两种由薄片式压电元件构成的换能器对比测试

为简化压电换能器制作工艺和减小结构尺寸,利用薄片式压电元件良好的力电转换特性,根据压电换能器结构不同的能量转换方式,设计并制备了冲击型和弯曲型两种换能器.通过建立对比试验,分析了两种结构的工作原理以及换能器的发电性能,并研究了加载条件的变化对换能器输出性能的影响规律.测试结果表明:弯曲型换能器在有限位移下,低频率加载时的发电性能和工作稳定性强于冲击型换能器.最后,根据对比结果提出了一种弯曲型换能器的有效封装结构.     

基于六端网络法的压电超声换能器优化设计

压电超声换能器传统四端网络设计方法忽略了压电陶瓷晶堆内部的机电耦合过程,使用该方法所设计的压电超声换能器尺寸误差大,输出的超声振幅较小。为了提高压电超声换能器尺寸设计精度、增大换能器输出的超声振幅,本文将考虑压电陶瓷晶堆内部机电耦合作用的六端网络引入到压电超声换能器的设计中,分别采用四端网络法和六端网络法设计得到两个不同尺寸的压电超声换能器A和B,通过有限元方法对比分析了两个换能器的固有频率和输出振幅,并进一步通过实验验证了设计理论与仿真分析的有效性。研究结果表明,在相同激励电压下,采用六端网络法设计得到的压电超声换能器B输出的超声振幅是换能器A输出振幅的1.5倍,六端网络法设计压电超声换能器可以提高所设计换能器的振动性能。      

基于摩擦式冲击驱动原理的压电驱动器运动分析

压电驱动器利用压电元件(PZT)伸长与收缩进行驱动,其优良的驱动性能被广泛应用在精密加工领域,为了克服其行程较短的缺陷,摩擦式冲击驱动可将压电元件(PZT)的行程进行放大。针对传统的摩擦式冲击驱动在低频情况下无法获得最大速度的问题,通过对摩擦式冲击驱动的4种运动情况进行理论分析和运动验证。结果表明,被驱动物体在高频驱动电压下可以获得稳定的驱动速度和较大的行程。     

辊式矫直机的两种矫直力计算模型对比研究

利用对中厚板辊式矫直机热态矫直时进行的现场力能参数测试的实验数据,把基于“虚拟支点”的矫直力新的计算模型与传统矫直力计算模型进行对比研究。结果表明传统的矫直力计算模型过于保守,新的计算模型更符合实际的矫直力状况。     

往复式和链篦式两种轧钢加热炉生产运行状况对比剖析

通过一年多的生产实践证明,水平往复式和链篦式两种炉排应用于中小型轧钢加热炉是可行的,能满足工艺要求,操作维修简便。其主要优点是不需要除尘设备,可以达到国家环保标准。与人工加煤相比,能大大减轻劳动强度,改造后在炉型不变的情况下可节约燃料费用47％以上。特别是受燃料条件限制,煤种变化又大的中小型企业及乡镇企业更有一定的生命力。     

常规和脉冲两种燃烧技术在车底式加热炉上的应用

介绍了常规和脉冲两种燃烧技术在车底式加热炉上的应用,重点介绍常规连续燃烧控制和脉冲燃烧控制的主要控制功能及控制软件。生产情况表明:两种燃烧控制可实现灵活切换,满足加热炉和热处理炉两种工艺要求,应用效果良好。     

Comparison of lubricants in cold thin-sheet rolling

The formation of a lubricant boundary layer at the metallic surface of the strip and rollers in rolling mills is theoretically described. Methods of heterogeneous friction are classified, and the effectiveness of lubricants is compared in the cold rolling of steel strip, in laboratory conditions.     

