奇异最优控制的开关结构研究

概述了奇异最优控制问题最优解的必要条件,讨论了边界条件、控制约束及末时间对控制函数开关结构的影响.讨论和计算实例表明,多目标打靶法(Multiple Shooting Method)是计算奇异最优控制问题的有效算法.     

各种软开关变换器的工作方式和存在的问题

以较大容量的变换器为对象,简略介绍了各种软开关变换器的原理、主要工作方式及其优缺点,归纳总结了软开关变换器的三种变换方式,列举了九种软开关变换器的电路形式。     

滑模变结构控制在DC-DC变换器中的应用

采用了一种控制DC－DC变换器的新型滑模控制器。利用该控制器可以产生优化PWM，以满足预期闭环动态性能。为了抑制抖振，提出了一种模糊滑模变结构控制器。仿真结果表明，应用滑模变结构理论控制DC－DC变换器不仅简化了设计和易于实现简单而且性能优良，模糊变结构控制优于传统滑模变结构控制。     

基于多要素的LTE系统切换算法与仿真

当前移动通信技术快速发展,WCDMA、TD-SCDMA移动系统都将通过LTE演进到4G。传统的LTE系统切换算法有:基于RSRP测量的硬切换算法、基于RSRP及RSRQ测量的联合的硬切换算法。但都无法提供最好的切换判断分析,从而导致切换频繁或切换失败。为了改进LTE系统传统切换算法,文章提出了基于多要素的切换算法,分析了基于多要素切换算法改进的思路。通过对小区负载水平方面仿真,仿真结果表明:小区初始负载水平越轻,UE在该小区驻留的时间越长;负载越重,UE在该小区驻留的时间越短。     

Ferroelastic domain switching and R-curve behavior in lead zirconate titanate (Zr/Ti = 52/48)-based ferroelectric ceramics

In this work, ferroelastic domain switching and R-curve behavior in lead zirconate titanate (Nb/Ce co-doped Pb(Zr_0.52Ti_0.48)O₃, ab. PZT-NC)-based ferroelectric ceramics were investigated, using the indentation-strength-in-bending (ISB) method. Firstly, Vickers indentation test examined the notable fracture anisotropy of PZT-NC ceramics between the poling direction and its perpendicular direction, and the crack open displacement (COD) profiles in the two directions were also theoretically calculated from the indentation fracture mechanics. And then two kinds of ferroelastic domain switching modes (in-plane and out-of-plane) were used for explaining such anisotropic propagation behavior of indentation cracks. The subsequent three-point bending test illustrated the dependence of fracture strength on indentation load and the rising crack growth resistance curves (R-curves) in two directions. The resulted R-curves were fitted by the Hill's type Growth Function successfully, giving the reasonable values of crack extension exponential (n), plateau fracture toughness (K_max), and initial fracture toughness (K_ini). The in-plane ferroelastic domain switching was identified as a more significant toughening mechanism for PZT-NC ceramics than the out-of-plane switching due to more switchable domains.     

Bipolar resistive switching behavior and conduction mechanisms of composite nanostructured TiO2/ZrO2 thin film

In this work, TiO₂/ZrO₂ bilayer thin film was prepared on fluorine doped tin oxide (FTO)/glass substrates by using a simple and low-cost chemical solution deposition method. Reproducible bipolar resistive switching (RS) characteristics in Au/TiO₂/ZrO₂/FTO/glass devices are reported in this work. TiO₂/ZrO₂ bilayer thin films prepared in this work shows reversible bipolar resistive switching and unidirectional conduction performances under applying voltage and these special performances of TiO₂/ZrO₂ bilayer thin films was first reported. Obvious resistive switching performance can be observed after setting a compliance current, the ratio of high/low resistance reached about 100 at a read voltage of +0.1V and −0.1V and the RS properties showed no obvious degradation after 100 successive cycles tests. The resistive switching characteristics of Au/TiO₂/ZrO₂/FTO/glass device can be explained by electron trapping/detrapping related with the vacancy oxygen defects in TiO₂/ZrO₂ bilayer thin film layer. According to slope fitting, the main conduction mechanisms of the sample are Ohmic and Space charge limited current mechanism.     

