The effect of calcining temperature on the properties of 0-3 piezoelectric composites of PZT and a liquid crystalline thermosetting polymer

We report on the optimisation of a recently developed high performance 0-3 piezoelectric composite comprising of the piezoelectric Lead Zirconate Titanate (PZT) powder and a liquid crystalline thermosetting matrix polymer (LCT). The matrix polymer is a liquid crystalline polymer comprising of an HBA-HNA backbone with phenylethynyl end-groups. The use of a high performance polymer makes the composite a possible candidate to be used in sensor applications at elevated temperatures. The composite properties were optimised by calcining the PZT powder at different temperatures, prior to mixing the powders into the LCT matrix. The aim is to study the effect of the calcining temperature on the piezoelectric properties of the composite The PZT powders were characterised by X-ray diffraction and scanning electron microscopy. The dielectric constant and piezoelectric charge constant (d ₃₃ ) of the composite samples was measured. It was found that a relationship exists between the calcining temperature of the PZT powder and the piezoelectric properties of the composites. A maximum voltage constant of g ₃₃  = 63 mVm/N was obtained for a composite containing 40% (by volume) of PZT powder calcined at 1150°C.     

一种求解0-1背包问题的混合粒子群算法

针对0-1背包问题,提出一种具有修复策略的、贪心算法与二进制粒子群算法相结合的混合智能算法.数值试验结果表明,该方法能在一定程度上克服早熟现象,且收敛速度较快.因此,应用该混合智能算法求解0-1背包问题是比较有效的.     

3U0越限报警信号的可靠来源分析

通过对不同来源的3U0越限报警信号的可靠性、实时性进行对比分析,得出电磁型过电压继电器依旧是产生3U0越限报警信号的最可靠手段,该继电器的3U0电压模拟量输入应取自电压并列屏开口三角试验芯抽出电压的小母线端子排,该3U0电压同时被接入测控装置的专用遥测板,该遥测板的线性采样量程应达到±200 V。对于智能站,测控装置应直接接收电压并列IED装置的GOOSE报文和SMV采样值报文来产生3U0越限报警信号和3U0电压。     

3-状态多桥设备网络系统可靠度计算的一个新算法

3-状态设备网络系统可靠度的模型和有效算法在文献中并不多见,本文在充分分析已有2-状态网络系统可靠度模型的基础上,建立了3-状态多桥设备网络系统可靠度计算的模型.文中利用条件概率性质和有关公式,将3-状态网络系统可靠度计算问题转化为2-状态网络系统可靠度计算问题的归约定理,给出了一个计算3-状态多桥设备网络系统可靠度的一个新算法,并对算法的效率进行了分析.算法具有思想简洁、容易扩展、易于计算机实现的特点.     

A Comparison of the Underwater Acoustic Performance of Cymbal-Based Projectors to 1-3 Piezocomposite Materials

The performance of two different cymbal actuator-based underwater acoustic projector designs is compared. One projector design is a 101 mm by 101 mm Thin Panel potted in polyurethane. The other is a 152.4 mm by 76.2 mm tungsten-backed flat panel embedded in a syntactic foam frame. Both projector designs are characterized in-air and evaluated in-water. The results of the in-water studies are based on a 100 Watt power supply. Comparing to 1-3 piezocomposite materials with the same radiating area and similar thickness, these cymbal-based projectors appear to be best suited for use at frequencies below 4–5 kHz, with particular emphasis in the 1 kHz range. The cymbal-based devices described in this study are strictly prototypes and are not designed for a specific application. Nevertheless, the results indicate that if the acoustic aperture of these projectors were scaled to the appropriate dimensions, they could meet the design goals of many low frequency Navy applications where source levels > 180 dB from a thin package are desired     

500kV变电站CTV3Uo频繁告警及主变噪声异常分析

高压直流输电系统单极大地运行时接地极电流对交流电网会产生一定影响,其中对中性点直接接地变压器的影响最大,接地极电流对电网影响的范围和程度也随接地极电流加大而增大.分析了特高压直流单极大地运行时对交流电网及中性点直接接地变压器的影响,总结了目前一些减小高压直流输电系统接地极电流对变压器偏磁影响的主要措施.     

IEC 61131-3功能块的开发与应用

IEC 61131-3是可编程序控制器(PLC)的编程语言的标准,功能块是该标准所规定的图形化编程语言功能块图的主要软件元素。本文通过一个工程实例介绍了功能块的设计、开发和使用,展现了功能块乃至IEC 61131-3标准的优点。