相对介电常数实时监测系统设计

为解决相对介电常数的快速测量以及长时间监测其随环境变化的问题,在研究不同填充介质对共面平板电容量值影响的基础上,提出了用同面电容法测量材料的相对介电常数。设计了包含同面多电极电容传感器、电容测量电路、单片机控制与液晶显示电路的测量系统,实现了相对介电常数测量。实验结果表明:该系统能有效地测量固体材料的相对介电常数,精度可达到5%。测量系统无需制样,只需将传感器测量区域靠近待测目标即可实现快速测量和长时间在线监测。     

厚管壁电容层析成像传感器特性研究

电容层析成像技术利用多电极电容传感器实现对多相流电介质分布进行可视化.通过对管道内径为10 mm,管壁厚度为5 mm的8电极电容传感器的数值模拟,研究了管道介电常数、管内介质介电常数以及径向电极对传感器电容绝对值、空满管电容变化值和传感器线性度的影响,分析了厚管壁下电容传感器的灵敏场特性,并给出了在高径极比条件下传感器设计的参数优化方案,为电容层析成像检测电路的设计提供相应的依据.     

基于太赫兹波谱的液体极性测量

太赫兹波能与极性液体的氢键发生强烈的共振吸收作用,分子极性越大,吸收作用越强。基于此特性,在0.2～1.0 THz波段利用太赫兹时域光谱技术对甲醇、乙醇、正丙醇、正丁醇四种一元醇液体的极性进行检测研究。根据测量得到的四种液体太赫兹波谱数据,得出了液体的极性与其太赫兹波谱的关系式,再利用此关系式求得四种液体的计算值。通过对四种液体极性的标准值和计算值比对,验证了所得液体极性求取公式的有效性。研究结果表明,四种不同液体的时域光谱因分子的极性差异有显著的不同,所用的液体极性测量方法能够对液体的极性进行快速有效的检测与鉴别,可为其他液体极性的检测提供参考。     

基于数字式电容检测的机油品质传感器

针对汽车机油更换周期的问题,设计了一种基于介电常数变化的机油品质检测传感器,通过测量电容值来反映机油的介电常数。传感器采用圆柱型电容结构,并以数字电容芯片AD7745和STC12C5A60S2单片机设计的处理电路实现对电容的快速、准确测量。污油和净油按不同比例混合后获得的样品用于传感器性能测试,并将试验数据与AH2500A型电容电桥的同步测试数据进行对比。结果显示,传感器测量的电容值与标准仪器的结果基本吻合,误差不超过±0.2%,且电容值与污油比例之间具有置信度为0.989 7的线性关系。     

一种新型的三维ECT传感器及三维图像重建方法

针对二维电容层析成像系统轴向分辨率低,对介电常数在轴向有显著变化介质的分布不适应,在分析电容层析成像基本原理的基础上,提出了一种新型的三维电容层析成像传感器结构。三维电容层析成像传感器检测电极分为3层布置在绝缘管道外壁,在测量时根据需求,采用双电极激励检测模式对同层或不同层之间极板阵列组合进行检测,以获得传感器内部介质的三维数据。实验结果表明,介质轴向分布图像更加客观和真实,与传统的单电极激励模式相比较,检测电容值得到提高,测量区灵敏度均衡性得到改善,图像重建精度得到提高。     

液态一元醇的太赫兹时域光谱研究

太赫兹波可以与极性液体中的氢键网络产生强的相互作用,作用越强吸收越强。鉴于此性质,利用太赫兹时域光谱技术对甲醇、乙醇、正丙醇在0.1~1THz波段内的太赫兹光谱进行了检测,发现其吸收光谱随分子极性的差异有显著的区别,并从中提取出了一元醇的吸收系数、折射率、介电常数等光学参数。在此基础上还利用对样品介电常数敏感的微孔金属片,通过产生的共振峰漂移进一步对不同一元醇进行了检测,结果表明太赫兹光谱技术结合微结构器件在液态化学及生物样品检测方面有潜在的应用价值。     