Influence of domain switching process on the electrical fatigue behavior of ferroelectrics

We report an experimental approach, designed based on the recent findings that domain switching in ferroelectric ceramics can be separated into three regimes during antiparallel electric field loading, to investigate the influence of domain switching process on the electrical fatigue behavior of ferroelectrics. Uniaxial compressive stress (−2 MPã -100 MPa) and thermal loading (20 °C–150 °C) were used to tune the domain switching process. Under the same loading condition, the bipolar electrical fatigue behavior of soft lead zirconate titanate ceramics was systematically characterized. The amplitude and frequency of the applied electric field are 2 kV/mm and 10 Hz, respectively. By analyzing the evolution of the domain switching process, combined with the measured polarization and strain response, as well as the cracks observed on the surface of the specimen, it is found that the fatigue of ferroelectric ceramics was mainly related to the domain switching process near the coercive electric field: the regime 2 defined in this paper. The underlying mechanism was further discussed by considering the interplay between the domain switching process with the main factors affecting the electrical fatigue of ferroelectrics, namely defect redistribution, charge carrier injection, and crack initiation.     

反应釜夹套多介质智能切换控制系统设计

为了解决反应釜夹套内多种介质切换时易因操作失误引起介质混乱的问题,提出了反应釜夹套多介质智能切换控制方案。在生产过程中进行升/降温操作时,程序通过介质标识位自动识别夹套内的当前介质,并通过压空操作时间标准判断夹套压空终点,可以自动完成介质压空及切换等操作。实际应用表明:该方案提高了夹套介质切换的可靠性。     

Anisotropic domain switching in Pb(Mg1/3Nb2/3)O3‐0.30PbTiO3 single crystals with rhombohedral structure

Anisotropic domain switching paths in [001]‐, [011]‐, and [111]‐poled Pb(Mg_1/3Nb_2/3)O₃‐0.30PbTiO₃ single crystals were studied by in situ polarized light microscopic driven by an antiparallel electric field. Orientation‐dependent electric field induced polarization and strain behaviors were investigated systematically. For [001]‐oriented crystals, only one‐step 71° switching occurred during the domain switching process, resulting in the appearance of stripe domain walls whose traces on (001) plane were along 45° or 135° with respect to [100] direction. But for [011]‐oriented samples, a two‐step 71° switching was observed during 109° switching and the projections of formed twin domain walls on the (011) plane are along 35.3° or 144.7° with respect to [01] direction. Moreover, a three‐step 71° switching was found during 180° switching in [111]‐oriented samples. It was demonstrated by the produced domain walls whose projections on the (10) plane are along 35.3°, 90° or 160.6° with respect to [11] direction. The energetically motivated mechanism based on multistep polarization switching process was also proposed to explain the anisotropic domain switching paths. Our results provided a visualized observation on the ferroelectric domain switching process and also laid the solid foundations for controlling polarization order parameter in ferroelectric single crystals.     

异步模拟移动床色谱的数值模拟

Asynchronous simulated moving bed chromatography (ASMBC), known also as the “VARICOL“ process, is more efficient and flexible than the well-known and traditional simulated moving bed chromatography (SMBC). A detailed model of ASMBC, taking account of non-linear competitive isotherms, mass transfer parameters, and complex port switching schedule parameters, was developed to simulate the complex dynamics of ASMBC.The simulated performance is in close agreement with the experimental data of chiral separation reported in the literature. The simulation results show that ASMBC can achieve the performance similar to SMBC with fewer columns and can achieve better performance than SMBC with the same total column number. All design and operation parameters can be chosen correctly by numerical simulation. This detailed ASMBC model and the numerical technique are useful for design, operation, optimization and scale-up of ASMBC.