Effects of defect dipoles on tunable dielectric response in relaxor ferroelectric ceramics

Tunable dielectric materials have drawn much attention due to their wide applications including capacitors and microwave tunable devices. Ferroelectrics materials have special spontaneous polarization which can be reversibly switched by an external electric field. Therefore, tunable dielectric constant can be easily achieved in ferroelectrics. However, the study of nonlinear dielectric response induced by defect dipoles is rarely concerned. Here, we report the effects of defect dipoles on tunable dielectric response under alternative current (AC) and direct current (DC) electric field in defect dipoles introduced Pb(Lu_1/2Nb_1/2)O₃–PbTiO₃ ceramics. A modified Rayleigh model is proposed to successfully characterize dielectric nonlinearity and reveals the interaction between domain walls and defect dipoles. The defect dipoles had more sensitive effect on dielectric response under AC field than that of defect dipoles-free samples. The drop of intrinsic dielectric contribution under AC field results from the detriment effect of defect dipoles. The irreversible contribution is altered by the movements of defect dipoles under AC field, subsequently inducing the nonlinearity of dielectric response. Samples with defect dipoles have larger tunable scope of dielectric properties than that of defect dipoles-free samples. The present work discovers the potential of application of defect dipoles-tuned dielectric response ferroelectrics in devices which requires both high AC and DC biases, and help to better understand the complex dielectric response of ferroelectrics.     

Reversible and irreversible domain wall dynamics in [011]C oriented relaxor ferroelectric single crystals

Domain wall motions mainly affect all kinds of properties of ferroelectric materials, such as piezoelectricity, dielectric response, and mechanical loss, and the extrinsic contributions associated with domain wall motions have always been an important issue. In this study, the reversible and irreversible extrinsic contributions to the dielectric properties of [011]_C-oriented 0.27Pb(In_1/2Nb_1/2)O₃-0.46Pb(Mg_1/3Nb_2/3)O₃-0.27PbTiO₃:Mn single crystals have been extracted by the Rayleigh analysis. We found that in the unpoled samples, the extrinsic contributions of reversible and irreversible domain wall motions to dielectric properties significantly reduced, whereas after poling, only the irreversible extrinsic contribution decreased. The pinning effect in the 2R domain structure is much weaker than that in the 4R domain structure, leading to the low enhancement of Q_m and a slight decrease in piezoelectricity caused by acceptor doping in 2R domain structure. This study explores the domain wall dynamics of acceptor-doped single crystals and mainly guides on further performance optimization in PbTiO₃-based relaxor single crystals.     

广西信息产业对经济增长的贡献分析

通过估算1995年到2003年广西信息产业的名义增加值和实际增加值,运用贡献模型分析了其对广西经济的名义贡献和实际贡献,从而了解到广西的信息产业经过多年的发展,虽初具规模,但还是比较落后的.由于受到资金、时间、人才等方面的限制,广西发展信息产业不能在所有领域全面出击,必须根据自己本身的各方面的优势来考虑信息产业发展的重点布局,实行反梯度推移战略,大力发展软件产业,实现广西信息产业的跨越式发展,从而达到改变广西信息产业的落后局面.     

Multiway independent component analysis mixture model and mutual information based fault detection and diagnosis approach of multiphase batch processes

Batch process monitoring is a challenging task, because conventional methods are not well suited to handle the inherent multiphase operation. In this study, a novel multiway independent component analysis (MICA) mixture model and mutual information based fault detection and diagnosis approach is proposed. The multiple operating phases in batch processes are characterized by non‐Gaussian independent component mixture models. Then, the posterior probability of the monitored sample is maximized to identify the operating phase that the sample belongs to, and, thus, the localized MICA model is developed for process fault detection. Moreover, the detected faulty samples are projected onto the residual subspace, and the mutual information based non‐Gaussian contribution index is established to evaluate the statistical dependency between the projection and the measurement along each process variable. Such contribution index is used to diagnose the major faulty variables responsible for process abnormalities. The effectiveness of the proposed approach is demonstrated using the fed‐batch penicillin fermentation process, and the results are compared to those of the multiway principal component analysis mixture model and regular MICA method. The case study demonstrates that the proposed approach is able to detect the abnormal events over different phases as well as diagnose the faulty variables with high accuracy. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2761–2779, 2013     

