On the Feasibility of Growing Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Single Crystals

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by two methods: from solution using PbO as a self‐fluxing agent (SC method) and directly from the melt without fluxing (MC method). In both growth methods, an allomeric Pb[(Mg_1/3‐Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal was used as a seed. X‐ray diffraction patterns of ground crystals showed that phase‐pure perovskite PZNT91/9 single crystals were successfully fabricated by the above two methods. The composition of the crystals obtained by both the SC and MC methods was analyzed using X‐ray fluorescence, which confirmed that the crystal composition is close to the nominal value, although volatilization of PbO and segregation during crystal growth are inevitable. The MC PZNT91/9 crystals exhibit excellent piezoelectric properties, with the piezoelectric constant, d₃₃, in the range of 1800–2200 pC N^–1. This value is comparable to that of the SC crystals. However, the MC crystals show an abnormal dielectric behavior. In contrast with the SC crystals, in the MC crystals a much broader dielectric peak appears in the dielectric response curves, accompanied by a much lower peak temperature of around 105 °C. Furthermore, frequency dispersion is apparent over a much wider temperature range (even more apparent than in pure relaxors), where a large, i.e., about 70 °C, full width at half maximum (FWHM) for the dielectric peaks is observed in the dielectric response. It is speculated that such an unusual phenomenon correlates with defects, microinhomogeneities, and polar regions in the as‐grown MC crystals. The origins of this abnormality have not been interpreted in detail until now. However, optical observation of the domain structure confirms that both the SC and MC crystals possess complex structural states.     

ZrSiO4/α-Al2O3反应烧结过程中非晶态物质的形成与演化

采用XRD和TEM等技术研究了ZrSiO4/α-Al2O3反应烧结过程中非晶态物质的形成及演化。结果表明，1400℃莫来石开始形成时体系中的液相是富Al2O3的，随着温度的升高，ZrSiO4分解速率加快及富Al2O3莫来石的形成，液相逐渐向富SiO2方向演化，液相的形成及其演化与莫来石的形成密切相关。     

Finite element analysis of advanced multilayer capacitors

We establish a systematic methodology to design and analyse electromagnetic components such as advanced multilayer ceramic capacitors (MLCCs) using the finite element (FE) method. We employ a coupled formulation to compute the interaction between the electric and magnetic fields. Unlike a linear distribution of current assumed in the circuit model, an accurate electrostatic solution to model the entire advanced MLCCs (4 × 4 × 27 = 432 cells) is presented. The FE solution is used to compute the lumped parameters for a range of frequencies. These lumped parameters are then used to compute the parasitic elements of the MLCCs. We introduce two algorithms to efficiently analyse the behaviour of a capacitor with changing frequency. The lower frequency (much below the self‐resonant frequency of the capacitor) algorithm separates the effect of the electric and magnetic fields and reduces the computational effort required to solve the FE problem, whereas, the high‐frequency algorithm couples the effect between the electric and the magnetic fields. We use these algorithms in conjunction with a new multiple scale technique to effectively determine the small values of R, L and C in MLCCs. The formulation, the implementation, and the numerical results demonstrate the efficacy of the present FE formulation and establish a systematic methodology to design and analyse advanced electromagnetic components. Copyright © 2003 John Wiley & Sons, Ltd.     

Mass Transfer in a Flat Gas/Liquid Interface using non‐Newtonian Media

Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients.     

一种平面结构的V波段上变频器

介绍了平面结构的V波段变频器，该变频器采用平衡变频结构，变频电路主体为平面结构，同时采用了E面探针结构的波导微带转换作为射频信号输出，文中给出了该上变频器的电路软件仿真结果和实测结果以及E面探针波导微带转换的仿真和测试结果，最后给出了该上变频器的实物结构。     

Development of core mode blocker with H/sub 2/-loaded Ge-B codoped fibres

A novel fabrication method of the core mode blocker by exposing H/sub 2/-loaded Ge-B codoped fibres to local electric arc discharge for application to the LPFGs-based tunable all-fibre bandpass filter with 6.5 nm bandwidth and 40 nm tuning range is presented.     

Study of Disk-Loaded Waveguide Filled with Plasma

Recently disk-loaded waveguide has been widely used in high-power traveling wave tubes (HPTWT). It has been shown in many experiments that the interaction efficiency and output power can be increased greatly by injecting plasma into the vacuum microwave device. Using field analysis, the dispersion characteristics and the interaction impedance of the disk-loaded waveguide filled with plasma are analyzed in a strong longitudinal magnetic field. In conclusion, the frequency of the TM₀₁ mode increases as the density of the plasma increases. It also can be found when the plasma density increases to a large scale, the TM₀₁ mode of the disk-loaded waveguide overlaps the TG mode, these two modes couple each other and form the new hybrid modes.     

大型结构试验和结构监测中的数据采集系统

结构试验和结构监测正在向大型化和复杂化发展,与之配套的数据采集系统也要能满足它们不断增长的需求。清华大学土木工程系开发了适用于土木工程结构试验与监测的集成数据采集系统 IMPDAS,它具有测点多,速度快,功能全等优点。它的任务,不仅仅是记录数据,而是集成并且管理数据,将各种数据信息有条理,有重点地反馈给试验者。本文将讨论计算机在大型结构试验和结构监测的数据采集及数据处理分析等方面的应用。     

西北低煤阶盆地生物成因煤层气成藏模拟研究

在美国粉河、澳大利亚苏拉特等低煤阶盆地煤层气勘探取得突破以前,一直认为具有商业价值的煤层气资源主要存在于中煤阶的煤层中,煤阶太低,一般含气量不高,不具有勘探价值。但是近几年来的发现证实,低煤阶盆地煤层厚度大,渗透率高,资源丰度大,含气饱和度高,同样可获得商业性气流,而且从其气体的成因来看,其中有很大一部分是生物成因的煤层气。利用煤层气成藏模拟装置对低煤阶含煤盆地的煤岩样品开展成藏模拟,从实验角度证明了中国西北地区虽然煤层煤阶较低,热成因气较少,但是却存在着具有商业价值的二次生物成因的甲烷气,再加上含煤层系众多,煤层厚度大,资源丰度极高,仍具有巨大的勘探潜力。