Ferroelectric and electromechanical performance of diverse engineered states of Mn-doped 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 ceramics

The materials processing history has a great influence on their properties and finally determines their application effect. In this paper, the ferroelectric, polarization-switching current, and strain properties of Mn-doped 0.75Pb(Mg_1/3Nb_2/3)O₃-0.25PbTiO₃ ceramics were studied in fresh state, aged state, and poled state, respectively. Compared with the symmetric polarization-electric-field (P-E) hysteresis loops, current-density-electric-field (J-E) curves, and bipolar electric-field-induced strain (S-E) curves in fresh state samples, asymmetric P-E loops, J-E curves, and bipolar S-E curves were obtained in poled state samples. Well-aged-state samples exhibit double hysteresis P-E loop, four peaks J-E curves, and symmetric S-E curves without negative strain. The symmetry-conforming short-range order (SC-SRO) principle of point defects and internal electric field E_i is employed to clarify the different phenomenon of three states. Results indicated that randomly oriented defect polarization P_D in aged samples can reverse the spontaneous polarization P_S back and result in the double hysteresis P-E loop and four peaks J-E curves. The oriented P_D and resulting E_i in poled-state samples will lead to the asymmetric loops and strain memory effect.     

A multilevel sampled‐data approach for resilient navigation and control of autonomous systems

Autonomous systems are rapidly becoming an integrated part of the modern life. Safe and secure navigation and control of these systems present significant challenges in the presence of uncertainties, physical failures, and cyber attacks. In this paper, we formulate a navigation and control problem for autonomous systems using a multilevel control structure, in which the high‐level reference commands are limited by a saturation function, whereas the low‐level controller tracks the reference by compensating for disturbances and uncertainties. For this purpose, we consider a class of nested, uncertain, multiple‐input–multiple‐output systems subject to reference command saturation, possibly with nonminimum phase zeros. A multirate output‐feedback adaptive controller is developed as the low‐level controller. The sampled‐data (SD) design of this controller facilitates the direct implementation on digital computers, where the input/output signals are available at discrete time instances with different sampling rates. In addition, stealthy zero‐dynamics attacks become detectable by considering a multirate SD formulation. Robust stability and performance of the overall closed‐loop system with command saturation and multirate adaptive control are analyzed. Simulation scenarios for navigation and control of a fixed‐wing drone under failures/attacks are provided to validate the theoretical findings.     

Mechanics-aided digital image correlation for the investigation of piezoelectric and ferroelectric behaviour of a soft PZT

The strain response of a polarised PZT was characterised using Digital Image Correlation (DIC). The DIC algorithm is based on a global approach and regularises the displacement field using the balance equations of solid mechanics. The measurement error is reduced by correcting the displacements that are mechanically not admissible. A ferroelectric test showed that the standard deviations of strain fields remain mostly under 1.2 × 10^?4 for an element size of 64 px. The standard deviation on the average value is 3 × 10^?6. The strain field is homogeneous and its average value is consistent with the strain obtained from a CCD laser measurement device. The longitudinal strain, transverse strain and polarisation response of the PZT were measured for bipolar and unipolar loadings ranging from 50 to 5000 V/mm. Material properties were extracted from these measurements. This work shows the advantages of a novel 2D-DIC algorithm for piezoelectric strain characterisation.     

嵌套式复合型材构件制造技术及其专用机床

嵌套式冷轧复合型材构件制造技术包括平整、加强筋成型、第一辊压模具组成型、冲孔、主截面成型、第二辊压模具组的横截面成型、嵌套合抱、第一构件与第二构件嵌套抱合后成为复合型材构件与第三辊压模具组紧贴等工序组成,在冲孔工序之前先完成加强筋成型工序,保证冲孔加工后的孔距尺寸精度,显著提高产品质量;上述所有工序都是设置在同一条生产线上的专用机床连续自动完成,实现了嵌套式冷轧复合型材构件的自动化生产,节约工时,降低产品成本。     

Tuning of dielectric and ferroelectric properties in single phase BiFeO3 ceramics with controlled Fe/Fe ratio

Single phase multiferroic BiFeO₃ (BFO) ceramics were synthesized with controllable amount of Fe²⁺ and oxygen vacancies in a very wide concentration range. Double ferroelectric hysteresis loops are observed in fresh BFO ceramics at room temperature without any aging processes. Detailed study shows that this is due to the defect dipoles which have preferential orientations antiparallel to the direction of spontaneous polarization, providing a driving force for domain back-switching. The dielectric constant of BFO could be enormously enhanced by 100 times by increasing the Fe²⁺ content, employing a polaronic relaxation process.     

用PCR技术检测水中隐孢子虫

介绍了一种检测水中隐孢子虫的巢式PCR方法：根据Cryptosporidium parvum 18s rRNA基因序列选用了两对引物，特异性扩增了该基因可变区中1056bp和435bp目标片段。加标试验表明，该方法的检测限为10个卵囊。     

嵌套连接冷弯斜卷边Z形连续檩条的受弯性能试验研究

本文对嵌套连接的冷弯斜卷边Z形连续檩条的受弯性能进行了试验研究。试验分两部分,一是搭接段极限承载力试验,以确定常用范围内搭接负弯矩段的极限承载力;二是两跨连续檩条试验,目的是确定搭接段截面的抗弯刚度。试验分上下翼缘均有自攻钉和仅上翼缘有自攻钉两种情况。对于承载力试验,搭接长度的范围为截面高度的3～5.625倍。通过对5种不同搭接长度和方式共30个试件的破坏性试验发现,破坏都是由受压下翼缘的屈曲引起,且破坏主要发生在搭接开始处。当中间支座处弯矩是搭接开始处弯矩的两倍时破坏出现在中间支座处,此时单个截面的承载力仍然与破坏发生在搭接开始处的情况接近。在试验所用试件的搭接长度范围内,搭接长度对承载能力的影响不大;但搭接段檩条下翼缘是否有自攻钉对搭接段承载能力有约5%的影响。对两跨连续梁,分搭接长度为跨度的10%和20%的两种情况,上下翼缘均有自攻螺钉和仅上翼缘有自攻螺钉两种构造,共进行了11个试验,试验结果表明,搭接长度较长时搭接     

双铅铋回路自然循环瞬态响应分析

为了研究液态金属双自然循环回路功率变化时的瞬态响应和回路的稳定性,利用SIMULINK在单个铅铋自然循环回路的基础上建立了双自然循环回路模型,并用FLUENT程序进行计算验证,分析了不同升功率和降功率过程中回路的流速振荡及双回路的稳定性。计算结果表明:延长升功率时间可减小流速振荡,且当升功率速率先慢后快时更有利于减小流速振荡和缩短流动到达稳定所需的时间;对于双自然循环回路,当降功率速率不同时,回路的流速均未发生明显的振荡,降功率速率对回路的稳定性影响并不显著。双自然循环回路比单回路更不稳定,通过减小中间换热面的热阻能有效提高双回路的稳定性。     

Programming with event loops and control loops – From actors to agents

Event loops are a main control architecture to implement actors. In this paper we first analyse the impact that this choice has on the design of actor-based concurrent programs. Then, we discuss control loops as the main architecture adopted to implement agents, and we frame them as an extension of event loops effective to improve the programming of autonomous components that need to integrate both reactive and proactive behaviors, in a modular way.