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121.
电磁流量计输出的流速信号非常微弱,且常叠加共模干扰,经信号调理电路放大后,会导致信噪比很低,甚至淹没有用信号.针对这问题提出了利用前置放大电路有效抑制共模干扰,对其进行定性、定量分析,给出实际可行的提高差动放大电路输入阻抗的设计,并进行分析、推导和对比计算,证明其可以很大限度抑制共模干扰,提高测量准确度. 相似文献
122.
123.
The use of electrochemically synthesized polyindole (PIN) film was investigated for protective coating on 304-stainless steel (SS). Polyindole was deposited via anodic oxidation of the corresponding monomer, indole in acetonitrile (ACN) solution containing LiClO4. It provided an adherent and stable coating on SS. The corrosion performance of coated and uncoated SS was investigated in 3.5% NaCl solution using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open-circuit potential–time (Eocp–t) diagrams. These tests demonstrated that PIN coating provided important barrier effect to SS for important immersion times in aggressive medium. 相似文献
124.
目的 打印输出技术是目前国内外图像复制领域的主流技术。打印机特征化旨在建立打印机输入控制值与输出色彩信息值之间的对应关系,保证打印输出图像各像素色彩值的准确性。基于可见光谱的打印机特性化过程,以图像光谱信息作为打印机特性化过程中的色彩控制依据,可避免基于色度的打印输出过程所固有的同色异谱问题,实现图像色彩复制领域最高级别的无条件颜色匹配。在广泛文献调研的基础上,本文回顾了打印机光谱特性化方法各部分研究的发展历程,分析介绍了该领域主要研究内容及其研究现状,对打印机光谱特性化方法流程进行了较为全面的综述。方法 以Yule-Nielsen修正的光谱Neugebauer模型(YNSN模型)为典型代表,从打印机墨量限制方法、正向光谱预测模型、反向光谱分色模型以及色彩匹配评价度量4个方面,对目前基于可见光谱的打印机特性化方法研究情况进行了总结与归纳,并结合现有研究存在的问题对未来研究发展趋势进行了展望。结果 综合近几年该领域研究发展情况,认为目前打印机光谱特性化方法研究在墨量限制算法合理性、正反向建模精度等方面已经取得了较为理想的结果。然而,尽管已有20多年的广泛研究,鉴于光谱数据的高维性以及具体应用场景的多样性,导致准确而高效的实现光谱打印机特性化仍然是一个极具难度的问题,特别在建模效率提高、模型适用性增强、模型物理意义提升以及评价度量综合性能优化等方面,目前研究仍存在较大的研究发展空间。结论 打印机光谱特性化是实现图像色彩信息高保真打印复制的必要手段,其今后将继续在图像复制领域起到非常关键作用。然而,由于基于光谱的打印机特性化过程涉及光谱学及色度学理论、半色调呈色理论、最优化计算理论、人眼视觉机理、数字加网技术等多种理论与技术,故其研究具有一定的难度与挑战性。本文对打印机光谱特性化方法研究现状进行了较为深入的介绍与分析,意在使国内同行对该领域有一个较为全面的了解,以期引起更多研究者对该领域的关注。由于篇幅所限,许多问题未及深究。 相似文献
125.
The use of electrochemical noise methods (ENM) to study thick, high impedance coatings 总被引:2,自引:0,他引:2
Gordon P. Bierwagen Carol S. Jeffcoate Junping Li S va Balbyshev Dennis E. Tallman Douglas J. Mills 《Progress in Organic Coatings》1996,29(1-4):21-29
Thick, high impedance organic coatings are those class of coatings used to provide corrosion protection to naval vessels, pipelines, gasoline storage tanks, and other large structures such as bridges and plant structures. These coatings, especially the newest generations now being used in practice, can provide exceptional protection and lifetime of performance such that properly and accurately assessing and differentiating among competing coatings is a very difficult task. The standard protocol of salt fog testing (ASTM B117), immersion testing, and outdoor exposure in a corrosive environment with subjective evaluation of a coating's performance durings and after testing, does not adequatcly rank and predict coating lifetimes for new coating systems, especially for the environmentally compliant coating systems such as powder coatings (especially the thick, fusion bonded epoxy (FBE) coatings used for pipelines), two component epoxy and urethane coatings and waterborne coatings. New, objective test methods are desperately needed by users and manufacturers of coatings. A relatively new electrochemical test procedure, electrochemical noise methods (ENM), as developed by Skerry and Eden, has been shown in our laboratory to be very successful in the ranking and prediction of relative coating performance. We have used the method successfully on naval ship coatings, several pipeline coatings and other related systems, and Skerry has used them successfully on industrial maintenance coatings. We have used these methods in conjunction with electrochemical impedance spectroscopy, d.c. resistance measurements and cyclic salt fog testing of the ProhesionTM type. In our studies of pipeline coatings, we needed to investigate thermal effects because of their extended range of use temperature. In these studies, we have discovered that electrochemical methods can be used for an in situ measurement of the Tg of coatings in electrolyte immersion. Further, the ‘plasticizing’ effect of aqueous electrolyte absorption as well as its relative irreversibility has been shown. For all coatings studied, ENM provided useful, objective, numerical data which rapidly ranks coatings and provides useful information on the relative lifetime prediction of coatings which may provide up to 30 years of service. 相似文献
126.