合成羧乙基硫代丁二酸的热力学计算与分析

以3-巯基丙酸和马来酸为原料合成羧乙基硫代丁二酸,选用较准确的基团贡献法估算了反应体系中各组分的标准生成焓、标准生成自由能、标准熵和热容等热力学数据,推导出了反应焓、反应自由能和反应平衡常数随温度的变化关系式。通过对反应体系的热力学计算与分析,验证了该反应在热力学上的可行性。     

土壤中LNAPL的自然衰减实验研究

目前,石油污染及其治理问题受到环境工作者的广泛关注。本文选用柴油作为LNAPL的代表,通过实验分析了LNAPL的自然衰减规律(挥发作用、生物降解作用和吸附作用等),估算了低浓度时各种作用对土壤中柴油去除的贡献率。结果表明,土壤中的LNAPL在自然条件下能发生一定的衰减作用,而且当浓度较低时,自然衰减作用对柴油去除率较高,达到了62.86%。因此,在适当的条件下,利用LNAPL的自然衰减作用可以有效地分解LNAPL化合物,达到降低污染物浓度的目的,为进一步研究LNAPL的治理和防护奠定了基础。     

基于特征贡献率的机械故障分类方法

为提高往复压缩机、航空发动机等复杂机械故障分类的准确率,依据特征参数对不同故障的敏感度存在差异的特性,提出一种狄利克雷过程混合模型(Dirichlet process mixture model,简称DPMM)与贝叶斯推断贡献(Bayesian inference contribution,简称BIC)相结合的分析方法。采用DPMM方法自学习机械振动信号高维特征的统计分布模型,并依据BIC理论计算得到各特征参数对模型的贡献率,通过对比观测数据与各类故障数据特征贡献率间的差异实现故障分类。试验结果表明,该方法的平均分类准确率比基于高斯混合模型(Gaussian mixture model,简称GMM)的故障诊断方法的平均分类准确率提高19.29%,比基于Relief算法的故障诊断方法的平均分类准确率提高32.71%,且该方法的时效性高,泛化性能强,能够更有效地进行复杂机械故障分类。     

基于朴素贝叶斯分类器的公共自行车系统故障诊断方法

针对公共自行车没有安装车载检测传感器、流动及停放区域较大、管理部门无法及时发现自行车故障等问题,提出了基于朴素贝叶斯分类器的自行车故障诊断方法。通过分析公共自行车系统(PBS)租用记录、维修记录和用户评价,选取15个状态分类特征作为自行车故障检测的特征向量;根据朴素贝叶斯分类器后验概率,获取每个状态分类特征对类的贡献率;以召回率作为评价指标来预测诊断故障自行车。采用杭州市PBS 2016年的相关数据对模型进行实践验证,通过预测模型输入特征值的优化,测试样本的召回率达85.79%,精度较为理想。     

基于特征相对贡献度对加权Mel倒谱的改进

在声纹识别系统的搭建过程中,提高识别率的一个重要做法是使语音信号中能够提取出的特征尽可能包含更多的说话人个性特征.为了探究特征参数各分量对识别系统性能的影响,文章基于高斯混合-通用背景模型(Gaussian Mixture Model-Universal Background Model,GMM-UBM)基线系统,研究...     

气候变化和人类活动对黄河流域内蒙古段典型支流径流变化的贡献

以黄河流域内蒙古段典型支流旗下营、准格尔站点控制流域为基础,采用累积量斜率变化率比较法,定量分析了径流变化、气候变化和人类活动对径流变化量的贡献。结果表明,径流量多年来呈减少趋势,随降水的增加而增加,随平均气温的升高而减少。径流量2000 s最小,相对1990 s减少了45.67%~58.26%。径流突变点为1981年。1981~2010年与1957~1980年相比,旗下营、准格尔两个水文站点控制流域气候变化对径流减少的贡献率分别为12.80%和23.46%,人类活动对径流减少的贡献率分别为87.20%和76.54%。