便携电容式棉花含水量测量仪

电容器容值大小与极板间材料的介电常数有关,用聚酰亚胺湿敏材料为介质构成测量电容,电容容值反映棉花含水量,据此原理设计了棉花含水量测量仪,介绍了测量探头主要组成部分及测量原理,分析了电容测量电路,给出了测量仪电路框图和主程序流程。解决了测量仪电路框图和主程序流程。解决了电阻测量法检测干燥棉花精度不足的问题,测量仪功耗低,体积小,符合便携要求。     

用于温度测试的光纤SPR传感器特性研究

表面等离子体波共振效应（SPR）对液体折射率变化非常敏感，而温度变化又会导致液体折射率和金膜复介电常数的改变。利用这一原理，可以考察温度变化对SPR共振效果的影响。采用相对光谱检测技术，获得相应的SPR反射光谱，并详细分析了共振波长和共振强度等参数随温度变化的特性曲线。定义耦合系数η，还可实现对不同液体温度下共振效应强度的评估。通过这些研究，进一步扩展了此类传感器的应用领域。     

应用探针式电容传感器检测发动机润滑油品质的研究

应用探针式电容传感器测量润滑油中固体颗粒含量的原理,是根据固、液体混合物在电容器两极板之间介质的介电常数变化而使电容发生变化。应用该原理设计出了一套润滑油油品监测系统,简称为YPT系统。应用该系统,对发动机润滑油中的铁、硅固体微粒含量变化与电容变化的相互关系进行了初步探讨,并建立起来了一种新的润滑油品质YPT评价标准。这个新的评定标准,为确定发动机润滑油的更换周期及预测发动机的使用寿命等方面的研究,提供了一种比较简便实用的科学依据。     

基于电容法与光干涉法相结合的油膜测量方法

通过将电容法膜厚测量仪耦合在球-盘点接触光干涉试验台上,搭建油膜厚度测量装置。通过对目标球-盘接触副采取合理的导电措施以及台架绝缘设施来保证润滑油膜电信号的提取,该装置可实现相同工况下膜厚度值及其相应的电信号(如油膜分压值和电容值)。在纯滚动接触情况下,分别对油润滑和脂润滑下的油膜进行测量,得到光干涉膜厚、油膜分压值和电容值随随卷吸速度的变化规律,并分析接触副电容随膜厚的变化。结果显示,随卷吸速度的增加光干涉膜厚升高而油膜分压值和电容值减小,电容值随着膜厚的增加而逐渐降低。实验结果初步验证了该测量系统的可行性,可为后续实际接触副内润滑状态的评估提供方案。     

The influence of the embedding medium when staining for electron microscopy: the penetration of stains into plastic sections.

Using a sectioned-section procedure it was found that only a few structures, e.g. the connective tissue elements, were deeply penetrated by phosphotungstic acid (PTA) and uranyl acetate (UA). Reynold's lead citrate appeared to penetrate more generally. Using stains selective for the embedding medium, and also observing the surfaces of shadowed sections, it was concluded that structures readily penetrated by polar stains were only poorly infiltrated by non-polar embedding media. It is argued that this differential infiltration leading to differential penetration by polar stains largely controls the pattern of staining of ultrathin sections by PTA and UA.     

非极性流体在微通道内的阻力特性分析

研究非极性流体在微通道内的流动特性。采用的微流动实验台通过测量不同极性液体流过矩形截面微通道中流量与压力,分析了不同极性流体的阻力特性。结果表明:对分子量较小的极性液体,微通道内流量-压差关系符合Hagen-Poiseuille定律,连续介质模型仍适用于微米尺度微通道;对分子量较大的非极性液体,常规理论在预测微通道内流量-压差、摩擦阻力系数-雷诺数关系时存在较大误差,须进行修正。     

The Effect of Wetting and Surface Energy on the Friction and Slip in Oil-Lubricated Contacts