BaTiO3系PTCR材料电学性能的复阻抗解析 总被引:9,自引:3,他引:9
采用复阻抗解析法研究了BaTiO3系PTCR材料晶粒、晶界的电学性能。结果表明:使用欧姆接触电极的PTCR材料等效电路的复阻抗为:晶粒电阻呈NTC特性,而晶界电阻天T〈Tc时呈NTC特性,T〉Tc时呈明显的PTC特性;PTC效应是一种晶界效应。 相似文献
127.
In this work diamond-like carbon films were deposited on the Ti–6Al–4V alloy, which has been used in aeronautics and biomedical fields, by electrical discharges using a magnetron cathode and a 99.999% graphite target in two different atmospheres, the first one constituted by argon and hydrogen and the second one by argon and methane. Films deposited using the argon/hydrogen mixture were called a-C:H, while films deposited using the argon/methane mixture were called DLC. Raman spectroscopy was used to study the structure of the films. The Raman spectra profile of the a-C:H films is quite different from that of the DLC films. The disorder degree of the graphite crystalline phase in a-C:H films is higher than in DLC films (a-C:H films present small values for the the ID/IG ratio). Potentiodynamic corrosion tests in 0.5 mol l−1 NaCl aqueous solution, pH 5.8, at room temperature (≈25 °C) were carried out as for the a-C:H as for the DLC coated surfaces. Comparison between the corrosion parameters of a-C:H and DLC coated surfaces under similar deposition time, showed that DLC coated surfaces present bigger corrosion potential (Ecorr) and polarization resistance than those coated with a-C:H films. Electrochemical impedance spectroscopy (EIS) was also used to study the electrochemical behavior of a-C:H and DLC coated surfaces exposed to 0.5 mol l−1 aqueous solution. The EIS results were simulated with equivalent electrical circuit models for porous films. The results of these simulations showed similar tendency to the one observed in the potentiodynamic corrosion tests. The DLC film resistance and the charge transfer resistance (Rct) for the DLC coated surface/electrolyte interface were bigger than the ones determined for the a-C:H coated surfaces. 相似文献
128.
Impedance spectroscopy study of hardened Portland cement paste 总被引:3,自引:0,他引:3
In this paper, the differential impedance analysis (DIA) has been applied to the study of the dielectric properties of hardened Portland cement paste. Two time constants are found in the impedance spectra obtained in the frequency region form 100 kHz to 15 MHz. One time constant has been attributed to the solid matrix and the other one to the liquid phase filling the pores. The effect of the cement paste-electrodes interface has been quantified using two different experimental set-ups. Measurements using direct contact between electrodes and cement paste have been compared with measurements using an air gap technique in which the specimen “floats” between the electrodes. The two referred time constants have been found in both types of measurements. The influence of drying on the dielectric parameters is also studied. 相似文献
129.
Logit模型下的道路拥堵收费策略改善效果分析 总被引:1,自引:1,他引:0
为探讨拥堵收费策略的改善效果,从出行者的综合成本出发,构建适用于拥堵收费的路阻函数和Logit交通分配模型,探讨拥堵收费下交通出行在路网上的重新分配.并以南京市应天大街高架为例设置了拥堵收费虚拟方案,应用路阻函数和交通分配模型进行分析后得出拥堵收费在交通出行量分布、出行分担率、道路服务水平和行程速度上的改善效果.结果表明:拥堵收费能有效引导交通出行的重新分布,提高路网总体通行效率和服务水平,可以认为拥堵收费对交通的改善具有一定效果,但改善效果和拥堵收费费率不是线性正比关系,本次虚拟收费方案下收费费率为5元/次时可取得最佳改善效果. 相似文献
130.
Six circularly polarized patch antennas with electromagnetic band gap (EBG) arranged at different locations were studied. These EBG antennas were compared in terms of impedance bandwidth, axial ratio (AR) bandwidth and radiation patterns. When the EBG cells were placed closer to the edge of the substrate, the EBG antenna had a larger front radiation and a narrower bandwidth. Integrating the EBG cells closer to the center of the patch resulted in a wider impedance bandwidth, a wider axial ratio bandwidth and a decreased front gain. 相似文献