amount of additives. It varied from 4500 to 15800 (GHz) and 1000 to 8000 (GHz) with additives V₂O₅ and CuO, respectively. The _f values were increased in positive values with V₂O₅ doped, while decreased in negative values with CuO addition. V₂O₅ and CuO additives effectively improved the densification and dielectric properties of BiNbO₄ ceramics. The correlation between the microstructure and the Qf value was observed with different additives.     

Sol–gel derived polycrystalline Cr1.8Ti0.2O3 thick films for alcohols sensing application

The powder sample of Cr_1.8Ti_0.2O₃ (CTO) was obtained by a sol–gel method. The thick films were developed on identical ceramic tubes of 4 mm length comprising of two Au-electrodes and printing an eight-layer film prepared by mixing CTO with glass powder and -terpinol as an organic vehicle. X-ray powder diffraction (XRD) patterns showed the formation of a single phase. The scanning electron microscope (SEM) images of the ceramic sensor treated at 850 °C revealed that the grain size was larger than 400 nm for the individual isolated grains on the surface, and the agglomerated dense spheroidal platelets had the size of 1–4 μm in diameter. The AC impedance measurement in ambient air showed that the resistance decreased nearly by two orders of magnitude with an increase in temperature in the range of 400–600 °C for both the powder sample and the thick film, and the activation energy E_a derived from the measurement was found to be 0.35 and 0.36 eV for the powder and the film, respectively. The films were exposed to various concentrations of alcohols (0.4–1.2 ppm of methanol and 1.0–5.0 ppm of ethanol), followed by determination of sensor response, sensitivity and reversibility and reproducibility. The origin of the gas response was attributed to the surface reaction of R-OH (R = methyl and ethyl group) with O⁻_(ads) to form adsorbed R-CHO, which was desorbed as a gas at 400 °C after the sensor departing from the gas.     

数据库锁资源的自适应管理

锁资源是DBMS的关键资源之一,锁资源的有效管理直接关系到系统性能的高低.提出基于规则引擎和神经网络预测器的锁资源参数自适应管理算法,通过不断监控数据库锁资源性能参数的变化,适时调整锁表参数,提高系统的吞吐量.实验结果显示,系统的吞吐量有16%左右的提高,证明本算法简单可行.     

浅谈材料运用与椅子设计的“骨肉”之情

随着时代的发展,工艺的进步,椅子的制作从木材的榫卯结合到金属材质的焊接再到塑料、玻璃纤维的压模成型;从皮革的缝制到棉麻布艺的胶合剂粘结……为实现椅子的种种功能,设计师们选用了各种材料,椅子也发展得千形万状。材料对于椅子来说是皮、是肉、更是骨。     

基于本体的关系数据库语义检索

以经济学领域本体为例,首先研究SemSORD基本原理和方法,然后提出基于关系数据库关键词检索(Keyword Search over Relational Databases,KSORD)技术实现的关系数据库语义检索模型,并实现相应的原型系统Si-SEEKER,最后提出该领域的研究挑战和技术发展趋势.     

Eutectic Growth in Three Dimensions

Critical experimental studies have been carried out to examine the stability of eutectic morphology in three-dimensional (3-D) samples under diffusive growth conditions. By directionally solidifying capillary samples of the well-characterized Al-Cu eutectic alloy, it is shown that the observed minimum spacing agrees with the value predicted by the Jackson and Hunt (JH) model, but the range of stable spacing is reduced significantly in three dimensions. The ratio of the maximum to minimum eutectic spacing in three dimensions is found to be only 1.2 compared to the predicted value of 2.0 in two dimensions. The narrow range of stable spacing is shown to be due to the instabilities in the third dimension that forms when the local spacing becomes larger than some critical spacing value, which corresponds to the maximum stable spacing. A new mechanism of lamellar creation in the third dimension is observed in which lamella with a local spacing larger than the critical value becomes unstable and forms a sidewise perturbation that becomes enlarged at the leading front and then propagates parallel to the lamella to create a new lamella. Alternately, an array of sidewise perturbations form, which then coalesce at their leading fronts and then become detached from the parent lamella to form a new lamella. This article is based on a presentation made in the symposium entitled “Solidification Modeling and Microstructure Formation: In Honor of Prof. John Hunt,” which occurred March 13–15, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.     

晶界添加氧化物对烧结NdFeB磁性能的影响

为了提高NdFeB磁体的磁性能,通过球磨混粉的方式,研究了通过在晶界上添加MgO,SiO2和CaO对烧结NdFeB磁性能的影响,并采用扫描电镜分析了添加物在晶界相中的分布。研究结果表明,晶界添加适量MgO可实现磁体剩磁、最大磁能积的提高,矫顽力几乎保持不变,在当前实验条件下,当添加量为0.1%时磁性能达到最大值。     

信息与通信安全的未来

现代化的社会中,信息化和网络化已经是社会发展的必然方向,但随着广泛的应用网络技术的使用,人们越来越关注这些领域的安全性,所以在信息与通信安全领域存在着很大的发展前景.     

Web服务在E-Learning中的应用分析

分析了Web服务应用在E-Learning中存在的问题和解决方案,说明利用Web服务可以解决E-Learning发展过程中存在的一系列问题,实现了E-Learning学习资源和系统功能的分布式存储、发现、共享和重用以及动态交换内容,使系统更加灵活和个性化.     

吹气法在线测量折流板脉冲萃取柱脉冲操作参数

在柱径为38、50和100mm的折流板脉冲萃取柱中，以30％TRPO煤油溶液和1mol/LHNO₃溶液为体系，研究吹气法在线测量脉冲萃取柱的脉冲频率和脉冲振幅。实验结果表明：吹气法所得的瞬时压降信号可准确确定脉冲频率，而瞬时压降信号的1个周期面积可确定脉冲振幅。峰面积值与脉冲萃取柱的板数和板开孔率参数成正比，与柱径和脉冲振幅成指数关系。在此基础上，得出了30％TRPO煤油/1mol/LHNO₃体系脉冲振幅的经验关联式，并在两相流条件下得到了验证。