This work shows the influence of solid–liquid interactions between engineering surfaces (steel and several types of DLC coatings) and lubricating oil (polyalphaolefin, PAO) on the coefficient of friction in the elastohydrodynamic lubrication (EHL) regime. Specifically, it confirms that the spreading parameter, rather than the contact angle, is the relevant parameter to evaluate the wetting behaviour of these surfaces with oils. Both the spreading parameter and the surface energy correlate very well with the friction in the EHL regime and can predict its behaviour. In particular, the polar component of the surface energy was found to correlate almost perfectly with the friction behaviour (a Pearson’s linear correlation coefficient of 0.999). By tailoring the wetting and surface energy—achieved by varying the DLC/DLC contacts with different types of DLC coatings—the coefficient of friction in the EHL regime was reduced by more than 30 % compared to steel/steel contacts. Poor wetting of the DLC coatings with a low surface energy is reflected in low values of the spreading parameter, which indicates easier slip of the lubricant over the solid surface due to shear action, and this leads to a lower viscous friction. A “Slip-inducing interaction model based on surface forces” is presented to explain why oil slip is promoted, particularly at surfaces with a low polar surface energy. The model suggests that a small number of permanent polar interactions, i.e. a larger proportion of intermittent dispersive interactions, results in less adhesive interactions between the predominantly non-polar liquid (oil) and the low polar surface (DLC), which enables easier slip at the solid–liquid interface.     

Poly(l‐lysine)‐graft‐poly(ethylene glycol): a versatile aqueous lubricant additive for tribosystems involving thermoplastics

The adsorption and aqueous lubricating behaviour of poly(l ‐lysine)‐graft‐poly(ethylene glycol) (PLL‐g‐PEG) have been investigated for tribopairs involving thermoplastic materials, including polypropylene, polyamide‐6,6 and polyethylene. A major finding is that PLL‐g‐PEG adsorbs onto both hydrophobic, non‐polar surfaces and hydrophilic, polar (negatively charged) surfaces from aqueous solution, and thus plays as a very unique and effective aqueous boundary lubricant additive for the sliding contact of thermoplastics against themselves as well as against many hydrophilic, polar materials, including metals (e.g. stainless steel) or ceramics (e.g. zirconia, ZrO₂). Copyright © 2007 John Wiley & Sons, Ltd.     

High‐speed optical imaging of liquid film flow and liquid macro‐slip over free surfaces with different surface energies

High‐speed optical imaging is introduced as a visualization method to investigate the film‐flow properties of liquids with different surface tensions and viscosities (water, poly‐alpha‐olefin oil, and glycerol) over free rotating surfaces with different surface energies and polarities (steel, and two different diamond‐like‐carbon ‐ DLC coatings, i.e. DLC, and F‐DLC). It was found that the polar surface energy strongly influences the structural dynamics of the liquid film's flow and the film's slip. Namely, a decrease in the polar surface energy results in a less stable film with de‐wetting areas and breakups into streams, as well as in a larger amount of film slip, which was most clearly expressed by the F‐DLC. It was also found that the combination of a high surface tension and a low viscosity provides the largest amount of liquid slip, with the most obvious breakup of the liquid film being observed with water, which clearly exhibits these properties.     

FTIR micro‐reflectance absorption spectroscopic analysis of chemisorbed reaction films for tribological applications

Chemisorbed reaction films (CRFs) were prepared by using iron (Fe) particles (100–200 mess size) and thio (sulfur) derivatives of ethyl octadecenoate and methyl 12‐hydroxy octadecenoate in the light viscosity paraffin liquid medium. The reaction was conducted in a simulated condition of tribo‐chemical situation. CRFs were obtained in solid amorphous phase. The CRFs were examined for elemental composition and layer analysis using C‐H‐N‐O‐S analyzer and Fourier transform infrared spectroscopy micro‐reflectance absorption spectroscopic technique. Further, the CRFs were isolated into organic solvent soluble fractions using polar solvents of increasing polar strength. Their elemental analyses were studied, and chemical constitutions were known. Friction coefficient and wear scar diameter were evaluated by high frequency reciprocating rig, PLINT TE‐77 machine. Thermal stability was studied using thermogravimetric analysis technique in nitrogen environment. These studies inferred that CRFs appeared varying in its composition, luster, phase, chemical structure and thermal stability. Nonetheless, these were also found anomalous in elemental distribution throughout the layer structure of the CRFs. Copyright © 2015 John Wiley & Sons, Ltd.     

