Exploring single electrode reactions in polymer electrolyte fuel cells

Utilising a pseudo-reference electrode in polymer electrolyte fuel cells allows for the separation of anodic and cathodic contributions to the entire cell impedance. Modelling the impedance responses by using equivalent circuits inhibits the investigation of kinetic parameters of the basic electrochemical reactions, which take place at single electrode-electrolyte interfaces. Therefore, we evaluate single electrode impedance measurements by a kinetic model, which is based on specific reaction pathways, either for the oxygen reduction reaction (ORR) or the hydrogen oxidation reaction (HOR). As a consequence, it is possible to obtain kinetic parameters for the specific reaction of interest. Furthermore, the information gained from the single electrode impedance measurements and the kinetic model can give insight into single reactions steps. In particular, the ORR has to include a chemical step in the reaction pathway.     

基于匹配策略融合的低误差快速图像拼接算法

针对目前多数拼接算法正确匹配率低、耗时及误差大的问题,提出了基于匹配策略融合的改进图像拼接算法。该算法首先仅在图像的重合区域提取SIFT特征点,并计算SURF特征描述符;其次,融合改进的最近邻比次近邻、双向交叉检查及匹配差值的阈值化3种匹配策略,结合坐标约束及RANSAC算法完成特征匹配;最后,提出利用配准参数计算任意图像到参考图像坐标空间的投影变换模型的方法,并利用多线程技术将所有图像投影至参考坐标系,经过亮度校正、加权融合后合成全景图。实验结果表明,提出的拼接算法正确匹配率提高了10~20%,拼接总耗时约为传统逐帧扩大式拼接算法的1/3,且累计误差大大降低,拼接图像畸变小。     

Preliminary evaluation of the anticorrosive properties of aircraft coatings by electrochemical methods

Strict regulations concerning the content of volatile organic compounds (VOCs) and heavy metals (Cr⁶⁺) in aircraft coating systems have increased the economic burden of the United States Air Force (USAF) in the area of coating maintenance. To this end, it is critical to have methods to characterize new coating systems in such a manner that the data can be used to predict accurately and reliably the expected lifetime of the coatings in service. Electrochemical noise method (ENM) and electrochemical impedance spectroscopy (EIS) are two techniques used to monitor extent and rate of corrosion. The USAF is currently employing these methods in order to supplement data acquired from traditional salt-spray methods. ENM and EIS are used to evaluate each component of the coating system and its contribution to corrosion prevention. Preliminary evaluations of an aircraft coating system on aluminum substrate (Al 2024-T3) produces resistance noise values of 10⁶ to 10⁷ Ω/cm². It is hoped that these results will form the basis of coatings that give increased USAF fleet service life and reduction in maintenance manpower and materials costs.     

A study of PtRuO2 catalysts thermally formed on titanium mesh for methanol oxidation

Platinum-based catalysts, for the electro-oxidation of methanol, have been made by thermal decomposition of chloride precursors onto titanium mesh. The catalysed electrodes were successfully operated in acidic methanol electrolytes. Electrochemical characterisation has been carried out using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic polarisations. A complete analysis of the electrochemical results showed that the preliminary performance of the catalysed titanium mesh was comparable to that achieved with carbon-supported PtRu catalysts. The catalysts formed on titanium mesh by thermal decomposition also exhibited dimensional stability. Catalysed titanium mesh therefore appears to be a promising alternative to carbon-supported catalysts for certain fuel cell applications.     

Polyaniline for corrosion prevention of mild steel coupled with copper

Polyaniline emeraldine base/epoxy resin (EB/ER) coating was investigated for corrosion protection of mild steel coupled with copper in 3.5% NaCl solution. EB/ER coating with 5-10 wt% EB had long-term corrosion resistance on both uncoupled steel and copper due to the passivation effect of EB on the metal surfaces. During the 150 immersion days, the impedance at 0.1 Hz for the coating increased in the first 1-40 days and subsequently remained constant above 10⁹ Ω cm², whereas that for pure ER coating fell below 10⁶ Ω cm² after only 30 or 40 days. Immersion tests on coated steel-copper galvanic couple showed that EB/ER coating offered 100 times more protection than ER coating against steel dissolution and coating delamination on copper, which was mainly attributed to the passive metal oxide films formed by EB blocking both the anodic and cathodic reactions. Salt spray tests showed that 100 μm EB/ER coating protected steel-copper couple for at least 2000 h.     

