Influence of SiO2 and CaO additions on the microstructure and magnetic properties of sintered Sr-hexaferrite

The effect of simultaneous addition of CaO and SiO₂ on the microstructure and magnetic properties of sintered SrO-excess Sr-hexaferrites was studied. Both additives markedly affect the grain growth behavior and the magnetic properties. CaO-additions promote densification, which results in increased remanence, but due to simultaneuous grain growth the coercivity drops to <100 kA/m. SiO₂ additions are known to suppress grain growth. Simultaneous addition of CaO and SiO₂ is shown to be very beneficial in tailoring a dense microstructure with relatively small grains. The ratio of CaO/SiO₂ was found to be optimum at about 1, and magnets with a remanence of 430 mT and a coercivity of 300 kA/m were obtained. Transmission electron microscopy (TEM) studies and investigations by energy-dispersive analysis of X-rays (EDX) in the scanning TEM (STEM) mode show that both CaO and SiO₂ are concentrated at grain boundaries and grain junctions forming an amorphous secondary phase.     

利用开源系统优化数字图书馆的高级应用

在信息急剧膨胀的今天,中国图书馆界已跨入数字图书馆阶段,但图书馆的技术力量相对薄弱,其服务手段和技术仍不能满足需要速成服务的读者,数字图书馆不能仅仅以搜索框的形式被动出现,图书馆人必须改善条件,应用新的技术来应对新的需求。本文将介绍一种技术:Drupal,并在此基础上优化数字图书馆的高级应用。     

虚拟样机协同设计并发控制策略研究 *

针对虚拟样机协同设计中数据量大、事务长、多层嵌套的问题 ,提出了一种基于事务语义的并发控制策略,阐述了并发控制机制中事务结构、事务提交、锁机制和冲突协调等关键性问题。根据数据要求生成复制事务,事务发生改变后 ,其他站点能够实时显示图形、实时读取数据。实例证明 ,基于事务语义的并发控制策略保证协同用户自由地操作共享资源 ,提高了并发控制的可靠性和数据的一致性。     

基于课程延续性的VFP教学改革

本文通过分析Visual Foxpro课程教学中存在的问题,从课程的延续性角度进行了教学改革探讨,在VFP与力公自动化软件数据交换方面,提出了合理编写教材、改革理论教学方法和加强实践教学等多种教改方法,同时对实践结果进行了分析。     

基于双处理器的自动准同期装置设计

电力系统运行中发电机的并网操作是一项基本的操作,它在操作准确、并网迅速的前提下,要求有极高的可靠性与稳定性来保证安全。论述了在双处理器(一个工作,另一个处于热备用的运行模式)的基础上实现的自动准同期装置,采用硬件冗余技术保证高可靠性;应用线性插值算法预测来自动捕捉合闸时机,能实现高精度、快速、可靠、平稳的并网操作。装置主要用于要求可靠性高且并网速度快、同期精度高的场合,如较大(100 MW以上)发电机的同期合闸操作,具有较好的应用前景。     

Role of gallium ion on the conducting properties of La0.7(Ba,Sr)0.3Mn1−xGaxO3 (x=0.0, 0.1 and 0.2) perovskite

The transport properties of Ga-doped La_0.7(Ba, Sr)_0.3Mn_1−xGa_xO₃ (x=0.0, 0.1 and 0.2) perovskite materials were investigated by admittance spectroscopy over a wide range of temperatures and frequencies. The electronic conduction was found to be dominated by thermally activated hopping and to depend strongly on Ga-content. Results have shown samples with x=0.0 and 0.1 exhibit a metallic behavior at low temperature and a semiconducting one at high temperature. The temperature (T_MI) of the metal–insulator transition was found to be about 180 and 120 K for samples with x=0.0 and 0.1, respectively. Ga doping leads to a depletion in the number of hopping electrons, which suppresses metallicity and pushes the system in semiconductor side. Besides, the activation energy (E_a) deduced from the variation of conductance as a function of temperature, was found to increase from 89 to 165 meV when x increased from 0.0 to 0.2. This increase can be explained by the decrease of charge carriers with increasing Ga-content.     

Influence of Zr/Ti atomic ratio and seed layer on the magnetoelectric coupling of Pb(ZrxTi1−x)O3 film-on-CoFe2O4 bulk ceramic composites

Lead zirconate titanate Pb(Zr_xTi_1−x)O₃ films with various Zr/Ti ratios of 20/80, 40/60, 52/48, 60/40 and 80/20 are deposited on highly dense CoFe₂O₄ ceramics using a simple chemical solution deposition. All Pb(Zr_xTi_1−x)O₃ films are polycrystalline and have no preferential orientations. The dielectric, ferroelectric, piezoelectric and magnetoelectric properties strongly depend on the Zr/Ti ratio. And the Pb(Zr_xTi_1−x)O₃ films with a Zr/Ti ratio close to morphotropic phase boundary exhibit best properties, whose magnetoelectric coefficient is over 1.5 times larger than those of other Zr/Ti ratios. The introduction of a PbO seeding layer between the Pb(Zr_0.52Ti_0.48)O₃ films and CoFe₂O₄ substrates facilitates the (100)-texture. Therefore, the magnetoelectric coefficient was enhanced by 1.5 times. The further improvement of the magnetoelectric coupling could be anticipated by fabricating Pb(Zr_0.52Ti_0.48)O₃ films with more or absolute (100)-texture and using conductive interfacial layer between two phases.     

基于网络技术的实时协同设计并发控制策略研究

为了解决计算机辅助协同设计中重启动频繁、死锁等问题，建立了一种实时协同设计并发控制模型。针对协同设计中数据量大、事务长、多层嵌套的特点，采用操作优先权模糊控制策略。通过图形对象全局ID和实体属性表的一致性维护，系统能够根据运行情况和用户需求自动进行操作优先权控制策略的调整。建立了并发控制机制中事务结构、事务提交、锁机制和冲突协调的联系，事务发生改变后其它站点能够实时显示、实时读取有效数据。实例证明，并发控制策略不仅让协同用户自由地操作共享资源，还能够保证具有高并发率和数据的实时一致性。     

基于后向区间选择偏最小二乘算法的软测量建模

偏最小二乘是在光谱多变量校正中广泛使用的一种算法,现已经发现高效的变量选择不仅能够提高模型的预测能力,也可大大降低模型的复杂度。为了建立具有鲁棒性和低复杂度的基于光谱的在线软测量模型,考虑到光谱变量之间高度相关这一事实,提出一种基于后向区间选择策略的偏最小二乘算法。该算法主要步骤是:先将光谱波长域细分为一定数量的等长子区间;再采用后向淘汰的策略,将各个子区间逐步淘汰,形成一个淘汰序列;最后,再反向选择一定数量的子区间建立最终的模型。通过一个实例以及与传统基于全谱的偏最小二乘算法比较,显示出了该算法的在建立软测量模型方面的优良性能。     

新型抗野值的Kalman滤波器研究

在Kalman滤波的量测值中,经常出现连续、成片的野值,不仅严重地影响了其稳定性,而且造成滤波精度下降。针对这一问题,提出一种基于可调因子的新型抗野值Kalman滤波器方法。该方法以野值新息均值和均方差为输入变量,利用模糊控制器改变可调因子的大小,从而实现新息的自动调整,即当新息较小时,对野值进行修正,而当新息较大时,剔除野值。仿真结果显示,该方法抗野值效果良好,提高了滤波精度。