State of the art of in-line nondestructive weld inspection of pipelines by ultrasonics

The in-line inspection of pipelines via the use of intelligent PIGs (pipeline inspection gages) that concerns the detection and sizing of metal loss (e.g., caused by corrosion) is a well-established technology for liquid pipelines as well as gas pipelines. Magnetic flux leakage and ultrasonic techniques are used for inspection. The application of conventional ultrasonic techniques is normally restricted to liquid lines because a liquid coupling medium is required. For reliable crack detection, only the ultrasonic technique has proven suitable. The cracking in pipelines is induced by fatigue crack growth and stress corrosion cracking in addition to manufacturing-related phenomena. The state of the art of in-line crack inspection is discussed, especially as regards typical examples of weld inspection. Special emphasis is placed on data evaluation and interpretation. The text was submitted by the authors in English.     

Cryopreservation of <i>Cyrtopodium hatschbachii</i> Pabst (Orchidaceae) immature seeds by encapsulation-dehydration

The aim of the present study was to investigate the efficiency of the encapsulation-dehydration technique for cryopreservation of Cyrtopodium hastchbachii Pabst seeds. Immature seeds of this species were cryopreserved by an encapsulation-dehydration technique. Seeds of five immature pods, 120 days after pollination, were encapsulated in 3% calcium alginate matrix and pretreated in liquid medium supplemented with 0.08 M sucrose (24 h), 0.15 M sucrose (24 h), 0.25 M sucrose (48 h), 0.5 M sucrose (24 h) and 0.75 M sucrose (24 h) in shaker at 60 rpm. Alginate beads were dehydrated 5 h in silicagel and immersed in liquid nitrogen for 12 h. Cryopreserved beads were thawed at 30°C for 1 min, rehydrated using the same liquid mediums [0.75 M sucrose (24 h), 0.5 M sucrose (24 h), 0.25 M sucrose (48 h) and 0.15 M sucrose (24 h)] and cultivated in half strength Murashige & Skoog medium (1962) with the addition of 2 g/L activated charcoal. Sixty four percent of seeds survived and developed into acclimatized plants after being cryopreserved. In this work, the encapsulation-dehydration technique was employed for first time in Cyrtopodium hatschbachii.     

Generalization of the polar representation in time domain fluorescence lifetime imaging microscopy for biological applications: practical implementation

The polar representation or phasor, which provides a fast and visual indication on the number of exponentials present in the intensity decay of the fluorescence lifetime images is increasingly used in time domain fluorescence lifetime imaging microscopy experiments. The calculations of the polar coordinates in time domain fluorescence lifetime imaging microscopy experiments involve several experimental parameters (e.g. instrumental response function, background, angular frequency, number of temporal channels) whose role has not been exhaustively investigated. Here, we study theoretically, computationally and experimentally the influence of each parameter on the polar calculations and suggest parameter optimization for minimizing errors. We identify several sources of mistakes that may occur in the calculations of the polar coordinates and propose adapted corrections to compensate for them. For instance, we demonstrate that the numerical integration method employed for integrals calculations may induce errors when the number of temporal channels is low. We report theoretical generalized expressions to compensate for these deviations and conserve the semicircle integrity, facilitating the comparison between fluorescence lifetime imaging microscopy images acquired with distinct channels number. These theoretical generalized expressions were finally corroborated with both Monte Carlo simulations and experiments.     

The effect of fluid properties and geometrical parameters of cantilever on the frequency response of atomic force microscopy

Nowadays, the atomic force microscopy plays an indispensable role in imaging and manipulation of biological samples. To observe some specific behaviors and biological processes, fast and accurate imaging techniques are required, and one way to speed up the imaging process is to use short cantilevers. For short beams, the Timoshenko model seems to be more accurate compared to other models such as the Euler–Bernoulli. By using the Timoshenko beam model, the effects of rotational inertia and shear deformation are taken into consideration. In this paper, the frequency response of a rectangular atomic force microscope (AFM) in liquid environment has been analyzed by using the Timoshenko beam model. Afterward, since the dynamic response of AFM is influenced by the applied medium, the effects of physical and mechanical properties (e.g., fluid density and viscosity) on the frequency response of the system have been investigated. The frequency responses of the AFM cantilever immersed in various liquids have been compared with one another. And eventually, to study the influence of geometry on the dynamic behavior of AFM, the effect of the cantilever's geometrical parameters (e.g., cantilever length, width and thickness) on the frequency response of the system has been studied.