Enhanced corrosion prevention effect of polysulfone–clay nanocomposite materials prepared by solution dispersion

A series of polymer–clay nanocomposite (PCN) materials containing polysulfone (PSF) and layered MMT clay were successfully prepared by effectively dispersing inorganic nanolayers of MMT clay in an organic PSF matrix via a solution dispersion technique. The synthesized PCN materials were subsequently investigated with a series of characterization techniques, including Fourier transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The prepared PCN coatings with low clay loading (1 wt %) on cold‐rolled steel (CRS) were found to be superior in corrosion prevention to those of bulk PSF, based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current and electrochemical impedance spectroscopy (EIS) in a 5 wt % aqueous NaCl electrolyte. The effects of material composition on the molecular barrier, mechanical strength and optical clarity of PSF and PCN materials, in the form of membranes, was also studied by molecular permeability analysis (GPA), dynamic mechanical analysis (DMA) and UV‐Visible transmission spectra, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 631–637, 2004     

一种基于压缩域的实时跟踪改进算法

在基于压缩域的实时跟踪算法中,判别函数对目标外观考虑不足易造成跟踪精度较低。为此,提出一种改进的基于压缩域的实时跟踪算法。利用稀疏测量矩阵提取候选目标的低维多尺度特征,并根据在线更新的特征概率分布,采用朴素贝叶斯分类器判别目标与背景,实现粗跟踪。通过视频帧间候选目标内部区域所具有的相似性,在粗跟踪的基础上实施基于动态目标外观模型的二次跟踪,在线寻找目标的最佳跟踪位置。对多种跟踪视频库的测试结果表明,该算法在不过量增加计算负荷的情况下能有效提高跟踪精度。     

Polyaniline as corrosion inhibitor for iron in acid solutions

In recent years, polymer amines have been studied as an efficient corrosion inhibitor for iron in acid media. In this article, the performance of water soluble polyaniline as corrosion inhibitor for iron in 0.5M H₂SO₄ has been evaluated by potentiodynamic polarization, linear polarization, and electrochemical impedance spectroscopy and compared with the performance of the aniline monomer. It has been found that polyaniline is an efficient inhibitor, since the maximum efficiency of 84% has been observed at a concentration of 100 ppm, whereas the monomer has accelerated the corrosion. FTIR studies have shown that the polyaniline is strongly adsorbed on the iron surface and inhibits the corrosion effectively. However, aniline has been found to improve the passivation tendency of iron at higher concentrations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2144–2153, 2006     

Zinc-rich powder coatings characterisation in artificial sea water: EIS analysis of the galvanic action

Two zinc-rich powder coatings are applied onto phosphatised steel substrate and are studied using electrochemical impedance spectroscopy (EIS). Measurements are performed before (dry experiment) and during immersion in artificial sea water. Before immersion, EIS spectra show that percolation threshold is not attained for coating A, while coating B presents an effective percolation. In this latter case, and in order to account for the distribution of the zinc particles within the coating described as isolated, semi-isolated and percolant grains, a distributed transmission line model is proposed. When panels are immersed, the model is modified due to the electrolyte penetration through the coating, in particular with the introduction of an ionic resistance. However, it is shown that EIS spectra are not significantly modified when this ionic resistance is changed.     

基于曲面形变的三维人脸样本配准

三维人脸样本是人脸识别、人脸动画等领域进行模型训练、算法设计及性能比较的重要数据平台。为了提高三维人脸样本的配准效果和配准速度,提出一种基于曲面变形的三维人脸样本配准方法。该方法通过对标准化样本实施一系列的变形操作来建立原始样本与标准样本之间的对应关系。然后基于该对应关系对原始样本进行配准处理,在处理过程中使用统计方法对样本上的毛刺点和空洞进行修补。实验结果表明,使用该方法可以快速、有效地对不同格式的原始样本进行配准。