Comparison of dobutamine electrocardiographic stress test and exercise test in two different groups of patients with unstable angina

DNA vectors expressing an antigen derived from a pathogen or a cancerous cell have been shown, after inoculation into experimental animals, to trigger de novo synthesis of foreign proteins, which induce an immune response. This immune response can be modulated by coinoculation of vectors encoding either cytokines or costimulatory molecules. A variety of cytokines such as granulocyte/macrophage colony-stimulating factor (GM-CSF), IL-2, IL-4, IL-12 and IFN-gamma, as well as the costimulatory molecule B7.1, have been tested to date for their ability to amplify the immune response to genetic vaccines. Although the results obtained thus far clearly show that coadministration of vectors expressing immunomodulatory molecules, such as cytokines, may increase the efficacy of genetic vaccines, this approach is currently considered unsuitable for use in human patients due to the potential side effects of persistent cytokine expression.     

Cross-lagged panel correlation: A test for spuriousness.

Cross-lagged panel correlation is a method for testing spuriousness by comparing cross-lagged correlations. True experiments control for spuriousness by random assignment, but random assignment limits true experimental studies to independent variables that can be manipulated. Like any statistical method cross-lagged analysis is based on a set of assumptions: synchronicity and stationarity. Different forms of stationarity have different consequences for both the changes in the synchronous correlations over time and the difference between cross-lags. Homogeneous stability is a necessary assumption in the identification of both the source and direction of a causal effect. Cross-lagged analysis is a low-power test, better adapted than either multiple regression or factor analysis for many questions in panel studies. Multiple regression must assume no errors of measurement in the independent variables and no correlated errors, while factor analysis must specify a particular factor structure. Two extended examples of cross-lagged analysis are discussed with special emphasis placed on the issue of stationarity and the estimation of reliability ratios. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of three commercial MIC systems, E test, fastidious antimicrobial susceptibility panel, and FOX fastidious panel, for confirmation of penicillin and cephalosporin resistance in Streptococcus pneumoniae

The performances of three commercial broth microdilution MIC assays adapted for use with fastidious organisms--the E test (ET), Fastidious Antimicrobial Susceptibility panel (FAS), and FOX Fastidious panel (FOX)--were compared with a MIC using Mueller-Hinton broth with 5% lysed horse blood (MHLHB) to confirm penicillin and cephalosporin resistance in clinical isolates of Streptococcus pneumoniae. Of the isolates screened for penicillin resistance, 5 (12.8%) were categorized as susceptible, 16 (41.0%) were categorized as intermediate, and 18 (46.2%) were categorized as resistant by MHLHB. Only the isolates exhibiting intermediate-to-resistant MICs were included in the comparison. Agreement within +/- 1 log2 dilution was found in 91, 21, and 76% of the ET, FAS, and FOX MICs, respectively, compared with the MHLHB MIC. No very major or major discrepancies occurred with the ET or FOX; however, two very major interpretive errors occurred with the FAS. Agreement between the ET and MHLHB for cefotaxime, ceftriaxone, and cefuroxime was 88, 85, and 100%, respectively. Less than 50% of cephalosporin MICs categorized as > 0.5 microgram/ml by MHLHB were detected by FAS or FOX. Of the methods compared, the ET was the most reliable alternative for susceptibility testing of pneumococci.     

Effects of au plating on small-scale resistance spot welding of thin-sheet nickel

The effects of Au plating on joint formation and joint strength in small-scale resistance spot welding (SSRSW) of Ni sheets have been investigated using tensile-shear testing, optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The results show that the mechanisms of the joint formation during the welding of Au-plated Ni sheets involve solid-state bonding, brazing, and fusion welding. The comparison between SSRSW of Au-plated Ni and bare Ni sheets and large-scale resistance spot welding (LSRSW) of Zn-coated steels is also discussed.     

高速压电板形仪工业化测试平台及其试验

 为提高高速压电板形仪的在线检测精度及可靠性,研究张力分布方式、速度制度及载荷特性等对板形检测信号的影响,研制了一套高速压电板形仪工业化综合测试平台（简称“ICP-ITS”）。该平台可实现板形仪的精确动态标定和误差测试分析,保证了板形信号的准确性。在此基础上,采用带钢驱动和轴向移动式压轮张力调节机构,模拟板形检测工业现场,实现了不同浪形的物理模拟和板形信号检测。试验结果表明,该平台能提高板形仪的检测精度,缩短板形仪的标定上线周期,对促进板形仪的工业化应用具有重要的现实意义。