Voltammetric method using a lead film electrode for the determination of caffeic acid in a plant material

This paper deals with development of an adsorptive stripping voltammetric method for determination of caffeic acid (CA) at a lead film electrode (PbFE). The working electrode was prepared in situ on a glassy carbon substrate as a “mercury-free” electrochemical sensor. The method is based on the accumulation by adsorption of caffeic acid on PbFE and then the oxidation of CA during the stripping step. In a acetate buffer based supporting medium the oxidation signal for caffeic acid was found to be proportional to the CA concentration in the range from 1 × 10⁻⁸ to 5 × 10⁻⁷ mol/L with the limit of detection equal to 4 × 10⁻⁹ mol/L (with preconcentration for 30 s). The method, operated in the square-wave voltammetric mode, was successfully applied to the determination of CA in a plant material (herbs of Plantago lanceolata). The content of caffeic acid received by the proposed method was in close agreement with that obtained by high performance thin-layer chromatography (HPTLC) combined with densitometry. This appears to be the first application of a lead film electrode to the determination of an organic compound in such complicated matrix.     

On the modelling of stability problems for thin plates with functionally graded structure

A conjunction of local apparent properties with a global design of structural elements is motivation for applying composites, which have space varying effective properties. This contribution deals with analysis of dynamics and stability problems for thin composite plates with a smooth and a slow gradation of macroscopic properties. The formulation of two mathematical models of these plates, based on a tolerance averaging technique, cf. Wo?niak et al. [18], is the aim of the paper. The general results are applied to the analysis of some special problems.     

Measurement of velocity distribution for air flow through perforated plastic foil ducts

In order to provide optimal air conditions in workplaces the requirements for mechanical ventilation systems are continuously improved. The most popular material used for air ducts is sheet steel. Due to its high costs and susceptibility to corrosion processes, other materials, e.g. PVC (polyvinylchloride) or other plastics should be used as duct materials more widely. Another advantage of plastic air ducts is simple installation, as no additional supporting constructions are required. Flow characteristics for plastic foil air ducts have not been established yet. Therefore, the velocity profile is investigated. The results of the research are compared with the mathematical model of the flow in smooth pipes.     

基于Fryze时域无功定义的无功电能的准确计量

针对目前无功功率计量算法在非正弦不平衡条件下的无功功率计量方面准确性的不足,在Fryze时域无功定义的基础上提出了一种适用于非正弦不平衡三相三线制系统的无功功率计量理论。根据Fryze时域无功定义将三相瞬时电流分解为有功电流分量和无功电流分量,并对三相瞬时电压和无功电流分量进行快速傅里叶变换,得到各次谐波无功功率的大小和方向,从而实现对非正弦不平衡三相三线制系统无功电能的准确计量。该方法将无功功率分为正向无功功率和反向无功功率,避免了同一谐波源产生的不同次数谐波的感性无功与容性无功相互抵消的情况。最后通过Matlab仿真验证了这一结论,为非正弦不平衡条件下系统无功电能的准确计量提供了理论依据。     

液压注塑机油泵电机节能控制系统设计

在对液压注塑机油泵电机的工作过程及能耗情况进行分析和对电机节能方案进行比较的基础上,提出了对电机转矩进行调节实现效率控制的液压注塑机节能方案及其实际应用测试结果.     

阿姆斯特丹的泽伊达斯地区：一个新城市景观

泽伊达斯地区（Zuidas）位于阿姆斯特丹南侧，距离斯希波尔机场仅6分钟车程。由于将大量的基础设施埋入地下，该地区创造出相当于巴黎拉德芳斯和伦敦道克兰地区同等规模的开发区域。其定位是建成一个城市集群的超级域市中心，而这个人口规模达到700万的城市集群除阿姆斯特丹之外，还包括了鹿特丹、海牙等城市。泽伊达斯地区在建设中为创造怡人且颇具动感的城市特质，采用了传统的街道格局和在荷兰绝无仅有的建设密度，同时高度混合了办公、公共娱乐和居住等多项重要功能。在居住功能中有相当一部分住宅是政府资助项目。当局意识到一个好的肌理结构一必须保证在较小的尺度上也存在多样性。对于泽伊达斯地区的开发而言，可持续性是最重要的一项内容。体现在：规定新建建筑的设计必须考虑未来使用功能的可变性，如办公楼可以转变为住宅，反之亦然；强调对空间和能源等有限资源的合理利用，通过将基础设施移至地下实现对土地的高效且灵活利用；同时还建立了区域范围内的冷热能源收集系统，也将对能源的可持续利用做出贡献。除了高密度之外，本次城市设计还对水景和绿化提出了指导性原则。     

礼花弹壳的力学性能试验与参数设计

对生产环保型礼花弹壳的环保型纸浆材料的性能进行研究,得到这些材料的力学性能参数;利用有限元分析方法对环保型礼花弹壳的受力情况与其直径、厚度的关系进行研究,首次导出了表述它们之间关系的理论公式,为礼花弹壳产品的设计提供了理论依据.     

Intestinal invagination in the adult

Idiopathic intestinal invagination is a relatively frequent process in children in comparison with cases of intestinal obstruction/subocclusion by invagination secondary to a tumor in adults which is unusual and more often observed in patients over the age of 60 years. Two clinical cases of intestinal obstruction in young adult males due to intestinal invagination by a tumor of the small intestine are presented. One case was due to a submucosal lipoma which lead to ileo-ileal intussusception and an ileo-cecal invagination by a terminal ileum lymphoma. The clinical and diagnostic aspects of this infrequent disease are discussed.     

Effect of narrowing oxirane adduct distribution on some properties of ethoxylated alcohol-based sulfosuccinic acid halfesters

Foaming and viscosity build-up properties are presented for sulfosuccinic acid derivatives of ethoxylated alcohols with broad- and narrow-range polyoxyethylene chains. Narrow-range ethoxylated alcohol-based sulfosuccinic acid halfesters show better foaming ability. The effect is especially visible at 50°C. Better viscosity build-up properties, as well as higher electrolyte resistance thereof, are also demonstrated.